Journal of Composites for Construction Design of FRP-Strengthened Infill Masonry Walls Subjected to Out-of-Plane Loading

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1 Journal of Composites for Construction Design of FRP-Strengthened Infill Masonry Walls Subjected to Out-of-Plane Loading --Manuscript Draft-- Manuscript Number: Full Title: Manuscript Region of Origin: Article Type: Manuscript Classifications: Keywords: Abstract: Corresponding Author: Corresponding Author Order of Authors: Design of FRP-Strengthened Infill Masonry Walls Subjected to Out-of-Plane Loading USA Technical Paper 11: Anchorage; 123: Design; 242: Masonry infill; 395: Strengthening and rehabilitation Fiber reinforced polymer; Walls; Masonry; Rehabilitation; Composite materials; Anchorages; Lateral pressure; Design FRP strengthening systems for infill masonry walls are typically designed to resist flexural stresses due to out-of-plane pressure. Previous research has shown that there are potential premature failure mechanisms due to shear sliding of the infill, which could reduce the effectiveness of the strengthening system. Current design guidelines for strengthening of masonry walls with fiber-reinforced polymers (FRP) do not include guidelines for infill masonry. This paper presents a rational approach for the design and analysis of FRP-strengthened infill masonry walls subjected to out-of-plane loading, including the effect of using FRP end anchorage. The approach is based on consideration of four potential mechanisms: arching, shear sliding, debonding of the FRP in the overlap region, and failure of the FRP end anchorage system. Predictions based on the proposed rational approach agree well with the measured values from two experimental programs. Dillon Stewart Lunn, Ph.D. North Carolina State University Raleigh, North Carolina UNITED STATES dslunn@ncsu.edu Dillon Stewart Lunn, Ph.D. Sami Hanna Rizkalla, Ph.D. Suggested Reviewers: John J. Myers, Ph.D. Associate Professor, Missouri University of Science and Technology jmyers@mst.edu He is an expert in FRP strengthening with an emphasis related to concrete and masonry structures. He has authored relevant papers including: Hrynyk, T., and Myers, J. J. (28). "Out-of-Plane Behavior of URM Arching Walls with Modern Blast Retrofits: Experimental Results and Analytical Model." J. Struct. Eng., 134(1), Khaled E. Galal, Ph.D. Associate Professor, Concordia University galal@bcee.concordia.ca He is an expert in FRP strengthening, including masonry structures. He has authored relevant papers including: Ghobarah, A., and Galal, K. (24). "Out-of-Plane Strengthening of Unreinforced Masonry Walls with Openings." J. Compos. Constr., 8(4), Khaled Soudki, Ph.D. Professor and Canada Research Chair in Innovative Structural Rehabilitation, University of Waterloo soudki@uwaterloo.ca He is an expert in FRP strengthening. He has authored relevant papers including: Chahrour, A. and Soudki, K. (25). "Flexural Response of Reinforced Concrete Beams Strengthened with End-Anchored Partially Bonded Fiber-Reinforced Polymer Strips." J. Compos. Constr., 9(2), Opposed Reviewers: Powered by Editorial Manager and Preprint Manager from Aries Systems Corporation

2 Additional Information: Question Is the article being considered for more than one journal?the Journal of Composites for Construction does not review manuscripts that are being submitted simultaneously to another organization or ASCE journal for publication. Response No. Is this article already published? Material that has been previously published cannot be considered for publication by ASCE. A manuscript that has been published in a conference proceedings may be reviewed for publication only if it has been significantly revised. If you answer YES, please provide further explanation in your cover letter. No. Have all the authors contributed to the study and approved the final version?all authors must have contributed to the study, seen the final draft of the manuscript, and accept responsibility for its contents. It is unethical to list someone as a coauthor who does not want to be associated with the study and who has never seen the manuscript. Was an earlier version of the paper previously considered and declined by ASCE?Declined manuscripts are sent through the review process again. If your manuscript has been submitted to us before under a different title, please provide that title in the space provided below. It is our policy to inform an editor that a manuscript has been previously reviewed, even when it has been reviewed by a different Division, Institute, or Council within ASCE. Do your table titles/figure captions cite other sources?if you used a figure/table from another source, written permission for print and online use must be attached in PDF format. Permission letters must state that permission is granted in both forms of media. If you used data from another source to create your own figure/table, the data is adapted and therefore obtaining permission is not required. Does your paper exceed 1, words? If YES, please provide justification in your cover letter. If you need help estimating word length, see our sizing worksheet at this link: Sizing Worksheet Yes. No. No. No. Estimates for color figures in the printed No. journal begin at $924. Cost increases depend on the number and size of figures. Do you intend for any figure to be printed Powered by Editorial Manager and Preprint Manager from Aries Systems Corporation

