Structural Analysis of Historic Construction – D’Ayala & Fodde (eds)

© 2008 Taylor & Francis Group, London, ISBN 978-0-415-46872-5

Strengthening of masonry structures with Fibre Reinforced Plastics: From

modern conception to historical building preservation

M.R. Valluzzi
DAUR, University of Padua, Italy

ABSTRACT: Modern techniques and innovative materials are often rapidly proposed and allowed in the current
practice, even for restoration of historical constructions, where fundamental preservation criteria have to be taken
into account.The large variability and complexity of masonry structures and typologies make particularly difficult
the preliminary choices for proper structural models and interventions, that should be based of suitable knowledge
of both existing and new materials, and of their interaction under environmental and loading conditions. Despite
the increasing number of specific studies of FRP reinforcement on masonry structures, still limited codes and
recommendations are available so far. Harmonization of test procedures and methods should be pursued, in order
to compare results and calibrate analytical and numerical models for design and assessment rules.

1 INTRODUCTION Despite the large accessibility to various prod-

ucts (bars, strips, laminates, sheets, cords, grids),
In the last two decades, among modern and innovative made of several reinforcing materials (carbon, glass,
solutions of intervention on existing structures, com- aramid, . . .) and applicable in different modalities on
posite materials, as FRP (Fiber-Reinforced Plastics), masonry structures (embedded inside grooves or bed
have been increasingly considered for strengthen- mortar joints, externally bonded or anchored), design
ing and repair of both modern and historic masonry rules for the interventions, feasibility recommenda-
constructions (buildings, bridges, towers) and struc- tions and procedures aimed at checking the effective-
tural components (walls, arches and vaults, piers and ness of the technique and monitoring are still under
columns). definition.
FRP material systems are composed of fibers Starting from extension of approaches proposed
embedded in a polymeric matrix, which bind and for concrete structures, and after the critical evalu-
protect the fibers themselves, in order to allow load ation of the impact of generalized interventions on
transferring and to activate their mechanical prop- historical structures (Giuffrè 1993, Tomazevic 1999,
erties. High tensile strength and stiffness-to-weight Binda et al. 2006), researches and studies have been
ratio, fatigue and corrosion resistance, easy in-situ more and more focused on the specific features of the
feasibility and adaptability, and progressive reduc- masonry material, by recognizing its lack of homo-
tion in production and distribution costs, are the main geneity and the large variability of typologies and
characteristics that encouraged the diffusion of these constituent basic materials and aggregations (brick,
materials at different levels: to improve the global stones, mortar, mixed arrangements, . . .).
behaviour in seismic zone (tying, connections among This approach has led to a new impulse for the
components, strengthening), to counteract specific upgrading of standards devoted to masonry in seis-
incipient or developed damage (high compression, mic zone, which often include reference to specific
shear and/or flexural conditions), and to repair very codes or recommendations on the possible applica-
specific local weaknesses depending on the peculiar tion of FRPs, unfortunately still very limited (e.g. the
construction typology. No yielding is exhibited prior OPCM 3431/2005 and CNR-DT 200/2004, in Italy;
fibres failure, and sensitivities to impact, notching ACI 440M/2004 in US).
and environmental agents could be present. Fibres The adoption of FRPs for strengthening is mainly
activate their characteristics along their prevalent dis- aimed at reinforcing masonry structures and compo-
tribution, whereas have negligible properties in the nents by increasing their ultimate capacity (strength
other directions. and displacement), and often this is achieved by

33
modification of mechanisms at collapse, which can
involve further resisting phenomena.
What essentially emerges from the analysis of a
number of works available in literature aimed at inves-
tigating the mechanical performances of strength-
ened structures and components, and from the code a) b)
proposals, are still needs of:
Figure 1. Textile sheets and laminates (a), and various
– definition and putting into practice specific cau- features of FRP bars (c).
tious criteria for possible application of composite
materials in the historical construction preservation
field;
– clarification of critical aspects of application tech-
nologies (e.g., bond and anchorage of textiles and
bars);
– standardization of methods and experimental pro-
cedures for the characterization of the mechanical
performance of strengthened components to define
proper design and assessment criteria; a) b) c)
– definition and validation of investigation proce-
dures for the evaluation of the effectiveness and Figure 2. Wet lay-up system (a), structural repointing
durability of the intervention. (b) and specific anchorage devices for bars (c).

