Effects of Modelling Assumptions on the Plan Irregularity Criteria for Single Storey Buildings

Abstract

For single-storey buildings, EN 1998-1 allows determination of the centre of lateral stiffness and the torsional radius by considering the translational stiffness represented by the moments of inertia of the cross-section of the vertical elements. Additionally, stiffness of the beam or shear deflections can affect the frame lateral stiffness changing the position of centre of stiffness or torsional radius. In order to investigate the influence of these two parameters, six different single storey buildings with different degree of plan irregularity were examined. All of these buildings were analysed for four different modelling assumptions, regarding the stiffness characteristic of the structural elements. Additionally, hand calculation of these structural features, according the recommendation of EN 1998-1 was carried out. Obtained results show that certain parameters have significant influence for structures with lower degree of plan irregularity, while some other parameters are more influential for structures with higher degree of irregularity. Hand calculated values for eccentricity and torsional radius are most conservative compared to the corresponding ones obtained from numerical analysis. Applied criteria for consideration of structural regularity in plan, prescribed in EN 1998-1, are compared with the criteria given by ASCE 7-10 and NZS 1170.5-2004. In order to compare the seismic response of considered single storey structures with different degree of irregularity in plan, detailed nonlinear time history analyses for seven different acceleration histories, applied in direction perpendicular to the axes of irregularity, scaled to three different levels of seismic hazard, were performed.