ABSTRACT
The paper addresses multistorey reinforced concrete (R/C) frames with setbacks in the upper part. Available experimental and field evidence is reviewed, followed by a case-study involving the design and assessment of a ten-storey frame with two large setbacks (equal to about 40% the length of the storeys below) at its top. The structure is designed to the provisions of Eurocode 8 (EC8) as a ductility class ‘M’ building irregular in elevation for a PGA of 0.25g, using multimodal analysis, as required by the code. It is then assessed using both push-over analysis and dynamic time-history analysis for selected input motions scaled to various intensities. It is found that the seismic performance of the structure is satisfactory, even for motions twice as strong as the design earthquake.