comparison with laminates but, due to the brittleness

2 MATERIALS AND COMPONENTS to folding, specific solution for anchorage should be
adopted (Figure 2). Small diameter bars or strips are
2.1 Strengthening materials used in the bed joints and a special care should be
taken in the repointing phase, in order to incorporate
Among different solutions addressed to masonry struc-
the new reinforcing system in the behaviour of the
tures, FRPs are usually proposed as application of
masonry. The aesthetics of the surface is commonly
near surface mounted bars (cylindrical or prismatic
preserved in this case.
reinforcement inserted in grooves cut on the masonry
surface) or structural repointing (bed joints reinforce-
ment) (Nanni et al. 2003), and externally bonded sheets 2.2 Masonry typologies and damage
or laminates (wet lay-up system) (Figure 1).
Existing masonry constructions could be part of
The use of Carbon and Glass fibres is predominant
modern constructive systems or historical contexts
in comparison with other types, due to their higher
(Figure 3). Their behaviour and proneness to dam-
accessibility on the market and of sufficiently high
age are connected to specific hazardous conditions
mechanical properties (usually compared with ordi-
(e.g., seismicity, subsidence, high lateral or vertical
nary steel), together with epoxy resins for external
loads), which consequently influence the choice of
gluing, and/or modified mortars for embedment in
intervention solution.
joints or grooves.
Therefore, classification of masonry and damage is
More recently, various inorganic products (cement,
fundamental, as it could be even very peculiar and
lime or clay grout) are introduced as support for
diversified among countries, depending on specific
fibres, in order to combine more suitable materials for
constructive and typologies history (Modena 1997,
the intervention on different components of existing
Binda et al. 2006).
structures.
Materials may be very different (solid or multi-
Textiles and sheets present the high advantage of
leaf sections), as well as their combination in struc-
flexibility, allowing disjointed portions or even whole
tural systems (load bearing or infill walls, vaults and
structures to be wrapped; nevertheless, a proper prepa-
columns).
ration of the surface of application is needed (sand-
In this context, FRP reinforcement could have
blasting, laying of primer and putty), and aesthetics
potential in (Figure 4):
reestablishment should taken into account. The bond
at the masonry-FRP interface is the main responsible – counteracting global or partial overturning (façades
for the mechanical performance of the intervention or corners of buildings) and improve collaboration
and of the strengthened component. among components;
On the contrary, application of bars do not require – in-plane or out-of-plane strengthening (walls under
particular preparation works of component surface in shear and bending);

34
 a)

a) b)

b)

Figure 3. Modern residential (a) and masonry historical c) d)

(b) buildings in severe conditions.
Figure 5. Loading test on masonry assemblages: vaults
(a) and pillars (b), in-plane (c) and out-of plane (d) testing on
walls.

