D3.4 - Critical review for the onsite control of the repair

Transkript

NEW INTEGRATED KNOWLEDGE BASED
APPROACHES TO THE PROTECTION OF CULTURAL
HERITAGE FROM EARTHQUAKE-INDUCED RISK
NIKER
Grant Agreement n°
244123
Deliverable 3.4
Critical review for the on-site control of the repair technique and
interventions
Due date: September 2010
Submission date: February 2011
Issued by: POLIMI
WORKPACKAGE 3: Damage based selection of technologies
Leader: POLIMI
PROJECT N°:
244123
ACRONYM:
NIKER
TITLE:
New integrated knowledge based approaches to the protection
of cultural heritage from earthquake-induced risk
COORDINATOR: Università di Padova (Italy)
START DATE:
01 January 2010
INSTRUMENT:
Collaborative Project
DURATION: 36 months
Small or medium scale focused research project
THEME:
Environment (including Climate Change)
Dissemination level: PU
Rev: FIN
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INTRODUCTION ..................................................................................................................... 3
1.1
Description and objectives of the workpackage................................................................. 3
1.2
Objective and structure of the deliverable ......................................................................... 3
2
GENERAL REMARKS ............................................................................................................ 4
3
IMPROVEMENT OF MASONRY QUALITY AND EQUILIBRIUM ............................................ 6
3.1
Strengthening of masonry walls ........................................................................................ 6
3.1.1 Grout injection ............................................................................................................... 6
3.1.2 Jacketing by R.C. plaster............................................................................................. 11
3.1.3 Structural Repointing (Deep repointing)....................................................................... 12
3.1.4 Bed-Joint Reinforced Repointing ................................................................................. 14
3.1.5 Anti-expulsion tie-rods ................................................................................................. 15
3.1.6 Insertion of artificial headers ........................................................................................ 15
3.1.7 FRP/SRP/SRG application .......................................................................................... 16
3.1.8 Confinement for columns and pillars............................................................................ 21
3.1.9 Vertical stiffening of earthen building elements ............................................................ 21
3.1.10 Others ......................................................................................................................... 21
3.2
Local repair of cracks or of decayed portions .................................................................. 22
3.2.1 Local Dismantling and Reconstruction (“scuci-cuci”) ................................................... 22
3.2.2 Grout injection of cracks .............................................................................................. 22
3.2.3 Bed Joint Reinforced Repointing ................................................................................. 22
3.2.5 Crack stitching and anchoring ..................................................................................... 22
3.2.6 Crack stitching for earthen buildings ............................................................................ 23
3.2.7 Others ......................................................................................................................... 24
3.3
Stability improvement...................................................................................................... 29
3.3.1 Enlargement ................................................................................................................ 29
3.3.2 Buttresses ................................................................................................................... 29
4
IMPROVEMENT OF SUB-ASSEMBLAGE CONNECTIONS ................................................. 31
4.1
Lack of connection between walls ................................................................................... 31
4.1.1 Tie beams ................................................................................................................... 31
4.1.2 Tie-rods ....................................................................................................................... 32
4.1.3 Hysteretic dissipation anchor ....................................................................................... 32
4.2
5
Lack of connections between walls and floors/roof ......................................................... 33
OPTIMIZATION OF VAULT PERFORMANCE ...................................................................... 34
5.1
Direct interventions (applied to vaults) ............................................................................ 34
5.1.1 Local Dismantling and Reconstruction (“Scuci-cuci”) ................................................... 34
5.1.2 Grout injection of the cracks ........................................................................................ 34
Damage based selection of technologies
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5.1.3 Structural Repointing (Deep repointing)....................................................................... 34
5.1.4 Bed Joint Reinforced Repointing ................................................................................. 34
5.1.6 Use of extrados R.C. jacketing .................................................................................... 34
5.1.7 Reducing the loads from extrados infilling ................................................................... 34
5.1.8 Extrados stiffening elements, mainly in barrel vaults (“Frenelli”) .................................. 34
5.2
Indirect interventions (supporting masonry stability) ........................................................ 35
5.2.1 Insertion of the tie-rods and confinement ..................................................................... 35
5.2.2 Buttresses ................................................................................................................... 35
6
SEISMIC IMPROVEMENT OF WOODEN FLOORS .............................................................. 36
7
IMPROVEMENT OF THE GLOBAL STRUCTURAL BEHAVIOUR ....................................... 40
8
FINAL REMARKS ................................................................................................................. 42
9
REFERENCES ...................................................................................................................... 43
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1 INTRODUCTION
1.1
DESCRIPTION AND OBJECTIVES OF THE WORKPACKAGE
WP3, in general, is aimed to the collection of information for increasing the existing state of
knowledge linking earthquake induced failure mechanisms, construction types and materials,
interventions, assessment techniques. According to the project document, other aims of the WP
are the follow:
Development of concepts for materials and intervention techniques based on the structured
database; definition of the main design parameters and requirements for materials and
intervention techniques;
Definition of the main on-site control techniques and strategies;
Development of advanced materials and improved techniques for intervention and to
produce/assemble those required for testing and case studies;
Development of laboratory procedures and choice of parameters for the final validation of
the durability, compatibility, and effectiveness of new techniques and materials;
Parameterization of all the above mentioned information to set the basis of optimized
design and required laboratory testing in following WPs.
1.2
OBJECTIVE AND STRUCTURE OF THE DELIVERABLE
The deliverable critically reviews the main on-site control procedure related to the retrofitting and
reinforcement techniques available in the state-of-art, described in the Deliverable D3.2.
The Deliverable is strictly correlate to Deliverable D3.3, which describes in detail the available
investigation techniques and methods for assessment.
In general, the NIKER project proposal tackles the problem starting from the basic consideration
that the best guarantee of compatibility, low intrusiveness, removability/reversibility, etc, is
essentially based on a „minimum intervention‟ approach. This means that interventions, utilizing
materials and components with different properties compared to the original substance and/or
implying significant changes of the original local/global structural behaviour, but also physical and
chemical properties, should be avoided as much as possible.
This also means that, rather than assertively assuming confusing concepts, we should provide the
technical data to define performance levels and control procedures of the building and of eventual
intervention.
The problems arising here are related to analyses performed on the basis of limited information
regarding the original structural system. Very often, dated design methods, which do not reflect the
actual strengthening technique as they are based on rule-of-thumb and/or odd material properties,
are applied. The control of the effect of the strengthening method and of the quality or
effectiveness of its application on existing masonry constructions is not required by any code or
standard, especially for existing masonry constructions.
The Deliverable examines the state of the art concerning this topic, starting from the repair
methods reported in D3.2 and remarking the lack of specific procedures or standards. Where
appropriate, comprehensive case studies and/or on-site experimental activities are synthetically
described.
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2 GENERAL REMARKS
Several unsuccessful results have underscored the need for adequate assessment prior to any
restoration or rehabilitation, but also due to the poor application of the repair technique or the lack
of compatibility. In fact, when neither the real state of damage nor the effectiveness of repairs is
known, the results of the intervention are also unpredictable. This was clearly shown by some
repair failure even when advanced materials had been used; there are now enough information to
support the choice of compatible materials and techniques for repair. The experience of the last
decades in repair, strengthening and prevention for the preservation of masonry buildings in
historic centres of seismic areas did teach that compatible or friendly techniques have to be
chosen in order to obtain positive results. It is also rather clear that too strict theoretical position on
the preservation of the Cultural Patrimony, as a historic document of the past cannot be always
practically applicable.
Intervention in heritage structures, involving either stabilization, repair or strengthening (in
particular, seismic retrofitting), should be subjected to a series of requirements or criteria oriented
to ascertain the efficiency of the solution together with its compliance with recognized conservation
principles. These principles are stated in international documents such as the Venice Charter of
1964 and, in a more specific way, in the ICOMOS / ISCARSAH Recommendations for the Analysis
and Restoration of Architectural Heritage (ICOMOS/ ISCARSAH, 2005) and the Annex on Heritage
Structures of ISO/FDIS 13822 (ISO/TC96/SC2, 2010).
These criteria should not be understood as absolute requirements, but as recommended
conditions assisting in the definition of optimal repair or strengthening solutions. In fact, complying
with all these criteria, in some cases, the priority choice may be impossible, therefore the
engineering judgment, is often necessary.
Between the several requirements it is worth to mention the monitorability and controllability.
Repair or strengthening measures whose performance and effect on the building are possible to be
controlled and were already validated experimentally and/or through numerical models are
available should be preferred. However, there are intervention techniques that have proven their
effectiveness when applied to structural elements, but when applied to a real case study the global
influence is of difficult practical assessment.
In this context, experimental validation in laboratory with the support of modelling is fundamental.
Moreover, in order to detect the performance of intervention it is necessary planning a programme
of monitoring and control that accompany any proposal for intervention before, during and after its
execution.
In the case of provisory or emergency actions, the monitoring of the provisional strengthening is of
fundamental importance. It will normally be important to know whether the strengthening (for
instance, a propping system) is actually working and resisting some load, and thus partly or totally
relieving the original structure, or whether the strengthening has not been in fact mobilized. This
will lead to very different decisions regarding the new strengthening system and the way to
implement it.
As aforementioned, an important requirement to be considered in the selection of any material or
technology used for repair and strengthening lays on the needed compatibility (chemical, physical,
mechanical, thermal, rheological...) between the newly added and the original parts.
A critical choice, regarding compatibility, is found in the use of traditional materials and techniques
against modern (or innovative) ones. The first ones are normally compatible to the original parts
due to the combination of similar properties. Moreover, the compatibility in the long term, and the
absence undesirable side-effects, has been proven through an experience of centuries. Ancient or
traditional materials mortars, such as lime mortar, have already proven their durability and
compatibility with other historical materials across long periods of time.
These techniques use traditional methods, materials and tools. They are easy to implement, and
can be carried out by companies of small size.
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Another advantage of traditional or historical structures is found in the fact that, having been used
historically to improve or strengthen many ancient structures (as in the case of ties), they can be
regarded as a “historical” devices which, if implemented now in a heritage structure, do not
severely impact on its original character and authenticity.
Modern and innovative materials and techniques may be considered for repair and strengthening
purposes provided that sufficient scientific research and experience are available on their adequate
performance and lack of compatibility problems with the original material.
It shall be noted that modern materials and techniques show in some cases severe compatibility
problems (as in the case of Portland cement or epoxy resins) when used to restore or strengthen
brick or stone masonry structures. In other cases, problems may not have been identified, but not
enough experience may have been gathered as to show that no damaging side effects will occur in
the long term.
According to the Venice Charter, where traditional techniques prove inadequate, the consolidation
of a monument can be achieved by the use of any modern technique for conservation and
construction, the efficacy of which has been shown by scientific data and proved by experience. In
turn, the ICOMOS/Iscarsah Recommendations mention that “the choice between “traditional” and
“innovative” techniques should be determined on a case-by-case basis with preference given to
those that are least invasive and most compatible with heritage values, consistent with the need for
safety and durability”.
