cf 2001 silva.pdf

Silva, P., J. Myers, A. Belarbi, G. Tumialan, K. El-Domiaty, and A. Nanni, "Performance of Infill URM Wall Systems Retrofitted with FRP Rods and Laminates to Resist In-Plane and Out-of-Plane Loads," Structural Faults and Repairs, London, UK, July 4-6,2001.

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PERFORMANCE OF INFILL URM WALL SYSTEMS RETROFITTED WITH FRP RODS AND LAMINATES TO RESIST

IN-PLANE AND OUT-OF-PLANE LOADS Pedro F. Silva 1 Assistant Professor of Civil Engineering John J. Myers 1 Assistant Professor of Civil Engineering Abdeldjelil Belarbi 1 Associate Professor of Civil Engineering

Khaled El-Domiaty 1 Graduate Research Assistant Jaime G. Tumialan 1 Graduate Research Assistant Antonio Nanni 1 V. & M. Jones Professor of Civil Engineering

1 University of Missouri-Rolla Rolla, MO, 65409, USA ABSTRACT Recent failures of masonry walls around the word have driven the development of new techniques for the repair and strengthening of un-reinforced masonry (URM) walls. Failure of URM walls can be caused by structural deficiencies, dynamic vibrations, settlement and in-plane and out-of-plane loads/displacements. A rather comprehensive research program on the retrofitting and repair of URM wall systems using FRP composites is being carried out at the University of Missouri-Rolla. This research program addresses retrofitting of infill URM walls to resist in-plane loading due to seismic action and its lateral effects, and out-of-plane resistance of URM walls subjected to seismic and wind loads, and blast events. INTRODUCTION Failure of masonry structures can be caused by structural weaknesses or overloading, dynamic vibrations, settlement, in-plane and out-of-plane deformations, and blast type loading. Current literature on masonry indicates that each of these causes can be prevented and/or lessened by upgrading of structures using FRP composites. In previous works dealing with the use of FRP laminates, variables such as loading configurations/mechanisms, strengthening schemes, and anchorage systems have been evaluated (Hartley, et al., 1996; Schweler et al., 1996; Velazquez, 1998). Validation of URM walls upgraded using FRP composites through experimental and analytical investigation of masonry wall components is currently underway at the University of Missouri-Rolla. This paper presents the scope of activities that are part of this research program dealing with the upgrade/retrofit of URM walls to resists large-scale events such as seismic, wind and blast loads. Infill URM walls in structural frames are a common construction practice widely used all over the world. Although these infill walls are not assumed to contribute to the overall axial and lateral load resisting mechanism of the structure, experimental and analytical studies have shown that the performance of these structural frames is significantly affected by the presence of infill walls. In addition, seismic events around the world have shown that the presence of these infill walls greatly affects the load distribution path of the seismic forces. As shown in Figure 1, URM walls are prone to excessive damage under in-plane seismic loading, leading to significant stiffness reduction in the lateral direction making these walls susceptible to out-of-plane collapse and resulting in potential financial and life losses.


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One of the common fallacies associated with the design of structural frames with infill URM walls is the assumption that design is conservative if the infill walls are ignored in the seismic analysis. However, preliminary investigations of a typical building with the characteristics indicated in Figure 1 show that this is not the case, and a more accentuated catastrophic collapse of the building may develop. This paper will address some of these issues related to the retrofit of infill walls and its impact on the seismic response of buildings. The performance of URM walls depends on the tensile strength of masonry to resist out-of-plane loads caused by high wind pressures or earthquakes. Due to this limitation, URM walls located at upper building stories can collapse due to higher seismic accelerations or wind pressures. This paper will also address conditions for the retrofit of infill walls with stiffness and strength deficiencies in the out-of-plane direction solely under out-of-plane loading, as a result of seismic or wind loads.