related to the improvement of the flexural capac-

ity and the behaviour in seismic area (Schwegler
1994, Saadatmanesh 1997, Triantafillou et al. 1997
and 1998, Borri et al. 2002, Corradi et al. 2002,
Brencich et al. 2005, Shrive 2006). Then, more spe-
a) cialized literature has been proposed, dealing with
specific experimental, analytical and numerical works
on subassemblages: arches and vaults (Briccoli Bati
et al. 2000 and 2001, Foraboschi 2001 and 2004,
Lourenço et al. 2001, Luciano et al. 2001, Valluzzi
et al. 2001, Barbieri et al. 2002, Basilio et al. 2004,
Oliveira et al. 2006, Borri et al. 2007, De Lorenzis
et al. 2005 and 2007, Baratta et al. 2007) (Figure 5.a);
columns and piers (Micelli et al. 2004, Aiello et al.
b) c) 2005 and 2007, Krevaikas et al. 2005, Nurchi et al.
2005, Corradi et al. 2007) (Figure 5.b); in-plane
Figure 4. Typical application of FRP textiles and bars in (Ehsani et al. 1997, Luciano et al. 1998, Valluzzi et al.
masonry: (a) vaults, (b) walls, (c) pillars. 2002, Haroun 2003, Cecchi et al. 2004, De Lorenzis
et al. 2004, Ascione et al. 2005, Hamid et al. 2005,
– confining under vertical loads (columns and piers); El-Gawady et al. 2005, El-DAkhakhni et al. 2006) and
– bonding support for curved shapes (arches and out-of-plane (Albert et al. 1998, Gilstrap et al. 1998,
vaults). De Lorenzis et al. 2000, Velasquez-Dimas et al. 2000,
Hamilton et al. 2001, Hamoush et al. 2001, Kiss et al.
2002, Kuzik et al. 2003, Galati et al. 2004, Li et al.
3 TEST METHODS AND ANALYSIS
2004,Foster et al. 2005, Turco et al. 2006, Mosallam
2007) behaviour of wall panels (Figure 5.c and d); and
3.1 Experimental procedures
on bond (Ehsani et al. 1997, De Lorenzis et al. 2000,
Several contributions from researches are focused Briccoli Bati et al. 2001, Casareto et al. 2003, Tan et al.
on the experimental behaviour of structural elements 2003, Savoia et al. 2003, Aiello et al. 2005 and 2006,
and assemblages. The main aim is to characterize Liu et al. 2005) (Figure 6).
the mechanical behaviour of strengthened elements, Harmonization of experimental procedures is a
in order to define simplified model for design and urgent need that international bodies of standardiza-
assessment. Very first contributions about application tion and related professional corporations should con-
on masonry concerned general aspects, especially sidered, in order to allow comparison among results.

35
 where M is the maximum moment at the section under
consideration, V is the corresponding shear force,
d the distance from the extreme compression fibre to
the centroid of tension reinforcement, fm
is the com-
pressive strength of masonry, An is the compressed
area of masonry, Af is the reinforcement area, P is
the axial load, ffe is the design strength of FRP, and
s in the spacing of horizontal reinforcement in the
vertical direction. For CNR DT/200, the analogy with
the design formulas proposed for reinforced masonry
beam, as in the Eurocode 6, is evident:

where t is the thickness of the wall, fvd is the design

shear strength of the wall by using a Coulomb fric-
Figure 6. Experimental tests on local mechanisms: pull-off tion law, Afw is the area of reinforcement parallel to
tests on surface (a), brick-FRP adhesion test (b), adhesion on the shear action, pf and α are the spacing and the
mortar joints (c), splitting of rods (d). inclination of the reinforcement, ffd is the strength of
the reinforcement, assumed as minimum between the
Especially for aspects non easy to clarify as the effec-
design tensile strength and the delamination load, γRd
tive contribution of the reinforcement on shear and
(equal to 1.2 in this case) is the partial safety factors
combined actions, as well as the influence of delamina-
for design, whereas partial factors applied on materials
tion in reducing the efficiency of the bond at the inter-
are γM and γf , for masonry and FRP respectively.
face, homogeneous methods should also be set to allow
Actually, in-plane rotation, and compression com-
proper calibration of analytical and numerical models.
bined with other conditions could affect the strength-
ened component subjected to lateral actions, and
3.2 Standards and recommendation proposals
proper limitation of the effectiveness of the interven-
Despite the several documents available as codes or tion due to lack of bonding and or environmental
guidelines for application of FRP in concrete struc- conditions should be taken into account (Figure 7).
tures, at present only the CNR-DT 200/2004 and the In this connection, the two documents still present
drafts of ACI 440 are available. several dissimilarity in the definition of reducing fac-
In both cases, the formulations proposed for rein- tors of the nominal tensile strength and the rupture
forced masonry, derived from of the theoretical strain of FRP for creep and environmental exposure,
approach of reinforced concrete, is mainly adopted. as evidenced in (Garbin et al. 2006), ranging from
Bond and shear are definitely the main problematic 0.80 to 0.30 for the Italian standard and from 0.55 to
aspect to clarify, as standard experimental methods are 0.20 for the US one, respectively for Carbon or Glass
not provided, and analytical models are often not in FRP. Moreover, proper coefficient (namely km and kv )
agreement among them. should be considered to take into account debonding
As an example, the well-known truss analogy is influence in flexural and shear capacity, depending on
considered for the analytical formulation of shear several factors, as: the strengthening systems and con-
behaviour, particularly suitable for infill walls, where figurations, the materials at the interface, the amount
the corner crushing limit is preferred to diagonal and distribution of FRP, etc. On the basis of exper-
cracking or sliding shear. The contribution of FRP imental results these coefficient can vary from 0.2
(Vm,f or VRd,f ) is added to the strength of plain masonry to 0.8, being particularly low under shear conditions
(Vm or VRd,m ) as follows. For ACI 440: (Garbin et al. 2006).
By considering the results available in literature
obtained by diagonal compression tests, an integration
of these data is possible. Actually, diagonal compres-
sion led to different failure mode (usually splitting),

