Metallic Dampers Research Articles

Experimental Study on Mechanical Properties of Shear Square Section Steel Tube Dampers

Based on the excellent performance of shear metal dampers in building seismic capacity, the traditional shear metal damper was optimized. A double-sided shear steel tube damper with simple structure, easy replacement, and wide application is proposed. In order to study the influence of different design parameters on its seismic performance, taking the steel tube length, height, width, thickness, and connection mode as variables, five groups of 15 specimens were designed for experimental research, and the failure modes, characteristic loads and displacements, hysteretic curves, skeleton curves, stiffness degradation curves, and energy dissipation capacity of each specimen were analyzed in detail. The test results showed that the hysteretic curves of each specimen were full and that the energy dissipation capacity was good. The greater the thickness of the steel tube was, the greater the load-bearing capacity of the damper and the larger the hysteresis loop area were. The greater the width of the steel tube was, the greater the equivalent stiffness was. As displacement amplitude increased, the equivalent stiffness of the specimen showed a downward trend. The two connection modes had their own advantages and disadvantages, and a damper with reasonable connection form would need to be selected according to actual engineering needs.

Development of a four-tube-assembled buckling-restrained brace for convenient post-earthquake damage examination and replacement

As a high-performance metallic damper, buckling-restrained braces (BRBs) have been widely employed in building structures to absorb the seismic input energy, resulting in mitigating the damage of main structural components. However, the restraining members of BRBs pose quite a challenge to the post-earthquake damage examination of inner core plates. In this study, a four-tube-assembled buckling-restrained brace (FTA-BRB) was proposed for the convenient post-earthquake damage examination and replacement. The restraining members of FTA-BRBs consist of four steel square tubes and U-shaped restraining hoops, which can be easily and rapidly assembled and disassembled using high-strength bolts. Cyclic tests of four specimens were conducted to gain insights into the seismic behavior of the FTA-BRB. Test results demonstrated that the proposed FTA-BRBs exhibited full and plump hysteretic loops. The restraining hoops failed and the core plate fractured under high strain amplitudes. No local buckling occurred at the steel square tubes during the testing, and thus the restraining elements can be reused resulting from a reduction of repair expenses. Moreover, the numerical model was constructed and verified by the test results. The effects on the hysteretic behaviors and failure modes of the number of restraining hoops were investigated. The contributions of this study can provide a reference for the application of BRBs in engineering structures.

Development of an innovative metallic damper for concentrically braced frame systems based on experimental and analytical studies

SummaryAlthough concentrically braced frames (CBFs) possess high lateral stiffness and strength, the buckling of compressive members indicates that a system does not have appropriate ductility. Therefore, CBF is not a successful system for high seismic regions. Comprehensive studies have been performed on this drawback concerning CBF systems. The use of a metallic damper is considered an appropriate method to enhance the behavior of CBFs. While metallic dampers improve the hysteretic behavior of the CBF, they impose additional costs on the structures. Therefore, in this study, a steel damper, which is economical and straightforward to construct and replace after a severe earthquake, was developed. The proposed damper was investigated experimentally and numerically. In addition, a parametric study was performed to evaluate the effect of the three types of damper mechanisms (shear, shear‐flexural, and flexural) with three types of buckling (elastic, inelastic, and plastic) on the behavior of the proposed damper. The experimental results, as well as the numerical results, indicate that the shear damper exhibits better performance than the other dampers in terms of strength and stiffness. Except in the case where the shear damper is accompanied by plastic buckling, it has a higher energy dissipation capability. In addition, a flexural damper with elastic buckling cannot be considered as an energy‐dissipating device because of the fracturing of the damper due to displacement near the elastic zone. Fundamental relationships were used to predict the behavior of these dampers, and these predictions showed good agreement with the finite element results.

Seismic performance of combined rotational friction and flexural yielding metallic dampers

A feature of designing combined rotational friction and flexural yielding metallic dampers, which could be used for prefabricated structures, was presented. The proposed dampers were composed of two energy dissipation systems with the friction damper (FD) by achieving rotational friction and metallic damper (MD) by yielding in flexure. To investigate the seismic performance of the proposed FD-MD connection, low cyclic experiments of rotational friction damper specimen and proposed FD-MD connection specimen were put forward. According to the experimental results, behaviors in hysteretic curves validated that they possessed excellent comprehensive performance of friction and plastic energy-dissipating ability. Consequently, the proposed FD-MD connection was capable of providing an alternative for precast structures in high seismic regions.