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4 Cover Letter Click here to download Cover Letter: CoverLetter.doc March 19, 213 Dear Prof. Smith and Prof. Chen, Please consider the enclosed paper entitled, Design of FRP-Strengthened Infill Masonry Walls Subjected to Out-of-Plane Loading, for possible publication in the IIFC 1 th anniversary special issue of the Journal of Composites for Construction. The paper proposes a rational approach for the design of FRP-strengthening systems for infill masonry walls, including the end anchorage for the FRP-strengthening system. The proposed rational approach considers potential failure mechanisms including arching, shear sliding, debonding, and anchorage failure. This paper presents original research that is highly relevant to the theme of the Journal of Composites for Construction and would be of interest to the journal s many subscribers. It considers the complex behavior of the application of composite strengthening systems to infill masonry walls and provides guidance for their design. We thank you for your consideration and we look forward to hearing from you at your earliest convenience. Please advise if it is too late for the special issue, in which case we would like for the paper to be considered for a regular issue of the journal. Best Regards, Dillon S. Lunn, Ph.D., A.M.ASCE Postdoctoral Scholar Department of Civil, Construction, and Environmental Engineering North Carolina State University Constructed Facilities Laboratory 2414 Campus Shore Dr. Campus Box 7533 Raleigh, NC Phone: (Cell) DSLUNN@ncsu.edu Sami H. Rizkalla, Ph.D., F.ASCE Distinguished Professor of Civil Engineering & Construction Department of Civil, Construction, and Environmental Engineering North Carolina State University Constructed Facilities Laboratory 2414 Campus Shore Drive Campus Box 7533 Raleigh, NC Phone: (Main) Sami_Rizkalla@ncsu.edu

5 *Manuscript Click here to download Manuscript: Lunn_Rizkalla_ASCE.docx 1 2 Design of FRP-Strengthened Infill Masonry Walls Subjected to Out-of-Plane Loading Dillon S. Lunn, A.M.ASCE 1 and Sami H. Rizkalla, F.ASCE ABSTRACT FRP strengthening systems for infill masonry walls are typically designed to resist flexural stresses due to out-ofplane pressure. Previous research has shown that there are potential premature failure mechanisms due to shear sliding of the infill, which could reduce the effectiveness of the strengthening system. Current design guidelines for strengthening of masonry walls with fiber-reinforced polymers (FRP) do not include guidelines for infill masonry. This paper presents a rational approach for the design and analysis of FRP-strengthened infill masonry walls subjected to out-of-plane loading, including the effect of using FRP end anchorage. The approach is based on consideration of four potential mechanisms: arching, shear sliding, debonding of the FRP in the overlap region, and failure of the FRP end anchorage system. Predictions based on the proposed rational approach agree well with the measured values from two experimental programs CE DATABASE SUBJECT HEADINGS Fiber reinforced polymer, Walls, Masonry, Rehabilitation, Composite materials, Anchorages, Lateral pressure, Design INTRODUCTION Retrofitting of masonry infill walls with fiber-reinforced polymers (FRP) has recently been considered as an effective system to increase the strength and ductility of masonry structures. The use of FRP strengthening can reduce the risk of collapse under extreme loading conditions such as possible differential pressure caused by a tornado. Current guidelines for strengthening of masonry walls with FRP, such as ACI 44.7R-1 (ACI Committee 44, 21), do not include guidelines for infill masonry. This paper presents a rational approach for the design of 1 Postdoctoral Scholar, Dept. of Civil, Construction, and Environmental Engineering, North Carolina State University, 2414 Campus Shore Dr., Campus Box 7533 Raleigh, NC, dslunn@ncsu.edu 2 Distinguished Professor, Dept. of Civil, Construction, and Environmental Engineering, North Carolina State University, 2414 Campus Shore Dr., Campus Box 7533 Raleigh, NC, sami_rizkalla@ncsu.edu

