Seismic Behavior Of Fiber-Reinforced Prestressed Wide-Beam Frames

A considerable amount of special reinforcement details for wide-beam joints are necessary to provide sufficient seismic resistance, recent investigations have identified fiber-reinforced concrete as a possible alternative to reduce the requirement of closely spaced ties. The emphasis of previous research focused on the seismic behavior of wide-beam joints. No research work on seismic behavior of wide-beam frames was found. This paper describes the investigation on the seismic performance of fiber-reinforced wide-beam frames the first time by using of quasi-static testing, pseudo-dynamic testing and nonlinear finite element analysis as following:(1) Experimental study on seismic behavior under low reversed cyclic loading of three unbonded-prestressed wide-beam frames designed with different volume fraction of steel fibers was carried out, the effects of steel fibers to the failure pattern, hysteretic behavior, energy dissipation, displacement ductility and rigidity degeneration etc. have been studied. The results show that the presence of steel fibers has significant effects not only on improving the cracking load, yielding load and ultimate load, changing the failure pattern, but also enhancing substantially the ductility and energy dissipation, contributing to reducing the rigidity degeneration, thus improving the seismic behavior of prestressed wide-beam frames.(2) Seismic evaluation of fiber-reinforced prestressed concrete wide-beam frame was performed by pseudo-dynamic testing. Dynamic response corresponding to input excitation and the influence of steel fibers to dynamic behavior of prestressed wide-beam frame are discussed. The results show that fibered reinforced wide-beam frames exhibit large displacement and large damping ratio after yielding of structure. Steel fibers contributed to causing less damage during high-level ground motion. Otherwise, steel fibers could not change the internal dynamic response such as stiffness, natural frequency and dynamic magnification factor of prestressed wide-beam frame. Quasi-static testing to damaged wide-beam frames shows that, the failure pattern and hysteretic behavior were same as that of undamaged frames, contribution of steel fibers to seismic behavior of damaged wide-beam frames were less than that of undamaged frames.(3) Nonlinear finite element analysis to 69 fiber-reinforced prestressed wide-beam frames was performed using the ABAQUS FEA program. Influence of steel fibers, axial compression ratio and PPR on mechanics behavior was discussed. The results showed that large axial compression ratio resulted in high ultimate loading capacity, but low ductility and energy dissipation. Large PPR caused a slight improvement on ultimate loading capacity, but low ductility and energy dissipation too. Steel fibers could effectively improve the ultimate loading capacity, ductility and energy dissipation, thus contributed to improving the mechanics behavior ofwide-beam frames, contribution of steel fibers to mechanics behavior decreased as the axial compressing ratio raise. The effect of torsion moment to lateral beam, stress of reinforcement and interaction between bar and concrete were discussed, some advice for seismic design were presented according to the study in this paper and previous research work.(4) Based on the experimental study, the hysteretic behavior of fiber-reinforced prestressed wide-beam frames was discussed. Two hysteretic models suitable for damaged and undamaged fiber-reinforced prestressed wide-beam frames were proposed sequentially. The hysteretic models consisted of a skeleton curves which based on the concept of three stage polygonal line with soften region and some hysteretic rules. The unload-reloading curves of the hysteretic models also based on a three stage polygonal line and a two stage polygonal line. Some numerical equations of the hysteretic models were presented for nonlinear analysis at the end of this paper.