36
 a) b)

Figure 7. Debonding of CFRP strips due to peeling (a), FRP

rupture beyond bonding limit (b).

Table 1. Diagonal compression tests.

Reference unit type disposition sides n. tests

Figure 8. Ultimate load of strengthened configurations
compared to reference strength of clay and concrete walls
Valluzzi 2002 clay diagonal 2 4
subjected to diagonal compression tests.
Yu 2004 clay horizontal 2 1
Yu 2004 clay vertical 2 1
Grando 2003 clay horizontal 2 1
Valluzzi 2002 clay net 2 9
Valluzzi 2002 clay diagonal 1 4
Gabor 2006 clay diagonal 1 3
Yu et al. 2004 clay horizontal 1 1
Yu et al. 2004 clay vertical 1 1
Grando 2003 clay horizontal 1 1
Tinazzi 2003 clay vertical 1 1
Valluzzi 2002 clay net 1 7
Tinazzi 2003 clay net 1 1
Yu 2004 concrete horizontal 2 1
Yu 2004 concrete vertical 2 1
Yu 2004 concrete horizontal 1 1
Yu 2004 concrete vertical 1 1
Grando 2003 concrete horizontal 1 3 Figure 9. Increase of load versus normalized maximum
Morbin 2003 concrete horizontal 1 1 strength of reinforcement.

between clay and concrete masonry, and the highest

values are mainly related to GFRP.
than modes involving friction (as for the application of By analyzing the data in comparison with the nor-
the Coulomb law, adopted in the formulation proposed malized maximum strength of the reinforcement ω,
by standards), but it is still widely considered on exper- given by the ratio of the maximum FRP tensile strength
imental basis, due to its particularly easy execution. (Ef Af εf ) and the reference value of the shear strength
More reliable combined vertical and lateral load set- of masonry τm , computed on the net diagonal area,
up are progressively adopted for shear, but available multiplied by the gross area of the panel Am , results
results on literature are still very limited. Uniformity are as in Figure 9.
for diagonal compression test should at least concern Double values of the strength are obtained in a rather
the dimensions of the walls, to be not lower than 1 m large range of maximum strength of the reinforcement.
for side, in order to avoid local effects in small size By defining an efficiency factor kv , as ratio between
elements. the increase of load measured by the diagonal test
The samples given in Table 1, available from appli- and the maximum normalized FRP strength, the high-
cation of mainly CFRP and GFRP sheets by wet lay-up est effectiveness is achieved by minimum amount
system, are rather comparable among them, even of reinforcement by using the diagonal symmetri-
deriving from different reinforcement configurations cal pattern (0.65–0.85 on clay bricks, halved in the
and type of support. case of single side applications); unidirectional pat-
By taking into account a reference mean value for tern (usually in the horizontal direction) shows a good
the strength of unreinforced panel of about 100 kN behaviour, equivalent or even better if compared with
and 140 kN for clay and concrete walls, respectively, grid patterns, even if symmetrical (Figure 10).
the increase of strength grouped by configurations is Also for bonding, the reference models are adopted
depicted in Figure 8. The best performances, due to from the concrete approach; many strength models
diagonal and symmetrical dispositions, are confirmed. have been developed in the last decade, but, again,
The improvement in shear strength is comparable the lack of standardization of harmonized procedures

37
 Figure 11. Double-lap shear test executed on CFRP sheets:
experimental set-up (a), fingerprint on brick after test (b),
Figure 10. Effectiveness factor for shear strength for differ- peeling of brick surface on FRP (c) (Panizza et al. 2008).
ent amount and configuration of FRP reinforcement.

