In this study a nonlinear dynamic analysis computer program for planar steel frames with semi-rigid connections is developed. The semi-rigid connections are modeled as a massless rotational spring element. This element has two nodes, one connected to the beam end, and the other to the column end. Its hysteresis behavior, under cyclic loads, is expressed by a moment-rotation relationship.

To analytically describe this behavior for use in the computer program, the actual moment-rotation behavior was idealized by piecewise linear segments. For connections which failed due to either excessive connection rotation or bolt fracture, three types of linear segment models were constructed for each connection specimen tested. These included the elasto-plastic, bilinear, and modified bilinear models. These models differ in complexity and the way in which the connection yield moment is defined. Comparing the experimental moment-rotation hysteresis loops recorded to those predicted by the analytical models, it is found that the modified bilinear model best idealized the behavior; however the elasto-plastic model is easiest to construct. For all bolted double web angle connections which failed due to beam web failed a separate trilinear model is suggested.

In order to develop rational moment rotation relationships, a total of 55 full-scale different types of commonly used semi-rigid connection specimens were tested to record their moment-rotation behavior under cyclic loads. These included double web angle (all bolted, and welded to beam web and bolted to column flange), top. and seat angle, flush end-plate, and extended end-plate connections. The failure modes observed are reported, which include either excessive rotation of the connection due to yielding or bolt fracture. Some of the all bolted double web angle connections failed due to beam web bearing failure. The moment-rotation hysteresis behavior of all connections was found to be nonlinear in nature.

In the dynamic analysis procedure presented, a Newton-Raphson iterative procedure is used to march along the moment-rotation curve for each connection spring element, and the dynamic equations of motion are solved using the constant acceleration method. No damping is considered in the analytical formulation, though due to the hysteresis behavior of the connection there will be some inherent damping. The computer program is shown to predict convergent solutions as the time step is refined to iteratively march the solution in the time domain. To further verify the computer program developed, results of a parametric study are also presented which investigate the effects of the connection moment-rotation model parameters, type of hysteresis model used, and different earthquake records on the sway response history of a frame. Actually, the dynamic computer program was an extension of a static analysis computer program developed for planar frames with semi-rigid connections. Details of this program are. presented first. In this formulation the monotonic (static) moment-rotation behavior of the semi-rigid connection is modeled by an exponential function, and geometric nonlinearity (P-Delta effects) of the frame members is considered. (Abstract shortened by UMI.)