Towards a Balanced Seismic Design Procedure for Strength and Ductility Requirement

该项目的主要目标是开发一种程序，以平衡结构的实际强度和钢框架所需的延性要求设计。钢结构弯矩框架广泛应用于所有地震区的中低层建筑。与钢筋混凝土框架不同，钢结构弯矩框架的构件尺寸通常受漂移限制；因此，结构的实际强度可能大大高于抗震规范的要求。不幸的是，钢材设计的这一独特特征并没有得到抗震规范的认可，而这些规范中规定的严格延性要求可能过于保守。此外，由于严格的延性要求主要是针对高地震区制定的，它在中低地震区的应用受到了质疑。建议的设计程序明确考虑了漂移限制所导致的有益的结构超强；所需的延展性被这种超强所平衡。除了抗震规定中采用的两种延性等级(特殊弯矩框架和普通弯矩框架)外，第三类(中间弯矩框架)将在该项目中开发。因此，可以实现为所有地震区提供更一致的安全水平的经济设计。将开发一种有效的计算机程序来计算结构的超强度。不同地震区的几个弯矩框架将按常规和建议的设计方法进行设计。当局会进行可行性研究，并会留意建议的设计方法所节省的费用。对两种方法设计的钢框架进行了非线性动力分析，比较了两种方法设计的钢框架的安全水平。

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.