The effects of the axial load variation on the seismic performance of existing RC buildings

It is well known that the axial load plays an important role in the evaluation of the structural capacity of RC columns. In existing buildings this problem can be even more rele-vant than in new ones, since the material can easily present poor mechanical properties. The paper is aimed at investigating the role of the axial load variation on the seismic performance of RC columns, evaluated in terms of limit chord rotation and shear force, according to the EC8 provisions. The study is developed with reference to a case-study, which is a doubly symmetric 4-storey RC building. A dynamic (time history) analysis has been performed by adopting a fiber model for the cross section of the concrete members, to determine the struc-tural response under the assumed seismic excitation. An ensemble of 7 ground motions, spec-trum-compatible with the elastic spectrum provided by EC8 has been assumed as seismic input. The combined effects of the strength variability and axial load variation have been checked on the seismic performance of the columns of the 1st storey, which presented the higher levels of compression and axial load variation.