American Journal of Engineering and Applied Science, 6 (1): 87-94, 2013 ISSN: 1941-7020 2014 M. Al-Nara et al., Thi open acce article i ditributed under a Creative Common Attribution (CC-BY) 3.0 licene doi:10.3844/ajeap.2013.87.94 Publihed Online 6 (1) 2013 (http://www.thecipub.com/ajea.toc) The Ue of Swimmer Bar a Shear Reinforcement in Reinforced Concrete Beam 1 Moayyad Al-Nara, 2 Naem Aha, 2 Abdelqader Najmi and 3 Taher Abu-Lebdeh 1 Department of Engineering Technology, Wet Virginia Univerity, Intitute of Technology, Montgomery, Wet Virginia 25136, USA 2 Department of Civil Engineering, Univerity of Jordan, Amman, Jordan 3 Department of Civil, Architectural and Environmental Engineering, North Carolina A and T State Univerity, NC 27411, Greenboro, United State Received 2012-09-30, Revied 2012-10-13; Accepted 2013-04-30 ABSTRACT The behavior of reinforced concrete beam at failure by hear i ditinctly different from their behavior by bending, which i conidered to be unafe mode of failure. The hear failure of beam i uually udden without ufficient advanced warning and the diagonal crack that develop due to exce hear force are coniderably wider than the flexural crack. The cot and afety of hear reinforcement in reinforced concrete beam led to the tudy of other alternative. Swimmer bar ytem i a new type of hear reinforcement. It i a mall inclined bar, with it both end bent horizontally for a hort ditance and welded to both top and bottom flexural teel reinforcement. Regardle of the number of wimmer bar ued in each inclined plane, the wimmer bar form plane-crack interceptor ytem intead of bar-crack interceptor ytem when tirrup are ued. Tet reult of everal reinforced concrete beam will be preented. The effectivene of the new wimmer bar ytem a related to the old tirrup ytem will be dicued. Beam deflection i alo targeted experimentally in the lab. Several deflection meaurement were taken to tudy the effect of uing new wimmer bar ytem on deflection. Alo the crack width of the teted reinforced concrete beam wa monitored. Keyword: Simmer Bar, Deflection, Beam, Crack, Stirrup 1. INTRODUCTION Beam carry load primarily by internal moment and hear. In the deign of a reinforced concrete member, flexure i uually conidered firt, leading to the ize of the ection and the arrangement of reinforcement to provide the neceary reitance for moment. Limit are placed on the amount of flexural reinforcement to enure ductile type of failure. Beam are then deigned for hear. Since hear failure i frequently udden with little or no advanced warning, the deign for hear mut enure that the hear trength for every member in the tructure exceed the flexural trength(abu-lebdeh et al., 2011). The hear failure mechanim varie depending upon the cro-ectional dimenion, the geometry, the Reinforced Concrete (RC) beam are important tructural element that tranmit the load from lab, to column. Beam mut have an adequate afety margin againt bending and hear force, o that it will perform effectively during it ervice life. At the ultimate limit tate, the combined effect of bending and hear may exceed the reitance capacity of the beam cauing tenile crack. The hear failure i difficult to predict accurately depite extenive experimental reearch. Shear failure in beam are caued by the diagonal crack near the upport providing no hear reinforcement. Beam fail immediately upon formation of critical crack in the high-hear region near the beam upport (Nawy, 2009). Whenever the value of actual hear tre exceed the permiible hear tre of the concrete ued, the hear reinforcement mut be provided. type of loading and the propertie of the member. Correponding Author: Moayyad Al-Nara, Department of Engineering Technology, Wet Virginia Univerity, Intitute of Technology, Montgomery, Wet Virginia 25136, USA 87
The purpoe of hear reinforcement i to prevent failure in hear and to increae beam ductility and ubequently the likelihood of udden failure will be reduced. Normally, the inclined hear crack tart at the middle height of the beam near upport at approximately 45 and extend toward the compreion zone. Any form of effectively anchored reinforcement that interect thee diagonal crack will be able to reit the hear force to a certain extent. In practice, hear reinforcement i provided in three form; tirrup, inclined bent-up bar and combination ytem of tirrup and bent-up bar. In building contruction, tirrup are mot commonly ued a hear reinforcement, for their implicity in