Bashar S. Mohammed 1, L.W. Ean 2 and Khandaker M. Anwar Hossain 1

Transcription

1 CFRP Composites for Strengthening of Reinfored Conrete s with Openings Bashar S. Mohammed 1, L.W. Ean 2 and Khandaker M. Anwar Hossain 1 1 Department of Civil Engineering, Ryerson University, 350 Vitoria Street, Toronto, Ontario, M5B 2K3 2 Civil Engineering Department, College of Engineering, University Tenaga Nasional, Km-7, Jalan Kajang-Puhong, Kajang, Selangor, Malaysia ABSTRACT This paper presents the results of a researh work aimed at investigating the potential used of externally bonded Carbon Fiber Reinfored Polymer (CFRP) omposite sheets as a strengthening solution for uniaxial retangular onrete walls with entral retangular in-plane s. Seventeen of 1/3 sale retangular onrete walls with and without entral retangular in-plane s of different sizes (5%, 10%, 20% and 30% of wall areas) are tested. In thikness diretion, one entral layer of steel fabris was used to reinfore the onrete walls. The walls were subjeted to uniaxial loading aligned with the longest edge of the onrete walls. The loading was applied eentrially (t/6) with respet to the mid-plane of the walls. Two different patterns were used to fix the CFRP to both surfaes of the walls whih are parallel to the midplane of the wall segments. The first pattern onsisted of applying four strips of CFRP parallel to the four edges of the suh that they framed the. In the seond pattern, CFRP strips were used to reinfore the walls in the viinity of the edges only, i.e. four CFRP strips were applied lose to the orners of the s, in an angle of 45 degrees with both adjaent edges of the. From the results of the researh work, it was found that CFRP strips applied at an angle of 45 degrees to both adjaent edges of the yielded a better ompressive strength ompared to the CFRP strips that framed the s. Keywords-Reinfored onrete wall,, ultimate load, Carbon Reinfored Polymer, CFRP, stress onentration, strengthening I. INTRODUCTION Reinfored onrete wall panels are ommonly used as a load bearing strutural elements. Uniaxial ation walls are defined as laterally supported and restrained against defletion along top and bottom supports. It is designed to resist in-plane vertial loads ating downward from the top of the wall and it, also transfers loads in one diretion to supports at the top and bottom. The wall panels often undergo aidental eentri loads due to the imperfetions in onstrution. Due to arhitetural or mehanial requirements and/or hange in the building s funtion; ut-out new s for provision of doors and windows or to aommodate essential servies suh as ventilation and air-onditioning duts is frequently required. Large s in RC wall panels ause disturbane in the stress path when onsiderable amount of onrete and reinforing steel have to be removed. Most of the investigations on uniaxial reinfored onrete wall panels are on solid walls and have led to ertain design reommendations suh as Amerian Conrete Institute ode ACI [1] and Australian Standard AS [2]. Hene, there are some researhers that have ontributed to the developments of empirial formula for RC wall panels with s [3-10]. The strutural effet of small s is often not onsidered due to the ability of the struture to redistribute stresses. However, for larger s the stati system may be altered when a onsiderable amount of onrete and reinforing steels have to be removed. This leads to a dereased ability of the struture to resist the imposed loads [11]. The presene of the s in the panels determines the load paths and reates stress onentrations around the, whih enourages raks to our first at the orners of the [12 and 13]. Therefore, the s in the wall panels need to be strengthened. The traditional strengthening methods for ut-outs in the literature are mostly by providing embedding of reinforing bars or steel plates [14, 15]. On the other hand, advaned omposites as an externally bonded reinforement have been extensively tested on their use for strengthening of beams and girders in flexure, shear and even to some extent in torsion. The use of Carbon Fiber Reinfored Polymer (CFRP) to strengthen existing slabs with s is beoming inreasingly popular [11]. This researh mainly fouses on the appliation of arbon fibers as the strengthening materials. A few researhers have studied the strengthening of strutural elements suh as slabs and beams with ut-outs using CFRP (eg:[11], [14],[15] and 1841 P a g e

