Nonlinear Finite-Element Analysis of Buckling Capacity of Pretwisted Steel Bars

摘要

This paper presents finite-element (FE) analysis to study the axial load capacity of pretwisted steel bars of rectangular cross sections. The FE simulations are conducted using the commercial software ABAQUS. The FE simulations include bars of 20- and 30-mm width, 3- and 6-mm thicknesses, and three different lengths of 300, 400, and 500 mm. The bar ends are gripped and embedded in cylindrical slips. A set of twisting angles, ranging between 0 and 270° with an increment of 15°, is considered for each length. Geometric imperfections as well as actual elastic-plastic behaviors have been implemented in nonlinear FE models. The column strengths, load-shortening curves as well as failure modes, were predicted. The FE model is initially verified by comparing the buckling capacity and mode of the simulated straight bars with the experiments and the AISC code. The bars are then twisted beyond their elastic limit, unloaded to remove elastic recovery, and subjected to axial displacement. FE simulations showed that the permanent twists have influenced the axial strength and the static performance of the pretwisted bars. This improvement is supported by the considerable increase in the critical buckling loads of the bars, particularly at twisting angles ranged between 15 and 90°. Two analytical models capable of predicting the critical elastic and inelastic loads were developed using the FE results and utilizing multiple regression analysis for permanent angles of twist up to 90°. Multiple regression analysis models were shown to accurately predict the buckling loads within a 90% or more confidence interval.