PROVISIONAL DESIGN GUIDELINES FOR THE STRENGTHENING OF MASONRY STRUCTURES SUBJECT TO IN-PLANE LOADING

Enrico Garbin1, Nestore Galati2, Antonio Nanni3, Claudio Modena4, Maria Rosa Valluzzi5

Abstract Masonry structures constitute a large percentage of the current buildings in most countries around the world. Structural weakness or overloading, dynamic vibrations, settlements, and in-plane and out-of-plane deformations can cause failure of unreinforced masonry (URM) structures. URM buildings have features that, in case of overstressing, can threaten human lives. These include unbraced parapets, inadequate connections to the roof, floor and slabs, and the brittle nature of the URM elements. Organizations such as The Masonry Society (TMS) and the Federal Emergency Management Agency (FEMA) have determined that failures of URM walls result in more material damage and loss of human life during earthquakes than any other type of structural element. In the last years, a growing interest has been direct to the application of FRP (Fiber Reinforced Polymer) materials as strengthening materials because they may provide solutions for the strengthening of masonry due to their easy application and their favourable structural performances. Nowadays few design guidelines are available to apply FRP on masonry structures. This paper presents a proposal for design recommendations for shear strengthening of unreinforced masonry walls with FRP systems. The proposed design protocol is within existing building codes for traditional materials and takes into account the recent experimental researches. The adopted methodology offers a rational attempt of in-plane upgrade of structural masonry walls with bonded FRP systems.

1 PhD Candidate, Department of Structural and Transportation Engineering, University of Padova, Via Marzolo

9, 35131, Padova, Italy. E-mail: garbin@dic.unipd.it . Tel.: +39 049 827 5631 2 Research Engineer, Center for Infrastructure Engineering Studies University of Missouri-Rolla, 223

Engineering Research Lab, 65409 Rolla, Missouri - USA. E-mail: galati@umr.edu . Tel.: 573-341-6223 3 Full Professor, Department of Structural Analysis and Design, University of Naples Federico II, Naples, Italy. E-

mail: antonio.nanni@unina.it . Tel.: +39 081 768 3687 4 Full Professor, Department of Structural and Transportation Engineering, University of Padova, Via Marzolo 9,

35131, Padova, Italy. E-mail: modena@dic.unipd.it . Tel.: +39 049 827 5613 5 Assistant Professor, Department of Structural and Transportation Engineering, University of Padova, Via

Marzolo 9, 35131, Padova, Italy. E-mail: valluzzi@dic.unipd.it . Tel.: +39 049 827 5576

Papers contained in these Proceedings have been reviewed in accordance with the policies of The Masonry Society

