Local–global approach in the seismic analysis of R/C frames including bond slip effects

In this work a new, mixed approach of analysis is proposed to study the effect of beam fixed-end rotations (FERs, mostly related to bar slip inside the joint core) on the seismic response of R/C frames subjected to a strong earthquake. In fact, the accuracy of FE analysis, with reference to both structural geometry and material non-linear behaviour, allows a detailed description of the phenomenon on a local scale. On the other hand, in the non-linear dynamic analysis of a whole frame, it is highly advantageous to make use of larger scale beam phenomenological models, from the point of view of both computational effort and output data processing. To combine the advantages of both scales of analysis a mixed approach is herein proposed. The results of the FE analysis provide the input data for the dynamic analysis of the frame, which is performed taking advantage of beam models. This procedure has been applied to an 8-storey 5-bay frame designed according to Eurocodes 2 and 8: its joints have been analysed under monotonic loading by means of a non-linear FE code. The numerical results provide the primary curve of a rotational spring simulating the FER effect in the adopted beam model. The results of the dynamic analyses on the complete frame show that bond deterioration plays a major role in terms of both lateral deformability and ductility requirements.