مطالعه ضریب رفتار دیوار برشی فولادی تقویت شده(با سخت کننده) به روش تحلیل دینامیکی افزایشی(‌IDA‌)‌

This study aims to thoroughly investigate the seismic behavior factor of multi-floor structures that are equipped with steel shear walls reinforced by horizontal and vertical stiffeners. Steel shear walls are critical components in modern structural engineering, designed to enhance lateral strength and stiffness, thereby improving the overall seismic resilience of buildings. In this research, the focus lies on understanding how different reinforcement configurations of stiffeners specifically horizontal and vertical stiffeners arranged in multiple rows affect structural performance under earthquake loading, as well as the corresponding behavior factor, which is an important parameter in seismic design codes. The investigation began with the detailed analysis of a single steel shear wall reinforced with stiffeners, where the numerical model was developed and validated using the Abaqus software platform. This validation step was essential to ensure that the computational model accurately represented the actual structural behavior under lateral loads, thereby building confidence in subsequent analyses. Following the validation phase, several structures of varying heights specifically 4- floor, 8- floor, and 12- floor buildings were modeled. Each structure featured four distinct types of steel shear walls: (1) unreinforced shear walls without any stiffeners, (2) shear walls reinforced with one row of horizontal and vertical stiffeners, (3) walls with two rows of stiffeners, and (4) walls equipped with three rows of stiffeners. This gradation allowed for a comprehensive comparison of how the number of stiffener rows impacts the seismic response. To simulate realistic earthquake scenarios, 9 different ground motion near fault records were applied to each structural model in a dynamic analysis framework called Incremental Dynamic Analysis (IDA). IDA is a robust technique that incrementally increases earthquake intensity to evaluate structural performance and estimate the behavior factor, which quantifies the ratio between elastic and inelastic responses and is crucial for seismic design considerations. The results revealed several important trends. As the number of stories increased from 4 to 8, the maximum lateral displacement experienced by the structures increased by approximately 30 to 40%. This increase was even more pronounced when moving from 8 to 12 stories, with displacements rising by about 60 to 70%. These findings highlight that taller buildings naturally undergo larger deformations under seismic forces. However, the introduction of stiffeners significantly mitigated these displacements. Specifically, the addition of a single row of horizontal and vertical stiffeners reduced lateral displacements by roughly 8 to 10%. When steel panels and peripheral stiffeners were incorporated, displacement reductions improved further, showing decreases of 5% and 15%, respectively. Most notably, the use of three rows of stiffeners resulted in substantial displacement reductions, ranging from 28% up to 40%. In terms of structural stiffness, the elastic modulus of the shear walls increased markedly with stiffener reinforcement. Compared to unreinforced walls, the elastic modulus improved by 33% with one row of stiffeners, 90% with two rows, and an impressive 165% with three rows of horizontal and vertical stiffeners. This increase in stiffness corresponds directly to enhanced seismic performance and reduced structural damage. Nonetheless, despite these improvements, it was observed that increasing the number of stories from 4 to 8 and 12 in steel shear walls with stiffeners significantly reduced the behavior factor by about 30 to 50%. This reduction stems from the amplified seismic forces and larger structural deformations inherent in taller buildings, which outweigh the benefits gained from stiffener reinforcements. In conclusion, the research demonstrated that adding multiple rows of both horizontal and vertical stiffeners to steel shear walls significantly influences the behavior factor and overall seismic performance of multi- floor buildings. These findings provide critical insights for engineers seeking to optimize steel shear wall designs to improve earthquake resilience, especially in mid- to high-rise constructions. However, the beneficial effect of stiffeners decreases in taller structures compared with shorter ones. Based on these findings and adopting a conservative approach for structures ranging from 4 to 12 stories, approximate response modification factors of R=2.5, R=4.0, R=5.5, and R=7.0 are proposed for unstiffened steel shear walls and steel shear walls with one, two, and three rows of stiffeners, respectively.