Figure 1. Damage of Infill URM Walls After a

Seismic Event (Turkey, 1999)

Many public and corporate buildings and installations have been built and are being built with little concern for the destructive effects of terrorist attacks and other forms of vulnerability to explosive blast effects. In addition, recent events around the world have shown the vulnerability of civil structures to excessive damage when subjected to blast loads. From a structural point of view, the blast scenario can be subdivided in three phases, each of which introduces a new set of engineering considerations. In the first phase, exterior walls, columns and windows are affected; in the second phase floor slabs and roofs; and in the last phase, the lateral load resisting frame. Amongst building components, masonry walls possess a reduced capacity against out-of-plane blast loading. The damage that occurs to a structure as a result of a blast loading can be correlated to the charge weight and stand-off distance. This correlation indicates key relationships and provides insight for conducting risk assessment and determining acceptable levels of protection for walls under such blast loadings. This analysis of risk assessment for masonry walls is necessary for many reasons. First, protection of buildings and their inhabitants can consume vast amounts of resources and yet never offer a guarantee of safety. Second, determining an acceptable level of protection is a concern because the magnitude of that at risk may vary. Third, after a threat or risk analysis is completed, one can estimate the size and location of the explosion to protect against. Finally, by using a well-established relationship that the intensity of a blast decays in relation to the distance from the explosion, one can adopt an idealized blast wave at the target, and develop design curves in terms of acceptable damage levels, charge weight, and stand-off distance. This research will provide insight and solutions to these ever-present issues facing the field of civil engineering. RESEARCH OBJECTIVES The main objective of this research program is to develop retrofit strategies that address the following conditions: (1) in-plane performance of infill URM walls due to seismic action and its effects on the lateral resistance, (2) out-of-plane resistance of URM walls subjected to seismic and wind loads, and (3)


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out-of-plane resistance of infill URM walls subjected to blast loading. The following are some of the research objectives that address the retrofit of infill URM to different loading conditions. After a comprehensive review of the literature (Dhanasekar et al., 1986; Leuchars et al, 1976; Stafford et al., 1992; Stuart et al., 1993; and Zarnic et al., 1994), integrated experimental and analytical studies were planned to investigate the capacity of infill URM walls. Experimental investigation include the testing of URM walls with the following retrofit schemes; (1) walls retrofitted with vertical FRP rods, (2) walls retrofitted with horizontal FRP rods, and (3) walls retrofitted with vertical FRP sheets. In addition, control URM walls will also be tested to obtain the mechanical behavior of concrete masonry units. Future plans include testing of additional walls with retrofit combinations of these schemes. The schemes previously described involve FRP laminate sheets lay-up (see Figure 2), and FRP near-surface mounted (NSM) rods (see Figure 3) (Tumialan et al., 2001). The test matrix for the different research areas contain un-reinforced masonry walls, retrofitted walls with FRP laminates, and retrofitted walls with FRP-NSM rods and their combinations. Un-reinforced masonry walls are masonry walls with no form of reinforcement or other structural support. They will serve as the control units for correlation with the retrofit walls.

Figure 2. FRP Sheets

Figure 3. FRP-NSM Rods

Analytical studies will enhance the experimental program by developing guidelines to predict the in-plane performance of infill URM walls. The design guidelines will complement existing documents developed by the American Concrete Institute for strengthening of structures with FRP composites (ACI 440, 2001a; ACI 440, 2001b). In-Plane Performance of Infill URM Walls Subjected to Seismic Loads Retrofit of infill walls are of great concern because it is expected that a significant increase in the horizontal load capacity and stiffness of URM walls may develop. These conditions must be addressed in the seismic response evaluation of structural frames with infill masonry walls. One of the aspects related to the retrofit of infill masonry walls is the stiffening effect of these walls and its impact on the overall progression of the plastic mechanism of structural frames in low to high-rise buildings. Regions selected to be primary energy dissipation locations, in case of a seismic event, may remain within the elastic range. This response will most likely lead to a significant increase in the displacement ductility demand at other locations predominantly in the plastic hinge of ground level columns, which may lead


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to vertical irregularities commonly defined as a soft-story plastic mechanism (Paulay and Pristley, 1992). This condition may lead also to other significant catastrophic failures if a proper seismic evaluation of a building is not performed. This is an area that will be addressed in this research program. As part of this research program, retrofitting strategies will be developed to provide efficient and economical techniques that can be used to either rehabilitate or retrofit un-reinforced infill masonry walls with FRP materials. Thus, the main objective of this experimental program that deals with retrofitting of infill URM walls with FRP materials subjected to in-plane loading is to develop a retrofit strategy that while economical will minimize the influence of the retrofit on the overall performance of structural frames in predominant seismic regions. Allowing some damage to develop in the infill walls but guaranteeing that no out-of-plane collapse occurs under a moderate to strong seismic event will accomplish this objective. In parallel, analytical studies will aim at establishing design and strengthening guidelines for masonry structures. These retrofit techniques were implemented to: (1) develop analytical models to predict the response of infill URM walls under in-plane loading, and (2) minimize the stiffening effect of infill URM walls retrofitted with FRP materials by allowing some level of damage to occur in the walls such that no out-of-plane collapse occurs under a moderate to strong seismic event.