for experimental tests, led to results often difficult to

compare. CNR DT/200 adopts as bond length le and
strength ffdd the following formulations:

where γFk = c1 · f · fmtm (N mm) is the characteristic
value of the fracture energy, Ef is theYoung modulus of
FRP in the direction of the applied force, tf is the FRP
thickness, fmtm = 0.1fmk is the mean tensile strength
of masonry (considered coincident with the strength Figure 12. Scheme of wall adopted for FE simulation: unre-
of the blocks), γM and γf ,D are partial safety fac- inforced wall (a), horizontal FRP strip application in lintels
tors, varying from 1.1–1.25 and 1.2–1.5, respectively, (b), vertical strips on main vertical walls to reinforce flexural
behavior (c), addition of horizontal strips on main vertical
depending on the certification of the entire bonding
sects to reinforce shear behavior (d).
system on the support, or of only the single materials.
c1 is a coefficient to identify on experimental basis or
to adopt equal to 0.015 (0.03 is proposed for concrete connection between reinforcement and masonry. The
with the same equation). comparison with the application of equations (5) and
The non homogeneity of masonry due to the pres- the elaboration of experimental data able to define effi-
ence of mortar joints, and the consequent influence in ciency laws for debonding as in (Panizza et al. 2008),
the bonding phenomenon of the different mechanical allowed to calibrate a FE model (with DIANA), in
properties and of the geometrical discontinuity, are not order to simulate the performance of shear and flexural
considered in the model; moreover, a unique signifi- strengthening with CFRP sheets applied in a masonry
cant value for the fracture energy along the connection wall including openings. The scheme of the model is
is assumed. depicted in Figure 12, and the comparison among the
A fundamental contribution to clarify these aspect main parameters at the interface between reinforce-
is done by several research groups (Briccoli Bati et al. ment and masonry, to be used for the model, are given
2001, Aiello et al. 2003 and 2006, Casareto et al. in Table 2. Experimental elaboration obtained by DL
2003, Basilio et al. 2005, Panizza et al. 2008), but shear tests have been considered, taking into account
different test procedures are adopted, thus comparison a reduction of 30% to obtain reasonable characteristic
of results is often unreliable. In particular, the most values, to compare to the ones computed according to
suitable arrangements could be the double-lap (DL) the CNR standard.
(Figure 11) and the single-lap shear test (SL), the latter The main characteristics of materials were derived
being the most effective, due to the problem of repro- from available experimental tests, or computed on the
ducing actual symmetry of load distribution in the DL basis of the national standards. For clay bricks, a char-
configuration, but not simple to realize, in comparison acteristic compressive strength of 41.2 MPa, a mean
with the former one. tensile strength of 2.4 MPa and an elastic modulus of
The identification of ffdd is crucial, as it represents 16 GPa, were assumed; a mortar M2.5 (MPa, com-
the parameter strictly related to the efficiency of the pression) was considered, whereas computed global

38
Table 2. Mechanical properties of materials.

Specific fracture FRP maximum

energy fk strength (delamination)
Material (N/mm) ffdd (MPa)