6 25 26 FRP-strengthened infill masonry walls subjected to out-of-plane loading, including the effect of using FRP end anchorage FRP strengthening systems for masonry are typically designed to resist out-of-plane flexural stresses. Previous research has shown that there are potential premature failure mechanisms resulting from shear sliding of the infill, which can significantly reduce the effectiveness of the strengthening system (Lunn et al., 212; Lunn and Rizkalla, 211). To achieve an efficient design which can delay or prevent premature failure, the following four potential mechanisms should be considered: arching, shear sliding, debonding of the FRP in the overlap region, and anchorage failure. The effectiveness of the proposed approach was evaluated by comparing the predicted maximum pressures that can be achieved by the strengthened infill wall to the measured maximum pressures from two extensive experimental programs conducted and reported by the authors (Lunn et al., 212; Lunn and Rizkalla, 211). These experimental programs investigated the behavior of full-scale FRP-strengthened infill masonry walls subjected to uniformly-distributed out-of-plane pressure using an airbag. Table 1 provides details of the specimens tested in the two programs. The one way infill wall specimens were not restrained on the sides and thus spanned in the vertical direction only, while the two way infill wall specimens were surrounded on all four sides by a reinforced concrete frame as shown in Fig. 1. Various end anchorages were tested including overlapping the FRP onto the supporting concrete frame and FRP anchors as shown in Fig. 2. The different types of FRP used were Glass FRP (GFRP), Polyethylene Terephthalate (PET), and Carbon FRP (CFRP). Table 1 also provides the height-to-thickness ratio, h/t, the width-to-height ratio, b/h, and the unified fiber reinforcement ratio, nρ f, where n is the modular ratio of the FRP with respect to the masonry material and ρ f is the FRP reinforcement ratio with respect to the masonry cross-section. Details of the proposed rational design approach including the various possible mechanisms are discussed in the following sections ARCHING MECHANISM The dominant out-of-plane resisting mechanism for infill masonry is the arching mechanism. Various approaches have been developed to estimate the resistance provided by the arching mechanism, including the Masonry Standards Joint Committee (MSJC) code (MSJC, 211). However, few researchers have studied the effect of FRP. Hrynyk and Myers (28) developed an approach which includes the contribution of the FRP. The approach

7 considers three possible failure modes: (1) crushing of the masonry in compression, (2) debonding of the FRP in the region of maximum moment, and (3) rupture of the FRP in the region of maximum moment. The assumptions include rigid-body deformations and small displacements of the wall under the effect of the out-of-plane loading. The factors considered in the model include: (1) temperature and shrinkage strains, (2) possible gaps between the top and sides of the wall with respect to the surrounding frame members, (3) in-plane rigidity of the surrounding frame members, (4) elastic shortening due to the in-plane arch thrust force, and (5) eccentricity of the arch thrust force measured from the wall centerline. The assumed free body diagram of an upper half of a wall demonstrating the arching mechanism is shown in Fig. 3. In this figure, the forces acting on the section are as follows: C and F TH are the compression forces at mid-height and at the top respectively, T is the tension force provided by the FRP at mid-span, W is the resultant force of the applied uniformly distributed lateral pressure, q, and R is the horizontal reaction at the top of the wall. F TH is also referred to as the thrust force of the arching action. The eccentricity, e, of the thrust force, F TH, with respect to the wall centerline is related to the thickness of the wall, t, through an assumed empirical constant, k. From strain compatibility and equilibrium, the maximum pressure corresponding to the arching mechanism, q ar, can be determined. Details of the equations used to determine the arching failure pressure, q ar, are provided by Hrynyk and Myers (28). In addition, a detailed numerical example is provided by the authors in a separate publication (Lunn, 213) Table 2 and Fig. 4 compare the measured maximum pressure to the predicted arching failure pressure for test walls reported by Lunn et al. (212) and Lunn and Rizkalla (211). The comparison clearly indicates that predictions based solely on the arching mechanism overestimated the maximum pressure for many of the tested walls failing due to other mechanisms including shear sliding and debonding in the overlap region. This suggests the need to consider other mechanisms in addition to arching. The results also indicate that the arching mechanism provides, in most cases, the upper bound value for the pressure at failure. It should be noted that for two-way infill walls, considering arching along the horizontal span direction is as important as the arching along the height of the wall. The likelihood of horizontal arching decreases as the width-to-height aspect ratio increases, but due to differences in strength between arching oriented perpendicular to bed joints and arching oriented parallel to bed joints as well as differences due to construction defects, shrinkage cracking, and boundary stiffness, it is possible for horizontal arching to govern the capacity, even for width-to-height aspect ratios greater than 1.. It should also be noted that