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3 IMPROVEMENT OF MASONRY QUALITY AND EQUILIBRIUM
The improvement of the masonry quality can be necessary to repair local damages, (e.g. cracks,
local discontinuities, etc.) or most extended damages, as in case of long term lack of maintenance
or general poor quality.
The repair technique, then, should be chosen considering the general criteria described in
Deliverable 3.2, in base to the extension of the damaged area, as well.
The equilibrium improvement of a single panel is related both to its masonry quality, geometric
characteristics (e.g. slenderness) and the connection with other structural elements and portions.
This last point has been extensively studied in the Delivarable 3.3.
The two strategies require different level of evaluation, local in case of masonry improvement and
global in case of equilibrium restoring.
3.1
STRENGTHENING OF MASONRY WALLS
3.1.1 Grout injection
Repair and strengthening by grouting of brick and stone masonry walls has been largely applied all
throughout Europe on historic buildings and dwellings; nevertheless no great effort was done in
advance and during the time to test the effectiveness of this technique.
Even if experimental and analytical research has been carried out in the past decades on these
techniques, nevertheless the effectiveness was always checked in terms of strength increase
rather than on chemical, physical and mechanical compatibility with the original masonry (Modena
et al., 1997a), (Binda et al., 1997). Few research was carried out in this direction on the
effectiveness of grout injections (Tomaževic and Turnsek, 1982), (Tomaževic, 1992 and 1999),
(Binda et al., 1993a,b), (Binda, 1994), (Modena and Bettio, 1994), (Laefer et al., 1996), (Valluzzi et
al., 2004). The conclusions recommended a careful approach and suggested a previous
knowledge of the masonry wall morphology and of the masonry characteristics, since some types
of walls could be not injectable.
This intervention consists on injecting grout mixtures of different types into the masonry, using
particular techniques, in order to:
1. reconstitute the structural continuity of the masonry;
2. increase the masonry homogeneity, filling voids, if existing;
3. improve the masonry mechanical properties (increase the masonry strength);
4. fill cracks in wall and other masonry structural elements (vaults, domes, etc…).
The main problems connected to the grout injection can be summarised as follows: a) the lack of
knowledge on the size distribution of voids in the wall, b) the difficulty of the grout to penetrate into
thin cracks (2.0-3.0 mm), even if microfine binders are used; c) the presence in the wall, of fine and
large size voids, which make difficult choosing the most suitable grain size of the grout (injecting
large size voids with a fine grained mix can in fact induce segregation); d) the segregation and
shrinkage of the grout due to the high rate of absorption of the material to be consolidated; e) the
difficulty of grout penetration, especially in presence of silty or clayey materials; f) the need for
sufficiently low injection pressure to avoid either air trapping within the cracks and fine voids or
even wall disruption. As known, the injection technique can fail when badly applied, with limits
connected to the masonry morphology, to the desegregation and sedimentation of the grouts, to
the mix characteristics (grain size distribution), to the operative technique.
Therefore, the effectiveness of a repair by grout injection depends not only on the characteristic of
the mix used, but also on its mechanical properties and on the injection technique adopted and
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once again on the knowledge of the wall type. The injectability of the grout is influenced by its
compatibility with the masonry to be repaired, as well.
Multiple leaf walls can be made with very poor mortars and stones but have very low percentage of
voids (less than 4.0% of the voids are not injectable) and have internal filling with loose material,
which is not injectable.
The aim can be fulfilled only knowing with good precision the morphology of the wall section, the
materials constituting the wall and their composition in order to avoid chemical and physical
incompatibility with grout, crack distribution, size, percentage and distribution of voids. Preliminary
applicability tests on selected area are highly recommended, as well as their visual inspection by
local dismantling.
As reported in Deliverable 3.3, the section morphology and the properties of the components
besides Non Destructive Tests, can be found by small local dismantling of the section and by
sampling from the inside mortar, brick and stones. If all the mentioned information can be referred
to the same area of the masonry, then the quality of it can be completely studied.
No specific standards were developed, even if it is a wide used technique. In Italy, after the main
earthquakes of Friuli (1976) and Irpinia (1980), recommendation for the application procedures are
shortly described in the following documents developed: Legge Regionale Friuli Venezia Giulia, DT
2 del Novembre 1977; Decreto 2 Luglio 1981, Circolare 30 Luglio 1981.
A methodology for on-site and laboratory testing of grout injections in multiple leaf stone masonry
walls was set up firstly by Binda, Baronio in collaboration with Modena who allowed on-site
injection of walls, in 1992 (Baronio et al., 1992). This methodology which is presented in Figure
3.2, (Binda et al., 1993b; Binda et al., 1994).
Different phases for the on-site control of injections can be proposed:
i.
the control of the grouts intrinsic characteristics (if needed) by applying fluidity control tests
(Marsh or ASTM Cone) (ASTM C939, 1994), and segregation control tests (ASTM C940,
1989).
ii.
injectability tests, as proposed by Binda et al. (1993b), carried out in laboratory or in-situ on
materials sampled from the internal part of walls. The sampled material are inserted in
Plexiglas cylinders and then injected (Figure 3.1) (ASTM C943, 1996). Injectability tests
proposed by Binda et al. (Binda 1993a, b), (Laefer 1996) calibrated to masonry a procedure
applied to soil. Compressive and splitting tests (Brazilian tests) on the injected cylinders in
laboratory can be carried out on the cylinders after the time necessary to reach the
hardening of the grout; other recommended tests of the grout are the sulphate content,
grain size distribution, segregation and shrinkage, mechanic characterisation, water
retentivity, together with addressed characterisation tests on the masonry.
Figure 3.1 - Injection of the cylinder in laboratory, (Binda et al., 1993; Binda et al., 2003b,c) (Source: POLIMI).
iii.
Survey of the injection phase, by the tracing of the permeability paths of the grout through
the voids net on maps (Miltiadou and Fezans, 2008);
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iv.
Assessment of the strengthening effectiveness through ND and MD techniques such as
sonic velocity pulse tests, tomography, flat-jack tests and visual inspection (partial
dismantling, endoscopy, coring).
It is worth to mention that the combined use of the ND and MD tests is useful in order to
crosscheck the results and limit the invasivity of the investigation phase.
Figure 3.2 - Methodology for testing repair by injection on-site and in laboratory, (Baronio et al., 1992; Binda et al.,
1993a).
Case study - Noto Cathedral
In Binda et al., 2001b and 2003b the on-site and laboratory research carried out by the authors on
the remaining of the Noto Cathedral are presented. Besides the study, based on the results of
surveys and tests, of the state of damage of materials and structures, the possibility of being
reused and the choice of the materials for the reconstruction of the piers and of the missing parts
and for repair and reinforcing, of the chemical, physical and mechanical compatibility of the new
materials with the existing ones were verified, as well.
Injectability tests proposed by Binda et al. (1993a,b) were carried out in laboratory on materials
sampled from the internal part of the piers and walls. Compressive and splitting tests on the
injected cylinders in laboratory gave respectively a compressive strength of 1.75 N/mm 2 and a
tensile strength ranging from 0.10 to 0.40 N/mm2 depending on the effectiveness of injection. The
injected material sampled from the piers was also tested but the dimensions of the specimens
were smaller than the ones of the cylinders. Compressive and tensile strength of these specimens
were ranging respectively from 0.9 to 5.0 N/mm2 and from 0.3 to 0.4 N/mm2.
The masonry behaviour was observed both during the injections and after 28 days which is the
necessary time to reach the hardening of the grout. After this time, the collapsed piers PA and PC
were dismantled to observe the grout penetration and diffusion.
Four different types of grouts were used for laboratory tests on-site, called C, N, M, P, and
respectively lime + pozzolana, hydraulic lime, hydraulic commercial binder, microfine.
Figure 3.3 shows another example of evaluation of the grout injection by a coupled used of pulse
sonic tests and double flat jack tests, repeated before and after the grout injection. From pulse
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sonic tests information about the grout diffusion are available but only with double flat jack test is
possible to obtain the mechanic behaviour within the elastic field by the change of the Elastic
Modulus. A direct visual inspection in selected point will confirm the quality of the grout diffusion.
In order to repeat the double flat jack test in the same position, the device could stay in the
masonry during the injection.
The whole procedure can be carried out only in the selected area. In other areas pulse sonic tests
could be repeated taking into account as another reference parameter the quantity of injected
grout.
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(Source POLIMI).
Sonic tests are quite potential in the evaluation of the possible favourable conditions of walls to be
injected, as well as after the intervention to control the migration of grouts through the
interconnected net voids and the restored compactness.
The use of sonic tomography in the injected zones (in particular in the belfry) confirmed their
validity in qualifying the masonry sections and evaluating the real effectiveness of the intervention
(Figure 3.4).
(a)
(b)
(c)
(d)
Figure 3.4 - Plan of a pillar with the scheme of a horizontal tomography and horizontal tomography at 3.05 m: (a) before
injections; (b) after injections; (c) percentage increase of sonic velocity, (Valluzzi et al., 2003c).
Further tests, in particular DT, could be carried out such as diagonal or shear diagonal tests.
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3.1.1.1 Effectiveness of grouting in earthen materials
Historic earthen materials are often affected by voids caused by erosion and activity of either
insects or bigger animals such as rodents. These voids reduce the load bearing capacity of the
walls (Langenbach, 2004; Fodde, 2008) and are clearly also a weakening factor when earthquakes
occur. Termite infestation, for instance, is thought by Langenbach (2004) to have been a key factor
leading to the collapse of some parts of the Bam Citadel in Iran in 2003.
When new material is used to fill the voids, attention should be paid to the density and stiffness of
the original material, in order to avoid differential stiffness between historic and repair material
which can harm the historic material in case of seismic loading.
Figure 3.5 - Replacement of damaged areas with new material, Abdullah Bin Salem Al-Damarki House, UAE.
Grouting of smaller voids with the aim of increasing the strength of earthen walls is claimed by to
be an effective technique. After experimenting with adhesion, cohesion, permeability, compressive
strength and pumping characteristics, for a mix of 1:2.5 moderately hydraulic lime to ceramic
microspheres, which results in a very porous material which in terms of density does not surpass
that of earthen materials.
Post-retrofitting monitoring or control techniques other than standard injection material
characterisation (Laboratory tests to characterise the compressive and flexural strength of the
mixture) are not typically carried out.
Sonic transmission tests or in-situ diagonal compression tests are viable but are not supported by
detailed laboratory evidence, nor necessarily justified in terms of cost.
Liberatore et al. (2006) carried out NDT sonic transmission tests on adobe walls and adobe walls
with ashlar facing. His results showed good correlation with the material at hand: they indicated its
poor quality, inhomogeneous nature, and the lack of connection between the ashlar facing and the
structure. In cases where visual observation is not possible without damaging the historic material,
sonic transmission tests could be used as a means to control the effectiveness of grouting. Some
examples showing lack of material integrity within earthen walls are shown in Figure 3.6.