CNR DT 200 0.04 335

DL shear tests 0.99 1660

properties of masonry were: 8.5 MPa for the compres-

sive strength, 8500 MPa and 3400 GPa for the elastic Figure 13. Comparison among plain masonry and three
and the shear moduli, respectively, and a Coulomb law strengthening configuration by using experimental elabora-
for shear strength calibrated with parameters equal tions and elastic-brittle law for FRP strips.
to 0.3 as cohesion and 0.4 as friction coefficient.
High-strength CFRP applied in strips 100 mm wide
were considerd, having nominal elastic modulus of
230 GPa and equivalent thickness of 0.165 mm. Loads
derived from a three storey building were assumed,
and the simulation of the effect on the base floor was
performed.
From Table 2, the maximum fracture energy and
the limit of experimental delamination are thus about
25 and 5 times higher than the valued proposed by
the code, respectively. Four configurations were con-
sidered, characterized by progressive reinforcement,
from plain masonry to global horizontal confinement,
up to application of horizontal and vertical strips on
Figure 14. Comparison among plain masonry and three
the main walls, 50 cm spaced (Figure 12). Non-linear strengthening configuration by using experimental elabora-
push-out analysis were performed, by considering pro- tions and elasto-plastic law for FRP strips.
gressive increase of horizontal acceleration, uniformly
distributed along the height of the wall. The comparison with models where fracture
The numerical results are given in Figures 13 to energy parameters are assumed as in the CNR stan-
15. To take into account a possible residual bond after dards revealed minor performances, thus confirm-
delamination occurrence, the comparison between the ing the proposed models being highly conservative
assumption of a elastic-brittle or elastic-plastic law for (Figure 15). This is surely safety oriented, but if not
the FRP behaviour was considered. controlled in its boundaries could induce overesti-
Despite the simplification adopted in the modelling, mation of FRP design, and consequent utilization of
several points can be discussed, by analyzing the dia- unnecessary reinforcement. Moreover, the sensitivity
grams which compare the imposed acceleration to of CNR assumptions to the elastic-plastic or elastic-
the displacement at the control point (Figure 12.a). brittle behaviour of FRP are less evident in comparison
First (Figure 13), by considering the experimental with experimental elaboration of basic parameters.
elaboration on fracture energy and delamination, the Finally, it is worth to remark that experimental
unreinforced model is subjected mainly to rocking, results on bond are available by tests where FRP is
confirming the high vulnerability of masonry build- glued only on brick surface, neglecting the signifi-
ings to rigid movements (a). The shear strength is not cant influence of mortar joints in the complex adhesion
activated in the walls, and the preliminary horizontal phenomenon involving the masonry.
tying is not able to increase the peak load, but only
to homogenize the plateau in the plastic branch (b).
By introducing vertical strips, the load is significantly
4 FEASIBILITY IN HISTORICAL BUILDINGS
increased, with minor differences between flexural (c)
and combined shear (d) reinforcement. The elasto-
4.1 Reference criteria
plastic behaviour of FRP is able to increase of about
25% the peak load in the complete strengthening con- Interventions to perform in historical environment
figuration, and to guarantee a constant plastic plateau cannot disregard to satisfy the specific requirements
(Figure 14). on which preservation is based.

39
Figure 15. Comparison among plain masonry and three
strengthening configuration by using CNR DT-200 for-
mulation and elastic-brittle or elasto-plastic law for FRP
strips.

It is worth to remark that, even in very hazardous

conditions, as mainly occur in seismic zone, a proper
compromise has to be taken among safety and preser-
vation, keeping priority the safeguard of human life.
This enable to reduce and control upgrading, in favour Figure 16. Repair intervention on masonry vault of Villa
of alternative measures of improvement, specifically Bruni (Padova): position and view of depressed structures
targeted to the large complexity of historic masonry propped before intervention (a), design and assessment with
and constructions (ICOMOS/ISCARSAH). Recent contribution of FRP sheets (b), scheme of global intervention
updating national codes (e.g., OPCM 3431/2005 seis- and detail of application of CFRP strips at extrados in severely
cracked zones (c).
mic code in Italy) finally provide specialized sections
for existing masonry, recognizing the differences in
typologies and materials, and by pointing out the great the identification of compatible binders with original
importance of preliminary knowledge, supported by masonry.
the suitable application of in-situ non-destructive (ND) Cautious approach should dominate, as well as the
and minor-destructive (MD) tests. basic principle that intervention now has not to pretend
Nevertheless, the Charter of Venice (1964), the to be definitive, as further more appropriate measures
Declaration of Amsterdam (1995) and the Charter of can be more reliable in the future.
Cracovia (2000), could be considered reference docu- The CNR DT-200 itself declare that interventions
ments for the definition of criteria and actions devoted with FRP on monuments and historical architecture
to Cultural Heritage. Minimum interventions, having have to be justified as indispensable for the building,
characters of “reversibility” (intended as substitutabil- and the respect of the above-mentioned principles of
ity or removability); use of materials and techniques restoration has to be guaranteed.
compatible with the original ones, able to guarantee
4.2 Some cases study and applications
durability to the intervention itself and, consequently,
to the building; respect to the original functions (both The current use of FRPs in restoration work, should
structural and of utilization), distinguishability of the be particularly cautious when dealing with historical
intervention; all these criteria should be considered constructions, as many restoration principles cannot be
when proposing repair or strengthening of historic fully satisfied. On the contrary, their high mechanical
structures. performances can be usefully exploited, where other
FRP has a great potential to improve the brittle systems fails or are more invasive. Especially tex-
behaviour of masonry components, but many aspects tiles and bars have the main advantage of not increase
related to its interaction with traditional materials and dimensions of strengthened sections, thus their use,
durability are still under experimental study, especially if properly designed to solve specific problems, can
due to the use of resins as bonding system. be targeted to large elements, but also to solve very
More recent studies are focused on the use of peculiar weaknesses, not only in standard bearing
organic matrixes, as FRCM (Fiber Reinforced Cemen- masonry constructions. Some examples are given in
ticious Matrix) or TRM (Textiles Reinforced Mortar) the following.
(De Lorenzis et al. 2004, Prota et al. 2006, Papanicolau Even if in large assemblages, FRP can be very ver-
et al. 2007), and could represent significant steps for satile to repair urgent local cracks, as part of combined

