Behavior of reinforced concrete girders under cyclic torsion and torsion combined with shear: Experimental investigation and analytical models
Torsion can be a significant action in many structural members that are part of civil engineering infrastructure. Gravity loads can induce torsional stresses in curved bridges and spandrel beams. Seismic loads can induce cyclic torsion combined with other actions in the beams and columns of bridges with outriggers. Reliable models are needed to predict the effect of torsional stresses on a reinforced concrete (RC) member's hysteretic load-deformation response, and also on the monotonic behavior at service and ultimate load levels. Little previous research has focused on the hysteretic behavior of RC members under cyclic torsion and torsion combined with other actions. This research study was intended to improve the understanding of the behavior of such members and provide analytical tools for analyzing their behavior. The experimental investigation consisted of two large-scale RC girders loaded under full-reversal cyclic torsion and torsion combined with shear to investigate the behavior of RC box girders. Of interest was the degradation of the torsional stiffness, the damage to the specimen due to reversed diagonal cracking, the characteristics of the shear-flow zone, the extent of the concrete softening, and the occurrence and severity of spalling of the concrete cover. The analytical portion consisted of developing rotating-angle truss models that can predict the hysteretic load-deformation behavior of RC members under cyclic torsion and torsion combined with shear. The first and second phases were intended to improve the analysis of members under pure torsion and torsion combined with other actions under service and ultimate load levels. The load-deformation behavior predicted by the models was compared to members available in literature and showed a close comparison. The third phase of the model was developed for use in a dynamic analysis and can predict the hysteretic behavior of an RC member under full-reversal torsion and torsion combined with shear. The hysteretic torque-twist behavior predicted by the model was in good agreement with the behavior of the two girders that are a part of this investigation and to members available in literature.