2 [16]). Even though CFRP is widely used as strengthening materials of existing strutures, yet to the best knowledge of the authors, urrently no researh work has been arried out on CFRP as a strengthening material to strengthen wall panel with ut-out s. Advantages of using FRP have been reported by other researhers [17-23]. The latest studies of uniaxial reinfored onrete walls with s by Saheb, and Desayi [5] led to developments of empirial equations to determine their ultimate strength. They arried out test on twelve panels; six were supported only at the top and bottom and the others were supported on four sides. Eah panel was provided with a window or a door in different regions. The test panels were subjeted to in plane vertial loads applied at an eentriity. Empirial equations were developed for panels with s by modifying the ACI formula and had introdued a redution parameter that allowed for the geometry of the s. The equations of ultimate loads for the wall panels with s under in-plane uniaxial load (equation 1) proposed by S. M. Saheb and P. Desayi [5] are; P uo = (k 1 k 2 α)p u (1) where, k 1 & k 2 = (onstants) k 1 = 1.25; k 2 = 1.22 P u = The ultimate load of an idential wall panel without under uniaxial ation from Madina Saheb, S. and Desayi, P. [24] α = Opening geometry parameter The equations 2,3 and 4 for ultimate loads of wall panels without s under uniaxial load were defined in S. M. Saheb and P. Desayi [24] as, P u = 0.55φ A g f + f yv f A sv 1 32t L for L<2.0 (2) and P u L = 0.55φ A g f + f yv f A sv 1 32t 2 For 2.0 (3) The geometry parameter, α defined as where = A o A + a L (4) A o = L o t; A = Lt; a = L 2 L2t ā ; ā = 2 L o ta o ; Lt L o t where L o and o = the dimensions of the a =the distane between enters of the gravity of panel setion in plan with and without an a o and ā = distanes of the enters of gravity of the and of a panel without an from the left edge of the panel, respetively. However, the empirial equations are subjeted to wall panels with onrete strength < 35MPa, slenderness ratio (H/t) < 12, aspet ratio (H/L) <0.67, thinness ratio (L/t) <18 and aspet ratio (H o /L o ) is 1~2. Comparisons between normal ompressive strength and high strength solid wall panels tested in uniaxial and biaxial ation had been reported by Doh and Fragomeni [25]. s in uniaxial ation are haraterized by horizontal raking at mid-span at failure, while walls in biaxial ation feature biaxial raking. The rak pattern of normal strength wall panel on the tension fae is horizontal (perpendiular to the loading diretion) with failure ourring near the entre of the panel, signifying bending failure being intensified by bukling. In ontrast, high strength panel developed a single large rak, ommening at the tension fae splitting in two separate parts. This indiates that the high strength onrete panels possessed a more brittle failure mode, with some yielding of reinforement taking plae before onrete failure. This suggests that the use of very slender and high strength onrete wall panels may beome dangerous in pratie, when only minimum reinforement is provided, as abrupt failure may our [25]. In uniaxial walls with s, it was noted that vertial and inlined raks formed in the beam strips while horizontal raks formed in olumn strips. [10, 24]. II. RESEARCH SIGNIFICANCE This paper presents an analysis of the related formulas suggested by researhers with the experimental results. The test panels for this researh are designed with onrete strength <25MPa, slenderness ratio (H/t) < 16, aspet ratio (H/L) <2, thinness ratio (L/t) <8, and aspet ratio (H o /L o ) 1.8. This paper also reports the rak patterns of the test panels and suggested the best strengthening pattern for wall panels with s strengthened with CFRP. III. EXPERIMENTAL WORK 3.1 Test Panels A total of sixteen 1/3 sale reinfored onrete wall panels with s omprising four idential series of four 1842 P a g e