Further research in this field is however required.
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Figure 3.6 - To the left, inner vertical discontinuities. To the right, voids due to lack of vertical (head) joints, Muwaiji Fort,
Al Ain, UAE.
Destructive in-situ diagonal compression tests when possible can complement sonic tests and in
the understanding of the effectiveness of a particular grouting material. Liberatore et al. (2006)
carried out in-situ diagonal compression tests on unreinforced adobe walls.
3.1.2 Jacketing by R.C. plaster
The aim of the technique is to connect the different leaves of a wall to produce a new section
constituted by the old one increased by the two jacketed reinforced parts. The idea behind it is to
have a thicker section, to increase compressive, tensile and shear strength and ductility (Modena
and Bettio, 1994; Modena et al., 1997b). The same technique has also been applied to connect
load-bearing and shear walls and also large cracks, as well. It was a technique proposed formally
in Italy after the earthquake in Friuli (Italy) by the documents: Legge Regionale Friuli Venezia
Giulia, DT 2 del Novembre 1977; Decreto 2 Luglio 1981, Circolare 30 Luglio 1981.
The technique consists in positioning a reinforcing grid (Ф = 6.0 to 8.0 mm) on both faces of a wall,
connecting the two grids with frequent steel connectors (4 to 6 connectors/sqm) and applying on
the two faces a rather thick cement mortar based rendering, which constitutes a sort of slab (Figure
3.7). The masonry panel, then, acquires high strength and stiffness, which is not always a positive
point by considering the overall behaviour of the building. Furthermore, the discontinuity due to the
floor presence produces further local decrease of stiffness and weakness (Figure 3.8), as well as
the unregularly layout of the reinforcing.
No addressed control procedures are available in literature or in standards.
Nevertheless, as main problems of this technique are related to design/execution aspects, like lack
of connections, insufficient covering/overlapping at corners or around openings, as well as
corrosion of the steel net, the use of NDT and instruments such as pacometer and thermovision is
of great importance as it can provide an on-site idea of the presence of the steel grid, with the
corner details. Moreover, additional analysis on the durability (or deterioration condition) of the
plaster and the control of the humidity content of the masonry, can be suggested. It is worth to
remark, however, that the recent use of FRP nets, applied with inorganic mortar, thus avoiding the
problem of corrosion, is considered among the possible innovative applications of this technique.
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Figure 3.7 - Layout of the R.C. jacketing reinforcing.
(a)
(b)
(c)
Figure 3.8 - (a) Damage to the change of stiffness; (b) wrong design: only a wall is reinforced; (c) lack of connection
between the walls and in correspondence to the floors, (Source: POLIMI).
3.1.3 Structural Repointing (Deep repointing)
Deep re-pointing is a widely applied technique in all types of masonry. However, deep re-pointing
is expected to be efficient in enhancing the mechanical properties of masonry only in some cases
and under several conditions. This operation involves the partial replacement of the mortar joints
with better quality mortar, in order to improve the masonry mechanical characteristics, and it
should be applied in case the deterioration is localized only in the mortar.
The described operation can increase the masonry resistance of both vertical and horizontal loads,
but the best results are obtained especially in terms of deformation, which are also greatly
diminished due to the confinement effect of the joints.
Actually, strength enhancement is expected only when a significant percentage of the initial weak
or deeply damaged mortar is replaced by a new more compact and rather stronger one, but not
excessively rigid and resistant to avoid creating areas in the masonry with inhomogeneous
behaviour (Figure 3.9). This is the case in rather thin masonries, provided that deep re-pointing is
applied on both sides of the masonry elements. Due to the fact that, normally, stone masonry
elements are rather thick, one cannot expect this technique to be efficient in this case.
Nevertheless, deep re-pointing (more or less deep) is applied to stone masonry as well, either in
rather thin elements (45 to 60 cm thick) or for other purposes, such as a preparatory step before
the application of grouting to masonry; in this case it can be applied in order to better confine the
injected material.
The aims of the deep repointing, provided that it is carried out with very good workmanship, are
multiple: (i) to connect in a rather thin section the stones of the external leaf substituting the original
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mortar in the joints when it is damaged, cracked and in any case very poor, (ii) to confine the wall
at a less extent than the jacketing, but with better results since the bond with the existing stones
and mortar can be better assured, (iii) to confine better the injected material when grout injection is
carried out, (iv) to provide a better penetration (14 cm over the thickness of the wall section) and
distribution of the mortar compared to the random penetration and distribution of a grout injection.
When cracks are also present, then they should be injected with grout and the deep repointing
becomes a complementary action. Eventually, when needed, steel transversal ties should also be
added in order to connect the leaves of the wall. This technique can be particularly efficient in the
case of two or three leaves stone walls reaching a thickness not higher than 60 cm.
Before deciding the application of the deep re-pointing technique an on-site investigation should be
carried out in order to provide the crack pattern of the walls, the thickness of the section (it should
be no more than 45 or 60 cm) and the morphology of the masonry itself (number of leaves, brick
and stone arrangement), physical and chemical characterisation of the materials (physical
properties of the units, brick or stones, salt content, type of mortar, grain size distribution,
binder/aggregate ratio, etc.).
The traditional repointing basically consists on filling the joints with mortar. The operation must be
careful performed in order to ensure the proper filling of the joints and, to this end, it must be done
in two layers: after placing a first layer of mortar, this must be treated on the internal part of the
joint to avoid formation of voids, then proceed to the application of the second repointing layer, until
the total filling of the joint, taking attention to the reposition on the external surfaces of any wedges
removed during the scrapping of the joints.
It is also crucial to perform the intervention in the depth of the masonry; it is frequent to found, in
fact, a malfunction of this technique, because it wasn‟t well applied in depth, but limited to an
aesthetic improvement of the surfaces rather than of increase in mechanical properties.
In general, the repointing is ineffective in cases where there is a poor execution of the intervention.
Figure 3.9 - Execution stages in the case of repointing performed on both sides of the wall, (Tomazevic, 1999).
A repair and preventive technique for double leaf masonry walls, including a repointing procedure,
was proposed in Binda et al. (2005) and Corradi et al. (2006, 2008): the deep re-pointing of the
masonry joints with an appropriate mortar, carried out on the two faces of the masonry. The repointing was carried out also in conjunction with grout injection and tested on-site on a wall of a
building, which was later on demolished.
Diagonal compression, simple compression and shear-compression tests were carried out on
masonry panels of various dimensions, which had been strengthened with either traditional or
innovative techniques. Concerning traditional method, panel injected with new lime based mixes
and panels repaired by deep re-pointing of mortar joints were tested.
The aim of the research was to characterise the behaviour of the masonry typical of the studied
areas and to study the effectiveness of the seismic upgrading and reinforcing work both on
undamaged and damaged walls. The tests carried out provided interesting indications for practical
utilisation of the studied techniques.
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An appropriate preliminary investigation on-site and in laboratory was carried out (Binda et al.,
2005) through: (i) an accurate geometrical survey of the masonry morphology (number of leaves in
the section, dimension of the leaves, type of connection between the leaves), (ii) characterisation
of the stones and of the mortars, (iii) survey of the physical and mechanical decay, (iv) crack
pattern survey.
Stones and mortar were sampled from the walls and laboratory tests were carried out. Chemical,
petrographic-mineralogical analyses were performed on the mortars in order to detect their
composition: type of binder, type of aggregates, binder/aggregate ratio, aggregate size and
dimensions. On the stones petrographic observations, physical analyses and mechanical tests
were performed. Based on to the results of the laboratory tests, appropriate materials were chosen
both for injection and repointing.
The morphology of the walls suggested that in some cases injection repairs were not appropriate
due to the fact that inside the masonry there was practically loose material and no voids were
present (Abbaneo et al., 1993) Therefore before applying the technique, appropriate tests were
carried out in laboratory on sampled materials and also on-site (Laefer et al., 1996).
The aims of the deep re-pointing are the following: (i) replace the damaged mortar on the wall
surface to a depth of 60 mm in order to adequately bond the stones, (ii) connect the stones
together and to the external part of the wall, (iii) confine the wall externally also in the case of
injection, (iv) provide a better penetration of the grout while avoiding leakage to the exterior. When
the re-pointing is successful, 120 mm of the wall section (in case of two leaf walls the thickness
varies from 500 to 650 mm) are well bond together and constitute good confinement for vertical
loads. This technique can assure more than injection, a uniform distribution of the material in the
external leaves. As said before, injection is not always successful if it cannot penetrate inside the
masonry and connecting the two leaves; in many cases transversal connector, are needed instead.
Regardless of this, injection is necessary when diffused cracks are present.
The choice of the repair materials has to be made following requirements, which cannot be
codified, but must be based on the respect of the existing materials and structures. Therefore a
previous investigation on the existing materials used for masonry, bricks, mortars for bedding and
pointing (or repointing) has to be carried out. Subsequently the grout for eventual injections and the
mortar for deep repointing have to be previously chosen also based on laboratory tests as: (i) grout
injectability tested on-site on a wall sample and in laboratory (Laefer t al., 1996) good commercial
premixes can be found or modified and adapted to the requested properties, (ii) choice of a mortar
for deep repointing which has good strength but no high stiffness and good adhesion with the
stones, (iii) choice of a mortar for the external repointing, compatible and aesthetically acceptable
compared to the existing repointing.
In situ and laboratorial testing, such as diagonal compression, shear-compression and simple
compression tests accompanied of inspection through local dismantling (control the penetration
and diffusion of the re-pointing and of the injection) can be performed on the material to assess the
effectiveness of this type of strengthening intervention. However, it must be pointed out that the
proposed tests are very invasive, and in most cases aren‟t allowed in historic buildings.
An effective alternative could be the double flat jack tests. Superficial (indirect) sonic wave test
(NDT) can also give information about the possible restored compactness of the surface of the wall
and thus of the effectiveness of the strengthening intervention.
3.1.4 Bed-Joint Reinforced Repointing
The reinforced repointing technique involves the insertion of reinforcement rods or plates inside the
joints, in steel or fiber reinforced polymer, on one or both sides of the wall, eventually connected in
the transverse direction. This originates a further reduction of the wall dilation and of the tensile
stresses in the resistant elements; it is also useful to prevent the out-of-plane deformation of the
external leaves of the multi-leaves walls and to increase the ductility and the ability to dissipate
energy of the structure.
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Figure 3.10 - Reinforced repointing on (a) one leave masonry wall; (b) multi-leave masonry wall with resistant external
leaves; (c) multi-leave masonry wall with external coating layer, (Binda et al., 2001a).
In general, the repointing is ineffective in cases where there is a poor execution of the intervention.
