Damped Braces Research Articles

Innovative Brace Damper System for Mitigating Seismic Response in High-Rise Steel Structures

This study investigates the seismic response of a G+14 steel frame building with composite columns using fluid viscous dampers. The effectiveness of these dampers is assessed through analysis employing the Equivalent Static Method, Response Spectrum Method, and Time History Analysis in ETABS. Results indicate a significant 40–60% reduction in displacement and storey drift, underscoring the efficacy of fluid viscous dampers in enhancing structural resilience. This research underscores the importance of innovative damping systems in mitigating seismic risks in tall steel buildings.

Reliability analysis of two archetype RC buildings with hysteretic dampers

The manuscript deals with a study on the performance/reliability analysis of steel hysteretic dampers designed for the seismic retrofit of RC frame structures at the Basic Design Earthquake, BDE (characterized by a 10 % probability of being exceeded over the reference lifespan, VR) for higher hazard levels, represented by a Maximum Considered Earthquake, MCE, with either 5 %/VR or 2.5 %/VR exceedance probabilities. Indeed, seismic codes prescribe that anti-seismic devices designed to satisfy the performance requirements at the BDE must be able to resist earthquakes of higher intensity. Therefore, γ-factors amplifying the design displacement or force must be considered for the design of the device capacity.The objective of the study consists in evaluating the over-demand caused on the steel dampers incorporated in dissipative bracing systems when passing from the BDE to the two higher hazard levels, and comparing this over-demand to the values of the corresponding γ-factors proposed in current codes. Dampers with various ductility factors are considered to include the majority of current hysteretic devices.The amplification factors recommended in the codes for hysteretic dampers are shown to be not suitable for guaranteeing the damper reliability; moreover, a dependence of the reliability of the retrofitted structures upon the ductility of the damped braces is highlighted.

A new friction–slip brace damper to improve seismic performance of braced frames

Global buckling in compression braces results in compression strength degradation, compression stiffness degradation, brace local buckling, and finally brace fracture. Consequently, the braces cannot achieve high energy dissipation capacity. The current study proposes a novel friction−slip damper employed in the middle of square−Hollow Structural Section (square−HSS) and H−shaped braces to prevent the strength and stiffness degradation of braces and improve their seismic responses. In these braces, slip prevents the global buckling of brace and friction dissipates a large portion of energy. To assess the performance of proposed damper, the hysteresis behaviors of square−HSS and H−shaped braces with the proposed friction−slip damper were compared with those of conventional braces both in bracing elements and in diagonal and chevron Special Concentrically Braced Frames (SCBFs) through modeling the numerical models in ABAQUS finite element software validated with two experimental studies. The study findings showed that in the models equipped with the friction−slip damper, the braces experienced no global buckling, local buckling, yielding, plastic hinge, damage, and fracture. Additionally, the obtained results indicated that no degradation was observed in the strength and stiffness of the models with the friction−slip damper than the conventional models. Consequently, a 186.3% increase in energy dissipation capacity was experienced by installing the proposed damper in the middle of braces. Moreover, the results showed that the beams of chevron SCBFs with the friction−slip damper experienced no unbalanced force and thus, no deflection resulting in the stiffness and strength degradation in the tension and compression braces was observed in the chevron beams.

Seismic Upgrade of Steel Frame Buildings by Using Damped Braces

Supplementary energy dissipation has proved to be an effective way of protecting structures from the disastrous effects of earthquakes and has been used in the last decades both in new and in existing constructions. In this regard, various procedures for the design of the damping system for the seismic retrofit of buildings have been formulated over the years, mainly focused on reinforced concrete (RC) constructions, which represent the largest part of the existing stock in many seismic-prone countries. The study deals with the assessment of a displacement-based design procedure for proportioning the damping system recently proposed in the literature for RC framed buildings, with the goal of establishing a good practice for the application of the procedure to steel buildings as well. The method was applied to three case-study frames, regular in plan and in elevation, which were assumed as being representative of old structures designed without consideration of seismic requirements. The retrofit was performed by using chevron braces equipped with dampers with an elastic-perfectly plastic behavior. The method aimed at defining the properties of the dampers to achieve a target performance in terms of the maximum lateral deflection for a specific level of seismic intensity. The effectiveness and reliability of the proposed procedure was eventually assessed by evaluating the seismic performance of the upgraded steel structures in static and dynamic non-linear analyses.