Out-of-Plane Performance of Infill URM Walls Subjected to Seismic and Wind Loads URM walls are commonly used as interior partitions or exterior walls bound by steel or concrete frames forming the building envelope. Stiff frames may restrain the movement of the wall when subjected to out-of-plane loading. As a consequence, in-plane clamping forces are generated producing a load resisting mechanism. It is well documented that this phenomena, known as arching action, improves the flexural behavior of the wall. At the ultimate limit state, due to the compressive stresses at the upper and lower boundary regions of the wall, the masonry units along the edges are fractured. It has been reported that for a slenderness ratio over 30, the effect of arching action is small (Angel, 1994). The influence of arching mechanisms in the behavior of retrofitted walls needs to be taken into account to fully realize the effectiveness of strengthening strategies because depending on the strengthening scheme, this could either under or overestimate the wall capacity. Out-of-Plane Performance of Infill URM Walls Subjected to Blast Loading An on-going research program at UMR has for objective the development of experimental data concerning with blast loading and the associated effects on un-reinforced masonry walls strengthened with FRP composites. Two parameters exist that are fundamental in determining the blast pressures experienced by a structure. These parameters include the charge weight, Q, and the stand-off distance, R. The charge weight is the actual explosive material itself expressed in terms of mass. The stand-off distance is defined as the distance between the explosive charge and the structure under loading, in this case the masonry walls. These two main variables (i.e. Q and R) will be evaluated in this research program as it relates to damage of masonry wall components. A total of 16 walls reflecting different retrofit techniques are scheduled for testing. In these tests, three different types of retrofit techniques will be implemented and damage levels to these walls will be established as a function of the charge weight and stand-off distance. In addition, the damage that occurs to the masonry walls as a result of the blast loading can be measured and correlated to the original two parameters. This correlation will indicate key relationships and provide insight for conducting risk assessment and determining acceptable levels of protection for walls under such blast loadings.


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RESEARCH PROGRAM In-plane Performance of Infill URM Walls Subjected to Seismic Loads The first part of this test program was developed to access the in-plane performance of URM walls with different types of retrofit schemes. Test Setup The test setup is shown in Figure 4. The test frame consists of three main parts: a reaction frame, a sliding frame and a chair frame. The load was applied to the sliding frame by a hydraulic jack that was attached to the reaction frame by means of a W-section steel beam. The concrete masonry units (CMU) were assembled on a reinforced concrete (RC) support block, which was tied down to the laboratory strong floor. On the top of the wall, a RC beam was installed, which was used to provide load transfer from the sliding frame to the walls. Two steel beams that were connected to the sliding frame accomplished the load transfer to the top RC beam. During testing, the sliding frame was restrained from rotation by a chair frame that was tied-down to the laboratory strong floor. In order to prevent sliding of the walls at the interface between the bottom and top RC beams, steel angles were attached. This was necessary to simulate the boundary conditions of infill URM walls under in-plane loading. The concrete CMUs were two-core hollow block that have the nominal sizes 4in.×8in.×12in. (10.2cm×20.3cm×30.5cm). The net area of the blocks is 27.75in.2 (179.0cm2) and the net area compressive strength is 1500psi (0.01MPa) based on the average of 4 unit tests. The nominal size of the walls is 88in. (223.5cm) high by 48in. (121.9cm) long by 4in. (10.0cm) wide.