Optimization of the Curved Metal Damper to Improve Structural Energy Dissipation Capacity

Structural curved metal dampers are implemented in various applications to mitigate the damages at a specific area efficiently. A stable and saturated hysteretic behavior for the in-plane direction is dependent on the shape of a curved-shaped damper. However, it has been experimentally shown that the hysteretic behavior in the conventional curved-shaped damper is unstable, mainly as a result of bi-directional deformations. Therefore, it is necessary to conduct shape optimization for curved dampers to enhance their hysteretic behavior and energy dissipation capability. In this study, the finite element (FE) model built in ABAQUS, is utilized to obtain optimal shape for the curved-shaped damper. The effectiveness of the model is checked by comparisons of the FE model and experimental results. The parameters for the optimization include the curved length and shape of the damper, and the improved approach is conducted by investigating the curved sections. In addition, the design parameters are represented by B-spline curves (to ensure enhanced system performance), regression analysis is implemented to derive optimization formulations considering energy dissipation, constitutive material model, and cumulative plastic strain. Results determine that the energy dissipation capacity of the curved steel damper could be improved by 32% using shape optimization techniques compared to the conventional dampers. Ultimately, the study proposes simple optimal shapes for further implementations in practical designs.

Characterization of energy dissipative cushions made of Ni–Ti shape memory alloy

Earthquake-resistant design of structures requires dissipating seismic energy by deformations of structural members or additional fuse elements. Owing to its easy-to-produce, plug-and-play, high equivalent damping ratio, and large displacement capacity characteristics, energy dissipative steel cushions (SCs) were found to be an efficient candidate for this purpose. However, similar to other conventional metallic dampers, residual displacement after a strong shaking is the most notable drawback of the SCs. In this work, cushions produced from Ni–Ti shape memory alloy (SMA) are evaluated numerically by experimentally verified finite element models to assess their impact on the performance of earthquake-resistant structures. Furthermore, a reinforced concrete testing frame is retrofitted with energy dissipative steel and Ni–Ti cushions. Performance of the frames (e.g. dissipated energy by the cushions, hysteretic energy to input energy ratio, maximum drift, and residual drift) with different types of cushions are evaluated by nonlinear response history analyses. The numerical results showed that the SCs are effective to reduce peak responses, while Ni–Ti cushions are more favorable to reduce residual drifts and deformations. Hence, a hybrid system, employing the steel and SMA cushions together, is proposed to reach optimal seismic performance.

Pounding mitigation of a short-span cable-stayed bridge using a new hybrid passive control system

This paper investigates the effectiveness of a new hybrid passive control system on the seismic response of an existing steel cable-stayed bridge considering the pounding effect. The proposed hybrid passive control system comprises a seismic isolator and a metallic damper. The bridge is located in a high seismic zone and has suffered several damages including the earthquake-induced pounding damage during the 1988 earthquake. Thereby, the proposed hybrid passive control system was investigated for seismic retrofitting of the bridge to mitigate the seismic damages due to future earthquakes. The hybrid control system was placed at the bridge ends and the tower–deck connection. A detailed three-dimensional finite element model of the bridge was created and validated with the earlier experimental results. A comparative analysis was performed through a series of nonlinear dynamic time-history analyses on the bridge equipped with the proposed and other control systems. The results showed that the hybrid control system reduced the bridge’s longitudinal seismic displacement, mitigated the pounding of the bridge with abutments and improved the overall seismic performance of the bridge.

