Definition of inelastic displacement demand spectra for precast industrial facilities with friction and fixed beam-to-column joints

Abstract

Portal-frame reinforced concrete precast industrial facilities built in Italy between 1960 and 1990 have shown high vulnerability during recent seismic events interesting Emilia region. Post-earthquake damage observations have shown that most of collapses interested portal-frame structures arranged with dry beam-to-column friction joints because of the loss of support due to sliding of beams with respect to columns. At the same time severe damage to column base cross-sections was recognized even in the case of portal-frame systems with beam-column connection devices (fixed joints). The paper investigates the dynamic behaviour of portal-frame precast industrial facilities, especially addressing the inelastic displacement demand as function of the generalized mechanical response of beam-to-column joints. Portal-frames are idealized as 2D inelastic single degree of freedom systems. A framework based on a parametric model developed in OpenSees is defined to build inelastic spectra of maximum relative beam-column displacement demands and maximum column top displacement demands. Inelastic displacement demand spectra are defined for four different sites in Italy (Messina, Mirandola, Naples and Turin), characterized by different seismic hazard. Analytical expressions of spectra approximating numerical results are finally derived to be used for rapid displacement capacity/demand assessments of portal-frame industrial buildings with friction joints or fixed joints. The approach can account vertical component of seismic excitation in a simplified way and can be also used to assess the effectiveness of retrofitting interventions.