8 two specimens, 2-2 and 2-4, were not predicted or observed to fail due to the arching mechanism. These single- wythe, two-way walls had a large height-to-thickness ratio (26.2) which, combined with the effect of the strengthening system, prevented the arching mechanism from crushing the masonry or debonding the FRP in the region of maximum moment. mechanisms. These walls are a further example of the need to consider additional failure SHEAR SLIDING MECHANISM Most existing shear sliding equations for masonry consider only the initial conditions, which assume that the mortar joint is uncracked and that the frictional component of the shear resistance is related to the precompression forces. Unlike existing approaches, the proposed approach presented in this paper, considers the effects of cracking and arching on the resistance to shear sliding. Shear sliding is more critical at the top bed joint of an infill wall where the precompression forces are typically minimal and there is the potential for shrinkage of the mortar and construction defects causing gaps. The resistance to shear sliding along the top bed joint, V n, is composed of cohesive and frictional components, as given in Eq. (1). The cohesive component is the product of the cohesion, c, and the effective shear area, A eff. The frictional component is the product of the friction coefficient, μ, and the thrust force, F TH. The shear sliding resisting force, V n, can be converted to an equivalent pressure corresponding to shear sliding, q ss, acting on the face of the infill wall bound by the height, h, and width, b, of the wall, respectively, using Eq. (2) V n q ca F (1) eff TH V bh (2) ss 2 The mechanism is complicated by the fact that both the effective shear area and the thrust force vary with the increase of the applied pressure due to the formation of the arching mechanism. Before cracking, the total net area of the bed joint resists shear sliding, and, at this loading level, the thrust force can be ignored, as expressed in Eq. (3) and shown in Fig. 5(a). n Before Cracking:

9 A A (3a) eff n F (3b) TH Since the cracking pressure is typically much less than the pressure corresponding to shear sliding, the sliding resistance after cracking is more critical for design. After cracking, the effective shear area is greatly reduced and the thrust force increases substantially, as shown in Fig. 5(b). Finite element analysis (Lunn, 213) indicates that the effective shear area is reduced to approximately 2% of the total net area of the bed joint and therefore can be conservatively assumed as 1% of the total net area, as given in Eq. (4a). This behavior is evident by the finite element analysis of an FRP-strengthened infill wall with FRP anchors shown in Fig. 6(a) and Fig. 6(b) for the reduction of the effective shear area and increase in thrust forces respectively. The thrust force can be expressed as a function of the applied pressure, q, the height, h, and width, b, of the infill wall, and an empirical shear sliding factor, α ss, as given in Eq. (4b) After Cracking: A. 1 (4a) eff A n F ss qbh (4b) TH Assuming the cohesion is.4 MPa and the friction coefficient is.45, as typically used by the Masonry Standards Joint Committee (MSJC) code (MSJC, 211), and combining Eq. (1), Eq. (2), and Eq. (4), the maximum pressure, q ss, corresponding to shear sliding can be determined using Eq. (5). The shear sliding factor, α ss, depends primarily on the unified fiber reinforcement ratio, nρ f, and the height-to-thickness ratio of the infill wall (h/t). Since the FRP strengthening increases the flexural stiffness of the infill wall, the flexural deformation is typically less in comparison to an unstrengthened infill wall. This behavior leads to a reduction of the rate at which thrust forces develop with respect to the applied pressure. Similarly, infill walls with larger height-to-thickness ratios develop thrust forces more slowly than walls with smaller height-to-thickness ratios. The measured maximum pressures of walls failing due to shear sliding from the experimental program reported by Lunn and Rizkalla (211) were used to develop the empirical shear sliding factor given in Eq. (5). It should be noted that for some infill walls, especially those without FRP strengthening and with a small height-to-thickness ratio, the calculated shear sliding factor may

10 lead to a negative output for the shear sliding pressure, q ss, which suggests that shear sliding will not occur for such infill walls q ss.8an, in MPa (5) bh 1.9 t Where, 3.8 h 1 1n ss Table 3 compares the predicted maximum pressure by considering arching (as discussed previously) and shear sliding to the measured maximum pressure of walls failing due to shear sliding from the experimental program reported by Lunn and Rizkalla (211). For walls with No Overlap of the FRP onto the supporting frame, as shown in Fig. 2(a), the predicted maximum pressure is the minimum of the maximum pressures corresponding to the ss f arching mechanism and shear sliding, respectively. In every case considered, the predicted shear sliding pressure controlled. The resulting predicted maximum pressure, q n, correlates well with the measured maximum pressures as shown in Fig DEBONDING OF FRP IN OVERLAP REGION The experimental results reported by Lunn and Rizkalla (211) clearly indicate that using an overlap of the FRPstrengthening onto the surrounding concrete frame can increase the maximum pressure for infill masonry walls. The research indicates that the increase in the resistance is influenced by several factors: (1) the contribution of the FRP bond strength within the overlap region, (2) the increase in the frictional resistance along the bed joint as a result of the delay in shear sliding caused by the FRP bond, and (3) the contribution of the dowel force, P d, of the FRP strengthening system within the overlap region, as shown in Fig. 8. The first two factors affect the pressure at which shear sliding occurs and the third factor influences the response after the initiation of shear sliding. Based on these factors, the horizontal reaction force, R, can be estimated as the summation of the frictional component due to the thrust force, F TH, and the FRP dowel force, P d, as given by Eq. (6), where α db is an empirical debonding factor used to relate the thrust force to the applied pressure, q. It should be noted that due to the significant sliding of the wall and the reduction of the contact area, the effect of the cohesion is ignored in Eq. (6). Therefore the equivalent pressure corresponding to debonding of the FRP in the overlap region, q db, can be determined using Eq. (7).

