Estimation of seismic response parameters and capacity of irregular tunnel-form buildings

Abstract

Insufficient information about the seismic performance of tunnel-form buildings and limited relevant design codes and standards are the main barriers towards application of these systems in seismically active areas. Vertical and horizontal irregularity of typical tunnel-form buildings is another cumbersome challenge restricting the application of these systems. To address these issues, this study aims to evaluate the seismic behaviour of tunnel-form buildings with horizontal irregularity and develop appropriate design methodologies. Based on the results of 3, 5, 7 and 10-storey buildings, new response modification factors are proposed as a function of seismic demand and expected performance level. Fragility curves are also derived for various levels of intensity, and simple equations are introduced to estimate uncoupled frequency ratios. The results, in general, demonstrate the flexible torsional behaviour of irregular tunnel-form structures and their adequate seismic resistance capacity. The buildings studied herein, managed to satisfy the immediate occupancy performance requirements under design-basis earthquake, which implies that the plan regularity requirement for tunnel-form buildings in seismic codes may be too conservative. Moreover, it is concluded that using response modification factor equal to 5 can generally result in sufficient stability and adequate performance level under both design basis and maximum considered earthquake scenarios.