Critical Buckling Strains in Thick Cold-Formed Circular-Hollow Sections under Cyclic Loading

Abstract

Contrary to the large dataset of test results exploring the monotonic bending response of steel tubes, the corresponding dataset of cyclic bending tests remains very small. Seven compact and semicompact S355J2H cold-formed circular-hollow sections with diameter to thickness (D/t) ratios between 20 to 60, representative of piles used in piers and wharves, were brought to failure in three-point cyclic bending tests. Digital image correlation was employed to estimate average cross-sectional curvatures, and hence the critical bending strains, during local buckling at the midspan plastic hinges. These estimates were compared against those from two simplified localized hinge models and differed by up to a factor of two. A parametric study was performed with a validated finite-element model to ascertain the suitability of proposed design equations at predicting critical strains in piles with D/t from 20 to 60 under cyclic loading. Test and simulation data both show that critical buckling strains are lower under cyclic loading than under monotonic loading. This work can inform the future development of seismic design standards such as ASCE 61.