11 R F TH P d (6) Where, F TH db qbh R q db (7) bh To determine the dowel force, P d, Dai et al. (27), introduced a relationship between the interface peeling energy, G fs, and the peeling angle, θ. It should be noted that Dai et al. (27) formulated the relationship for the case when peeling occurs on both sides of the applied load. For the case of FRP-strengthened infill walls, the peeling typically occurs on one side and thus the proposed dowel force in this paper has been modified to represent the case of a masonry infill wall with peeling occurring on one side. The modified relationship is given by Eq. (8), where E f and t f are the modulus and thickness of the FRP, respectively. Dai et al. s research indicated a significant scatter in the interface peeling energy, G fs, with minimum and maximum values of.2 N/mm and 1.2 N/mm, respectively. Using a representative value of.5 N/mm, the peeling angle can be estimated from Eq. (8). The dowel force, P d, is the horizontal component of the tension resistance of the FRP, for an assumed relative displacement between the infill and the supporting concrete frame, Δ, and a peeled length, L p, measured vertically along the RC frame as shown in Fig. 8. Using the estimated peeling angle, the dowel force can be determined from Eq. (9), where ε f and b f are the strain and the width of the FRP, respectively. Assuming the same friction coefficient,.45, as typically used by the Masonry Standards Joint Committee (MSJC) code (MSJC, 211), the pressure corresponding to debonding of the FRP in the overlap region, q db, may be determined from Eq. (1). The measured maximum pressure of walls that failed due to debonding in the overlap region from experimental programs reported by Lunn et al. (212) and Lunn and Rizkalla (211) were used to develop the proposed empirical equation for the debonding factor, α db. E f t f G fs (8) 2 cos 2 1 cos sin cos 1 P E b t sin (9) d Where, 1 cos 1 q db f f f f bh 1.9 f 2Pd (1) t Where, 3.5 h 1 1n db db f.5

12 Table 4 compares the predicted maximum pressure by considering arching (as discussed previously) and debonding in the overlap region to the measured maximum pressure of walls failing due to debonding in the overlap region from the experimental programs reported by Lunn et al. (212) and Lunn and Rizkalla (211). For walls with Overlap of the FRP onto the supporting frame, as shown in Fig. 2(b) and Fig. 2(c), the predicted maximum pressure is the minimum of the maximum pressures corresponding to the arching mechanism and debonding, 177 respectively. In every case considered, the predicted debonding pressure controlled. The resulting predicted 178 maximum pressure, q n, correlates well with the measured maximum pressures as shown in Fig ANCHORAGE FAILURE End anchorage of the FRP strengthening system has become a typical detail for most FRP strengthening systems for 182 concrete and masonry structures. For masonry infill walls, Lunn (213) reported several anchorage systems including FRP anchors, shear keys, embedded bars, and steel shear restraints. For the case of FRP anchors, shown in Fig. 2(d), failure of the anchors have been reported to be the result of pullout of the anchors from the substrate, rupture of the anchors, or a combination of pullout and bond failure, Lunn et al. (212). Sliding of the infill wall causes debonding of the FRP strengthening up to the level of the FRP anchors, eventually leading to failure of the FRP anchors. Typical debonding of the anchorage is shown in Fig. 1. At ultimate, the nominal horizontal reaction, R, is the summation of the frictional component due to the thrust force, F TH, and the lateral component of the anchorage capacity, N a. By the time the anchorage fails, the wall may have displaced enough such that arching action is no longer effective and the thrust force diminishes. Therefore, the maximum pressure corresponding to anchorage failure, q an, can be estimated based on the anchorage capacity only, as proposed in Eq. (11). The capacity of the anchors depends primarily on (1) the embedment depth of the anchor, (2) the compression strength of the concrete substrate, (3) the dimensions of the anchor and anchor hole, and (4) the rupture strength of the anchor. This capacity can be determined from the manufacturer or by using the available literature on FRP anchors (Kim and Smith, 21). 196 q an 2N a (11) bh

