Comparison of Seismic Rehabilitation Methods of Moment Frame Steel Structures with Torsional Irregular Plans

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Comparison of Seismic Rehabilitation Methods of Moment Frame Steel Structures with Torsional Irregular Plans

ارائه دهنده: Provider: Heydar Mohebbi Amir Hoseini

اساتید راهنما: Supervisors: Mostafa Moghadasi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Mohammad Sadegh Ketabi- Fereydoon Rezaei

زمان و تاریخ ارائه: Time and date of presentation: 2026

مکان ارائه: Place of presentation: 45

چکیده: Abstract: Given the continuous development and updating of structural design codes and the location of Iran in one of the world's seismically active regions, the reassessment and reanalysis of existing structures, particularly older steel structures designed in accordance with the seismic provisions and criteria of the First Edition of the Iranian Standard No. 2800, are of significant importance. Such assessments can identify structural deficiencies under seismic loading, thereby contributing to the prevention of substantial human and financial losses and, where necessary, providing a basis for implementing seismic retrofit measures. Among existing structures, a considerable number exhibit torsional irregularity in plan. Accurate assessment of the seismic response of such structures, owing to the complexity of their behavior under seismic excitation, requires the use of advanced analytical methods, including nonlinear time-history analysis. Accordingly, the present study aims to compare the performance of different seismic retrofit methods for steel structures equipped with moment-resisting frame systems and exhibiting torsional irregularity in plan. In this study, three steel structural models with moment-resisting frame systems in both principal directions of the building, having 5, 10 and 15 stories, were considered. Initially, the structural models were evaluated using response spectrum analysis in accordance with the provisions of the First Edition of Iranian Standard No. 2800. Subsequently, to provide a more accurate assessment of the nonlinear seismic response of the structures, nonlinear time-history analyses were conducted in accordance with the provisions of Iranian Publication No. 360. The analytical results indicated that none of the initial structural models satisfied the acceptance criteria corresponding to the Life Safety (LS) performance level, and all models therefore required seismic retrofit measures. Accordingly, four retrofit schemes were implemented, including local strengthening of beams and columns, and the addition of eccentric, concentric, and buckling-restrained bracing systems. Among the investigated methods, local strengthening of structural members was unable to provide an effective solution for reducing interstory drift and preventing the formation of plastic hinges at the Life Safety performance level. In contrast, the addition of eccentric, concentric, and buckling-restrained bracing systems provided effective solutions for these purposes. Among the investigated retrofit schemes, the addition of concentric bracing combined with local strengthening of the columns adjacent to the braced bays exhibited the best overall performance. This retrofit configuration effectively controlled the formation of brittle flexural plastic hinges in the columns, which are force-controlled members, while achieving the greatest reduction in interstory drift and maintaining plastic hinge formation within the specified acceptance limits.