An alternative approach to the analytical determination of the moment capacity of a thin-walled channel steel section beam

An analytical method of combined plastic mechanism and elastic approaches has been developed to predict the moment capacity of a thin-walled channel steel section beam. The plastic mechanism approach is performed by analyzing an idealized model of bending-plastic-hinge-collapse mechanism of the beam bent about its minor neutral axis. This approach adopts a concept of the equilibrium between external energy and the one dissipating in the hinge mechanism. Another analytical approach has been done by analyzing the investigated beam according to an elastic-bending theory. In the elastic analysis, the application of an effective width concept has also been considered to account for the effect of local buckling on the bending element of the beam. These both analytical approaches are then used in the method of cut-off strength to estimate a theoretical moment capacity of the beam bent about its minor neutral axis. An attempt has also been carried out to correlate the estimated moment capacity obtained to another one about a major neutral axis. In order to assess the accuracy of the analytical method developed, its predicted results are verified using the data obtained from experiments and a design code specially used for cold-formed steel structural members. The data of moment capacity about the minor neutral axis is compared to the one measured in a number of flexural-bending tests to failure on the similar channel steel section beams. Meanwhile, the data of moment capacity about the major neutral axis is compared to the one calculated using the design code. A statistical analysis of verified data populations indicates that the mean value of deviated data from experimental one is 1.025 with the standard deviation of 0.087 and from the design code is 1.004 with the standard deviation of 0.111. These statistical measures clearly mean that the analytical model presented herein, on average, tends to estimate conservatively the moment capacity of the investigated beam about its both unsymmetrical and symmetrical–neutral axes by less than 5% and this is certainly still within acceptable limits of ±20%.