Estimation of seismic drift and ductility demands in planar regular X‐braced steel frames

Abstract

This paper summarizes the results of an extensive study on the inelastic seismic response of X-braced steel buildings. More than 100 regular multi-storey tension-compression X-braced steel frames are subjected to an ensemble of 30 ordinary (i.e. without near fault effects) ground motions. The records are scaled to different intensities in order to drive the structures to different levels of inelastic deformation. The statistical analysis of the created response databank indicates that the number of stories, period of vibration, brace slenderness ratio and column stiffness strongly influence the amplitude and heightwise distribution of inelastic deformation. Nonlinear regression analysis is employed in order to derive simple formulae which reflect the aforementioned influences and offer a direct estimation of drift and ductility demands. The uncertainty of this estimation due to the record-to-record variability is discussed in detail. More specifically, given the strength (or behaviour) reduction factor, the proposed formulae provide reliable estimates of the maximum roof displacement, the maximum interstorey drift ratio and the maximum cyclic ductility of the diagonals along the height of the structure. The strength reduction factor refers to the point of the first buckling of the diagonals in the building and thus, pushover analysis and estimation of the overstrength factor are not required. This design-oriented feature enables both the rapid seismic assessment of existing structures and the direct deformation-controlled seismic design of new ones. A comparison of the proposed method with the procedures adopted in current seismic design codes reveals the accuracy and efficiency of the former.

Dimensional Response Analysis of Multistory Regular Steel MRF Subjected to Pulselike Earthquake Ground Motions

“…An accepted way for estimating the maximum interstorey drift ratio along the height of the frame (IDR max ) is via correlation studies with the maximum roof drift u r,max /H (Karavasilis et al 2007). By analysing the response databank described in this paper, the ratio β= (u r,max /Η)/IDR max was found to be strongly dependent on the number of stories.…”

Estimation of peak displacements in steel structures through dimensional analysis and the efficiency of alternative ground-motion time and length scales

“…Besides, the tension elongation and compression buckling of bracing members in CB structures induce several levels of pinching behaviour which are typically unaccompanied by major strength degradation and can also build characteristic dynamic effects which warrant specific consideration [10]. To this end, Karavasilis et al [16] performed an extensive statistical study on X-braced steel buildings subjected to ordinary ground-motions and proposed simple formulae for estimating their global and local drift and ductility demands. Similarly, Málaga-Chuquitaype and Elghazouli [27] examined the inelastic response of CB structures under constant relative strength scenarios and developed noniterative equivalent linearization expressions for assessing their peak deformations.…”

Seismic damage estimation of in-plane regular steel moment resisting and x-braced frames

“…The aforementioned process led to a family of 6(n s ) 3(λ) 3(α) = 54 x-braced frames (XBF), which allows the study of the seismic damage observed at XBF with variations in their four structural characteristics n s , α, λ and T. Data of the frames, including nominal values for n s , α, λ and T as well as the sections of the columns and braces are depicted in Table 2 taken from [26,27] and reproduced here for reasons of completeness. The beam sections consist of standard IPE300…”