• Advances in concrete construction
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• v.13 no.4
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• pp.339-347
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• 2022

Retrofitting in reinforced concrete structures has been one of the most important research topics in recent years. There are several methods for retrofitting RC moment-resisting frames. the most important of which is the use of steel bracing systems with yielding dampers. With a proper design of yielding dampers, the stiffness of RC frame systems can be increased to the required extent so that the ductility of the structure is not significantly reduced. In the present study, two experimental samples of a one-third scale RC moment-resisting frame were loaded in the laboratory. In these experiments, the retrofitting effect of RC frames was investigated using Non-uniform Slit Dampers (NSDs). Based on the experimental results of the samples, seismic parameters, i.e., stiffness, ductility, ultimate strength, strength reduction coefficient, and energy dissipation capacity, were compared. The results demonstrated that the retrofitted frame had very significant growth in terms of stiffness, ultimate strength, and energy dissipation capacity. Although the strength reduction factor and ductility decreased in the retrofitted sample. In general, the behavior of the frame with NSDs was evaluated better than the bare frame.

• Steel and Composite Structures
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• v.43 no.5
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• pp.565-579
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• 2022

This study investigated the yielding capacity and performance of seismic dampers constructed with steel ring plates using numerical and analytical approaches. This study aims to provide an analytical relationship for estimating the yielding capacity and initial stiffness of steel ring dampers. Using plastic analysis and considering the mechanism of plastic hinge formation, a relation has been obtained for estimating the yielding capacity of steel ring dampers. Extensive parametric studies have been carried out using a nonlinear finite element method to examine the accuracy of the obtained analytical relationships. The parametric studies include investigating the influence of the length, thickness, and diameter of the ring of steel ring dampers. To this end, comprehensive verification studies are performed by comparing the numerical predictions with several reported experimental results to demonstrate the numerical method's reliability and accuracy. Comparison is made between the hysteresis curves, and failure modes predicted numerically or obtained/observed experimentally. Good agreement is observed between the numerical simulations and the analytical predictions for the yielding force and initial stiffness. The difference between the numerical models' ultimate tensile and compressive capacities was observed that average of about 22%, which stems from the performance of the ring-dampers in the tensile and compression zones. The results show that the steel ring-dampers are exhibited high energy dissipation capacity and ductility. The ductility parameters for steel ring-damper between values were 7.5 to 4.1.

• Earthquakes and Structures
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• v.1 no.3
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• pp.307-326
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• 2010

This paper is concerned with the optimal seismic design of added viscous dampers in yielding plane frames. The total added damping is minimized for allowable values of local performance indices under the excitation of an ensemble of ground motions in both regular and irregular structures. The local performance indices are taken as the maximal inter-story drift of each story and/or the normalized hysteretic energy dissipated at each of the plastic hinges. Gradients of the constraints with respect to the design variables (damping coefficients) are derived, via optimal control theory, to enable an efficient first order optimization scheme to be used for the solution of the problem. An example of a ten story three bay frame is presented. This example reveals the following 'fully stressed characteristics' of the optimal solution: damping is assigned only to stories for which the local performance index has reached the allowable value. This may enable the application of efficient and practical analysis/redesign type methods for the optimal design of viscous dampers in yielding plane frames.

• Smart Structures and Systems
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• v.23 no.4
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• pp.329-335
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• 2019

Structural fuses are made up from oriented steel plates to be used to resist seismic force with shear loading resistance capabilities. The damage and excessive inelastic deformations are concentrated in structural fuses to avoid any issues for the rest of the surrounding elements. Recently developed fuse plates are designed with engineered cutouts leaving flexural or shear links with controlled yielding features. A promising type of link is proposed to align better bending strength along the length of the link with the demand moment diagram is a butterfly-shaped link. Previously, the design methodologies are purely based on the flexural stresses, or shear stresses only, which overestimate the dampers capability for resisting against the applied loadings. This study is specifically focused on the optimized design methodologies for commonly used butterfly-shaped dampers. Numerous studies have shown that the stresses are not uniformly distributed along the length of the dampers; hence, the design methodology and the effective implementation of the steel need revisions and improvements. In this study, the effect of shear and flexural stresses on the behavior of butterfly-shaped links are computationally investigated. The mathematical models based on von-Mises yielding criteria are initially developed and the optimized design methodology is proposed based on the yielding criterion. The optimized design is refined and investigated with the aid of computational investigations in the next step. The proposed design methodology meets the needs of optimized design concepts for butterfly-shaped dampers considering the uniform stress distribution and efficient use of steel.