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Introduction Recent earthquakes have shown that performance of unreinforced masonry (URM) walls are often not adequate. As masonry buildings, in various typologies, represent a large part of the existing building stock, significant experimental research has been carried out in the last few decades to investigate the cause of damage and develop technologies suitable for seismic retrofit and rehabilitation of existing masonry buildings (Tomaževič 2000). These and other factors, such as change in use, design or construction imperfections, deterioration-related damage, or requirement of upgrading of lateral strength from modern building code, prompt the structural repair or strengthening of masonry buildings. Repair and strengthening of existing masonry structures has been traditionally done using conventional materials and construction techniques. Externally bonded steel plates, reinforced concrete overlays, grouted cell reinforcements, and external post-tensioning are just some of the many traditional techniques available. Moreover, innovative techniques of applying FRP (Fibre Reinforced Polymer) materials on civil structures have been developed in the last years. FRP composites in the form of laminates or bars can provide viable solutions of strengthening of URM walls subjected to overloading both in out-of-plane and in-plane directions. FRP materials have many advantages, as high strength and durability, improved corrosion resistance, lower installation costs, on-site versatility of use, and minimum changes in the member size after repair, but especially the very low weight in comparison to traditional retrofitting techniques. In fact, traditional techniques often add high quantities of weight to the structures, which change their seismic behaviour and can require expensive upgrades of the foundations (Lissel 2003; Triantafillou 1998). Nowadays, due to the great variability of masonry properties, few guidelines, still in progress, are available for the design of FRP strengthening systems applied on masonry structures (ACI 440M 2004; CNR-DT200 2004). Design rules are proposed by other guidelines concerning FRP applied on concrete (ACI 440.1R-03 2003; ACI 440.2R-02 2002; Fib Bulletin 14 2001). Moreover, for historical masonry structures specific considerations have to be taken into account to prevent any aesthetics alteration of the structures (Modena 1997). Past researches on FRP reinforcement systems have shown a good correlation between the flexure or the out-of-plane behaviour and the strength design approach (Triantafillou 1998; Lissel 2003; Tumialan 2003; Hamilton 2001). Moreover, previous investigations have demonstrated that shear capacities of URM walls can be remarkably increased by the use of FRP composites (Schwegler 1996; Li 2001; Tumialan 2001; Hamid 2005). Glass Grid Reinforced Polyurea (GGRP) was successfully used by Yu et al. (2004) to strengthen URM walls subject to in-plane loads. Some authors have reported an improvement of the shear performance both for cross and grid layout of strengthening and continuum retrofitting (Lissel 2003; Valluzzi 2002; Micelli 2003; Marcardi 2003; Gu 2003; Stratford 2004, Capozucca 2004; ElGawady 2005; Li 2004; Grando 2003; Secondin 2003; Turco 2003). Only few authors have reported a minor improvement in the shear strength and a noticeable difference in the post crack phase with larger deformation than the URM case (Lissel 2003; Marshall 2000). In (Valluzzi 2002) different behaviours for single or double side of strengthening configuration have been detected. Moreover, the authors have noticed that an appropriate FRP

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development length have to be designed like in (Micelli 2003), despite the bond behaviour of FRP strips bonded on masonry is still studied (Ceroni 2003; Corradi 2004; Basilio 2005, Aiello 2006). Furthermore, in (Lissel 2003; Marshall 2000) the difference between the diagonal and the shear-compression test are pointed out, the authors concluded that for future research the second test set-up should be used. Finally, besides the necessity of further experimental researches, the FRP materials have already shown their great possibility (Lissel 2003; Bakis 2002), allowing their introduction in the masonry field. Based on the above mentioned experimental contribution and codes (ACI 440M 2004; CNR-DT200, 2004), a provisional design for structural masonry walls strengthened with FRP systems under in-plane loads is proposed. It is worth to notice that in modern masonry construction the bearing walls behave as a shear walls as well, thereby being subjected, in addition, to vertical compressive stresses (Schneider 1980); hence these walls will be denominated as structural walls. The proposed recommendations given in this paper apply only for rectangular cross-sections. The walls here considered are in plane loaded masonry walls and the main failure modes examined for unreinforced walls are: sliding shear, diagonal cracking and flexural failure. The flexural and shear strengthening systems considered are FRP laminates, Near Surface Mounted (NSM) FRP bars and Glass Grid Reinforced Polyurea (GGRP). The strength design approach of reinforced masonry members is adopted. The recommendations are based on principles of equilibrium and compatibility and on the constitutive laws of the materials. Some basic details are suggested, although they need further development.

Design philosophy

Strength design methodology The adopted strength design approach of reinforced masonry members is in agreement with the Building Code Requirements for Masonry Structures (ACI 530-02 2002) and with other ACI documents on masonry (ACI 530.1-02 “Specification for Masonry Structures’, ACI 530-02 “Commentary on Building Code Requirement for Masonry Structures”, ACI 530.1-02 “Commentary on Specification for Masonry Structures”). A similar strength design approach can be developed on the framework of Eurocode6 using a suitable adaptation. The strength reduction factors, φ, given in Building Code Requirements for Masonry Structures (ACI 530-02 2002), together with the load factors given in ASCE 7-98 (2000) “Minimum Design Loads for Building and Other Structures” are considered.

Design materials properties As for materials, masonry and FRP systems are considered. Masonry properties should be obtained from the Building Code Requirements for Masonry Structures (ACI 530-02 2002) or equivalent codes or as provided by the producers. Concerning the FRP systems, the material properties are those provided by the manufacturers.

