A proposal for improving the behavior of CBF braces using an innovative flexural mechanism damper, an experimental and numerical study

Ali Ghamari,Seong‐Hoon Jeong 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.3

Despite the considerable lateral stiffness and strength of the Concentrically Braced Frame (CBF), it suffers from low ductility and low seismic dissipating energy capacity. The buckling of the diagonal members of the CBF systems under cyclic loading ended up to the shortcoming against seismic loading. Comprehensive researches have been performing to achieve helpful approaches to prevent the buckling of the diagonal member. Among the recommended ideas, metallic damper revealed a better success than other ideas to enhance the behavior of CBFs. While metallic dampers improve the behavior of the CBF system, they increase constructional costs. Therefore, in this paper, a new steel damper with flexural mechanism is proposed, which is investigated experimentally and numerically. Also, a parametrical revision was carried out to evaluate the effect of thickness, slenderness ratio, angle of the main plate, and height of the main plates on the proposed damper. For the parametrical study, 45 finite element models were analyzed and considered. Experimental results, as well as the numerical results, indicated that the proposed damper enjoys a stable hysteresis loop without any degradation up to a high rotation equal to around 31% that is significantly considerable. Moreover, it showed a suitable performance in case of ductility and energy dissipating. Besides, the necessary formulas to design the damper, the required relations were proposed to design the elements outside the damper to ensure the damper acts as a ductile fuse.

Improving the hysteretic behavior of Concentrically Braced Frame (CBF) by a proposed shear damper

Ali Ghamari,Hadi Haeri,Alireza Khaloo,Zheming Zhu 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.30 No.4

Passive steel dampers have shown favorable performance in last earthquakes, numerical and experimental studies. Although steel dampers are more affordable than other types of damper, they are not economically justified for ordinary buildings. Therefore, in this paper, an innovative steel damper with shear yielding mechanism is introduced, which is easy to fabricate also can be easily replaced after sever earthquakes. The main goal of implementing such a mechanism is to control the possible damage in the damper and to ensure the elastic behavior of other structural components. The numerical results indicate an enhancement of the hysteretic behavior of the concentrically braced frames utilizing the proposed damper. The proposed damper change brittle behavior of brace due to buckling to ductile behavior due to shear yielding in proposed damper. The necessary relations for the design of this damper have been presented. In addition, a model has been presented to estimate load-displacement of the damper without needing to finite element modeling.

Experimental investigating the properties of fiber reinforced concrete by combining different fibers

Ali Ghamari,Javad Kurdi,Alireza Bagher Shemirani,Hadi Haeri 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.25 No.6

Adding fibers improves concrete performance in respect of strength and plasticity. There are numerous fibers for use in concrete that have different mechanical properties, and their combination in concrete changes its behavior. So, to investigate the behavior of the fiber reinforced concrete, an in vitro study was conducted on concrete with different fiber compositions including different ratios of steel, polypropylene and glass fibers with the volume of 1%. Two forms of fibers including singlestranded and aggregated fibers have been used for testing, and the specimens were tested for compressive strength and dividable tensile strength (splitting tensile) to determine the optimal ratio of the composition of fibers in the concrete reinforced by hybrid fibers. The results show that the concrete with a composition of steel fibers has a better performance than other compounds. In addition, by adding glass and propylene fibers to the composition of steel fibers, the strength of the samples is reduced. Also, if using the combination of fibers is required, the use of a combination of glass fibers with steel fibers will provide a better compressive strength and tensile strength than the combination of steel fibers with propylene.

An Innovative shear link as damper: an experimental and numerical study

Ali Ghamari,Young-Ju Kim,Jaehoon Bae 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.4

Concentrically braced frames (CBFs) possess high stiffness and strength against lateral loads; however, they suffer from low energy absorption capacity against seismic loads due to the susceptibility of CBF diagonal elements to bucking under compression loading. To address this problem, in this study, an innovative damper was proposed and investigated experimentally and numerically. The proposed damper comprises main plates and includes a flange plate angled at θ and a trapezius-shaped web plate surrounded by the plate at the top and bottom sections. To investigate the damper behaviour, dampers with θ = 0°, 30°, 45°, 60°, and 90° were evaluated with different flange plate thicknesses of 10, 15, 20, 25 and 30 mm. Dampers with θ = 0° and 90° create rectangular-shaped and I-shaped shear links, respectively. The results indicate that the damper with θ = 30° exhibits better performance in terms of ultimate strength, stiffness, overstrength, and distribution stress over the damper as compared to dampers with other angles. The hysteresis curves of the dampers confirm that the proposed damper acts as a ductile fuse. Furthermore, the web and flange plates contribute to the shear resistance, with the flange carrying approximately 80% and 10% of the shear force for dampers with θ = 30° and 90°, respectively. Moreover, dampers that have a larger flange-plate shear strength than the shear strength of the web exhibit behaviours in linear and nonlinear zones. In addition, the over-strength obtained for the damper was greater than 1.5 (proposed by AISC for shear links). Relevant relationships are determined to predict and design the damper and the elements outside it.