Shaking table test and simulation of 12-story buildings with metallic dampers located on soft soil

In this study, shaking table tests are carried out on 12-story reinforced concrete frames with metallic dampers located on soft site, and the corresponding fixed-base structures with metallic dampers are also proposed for comparison. The superstructure is connected with the 3-by-3 pile foundation by the pile cap in a designed shear laminar container, which exhibits a good ability of reducing the boundary effect. Three earthquake inputs, which include one artificial earthquake (Shanghai bedrock wave) and two recorded Kobe and Chi-Chi earthquakes with various peak ground accelerations (PGAs) are used in the shaking table test. A series of investigation are carried out on the test phenomenal, which consist of dynamic characteristics of the models, seismic analysis of the soil, and also the working mechanism of pile-soil-structure interaction (PSSI). Then, the hysteretic behavior and aseismic performance of metallic dampers in the PSSI system and fixed-base condition are compared. Finally, a nonlinear three-dimensional finite element model is built to establish a proper numerical method for the PSSI system with metallic dampers. The experimental and simulation results indicate that the PSSI system has longer periods, larger damping ratio and less decreasing degree of frequency after tests than the fixed-base condition. Meanwhile, under these earthquakes, PSSI tends to reduce the structural peak acceleration, story shear force and the elastic displacement. However, the total deformation of the superstructure is amplified significantly due to the rocking and translational deformation in PSSI system. Moreover, the hysteretic performance of the metallic dampers are degraded greatly by PSSI effect. Therefore, the PSSI effect should be considered in the design of tall buildings with metallic dampers, because the seismic analysis of the structure may be unrealistic and the performance of the metallic dampers may be overrated when it is ignored.

Cyclic behaviour of a novel torsional steel-tube damper

A novel metallic damper with torsional-yielding on the circular steel tube, called torsional steel-tube damper (TSTD), is proposed in this paper. Four specimens are designed for testing under cyclic loading to investigate their cyclic behaviour. The torsional-yielding mechanism contributes to the uniform yielding at the tube wall, results in an outstanding hysteretic performance and a high equivalent viscous damping ratio of about 0.5. Then the finite element analysis method is used for simulating the tested specimens, and the stress, strain, and parametric influence of the damper model are analyzed. Furthermore, a modified Bouc-Wen model is proposed to describe the cyclic behaviour of the tested specimens. The particle swarm optimization algorithm is used for identifying the model parameters. The identification results indicate that the modified Bouc-Wen model can accurately predict the hysteretic behaviour of the proposed damper. Finally, the proposed damper is implemented in a reinforced concrete frame model, and the nonlinear dynamic analysis method is adopted to assess the feasibility of the damper.

Analysis on the optimal damper quantity of energy dissipation structure

In practical application, the design of energy dissipation usually adopts the concept design, that is, to estimate damper quantity by repeating calculation. However, few studies have quantitatively analyzed the energy dissipation structure. This paper proposed two analysis methods to analysis the damper quantity of energy dissipation structure, the multiple-yield-strength method, and the damping-performance-curve method. Both of them can calculate the optimal damping quantity of the structure by adding metal dampers. The multiple-yield-strength method refers to that the yield strength of the metal damper is set by the multiple of the yield strength of the original structure. The optimal damper quantity of metal dampers can be analyzed by time history analysis. The damping-performance-curve method refers to that the target story displacement of the original structure is set. According to the relationship between the target displacement and the shear force in the damping-performance-curve, the stiffness of the original structure to achieve the target story displacement angle is derived, the stiffness is taken as the optimal damping of the metal damper. The optimal damping quantity is added to the original structure for comparative study which is calculated by the two methods. Both of them have reference value, and it could be beneficial for the promotion of energy dissipation.

Seismic performance of a new S-shaped mild steel damper with varied yielding cross-sections