40
Figure 17. Repair intervention on masonry vaults of S.ta
Corona Church in Vicenza: view of church and detail of
cracked cross vault (a), scheme of intervention at extrados
and view of FRP application combined with injections (b).

intervention. As an example, the consolidation of the

very depressed thin vault of the central hall of Villa
Bruni in Megliadino S. Vitale (Padova), has included
the repair with FRP strips of the main cracks at the Figure 18. Intervention on church of S.ta Maria in Organo
intrados and the extrados, together with other tying (Verona): view of church and position of longitudinal cracks
measures acted by the timber beams of the floor. FRP on main vault (a), application of FRPs on ribs and side
walls (b), scheme of intervention and final view after
strips were designed and assessed by using a specific
protection of strips (c).
method applied to vaults, taking into account the mod-
ified failure mechanisms of the strengthened structure
(Valluzzi et al. 2002 and 2004).
Other applications on vaults can be combined with
injections, as well as ties, to improve the global
behaviour, as in the church of S.ta Corona of Vicenza,
where cross vaults have been reinforced at their
extrados with strips 20 cm wide in their longitudinal
direction (Figure 17).
In the church of S.ta Maria in Organo of Verona,
the intervention with FRP has been limited to the in-
plane reinforcement of the walls stabilizing the vaults
from the sides and to existent transversal ribs, as well
as new ones, provided in the longitudinal direction
(Figure 18). Figure 19. Intervention with CFRP in capital of ‘Palazzo
Finally, specific applications where the high ver- della Ragione’ of Padova: original confining rings (left) and
satility of FRP laminates can hardly even the per- FRP strengthening (right).
formances of other materials, are the local repair of
weaknesses in stone elements, being part of structures a equestrian statue characterizing the marble monu-
or monuments. As an example, the confining of capi- mental tomb of Cansignorio in Verona, particularly
tals can be performed, to substitute or integrate actual deteriorated by metal oxidation and environmental
metal rings, as executed at the top of the columns of aggression. A system of superimposed layers of CFRP
the ‘Palazzo della Ragione’ in Padova. CFRP strips has allowed to rebuild the loose parts of the bearing
have been positioned after restoring of the capitals elements, re-establishing the aesthetics of the statue
and successively hidden beneath the historical original (Gaudini et al. 2008).
metal confining elements (Figure 19). Another pecu- Therefore, in monuments, where the aesthet-
liar example is the reinforcement of the basement of ics could be the most important requirement, the

41
 more and more increasing. Nevertheless, many aspects
still are under investigation, and specific experimental
procedures and models need to be homogenized in
standards and recommendations.
Therefore, from more and more modern concep-
tions, today more than in the past, we need to resume
traditional values, in order to not forget our learning
from history and to respect constructive specificity
and functions of the original structures. Innovative
solutions can be very useful even in the Cultural
Heritage context, provided that we are able to recog-
nize their limits, and to pursue the clarification of all
aspects (both positive and negative) that are involved
in the delicate question of the preservation of historical
constructions.

ACKNOWLEDGEMENTS

Figure 20. Intervention on ‘Arca of Cansignorio’ (Verona): The author wish to acknowledge C. Bettio, E. Garbin,
view of deteriorated hoof and first phase of intervention (a), G. Guidi and M. Panizza for their contribution in the
protecting lime putty and final view of the statue after researches and applications and for data processing
intervention (b). and modelling.

intervention can be focused on a precise defect to

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