This project is a coordinated effort of experimental work analysis in order to be responsive to two major problems: verification mathematical modelling and prediction of the capacity of actual structures. The emphasis of this project is placed on steel structures and components. The experimental and analytical laboratory studies to be carried out can be conveniently grouped under three main headings: (1) equipment, (2) frames, and (3) joints. These studies complement the scale field tests on existing motion earthquakes which are underway or being proposed. The study of equipment includes investigation of the failure modes supported correlation equipment response. For the steel frame study a 4' x 6' shaking table will be used to study the response due to the horizontal motion and the effects of vertical irregularity of frame stiffness. Detailed nonlinear models will be developed for selected structures. For joint study biaxial full-scale steel-moment connection tests will be conducted and compared with the analytical prediction. The investigators are all competent researchers of proven track record. The Principal Investigator is a leader in the field and is highly experienced in the practical problems of seismic-resistant design. This research will fill some of the gaps in the current knowledge base about the nonlinear structural behavior and will lead to techniques for improved reliable design of structures subjected to strong earthquake shaking. A two-year continuing grant is recommended.