Seismic Behavior of Coupling Beams Constructed With Various Types of Steel Fiber Reinforced Concrete

Abstract eng:
A An experimenttal study was conducted c to ev valuate the usee of various typpes of steel fibeer reinforced cconcrete (SFRC C) in order tto eliminate th he need for diagonal bars an nd relax transv verse reinforceement requirem ments in earthqquake-resistantt coupling bbeams. Eight precast, p large-sscale coupling beam b specimen ns, five with a span-to-depthh ratio (ln/h) of 3.0 and three w with ln/h = 22.0, were testeed under large displacement reversals. In addition a to the span-to-depth ratio, experim mental variablees were: 1) ttype of SFRC (fiber type and d dosage); and 2) peak shear stress s demand.. Three types oof hooked steel fibers were evvaluated in vvolume fractio ons of 1.0%, 1.25% or 1.5% for a total of six SFRC mixxtures investigaated. Peak sheaar stress demannd, on the oother hand, ran nged between approximately y 6 and 12 ′ [psi]. In addiition to the couupling beam teests, all SFRC C materials iinvestigated were w tested und der four-point bending, direcct tension and compression iin order to corrrelate materiall behavior w with coupling beam seismic performance. p In geneeral, SFRC cou upling beams without w diagonaal reinforcemennt and with ln//h ≥ 2.0 can acchieve drift cappacities of aat least 5% wh hen subjected to shear stresss reversals of magnitude m rangging from 6 too 10 ′ [psi]. The behaviorr of all the SFRC couplin ng beams was heavily contro olled by flexurral deformationns, which conttributed approoximately 70-80% to the ttotal applied drift. d For desig gn purposes and based on tesst results, threee classes of SF FRCs are proposed dependinng on their pperformance under u four-poin nt bending. Lim mits to couplin ng beam shearr stress and spaan-to-depth rattio are linked to each of tthe three classees of SFRC in order to achiev ve a drift capaccity of at least 6%. The transverse reinforrcement requirrements for po otential plastic hinge regions in columns off special momeent frames iin ACI 318-14 4 were found to o be adequate to t provide con nfinement to thhe end regions of coupling beeams, over halff the beam ddepth from thee wall faces. Trransverse reinfforcement in th he middle regioon of SFRC cooupling beams,, on the other hhand, must bbe designed su uch that the ex xpected shear stress s resisted by the SFRC does not exceeed a limit of 44, 3 and 2 ′ [psi] for ccoupling beam ms constructed with w SFRC Claass 1, 2 and 3, respectively. Expecteed flexural caapacity can be estimated based b on the use of a plaastic stress diistribution assuuming all rreinforcement over the tensio on half of the beam b depth reaaches a stress oof 1.1 times thee measured yieeld strength or 1.25 times tthe nominal yiield strength. It I is also recom mmended that strength calcuulations be ran without axial force and witth an axial fforce of 0.1f’cAg. For adequaate spread of plasticity, p interrmediate doweel reinforcemennt at the beam m ends must bee designed such that the shear associated with the ex xpected flexurral strength at the end of thhe dowels, negglecting the SF FRC postccracking streng gth, ranges bettween 1.0 and 1.1 times the shear correspoonding to the eexpected flexuural strength att the beam eend.

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