We show the results of response spectrum analyses performed on a 1980’s steel structure with a seismic-resistant system made of RC walls. The aim is to quantify the impact of different choices, usually left to the engineering judgment, on the evaluation of the seismic demand for structures like that of the case study. The analyses show that seismic demand can increase of 170% passing from stiff to soft ground, revealing how site effects can be far more important than other issues related to concrete cracking and foundation stiffness. Therefore, a study of local seismic site response is crucial for tall buildings.
