Seismic Evaluation Strategies

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2.1 General
Seismic evaluation and retrofitting strategies are mainly focused in this thesis. However, there are many good references that can be used as a starting point for research such as ATC40 manual for seismic evaluation and retrofitting of concrete buildings. This chapter focuses on recent contributions related to seismic evaluation and various retrofitting schemes and past efforts most closely related to the needs of the present work. For, the purpose of the present investigation, the literature is break down into following areas:
a) Seismic evaluation.
b) Retrofitting strategies.
2.2 Seismic Evaluation
This section describes previous contributions made in the field of seismic evaluation of buildings. Also, highlights various research
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1 and 21 highlights the nonlinear static pushover analysis. It is an efficient method for the performance evaluation of a structure subjected to seismic loads. Also ATC40 covers step by step procedures for pushover analysis to determine the capacity curve, capacity spectrum method and displacement coefficient method were briefly elaborated. By using these procedures this report is detailed with modeling aspects of the hinge behavior, acceptance criteria and locate the performance point. Hence, ATC40 serves as guideline for the starting of seismic evaluation process.
Federal Emergency Management Agency document 356 (FEMA356)2 contains simplified nonlinear analysis procedure (pushover analysis) to determine the displacements demand imposed on the building expected to inelastically and the conversion of the results to the capacity diagram are based only on the fundamental vibration mode of the elastic
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Model unit frames constructed for experimental investigations were 1:3 scaled models of a typical 3 m x 3 m unit ductile frame. The full size unit frame was selected from a typical 4 storied, 3-bay portal frame of a building. The seismic loading on the frame was determined using an equivalent static method. The RC frame was then analyzed for the combined effects of gravity and seismic loading and was designed and detailed according to the ACI code provisions for ductile RC frames. Pushover tests were conducted on scaled models of ductile unit frames, directly braced by X and Knee steel braces. To design the X bracing and knee-bracing systems, the excess seismic load on each frame, due to the increased elastic stiffness of the combined RC frame and bracing system, was determined and the relevant braces were designed for these excess loads. Test outcomes indicate that the yield capacity and the strength capacity of a ductile RC frame could be increased and its global displacements could be decreased to the desired levels by directly adding either an X bracing or a knee-bracing system to the frame. Steel X bracing could provide a stiffer bracing system but reduces the ductility of the ductile frame. Knee bracing could be employed to provide the desired ductility level for a ductile design. It was concluded that both X-bracing and knee-bracing systems might be used to design or retrofit for a

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