In this paper, a novel replaceable metallic energy dissipation device named S-shaped mild steel damper with varied yielding cross-sections (VYSSD) is proposed. The VYSSD mainly consists of consumption plate, outer limit plates and fixed bottom plate, in which the consumption plate is the energy dissipation element and can be easily replaced after earthquakes. Under action of external loads, section curvature of each segment of the consumption plate changes and the sections gradually enter yielding state to dissipate energy through flexural plasticity. A total of 18 VYSSD specimens were cyclically tested under quasi-static and fatigue loads to investigate the hysteretic behavior and seismic performance. The results show that the VYSSD has pump hysteretic loops, good low cycle fatigue performance and desirable displacement capacity. It is capable of avoiding plastic deformation concentration of traditional metallic dampers, and the failure mode is dominated by fatigue crack propagation. Moreover, a solid finite element model which can effectively simulate the hysteretic behavior and plasticity development of VYSSD was built, and the practical design formulas were suggested through parametric studies considering different geometric dimensions. Finally, a representative 20-story benchmark model was employed for seismic resilient application of the VYSSD. The structures with and without damper retrofitting were numerically modelled for conducting nonlinear dynamic analysis and seismic fragility analysis. The analyses illustrate that the VYSSD can significantly enhance the structural seismic performance, and exceedance probabilities of damage, demolition and collapse for the damper-fused structure are much lower than that of the original structure.

An innovative C-shaped yielding metallic dampers for steel structures

This paper proposed a new passive metallic damper, termed C-Shaped Damper (CSD), for a braced frame structure. The proposed system dissipates the earthquake energy using some sacrificial C-Shaped elements and protects the main elements of structures from plastic deformation and failure. This study investigated energy dissipation and behavior of CSD through numerical and analytical methods. For this purpose, parametric investigations were carried out analytically and numerically. Parametric studies considered the effect of vertical and horizontal diameters of CSD, thickness, and depth of the CSD on its behavior. A good agreement was observed between analytical and numerical results. The numerical results demonstrate that the yielding force was directly related to the thickness and depth of the CSD. Also, by the increasing horizontal diameter, yielding force and energy dissipation decreased. The results indicated suitable energy dissipation and steady hysteretic behavior of the CSD under cyclic loading with a salient characteristic such as being easily replaceable after failure.

Research on seismic behavior of unbonded post-tensioned concrete wall with vertical energy-dissipating connections

An unbonded post-tensioned (PT) concrete wall system with vertical energy-dissipating connections (UPTW-VEC) is proposed that consists of precast wall panels, several X-shaped metal dampers (XMD), mild steel energy-dissipating bars (ED bars) and PT tendons. In this wall system, the precast wall panels are assembled through XMDs along the vertical joints and ED bars along the horizonal joints to provide the energy-dissipating capacity. The PT tendons installed at the wall toes are used to provide the self-centering capacity. In addition, each wall toe is protected by a steel jacket from the concrete corners spalling or crushing. Firstly, the hysteretic behavior of XMD was studied experimentally. Then, the seismic behavior of the unbonded post-tensioning concrete wall with different parameters were investigated experimentally based on four specimens. It was shown that the wall panels were resilient after tests and the cracks were only observed near the embedded plate in wall panels. In addition, a simplified analysis method was proposed, and the theoretical results matched well with the experimental results. Finally, the finite element analysis (FEA) model of UPTW-VEC was established. Following validating through the experimental results, a parametric study was conducted to investigate the influence of critical parameters on the seismic behavior of UPTW-VEC.

Seismic performance study on critically damaged masonry piers retrofitted using shear-compressive metal dampers

To realize the rapid repair of severely damaged masonry piers after an earthquake, an innovative type of replaceable metallic yielding device with buckling restrained core plates was conceived and studied. The new devices refer to the alternative shear-compressive metal dampers (SCMDs) that were designed as a replacement for damaged masonry piers. By replacing piers with SCMDs, actions and deformations of the retrofitted walls were easier to be absorbed by the SCMDs. To validate the new repair method, two comparative quasi-static tests of multi-story masonry models were performed before and after retrofitting, and a series of in-plane seismic behaviors, including hysteretic behavior, skeleton curve, stiffness degradation, ductility, and energy dissipation, of test walls were analyzed comparatively. According to the test results, it can be observed that the designed SCMDs had stable working performance, significant energy dissipation, and sufficient deformability throughout the loading process. Moreover, the designed SCMDs improved the seismic capacity of the repaired masonry wall effectively. The ductility of the retrofitted wall improved significantly and the ductility coefficient increased from 2.88 to 3.02. Furthermore, the energy dissipation behavior of the retrofitted wall enhanced substantially in the ultimate and failure stages with the energy dissipation increasing by 30.96% and 31.10% compared to that of the original wall, respectively.

