SINGULARITIES IN RC BEAM ELEMENTS WITH FINITE-LENGTH HINGES

Several models have been presented in the literature for reinforced co ncrete (RC) beam elements with finite-length hinges to facilitate anal yses of the inelastic response of reinforced-concrete frame structures . Such models are considered an improvement on the conventional zero-l ength hinge (point hinge) model, which seems an unrealistic representa tion of RC elements undergoing inelastic deformations and is viewed as theoretically inconsistent. This paper identifies two singularities t hat could arise in the formulation of member models with finite-length hinges. The singularities are more likely to be encountered in frame analysis under cyclic loads (earthquake), than under monotonically inc reasing loads. Two singularity points are identified in the formulatio n of the model. One singularity point is due to the direction dependen cy of the stiffness, and can be avoided if an additional condition is imposed in the formulation to take care of this factor. The other sing ularity point has physical significance and corresponds to the critica l softening parameter, beyond which a member cannot sustain equilibriu m.