• Earthquakes and Structures
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• v.14 no.1
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• pp.1-10
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• 2018

Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.381-388
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• 2001

Behavior characteristics of coil shaped elastoplastic dampers, a sort of hysteretic damper, are studied on through experiments and numerical analyses. The coil shaped elastoplastic damper shows bilinear force-deformation relationship, and no stress concentration is occurred in the device. Numerical model, which is constructed through calibration with experimental results, shows good agreement with experiment, The coil shaped elastoplastic damper has lower yielding strength and stiffness under transversal loading compared to axial leading. Additional studies are required on behavior characteristics according to configuration variation of coil shaped elastoplastic dampers.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1499-1528
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• 2015

The yielding mechanisms of reinforced concrete (RC) structures are the main cause of the collapse of RC buildings during earthquake excitation. Nowadays, the application of earthquake energy dissipation devices, such as viscous dampers (VDs), is being widely considered to protect RC structures which are designed to withstand severe seismic loads. However, the effect of VDs on the formation of plastic hinges and the yielding criteria of RC members has not been investigated extensively, due to the lack of an analytical model and a numerical means to evaluate the seismic response of structures. Therefore, this paper offers a comprehensive investigation of how damper devices influence the yielding mechanisms of RC buildings subjected to seismic excitation. For this purpose, adapting the Newmark method, a finite element algorithm was developed for the nonlinear dynamic analysis of reinforced concrete buildings equipped with VDs that are subjected to earthquake. A special finite element computer program was codified based on the developed algorithm. Finally, a parametric study was conducted for a three-story RC building equipped with supplementary VD devices, performing a nonlinear analysis in order to evaluate its effect on seismic damage and on the response of the structure. The results of this study showed that implementing VDs substantially changes the mechanism and formation of plastic hinges in RC buildings.

• Steel and Composite Structures
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• v.30 no.4
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• pp.383-392
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• 2019

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.

• Earthquakes and Structures
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• v.19 no.3
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• pp.215-226
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• 2020

A self-centering wall (SCW) is a lateral resistant rocking system that incorporates posttensioned (PT) tendons to provide a self-centering capacity along with dampers to dissipate energy. This paper investigates the rocking responses of a SCW with base viscous dampers under a sinusoidal-type pulse considering yielding and fracture behaviour of the PT tendon. The differences in the overturning acceleration caused by different initial forces in the PT tendon are computed by the theoretical method. The exact analytical solution to the linear approximate equation of motion is also provided for slender SCWs. Finally, the effects of the ductile behaviour of PT tendons on the rocking response of a SCW are analysed. The results demonstrate that SCWs exhibit two overturning modes under pulse excitation. The overturning region with Mode 1 in the PT force cases separates the safe region of the wall into two parts: region S1 with an elastic tendon and region S2 with a fractured tendon. The minimum overturning acceleration of a SCW with an elastic-brittle tendon becomes insensitive to excitation frequency as the PT force increases. After the plastic behaviour of the PT tendon is considered, the minimum overturning acceleration of a SCW is increased significantly in the whole range of the studied w_g/p.

• Smart Structures and Systems
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• v.21 no.3
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• pp.359-371
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• 2018

Strong seismic events commonly cause large drift and deformation, and functionality failures in the superstructures. One way to prevent functionality failures is to design structures which are ductile and flexible through yielding when subjected to strong ground excitations. By developing forces that assist motion as "negative stiffness forces", yielding can be achieved. In this paper, we adopt the weakening and damping method to achieve a new approach to reduce all of the structural responses by further adjusting damping phase. A semi-active control system is adopted to perform the experiments. In this adaptation, negative stiffness forces through certain devices are used in weakening phase to reduce structural strength. Magneto-rheological (MR) dampers are then added to preserve stability of the structure. To adjust the voltage in MR dampers, an inverse model is employed in the control system to command MR dampers and generate the desired control forces, where a velocity control algorithm produces initial required control force. An extensive numerical study is conducted to evaluate proposed methodology by using the smart base-isolated benchmark building. Totally, nine control systems are examined to study proposed strategy. Based on the numerical results of seven earthquakes, the use of proposed strategy not only reduces base displacements, base accelerations and base shear but also leads to reduction of accelerations and inter story drifts of the superstructure. Numerical results shows that the usage of inverse model produces the desired regulated damping, thus improving the stability of the structure.