3 speimens eah are asted. Tables 1 and 2 show the dimensions of wall panels and s. All the test panels are 400mm width and 800mm height. Series one designated WO1-WO4, are 50mm thik and 3 other series were 40mm in thikness. Series one and two designated as WO1-WO4 and WO1a-WO4a, respetively are tested without CFRP; while series three and four designated as WO1b-WO4b and WO1- WO4, respetively are tested with CFRP strengthened wall s. panels are tested with different sizes of s. Opening sizes inrease by perentage of wall area of 5%, 10%, 20% and 30%. Aspet ratio (H/L), slenderness ratio (H/t) and thinness ratio (L/t) are 2, 16 and 8 respetively for wall series one. For series two, three, and four, aspet ratio (H/L), slenderness ratio (H/t) and thinness ratio (L/t) are 2, 20 and 10, respetively. Figures 1 shows the detail of the wall panels in series. The perentages of reinforements are kept the same in all the speimens. The purpose is to study the influenes of sizes on the strength and the behavior of wall panels tested in uniaxial ation. The panel reinforements are in one layer plaed entrally within the panel ross-setion. The reinforement ratios ρ v andρ for wall series one are and 0.007, respetively while for series two, three, and four are and 0.009, respetively. These reinforement ratios satisfy the minimum requirements in the ACI [1]. Figure 2 shows a solid wall, SW2 size 400x800x40 mm as a ontrol wall for omparison of CFRP appliation. Reinforement ratios for SW2 are the same as series 2, 3 and 4. TABLE 1: DIMENSIONS OF WALL PANELS SERIES 1 H L t Ho Lo SW WO1a,b, WO2a,b, WO3a,b, WO4a,b, % of wall Size Opening Size H L t Ho Lo WO WO WO WO Note: 1. Dimensions in millimeters. 2. Series two, three, and four with 40mm thikness Fig. 1: Series one (panels with, details of reinforement and shemati loading on one speimen) TABLE 2: DIMENSIONS OF WALL PANELS SERIES 2, 3, 4 AND SOLID WALL. % of wall Size Opening Size 1843 P a g e

4 widt of required CFRP = CFRP setional Area,A f tikness of CFRP (8) Note: Dimensions in mm. Fig. 2: Details of reinforement and shemati loading of solid wall panel. 3.2 CFRP Strengthened Panel Opening CFRP are applied around panel s to strengthen the wall panels. The method to alulate the required setional areas of CFRP for strengthening panel s has not been developed in design ode. Enohsson et al.[11] have introdued a simplified method to estimate the amount of CFRP required to strengthen the s in biaxial onrete slabs. The outome of the work an also be used for ast and made s in uniaxial onrete slabs and in onrete walls. They suggested that traditional method followed BBK 04 (The Swedish building administration handbook of onrete strutures) is used to alulate the required steel reinforement for slabs or walls with s. The additional steel reinforement replae the ut-out reinforement are given at least the same length, as it would have had if the had not exist. The simplified method is to onvert the alulated designed required steel reinforements to neessary amount of CFRP. Required area for CFRP are given as equation 5 below, assuming onrete and reinforement have a perfet bond, so that the expression for the setional area of CFRP beomes only dependent on the level arms and the elasti modulus of the steel. A f = E s2 E f x = a 0.85 a = A s2f yv 0.85f L t u x t x 2 As2 (5) (6) (7) where; E s2 = Modulus of elastiity for additional steel reinforement. E f = Modulus of elastiity for CFRP. t = Depth of the slab or thikness of the wall. u = Distane from the bottom tensile side to the entre of gravity of the steel bars. x = Distane from the top ompression side to neutral axis A s2 = Area of additional steel reinforement a = Depth of the equivalent retangular stress blok f yv = yield strength of steel f = onrete ompressive strength L = width of wall Anhorage length of CFRP is defined from the outermost rak of the wall (un-raked setion) whih is at the orners of the s. Effetive anhorage length, l b,max defined as equation 9 by fib Bulletin 14 [26]. An inrease in anhorage length l b,max does not result in resisting tensile stresses due to the limitation of frature energy [26]. CFRP is used to strengthen wall panel s in two patterns, whih is along the orners and 45 to the orners. Length and width of the applied CFRP are shown in Tables 3 and 4. Figure 3 shows the CFRP pattern used to strengthen the wall panel s. l b,max = C E f t f f u f tm (9) where; C = 1.44 ; onstant E f = Modulus of elastiity for CFRP, MPa t f = Thikness of CFRP, mm f u = Charateristi value of the onrete ompressive strength f tm = Mean value of the onrete tensile strength, MPa. TABLE 3: WIDTH AND LENGTH OF THE APPLIED CFRP SHEETS ALONG (0/90 ) PANEL OPENING (SERIES 3). Length of Width of Width of CFRP Length of CFRP 0 along the Length of CFRP 90 along the WO1b WO2b WO3b WO4b P a g e