13 Table 5 compares the predicted maximum pressure by considering arching (as discussed previously) and anchorage failure to the measured maximum pressure of walls failing due to FRP anchor pullout from the experimental program reported by Lunn et al. (212). For walls with FRP anchors, as shown in Fig. 2(d), the predicted maximum pressure is the minimum of the maximum pressures corresponding to the arching mechanism and anchorage failure, respectively. For the PET-strengthened specimen with FRP anchors, 1-6, anchorage failure controlled the predicted maximum pressure. For the GFRP-strengthened specimen with FRP anchors, 1-5, arching was predicted to cause crushing of the masonry prior to reaching the pullout strength of the FRP anchors; however, the observed mode of failure was FRP anchor pullout at an applied pressure exceeding the predicted value for crushing. This indicates that the arching analysis can be conservative if sufficient anchorage is provided to delay premature mechanisms. It should be noted that the predicted anchorage failure pressure, q an, exceeded the measured maximum pressure by approximately 6%. This overestimate may be partly attributable to a shallower embedment depth than expected and highlights the need for strict quality control practices for FRP anchor installation. The overall predicted maximum pressure, q n, correlates well with the measured maximum pressure as shown in Fig DESIGN PROCESS It is recommended to use a strength reduction factor of φ =.6 for the design for the four mechanisms considered in the proposed rational approach. This recommendation is based on the strength reduction factor required by the MSJC code (MSJC, 211) for infill masonry and the ACI design guidelines for FRP-strengthening of masonry for out-of-plane loading (ACI Committee 44, 21). Justification for the use of this low value is based on the typical brittle failure observed from the experimental programs. The reduced nominal capacity, φq n, should be designed to exceed the factored ultimate loading, q u, as given in Eq. (13): qn q u (13) A detailed design example using the proposed approach is presented in (Lunn, 213). The design process is summarized as follows: The first step in the proposed design process for FRP strengthening of infill masonry walls 221 is to determine the amount of FRP required by considering the arching mechanism. For a particular FRP strengthening system, the cross-sectional area of the FRP necessary to resist the design pressure is determined through a trial and error process using the analysis approach presented by Hrynyk and Myers (28). Next, the

14 anchorage system is designed in order to prevent premature failure mechanisms. The case of No Overlap may be considered, in which the FRP is not overlapped onto the supporting frame and no anchorage is provided. In this case, the pressure corresponding to shear sliding is determined using the approach presented in this paper and is compared to the design pressure. If No Overlap is inadequate to resist the design pressure, then overlap of the FRP onto the supporting frame should be provided. The pressure corresponding to debonding of the FRP in the overlap region is determined using the approach presented in this paper. If Overlap alone is insufficient to resist the design pressure, then an additional form of anchorage should be provided. The size, number, and configuration of FRP anchors is determined using the pullout strength of the anchors and requiring that the anchors be capable of resisting the full lateral force produced by the design pressure. Alternatively, other types of anchorage may be used, such as embedded FRP bars or steel shear restraints, and these should also be designed to resist the full lateral force produced by the design pressure CONCLUSIONS Design of FRP strengthening systems for infill masonry structures for out-of-plane loading should consider four potential mechanisms: arching, shear sliding, debonding of the FRP in the overlap region, and end anchorage failure. The first limit state, related to arching, considers the failure modes of masonry crushing in compression and FRP debonding (or rupture) in tension and represents an upper bound of the capacity of the wall. This arching analysis can be used to design the FRP system. The other three limit states can be used to determine what type of end anchorage is required to prevent premature failure. Comparison between the predicted maximum pressure using the proposed rational approach and the measured maximum pressure from two experimental programs conducted by the authors showed good correlation. Overall, the predicted values were not overly conservative and correctly identified the controlling limit state in the majority of cases ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support of the NSF I/UCRC Center for Integration of Composites into Infrastructure. The authors would especially like to thank Fyfe Company, LLC, Nippon Steel and Sumikin Materials Co., Ltd. Composites Company, Grancrete, Inc. and Maeda Kosen Co. Ltd. 251