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FRP Design Material Properties The FRP material is considered linear elastic up to failure. The material properties guaranteed by the manufacturers should be considered as initial values that do not include the effects of long-term exposure to the environment. As long-term exposure to various type of environments can reduce the tensile strength and creep rupture and fatigue endurance of the FRP systems, the material properties used in design equations should be reduced based on the type and level of environment and loads exposure. Equations [1] to [2] take into account the environment exposure providing the design tensile properties. To be consistent with ACI codes, the design tensile strength, fuf , and the design rupture strain, fuε , are determined according to ACI 440.2R-02 (2002). *

fu E fuf C f= [1]

*fu E fuCε = ε [2]

Where EC is the environment reduction factor summarized in Table 1. The code CNR-DT200 (2004) provides the same values for the coefficient EC . *

fuf is the guaranteed tensile strength

of FRP provided by the manufactures, *fuε is the guaranteed rupture strain of the FRP

system. The design modulus of elasticity is assumed to be the same as the average value reported by the manufacturers: ,f f aveE E= .

Table 1. Environment reduction factors Exposure condition Fibre type Environment reduction factor CE

Carbon 0.95 Glass 0.75 Masonry, interior

exposition Aramid 0.85 Carbon 0.85 Glass 0.65 Masonry, exterior

exposition Aramid 0.75 Carbon 0.85 Glass 0.50 Masonry, aggressive

environment Aramid 0.70

Reduction for debonding at ultimate FRP debonding can occur if the force in the FRP can not be sustained by the interface between the FRP system and the substrate. In order to prevent the FRP debonding, a limitation should be placed on the stress and strain level developed in the laminate. This limitation should be computed by means of bond analytical/numerical model or by means of experimental tests, as it depends on the anchor length and the material properties of the masonry and FRP system. In this design guideline a simplify approach is considered, where the FRP debonding in flexure or shear is accounted through a parameter mk , and a minimum anchor length of 300 mm is required for the FRP system (CNR-DT200 2004): FRP laminates and FRP bars with a maximum diameter of 10 mm. The effective design strength and strain,

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fef and feε , of the FRP material are determined by the equations [3] and [4]. The values for the parameter mk are summarized in Table 2, they are based on test results on unreinforced masonry (URM) walls strengthened with GGRP, FRP laminates and NSM FRP bars (Tumialan et al., 2003; Galati et al., 2004; Yu et al., 2004). It is noticed that in the case of GGRP laminates it is reasonable to conservatively assume mk = 0.65 for the case of FRP laminates applied on puttied masonry. *

fe m fu m E fuf k f k C f= = [3]

*fe m fu m E fuk k Cε = ε = ε [4]

Table 2. mk Factors for different strengthening systems

Strengthening System Limitations Resin Type km GGRP - Polyurea 0.65

If putty is used Epoxy 0.65(1) FRP Laminates If putty is not used Epoxy 0.45(1) FRP rectangular bars, Groove having the

same height of the bar and width 1.5 times the one of the bar

Epoxy 0.65(2)

FRP circular bars, Square groove 1.5 times the diameter of the Bar(4) Epoxy 0.35(2) NSM FRP Bars

FRP circular bars, Square groove 2.25 times the diameter of the Bar

Epoxy / LMCG(3) 0.55(2)

(1)Based on Tumialan et al., 2003; (2)Based on Galati et al. 2004; (3)Latex Modified Cement Grout; (4)Latex Modified Cementitious Grout can not be used with a standard square groove having dimensions 1.5 times the diameter of the bar

Reductions for creep rupture at service Walls subjected to sustained load such as retaining or basement walls, creep rupture considerations need to be taken into account (ACI 440.2R-02 2002). In such cases, for serviceability assessment, the designed admissible tensile stress, ,f sf , should not exceed the values given in Table 3. For comparison in Table 3 are reported also the values provided by CNR-DT200 (2004), which are less conservative than those chosen and provided by ACI 440.2R-02 (2002).

