15.08: Influence of deterioration modelling on local deformation demands in steel moment frames

Abstract

This paper assesses the influence of the cyclic strength and stiffness degradation on the local demands in moment resistant steel frames (MRF), designed according to Eurocode 8. For steel structures, local demand is frequently evaluated by means of plastic rotation of structural members. This local response is relevant both for the design of new structures and particularly for the assessment or safety evaluation of existing structures. Recent studies have illustrated the weaknesses of the local demand prediction methods based on linear analysis. When predictions based on linear analysis were contrasted against nonlinear models, mismatches up to 100% were found. However, those nonlinear analysis approaches have not considered the effect of cyclic strength and stiffness degradation. In this study, degradation models are used and calibrated for assessing structural collapse scenarios. A set of twelve MRF systems, designed according to the provisions of Eurocode 3 and Eurocode 8, are examined using two different modelling approaches: a degrading model and a conventional nondegrading approach. The frames are subjected to different levels of given inelastic demands by means of a scaling procedure using a suite of ground motion records. Plastic rotations are directly measured during the nonlinear analyses and consequently contrasted to quantify the effect of degradation at different levels of induced inelasticity. It is shown that using degrading models results in local inelastic rotations which can be significantly higher, reaching up to 25% more than without degradation. Finally, the implications of the findings on current European seismic design procedures are outlined.