Seismic Behavior of an Innovative Four-Layer Steel Shear Wall

Alireza Abbaszadeh,Ali Ghamari,Vahid Broujerdian 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.11

The steel shear wall has been introduced as a system with high stiffness and strength and a considerable capability in absorbing seismic energy. Due to its special advantages compared to other lateral load-resistant systems, this system is being used in tall buildings more and more frequently. Ductility and energy absorption are important parameters to be considered when choosing a robust lateral load-resistant system. By increasing the ductility and energy absorption of the structures, their seismic performance and safety are improved. Ideally, a structural system should provide both ductility and energy absorption in an economic way. This study presents the numerical simulation of the seismic behavior of a recently developed four-layer steel shear wall composed of corrugated and flat sheets. The simulations were performed using finite element software ABAQUS. Nonlinear static analysis was used to derive seismic parameters. The results showed that the corrugated sheets surrounded by flat sheets provide greater seismic parameters such as ductility and over-strength compared to double corrugated walls. According to the results, the calculated R-factor, displacement amplification factor, and the overstrength factor of the proposed wall were 4.58, 8.21, and 1.26, respectively. Furthermore, to use the seismic parameters of the shear wall, some relationships have been presented for incremental strength and stiffness coefficients without the need for finite element modeling. Compared to the finite element results, the presented relations had good accuracy.

Experimental and numerical study of a steel plate-based damper for improving the behavior of concentrically braced frames

Denise-Penelope N. Kontoni,Ali Ghamari,Chanachai Thongchom 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.47 No.2

Despite the high lateral stiffness and strength of the Concentrically Braced Frame (CBF), due to the buckling of its diagonal members, it is not a suitable system in high seismic regions. Among the offered methods to overcome the shortcoming, utilizing a metallic damper is considered as an appropriate idea to enhance the behavior of Concentrically Braced Frames (CBFs). Therefore, in this paper, an innovative steel damper is proposed, which is investigated experimentally and numerically. Moreover, a parametrical study was carried out to evaluate the effect of the mechanism (shear, shear-flexural, and flexural) considering buckling mode (elastic, inelastic, and plastic) on the behavior of the damper. Besides, the necessary formulas based on the parametrical study were presented to predict the behavior of the damper that they showed good agreement with finite element (FE) results. Both experimental and numerical results confirmed that dampers with the shear mechanism in all buckling modes have a better performance than other dampers. Accordingly, the FE results indicated that the shear damper has greater ultimate strength than the flexural damper by 32%, 31%, and 56%, respectively, for plates with elastic, inelastic, and plastic buckling modes. Also, the shear damper has a greater stiffness than the flexural damper by 43%, 26%, and 53%, respectively, for dampers with elastic, inelastic, and plastic buckling modes.

Improving the seismic behavior of diagonal braces by developing a new combined slit damper and shape memory alloys

Farzad Vafadar,Vahid Broujerdian,Ali Ghamari 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.82 No.1

The bracing members capable of active control against seismic loads to reduce earthquake damage have been widely utilized in construction projects. Effectively reducing the structural damage caused by earthquake events, bracing systems equipped with retrofitting damper devices, which take advantage of the energy dissipation and impact absorption, have been widely used in practical construction sites. Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. In this research, a new system in diagonal braces with slit damper combined with SMA is investigated. The diagonal element under the effect of tensile and compressive force turns to shear force in the slit damper and creates tension in the SMA. Therefore, by creating shear forces in the damper, it leads to yield and increases the energy absorption capacity of the system. The purpose of using SMA, in addition to increasing the stiffness and strength of the system, is to create reversibility for the system. According to the results, the highest capacity is related to the case where the ratio of the width of the middle section to the width of the end section (b1/b) is 1.0 and the ratio of the height of the middle part to the total height of the damper (h1/h) is 0.1. This is mainly because in this case, the damper section has the highest cross-section. In contrast, the lowest capacity is related to the case where b1/b=0.1 and the ratio h1/h=0.8.