5 TABLE 4: WIDTH AND LENGTH OF THE APPLIED CFRP SHEETS AT THE CORNER (45 ) OF PANEL OPENING (SERIES 4). Length of Width of Width of CFRP Length of CFRP WO WO WO WO (a) CFRP pattern 1 (b) CFRP pattern 2 Fig. 3: CFRP patterns used to strengthen wall panel s. 3.3 Materials The onrete used for all the speimens in this researh were having the mixture proportions of (ement: fine aggregate: oarse aggregate: water) 1:2.638:2.149:0.63. Ordinary Portland Cement (OPC) Type I whih onforms to the requirement of ASTM C was used in the onrete mix. The oarse aggregates used were graded 10 mm maximum sized rushed stone. Average onrete slumps for the onrete is approximately 75 mm whih is medium slump. Compressive strength ( f u ) of 100 mm ubes at the age of testing the wall panels is shown in Table 5. Cylinder strength is taken to be equal to 0.8 x f u. Compressive test is onduted just before the wall panels are tested. Average onrete tensile strength taken from splitting tensile strength test of onrete ylinder for Series two, three, and four is 1.46 MPa. The onrete ompressive and splitting strengths are the mean values of three test ubes and ylinders respetively. Modulus of elastiity and Poisson ratio of the onrete ylinders are 21GPa and 0.21, respetively. Reinforements used are 5mm in diameter steels with average proof yield strength of 478 MPa and modulus of elastiity of 2.05x10 5 MPa. Clear over of 15mm is given over the reinforements. Table 6 shows material properties of the CFRP sheets. The wall panels are tested on the 14 th day of uring by wet gunny bag. The wall panels strengthened with CFRP are ured with the gunny bag for 7 days, and applied with the CFRP on the 7 th day. The wall panels with applied CFRP then air ured with humidity of 70-75% and temperature of 28 C-33 C. TABLE 5: COMPRESSIVE STRENGTH OF THE TEST CUBES ON TESTING DAY. Series No wall Average Compressive Strength for Conrete Cube, f u,mpa Average Compressive Strength for Conrete Cylinder, f u,mpa (0.8xf u ) WO WO WO WO SW WO1a WO2a WO3a WO4a WO1b WO2b WO3b WO4b WO WO WO WO TABLE 6: Material Properties of CFRP Sheet (MAPEWRAP C UNI-AX 300/40) Produt UNI- AX 300/40 Fabri Thikness Tensile Strength (MPa) Tensile Modulus of Elastiity (GPa) Elongation at Breaking Point (%) Note: UNI-AX denotes uni-diretional ontinuous arbon fibre fabri, 300 denote mass per ross setional area (g/m 2 ) and 40 denote height in m for 50m rolls paked in arton boxes P a g e

6 3.4 Test Set Up The wall panels are tested using a hydrauli jak of 30 tone apaity. The hydrauli jak transmits a uniformly distributed load aross the top through a top plate to a 20 mm diameter steel bar at an eentriity of t/6. The arrangements are to ensure a distributed loading at an eentriity with pinned onditions. Figure 4 shows a two point load arrangement. The wall panels are similarly supported at the bottom. Details of the simply supported top pinned edge are shown in Figure 5. Surfae strains and lateral defletions are measured at seleted loations at eah stage of loading using strain gauges and Linear Variable Differential Transformers (LVDT) respetively. Positions of LVDTs are shown in Figure 6. LVDTs are plaed midway between the edges of the wall panel and the edges of. Every attempt is made to develop pinned-ended ondition at the top and bottom of the walls. One additional LVDT is plaed at the top edge to asertain the amount of panel movement within the frame in order to hek the pinned- ended ondition. Strain gauges are plaed at the orners and sides of the s to reord the strains during the testing. Arrangements of strain gauges on both faes are shown in Figure 7. Fig. 5: Top and bottom restraint Fig. 6: Arrangement of LVDT Fig. 4: Arrangement for Two Point Load Distribution Fig. 7: Arrangements for Strain Gauges 1846 P a g e

