SummaryDiagrid system is known for its efficient structural behavior besides its outstanding aesthetic characteristics and architectural flexibility. However, a brief existing study on the nonlinear performance of the diagrid system has reported an inefficient nonlinear behavior. Diagrid with fused‐shear link is a newly introduced system that can solve this flaw in the conventional diagrids and keep the advantages as well. In this paper, this newly introduced system is called eccentric diagrid system (EDS). Benefits of the EDS are presented, and a series of nonlinear pushover and time history analyses are conducted to compare EDS with the conventional diagrid system (CDS). In this manner, three different configurations for both EDS and CDS with diagrid angles of 45°, 63.4°, and 71.6° are chosen for two different 12‐ and 18‐story buildings. The models are designed based on an R‐factor equal to 3.6 and 5 for CDS and EDS frames, respectively. Then, the assumed R‐factor for EDS is verified according to Federal Emergency Management Agency P695, and the priority of members yielding is spotted. The results show that EDS can effectively enhance the post‐yield performance and seismic characteristics of the structure relative to CDS, including ductility and overstrength ratio more than 2.5 and 1.3 times, respectively.
One of the main challenges in seismic assessment of existing structures is estimating the displacement demand under earthquake motions. Displacement coefficient method introduced in current code and instructors correlates displacement of an equivalent single degree of Freedom (ESDOF) system to roof or any story of corresponding MDOF. An important coefficient in this method, , defines the ratio of inelastic to elastic displacement of ESDOF. The effects of soil structure interaction (SSI) on parameter for SDOF has been investigated by many researchers, however, this parameter on MDOF system, itself, has not been properly investigated. This is a challenging issue since many influential behaviors cannot properly be addressed in ESDOF systems such as: P-delta effects, higher mode effects, forming of plastic hinges and their sequences considering strength and stiffness deterioration, and nonlinear SSI. In this study, to investigate this approach, seven buildings representing a reasonable range of effective period as MDOF systems were selected (three moment resisting frames and four shear wall buildings) and designed with different strength reduction factors (R=3, 4, 5 & 7). To investigate the effect of SSI on responses, the foundations were designed with (1.5, 3, 4 & 5) factor of safety vertical (FSV) to cover all probable rocking and uplifting behaviors. All designed buildings were analyzed for far-field Design Basis Earthquake (DBE), Maximum Considered Earthquake (MCE), and near field pulse-like earthquake records. The responses were investigated for the effects of SSI on global response of buildings considering both R-factor and FSV as well as MDOF displacement inelastic ratio ( ) and modified amplification factor coefficient ( ). The results showed that the method suggested by ASCE-41-17 for prediction of inelastic displacement ratio underestimates the responses in shorter period buildings and overestimate for longer period buildings for all values of R-factors and FSV. The results showed that the coefficient of introduced in ASCE-41-17 should include the effects of structural and SSI nonlinearity instead of elastic mode participation factors. Based on results, two practical equations and methods were proposed to enhancing displacement coefficient method considering SSI effects on MDOF systems.
Following a severe disaster, a quick and reliable evaluation of the structural damage state is one of the crucial steps to making decisions and disaster management. Based on a realistic estimate of types and levels of damages, decisions related to the structural performances, repair possibility, or in severe cases, a replacement could be made. In available technical literature, reporting the classification of damaged buildings is limited and based on numerical studies, laboratory tests, and inspector’s judgment. Presented results in current research are from a comprehensive and meticulous investigation of more than 81 damaged steel and RC buildings after the Sarpol-e Zahab (Iran) earthquake. Considering this valuable collected information, a novel qualitative-quantitative approach is introduced to classify damaged steel and RC buildings into 5 damage states, both for structural and non-structural components. For this purpose, weights are attributed to each type of damage, according to the severity of the damage observed in each component and its influence on the damage to the entire building. Then, the damage index of each structure is obtained using the proposed relation, and results are compared with field observation for verification. Finally, empirical vulnerability curves of investigated buildings are developed based on the proposed damage index and spectral acceleration at fundamental periods of structures as an intensity measure.
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