Table 3. ,f sf for different fibre types Fiber Type ACI 440.2R-02 CNR-DT200

Carbon 0 55 fu. f

0 80 fu. f

Glass 0 20 fu. f

0 30 fu. f

Aramid 0 30 fu. f

0 50 fu. f

Masonry Masonry, as composite material, shows a nonlinear behavior in compression and a negligible tensile strength. The stress resultant for masonry should be determined from an appropriate non-linear stress-strain relationship or by a rectangular stress block suitable for the particular

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level of strain in the masonry. In this guideline the stress block has dimensions 'mfγ and 1cβ

(see Figure 2). Alternatively to Building Code Requirements for Masonry Structures (ACI 530-02 2002), where the values of β1 and γ are equal to 0.8, the expressions shown in equation [5] can be assumed (Galati 2003):

2

1'' '

1 2

1 '' '

ln 14 tan2 0.90

ln 1

mm m

mm m

mm m

mm m

and

εε εεε ε

β γεε ε βεε ε

−⎛ ⎞⎛ ⎞⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎜ ⎟+− ⎜ ⎟⎢ ⎥⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎝ ⎠= − =

⎛ ⎞ ⎛ ⎞⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟+⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎝ ⎠

[5]

where ' '(1.71 ) /m mmf Eε = , ( )1 'tan /m mε ε− is computed in radians, '

mf is the specified compressive stress of masonry, c the distance from extreme compression fibre to the neutral axis, '

mε the strain level in the masonry at the stress 'mf and mε the strain in masonry. The

strength and the modulus of elasticity of the masonry, mE , can be computed as recommended in the Building Code Requirements for Masonry Structures (ACI 530-02 2002) as '700m mE f= , for clay masonry and '900m mE f= , for concrete masonry. The maximum usable strain, εmu, at the extreme compressive side is assumed to be 0.0035 for clay masonry and 0.0025 for concrete masonry.

Design procedure

General considerations The most relevant in-plane loads for masonry walls are the seismic actions. In case of earthquake the structure will be subject to a series of cyclic horizontal forces, which will often cause high additional bending and shear stresses in the walls, exceeding the elastic range of the masonry materials. Structural walls, which are the basic resisting element to seismic loads, may be damaged, and if they have not been properly designed and detailed to withstand inelastic deformation and to dissipate energy, the induced inertia forces might cause heavy damage or even collapse of the building (Tomaževič, 2000). According to the results of earthquake damage analysis, three types of mechanisms and failure modes can be detected in unreinforced structural masonry walls when subjected to in-plane loads: sliding shear failure (see Figure 1a), diagonal cracking mode (see Figure 1b), flexural failure (see Figure 1c). The mechanisms depend on the geometry of the wall (height/width ratio) and quality of materials, but also on boundary restraints and loads acting on the wall (Tomaževič, 2000).

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Figure 1. Typical failure modes of unreinforced masonry walls, subjected to in-plane loads: a) Sliding Shear failure; b) Shear failure; c) Flexural failure, with masonry crushing at the corner (Tomaževič 2000) In terms of design, masonry strengthened with externally bonded FRP systems may be treated following the procedure of modern design codes. Frequently, masonry strengthened by FRP materials is considered as reinforced concrete structures because of lack of specific knowledge (Triantafillou, 1998). The failure modes for FRP strengthened walls subject to in-plane loads can be summarized as: • FRP debonding due to shear transfer mechanisms at the interface (masonry/FRP

debonding may occur before flexural failure). Debonding starts from the shear cracks or from the horizontal flexural cracks.

• Flexural failure, which can be either by rupture of the FRP laminate or masonry crushing. Typically, flexural failure in masonry walls strengthened at high reinforcement ratio is due to compressive crushing. FRP rupture is less desirable than masonry crushing, as it that can provide some ductility to the failure mode (Triantafillou, 1998). Both failure modes are acceptable in governing the design of in-plane loaded walls.