15 REFERENCES ACI Committee 44. (21). Guide for the Design and Construction of Externally Bonded Fiber Reinforced Polymer Systems for Strengthening Unreinforced Masonry Structures (ACI 44.7R-1). American Concrete Institute, Farmington Hills, Michigan Dai, J., Ueda, T., and Sato, Y. (27). Bonding Characteristics of Fiber-Reinforced Polymer Sheet-Concrete Interfaces under Dowel Load. J. Compos. Constr., 11(2), Hrynyk, T., and Myers, J. J. (28). "Out-of-Plane Behavior of URM Arching Walls with Modern Blast Retrofits: Experimental Results and Analytical Model." J. Struct. Eng., 134(1), Kim, S. J., and Smith, S. T. (21). "Pullout Strength Models for FRP Anchors in Uncracked Concrete." J. Compos. Constr., 14(4), Lunn, D.S. (213). Behavior and Modeling of Infill Masonry Walls Strengthened with FRP using various End Anchorage. Ph.D. Thesis, North Carolina State University, Raleigh, NC, USA Lunn, D.S., Rizkalla, S.H., Maeda, S., and Ueda, T. (212). FRP Anchorage Systems for Infill Masonry Structures. Proc., Third Asia-Pacific Conference on FRP in Structures (APFIS 212), Hokkaido, Japan Lunn, D. S., and Rizkalla, S. H. (211). "Strengthening of Infill Masonry Walls with FRP Materials." J. Compos. Constr., 15(2), Masonry Standards Joint Committee (MSJC) (211). Building Code Requirements for Masonry Structures (TMS 42-11/ACI 53-11/ASCE 5-11). The Masonry Society, American Concrete Institute, and the American Society of Civil Engineers, Boulder, Farmington Hills, and Reston. 278

16 FIGURES AND TABLES Table 1: Test Specimens 281 Wall Type One-way (Lunn et al., 212) Two-way (Lunn and Rizkalla, 211) Specimen End FRP Height, h Width, b Thickness, t No. Anchorage Type (mm) (mm) (mm) nρ FRP 1-1 Overlap GFRP Overlap PET Overlap CFRP Overlap CFRP FRP Anchors GFRP FRP Anchors PET Overlap GFRP Overlap GFRP Overlap GFRP No Overlap GFRP No Overlap GFRP No Overlap GFRP No Overlap GFRP No Overlap GFRP No Overlap GFRP (a) One-way Infill Wall (b) Two-way Infill Wall Fig. 1: Typical Test Specimens

17 284 RC Frame RC Frame FRP Infill Wall FRP FRP Infill Wall FRP Front View Profile View Front View Profile View (a) No Overlap (b) Overlap (Externally Bonded) NSM FRP NSM FRP FRP Anchors FRP Anchors Front View Cross-section View Front View Profile View (c) Overlap (Near Surface Mounted (NSM)) (d) FRP Anchors Fig. 2: FRP Anchorage Systems kt t F TH R R h/2 W q 287 C T z Upper Half of Wall RC Frame Infill FRP FRP - Strengthened Masonry Infill R 288 Fig. 3: Arching Mechanism for FRP-strengthened Infill Walls

18 Predicted Arching Failure Pressure (kpa) Table 2: Arching Predictions using Hrynyk and Myers (28), kpa Specimen No. Predicted Arching Failure Pressure Measured Maximum Pressure Ratio of Predicted to Measured Observed Failure Mode Debonding Debonding Debonding Debonding Anchor Failure Anchor Failure Debonding Debonding Debonding Shear Sliding Shear Sliding Shear Sliding Shear Sliding Shear Sliding Shear Sliding Observed Failure Mode: Shear Sliding Debonding Anchor Failure Measured Maximum Pressure (kpa) 298 Fig 4: Arching Predictions using Hrynyk and Myers (28)

19 Normalized Shear Area (A eff /A n ) Thrust Force (kn) RC Frame FRP RC Frame FRP R V N = c *A n V N = c*a eff + μ F TH Infill Infill F TH q 35 (a) Prior to Cracking Anchorage Region (b) After Cracking RC Frame Infill FRP R FRP - Strengthened Masonry Infill 36 Fig. 5: Shear Sliding Mechanism for FRP-strengthened Infill Walls with No Overlap First Crack Ultimate Applied Pressure (kpa) Ultimate First Crack Applied Pressure (kpa) (a) Effective Shear Area (b) Thrust Force Fig. 6: Finite Element Analysis of Shear Sliding Mechanism Table 3: Maximum Pressure for FRP-strengthened Infill Walls with No Overlap, kpa Specimen No. Arching, q ar Shear Sliding, q ss Predicted Maximum Pressure Measured Maximum Pressure Ratio of Predicted to Measured

20 Predicted Maximum Pressure (kpa) Measured Maximum Pressure (kpa) 313 Fig 7: Maximum Pressure for FRP-strengthened Infill Walls with No Overlap 314 RC Frame P d FRP R L p μf TH Infill F TH θ T Δ q Infill FRP 315 Anchorage Region RC Frame R FRP - Strengthened Masonry Infill Fig. 8: Debonding Mechanism for FRP-strengthened Infill Walls with Overlap Table 4: Maximum pressure for FRP-strengthened Infill Walls with Overlap, kpa Specimen No. Arching, q ar Debonding, q db Predicted Maximum Pressure Measured Maximum Pressure Ratio of Predicted to Measured

