Experimental study on hysteretic behavior of steel moment frame equipped with elliptical brace

Habib Ghasemi Jouneghani,Abbas Haghollahi 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.6

Many studies reveal that during destructive earthquakes, most of the structures enter the inelastic phase. The amount of hysteretic energy in a structure is considered as an important criterion in structure design and an important indicator for the degree of its damage or vulnerability. The hysteretic energy value wasted after the structure yields is the most important component of the energy equation that affects the structures system damage thereof. Controlling this value of energy leads to controlling the structure behavior. Here, for the first time, the hysteretic behavior and energy dissipation capacity are assessed at presence of elliptical braced resisting frames (ELBRFs), through an experimental study and numerical analysis of FEM. The ELBRFs are of lateral load systems, when located in the middle bay of the frame and connected properly to the beams and columns, in addition to improving the structural behavior, do not have the problem of architectural space in the bracing systems. The energy dissipation capacity is assessed in four frames of small single-story single-bay ELBRFs at ½ scale with different accessories, and compared with SMRF and X-bracing systems. The frames are analyzed through a nonlinear FEM and a quasi-static cyclic loading. The performance features here consist of hysteresis behavior, plasticity factor, energy dissipation, resistance and stiffness variation, shear strength and Von-Mises stress distribution. The test results indicate that the good behavior of the elliptical bracing resisting frame improves strength, stiffness, ductility and dissipated energy capacity in a significant manner.

Experimental and analytical study in determining the seismic performance of the ELBRF-E and ELBRF-B braced frames

Habib Ghasemi Jouneghani,Abbas Haghollahi 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.5

In this article the seismic demand and performance of two recent braced steel frames named steel moment frames with the elliptic bracing (ELBRFs) are assessed through a laboratory program and numerical analyses of FEM. Here, one of the specimens is without connecting bracket from the corner of the frame to the elliptic brace (ELBRF-E), while the other is with the connecting brackets (ELBRF-B). In both the elliptic braced moment resisting frames (ELBRFs), in addition to not having any opening space problem in the bracing systems when installed in the surrounding frames, they improve structure’s behavior. The experimental test is run on ½ scale single-story single-bay ELBRF specimens under cyclic quasi-static loading and compared with X-bracing and SMRF systems in one story base model. This system is of appropriate stiffness and a high ductility, with an increased response modification factor. Moreover, its energy dissipation is high. In the ELBRF bracing systems, there exists a great interval between relative deformation at the yield point and maximum relative deformation after entering the plastic region. In other words, the distance from the first plastic hinge to the collapse of the structure is fairly large. The experimental outcomes here, are in good agreement with the theoretical predictions.

Experimental study of failure mechanisms in elliptic-braced steel frame

Habib Ghasemi Jouneghani,Abbas Haghollahi,S. Bahram Beheshti-Aval 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.2

In this article, for the first time, the seismic behavior of elliptic-braced moment resisting frame (ELBRF) is assessed through a laboratory program and numerical analyses of FEM specifically focused on the development of global- and local-type failure mechanisms. The ELBRF as a new lateral braced system, when installed in the middle bay of the frames in the facade of a building, not only causes no problem to the opening space of the facade, but also improves the structural behavior. Quantitative and qualitative investigations were pursued to find out how elliptic braces would affect the failure mechanism of ELBRF structures exposed to seismic action as a nonlinear process. To this aim, an experimental test of a ½ scale single-story single-bay ELBRF specimen under cyclic quasi-static loading was run and the results were compared with those for X-bracing, knee-bracing, K-bracing, and diamond-bracing systems in a story base model. Nonlinear FEM analyses were carried out to evaluate failure mechanism, yield order of components, distribution of plasticity, degradation of structural nonlinear stiffness, distribution of internal forces, and energy dissipation capacity. The test results indicated that the yield of elliptic braces would delay the failure mode of adjacent elliptic columns and thus, help tolerate a significant nonlinear deformation to the point of ultimate failure. Symmetrical behavior, high energy absorption, appropriate stiffness, and high ductility in comparison with the conventional systems are some of the advantages of the proposed system.

Topology optimization of steel plate shear walls in the moment frames

Mohammad Hadi Bagherinejad,Abbas Haghollahi 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.6

In this paper, topology optimization (TO) is applied to find a new configuration for the perforated steel plate shear wall (PSPSW) based on the maximization of reaction forces as the objective function. An infill steel plate is introduced based on an experimental model for TO. The TO is conducted using the sensitivity analysis, the method of moving asymptotes and SIMP method. TO is done using a nonlinear analysis (geometry and material) considering the buckling. The final area of the optimized plate is equal to 50% of the infill plate. Three plate thicknesses and three length-to-height ratios are defined and their effects are investigated in the TO. It indicates the plate thickness has no significant impact on the optimization results. The nonlinear behavior of optimized plates under cyclic loading is studied and the strength, energy and fracture tendency of them are investigated. Also, four steel plates including infill plate, a plate with a central circle and two types of the multi-circle plate are introduced with equal plate volume for comparing with the results of the optimized plate.

