Center for Cold-Formed Steel Structures Library


SUMMARY Shear diaphragm action of properly designed light gage steel panels used for floors, roofs, and walls in steel buildings increase the stiffness and strength of such buildings. Considerable savings in weight and cost can be realized if full account of this action is taken in design. To make good use of the diaphragm action, detailed knowledge on diaphragm response to loading is essential. An efficient computer program has been prepared to analyze light gage steel shear diaphragm behavior in the linear and nonlinear ranges of response, up to collapse. The program uses figinite element concepts for analysis, and has routines to deal with the beams, purlins, panels, and connections. Beams and purlins are modeled by conventional flexural elements with three degrees of freedom at each node. Panels are represented by rectangular orthotropic plane-stress plate elements. Two different models for corrugated panels are proposed. One model makes use of an average effective shear modulus along the entire panel length, while in the other two different shear moduli are attributed to the end and central regions of the panel. The connections are modeled by spring elements, and, according to location, several different models utilizing these spring elements are used. The non-linear analysis is based on experimental evidence that, in general, the connections are the only important source of non-linearity up to collapse. For this reason, only the connection behavior is represented by a non-linear function. All other components of the diaphragm assembly are assumed to remain elastic throughout the loading range. The connectors can be either welds, used for heavily-stressed shear diaphragms, or screw fasteners, used for more lightly loaded installations. In both cases, the non-linear force-displacement relation used for the connection is a multi-linear approximation of the load-displacement curve obtained from a shear test of the connection and the small region around it. The program uses a frontal routine for the solution of the stiffness equations. The non-linear analysis is done by the residual force method, which utilizes the original elastic stiffnexx matrix at every stage of the analysis, and which arrives at the correct solution for each load increment through an iterative procedure. A modified Aitken accelerator is used to speed the convergence. In order to reduce the task of preparing input data, a mesh generator has been written. This mesh generator requires only simple basic data for the generation of the complete finite element mesh, for most practical diaphragms. The computer program has been employed to analyze diaphragms for which test results are available. Both linear analyses up to the elastic limit, and non-linear analyses up to and beyond the elastic limit have been conducted. For three of the four diaphragms analyzed, very good agreement between numerical and experimental results have been obtained. For a standard corrugated diaphragm, numerical results in the non-linear range show a more flexible behavior than in test. Detailed analysis indicates that this is most probably due to unavailability of correct connection test data for use in analysis. The force distribution in the diaphragms, overall diaphragm deflections, and seam slips are found at different ranges of response. As a result of the analyses, it is confirmed that connection non-linearity is the most important factor in the nonlinear range of diaphragm response, differences in shear modulus being only of secondary importance. It is concluded that the computer program developed is an efficient and dependable tool for research and design.


Civil, Architectural and Environmental Engineering


American Iron and Steel Institute

Research Center/Lab(s)

Wei-Wen Yu Center for Cold-Formed Steel Structures



Publication Date


Document Version

Final Version

Document Type

Report - Technical

File Type




Technical Report Number

Report No. 363