Figure 4. In-Plane Walls Test Setup

The walls were built by a group of experienced masons using construction techniques representative of good workmanship. The specimens were built in two continuous days; half of the wall panel was built during the first day and the other half was built the following day. Then the specimen was cured in natural condition for at least 30 days before testing. The test units are as follows; (1) a controlled URM wall that will be used to obtain the mechanical behavior of concrete masonry units and establish


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efficiency of the different retrofit schemes, (2) a wall retrofitted with 4 - #3 (D9.5) vertical FRP rods, (3) a wall retrofitted with 10 - #2 (D6.4) horizontal FRP rods, and (4) a wall retrofitted with 4 – 2.5in. (63.5 mm) carbon FRP sheets. Testing of the first three test units have been completed and testing of the fourth test unit is scheduled for completion in the near future. Table 1 presents the test matrix for this part of the research program.

Table 1. Test Matrix

Test Unit Retrofit Scheme Test Unit Retrofit Scheme 1A Controlled Unit –No Retrofit 1C 10 - #2 (6.35) Horizontal Glass FRP Rods

1B 4 - #3 (D9.53) Vertical Glass FRP Rods 1D 4 - 2.5in. (63.5mm) Vertical Carbon FRP

Sheets

Test Unit 1A Test Unit 1B

Test Unit 1C Test Unit 1D

Recorded forces and displacements included those measured by the load cell, and linear variable displacement transformers (LVDTs). The load cell was positioned between the hydraulic jack and the sliding frame. The LVDTs were installed on the top and mid-height of the walls to obtain the lateral displacements of the wall at the top and mid-height, respectively. Preliminary Experimental Results Design codes around the world impose inter-story drift limitations to reduce among many other factors damage to non-structural components and personal comfort. In the United States the uniform building code (ICBO-UBC 1997) limits the inter-story drift to 2% for structures having a fundamental period greater than 0.7 sec., and 2.5% for those structures with a fundamental period less than 0.7 sec. Thus, one of the main objectives of the experimental part of this research program is to evaluate/assess the damage level of the tested walls within these two design drift levels. Figure 5 presents the test results of the three test units completed up to date and the position of the 2% and 2.5% drift level for the tested walls. Test results indicate that before debonding of the vertical rods occurred, no significant difference was registered between test units 1B (vertical rods) and 1C (horizontal rods). However, after this damage level the response of test unit 1B was significantly different in relation to the response of test unit 1C.

0.0 25.4 50.8 76.2 101.6 127.0

Lateral Displacement (mm)

0

22

44

66

88

Lat

eral

Loa

d (k

N)

0.00 1.00 2.00 3.00 4.00 5.00Lateral Displacement (in.)

0

5

10

15

20

Lat

eral

Loa

d (k

ips)

Test Unit 1ATest Unit 1BTest Unit 1C

2% Drift

2.5% Drift

Figure 5. Load-Deformation Diagram


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The load capacity of test units 1B and 1C were approximately three and six times higher than of test unit 1A, respectively. Preliminary investigation indicates that the higher horizontal load achieved by test unit 1C in relation to test unit 1B may be due to the fact that with horizontal FRP rods, slipping of a column of blocks cannot develop and so the wall serves as a whole unit until the horizontal rods begin to pull-out. This leads to a preliminary conclusion that retrofitting of URM walls with horizontal FRP rods may lead to higher horizontal load capacities. Out-plane Performance of Infill URM Walls Subjected to Seismic and Wind Loads An experimental program is under way to evaluate the effectiveness of FRP laminates as a means to strengthen URM walls subjected to out-of-plane loads. Masonry specimens built with different kinds of masonry units were strengthened with Aramid FRP (AFRP) and Glass FRP (GFRP) laminates for out-of-plane loading. The slenderness ratio of the specimens is equal to 12. The specimens were tested under four-point bending to study their flexural behavior, and the test setup is shown in Figure 6.

Figure 6. Out-of-Plane Walls Test Setup

For high amount of reinforcement ratio, shear failure will most likely occur. Based on the experimental results it is expected to use a linear elastic cracked section for the analysis of the strengthened sections. This consideration can be used for the development of guidelines for flexural strengthening of URM walls. Figure 7 illustrates the relationship between the experimental - theoretical flexural capacity ratio, and the reinforcement ratio index, ωf, expressed as

( )( )thfE mff /'/ρ , whereρf is the FRP laminate reinforcement ratio, Ef is the FRP laminate Young’s modulus, mf ' is the masonry concrete strength, h is the height of the wall and, t is the thickness of the masonry unit.