Proposing a butterfly-liked metallic damper for passive energy dissipation in structures

A novel energy dissipating device, a butterfly-liked metallic damper (BLMD), is proposed in this paper. The main features of the proposed damper with low fabrication cost are easily assembled and replaced in various damper brace configuration systems, such as toggle brace damper system (TBDS) and diagonal brace damper system (DBDS). A series of experiments for identifying the hysteretic behaviour of BLMDs was conducted. Experimental results showed that a BLMD with a superior hysteretic curve had acceptable ductility and energy dissipation behaviours under quasi-static cyclic loading. In addition, BLMDs were installed in different brace systems in sixteen-story concrete frame structures, and the dynamic responses of the buildings to seismic excitations were compared and analysed. The results indicate that this BLMD provides superior vibration control and can significantly improve seismic performance of structures during strong earthquakes.

Probability Distribution of ADAS Metal Dampers in R.C. Buildings Using Nonlinear Analysis

This study discusses the effect of metallic yielding dampers (ADAS) on the behavior of reinforcement concrete buildings when exposed to seismic shocks. The objective of the study is to reduce the negative impacts on the main structural elements (plastic, fall) by using the technique of metallic dampers. The method of metallic dampers is one of the modern ways based on the principle of dissipating the resulting energy from the seismic shock and reducing the needed energy in the main structural elements of the building to keep it in a flexible state. This technique also provides a controlling mechanism for story displacement, the handling of the soft story mechanic and the torsion mechanic of the buildings. In this study, the effect of the addition of ADAS dampers on the construction behavior was observed in terms of (building period, base shear, roof displacement, roof acceleration, story displacement, dissipative energy). Based on the preceding, this study will give the possibility of predicting the behavior of the building when using ADAS metal dampers in the reinforced concrete structures with their distribution methods.

Finite Element Analysis to Determine Stiffness, Strength, and Energy Dissipation of U-Shaped Steel Damper under Quasi-Static Loading

In seismic areas, the application of structural dampers becomes compulsory in the design of buildings. There are various types of dampers, such as viscous elastic dampers, viscous fluid dampers, friction dampers, tune mass dampers, yielding/ metallic dampers, and magnetic dampers. All damper systems are designed to protect structural integrities, control damages, prevent injuries by absorbing earthquake energy, and reduce deformation. This paper is a part of research investigating the behaviour of the U-shaped steel damper (as one type of metallic damper) that can be applied to the buildings in seismic areas. The dampers are used as connections between the roof and supporting structure, with the two general purposes. The first is to control the displacement of roof under an earthquake, and the second is to absorb seismic energy through the plasticity of some parts in dampers. If a strong earthquake occurs, the plasticity will absorb the seismic energy; therefore, heavy damage could be avoided from the roof’s mainframes. In this paper, several models of U-shaped steel dampers are introduced. Several parameters, such as elastic stiffness, maximum strength, and energy dissipation, are determined under two conditions. Firstly, static analysis of the proposed damper under variation of U-steel plate configurations, searching the model with more significant energy dissipation. Secondly, static analysis of the unsymmetrical and symmetrical damper under different loading directions. An in-house finite element program that involves both geometrical and material nonlinearities is developed as a problem solver. A quasi-static lateral loading is given to each model until one cycle of the hysteresis curve is reached (in the displacement range between -20 mm to +20 mm). The above parameters are calculated from the hysteresis curve. From the results, the behaviour of the U-steel damper can be described as follows. Firstly, increasing the energy dissipation in the lateral direction can be done by increasing the lateral stiffness of the damper. However, it can reduce the maximum elastic deformation of the damper. Secondly, under the random direction of loading, a symmetrical shape can increase the energy dissipation of the damper.

