Evaluating the Behaviour Factor of Medium Ductile SMRF Structures

In seismic codes, the capacity of structures is calculated using capacity design procedure based on the concept of base shear. The critical parameter in this procedure is the behaviour factor (q-factor), which allows designing the structures at the ultimate limit state accounting for their ductility and reserve strength. In this paper, the q-factor is evaluated for medium ductile steel moment-resisting frames (SMRF) using pushover analysis. The influence of specific parameters, such as the stories number, the “Column/Beam” capacity and the local response of structural members, is studied. The results show that the most important parameter that affects the q-factor is the local response of first-storey columns, while the “Column/Beam” capacity has a less effect on this factor. Furthermore, it is observed that the q-factor value assigned to the studied frames in Eurocode-8 is systematically underestimated for low-rise frame, while the use of this value for high-rise frame is potentially unsafe

Overstrength and ductility factors of XBF structures with pinned and fixed supports

In today's time, most seismic design codes are based on a linear elastic force-based approach that includes the nonlinear response (ductility and over strength) of the structure through a reduction factor (named behavior factor q in Eurocode 8 [EC8]). However, the use of a prescribed q-factor that is constant for a given structural system may fail in providing structures with the same risk level. This paper focuses on the estimation of actual values of q-factor for X-braced steel frames (XBFs) designed according to the European codes and comparing these values to those suggested in EC8. For this purpose, a nonlinear pushover analysis has been performed. The effects of specific parameters, such as the stories number, the brace slenderness ratio, the local response of structural members, and the support type, are evaluated. The results show that the most important parameter that affects the q-factor is the brace slenderness ratio, while the support type has less effect on this factor. Furthermore, a local strength criterion has been proposed to implicitly ensure that the suggested value of the q-factor is conservative

Evaluating the Behaviour Factor of Concentric X-Braced Steel Structures

International audienceThe behaviour factor ( q -factor) is a factor introduced in Eurocode-8 (EC8) to reduce the seismic elastic forces of structures obtained from an elastic analysis accounting for their ductility and overstrength. Seismic codes, especially the EC8, gives a constant value for q -factor, since change in structural characteristics of building change in behaviour of braced steel structures and that affects on q -factor. In this paper, the q -factor is evaluated for X-braced steel structures using pushover analysis. The effects of brace slenderness ratio and stories number are investigated. The results of this study indicate that the most important parameter that affects the q -factor is the brace slenderness ratio. Furthermore, the EC8 recommends a higher than actual value of q -factor, which is potentially unsafe