Evaluation of the seismic performance of off-centre bracing system with ductile element in steel frames

Mohammad Bazzaz,Ali Kheyroddin,Mohammad Ali Kafi,Zahra Andalib 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.5

In order to evaluate the dynamic behavior of passive energy dissipation system, two steps need to be considered for prediction of structural response in the presence of ductile element in an off-centre bracing system. The first is a detailed analysis of the proposed ductile element and the second is the effect of this ductile element on an off-centre bracing system. The use of ductile bracing system is expanding in steel structures in order to increase the force reduction factor. Therefore, regarding the nonlinear behavior of steel material used in an off-centre bracing systems and using ductile element in OBS bracing systems, the seismic evaluation of the mentioned systems seems to be necessary. This paper aims to study linear and nonlinear behavior of steel frames with off-centre bracing system and ductile element, in order to get the best position of these bracing elements. To achieve this purpose, the modeling has been done with ANSYS software. The optimum eccentricity has been obtained by modeling three steel frames with different eccentricities and evaluating the results of them. The analytical results showed that the model OBS-C with 0.3 eccentricities has higher performance among the models.

Numerical comparison of the seismic performance of steel rings in off-centre bracing system and diagonal bracing system

Mohammad Bazzaz,Zahra Andalib,Ali Kheyroddin,Mohammad Ali Kafi 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.4

During a seismic event, a considerable amount of energy is input into a structure. The law of energy conservation imposes the restriction that energy must either be absorbed or dissipated by the structure. Recent earthquakes have shown that the use of concentric bracing system with their low ductility and low energy dissipation capacity, causes permanent damage to structures during intense earthquakes. Hence, engineers are looking at bracing system with higher ductility, such as chevron and eccentric braces. However, braced frame would not be easily repaired if serious damage has occured during a strong earthquake. In order to solve this problem, a new bracing system an off-centre bracing system with higher ductility and higher energy dissipation capacity, is considered. In this paper, some numerical studies have been performed using ANSYS software on a frame with off-centre bracing system with optimum eccentricity and circular element created, called OBS_C_O model. In addition, other steel frame with diagonal bracing system and the same circular element is created, called DBS_C model. Furthermore, linear and nonlinear behavior of these steel frames are compared in order to introduce a new way of optimum performance for these dissipating elements. The obtained results revealed that using a ductile element or circular dissipater for increasing the ductility of off-centre bracing system and centric bracing system is useful. Finally, higher ductility and more energy dissipation led to more appropriate behavior in the OBS_C_O model compared to DBS_C model.

Evaluating the Seismic Performance of Off-centre Bracing System with Circular element in Optimum Place

Mohammad Bazzaz,Mohammad Ali Kafi,Ali Kheyroddin,Zahra Andalib,Hamed Esmaeili 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.2

Braced structures with concentric braces are among earthquake resistant systems that are widely used in frames with jointconnections. Ductility, dissipation of energy and decreasing in base shear are the benefits of these bracing systems. Despite thebenefits mentioned limited ductility of concentric braces, however, caused poor functionality against earthquake. Therefore inthis paper, new bracing system using circular element (circular dissipater) has been evaluated, in order to replace damagedmember without needing rehabilitation or repair of general system. So using nonlinear software package ANSYS a frame withoff-centre bracing system with optimum eccentricity (OBS-C-O) and another frame with same specifications without circularelement (OBS) has been created. The function of general system has been studied for the first time. Linear and nonlinearbehavior of these two frames compared to each other so the benefits of this circular element in an off-centre bracing systemare highlighted. The analytical results and comparison between plots of these two models showed that the first model has higherperformance than the others.

Nonlinear finite element modeling of the self-centering steel moment connection with cushion flexural damper

Ali Nazeria,Reza Vahdani,Mohammad Ali Kafi 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.87 No.2

The latest earthquake’s costly repairs and economic disruption were brought on by excessive residual drift. Selfcentering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model’s findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD’s seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

Performance of innovative composite buckling-restrained fuse for concentrically braced frames under cyclic loading

Masoud Mohammadi,Mohammad A. Kafi,Ali Kheyroddin,Hamid R. Ronagh 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.2

Concentrically Braced Frames (CBFs) are commonly used in the construction of steel structures because of their ease of implementation, rigidity, low lateral displacement, and cost-effectiveness. However, the principal disadvantage of this kind of braced frame is the inability to provide deformation capacity (ductility) and buckling of bracing elements before yielding. This paper aims to present a novel Composite Buckling Restrained Fuse (CBRF) to be utilized as a bracing segment in concentrically braced frames that allows higher ductility and removes premature buckling. The proposed CBRF with relatively small dimensions is an enhancement on the Reduced Length Buckling Restrained Braces (RL-BRBs), consists of steel core and additional tensile elements embedded in a concrete encasement. Employing tensile elements in this composite fuse with a new configuration enhances the energy dissipation efficiency and removes the tensile strength limitations that exist in bracing elements that contain RL-BRBs. Here, the optimal length of the CBRF is computed by considering the anticipated strain demand and the low-cyclic fatigue life of the core under standard loading protocol. An experimental program is conducted to explore the seismic behavior of the suggested CBRF compare with an RL-BRB specimen under gradually increased cyclic loading. Moreover, Hysteretic responses of the specimens are evaluated to calculate the design parameters such as energy dissipation potential, strength adjustment factors, and equivalent viscous damping. The findings show that the suggested fuse possess a ductile behavior with high energy absorption and sufficient resistance and a reasonably stable hysteresis response under compression and tension.

Investigation of performance of steel plate shear walls with partial plate-column connection (SPSW-PC)

Mojtaba Gorji Azandariani,Majid Gholhaki,Mohammad Ali Kafi,Tadeh Zirakian,Afrasyab Khan,Hamid Abdolmaleki,Hamid Shojaeifar 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.1

This research endeavor intends to use the implicit finite element method to investigate the structural response of steel shear walls with partial plate-column connection. To this end, comprehensive verification studies are initially performed by comparing the numerical predictions with several reported experimental results in order to demonstrate the reliability and accuracy of the implicit analysis method. Comparison is made between the hysteresis curves, failure modes, and base shear capacities predicted numerically using ABAQUS software and obtained/observed experimentally. Following the validation of the finite element analysis approach, the effects of partial plate-column connection on the strength and stiffness performances of steel shear wall systems with different web-plate slenderness and aspect ratios under monotonic loading are investigated through a parametric study. While removal of the connection between the web-plate and columns can be beneficial by decreasing the overall system demand on the vertical boundary members, based on the results and findings of this study such detachment can lower the stiffness and strength capacities of steel shear walls by about 25%, on average.