Estimation of nonstructural stiffness in instrumented steel frames

Abstract

Lateral stiffness of nonstructural components may significantly influence the initial stiffness of the entire structure and consequently alter its dynamic characteristics. While methods for simulating structural members are well-established, approaches for modeling nonstructural components that also participate in seismic response are notably less developed. In this paper a simplified, physically-intuitive approach for estimating the stiffness of nonstructural members based on vibration recordings of buildings is presented. The method comprises two components: (1) identifying the instants during the time history wherein components of interstory velocity are negligible, such that damping forces are zero, and (2) at these instants, using static analysis to estimate story shears and story torsion in the structural members by applying the recorded displacements to the entire structure, and the accelerations to all masses above the story of interest. The method derives from first-principles of dynamics and structural analysis, and is assessed against experimental data from three datasets that include shake table data on steel frames with nonstructural walls as well as quasi-static tests on the similar walls. The results are critically discussed in the context of their prospective applications in practical settings, and limitations are summarized.