Figure 7. Influence of Amount of FRP Reinforcement


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The experimental data used for plotting Figure 7 was obtained from previous investigations (Velazquez, 1998, and Hamilton et al., 1999) where AFRP and GFRP laminates were used as strengthening material. Mostly, the tests showed that the strengthened specimens failed due to debonding of the laminate. Since the ratio Mexperimental - Mtheoretical shown in Figure 7 averages about 0.5, for design considerations the effective strain efe in the FRP laminate can be limited as about half of the strain at ultimate in the laminate efu. Also, the reinforcement ratio index ωf may be limited to 0.5 to prevent the occurrence of shear failure. One of the main objectives of this research is to validate these limits. Based on these discussion, different amounts of reinforcement will be studied to observe its incidence in different modes of failure. The FRP laminate reinforcement ratios, ρf, are 25, 50, 75, 100 and 200 percent of the balanced ratio. The balanced ratio corresponds to the state where the crushing of masonry and rupture of FRP laminate occur. It is expected to observe delamination of the FRP laminate from the masonry substrate as a predominant mode of failure.

Out-of-Plane Performance of Infill URM Walls Subjected to Blast Loading As a preliminary study, a total of sixteen unreinforced masonry walls (URM) will be tested. Part of the experimental test setup displacement transducers and strain gages devices will be installed to supply needed data. Different types of retrofit techniques will be implemented and damage levels to these walls will be established as a function of the charge weight and stand-off distance. URM’s will serve as the control units for correlation with the retrofitted walls, which consist of E-glass FRP rods and sheets applied to the bare masonry walls. Test Setup The test setup for blast loads is shown in Figure 8. The walls have been constructed on concrete strip footings back-to-back as illustrated in Figure 9. The entire testing program consists of two series of eight of these back-to-back footings. The infill wall will have boundary members (concrete footing / beam) on the top and bottom of the wall.

2’-1”

Centerline of two footings

Inside face of Masonry Wall. Location of wall onFtg B will be the same, just mirrored.

Ftg. BFtg. A

Concrete boundary element

Steel Frame

Charge

2’-1”


Inside face of Masonry Wall. Location of wall onFtg B will be the same, just mirrored.

Ftg. BFtg. A

Concrete boundary element

Steel Frame

Charge

Figure 8. Side View of the Wall and Frame


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3’-0”0.91m)

3’-3 ½”(1.00m)

3’-0”0.91m)

8’-0” (2.44m)

4’-0” (1.22m) long wall, centered on 8’-0”(2.44m) wide footing

Masonry Wall

Concrete Beam on top of masonry wall

4”-9”(10.16cm) thick wall

2’-1”(63.5cm)

3’-8 ¾” (1.14m)centerline of frame to inside face of masonry wall


Ftg. B

Ftg. A3’-0”0.91m)

3’-3 ½”(1.00m)

3’-0”0.91m)

8’-0” (2.44m)

4’-0” (1.22m) long wall, centered on 8’-0”(2.44m) wide footing

Masonry Wall

Concrete Beam on top of masonry wall

4”-9”(10.16cm) thick wall

2’-1”(63.5cm)

3’-8 ¾” (1.14m)centerline of frame to inside face of masonry wall


Ftg. B

Ftg. A

Figure 9. Plan of Strip Footings (2 wall series)

A structural steel frame designed to withstand the blast loading will support the boundary members. The structural steel frame is composed of 6in. x 6in. x 3/8in. (15.24cm x 15.24cm x 0.10cm) tube sections and miscellaneous steel plates and angles (see Figure 10. Two types of data acquisition sensors will be used to characterize the pressure wave distribution and acceleration of the test walls subjected to the blast loading. These sensors include pressure transducers and accelerometers in conjunction with a data acquisition system with an appropriate sampling rate to capture the blast wave. Two protocols for testing have been developed. The first protocol has been developed to calibrate the pressure wave such that at a later date, simulation models can be developed to investigate the performance of the various retrofitted systems under additional charge weights, stand-off distances, and masonry block configurations which are described as next.

Figure 10. Steel Frame Before w/out attached Walls

Protocol # 1 (Calibration of Pressure Waves and Instrumentation) This phase will only be conducted on the first wall in the test series. It is necessary to validate the theoretical pressure values obtained from numerical equations with real experimental values. It is also important to calibrate and test the instrumentation before proceeding with the entire test series. Initially,


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two charges of TNT dynamite – 0.22lbs (0.1kg) at 26ft-3in. (8m) of standoff distance - will be used in this test (below the minimum threat level standard of the DOE) as illustrated in Figure 11.