Several experimental researches aimed at the control of the effectiveness of the technique to
prevent or to repair long term compressive damages of masonry are available. The strengthening
by confining steel bars (Binda et al., 1999), (Binda et al., 2001a), (Modena et al., 2002), (Valluzzi et
al., 2005a) or CFRP thin strips (Valluzzi et al., 2003a,b), (Tinazzi et al., 2003), (Saisi et al., 2004),
(Valluzzi et al., 2005b), (Garbin et al., 2009) were particularly explored.
However, in literature there are not examples of calibrated procedures aimed to on-site control the
technique. In this context, tools such as the pacometer can be used for the identification of the bars
and the thermovision technique can be used for the detection of possible lack of adhesion.
3.1.5 Anti-expulsion tie-rods
The technique of inserting metal ties inside the walls has as main purposes to limit the deformation
of the walls and to improve their shear behaviour.
There are not examples in the state-of-art of on-site procedures aimed to control the technique.
However, a dynamometer key or strain gauges can be used to assess the tension levels on the
rods.
Figure 3.11 - Positioning of anti-expulsion tie-rods.
3.1.6 Insertion of artificial headers
Insertions of artificial headers in R.C. or steel are proposed in technical literature and handbooks.
The aim of the application is to reinforce multiple leaf masonry by the insertion of connecting
elements.
In a passing through hole drilled in the masonry, the steel reinforcement is placed and then
injected. The technique is rather invasive and requires the presence of several headers in a wall to
be effective. Furthermore, other difficulties could concern the real possibility of connecting the wall
and stress transferring.
There are not examples in the state-of-art of on-site procedures aimed to control the technique.
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3.1.7 FRP/SRP/SRG application
FRP/SRP/SRG materials, that greatly meet the concept of „engineered material‟, are being more
and more applied for the restoration of vertical and horizontal structural elements as well as
isolated monuments (statues, etc). This reinforcement is made of different kinds of fibers (carbon,
glass, polyvinylalcohol, etc…) impregnated in a polymeric matrix. Due to high strength and
stiffness-to-weight ratio, fatigue and corrosion resistance, and their exceptional capacity to be
tailored to specific needs, along with decreasing raw materials and production costs, advanced
composites have progressively extended their initial fields of applicability, typically limited to the
aerospace sector.
Their flexibility and somewhat easy application allow a wide range of intervention scenarios for
existing structures, characterized by different damage conditions. The state of art is generally
limited to the evaluation of the mechanical properties, without the exploring of the real behaviour of
the assemblage in the natural aggressive environment, generally characterises by the presence of
moisture and salt, thermal cycles, frost-defrost actions.
As demonstrate by the application of surface treatment, masonry could be damaged by the salt
crystallisation, progressively spalling the treated superficial layers. Furthermore, at present, the
local mechanisms involved in the failure of masonry structures strengthened by FRP laminates
(such as delamination, etc…) still need to be experimentally and numerically deepened. For
SRP/SRG materials a few first applications for concrete and less for masonry are available, but no
guidelines are available. Testing and numerical activities to be carried out during the project,
integrated for FRP by the data already being collected into the data-base of the dedicated RILEM
223MSC committee, will produce developed design methods for FRP and new design methods for
SRP/SRG.
Other meaningful limits concern the application procedure, which requires smooth surfaces and the
removal of the ancient plaster. As in case of R.C. jacketing, the intervention could be effective if
applied uniformly on the building, on two sides of the wall and with a peculiar care to the corners,
floors and to the overlapping of the materials.
The use of composite materials in strengthening and restoring interventions on existing structures
is continuously increasing. During the last decades, many researchers have developed new
strategies, technical solution and analyses. Technical recommendations (CNR-DT 200/2004, 2004;
AC 178, 2008) for the design and construction of strengthening techniques with fibre-reinforced
composite material (FRP) systems have been published to provide an aid to designers interested
in the field of composite materials and to avoid their incorrect application (Olivito and Zuccarello,
2009).
Therefore, it is widely accepted that quality of construction is one of the most important factors that
affect long-term performance of FRP repair systems. Some procedures defined by the producers
suggest the local evaluation of the adhesion by pull-out tests, but only as calibration test in select
area preliminary to the application. In literature, even if the technique is widely proposed in most
intervention on historic buildings, there have not been developed addressed and systematic on-site
control procedures, except for the pull-off test, and few studies are still in progress and limited to
laboratory applications.
In order to assure an effective FRP reinforcement, perfect adhesion between FRP and substrate
(concrete or masonry) must be obtained; for this reason, it is essential to assess the quality of
bonding with a quality control process, starting before the installation of the system (specific
procedures for track and inspection all FRP components prior to installation, inspection of all
prepared surfaces prior to FRP application) and continuing through and after the application
(inspection of the work in progress to assure conformity with specifications, obtaining quality
assurance samples, inspection of all completed work, performing tests for approval, repair of any
defective work).
For these purposes, partial destructive testing, included in standards such as pull-off, shear tests
and laboratory testing of panels or resin samples, mainly aim at characterizing substrate properties
and bonding quality, but it can only be performed outside the critical zone of structural elements or
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on purposely made samples. Despite the high potential of non destructive methods for in-situ
evaluation of bond efficiency between FRP and structure, current standards at present provide only
general indications on their applications (visual inspection, acoustic tap testing, ultrasound and
thermal imaging methods). These methods identify the dimensions and positions of defects in the
adhesive layer as typical parameters (Corvaglia and Largo, 2008).
In the following the results of semi-destructive and non-destructive techniques conducted for the
quality control and monitoring of FRP applications to masonry are reported.
The application must be made with a temperature greater than 5.0°C and low humidity, because
low temperature retard the polymerization and humidity decrease the characteristic of polymer
resin. Studies on this field are currently in progress, as for example the ones developed by Binda
et al. (2011) and Valluzzi et al. (2011).
In literature there are not examples of control procedures. For the on-site control of the repair using
this technique it is possible to assess the installed stress through the application of the pull-off test
or thermovision.
3.1.7.1 Acceptance criteria
Corvaglia and Largo, (2008) propose for all the installer FRP areas a visually inspected for
detection of any defects, such as:
voids and air encapsulation between concrete and layers of primer, resin, or adhesive and
within the FRP system itself;
delaminations between layers of FRP system;
broken or damaged edges of the FRP system;
wrinkling and buckling of fibre and fibre tows;
discontinuities due to fracture of fibres, breakage in the fabric, or cracks in pre - cured
shells;
cracks, blisters, and peeling of the protective coating;
resin - starved areas or areas with non - uniform impregnation or wet - out;
under cured resin;
incorrect fibre orientation.
Then Corvaglia and Largo, (2008) proposes also a classification of bonding defects. Acceptability
of defects depends on the size, location and number of defects in a specific area while the repair
methods depend on the type of material, the form of degradation and the level of damage.
Minor delaminations (area < 7.0 cm2) may be repaired by epoxy resin injection, middle level
damages, including localized FRP laminate cracking or abrasions that affect the structural integrity
of the laminate (7.0 < area < 80.0 cm2), should be repaired by bonding FRP patches (with the
same characteristics, such as thickness and ply orientation, as the original laminate) over the
damaged area. Major damages (including peeling and debonding of large areas, area > 80.0 cm2)
may require removal of the affected area, reconditioning of the cover concrete, and replacing the
FRP laminate.
Through on-site tests to be carried out after the application of reinforcements, it can get useful
information especially on the presence of defects at the interface. Available techniques are partially
destructive techniques and non destructive tests.
Quality control of the installation must include at least one round of semi-destructive tests for the
mechanical characterization of the interface and one non-destructive mapping to assess the
homogeneity of the application. Also it is important to provide a monitoring of the behavior of
reinforcements over time, because the long-term behavior of FRP reinforcement is not well known
(Bastianini et al., 2005).
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3.1.7.2 Partially destructive techniques
Semi-destructive tests should be performed on portions of reinforcement produced solely for the
tests without damaging the reinforcement. The tests will be significant only if the specimens will be
created near the reinforcement, by the same operator and using the same materials and the same
procedure and when exposed to the same environmental conditions.
Surface adherence pull-off test
This type of test, which is commonly used to verify the bond strength of overlay or repair materials
applied on a different substrate (see ISO 4624, 2002; ASTM D4541, 2009; UNI-EN 1015-12, 2002;
ASTM C1583, 2004), consists in:
Cutting a circular (diameter ≥ 40.0 mm) or square area (wide ≥ 40.0 mm) on the surface,
taking care not to overheat FRP and also get the incision of the substrate to a thickness of
1.3 ± 0.5 mm.
Pulling off that area, normally to the surface, after the gluing of an apposite aluminium plate
able to accommodate a linking bolt.
The tests are performed by means of a special portable tester and provide as a result the ultimate
pull-off strength value.
Figure 3.12 - Performing of pull-off tests, (Source: UINPD).
According to CNR-DT 200/2004 (2004), FRP application may be considered acceptable if at least
80.0% of the tests return a pull-off stress not less than 10.0% of masonry support compressive
strength, provided that failure occurs in the support itself.
The pull-off tensile strength, fp-o, was evaluated as the average stress on the area, according to
ASTM C1583 (2004).
Surface adherence shear test
Shear-tearing tests are used to assess the quality of bond between FRP and masonry substrates.
These tests can be conducted only when it is possible to pull a portion of the FRP system in its
plane located close to an edge detached from the masonry substrate.
The tests were carried out using the same device used for pull-off tests. In particular, metallic
elements were set up onto the masonry wall and through the FRP strip, with the aim of connecting
the entire test device. Then the FRP element was tightened until collapse. At the end of the test,
the failure tearing force was obtained (ASTM D0905, 1998).
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Figure 3.13 - Shear tearing test: (a) stress distribution; (b) test result, (Olivito and Zuccarello, 2009).
In this case, FRP application may be considered acceptable if at least 80.0% of the tests return a
peak tearing force not less than 5.0% of masonry support compressive strength (CNR-DT
200/2004, 2004; Olivito and Zuccarello, 2009).
Surface adherence torque test
A ring disc is glued on the FRP strengthening surface and partial coring is performed at the outer
and inner diameter, extending 5.0 mm into the concrete. After hardening the disc is twisted off. In
this type of test the bond interface is submitted to torque (fib Bulletin No. 4).
3.1.7.3 Non destructive techniques
It is well known that the success of FRP materials strongly depends on how well they are bonded
to the substrate. For this reason there is a need to detect and characterise defect after their
application. There are many non-destructive techniques for the evaluation of interface and bonding
defect and for monitoring long-term behaviour of the strengthening intervention.
Tap tests
Tap test seems to be the easier method to be used for the identification of defects at the FRP
substrate interface or inside the FRP; this because the infrastructures inspectors are quite familiar
with tap tests and simply need to be trained to hear the difference between bonded and unbonded
laminates, which is somewhat similar to the difference between sounding and damaged concrete.
However scanning very large areas of reinforced structures with tap test could be very expensive
in terms of time and safety (Corvaglia and Largo, 2008).
