Measurement, Characterization, and Modeling of Initial Geometric Imperfections in Wide-Flange Steel Members Subjected to Combined Axial and Cyclic Lateral Loading

Wide-flange (W-shape) steel members are known to have initial geometric imperfections. A three-dimensional noncontact laser-scanning technique is used to measure the imperfection fields in fourteen specimens. A spectral approach that models the imperfections in each plate of the W-shape member as a two-dimensional random field is employed to characterize the imperfections and capture the existence of periodicity in them. The proposed modeling approach along with the traditional modal approach are used to study the sensitivity of numerical models to initial geometric imperfections. The studies are conducted at both member and system levels using a set of column and frame models employing deep W-shape columns under combined axial and lateral cyclic loading. It is shown that although initial geometric imperfections can, in certain situations, influence column buckling behavior as well as frame collapse mode, their effect on nonlinear cyclic behavior is generally small and inconsistent. Based on this finding, it is recommended that initial geometric imperfections need not be incorporated in high-fidelity numerical models of W-shape members subjected to combined axial and cyclic lateral loads. However, this is conditioned upon the use of a computational platform with sufficient numerical precision to capture the early small deformations that promote geometric nonlinearity in the response.