Browsing by Author "AL-oda, Hasan Ali Hani"
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Item COMPARISON OF DIFFERENT LOAD PATTERNS FOR PERFORMANCE BASED SEISMIC RESPONSE OF BUILDINGS(2022-01-21) AL-oda, Hasan Ali Hani; Sönmez, ErtanModern seismic codes are increasingly using performance-based design methods that employ nonlinear static (pushover) and dynamic (response history) analyses to determine more realistic behavior of structures under earthquake loads. Nonlinear analysis methods consider the inelastic behavior including strength and stiffness degradation and the dynamic characteristics of the structures. Although the advancements in computer processing power have made both nonlinear static and dynamic analyses more accessible to the practicing engineers, relative simplicity of pushover analyses have made them more popular in engineering practice. In this thesis, different lateral load patterns commonly used in seismic pushover analysis are examined and their effects on the global behavior and the performance of building structures are compared. Buildings are assumed to be made of reinforced concrete. Three different building heights (3-, 7-, and 10-story) and two different layouts (regular square layout and irregular L-shape layout with re-entrant corner) are considered. Effects of infill walls are also studied for buildings with regular layout. Seismic responses of the buildings are computed using SAP2000 software by four different analysis methods: (i) linear static analysis using equivalent lateral force (ELF) method, (ii) linear response history analysis (RHA), (iii) nonlinear static (pushover) analysis, and (iv) nonlinear response history analysis. In nonlinear analyses, lumped plastic hinges at the frame element ends are employed. M3 hinges are used in beam elements and P-M2-M3 hinges are used in column elements. Hinge properties are determined in accordance with FEMA-356. Seismic loads are calculated assuming buildings were at a location having a Site Class B (rock) based on ASCE 7- 10. For response history analyses, scaled acceleration records of 1940 El Centro earthquake are used. Limited studies are also performed to investigate application of fiber hinges, softer soil conditions (Site Class C), and effects of infill walls in the 7- story building model with regular layout. Three different pushover lateral load patterns that are based on uniform acceleration (UA), fundamental mode (FM) and the method of modal combination (MMC) are considered. For each analysis method and pushover lateral load patterns, various response parameters (including performance points, story displacements, story drifts, plastic hinge locations, etc.) are computed for all models and compared with the results of other cases. The results have indicated that MMC lateral load pattern in general have better agreement with nonlinear response history analysis results compared to the other load patterns. MMC has the advantage of being a relatively simple method to establish a force pattern that includes the effects of higher modes by combination of multiple mode shapes. From comparison of the results for buildings with regular and irregular layouts, it is observed that all three load patterns give somewhat similar pushover results in regular 3-story buildings and the differences in the results become more pronounced as the number of stories (or building height) increases and when the building layout is irregular. Since the higher modes have a greater contribution to the dynamic response in irregular buildings and taller buildings, the differences between the pushover and nonlinear RHA results increase in these buildings. MMC load pattern is considered to be a more appropriate choice as it gives more accurate and reliable results due to consideration of higher modes. FM load pattern leads to higher story displacements and drifts in regular buildings and lower story displacements and drifts in irregular buildings except the 3-story building. MMC load pattern usually leads to similar or lower story displacements and drifts in all cases when compared to UA load pattern. Presence of infill walls have increased the pushover capacities of the regular buildings, increasing the base shear about 15-25 % and decreasing the corresponding roof displacement about 20-30 % at the performance point.