Ultrasonic pulse echo techniques
Ultrasonic pulse echo techniques can be reliable in detecting defects in application of composites
on homogeneous supports. Therefore, in case of masonry structures, this technique can be used
for stone elements (like capitals or statues), whereas for more complex compositional patterns
other methods should be applied.
Thermovision
Infrared thermovision could be a fast, reliable and confident non destructive testing technique for
the evaluation of bonding defects in FRP. In Huang (2010) is explored the used of thermovision to
verify the presence of detaching, but the procedure is developed in laboratory.
However, the setup of IR technique for the detection of a particular defect (delamination, lack of
bonding) in an FRP reinforced structure needs a specific calibration, leading to the proper definition
of the operational parameters (active/passive approach, distances, time – windows, algorithms)
(Corvaglia and Largo, 2008; Valluzzi et al. 2009).
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(a)
(b)
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Figure 3.14 - Thermographic processing by various algorithms, indicating main discontinuities (artificial defects are
incorporated): (a) second principal projection, by PCA; (b) second phase map, by PPT; (c) map of time of maximum
normalized contrast, by TT, (Valluzzi et al., 2009).
Infra-red thermovision is based on the principle that heat transfer in any material is affected by the
presence of subsurface flaws or any other change in the thermal properties of the material. The
changes in heat flow cause localised energy differences on the surface of the test object, which
can be measured using an infrared detector (thermocameras). Through data processing, the
measured infrared radiation levels are transformed into their corresponding temperature
distributions and recorded in the form of thermograms. Irregularities in the thermogram indicate the
presence of anomalies in the test object. The relationship between the surface temperature and
T 4 where E is the
emitted radiation is based on the Stefan–Boltzmann principle and is E
-2
radiant emissivity (W m ), T is the absolute temperature (K), is the unitless emissivity of the
investigated object and is the Stefan–Boltzmann constant equal to 5.67 x 10-8 W m-2 K-4.
Infrared thermovision can supply significant qualitative and quantitative information on bonding of
FRP materials applied to structural substrates, both preliminary and in-situ periodic investigation,
by means of a reliable low-time-consuming procedure. The images can be stored in a digital format
and a history of the material degradation can be easily examined and visualised as well as
compared to a previous situation by retrieval of archived images (Valluzzi et al., 2009).
It is known that infrared thermovision has some limitations when dealing with deep and low thermal
resistance defects, but it has proved to be still useful in conjunction with high-depth techniques
(Meola, 2007).
Two thermographic techniques can be applied, namely passive and active techniques.
In some in situ structures, the passive thermographic technique is adopted, which can be applied
only if the natural infrared radiation emitted by the object because of a sufficient exposure to sun
light can be utilised.
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In the active thermovision technique, thermal energy is applied externally and uniformly onto the
test object and transient heat transfer phenomena occur. In this way, the surface temperature of
the object is monitored as a function of time by measuring the emitted radiation. Enough care is
taken to avoid the reaching of glass transition temperature for the epoxy resin, equal to about 50
°C. By means of the thermocamera, it is possible to detect the infrared radiation emitted.
(a)
(b)
Figure 3.15 - Active thermography technique, (Feo-Prota, 2005). (a) Heating cycle; (b) Cooling cycle.
The active, transient thermographic method is based on the capacity to analyze the intensity of
infrared radiation released by materials when the surface temperature is conditioned by an
imposed heat flux. Heating system, test set-up and choice of algorithm for analysis must all be
selected and calibrate to the specific problem to be solved.
3.1.8 Confinement for columns and pillars
Confinement is a basic technique to overcome the horizontal actions on an element or a structure
that suffer from lesions caused by compression. It increases the compression strength capacity
and improves the stability of structural element or global behaviour of the structure. Steel and
advanced polymers are of the common materials used for this purpose.
In state-of-art there are not experimental procedures to evaluate the long term effectiveness or the
tension in the confinement, however deformometer or strain-gauges can be used to monitor the
tension levels on the confinement. The tension value, that in modern applications could be
designed, is not clearly suggested by a standard procedure.
3.1.9 Vertical stiffening of earthen building elements
The techniques, described in the Deliverable D3.2 (Tolles et al., 1996; Tolles et al., 2006), are
proposed up to now only on prototypes, and studied for mechanic aspects. Durability and
applicability on real cases and the following control procedures are not yet studied.
Further laboratory research is required beforehand in order to estimate the parameters described
in the following, that allow improving the understanding of vertical stiffening of earthen buildings:
Increase in out-of-plane stiffness;
Improvement in in-plane behaviour;
Bonding FRP-grout and grout-historic masonry;
Stiffness of earthen material;
Density of earthen material.
3.1.10 Others
3.1.10.1
Geotextile Mesh as containment reinforcement to Adobe Walls
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Also in this case the technique, described in the Deliverable D3.2 (Torrealva, 2009 a,b), was tested
only on new laboratory prototypes and considering only mechanic aspects. Durability and
applicability on real cases and the following control procedures are not yet studied.
3.2
LOCAL REPAIR OF CRACKS OR OF DECAYED PORTIONS
It is worth to remind that very seldom the repair of cracks is be able to reconstruct the previous
situation. Some information about eventual movement between the parts could derive by
monitoring systems. As known, monitoring should be prolonged for at least 18 months in order to
take into account thermal deformation.
The monitoring devices should have the highest possible sensibility, as described in D3.2.
However, this simply technique is seldom proposed even if applicable to evaluated all the repair
technique.
3.2.1 Local Dismantling and Reconstruction (“scuci-cuci”)
The local dismantling and rebuilding (“scuci-cuci”) methodology aims to restore the wall continuity
along cracking lines (substitution of damaged elements with new ones, reestablishment of the
structural continuity) and to recover heavily damaged parts of masonry walls. The use of materials
that are similar, in terms of shape, dimensions, stiffness and strength, to those employed in the
original wall is preferable. Adequate connections should be provided to obtain a monolithic
behaviour. The effectiveness of the intervention is strictly connected to the recovering of the
previous wall properties; otherwise the seismic actions could expel the intervention
This intervention consists on the rebuilding or replacing part of the masonry, locally damaged. The
goal of this technique is to restore the structural integrity of the wall portion.
Even if in literature there are not suggested control procedures, single flat jack tests could give
information about the possible stress distribution in case of wide interventions.
3.2.2 Grout injection of cracks
The control procedure is commented in Section 3.1.1.
3.2.3 Bed Joint Reinforced Repointing
The reinforcement of the bed joint is commented in Section 3.1.4.
The application of FRP/SRP/SRG is commented in Section 3.1.7.
The technique could be applied locally to repair cracked panel, even if the change of the property
such as the increase of stiffness should be carefully taken into account.
3.2.5 Crack stitching and anchoring
In general, crack stitching consists in locally joining two independent wall sections, which can rock
or overturn about their base, by means of “stitches”, i.e. joining built-in elements inserted at
staggered points.
The effectiveness of the crack stitching in terms of restoring structural continuity or uniform load
distribution of horizontal loads on a wall is related to the diffusion of the intervention, since force
transfer is limited to the points where the stitches are introduced.
In literature there are not examples of addressed investigation to evaluate the effectiveness of the
technique. However, radar was already applied in order to map the presence of metal nails in past
interventions. The radar is able to locate the metal elements but does not give information about
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the effectiveness of the technique or about the eventual corrosion, in long term maintenance
programs.
3.2.6 Crack stitching for earthen buildings
Crack monitoring
The assessment of whether crack repair is effective can be carried out by means which do not
fundamentally differ from those used masonry, other than in their practical applicability.
The most economic and straightforward technique to assess whether the repair of cracks in
earthen buildings has been effective is the use of plaster patches, thanks to which it is
possible to evaluate whether or not movement is occurring thereafter. After cracks take place,
more precise monitoring techniques can be carried out to assess whether sections continue to
separate and at which rate. These are the use of reference points, grid crack monitor and
demountable (mechanical and digital) strain gauges.
1. Plaster patches
Plaster patches (or gypsum strips) were applied routinely after crack repair in order to
evaluate its effectiveness but also to evaluate the effectiveness of global stability
measures (Figure 3.16). Since plaster strips do not indicate thermal expansion and
contraction, crack depth nor bi-directional movements, further monitoring is
recommended for cases in which further information is required, for instance to
determine the nature of the crack. Vertical shear cracks in massive earth walls can be
expected every 10.0-12.0 m (Fodde, 2008) due to thermal expansion and contraction
not being absorbed for higher lengths.
However the usefulness of such elements is debatable due to their low resolution. The
device is able to detect only consistent structural movement, and does not give
information to the real causes that could be related to environmental conditions or
normal thermal movement of the whole structure.
Figure 3.16 - Plaster Patch installed after restoration of Abdullah Bin Salem Al Damarki House to assess effectiveness of
repair.
2. Reference points
Scratch marks or metal pins can be drawn on opposite sides of a crack, and the
distance between the marks is then measured with a micrometer or dial gauge to
determine movement. Both horizontal and vertical movement in two directions can be
measured by means of three reference points, i.e. triangle vertices. The procedure
required precise periodic measurements. Due to the simplicity of the procedure and to
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the precision of the measurement, the procedure is highly recommended for all the
structure.
3. Grid crack monitor
Crack meters also allow movement in two directions to be measured. A common
device consists of two plastic plates, one opaque plate containing a grid and one
translucent plate showing a set of cross hairs. Movement, measured by noting the
location of the cross hairs with respect to the grid, relies on the plates being fixed to the
wall segments. However the usefulness of such elements is debatable due to their low
resolution. The device is able to detect only consistent structural movement, and does
not give information to the real causes that could be related to environmental
conditions or normal thermal movement of the whole structure.
4. Demountable Mechanical strain gauge (DEMEC)
DEMEC Strain Gauges are used on locating pads, which are attached to each side of a
crack, or holes, which can be drilled directly into the material at hand if required.
DEMEC gauges can be mechanical or digital. High resolution systems are
recommended. The problems are often related to the high data quantity and the
processing, not easily possible for all the buildings all over the world.
Further measures
A methodology for diagnosis and repair should include crack mapping based on photographic
records. Thermovision for visible, or shallow cracks respectively and sonic transmission tests for
structural cracks in earthen buildings are not normally carried out within current on-site practices.
In situ sonic transmission tests have been carried out by Liberatore et al. (2004) on an adobe wall,
showing good correspondence to in situ mortar penetration tests and diagonal compression tests.
Assessment of the quality of earth repointing mortar over time: Penetrometer Tests
The quality of new earthen mortar in masonry can be assessed by means of the Schmidt Hammer
test, the Windsor Penetrometer (ASTM C803), the Liberatore and Spera Penetrometer and
Felicetti and Gattesco Penetrometer.