• Shear Failure, which can be either sliding shear failure or diagonal cracking mode. The FRP reinforcement is considered working only in tension, neglecting any compressive strength. The FRP reinforcement can either be applied on one or both sides of the walls. Based on the principles of capacity design, undesirable modes of failure in the masonry walls should be avoided. The application of FRP reinforcement can modify the failure mode from brittle shear to flexural failure.

Nominal flexural strength As mentioned, concerning flexural strength the FRP rupture is less desirable than masonry crushing. If possible, the nominal flexural strength should be smaller than the shear strength. Where combined bending and axial forces are encountered, the simple interaction formula shown in equation [6] can be used as ultimate strength design criteria (Schneider 1980). This approach is very conservative, and nondimensional interaction curves may be developed for structural masonry walls.

1u u

n n

P MP Mφ φ

+ ≤ [6]

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In the equation [6] uP is the factored axial load, nP the nominal axial strength, uM the factored moment at section, nM the nominal moment capacity, φ the strength reduction factor. The computations are based on the equilibrium of force and strain compatibility. The geometry of the uncracked cross-section is given in Figure 2-b. The distribution of strain and stress in the FRP reinforced masonry for a rectangular section under out-of-plane and axial loads are shown in Figure 2-c. The nominal axial strength, nP , (Figure 2) should be evaluated according to the Building Code Requirements for Masonry Structures (ACI 530-02 2002). As indicated in Figure 2-c, in all calculations the tensile contribution of the FRP is limited to the reinforcement further away from the compression zone. The contribution of the other reinforcements subject to tension may be included. Using the stress distribution for a cracked masonry cross-section subject to flexural and axial load, the equations of equilibrium and compatibility are given as in the following: ( )( )1m

'u f ff c t P A fγ β − = [7]

( )( ) 11 2 2 2

'n m f f

cl lM f c t A f dβ⎛ ⎞ ⎛ ⎞= γ β − + −⎜ ⎟⎜ ⎟⎝ ⎠⎝ ⎠

[8]

f m fm

c d c dε ε εε +

= =−

[9]

Where fA is the area of the FRP reinforcements working in tension. nM and nP are related to the centre of gravity, G, of the uncracked cross-section.

Failure mode The flexural capacity of a load bearing wall strengthened with FRP systems is dependent on the failure mode, which can be governed by masonry crushing or FRP rupture/debonding. The failure mode can be determined by comparing the FRP reinforcement ratio, fΘ , (Eq. [10]) to the balanced reinforcement ratio, fbΘ , (Eq. [11]).

ff

At d

Θ = [10]

' '

1 1' 'f mum mu u m u

fbfe mu fe m fue f mu fe m

Ef P f Pf td f f E f td f

εεγ β γ βε ε ε

⎡ ⎤ ⎡ ⎤Θ = − = −⎢ ⎥ ⎢ ⎥

+ +⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦ [11]

If the reinforcement ratio is below the balanced ratio ( f fbΘ < Θ ), FRP rupture/debonding failure mode governs the failure. Otherwise, ( f fbΘ > Θ ) masonry crushing is predominant.

URM Walls Strengthened with FRP Laminates URM Walls Strengthened with NSM FRP Bars

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ε

ε

A = n t w

f

β c = a

γ f '

Reinforced Masonry Section

N.A.

cd - c

h

MP

l

G f

d

W

t d

l

t

u u

f f f (a)

(b)

(c)

tr

fsf

Y

X

f

f

m

f

f

1

c

vu

ε

ε

A

f

β c = a

γ f '

Reinforced Masonry Section

N.A.

cd - c

h

MP

l

G f

d

d

l

t

u u

f (a)

(b)

(c)

tr

sf

Y

X

f

m

f

f

1

c

vu

Figure 2. Wall under in-plane loads, (a) forces acting on the wall, (b) geometric parameters of the uncracked section, (c) internal strain and stress distribution for a horizontal rectangular section

Nominal flexural capacity When f fbΘ > Θ , the failure initiates by crushing of the masonry, and the stress distribution in the masonry can be approximated with a rectangular stress block defined by the parameters β1 and γ. Based on the equations from [7] to [9] , the following equations can be derived:

( )2 2 2 2 2

'n m u f f u

a l a l aM f at d P d A f d P⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞= γ − − − = − + −⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠

