Seismic assessment of an S-shape building with expansion joints

An elastic analysis of an existing 20-storey reinforced concrete moment resisting frame divided in 3 blocks shows that beams supported on corbels of the adjacent block at the expansion joint loose their support when each independent block vibrate on its own under earthquake. Different reconnection hypothesis were considered, ranging from fixing totally each block to the adjacent one to more flexible options leaving some free relative move between blocks. An elastic modal superposition followed by a pushover analysis considering the final reconnection principle were made. The degrees of freedom of the joint reconnections were observed to be an important parameter. The solution found leaves a free relative rotational move between blocks and a flexible translational movement, so that forces at the connection do not become uselessly high. The springs used (long tie rods) work essentially elastically so that no permanent relative displacement exists between blocks after an earthquake.