冷弯薄壁受压C形截面局部屈曲荷载和承载力

为研究板组效应对冷弯薄壁受压C形截面局部屈曲荷载和承载力的影响,对组成其截面各板件局部屈曲时的变形协调情况进行理论分析,提出考虑该效应的腹板局部屈曲计算模型,基于能量法和静力平衡条件推导了冷弯薄壁受压C形截面局部屈曲荷载的解析解,并分别与有限条法和中国规范GB 50018—2002规定的方法进行对比.将所推导的解析解引入直接强度法,对21根冷弯薄壁C形受压短柱试验的承载力进行计算,并分别与承载力试验结果和按GB 50018—2002规定方法计算的承载力进行对比分析.结果表明:在屈曲荷载方面,本文推导的解析解合理可靠,而按中国规范规定的方法则存在系统误差,当截面高宽比小于4.5时,其结果偏于保守,当截面高宽比大于4.5时,其结果偏于不安全;在承载力方面,按本文方法计算的承载力与试验结果较为接近,合理可靠,而按中国规范规定方法计算的承载力较保守,并且随着截面宽高比的增大,保守趋势不断增大.     

Pilot study: lateral braced C-sections under bending

The overall behavior under uniform load of cold-formed steel C-sections assemblies was investigated. Each test assembly consisted of C-sections acting as beams having a track section to restrain its ends. A lateral brace to restrain the C-sections from rotation was provided at mid-span. To better understand the influence of the brace on the flexural behavior, an experimental investigation was carried out with particular emphasis placed on the study of the effect of the mid-span brace connection when wallboard was attached to the tension flange. The tested moment capacities are compared to predictions based on the 1996 edition American Iron and Steel Institutes' Specification for design of cold-formed steel structural members.     

A new formulation for distortional buckling stress in cold-formed steel members

Distortional buckling of compression members usually comprises rotation and translation of each flange and lip about the flange-web connection in opposite directions. The present procedures for the calculation of elastic distortional buckling stress in the literature are very complex, cumbersome and have long expressions. In this paper a new neural network (NN) based formula is proposed for the determination of the elastic distortional buckling stress of cold-formed steel C-sections with both end sections pinned. The focus of this study is on the distortional buckling, for which existing results are for sections subjected to pure compression and/or pure bending only. The data used for training and testing NNs is taken from Schafer’s report. The NN-based estimates are compared with the experimental, numerical and analytical results of different researchers and methods. It was found that the proposed NN based-formula is practical in predicting the elastic distortional buckling stress of cold formed steel C-sections.     

On the mechanics of distortion in thin-walled open sections

This paper addresses the distortional kinematics and mechanics of thin-walled sections and provides clear definitions of cross-section properties that characterise the distortional deformation, as it is usually done for conventional modes (axial, bending and torsion). In particular, a procedure to build the distortional displacement field of a given thin-walled section is described. The first part of the paper describes the essentials of distortion in comparison with the conventional modes of classical beam theories. It is shown that primary warping is the key factor that controls the distortion of thin-walled sections. Then, an analytical procedure to determine the distortional warping displacement distribution of a given cross-section is described, on the basis of orthogonality conditions existing between the distortional and conventional modes. Next, an overview of the kinematical assumptions underlying the distortional deformation is presented and a simple procedure to build distortional displacement fields of thin-walled sections is provided. This procedure is then applied to obtain the distortional displacement field of C-sections and general expressions of distortional cross-section properties are given. Finally, a simple example is presented to illustrate how the distortional displacement field of a C-section is built, on the basis of simple kinematics principles. The distortional critical stress and half wavelength are determined and good agreement with exact numerical estimates is found.