Dynamic response of steel frames with semirigid connections

An experimental and analytical program was conducted on a full-scale steel frame structure with bolted semi-rigid connections subjected to seismic base accelerations. Separate static and cyclic tests were conducted on the connection subassemblage from the full-scale frame in order to establish models of moment-rotation behavior to be incorporated in a dynamic analysis program of the complete structure.; Two connection types were investigated in the subassemblage tests; one consisted of top and bottom flange angles and double web angles, the second was similar but without web angles.; The connections with web angles displayed stiffer moment-rotation response than those without web angles in both static and cyclic tests. In the cyclic tests, both connection types displayed stable hysteretic behavior at each displacement amplitude; additionally, each succeeding increase in amplitude was accompanied by an increase in hysteresis loop area. The hysteresis loops exhibited a "pinching" effect under cyclic loading, the degree of pinching becoming more pronounced at the higher displacements. The cyclic tests were terminated due to fatigue crack initiation and propagation in the flange angle(s).; The full-scale structure, erected using connections without web angles, was subjected to a series of seismic base accelerations of increasing intensity. Through the full range of testing, the members of the test frame generally remained elastic, with the only evidence of inelastic response being confined to the connection elements and the flanges of the columns adjacent to the connections. At no point in the testing series was fatigue cracking detected. It was demonstrated that the semi-rigid connections dissipated energy which contributed to a reduction of dynamic frame displacements relative to those estimated by analysis of a linearly elastic system.; The hysteretic behavior from the full-scale frame tests was closely replicated by the cyclic test of the geometrically similar connection subassemblage.; Based on the results of the connection subassemblage tests, two semi-empirical analytical models of moment-rotation behavior were examined for use in predictive analyses of the full-scale structure. The first was a commonly used bilinear model, while the second was more sophisticated in that it modeled the observed hysteretic "pinching" effect. These two models, when incorporated into the dynamic analyses, provided reasonable approximations to the experimentally measured response of the full-scale structure.