Within the field of earthen constructions, the Schmidt Hammer (Röhlen and Ziegert, 2010) and the
Liberatore and Spera Penetrometer (Liberatore et al. 2006) have been used, with promising
results. The advantage of Liberatore and Spera´s Penetrometer over the Schmidt Hammer, which
can only test surfaces, is that it can reach a depth of up to 40.0-50.0 mm). For details of the latter
penetrometer, see Liberatore et al. 2001.
Penetration test has been used by Liberatore et al. (2006) to assess the quality of mortar in adobe
masonry and could therefore also be used to assess the quality and deterioration of quality of
repointing mortar over time, as well as allow a comparison to be made between the mechanical
properties of repair materials and of original materials.
Limits of the previous procedure are related to the presence on eventual aggregates.
3.2.7 Others
3.2.7.1 Improvement of weathering performance of earthen materials
These interventions are generally superficially and valuable by direct inspections. However, other
technique as in case of plaster could be suggested, even not specifically documented for earthen
materials: thermovision to evaluate the detachment or Karsten pipes for the water absorptions.
Moisture
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Moisture is a common cause of damage to earthen constructions, which results in compressive
strength reduction (see Figure 3.17) as with some masonry materials, but also in considerable
base erosion with cross sectional reductions that are not commonly encountered in other forms of
masonry other than tuff stone or weak calcarinite masonry.
Figure 3.17 - Dependency of compressive strength on moisture content in rammed earth, (Ziegert, 2003).
While erosion due to rainwater, which causes channels of increasing depth, can be controlled
relatively straightforwardly by means of overhanging roof and regularly maintained wall plaster,
damage due to rising damp and waterborne salts is not as simple to avoid. Reductions in
cross section are very common and though reparable are bound to reoccur if the cause of the
damage is not identified and eradicated. In earthquakes, this type of damage can be
responsible for out-of-plane failure (Figure 3.18).
Figure 3.18 - Moisture damage contributions to instability. Out-of-plane instability (or a contribution to instability) is
caused by weakening or erosion, usually at the base, or saturation or repeated wet/dry cycles resulting in weakened slipplanes at the base of the wall along which the wall can slip and collapse.
Water management and its monitoring
Avoiding moisture increase at the base of walls is therefore essential to decrease the risk of wall
overturning in earthquakes.
This can often be done by ensuring that appropriate land drainage in areas adjacent to the
structures provided, so that ponding is avoided. Ponding, or the localised collection of water at the
wall base, can lead to a reduction in the load bearing capacity of the foundation if the plastic limit of
the soil is reached (Fodde, 2008) which can result in structural cracks in the walls.
Once water management on-site is applied, measures to control its effectiveness in reducing wall
moisture in the walls are the following:
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1. Limited depth moisture meters
The moisture content of earthen masonry can be conveniently measured with moisture meters.
ZRS use GANN Hydromette RTU 600 with Probe pricks (Figure 3.19), electrode tips and 60.0 mm
insulated, active electrode but there are several types of moisture meters on the market, which
measure one or more of several related electrical properties, including the conductivity (or
conversely, the electrical resistance), the impedance, or the fringe capacitance of a material, since
the presence of water significantly alters these properties.
Since the presence of salts also significantly affects the electrical properties by increasing
conductivity, great care is needed in interpreting results, since meters do not differentiate between
moisture conductivity and salt conductivity.
Although moisture assessment should therefore not rely on moisture meter readings solely and
these meters should be used with caution, they are a useful aid in carrying out comparative studies
and studies of moisture content changes over time: determining the absolute moisture level may
not be particularly useful anyway, but when moisture contents are compared over time, they can
indicate moisture content increase and decrease rates and therefore also indicate whether
moisture management of a site where an earthen construction is present is effective.
If the same meter is used throughout a moisture investigation, the effectiveness of water
management to avoid rising damp in walls can be quantified qualitatively by means of a
comparative study.
The top of walls above the rising damp zone as well as their base should be checked for any
moisture that may indicate another source of damp.
Since moisture meters can only measure values up to 8.0 cm in depth, and surfaces are bound to
be dryer than wall cores, measures can be taken after the outermost part of the wall is removed,
which results however in destruction of historic material. Moisture contents of walls near-surface up
to a depth of 6.0 to 8.0 cm are usually estimated, (Table 3.5).
Figure 3.19 - Measurement of superficial moisture content obtained by means of GANN Hydromette at Al Jahili Tower, Al
Ain.
Table 3.1 - Moisture content values obtained by means of GANN Hydromette at Al Jahili Tower, Al Ain, (Source: ZRS
2009).
o
Sample N .
Metering
shaft
Height of
extraction
(from finished
floor)
[cm]
Material
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Displayed
Value
[cm]
[Digits]
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o
Sample N .
Metering
shaft
Material
Height of
extraction
(from finished
floor)
[cm]
Depth of
extraction
Displayed
Value
[cm]
[Digits]
1
0
Loam rendering, surface, undamaged
5
0 - 0.5
78
2
0
Earth block, surface, undamaged
5
~5
84
12
1
5
~5
135
14
1
Loam rendering, surface, hollow
80
0 - 0.5
103
15
1
80
~5
129
Higher moisture readings were found within the earth blocks, while earth plasters contain smaller
amounts of moisture. At surface test points local climatic conditions allow water to evaporate
quickly. Measurements in the wall base and splash water areas showed higher values than areas
of 0.80 m height. These are indications for capillary rising water.
2. Conductivity Meters
Conductivity meters enable low cost scans to be made of the sub-surface conductivity of stone and
masonry structures with the advantage that the actual height of water rise at the core of the wall,
which is generally greater than what is shown or what can be measured on its surface. Since the
method is non destructive and non-invasive, it can well supplement the aforementioned limitations
of moisture meters when sub-surface masonry water content is to be assessed (Table 3.2).
Furthermore, the test still requires preliminary calibration procedures for most of masonry
components.
A widely available conductivity meter is the Geonics EM 38, originally designed to measure the
electrical conductivity of soil for agricultural purposes to an effective depth of up to 1.5m
(www.geonics.com) which has successfully been used to determine moisture location in brick
masonry by Clark and Forde (2003a and 2003b). Although the technique is not current practice in
earthen construction and has not been thoroughly tested, some values are found in the literature
for earthen materials.
Table 3.2 - Conductivity values for earthen materials from the literature.
Conductivity range (mS / m)
Rock Type
Colla et al. 1997
Telford et al. 1976
Argillites
1-80
80-100
Unconsolidated Wet
Clay
200
Clays
10-1000
10-1000
Alluvium and Sands
80-100
80-100
Top soil
Culley et al. 1975
30-700
3. Sample removal and its moisture measurement
Moisture content analysis based on sample removal can be used along moisture meters to
complement their results. For these purposes, ZRS employs the Darr-test, which is used to
establish the correct moisture content by means of sampling, drying and weighing.
The Darr-test is applied for quantitative analysis of moisture contents in most ZRS projects. In
order to allow expression of water from the pores (micro-, capillary, and air pores) only and not to
express the stratum water bound in the clay minerals, a kiln-drying temperature of 40 °C is used,
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analogous to the analysis of gypsum (Ca2SO4 + 2 H2O). The hygroscopic influence of salts can
be determined through analysis of water contents at 50 % RH and 80 % RH, likewise. Some
results for the Al Jahili Tower (UAE) are shown in Table 3.3.
Table 3.3 - Moisture content within building units at different conditions, results m-% is mass water content, RH is relative
humidity, (Source: ZRS).
Sample
No.
Material
Height of
extraction
(from
finished
floor)
[cm]
Depth of
extraction
Water
content at
extraction
Water
content at
23 °C / 50
% RH
Water
content at
23 °C / 80
% RH
[cm]
[m-%]
[m-%]
[m-%]
1
Loam rendering, surface,
undamaged
5
0 - 0.5
0.92
1.51
2.44
2
Earth block, surface,
undamaged
5
~5
1.10
2.27
3.33
3
Earth block
5
30
1.29
2.12
2.90
4
undamaged
80
0 - 0.5
0.79
1.66
2.53
5
undamaged
80
~5
1.01
2.31
3.44
6
Earth block
80
30
0.96
1.99
2.78
11
hollow
5
0 - 0.5
0.90
2.23
3.66
12
undamaged
5
~5
1.19
2.34
3.24
13
Earth block
5
40
1.63
2.84
3.95
4. Consolidation, plastering and its monitoring
Coving, or base erosion caused by rising damp and salt crystallisation, can be repaired by means
of consolidation and shelter coating.
Consolidation consists in applying new mud bricks to the existing decayed wall. Fodde (2008)
recommends brushing-off of all loose earth off the ground surface, and applying a sheet of
geotextile before laying the first brick course, most likely to avoid crack formation when localised
parts of the wall base lose their foundation. The author also cites the insertion of wooden pins to
ensure connection between the new masonry and the historic fabric. This type of consolidation
repair is often carried out by ZRS with the difference that no geotextile nor pins are used (see
Figure 3.20).
Monitoring of this kind of repair work can be carried out by inserting plastic pins in the new repair
masonry in order to have reference points from which erosion patterns can be measured.
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Figure 3.20 - Consolidation without geotextile (wall base) and shelter coating (wall top), Al Jahili Fort, Al Ain (UAE),
(Source: ZRS).
Shelter coating, i.e. the application of a compatible cover as protection to historic material, is only
effective if continuous maintenance, especially after heavy precipitation has occurred. Fodde
(2008) suggests regular inspection and monitoring by means of photographs, with particular
attention to the capping level which when affected by erosional loss allows water to penetrate
inside the coating thus affecting the stability of both historic wall and shelter coating. Inserting
plastic pins in the repair coating in order to have reference points from which erosion patterns can
be measured might also be a useful means of monitoring.
3.3
STABILITY IMPROVEMENT
3.3.1 Enlargement
Masonry enlargement has been used traditionally to increase the load bearing capacity of walls, by
applying it on the intrados, to increase the capacity of vaults or to increase wall stability. In this last
case, frequently the thickness of the new leaf can change in the height, working as a sort of
buttress.
Enlargement refers to the addition of new material (such as an additional leaf of new masonry) to
an already existing member, with adequate connection or interlocking, in order to increase its
section and hence mechanical capacity.
Mechanical compatibility requires (1) the use of a not too different material, regarding stiffness and
strength, with respect to the original one, and (2) a good connection between the original member
and the added material.
None specific control procedure is available in literature or standards. Nevertheless, the use of
radar or sonic technology can be suggested to assess the connection or the interlocking between
the original member and the added material, as this characteristic is one of the most conditioning
to the effectiveness of this technique.
3.3.2 Buttresses
It consists of the addition of massive elements to laterally prop a structure. Buttresses resist lateral
forces and deformations essentially thanks to their self weight. Buttresses contribute to prevent
from failure mechanisms related with lateral deformation. Buttresses originally built as part of the
entire original construction may be very efficient, as they are normally built in a homogeneous way
with the rest of the structure (with the same type of masonry, well interconnected to the rest, while
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also sharing a unique foundation). Conversely, buttresses built as a later strengthening device,
after the construction of the original parts, may show limited efficiency due to lack of satisfactory
interlocking or differential settlements separating them from the rest. Furthermore, when the
buttresses are built as later additions, the structure will need to deform to significant extent in order
to mobilise the new buttress.