7 IV. RESULTS AND DISCUSSIONS e TABLE 8: P uo AND P u FOR TEST PANELS. 4.1 Failure Load of Panels with Openings in in-plane Uniaxial Ation Table 7 shows the theoretial failure loads, P uo and the experimental failure loads, P e uo. The theoretial failure loads are alulated from the empirial formula by Saheb and Desayi [5] in equation 1. P u for the test panels are alulated from equation 3 for φ = 1 (φ is apaity redution fator). P e uo /P uo < 1 whih the theoretial failure loads are less than experimental failure loads and it is onservative to use in design. e TABLE 7: P uo AND P u FOR TEST PANELS. e P uo P uo P e uo /P uo WO WO WO WO SW WO1a WO2a WO3a WO4a Note: P u of the WO1-4 =179.84kN; P u of the WO1a-4a =97.96kN. Table 8 shows the theoretial failure loads, P uo and the e experimental failure loads, P uo of test panels strengthened with CFRP. The theoretial failure loads are alulated from the empirial formula by Saheb and Desayi [5] in equation 1 for test panels without CFRP. P e uo / P uo ratios show that appliation of CFRP had inreased the load apaity of the test panels, where the experimental values of test panels with applied CFRP are larger than experimental values of test panels without CFRP. It shows that test panels with applied CFRP along the orners inreased the load apaity by roughly 34% and applied CFRP 45 ο at the orners of the test panels inreased the load apaity by 55%. e P uo P uo WO1b WO2b WO3b WO4b WO WO WO WO Note: P u of the WO1a-4a =97.96kN. 4.2 Crak Patterns of Panels with Openings in in-plane Uniaxial Ation Crak patterns for the tested panels were observed. The solid wall panel has defleted in a single urvature with the maximum defletion ourring at the entre of the wall panel and failure near the entre of the wall panel. The raks were observed horizontally near entre of the wall panel. Figure 8 shows rak pattern of 40 mm thik solid wall on the tension fae after failure. e P uo P uo / e P uo e P uo / e P uo Fig. 8: Crak pattern of 40mm thik solid wall on the tension fae after failure. On the other hand, the wall panels with an tested under in-plane uniaxial ation defleted in a single urvature with a maximum defletion ourring near the middle of the wall panels. The raks initiate from the entre of the, parallel with the loading diretion towards the applied loads. Followed by that is a rak from the entre of the, parallel with the loading diretion towards the 1847 P a g e

8 bottom of the wall panel. Besides that, the raks also ourred near the middle of the wall panels, perpendiular to the loading diretion whih leads to the failure of the wall panels. Portions of the panel above and below the behave as beam strips and those adjaent to an as olumn strips. The behavior was notied through the rak patterns on the tested wall panels. Horizontal rak patterns developed on the olumn setions, while vertial and inlined raks were formed in the beam strips. A horizontal rak was formed at the orner of the in where hanges of smaller ross setion area. Failure in all panels was mostly due to the bukling of slender olumn strip of the panel. The rushing of onrete on the ompression faes of the olumn strips of the speimens is notied in all speimens along the failure setion. Figure 9 shows some figures of the onrete rushed in the ompression fae. Crushing of the ompression fae is notied mostly in wall panels with small s. Craks before failure are not very obvious in wall panels with big. Sudden and explosive types of failure are observed in all the test panels. It an be observed that the major horizontal raks that leads to failure of the walls for small (5% and 10%) forms at the olumn strips near middle of the wall. On the other hand, the major horizontal raks for large walls (20% and 30%) initiated from the orners of the s. Figure 10 shows some samples of the rak patterns. WO2 WO4a Fig. 10: Crak patterns on the tension fae after failure of the wall panels with s. panels with s strengthened with CFRP displayed different rak pattern ompared to the wall panels without CFRP. Different patterns of CFRP strengthening. Method show different rak patterns as well. Figure 11 shows some rak patterns for the wall panels with s strengthened with CFRP pattern 1, where the CFRP applied along the wall panel. The failures ourred in tension fae whereby the CFRP will either be ruptured or torn from the onrete when the fore applied is greater than the CFRP tension apaity. The failure of onrete took plae after the CFRP have been torn from the onrete surfae. The advantages of applying CFRP along the wall panel is that the wall panels will only fail in olumn strips, either near the entre of the wall or horizontally from the orner. Fig. 9: Crushing of onrete in ompression fae. WO1b WO4b Fig. 11: Crak patterns on the tension fae after failure of the 40mm thik wall panels with s strengthened with CFRP pattern P a g e