(b) SIDE VIEW

Q1, Q2 26’-3”(8 m)

4’-0”(1.22 m)

Wall #1

(c) INSTRUMENTATION LAYOUT

Q1Q2

Wall #1

(a) TOP VIEW

Pressure Transducer

Accelerometer

26’-3”(8 m)

(b) SIDE VIEW

Q1, Q2 26’-3”(8 m)

4’-0”(1.22 m)

Wall #1

(c) INSTRUMENTATION LAYOUT

Q1Q2

Wall #1

(a) TOP VIEW

Pressure Transducer

Accelerometer

26’-3”(8 m)

Figure 11. Protocol #1 - Calibration Set-up

Protocol # 2 (Standard Test Protocol) Following the successful completion of protocol #1, the 16 walls will be subjected to different levels of threats (variable TNT charges at variable standoff distances) based on the Department of Defense Antiterrorism / Force Protection Construction Standards. The wall numbers and test matrix are shown below in Table 2. Figure 12 illustrates the retrofitting schemes that will be undertaken in this study. Table 3 details the initial charge weight and stand-off distance that will be used to meet the threat specific standards for the walls. The charge weight is based on the use of TNT dynamite. There will be a fire of one charge per 10-minute blast window at the charge values and stand off distances outlined in the test matrix.

Table 2. Test Wall Matrix Retrofiting Schemes

Wall Number Symbol Wall Number Symbol Wall #1 U1 Wall #9 B1 Wall #2 U2 Wall #10 B2 Wall #3 U3 Wall #11 B3 Wall #4 U4 Wall #12 B4 Wall #5 A1 Wall #13 C1 Wall #6 A2 Wall #14 C2 Wall #7 A3 Wall #15 C3 Wall #8 A4 Wall #16 C4

Legend: U – Unreinforced A – Retrofit A B – Retrofit B C – Retrofit C


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Therefore, the damage that occurs to masonry walls as a result of the blast loading will be measured and correlated to the charge weight and stand-off distance. This correlation will indicate key relationships and provide insight for conducting risk assessment and determining acceptable levels of protection for walls under such blast loadings. This analysis of risk assessment for masonry walls is necessary for many reasons. Protection of buildings and their inhabitants can consume vast amounts of resources and yet never offer a guarantee of safety. Determining an acceptable level of protection is a concern because the magnitude of that at risk may vary. After a threat or risk analysis is completed, one can estimate the size and location of the explosion to protect against. By using the well-established relationship that the intensity of a blast decays in relation to the distance from the explosion, one can adopt an idealized blast wave at the target, and design curves in terms of acceptable damage levels, charge weight, and stand-off distance.

(a) Unreinforced (b) Retrofit A (c) Retrofit B (d) Retrofit C (Horiz. FRP Rods) (Vert. FRP Rods) (Vert. FRP Sheets)

Figure 12. Retrofitting Schemes

Table 3. Threat Specific Standards

Threat Level Walls Tested Minimum (Q=0.22lbs, R=13’-0”m) (Q=0.1kg, R=4m)

U1, A1, B1, C1

Low (Q=1.10lbs, R=13’-9”) (Q=0.5kg, R=4.2m)

U2, A2, B2, C2

Medium (Q=2.20lbs, R=13’-0”) (Q=1.0kg, R=4m)

U3, A3, B3, C3

High (Q=3.31lbs, R=11’-9”) (Q=1.5kg, R=3.6m)

U4, A4, B4, C4

Special Case (Q=5.51lbs, R=5’-3”) (Q=2.5kg, R=1.6m)

U1, A1, B1, C1

SUMMARY AND CONCLUSIONS This research program includes experimental and analytical investigations, which addresses the performance of URM walls under in-plane and out-of-plane loading. In the experimental program FRP bars and laminates with different configuration and strengthening schemes will be implemented to prevent such failures. On the other hand, the analytical study will aim at establishing design and strengthening guidelines for masonry structures that are in compliance with the American Concrete Institute committee ACI-440 and the Masonry Standards Joint Committee (MSJC). This paper presents the design concept that was used to retrofit URM walls for in-plane and out-of-plane loading and some preliminary experimental results. FRP composites offer great benefits for the strengthening of masonry elements. Previous investigations have proven that FRP composites can remarkably increase flexure and shear capacities. Design protocols and recommendations for proper engineering and installation procedures, which are key to success, need to be developed.