fabrication and intallation. Normally, pacing between tirrup i reduced to reit high hear tre. Congetion near the upport of RC beam due to the preence of the cloely paced tirrup increae the cot and time required for intallation. The ue of bent-up bar along with tirrup had been ued in the pat. In cae where all the tenile reinforcement i not needed to reit bending moment, ome of the tenile bar where bent-up in the region of high hear to form the inclined leg of hear reinforcement. For example, beam provided with 4 bar of main tenile reinforcement, 2 bar may be bent diagonally in hear region and ued a hear reinforcement, while the other 2 bar will be left traight up to the upport. The ue of bent-up bar i not preferred nowaday. Due to difficultie in contruction, bent-up bar are rarely ued. In beam with mall number of bar provided, the bent-up bar ytem i not uitable due to inufficient amount of traight bar left to be extended to the upport a required by the code of practice. In thi tudy, everal reinforced concrete beam were teted uing new hear reinforcement wimmer bar ytem. Beam with traditional tirrup a hear reinforcement were alo teted in order to tudy the effectivene of the new wimmer bar ytem. Thee beam are ued a reference beam. In thi invetigation, all of the beam are uppoed to fail olely in hear, o adequate amount of tenion reinforcement were provided to give ufficient bending moment trength. Thi tudy aim at invetigating a new approach of deign of hear reinforcement through the ue of wimmer bar provided in the high hear region. The main advantage of thi type of hear reinforcement ytem are: flexibility, implicity, efficiency and peed of contruction. Piyamahant (2002) howed that the exiting reinforced concrete tructure hould have tirrup reinforcement equal to the minimum requirement pecified the code. The theoretical analyi how that the amount of tirrup of 0.2% i appropriate. The tudy concluded that mall 88 amount of web reinforcement i ufficient to improve the hear carrying capacity. The tudy focued on the applicability of the uperpoition method that ued in predicting hear carrying capacity of reinforced concrete beam with a mall amount of web reinforcement at the hear pan ratio of 3. Alo the failure mechanim were conidered when mall amount of tirrup ued. Leley and Julio (2008) dicued the reult of experimental reearch performed to tet the hypothei that the effective depth doe not influence the hear trength of reinforced concrete flexural member that do not contain web reinforcement. The reult of eight imply upported reinforced concrete beam tet without hear and kin reinforcement were invetigated. The beam were deigned uch that the effective depth i the variable while the value of other traditionallyconidered parameter proven to influence the hear trength (uch a the compreive trength of concrete, longitudinal reinforcement ratio, hear pan-to-depth ratio and maximum aggregate ize) were held contant. The value elected for the parameter held contant were choen in an attempt to minimize the concrete hear trength. Hamouh et al. (2010) preented everal reult of experimental invetigation on ix reinforced concrete beam in which their tructural behavior in hear wa tudied. The reearch conducted wa about the ue of additional horizontal and independent bent- up bar to increae the beam reitance againt hear force. The main objective of that tudy were tudying the effectivene of adding horizontal bar on hear trength in rectangular beam, the effectivene of hear reinforcement and determining the optimum amount of both type of hear reinforcement to achieve a hear capacity imilar to that of a normal link ytem. From experimental invetigation of the ytem it wa found that, the ue of independent horizontal and bentup bar a hear reinforcement were tronger than conventional hear reinforcement ytem. 1.1. Swimmer Bar A wimmer bar i a mall inclined bar, with it both end bent horizontally for a hort ditance, welded at the top and the bottom of the longitudinal bar a hown in Fig. 1-3. There are three major tandard hape; ingle wimmer, rectangular hape and rectangular hape with cro bracing. Several addition to thee tandard hape can be explored, uch a addition of horizontal tiffener bar in the rectangular hape, dividing the large rectangle horizontally into maller rectangle. Additional wimmer bar can alo be ued. By adding one more wimmer bar to the rectangular hape, the large rectangular hape will be divided vertically into two rectangle.