9 Figure 12 shows some rak patterns for wall panels with s strengthened with CFRP pattern 2. The rak patterns for wall panels in this bath are similar to wall panels with s without CFRP. The raks were initiated vertially from the top or bottom of the wall panel towards upper or lower support, followed by horizontal raks at the olumn strips. The raks at the olumn strips were not originated from the orners. The raks that happened near the applied CFRP will went around the CFRP beause the CFRP resisting the fore. (a) (b) Fig. 13: Failure mode of wall panels with s strengthened with CFRP pattern 1 in tension fae. WO2 WO4 Fig. 12: Crak patterns on the tension fae after failure of the 40mm thik wall panels with s strengthened with CFRP pattern 2. CFRP in the ompression fae is normally either peeled off or fratured due to the ompression fore. The CFRP is weak in ompression and is easily peeled off when the tension fae has reahed the failure. Figure 14 shows a few sample of failure in ompression fae. 4.3 Failure Modes of Bond between Conrete and CFRPstrip panels with s strengthened with CFRP have been tested with 2 patterns. Pattern 1 is where the CFRP is applied along the wall panels with a ertain anhorage length while CFRP pattern 2 is applied 45 degree to the wall orners. Failure modes of both CFRP pattern were observed and ompared to the failure modes mentioned in Tehnial Report fib [26]. Figure 13 shows the failure mode of wall panels with s strengthened with CFRP pattern 1. It shows where full omposite ation of onrete and FRP is maintained until the onrete reahes rushing in ompression or the FRP fails in tension [26]. De-bonding in the adhesive also happen as the tensile and shear strength of the adhesive (epoxy resin) is usually higher than the tensile and shear strength of onrete, failure will normally our in the onrete. In this ase, a thin layer of onrete (a few millimetres thik) will remain on the FRP reinforement [26]. Fig. 14: Failure mode of wall panels with s strengthened with CFRP pattern 1 in ompression fae. Figure 15 shows some failure mode of wall panels with s strengthened with CFRP pattern 2. The raks happened around the CFRP sine the CFRP has strengthened the rak path. Figure 16 (a) shows another failure mode of wall panels with s strengthened with CFRP pattern 2 on the tension fae. The wall panel experiened de-bonding in the adhesive. This is also one of the failure modes of the bond between onrete and CFRP-strip desribed by Shilde and Seim [27]. The onrete wedge was learly seen on the peeled CFRP. Figure 16 (b) shows the CFRP-strip that was lean from any onrete wedges. There was just a thin layer a few 1849 P a g e

10 millimetres thik of onrete remained on the CFRP. This failure mode met another failure mode that was mentioned by Karsten Shilde and Werner Seim [27] whih was failure of the adhesive over the whole bond length. (a) (b) Fig. 15: Failure mode of wall panels with s strengthened with CFRP pattern 2 in tension fae. (a) Fig. 16: Failure mode of the wall panels with s strengthened with CFRP pattern 2 in (a) tension fae and (b) ompression fae. V. CONCLUSIONS The following an be onluded from this paper. a. The ultimate loads of the wall panels dereased as the sizes inreased. b. Saheb and Desayi [5] existing empirial equation shows that theoretial failure loads are less than experimental failure loads and it is onservative to use in design.. The experimental failure loads of the wall panels show that wall panels with s strengthened with CFRP inrease the load apaity. The wall panels with s strengthened with CFRP resisted axial load more than solid wall. (b) d. It shows that test panels with applied CFRP along the orners inreased the load apaity by roughly 34% and applied CFRP at the orners of the test panels inreased the load apaity by 55%. e. The wall panel s strengthened with CFRP at 45 to the orners resisted higher axial load ompared with the pattern whih was strengthened around the wall panel s. f. Crak patterns (i) The solid wall panel defleted in a single urvature with the maximum defletion ourring at the entre of the wall panel. The raks were observed horizontally near entre of the wall panel. (ii) The wall panels with s defleted in a single urvature with a maximum defletion ourring near the entre of the wall panels. Portion of the panels, above and below the s behaved as beam strips and those adjaent to the s as olumn strips. The behavior was notied through the rak patterns on the tested wall panels. Horizontal raks developed on the olumn strips, while vertial and inlined raks were formed in the beam strips. Failure in all panels was mostly due to the bukling of slender olumn strips. (iii) The wall panels with s strengthened with CFRP applied along the s experiened failures in tension fae whereby the CFRP will either be frature or torn from the onrete. The failure of the onrete took plae after the CFRP were torn from the onrete surfae. One of the advantages of applying CFRP along the wall panel s is that the wall panels will only fail in olumn strips, either near the entre of the wall or horizontally from the orners. (iv) The panels with s strengthened with CFRP applied at 45 to the orners had a similar rak patterns to wall panels with s without CFRP. The raks at the olumn strips were not originated from the orners. The raks that ourred near the applied CFRP would go round the CFRP beause the CFRP was resisting the fore. g. Failure mode (i) panels with s strengthened with CFRP around the s showed that full omposite ation of onrete and FRP was maintained until the onrete reahed rushing in ompression or the CFRP failed in tension P a g e

