Seismic shear demands in multi-storey steel frames designed to Eurocode 8

This paper investigates the influence of the frequency content of ground motion, as well as structural parameters and the level of inelasticity, on the shear demands in frames designed to comply with Eurocode 8 provisions. The investigation of the shear demands focuses on both the base shear and individual storey shears. To represent a wide range of structural characteristics, 39 steel moment-resisting frames are designed and considered in the analyses. The mean period, Tm, is employed as a measure of the frequency content of ground motion. Seventy-two records are selected from a broad range of seismological scenarios and these records have mean periods ranging from 0.31 to 0.98 s. Incremental dynamic analysis (IDA) is used to investigate the influence of various structural parameters for different levels of nonlinearity by scaling the ground motions in order to simulate four levels of the behaviour factor, q. The results of the parametric study demonstrate that the base shear is significantly influenced by the period ratio T1/Tm (i.e., the ratio of the fundamental period of the structure T1 and the mean period Tm of the motion), the behaviour factor, the plasticity resistance ratio and the relative storey stiffness ratio. On the other hand, storey shear demands are found to depend strongly upon the normalised height (i.e., the height to a given storey divided by the total height of the frame) in addition to the behaviour factor, period ratio and plasticity resistance ratio. Robust regression models are proposed for the prediction of these shear demands. Finally, the implications of the findings with reference to European seismic design procedures are explored.

► The influence of ground motion frequency content on base shear and storey shear demands is examined.
► Incremental nonlinear dynamic analyses are carried out using a large suite of frames and ground motion records.
► Key parameters include the period ratio, behaviour factor, normalised height and resistance and stiffness ratios.
► Prediction models for base shear and storey shears are proposed and their consideration in design is discussed.