Max Gündel

Influence of variability of material mechanical properties on seismic performance of steel and steel–concrete composite structures

Modern standards for constructions in seismic zones allow the construction of buildings able to dissipate the energy of the seismic input through an appropriate location of cyclic plastic deformations involving the largest possible number of structural elements, forming thus a global collapse mechanisms without failure and instability phenomena both at local and global level. The key instrument for this purpose is the capacity design approach, which requires an appropriate selection of the design forces and an accurate definition of structural details within the plastic hinges zones, prescribing at the same time the oversizing of non-dissipative elements that shall remain in the elastic field during the earthquake. However, the localization of plastic hinges and the development of the global collapse mechanism is strongly influenced by the mechanical properties of materials, which are characterized by an inherent randomness. This variability can alter the final structural behaviour not matching the expected performance. In the present paper, the influence of the variability of material mechanical properties on the structural behaviour of steel and steel/concrete composite buildings is analyzed, evaluating the efficiency of the capacity design approach as proposed by Eurocode 8 and the possibility of introducing an upper limitation to the nominal yielding strength adopted in the design.

Reliability Analysis on Capacity Design Rules for Steel Frames

Capacity design rules are applied to ensure the intended plastic behaviour of structures subjected to earthquakes. They need to cover scattering due to the seismic action and material strength. Recent evaluations of data of structural steel from European producers show for low steel grade an overstrength, which is higher than covered by the recommended value in DIN EN 1998-1. In this paper results of reliability analysis performed on this topic are presented. For this purpose a stochastic model for the seismic action was derived, which enables to perform the investigations via push-over analysis instead of time-consuming non-linear time history analysis. The main findings are discussed in the view of adjustments of design rules in DIN EN 1998-1 and European product standards, respectively.