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

In recent years, a new generation of seismic lateral force resisting systems has been proposed that sustains little or no damage under severe earthquakes thus reducing the repair time and cost. This has stimulated the development of many types of self-centering (SC) earthquake-resistant systems even based on innovative materials. Among them, shape memory alloy (SMA) dampers have been proposed that use superelastic nitinol wires to dissipate energy and self-center the structure. Many studies have been dedicated to SMA-brace devices applied to steel moment frames. Only a few studies have employed these devices for the seismic retrofit of existing reinforced concrete buildings. Moreover, their applicability has been experimentally and numerically tested only on small scale brace-components, while applications to real RC buildings are still lacking. Finally, there is a general lack of reliable design procedures. This paper presents a study that investigates the seismic performance of a reinforced concrete building retrofitted with self-centering (SC) shape memory alloy (SMA) braces. A design procedure is applied that satisfies displacement-based performance criteria and allocates the damped braces over the height according to an optimal damper distribution rule. Finally, nonlinear response-history analyses are carried out to evaluate the effectiveness of both the self-centering retrofit solution and the design procedure. The results show the excellent recentering behavior of the SC-SMA braces together with their not negligible energy dissipation capacity.

Seismic Response Analysis of 2-Storey Mosque Structure Using Diagonal Brace Damper and Toggle Brace Damper

Mosque structure are typical public building where Muslim follower doing their worship and social activities. These structures are common in Indonesia where the dangerous earthquake usually happens. This paper is aimed to study of passive control of a typical 2-storey Mosque structure using diagonal and toggle brace damper. At the first, we build a simplified structure model of 2 degree of freedom (2DOF) for controlled and uncontrolled system. In this study, we create 5 cases where case 1 as uncontrolled system. Then we compared the dynamic responses of the structure cases subjected to 1940 El Centro earthquake record using time history analysis (THA). The effect of the geometric configuration of the damper attached to the structure which influenced by the magnification factor will be studied.

Multi‐performance objectives optimum design method and vibration control application of generalized toggle–brace–damper system

AbstractThe toggle–brace–damper system (TBDS) is an effective displacement amplification damper occupying a large building space. The small deformation solution, which is widely used, cannot describe the feature that the displacement amplification capacity varies with the lateral displacement of the TBDS. This is not conducive to investigate the performance of the TBDS comprehensively. Therefore, the geometric design and optimization of the TBDS are lack of a theoretical basis. A generalized toggle–brace–damper system (GTBDS), a generalized form of TBDS, is proposed. It has a flexible layout and optimizes the space available. We also introduce an amplification factor of displacement increment (AFDI) that can accurately describe the performance of the GTBDS. The amplification capacity and the geometric sensitivity are two aspects of the performance. The influence of geometric parameters on the performance of the GTBDS is clarified based on the AFDI. Some regulations are also proposed to compare the performance of GTBDSs with different geometric constructions. Two geometric parameter optimization methods of the GTBDS are proposed to balance its amplification capacity, operation safety and geometric sensitivity. The relationship between the displacement amplification capacity and the energy dissipation capacity of the GTBDS is examined. The existing modal energy dissipation method (MEDM) is extended to calculate the additional damping ratio (ADR) provided by the GTBDS. Combining the calculation method of ADR and the geometric optimization methods of GTBDS, a multiperformance objectives design method of the GTBDS is proposed. The case analysis verifies the effectiveness and the feasibility of the design method.

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.

Combination of different types of damped braces for two-level seismic control of rc framed buildings

Hysteretic damped braces (HDBs) represent an effective and low-cost solution for the seismic retrofitting of reinforced concrete (RC) framed structures. However, notable damage to nonstructural elements can be observed at the serviceability design earthquake (SDE), when activation forces of the HDBs are set too high in order to attain structural safety (SS) performance level at the basic design (BDE) and/or maximum considered (MCE) earthquakes. Moreover, HDBs designed at the immediate occupancy (IO) performance level prevent nonstructural damage of MIs under SDE but may collapse and/or induce structural damage for high intensity seismic loads, due to early activation which renders them unable to develop large energy dissipation. On the other hand, as regards significantly increasing dissipation without extra stiffness, nonlinear fluid viscous damped braces (VDBs) offer a promising solution provided that limit states of the VDs are not exceeded. This work proposes a two-level displacement-based design procedure, where HDBs, ensuring SS at the MCE, are combined with HDBs and VDBs, calculated for IO at the SDE. Gap-hook elements attached in series or in parallel to the HDBs are also examined, with the aim of preventing their deformation at MCE and delay their activation at SDE, respectively. A six-storey RC framed structure designed in L'Aquila (Italy) for moderate seismic loads is to be retrofitted in a high risk-seismic region. The OpenSEES platform is considered for the numerical modelling of the original and retrofitted structures. Nonlinear multi-stripe analyses are carried out with reference to actual real records scaled to the SDE, BDE and MCE seismic intensity levels assumed in the current Italian code.

