نیاز به برش قاب مقاوم خمشی فولادی در معرض لرزش گسل نزدیک و دور Shear Demands of Steel Moment-Resisting Frames Under Nearand Far-Fault Seismic Excitations

1 Introduction There are various analytical methods to evaluate the seismic demands of different types of structures for design purposes and other practices. In spite of the ongoing developments in new complicated analytical approaches (e.g., adaptive pushover analysis, incremental dynamic analysis and time-endurance analysis methods) which offer more precise estimations for the seismic response of structures, the conventional static procedures are currently the most frequent approaches for analyzing and designing building new structures (ASCE 07-10; Iranian seismic design code) as well as the seismic assessment of existing structures (FEMA 356; ASCE 41-13). This is due to the simplicity and applicability of these methods in modeling, analyzing and processing the results. For this reason, the improvement in static procedures’ accuracy is a necessity for the structural engineering community. According to the Iranian code for seismic design of structures, the application of static analysis method is valid for a wide range of structures which satisfy the regularity requirements and some other limiting specifications. In this method, the design base shear is calculated based on the dynamic behavior characteristics of equivalent single-degree-of-freedom system. The base shear is then distributed along the height of structure in the form of pseudolateral forces. Seismic response quantities are then calculated using the static analysis methods. Therefore, the pattern of lateral force distribution over the height of structure as well as the estimation of base shear demand significantly influences the seismic response evaluations. The primary criteria for design of steel frames, especially mid- and high-rise frames, are limiting the story drift ratio (IDR) demands to prescribed values. According to the fourth edition of Iranian seismic design code for structures with 5 stories or less, the maximum IDR of all stories considering the second-order geometric nonlinearity must be limited to the 0.025. This limit is 0.02 for buildings with more than five stories. Besides the limiting lateral displacements to prescribed values, the strength capacity of the elements must sufficiently satisfy the capacity design specifications to ensure the stability of individual members. In other words, each structural member must be designed to resist internal force/moment actions.