Effects of the inherent damping modelling approaches on the seismic demand of nonstructural elements

The importance of nonstructural elements in the overall seismic performance of buildings highlights the need for accurate and precise calculations of their seismic demand and response. Currently, building codes and other guideline documents suggest values and modelling approaches to consider the inherent damping of the structural system. However, these recommendations were developed focusing only on the structural response, neglecting the effects they can have on the nonstructural seismic demand. In addition, bad design practices along with misinterpretations of damping formulations can lead to erroneous evaluation of the seismic demand on nonstructural elements, and therefore, to under- or overestimate their seismic capacity. This study evaluates the impact of diverse inherent structural damping modelling assumptions on the seismic demand of nonstructural elements through the evaluation of different floor response spectra. The results were obtained from an archetype reinforced concrete framed structure subjected to non-linear time history analyses using several seismic intensity levels. The inherent damping in the archetype building was modelled following commonly used assumptions such as mass proportional damping, stiffness proportional damping, and Rayleigh damping, considering also the use of initial or tangent stiffness, and two different levels of equivalent viscous damping, The results show that the modelling assumptions of the inherent damping can have significant effects on the floor response spectra, hence, on the seismic demand of nonstructural elements, exhibiting mean differences between the maximum and minimum response parameter of up to three times the minimum value.