bar ytem i integrated fully with the longitudinal teel bar. Several option of the wimmer bar ytem are ued in order to improve the hear performance of the reinforced concrete beam, reduce the amount of crack, reduce the width and the length of crack and reduce overall beam deflection. Different bar diameter can be ued in order to add tiffne to the teel cage and increae hear trength of the reinforced concrete beam. 1.2. ACI Code Proviion for Shear Deign According to the ACI Code, the deign of beam for hear i to be baed on the following relation Equation 1: Fig. 1. Single wimmer bar ytem v u φ v (1) n where, V u i the total hear force applied at a given ection of the beam due to factored load and V n = V c + V i the nominal hear trength, equal to the um of the contribution of the concrete and the web teel if preent. Thu for vertical tirrup Equation 2: d φavjc vu φ vc + (2) and for inclined bar Equation 3: Fig. 2. Rectangular wimmer bar ytem Vu φ Vc + φ + d Avfyc (in coa) (3) where, A ʋ i the area of one tirrup, α i the angle of the tirrup with the horizontal and S i the tirrup pacing. The nominal hear trength contribution of the concrete (including the contribution from aggregate interlock, dowel action of the main reinforcing bar and that of the un-cracked concrete) can be implified a hown in Equation 4: V = 0.17λ f b d (4) c ' c w Fig. 3. Rectangular wimmer bar ytem with cro bracing Addition of two more wimmer bar will divide the large rectangle vertically into four mall rectangle. A combination of horizontal bar and additional wimmer bar may alo be explored. Thi wimmer 89 where, b w and d are the ection dimenion and for normal weight concrete, λ = 1.0. Thi implified formula i permitted by the ACI code expreed in metric unit. 1.3. Suggeted Method of Deigning Swimmer Bar The analyi of needed hear reinforcement uing wimmer bar ytem i baed on the tru analogy concept. If S 1 i the wimmer bar pacing in a ingle
tru analogy, n i the number of bar and A i the area of teel of a ingle wimmer bar, then Equation 5 and 6: S1 = na (5) And: T T V 1 = = S n ina (d d')(cotβ+ cot α) 1 (6) where, T i the tenion force in the bent bar, i the pacing of the wimmer bar, α i angle between the tenion force and the horizontal in the triangular tru and β i the angle between the imulated concrete trut and the horizontal in the triangular tru. If there are n wimmer bar within the 1 length of the analogou tru chord and if A v i the area of teel of one wimmer bar, then Equation 7: T = navf (7) yt where, ƒ yt = trength of tranvere reinforcement and Equation 8: nav = V n (d d')ina(cotβ+ cota)f yt (8) In the cae of diagonal tenion failure, the compreion diagonal make an angle β = 45 with the horizontal, thu Equation 6 become Equation 9: V Avf (d d') yt = [ina(1+ cota)] (9) Which can be implified a Equation 10: Avf (d d') V (in cot ) yt = α+ α (10) Which i imilar to thoe ued by ACI code Equation 11: Vn = V + Vc (11) 1.4. Teted Beam Six reinforced concrete beam were prepared for the tet, B1 through B6. All of the ame dimenion 2000 mm length, 200 mm width and 250 mm depth. The effective length wa alo kept at contant value of 1800 mm. Thee beam were deigned with 3ø14 mm top teel and 4ø16 mm bottom teel reinforcement. Reference beam 90 B1 wa deigned with 10ø8 mm at 600 mm pacing vertical tirrup at either ide. Table 1 how detail of the hear reinforcement of each beam and Fig. 4 how detail of the teel reinforcement for the beam B2. The Beam B3 and B4 i imilar but the wimmer bar are of 12 mm and 10 mm in diameter repectively. Beam B5 ue cro bracing of 8 mm in diameter and the wimmer bar are at a larger pacing of 275 mm compared to the pacing of 137.5 mm ued in the beam B2. The beam B6 doe not ue any cro bracing and the wimmer bar are paced at 275 mm imilar to the beam B5. The compreive trength of concrete i meaured according to ASTM C 192-57. Fifteen concrete ample were prepared. The compreive trength of concrete i meaured at the 28th day. The concrete compreive trength reult range between 34.9 N/mm 2 to 37.2 N.mm 2. 1.5. Tet Procedure Prior to teting, the urface of the pecimen wa painted with white emulion to make it eay to detect and follow crack in the concrete beam. At age 28 day, the reinforced concrete beam were prepared for teting. Line locating the poition of point load, upport and the middle of each beam were marked. Beam were placed in the teting frame that ue hydraulic jack. The tet wa carried out with the pecimen placed horizontally in a imple loading arrangement. The beam were upported by olid round teel on their two edge a imply upported member. The effective length of each beam wa kept at1800 mm meaured from the center of each upport. All the beam were deigned to enure that the beam will only fail in hear rather than in flexure. To enure that hear crack will occur near the upport, two point load were applied ymmetrically to the beam with a v le than 2.5d. In thi teting, a v 550 mm, where a v i hear pan (the ditance from the point of the applied load to the upport) and d i the effective depth of a beam. A loading jack wa placed at the mid-pan poition above the beam. The load wa applied by jacking the beam againt the rig bae member at a contant rate until the ultimate load capacity of the beam wa reached. A univeral column ection wa ued to tranfer the load to the beam at two point load via tranfer girder. A reaonable time interval wa allowed in between 20.0 kn load increment for meauring deflection, marking crack, meauring the hear reinforcement train and recording the ultimate load. Each beam took about 2 h to complete the tet.