Improving the seismic performance of reinforced concrete frames using an innovative metallic-shear damper

In reinforced concrete (RC) frames, the applied seismic energy is dissipated through the ductile behavior of RC moment resisting frames. The main elements of the RC frames carry the gravity loads in addition to the seismic loads. Since the RC frames are sensitive to gravity loads, the ductility of the frames is reduced by increasing the gravity loads. Moreover, because of the low stiffness of the RC moment frames, huge member sizes of structural elements are required to control lateral drifts under lateral loading. In addition, the existing RC moment frame buildings with non-ductile characteristics pose a considerable hazard during earthquakes. To solve the mentioned problems, an innovative metallic damper with a shear link (metallic-passive energy damper) was developed in this paper. The proposed damper not only enjoys an easy fabrication and a good seismic performance but also can be easily replaced after a severe earthquake. Since the damper does not carry the gravity loads, replacing the damper does not affect the severability of the building during repairing. The main goal of this study is to confine the plastic deformation in the proposed damper. The numerical results indicated that the proposed damper improved the behavior of the RC frame in elastic and inelastic zones. It enhanced the shear capacity, shear stiffness, energy absorption, and ductility of the RC moment resisting frame. The results indicated that the proposed damper enhances the shear stiffness and the ultimate shear capacity from a minimum of 11% to a maximum of 24% and from a minimum of 11% to a maximum of 48%, respectively. Also, the proposed damper improved the yielding strength from a minimum of 53% to a maximum of 61%. Moreover, the dynamic analysis indicated that the damper improved the behavior of the system in the case of maximum lateral displacement and base shear. Based on the time-history dynamic analysis, dampers in the 5- and 10-story frames are more effective compared to the 15-story frame. This result confirms the suitable performance of the proposed damper. Herein the required equations and the recommendations for the design of the proposed metallic-shear damper have been presented.

Numerical evaluation of SMA-based multi-ring self-centering damping devices

This paper introduces the innovative concept of SMA-based multi-ring (SBMR) self-centering damping devices and numerically evaluates their performance and effective design. The SBMR devices are passive metallic dampers consisting of two types of concentric circular rings with rectangular cross-section: (a) superelastic (SE) rings and (b) supplemental energy dissipating (ED) rings. The rings are tightly fitted into each other such that their diametric deformations are constrained. The SE rings are made of SE shape memory alloys (SMA) (e.g., Nitinol), thereby providing the SBMR devices with both self-centering and hysteretic damping. The ED rings are made of metals with higher hysteretic damping capacity to supplement the damping of the SE rings. The SBMR devices can resist both tension and compression (without buckling) in multiple directions, allowing their installation via cross-bracing systems. To evaluate the SBMR devices, they were simulated through 3D nonlinear finite element models. The general response/behavior of the proposed devices and the effects of brace design and orientation on their response were examined. The SBMR devices were found capable of producing more than 100% higher damping compared to single SE SMA rings, particularly under small deformations. Moreover, brace design and orientation were found to have little to no effect on the performance of the SBMR devices.

Effect of damper failure on the seismic loss assessment of retrofitted steel moment-resisting frames

Metallic yielding damper is widely utilized to improve the seismic resilience of steel moment-resisting frames. It is a kind of displacement-depended damper and may fail when the ultimate displacement is reached under strong earthquakes. Nevertheless, little research has considered the damper failure behavior in seismic loss assessment of damper-retrofitted steel frames. In this paper, three representative buildings, including a 3-story, 9-story and 20-story steel frame, are retrofitted by a high efficient bending-yield metallic damper. The damper is designed based on the stiffness and displacement demands, and able to keep normal working under maximum considered earthquakes. Numerical models of the retrofitted steel frames with and without considering damper failure are then built, and cyclic behavior of the damper element is validated through the experimental results. Subsequently, nonlinear dynamic analysis is performed to evaluate effectiveness of the design procedure, and incremental dynamic analysis (IDA) is conducted to discuss the effect of damper failure on structural seismic fragility. Combing with the obtained seismic fragility curves, the effect of damper failure on the seismic losses of steel moment-resisting frames are quantitatively assessed using a story-based loss estimation methodology. The results show that the employed damper can effectively mitigate dynamic responses of low-, mid- and high-rise frames; the effect of damper failure on IDA curves is significant at relatively large seismic intensity, especially for the high-rise frame; ignoring the damper failure would lead to significant underestimation of collapse and demolition probability; the models without considering damper failure present higher expected total losses, and the damper failure has few effects on the expected annual losses.