11 (ii) panels with s strengthened with CFRP 45 at the orners experiened the yielding of the tensile reinforement followed by rushing of the onrete while the CFRP was still intat to the onrete. The failure ourred at the plae whih was not strengthened by CFRP. ACKNOWLEDGEMENT The authors would like to aknowledge sponsor of CFRP by Mapei (M) Sdn Bhd, sponsor of steel plates by Dynami Building System Sdn Bhd, and tehnial supports from GT Instrument Sdn Bhd. Gratitude also goes to University Tenaga Nasional for providing failities of the researh. REFERENCES [1] ACI 318 (2002). Building Code Requirements for Reinfored Conrete ACI318-02, Amerian Conrete Institute, Detroit, pp [2] Standard Australia, Australian standard 3600, Conrete Struture, Sydney, [3] A. E. seddon, The strength of onrete walls under axial and eentri loads, Sym. On strength of Conr. Strut., Cement and Conr. Asso., London, U.K., 1965, pp [4] Z. A. Zielinski, M. S. Troitsky, and H. Christodoulou, Full sale bearing strength investigation of thin wallribbed reinfored onrete panels, ACI Strutural Journal, V. 79, No. 32, 1982, pp [5] S. M. Saheb, and P. Desayi, Ultimate strength of RC wall panels with s. Journal of Strutural Engineering, ASCE, V. 116, No. 6, 1990, pp [6] S. Fragomeni, P. A. Mendis and W. R. Grayson, Review of reinfored onrete wall design formulas, ACI Strutural Journal, V. 91, No. 50, 1994, pp [7] C. P. Taylor, P. A. Cote, and J. W. ae, Design of slender reinfored onrete walls with s, ACI Strutural Journal, V. 95, No. 4, [8] A. Benayoune, A. A. A. Samad, A. A. A. Ali, and A. A. Abbasovih, Load bearing wall panels with s, International Conferene on Industrialized Building System, Kuala Lumpur, Malaysia., 2003, pp [9] N. A. A. A. Farah, A. A. A. Abang, S. J. Mohd, A. A. S. Abdul, and D. N. Trikha, Ultimate strength of preast onrete sandwih panel with under axial load, IEM Journal, V. 65, No.1/2, 2004 pp [10] Doh, J. H. and Fragomeni, S. (2006). Ultimate load formula for reinfored onrete wall panels with s Advanes in Strutural Engineering. Vol. 9, No. 1. pp [11] O. Enohsson, J. Lundqvist, B. Taljsten, P. Rusinowski, and T. Olofsson, CFRP strengthened s in twoway onrete slabs-an experimental and numerial study, Constrution and Building Materials. V. 21, 2006, pp [12] Mohammed B. S., H. A. B. Badorul and K.K. Chong, Behavior of axially loaded fired-lay masonry panels with s, The Indian Conrete Journal, V. 83, No.4, 2009, pp [13] Mohammed B. S., H. A. B. Badorul and K.K. Chong, The Effets of Opening on the Strutural Behavior of Masonry Subjeted to Compressive Loading - Strain Variation The Open Civil Engineering Journal, V. 3, 2009, pp [14] P. Casadei, T. Ibell and A. Nanni, Experimental results of one-way slabs with s strengthened with CFRP laminates, Proeedings, Fiber-reinfored polymer reinforement for onrete strutures, FRPRCS-6, Singapore, July 2003, pp [15] S.T. Smith and S. J. Kim, Strengthening of one-way spanning RC slabs with utouts using FRP omposites, Constrution and Building Materials, V. 23, 2009, pp [16] T. E. Maaddawy and S. Sherif, FRP omposites for shear strengthening of reinfored onrete deep beams with s, Constrution and Building Materials, V. 89, 2009, pp [17] H. T. Cheng, B. S. Mohammed and K.N. Mustapha, Load-defletion analysis of pretensioned inverted T- beam with web s, Key Engineering Materials, V , 2009, pp [18] H. T. Cheng, B. S. Mohammed and K.N. Mustapha, Interation diagram and response surfae plot of pretensioned inverted T-beam with web s, International Journal of Modeling, Identifiation and Control. V.7, 2009, pp P a g e

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