Fig. 4. Detail of beam B2 Table 1. Shear reinforcement of beam ued in thi tudy Shear reinforcement ------------------------------------------------------------------------------------ Beam No. Stirrup Swimmer bar-ytem Total weight of teel cage (N) B1 8ø8 @ 550 mm - 257.0 B2 - Single wimmer ø14 @137.5 mm 263.0 B3 - Single wimmer ø12 @ 137.5 mm 255.0 B4 - Single wimmer ø10 @ 137.5 mm 243.0 B5 - Two wimmer with cro ø8 @ 275 mm 240.0 B6 - Two wimmer ø8 @ 275 mm 230.0 1.6. Behavior of Beam under Load The firt beam deignated a B1 i ued a a reference beam where traditional tirrup were ued a hear reinforcement and no wimmer bar. Loading tarted at 30 kn, where hair crack appeared in the bottom face between the two applied load. When loading reached 60 kn hair crack appeared at the right ide of the beam. At the load of 200 kn hear crack increaed in width and length. Finally, hear failure occurred at the load of 260 kn. The beam deignated a B2 howed ome hair crack at the load of 140 kn. When the load reached 180kN more hair crack appeared at the moment region, then by 91 raiing the load up to 220 kn hear crack appeared at right ide of the beam. Finally, hear failure occurred at 310 kn a hown in Fig. 5. Similarly, beam B3, B4, B5 and B6 were tudied during the tet. Table 2 how a ummary of the tet reult. Beam B2 and B3 howed a ubtantial improvement in the load carrying capacity due to the ue of wimmer bar ytem compared with the traditional tirrup ytem. With minor change in the amount of teel reinforcement thee two beam improved the hear trength by 19.23 and 17.31% repectively and with repect to the reference beam B1. The beam B4 exhibited a ubtantial improvement in hear trength performance of approximately 10% compared to the reference beam B1, but with le total
teel reinforcement of about 5% and ubtantial decreae in hear reinforcement. The load deflection behavior of thi beam i imilar to the reference beam B1. The beam B5 and B6 ued much le total teel reinforcement compared to the reference beam B1 of 6.62 and 10.51% repectively. In thee beam 8 mm diameter wimmer bar were ued at large pacing of 275 mm that reduced the amount of teel hear reinforcement ubtantially. Thi kind of hear reinforcement i recommended in cae of very congeted teel reinforced beam, where hear failure i not of a concern. 1.7. Beam Deflection A can be noticed from Fig. 6 all beam exhibited the ame load deflection behavior up the load of 140 kn and deflection of about 4.5 mm, where ubtantial crack were oberved. At thi tage, the beam howed imilar tiffne, but beyond thi tage, beam tarted to how different behavior due different hear reinforcement. Beam B2 and B3 howed higher reitance to deflection compared to the reference beam B1, the beam which wa reinforced by regular tirrup a hear reinforcement. The wimmer bar ued in thee two beam added tiffne to the teel cage ued. Beam B4 howed imilar behavior to the reference beam but at a higher load carrying capacity. Beam B5 and B6 howed le rigidity compared to the reference beam B1 when loaded by twopoint load due to ubtantial reduction in teel hear reinforcement ued in thee two beam. Table 2. Tet reult ummary Ultimate load Wt of teel %Inc./ Dec. in gage %Inc./ Dec. in No. (kn) at failure Cage (N) Wt w.r.t B1 trength w.r.t B1 B1 260 257 0.00 0.00 B2 310 263 2.33 19.23 B3 305 255-0.78 17.31 B4 285 243-5.45 9.62 B5 240 240-6.62-7.69 B6 220 230-10.51-15.38 Fig. 5. Beam B2, hear failure at the load of 310 kn 92
Fig. 6. Central meaured beam deflection of all teted beam, B1-B6 2. CONCLUSION Experimental tet reult howed ubtantial improvement in the hear performance of the reinforced concrete beam by uing the new wimmer bar ytem in comparion with the traditional tirrup ytem. The beam deflection i alo reduced along with the number and width of crack in the teted beam under progreive applied load. The new wimmer bar ytem can be at a great advantage over the traditional tirrup ytem when ued in congeted reinforced concrete beam. 93 3. REFERENCES Abu-Lebdeh, T., S. Hamouh, W. Coi and M. Al Nara, 2011. High rate-dependent interaction diagram for reinforced concrete column. Am. J. Eng. Applied Sci., 4: 1-9. DOI: 10.3844/ajeap.2011.1.9 Hamouh, S.A., T. Abu-Lebdeh and T. Cummin, 2010. Deflection behavior of concrete beam reinforced with PVA micro-fiber. Cont. Build. Mater., 24: 2285-2293. DOI: 10.1016/j.conbuildmat.2010.04.027
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