[12]

( )

1 'f f u

m

A f Pa c

f tβ

γ+

= = [13]

1f f mu

d af Ea

βε −= [14]

In the case of masonry crushing, the following values for the stress in the FRP reinforcement , ff , and the distance from extreme compression fibre to the neutral axis, c , can be obtained:

2

'1

2 2 2 2f mu f muu m u u

f f mu fuef f f f

E EP f P Pf E fA A A

ε εγβ ε⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎜ ⎟= − + − − + ≤⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟Θ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎝ ⎠

[15]

2

'1

'1 1 2 2 2 2

f f mu f muu m uf mu

m f f f

d E EP f Pac Ef A A

ε εβ γ εβ β γ

⎡ ⎤⎛ ⎞ ⎛ ⎞Θ ⎢ ⎥= = − + − −⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥Θ⎝ ⎠ ⎝ ⎠⎢ ⎥⎣ ⎦

[16]

FRP debonding or failure: When f fbΘ < Θ the failure of the wall is starts by rupture/debonding of the FRP, and the equivalent stress block depends on the maximum strain reached by the masonry. In this case

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an iterative process, based on the equations from [7] to [9], should be used to determine the equivalent stress block.

Nominal shear strength The design shear strength for in-plane wall shall be in accordance with Eq. [17]: n uV Vφ ≥ [17] where nV is the nominal shear strength, uV the factored shear at section. Following the Building Code Requirements for Masonry Structures, the nominal shear capacity can be evaluated as [18]: ,n m m fV V V= + [18] where mV is the masonry shear capacity and ,m fV the shear capacity provided by the FRP system. The nominal shear capacity, nV , shall not exceed the following limits according to the Building Code Requirements for Masonry Structures (ACI 530-02 2002). The shear strength provided by the masonry shall be computed using equation [19]. The value of /M V t should not be taken greater than 1.0.

'4.0 1.754m n m

M PV A fV d

⎡ ⎤⎛ ⎞= − +⎢ ⎥⎜ ⎟

⎝ ⎠⎣ ⎦ [19]

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, and P is the axial load.

Shear resistance provided by the FRP system: Following the Building Code Requirements for Masonry Structures, and avoiding the failure of the masonry compression struts, the shear resistance provided by the FRP system can be determined as in the equation [20], when a strut and tie model can be guaranteed by the presence of vertical and horizontal FRP reinforcements, with horizontal reinforcements spaced at a distance equal to s in the vertical direction.

, 0.5 f fem f

A f dV

s= [20]

When the shear resistance is provided by the FRP system placed only in the horizontal or vertical direction the shear strength provided by FRP reinforcements can be computed as: ,m f v f fuV k A f= [21]

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where the parameter vk accounts for the orientation angle of the fibres with respect to the direction of the failure surface opening, here simply assumed equal to 45°. The parameter vk should be determined experimentally and related to the specific FRP and masonry wall application. In absence of a comprehensive experimental campaign the conservative vk factors presented in Table 4 can be used. They are valid when the anchor length, al , equal or higher than the effective length, el , is provided, as illustrated in Figure 3. In absence of any experimental and analytical evaluation, the anchor length should be set no less than 300 mm (CNR-DT200 2004) from the cracked section, or suitable anchor systems should be adopted.

FRP Laminates in the horizontal direction NSM FRP Bars in the vertical direction a el l≥a el l≥

a el l≥a el l≥

Figure 3. Some examples of minimum anchor length needed for shear design.