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ACKNOWLEDGEMENTS The authors acknowledge the financial support of the NSF Industry /University Cooperative Research Center for the repair of bridges and buildings (RB2C) REFERENCES American Concrete Institute (ACI), Committee 440, (2001a), "Guide for the Design and Construction of

Externally Bonded FRP Systems for Strengthening Concrete Structures," September 2000 (document under review).

American Concrete Institute (ACI), Committee 440, (2001b), "Guide for the Design and Construction of Concrete Reinforced with FRP Bars," January 2001 (document under review)

Angel R., Abrams D.P., Shapiro D., Uzarski J., and Webster M, (1994), “Behavior of Reinforced Concrete Frames with Masonry Infills,” Structural Research Series Report No. 589, Department of Civil Engineering, University of Illinois at Urbana-Champaign, March 1994.

Department of Defense, (1999) “Interim Department of Defense Antiterrorism/Force Protection Construction Standards”.

Dhanasekar, M., and Page, A W., (1986),“Influence of Brick Masonry Infill Properties on the Behavior of Infill Frames”, Proceedings of the Institution of Civil Engineers, V81 pt 2 Dec 1986, London, p 593-605.

Hamilton H.R. III, Holberg A., Caspersen J., and Dolan C.W, (1999), “Strengthening Concrete Masonry with Fiber Reinforced Polymers,” Fourth International Symposium on Fiber Reinforced Polymer (FRP) for Reinforced Concrete Structures, Baltimore, Maryland, November 1999.

Hartley A., Mullins G., and Sen R. (1996), “Repair of Concrete Masonry Block Walls using Carbon Fiber,” Advanced Composite Materials in Bridges and Structures, Montreal, Quebec, 1996, pp. 795-802.

International Conference of Buildings Officials (ICBO), (1997), ”Uniform Building Code, Structural Engineering Design Provisions,” UBC 1997, Volume 2, USA 1997.

Leuchars, J. M., and Scrivener, J. C., (1976), “Masonry infill panels subjected to cyclic in-plane loading”, Bulletin of the New Zealand National Society for Earthquake Engineering, V 9 n 2 June 1976 p 122-131.

Paulay T., and Priestley M.J.N., (1992), “Seismic Design of Reinforced Concrete and Masonry Buildings,” John Wiley & Sons, Inc., New York, 1992.

Schwegler G., and Kelterborn P. (1996), “Earthquake Resistance of Masonry Structures strengthened with Fiber Composites,” Eleventh World Conference on Earthquake Engineering, Acapulco, Mexico, 1996.

Stafford, Smith, B. (1992), “Behavior of the square infill frames”, Journal of Structural Division, ASCE, pp 381-403.

Stuart Foltz, and Charles W.C. Yancey, (1993), “The Influence of Horizontal Reinforcement On the Shear Performance of of Concrete Masonry Walls”, Masonry: Design and Construction, Problems and Repair, 1993. p33-58.

Tumialan J.G., Tinazzi D., Myers J., Nanni A., (2000), “Field Evaluation of Unreinforced Masonry Walls Strengthened with FRP Composites subjected to Out-of-Plane Loading,” 2000 Structures Congress, American Society of Civil Engineers, Philadelphia, Pennsylvania, May 2000.

Tumialan, J.G., Huang, P-C., Nanni, A., and Silva, P.F., (2001), "Strengthening of Masonry Walls by FRP Structural Repointing," Non-Metallic Reinforcement for Concrete Structures - FRPRCS-5, Cambridge, England, July 2001.

Velazquez J.I., (1998), “Out-of-Plane Cyclic Behavior of URM Walls Retrofitted with Fiber Composites,” Ph.D. Dissertation Department of Civil Engineering and Engineering Mechanics, The University of Arizona.

Zarnic, Roko., (1994), “Experimental investigation of the R/C frame infill by masonry wall”, International Journal for Engineering Modelling, V 7 n 1-2, 1994. p 37-45.

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