Behavior of Diaphragm-Braced Columns and Beams

A compression member that is supported continuously or at frequent intervals along its length fails at a load which can be somewhere between its maximum capacity when unbraced and its failure load when fully braced. A diaphragm can be used to provide such bracing and, if attached to two identical parallel members and constrained to deform as the members deflect laterally, may be assumed to be in a state of pure shear. A theory predicting the failure load of elastic I-section members laterally restrained by shear-resistant diaphragms is developed. The shear rigidity, which can vary substantially because of the connector and other details, is the principal characteristic of the diaphragm considered. This rigidity was determined experimentally. A test series of double-column-diaphragm assemblies gave good agreement between the theoretically predicted values and the test failure loads.