Table 4. vk Factor for different FRP systems

FRP System Strengthening Layout Adhesive Type

Concrete Masonry

Clay Masonry

GGRP One or Both Sides Polyurea 0.5(1) 0.5(1) FRP Laminates One Side Epoxy 0.2(2) 0.6(2) FRP Laminates Both Sides Epoxy 0.3(2) 0.8(2)

NSM FRP Bars not in the Bed Joints One Side Epoxy 0.3(3) 0.7(3) NSM FRP Bars not in the Bed Joints Both Sides Epoxy 0.5(3) 0.8(3) NSM FRP Bars not in the Bed Joints

(Groove 2.25 Diameter of the bar) One or Both Sides LMCG 0.6(3) 0.6(4)

NSM FRP Bars in the Bed Joints (FRP Structural Repointing) One or Both Sides Epoxy 0.4(2) 0.6(2)

NSM FRP Bars in the Bed Joints, Groove 2.25 Diameter of the bar One or Both Sides LMCG 0.6(2) 0.6(5)

(1) Based on experiments (Yu, 2004); (2) Based on experiments (Grando, 2002); (3) No experimental evidence. It is conservative to assume the same value as for FRP Laminates; (4) No experimental evidence. It is conservative to

assume the same value as for FRP Laminates; (5) No experimental evidence. This value was reasonably assumed to be conservative, based on the results on the concrete masonry.

Conclusions The design methodology proposed in this paper offers a first rational attempt to be considered by engineers interested in in-plane upgrade of masonry walls with externally bonded FRP systems. The case of structural walls was considered. Additional experimental

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work as well as a reliability analysis are needed in order to determine a more comprehensive set of design factors. Actual research work concerns the definition of a large set of values for the parameter vk and the practical use of the proposed provisional guidelines through the development of simulated designs.

Acknowledgments The authors would like to acknowledge the financial support of the National Science Foundation Industry/University Cooperative Research Center – Repair of Bridges and Buildings with Composites (RB2C), Bondo Corporation and Techfab for their financial support.

References

ACI 440M 2004: ACI 440M Guide Draft-1, “Guide for the Design and Construction of Externally Bonded FRP System for Strengthening Unreinforced Masonry Structures”, ACI Committee 440, USA, 2004, ACI, 80 pp.

ACI 440.1R-03 2003: ACI 440.1R-03, “Guide for the Design and Construction of Concrete Reinforcement with FRP Bars”, ACI Committee 440, USA, 2003, ACI, 42 pp.

ACI 440.2R-02 2002: ACI 440.2R-02, “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures”, ACI Committee 440, USA, 2002, ACI, 45 pp.

ACI 530-02 2002: ACI 530-02, “Building Code Requirements for Masonry Structures”, ACI Committee 530, USA, 2002, ACI, 58 pp.

ASCE 7-98 2000: ASCE 7-98, “Minimum Design Loads for Building and Other Structures”, Structural Engineering Institute of the ASCE, USA, 2000, 352 pp.

Aiello 2006: Aiello, M.A.; Sciolti, S.M., “Bond analysis of masonry structures strengthened with CFRP sheets”, Construction and Building Materials, No. 20, 2006, Elsevier, pp. 90–100

Bakis 2002: Bakis, C.E.; Bank, L.C.; Brown, V.L.; Cosenza, E.; Davalos, J.F.; Lesko, J.J.; Machida, A.; Rizkalla, S.H.; Triantafillou, T.C. “Fiber-Reinforced Polymer Composites for Constrution – State-of-the-Art Review”, Journal of Composites for Construction, Vol. 6, Iss. 2, May 2002, pp. 73-87

Basilio 2005: Basilio, I.; Oliveira, D.; and Lourenço, P.B., “Experimental Characterization of FRP-Masonry interface behaviour”, Proc. of the 5th Int. Conference AMCM 2005, Gliwice, Ustroń, Poland, 2005, 8 pp. (CD-ROM)

Capozucca 2004: Capozucca, R. and Pascucci, V., “Shear behaviour of masonry Panels strengthened by CFRP”, Proc. of the Mechanics of Masonry Structures with FRP-materials: Modeling, Testing, Desing, Control, Venezia, Italy, 6-8 December 2004, Ed. Cortina, pp. 95-105

Ceroni 2003: Ceroni, F.; Pecce, M.; Manfredi, G.; and Marcari G., “Experimental bond behaviour in masonry elements externally reinforced with FRP laminates”, Proc. of the International Conference Composite in Constructions-CCC2003, Cosenza, Italy, September 16-19, 2003, Ed. Bios, pp. 313-318

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