None specific control procedure is available in literature or standards. Nevertheless like mentioned
before for the enlargements, the use of radar or sonic technology can be suggested to assess the
connection or the interlocking between the original member and the added material, as this
characteristic is one of the most conditioning to the effectiveness of this technique.
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4 IMPROVEMENT OF SUB-ASSEMBLAGE CONNECTIONS
Masonry building represents a box-type structural system composed of vertical structural elements
- walls - and horizontal structural elements - floors and roofs. Vertical loads are transferred from
the floors, acting as horizontal flexural members, to the bearing walls, and from the bearing walls,
acting as vertical compression members, to the foundation system.
The observations of masonry buildings when subjected to earthquakes have shown that the
behaviour is strongly dependent on how the walls are interconnected and anchored and to floors
and roofs. It is generally recognized that a satisfactory seismic behaviour is attained only if out-of
plane collapse is prevented and in-plane strength and deformation capacity of walls can be fully
exploited.
It has to be mentioned that masonry walls exhibit enhanced vulnerability to out-of-plane bending
(low bending moment capacity mobilized under limited imposed inflexion). This pronounced
vulnerability is negatively affected by all the above mentioned conditions that limit the box action of
buildings, as well as by the poor quality of construction type of masonry and the poor quality of
building materials.
This structural behaviour is strictly connected to the presence and to the quality of the constraints
between walls and floor/roof structures. The presence of ties is another relevant factor in the
effectiveness of the constraints. The influence of the connection between orthogonal walls in the
overturning mechanism has been studied by various authors (de Felice, 2001; D‟Ayala, 2003).
As detailed in Figure 4.1, unstrained wall could globally overturn, while the presence of the floor
constraint due to friction changes the kinematic mechanism triggered by a higher energy. Similar
effects are due to the constraints of roofs structures and ties.
Within the project, the Deliverable 6.1 deeper explores this topic.
Figure 4.1 - Effects of the constraints imposed by floors and vaults, (Carocci, 2001). A unconstrained wall, B floor
constraint; C wall not restrained by roof structures; D roof restraining; E vault thrusting; F tied vault.
4.1
LACK OF CONNECTION BETWEEN WALLS
Besides global extensive interventions, like insertion of tie beams or tie-rods, local improvement of
the connection can be carried out by the techniques described on Section 3.2.5 to stitch cracks.
4.1.1 Tie beams
The introduction of sub-assemblage connections, as an effective alternative to the introduction of
independent structural frames to reinforce structures, is acknowledged by the most updates
seismic codes, thanks to researches and post-earthquake documented surveys. Different types of
tie beams can be used on the reinforcement of historical structures, Figure 4.2, such as: (i)
reinforced concrete beams (limited to short height), (ii) reinforced masonry beams and (iii) steel
beams.
None specific control procedure is available in literature, however it can be suggested the use of
the pacometer to identify and assess the positioning of the rebars and the use of the sclerometer to
assess the quality of the concrete.
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(a)
(b)
Figure 4.2 - Different types of tie beams applied to historical constructions, (Source: UNIPD). (a) Reinforced masonry
beams. (b) Steel beams.
4.1.2 Tie-rods
Metal ties are widely used in traditional buildings as wall-to-wall and wall-to-floor connections
aiming to improve the integrity of the structure. Knowing the concept and details of the original use
is often a prerequisite for making a right decision on the repair method. Low cost and easy
installation, easy maintenance and repair are the great advantages of the techniques.
When easy accessible (e.g. in arches, Figure 4.3), the tie tension could be tested by using dynamic
methods (Briccoli Bati and Tonetti, 1993).
The evaluation of the tie tension could be periodically evaluated, as a maintenance procedure, or
after some aggressive event like an earthquake.
(a)
(b)
(c)
Figure 4.3 - Experimental setup for the tie tension control, (Source: UNIPD).
4.1.3 Hysteretic dissipation anchor
Paganoni and D‟Ayala (2009) developed, within the framework of a Knowledge Transfer
Partnership (KTP) between the University of Bath and Cintec International Ltd, a dissipative device
specifically designed to address the lack of passive systems for the seismic protection of heritage
buildings.
The device is conceived as add-on for stainless steel ties. Thanks to either the hysteretic
properties of a stainless steel element, shaped to optimise its post-elastic behaviour, or a friction
mechanism set to be triggered for a certain level of pulling force, the device allows small relative
displacements, dissipating energy and hence reducing the impact of seismic force on the walls,
and controlling damage. The system has the considerable advantage of being compatible with
existing as well as post-installed anchors.
Initial experimental work (Paganoni and D‟Ayala, 2009) included tests in pseudo-static and
dynamic regime of the dissipating device on its own.
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A campaign of pull-outs tests aimed at characterise the behaviour of strength-only and dissipative
anchors in low shear capacity walls (Paganoni and D‟Ayala, 2010) followed.
Also in this case the technique, described in the Deliverable D3.2, was tested only on new
laboratory prototypes and considering only mechanic aspects. Durability and applicability on real
cases and the following control procedures are not yet studied.
4.2
LACK OF CONNECTIONS BETWEEN WALLS AND FLOORS/ROOF
Traditional intervention concerning the connection between walls and floors/roofs concerned the
tying of the main beams by metals anchoring elements. In this way the wooden beams were
slightly tensioned. Wooden tie beam was another effective way to connect as commented in
Section 4.1.1.
Modern interventions were mainly addressed to replacing of timber structures with R.C. or mix
clay/R.C. floors/roofs. The connection were realised through the R.C. tie beams, with the effects
already commented in Section 4.1.1.
The anchoring of the floor beams to the walls is aimed at prevent the beam slipping and
hammering. Furthermore, the effectiveness of the connection is important to distribute shear action
and restrain the walls preventing possible overturning.
As control procedures for these types of intervention it is possible to use, for example, dynamic
identification to control the state of tension on the ties or to use radar technology or a pacometer to
identify and assess the positioning of the reinforcements.
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5 OPTIMIZATION OF VAULT PERFORMANCE
It is possible to classify the vaults collapse mechanisms based on its causes. Among the possible
sources of damage it is possible to distinguish:
i.
ii.
iii.
5.1
The relative displacement of the supports;
a. Displacement of the supports on the orthogonal direction to the generatrix line of the
vaults;
b. Differential settlement of the piers;
c. Longitudinal sliding.
The variation of the load to which the vaults and piers are subjected;
The decay of masonry.
DIRECT INTERVENTIONS (APPLIED TO VAULTS)
5.1.1 Local Dismantling and Reconstruction (“Scuci-cuci”)
The technique is commented in Section 3.2.1 related to masonry repair.
5.1.2 Grout injection of the cracks
5.1.3 Structural Repointing (Deep repointing)
5.1.4 Bed Joint Reinforced Repointing
5.1.6 Use of extrados R.C. jacketing
The aim of this technique is to remove the extrados heavy filling and replacing them with other
lighter structures for decrease the loads on the vaults.
Comments concerning the wall jacketing are referred in Section 3.1.2 related to masonry repair.
5.1.7 Reducing the loads from extrados infilling
In some situation the reducing of the thrust could be necessary. In this case, the infilling could be
slightly and slowly reduced symmetrically. As know, in common situation infilling has an
equilibrating action.
An alternative strengthening system should be built up, particularly during the working phases.
Although in standards there are not examples of control procedures, it can be suggested the use of
radar technology properly accompanied of careful in-situ inspection.
5.1.8 Extrados stiffening elements, mainly in barrel vaults (“Frenelli”)
Stiffening masonry elements were frequently added in the past. They could be built with the vault
or added at the extrados in a second time. FRP can be used for strengthening together with this
stiffening masonry elements. This is an interesting application in what concerns the preservation
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criteria, as the composite can be applied on the stiffening masonry elements without “touching” the
existing elements, Figure 5.1.
In standards there are not examples of control procedures for this type of intervention; however it
can be suggested the use of displacement transducers to control the crack between the vault and
the “frenelli” and when the FRP is used the control procedures referred in Section 3.1.7 can be
applied.
C
C
Figure 5.1 - Intervention on Arches and Vaults - Palazzo Ducale di Urbino, (Source: UNIPD).
5.2
INDIRECT INTERVENTIONS (SUPPORTING MASONRY STABILITY)
5.2.1 Insertion of the tie-rods and confinement
The technique is commented in Section 4.1.2 related to the wall connections.
The tie tension control through dynamic identification is an effective procedure to evaluate the
effectiveness of the intervention. This technique is also applicable to anchorages.
5.2.2 Buttresses
The technique is commented in Section 3.3.2 related to masonry walls repair.
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6 SEISMIC IMPROVEMENT OF WOODEN FLOORS
In most cases, the wooden floors present in historical constructions are considered deformable
until some elements are added to increase the in-plane stiffness (ex: reinforced concrete slabs),
and until appropriate connections with the perimetral walls are established. Indeed, in the historical
constructions, the floor can hardly be considered as an in-plane bracing element, but rather as a
dead load that unloads horizontally, during a seismic event, on the masonry, (Barbisan and Laner,
1997).
The in-plane stiffening of the floors, even limited, allows to distribute diversely the seismic actions
among the vertical elements, and implies, generally, an increased of resistance, which improves
the structure robustness, (Barbisan and Laner, 1997).
The need to stiffen the floors in their plane, ensuring the connection to the walls, is almost
exclusive of wooden floors, because in the floor solutions in mixed steel-tile or in reinforced
concrete-tile, the in-plane stiffness is usually always assured by the concrete layer, while the
connection to the perimetral walls is ensured by a R.C. beam, (Bazzana, 1999).
However, it should be considered that the transformation of flexible floor into in-plane rigid floors
leads to a redistribution of the horizontal loads over the walls that can have positive or negative
effects, depending on the geometry of the structure and on the mechanical characteristics of the
materials that compose it. Indeed, the stiffening of wooden floors, unless accompanied by
adequate monitoring and improvement of the mechanical characteristics of the supporting walls
that result more loaded (in-plane) with this redistribution, can even be harmful.
In this regard, it is known how important is for the global behaviour of a structure to consider the
stiffness of each material that composes it, because the combination of materials with very
different stiffness causes abnormal and fragile behaviours if the structure is subjected to dynamic
actions, as in the case of seismic actions.
In the Section 6 of the Deliverable D3.2 are summarized the main stiffening techniques used, that
range from the execution of a reinforced concrete layer, to the use of steel ties, beams or plates,
and reinforcement techniques according to the principles of sustainability, with the use of wood
elements. The types of intervention are presented according to the type of material used and
summarised as follow:
Improvement interventions through the use of wood (IPM)
1. Orthogonal or diagonal planking;
2. Only wood technique - Timber flange connected by dowels to main beams, (Modena et al.,
1997c).
