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Effect of Link Beam Length of the Eccentric Bracing System on Seismic Rehabilitation of Weak Reinforced Concrete Frames

Niknam Touraj, Saberi Hamid, Saberi Vahid, Sadeghi Abbasali, Noroozinejad Farsangi Ehsan

Civil and Environmental Engineering Reports

2022

Vol. 32, no. 1

152--175

In this study, a reinforced concrete (RC) reference specimen with compressive strength of 250 kg/cm2 and the weak RC specimen for seismic rehabilitation with compressive strength of 150 kg/cm2 were examined in two types of structures with 6 and 12-stories. The link beam lengths of 50, 80, and 100 cm have been used in 6 and 12-stories prototypes under the effect of 7 earthquake records. The nonlinear dynamic analyses are performed. Then, The behavior of the link beam depends on its length. For short link beam lengths, shear behavior is serious, then for medium lengths, shear-flexural behavior is important, and finally, long lengths will have flexural behavior for the beam. In eccentrically braced frames, the details of the link beam and the fit of the other members must be done in such a way as to ensure its proper ductility. According to the obtained results, the performance of short link beams is much better than long link beams, and short link beams provide more energy dissipation and, at the same time, more ductility. Therefore, in the design of the link beam, mainly the shear of the link beam is considered as a ductile component. The axial force in the link beam, which is due to the application of lateral load to the structure, reduces both the bending capacity and the inelastic deformation capacity of the link beam, so it can be explained that in steel eccentric braces, the link beam is symmetrical between the two main components of the brace and it can affect the strength of the structure against lateral loads.

Investigation of the Occurrence of Progressive Collapse in High-Rise Steel Buildings with Different Braced Configurations

Saberi Hamid, Saberi Vahid, Sadeghi Abbasali, Pooyasefat Abbas, Noroozinejad Farsangi Ehsan

Civil and Environmental Engineering Reports

2021

Vol. 31, no. 4

33--54

The progressive collapse phenomenon refers to a chain of damages in a structure where all or a large part of the structure is destroyed by an initial local collapse in it, which can lead to very disastrous results. Therefore, the prevention of progressive collapse has become a necessary action in the design and analysis of buildings and it is vital to investigate this topic more accurately. This study aims to present a proposed pattern in the configuration of braces at the height of a high-rise steel building for reducing the probability of progressive collapse. In this regard, the vertical displacement of 18-story structure with four scenarios of column removal and five concentric bracing patterns including V, Inverted V, X, discontinuous X-bracing at height, and a combination of Xbracing in the side spans and discontinuous X-bracing at height in the middle spans are investigated and compared. In this study, the Alternative Path Method (APM) is used based on the GSA guideline for the analysis of progressive collapse. The results of this research showed that the use of X-bracing in the side spans and discontinuous X-bracing in the middle spans in nonlinear static and dynamic analyses performed better in reducing the probability of progressive collapse than other bracing configurations. Finally, it is recommended to use discontinuous X-bracing at the height that would place the bracings in one direction and providing alternative paths for force transferring in the structure.