Study on Topology Optimization of Perforated Steel Plate Shear Walls in Moment Frame Based on Strain Energy

Mohammad Hadi Bagherinejad,Abbas Haghollahi 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

Perforated steel plate shear walls (PSPSWs) are requested for passing the equipment and creating the accessing spaces. Also, the studies showed the PSPSWs enhance the ductility. In this paper, topology optimization (TO) is used to introduce a new form of the PSPSW in the moment frames based on the strain energy as the objective function. The TO is conducted using the sensitivity analysis, SIMP method and method of moving asymptotes. Four amounts of aspect ratio (0.67, 1.0, 1.5 and 2.0) and three plate thicknesses (2 mm, 4 mm and 8 mm) are defi ned in the TO and their eff ects are considered in the results. For a comprehensive study, the results of TO are compared with the three usual forms of PSPSW with circular holes and a previous optimized model. The material volume is equal for the plates with the identical aspect ratio and plate thickness. The cyclic behavior of all the models is investigated and compared in terms of strength, energy dissipation and fracture tendency. The analytic hierarchy process (AHP) is applied to score and determine the best model and form. The AHP method illustrated that the optimized models have a better performance. The results of the AHP method show that the optimized model in this study obtained 22.07% of the score from 100%, while the scores of the prior optimized model and three traditional models are 20.67%, 19.36%, 19.06% and 18.84%, respectively.

New form of perforated steel plate shear wall in simple frames using topology optimization

Mohammad Hadi Bagherinejad,Abbas Haghollahi 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.3

This study presents a practical application of topology optimization (TO) technique to seek the best form of perforated steel plate shear walls (PSPSW) in simple frames. For the numerical investigation, a finite element model is proposed based on the recent particular form of PSPSW that is called the ring-shaped steel plate shear wall. The TO is applied based on the sensitivity analysis to maximize the reaction forces as the objective function considering the fracture tendency. For this purpose, TO is conducted under a monotonic and cyclic loading considering the nonlinear behavior (material and geometry) and buckling. Also, the effect of plate thickness is studied on the TO results. The final material volume of the optimized plate is limited to the material volume of the ring-shaped plate. Finally, an optimized plate is introduced and its nonlinear behavior is investigated under a cyclic and monotonic loading. For a more comprehensive view, the results are compared to the ring-shaped and four usual forms of SPSWs. The material volume of the plate for all the models is the same. The results indicate the strength, load-carrying, and energy dissipation in the optimized plate are increased while the fracture tendency is reduced without changing the material volume.

Nonlinear seismic behavior of elliptic-braced moment resisting frame using equivalent braced frame

Habib Ghasemi Jouneghani,Abbas Haghollahi,Mohammad Talebi Kalaleh,S. Bahram Beheshti-Aval 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.1

Recently, the elliptic-braced moment resisting frame (ELBRF) which is a new lateral bracing system installed in the middle bay of the frame in the facade of buildings is introduced. This system not only prevents a solution for opening space problem in view of architectural aspects, but also improves the structural behavior. The main drawback of its using in view of numerical modeling in multistory buildings is lack of curved frame element in design and analysis software. To overcome this shortcoming, in this paper, for the first time, an equivalent element for elliptic brace is presented for ELBRF through a laboratory program and nonlinear finite element analysis, which will contribute to its accurate and easy modelling and design. To evaluate the hysteresis behavior of the equivalent element, an experimental test on a ½ scale was conducted for a single-story single-bay ELBRF specimen under cyclic quasi-static loading and the results were compared with those for the equivalent element in a story base model. Good agreement was observed between the experimental and analytical outcomes. The seismic demand analyses of ELBRF and frame with equivalent bracing system in 3, 5, 7, and 10 stories were carry out through different loading patterns in Nonlinear Static Pushover Analysis (NSPA) and Nonlinear Time History Analysis (NTHA) with 20 earthquake records using OpenSees software. Story drift, displacement, and story shear were evaluated. Relatively accurate estimations were achieved by NSPA in comparison with NTHA. Also, the seismic performance of the equivalent element for the ELBRF system against earthquake was examined and then response modification factor (R factor) was acquired. The values of 8.5 and 12.2 for the R factor were calculated at the ultimate and the allowable stress limit states, respectively.

Theoretical formulation for calculating elastic lateral stiffness in a simple steel frame equipped with elliptic brace

Habib Ghasemi Jouneghani,Nader Fanaie,Abbas Haghollahi 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.3

Elliptic-braced simple resisting frame as a new lateral bracing system installed in the middle bay of frame in building facades has been recently introduced. This system not only creates a problem for opening space from the architectural viewpoint but also improves the structural behavior. Despite the researches on the seismic performance of lateral bracing systems, there are few studies performed on the effect of the stiffness parameters on the elastic story drift and calculation of period in simple braced steel frames. To overcome this shortcoming, in this paper, for the first time, an analytical solution is presented for calculating elastic lateral stiffness in a simple steel frame equipped with elliptic brace subjected to lateral load. In addition, for the first time, in this study, a precise formulation has been developed to evaluate the elastic stiffness variation in a steel frame equipped with a two-dimensional single-story single-span elliptic brace using strain energy and Castigliano’s theorem. Thus, all the effective factors, including axial and shear loads as well as bending moments of elliptic brace could be considered. At the end of the analysis, the lateral stiffness can be calculated by an improved and innovative relation through the energy method based on the geometrical properties of the employed sections and specification of the used material. Also, an equivalent element of an elliptic brace was presented for the ease of modeling and use in linear designs. Application of the proposed relation have been verified through a variety of examples in OpenSees software. Based on the results, the error percentage between the elastic stiffness derived from the developed equations and the numerical analyses of finite element models was very low and negligible.