Experimental verification of viscous damping modeling for inelastic time history analyzes

Inelastic time history analyzes (ITHA) are recognized as the most suitable tool for describing the behavior of structures under seismic actions. It is clear that the reliability of ITHA results is strongly dependent on the modeling choices. One of the aspects still debated, in spite of a large amount of research, is the modeling of viscous damping forces. In the case of a single degree of freedom (SDOF) structure, the damping not represented by hysteretic response is commonly assumed proportional to the square root of the system stiffness: typically in the research papers it is not declared whether the initial or tangent-stiffness is considered. Recent research has shown that initial or tangent-stiffness proportional damping can give very different results in terms of energy dissipation, and peak response displacement. In this work, experimental and numerical tests performed to defect the most appropriate model are described and discussed.