The main objective of this project is to develop a procedure to balance the structure's actual strength and the required ductility requirements for steel frame design. Steel moment frames are popularly used for low-to medium- rise buildings in all seismic zones. Unlike reinforced concrete frames, member sizes of steel moment frames are quite often governed by drift limits; therefore the structure's actual strength may be significantly higher than that required by seismic codes. Unfortunately, this unique feature of steel design is not recognized by seismic codes, and stringent ductility requirements as specified in these codes may be too conservative. Furthermore, since the stringent ductility requirements are developed primarily for high seismic zones, its application to moderate or low seismic zones has been questioned. The proposed design procedure considers explicitly the beneficial structural overstrength resulting from drift limitations; the required ductility is balanced by this overstrength. In addition to two ductility classes (Special and Ordinary Moment Frames) which have been adopted in seismic provisions, a third class (Intermediate Moment Frame) will be developed in the project. Thus an economic design which provides a more consistent safely level for all seismic regions can be achieved. An efficient computer program will be developed to compute structural overstrength. Several moment frames located in different seismic zones will be designed by both the conventional and proposed design methods. Feasibility study will be conducted and cost savings resulting from the proposed design method will be noted. Safety level of steel moment frames designed by both methods will also be compared by performing nonlinear dynamic analysis.