21 Predicted Maximum Pressure (kpa) One-way Walls Two-way Walls Measured Maximum Pressure (kpa) 32 Fig 9: Maximum Pressure for FRP-strengthened Infill Walls with Overlap 321 RC Frame Anchor N a μf TH FRP q R Infill F TH Infill FRP Anchorage Region RC Frame R Fig. 1: Anchorage Failure Mechanism for FRP-Strengthened Infill Walls with FRP Anchors Table 5: Maximum Pressure for FRP-strengthened Infill Walls with FRP Anchors, kpa Specimen No. Arching, q ar Anchor Failure, q an Predicted Maximum Pressure FRP - Strengthened Masonry Infill Measured Maximum Pressure Ratio of Predicted to Measured

22 Predicted Maximum Pressure (kpa) Measured Maximum Pressure (kpa) Fig 11: Maximum Pressure for FRP-strengthened Infill Walls with FRP Anchors 328

23 *Sizing Worksheet (.xls) Click here to download Sizing Worksheet (.xls): Sizing.xls ***Please complete and save this form then it with each manuscript submission.*** Note: The worksheet is designed to automatically calculate the total number of printed pages when published in ASCE tw format. Journal Name: ournal of Composites for Constructio Manuscript # (if known): Author Full Name: Dillon S. Lunn and Sami H. Rizkalla Author dslunn@ncsu.e The maximum length of a technical paper is 1, words and word-equivalents or 8 printed pages. A technical note should not exceed 3,5 w word-equivalents in length or 4 printed pages. Approximate the length by using the form below to calculate the total number of words in the tex it to the total number of word-equivalents of the figures and tables to obtain a grand total of words for the paper/note to fit ASCE format. Over must be approved by the editor; however, valuable overlength contributions are not intended to be discouraged by this procedure. 1. Estimating Length of Text A. Fill in the four numbers (highlighted in green) in the column to the right to obtain the total length of text. NOTE: Equations take up a lot of space. Most computer programs don t count the amount of space around display equations. Plan on counting 3 lines of text for every simple equation (single line) and 5 lines for every complicated equation (numerator and denominator). 1-column table = up to 6 characters wide 2. Estimating Length of Tables A. First count the longest line in each column across adding two characters between each column and one character between each word to obtain total characters. B. Then count the number of text lines (include footnote & titles) 1-column table = up to 6 characters wide by: 17 lines (or less) = 158 word equiv. up to 34 lines = 315 word equiv. up to 51 lines = 473 word equiv. up to 68 text lines = 63 word equiv. 2-column table = 61 to 12 characters wide 2-column table = 61 to 12 characters wide by: 17 lines (or less) = 315 word equiv. up to 34 lines = 63 word equiv. up to 51 lines = 945 word equiv. up to 68 text lines = 126 word equiv. C. Total Characters wide by Total Text lines = word equiv. as shown in the table above. Add word equivalents for each table in the column labeled "Word Equivalents." Estimating Length of Text Count # of words in 3 lines of text: Total # refs Divided by 3 Average # of words per line Count # of text lines per page # of words per page Count # of pages (don't add references & abstract) Title & Abstract Length of Text is Estimating Length of Tables & 3. Estimating Length of Figures A. First reduce the figures to final size for publication. Figure type size can't be smaller than 6 point (2mm). B. Use ruler and measure figure to fit 1 or 2 column wide format. 1-column fig. = up to 3.5 in.(88.9mm) C. Then use a ruler to check the height of each figure (including title & caption). 1-column fig. = up to 3.5 in.(88.9mm) wide by: up to 2.5 in.(63.5mm) high = 158 word equiv. up to 5 in.(127mm) high = 315 word equiv. up to 7 in.(177.8mm) high = 473 word equiv. up to 9 in.(228.6mm) high = 63 word equiv. D. Total Characters wide by Total Text lines = word equiv. as shown in the table above. Add word equivalents for each table in the column labeled "Word Equivalents." Total Tables/Figures: Total Words of Text: Total words and word equivalents: printed pages: 2-col. fig. = 3.5 to 7 in.(88.9 to mm) wide 2-column fig. = 3.5 to 7 in.(88.9 to mm) wide by: up to 2.5 in.(63.5mm) high = 315 word equiv. up to 5 in.(127mm) high = 63 word equiv. up to 7 in.(177.8mm) high = 945 word equiv. up to 9 in.(228.6mm) high = 126 word equiv. Tables Word Equivalents Figures Table Figure Please double-up tables/figures if additional space is (word equivalents) needed (ex. 2+21). 2 and 21 8 updated 1/16/3

24 wo-column edu words and xt and adding rlength papers subtototal plus headings TOTAL words printed pages Figures: Word Equivalents updated 1/16/3