Improvement interventions through the use of a reinforced concrete cooperating slab:
1. The Turrini - Piazza (1983) method;
2. The Alessi, Lamborghini, Raffagli (1989) system;
3. The Tampone (1992; 1996) system.
Improvement interventions through the use of steel elements:
1. Metallic plates;
2. Metallic diagonals;
3. Intervention using metallic plates and diagonals (Gattesco et al., 2007).
Improvement interventions through the use fibro-reinforced composite materials:
1. Intervention using FRP, (Angotti et al., 2005);
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2. Intervention using GFRP, (Borri et al., 2004).
However, for none of them there is a specific control procedure of their effectiveness.
Nevertheless, the bending stiffness increasing could be evaluated by standard load tests applying
a known load and by monitoring the related deformation, as generally happens for new structure.
This procedure, simply and effective, is not requested by any code but seldom proposed in the
control of existing wood floors.
MONU within the European project LICONS, which consisted of the development and validation of
low-intrusion systems for the rehabilitation of timber structures that combine the application of
epoxy adhesives, metallic or FRP composite strengthening and/or connection products and timber
prosthesis, has developed a protocol for the quality control of the strengthening phases. The
selection of advanced materials seeks to provide these systems with attributes such as reduced
mass, fast and easy of installation with a minimum of requirements on the job site and personnel,
versatility, structural efficiency, reduced visual impact and acceptable aesthetic aspect (COST
Action E3 2008).
Within the project the following Inspection forms were proposed.
Form C - Record of Inspections and Tests: Solid timber splice fabrication, (COST Action E3 2008).
Control, inspection or test and specifications to
be verified
(1)
DMM
Frequency
of
(2)
inspection
Sample
(3)
characteristics
100%
100%
S.M.
EN...
100%
100%
S.M.
Project
BoS specificat.
100%
100%
S.M.
Project
100%
100%
J.S.
Project
100%
100%
J.S.
Project
BoS specificat.
100%
100%
J.S.
Supporting
documentation
Resp.
(4)
SOLID TIMBER SPLICE FABRICATION
Visual Inspection: verification of timber
characteristics.
The solid timber splice and the element to be
repaired shall be of the same type of timber or,
should this not prove possible, they shall have
the same mechanical, durability and colour
characteristics. The use of timber with raised
natural durability can be justified, even if it is
different from the existing timber.
n.a.
Visual inspection: verification of anomalies and
flaws in the timber.
Timber shall be free, as much as possible, of
anomalies and flaws.
n.a.
Verification of moisture content: moisture
content of solid timber splice shall be between
14 and 16%.
moisture
meter
Verification of geometry: ±5mm tolerance in
cross-section, ±10mm tolerance in length.
BoS
Specification
Project
tape
measure
Verification of location, diameter and depth of
holes/slots: tolerance: ±4mm in location,
+4mm in diameter and +5mm in depth.
Verification of rods/plates characteristics.
n.a.
D3.4
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Grant Agreement n°
244123
Form D - Record of Inspections and Tests: Workshop, (COST Action E3 2008).
be verified
(1)
DMM
Supporting
documentation
Frequency
Sample
(4)
of
(3) Resp.
(2) characteristics
inspection
PREPARATION OF STRUCTURAL ELEMENTS TO BE
REPAIRED
Verification of propping.
n.a.
Project
100%
n.a.
S.M.
100%
n.a.
S.M.
Project
BoS specificat.
100%
n.a.
S.M.
Project
100%
n.a.
J.S.
Project
BoS specificat.
100%
n.a.
J.S.
100%
n.a.
J.S..
Project
moisture
BoS specificat.
meter
Verification of moisture content: timber shall
have moisture content below 20%.
Verification of cleanness of holes, slots and
gluing surfaces.
n.a.
DIMENSIONAL VERIFICATIONS
Verification of cutting of degraded timber areas:
tolerance of +10mm in length.
tape
measure
Verification of location, diameter and depth of
holes/slots: tolerance: ± 4mm in location, +4 mm
in diameter and +5mm in depth.
Verification of rods/plates characteristics.
n.a.
Project
BoS specificat.
Form E - Record of Inspections and Tests: Mixing and application of adhesives, (COST Action E3 2008).
Control, inspection or test
and specifications to be
verified
MIXING AND APLICATION OF
(1)
DMM
Supporting
documentation
Frequency of
(2)
inspection
Sample
(3)
characteristics
prEN XXX Part 1
1 per
adhesive kit
3 20cm3 pots;
1 thermal insulated box
S.M.
1 per
adhesive kit
2 pieces of structural
element identical to
intervention, each with
0.90m×0.065m×0.030
m; fill with adhesive
one of the pieces, that
should have a 3mm rim
all around; overlay the
other piece; let cure
prior to sending to lab
for testing
S.M.
1 per
adhesive kit
Piece of structural
element identical to
intervention; 5 glued
rods (minimum free
length: 24cm)
S.M.
Resp.
(4)
ADHESIVES
Characterization
adhesive cure.
tests
of
Thermal
insulated box +
thermocouple
system reading
prEN XXX Part 2
Verification of the adhesive
joint shear strength.
Verification
of
pull-out
resistance of glued rods.
(CEN TC193/SC1/WG11
N20
(CEN TC193/SC1/WG11
N21
Pull-out test
devices
prEN XXX Part 3
(CEN TC193/SC1/WG11
N22)
D3.4
38
NIKER
Grant Agreement n°
244123
Form F - Record of Inspections and Tests: Verification of final work (COST Action E3 2008).
be verified
(1)
DMM
Supporting
documentation
Frequency
Sample
(4)
of
(3) Resp.
(2) characteristics
inspection
VERIFICATION OF FINAL WORK
Visual inspection: the surface of the repaired
element shall be free of flaws and deformations.
n.a.
-
100%
100%
W.E.
Verification of the geometrical compatibility
between the solid timber splice and the structural
element.
Tape
measure
-
100%
100%
W.E.
D3.4
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Grant Agreement n°
244123
7 IMPROVEMENT OF THE GLOBAL STRUCTURAL BEHAVIOUR
In general, the interventions should be aimed at improving the structural connections, and reducing
horizontal diaphragm deformability, at increasing masonry strength; furthermore they should
improve the behaviour of vaults, arches, pillars, etc… Nevertheless, in numerous cases very
invasive structural modifications have been applied, probably as a result of the assumption that
they should provide a higher safety level, but without any definite proof of their effectiveness.
The improving of the global behaviour of a building could be evaluated by dynamic methods e.g. by
a stiffness increasing and/or a comparison with theoretical results, an example of this is the work
carried out by Casarin (2006) in the cathedral of Reggio Emilia.
The variation of the modal parameters evaluated before and after the intervention could be an
effective means to trace the effects of the strengthening, although a clear structural interpretation
of the observed variations needs accurate model-based investigations (Gentile et al., 2003 and
2007).
Structural monitoring, static and/or dynamic could be a reliable method of structural control over
time. Nevertheless most of time, the costs could be effort only for monumental or public buildings.
An example of structural monitoring is presented by Mazzon 2010 with a series of dynamic tests on
whole multi-leaf stone masonry building models, unstrengthened and strengthened through grout
injection. The execution of these shaking table tests allowed to evaluate the influence of the
considered strengthening technique on the overall dynamic behavior of the injected structure.
Furthermore, also the increasing of strength and the seismic response of the building models could
be evaluated.
Dynamic tests carried out on whole stone masonry buildings constitutes the core of the research.
The first significant difference between the un-strengthened and injected models is the sudden
decrease in all frequencies of unreinforced model at 0.25g, while both injected models show a
gradual decrease during the whole experiment (Figure 7.1). On the contrary, the repair model
manifests a wide localized increase, while the unreinforced model has a monotonic decrease. The
repair building behaves similarly to the injected one, even if the localised increase is lower.
Figure 7.1 - Comparison of the first three frequencies of all building models.
The analysis of the mode shapes of all models confirms the observations performed for the
previously presented elaborations. Both the identified mode shapes of the unreinforced model
show a sudden change, when heavy damage arose (Figure 7.2).
D3.4
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Grant Agreement n°
244123
(a)
(b)
Figure 7.2 - unreinforced model, (a) first and (b) second mode shape.
Differently, both injected structures exhibit a gradual variation in normalized modal deformations,
once again emphasizing as the use of lime grout is able to induce a gradual damage to masonry.
However, repairing intervention on the repaired model can only partially recover the initial
deformations of the unreinforced structure, unlike frequencies. Nonetheless, the reapir model
could sustain higher seismic loads than the URM one, limiting the overall degradation of both
identified mode shapes. The best overall behavior is exhibited by the strengthened model, since a
larger and gradual variation in modal deformations is allowed (Figure 7.3).
(a)
(b)
Figure 7.3 - Strengthened model, (a) first and (b) second mode shape (Mazzon, 2010).
D3.4
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Grant Agreement n°
244123
8 FINAL REMARKS
The general overview of the main repair techniques reported in Deliverable D3.2 showed several
criticisms in the decision process, lacking Standards/Recommendations but also guidelines which
could help in the choice.
Also most of research is mainly aimed at the study of mechanical aspects of the techniques,
without an addressed deepening of the laying down procedures and possible problems, the
durability, the maintenance aspects, the on-site controls etc...
It is worth to remind, that several handbook are available in literature, but most of them describe
shortly the single techniques. Up to now, the following aspects are not yet considered:
Maintenance suggestions and periodic controls/monitoring
Long term performance / durability
Life time
Standards and/or Recommendations
Parameters to take into account in analytic procedures
Laboratory controls and on-site controls
Control parameters of the effectiveness of the intervention
Analytic procedures and structural modelling.
Furthermore, for most of the studied techniques any control procedure or on-site test was
developed or requested by any international standard.
This fact leads to wide uncertainness concerning the control of the workmanship, application
mistakes or concerning the effectiveness of the techniques. In most case neither local calibrations
nor controls are suggested. The international debate, also concerning new strengthening methods,
does not touch what could be the meaningful parameters to evaluate on-site in order to define the
quality of the application.
Currently, on-site control of repair techniques are mainly visual techniques.
The lack of experimental test and control procedures is a critical point of the whole process.
Application mistakes or ineffective intervention are widely documented after most of the recent
earthquakes.
Some intervention techniques lead to significant modification of the original structural behaviour.
Even though those intervention techniques may be considered “in principle correct”, as they
contribute to significant resistance improvement and/or redistribution of seismic loads and/or
ductility enhancement, due to the limitations related with the theoretical/numerical models, the real
behaviour of the strengthened historic assets cannot be accurately predicted.
One of the frequent justifications is related to the costs of the testing procedure, without to take into
account that is indubitable that an ineffective or poor intervention has higher costs.
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D3.4 - Critical review for the onsite control of the repair

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