Damage protection of earthquake resistant structures by means of damped braces

Supplementary energy dissipation is an efficient technique for the retrofitting of as built framed buildings as long as the loss of capacity due to previous seismic degradation is evaluated properly. Most of the displacement-based design procedure of damped braces only considers the capacity curve of an initially undamaged structure, while the hysteretic energy is accounted for by an equivalent viscous damping. However, structures may be initially damaged by previous earthquakes, so the proportioning of the damped braces should include the effects of the cumulative damage caused by previous loading cycles. A displacement-damage-based design procedure is proposed and implemented by means of a computer-aided tool named DAMPERS (DAMage Protection of Earthquake Resistant Structures). The residual capacity that a building might experience when subjected to more than one earthquake during its nominal life is taken into account. The loss of capacity of the original structure is evaluated by a combined plastic-damage model, obtained as an in-parallel combination of elastic-perfectly plastic and elastic-softening damage mechanisms, and a damage index, accounting for the cyclic damage of each pair of mechanisms. An archetype six-storey reinforced concrete framed building, representative of the Italian residential housing stock constructed during the 1990s, is retrofitted with hysteretic damped braces designed assuming different damage evolution laws during previous earthquakes. Three configurations of masonry infills (MIs) are considered: bare frame, with nonstructural MIs; infilled frame, with a uniform in-elevation distribution of structural MIs; pilotis frame, with no MIs at the ground floor and structural MIs at the other floors. OpenSees is the computational platform for the nonlinear seismic analysis of the unbraced and damped braced structures, with reference to records scaled in line with the hypotheses adopted and considering failure modes of structural and nonstructural elements.

Seismic Retrofit of an Existing Reinforced Concrete Building with Buckling-restrained Braces

Background: The seismic retrofitting of frame structures using hysteretic dampers is a very effective strategy to mitigate earthquake-induced risks. However, its application in current practice is rather limited since simple and efficient design methods are still lacking, and the more accurate time-history analysis is time-consuming and computationally demanding. Aims: This paper develops and applies a seismic retrofit design method to a complex real case study: An eight-story reinforced concrete residential building equipped with buckling-restrained braces. Methods: The design method permits the peak seismic response to be predicted, as well as the dampers to be added in the structure to obtain a uniform distribution of the ductility demand. For that purpose, a pushover analysis with the first mode load pattern is carried out. The corresponding story pushover curves are first idealized using a degrading trilinear model and then used to define the SDOF (Single Degree-of-Freedom) system equivalent to the RC frame. The SDOF system, equivalent to the damped braces, is designed to meet performance criteria based on a target drift angle. An optimal damper distribution rule is used to distribute the damped braces along the elevation to maximize the use of all dampers and obtain a uniform distribution of the ductility demand. Results: The effectiveness of the seismic retrofit is finally demonstrated by non-linear time-history analysis using a set of earthquake ground motions with various hazard levels. Conclusion: The results proved the design procedure is feasible and effective since it achieves the performance objectives of damage control in structural members and uniform ductility demand in dampers.

Energy dissipation enhancement through multi-toggle brace damper systems for mitigating dynamic responses of structures

A novel energy dissipation system named multi-toggle brace damper (MTBD) system is proposed in this paper. A theoretical mechanism for analysing the magnification factor of the MTBD system is established. Based on the finite element models (FEMs) simulated by ABAQUS, several single-story two-dimensional frame models with fluid viscous damper are investigated and compared with the theoretical mechanism. The magnification factors of the MTBD systems are compared with those of the traditional toggle brace damper (TTBD) systems. In addition, the dynamic responses of several three story three-dimensional reinforced concrete frame structures with different brace damper systems under various earthquake excitation levels are considered and investigated. The results show that the theoretical mechanism of the MTBD system is almost identical with the FEMs. Compared with the concrete frame with the TTBD system, the MTBD system has a larger amplification factor, a fuller hysteresis loop and a more obvious energy dissipation effect. The roof maximum displacements of the concrete frame structures with MTBD system are reduced by 41.1% on average. The MTBD system can significantly enhance the vibration control effect and reduce the dynamic response of the superstructures.

Experimental dynamic characterization of friction brace dampers and application to the seismic retrofit of RC buildings

Previous earthquakes have caused extensive damage to reinforced concrete (RC) structures with insufficient lateral force resistance or energy dissipation capacity. There is a need to retrofit vulnerable existing RC buildings, particularly those not originally designed for seismic effects or designed to an outdated seismic specification. This study investigates the use of friction dampers as displacement-dependent energy dissipation devices to retrofit RC moment frame structures. First, an experimental program was conducted to characterize the dynamic behavior of friction brace dampers with several different materials, finding that a sintered metal compound provided a stable friction coefficient of 0.4. A strength-based equivalent linearization design procedure was then developed based on the required friction slip force and considering the cracked state of the existing RC structure. A four-story RC school building was then designed using the proposed retrofit design method, validated using nonlinear response history analysis and compared to a previous retrofit scheme that employed buckling-restrained braces (BRBs) and a stiffness-based equivalent linearization design method. The analysis results suggest that the proposed retrofit design method and friction brace dampers are effective in reducing the maximum story drift.

In-plane and out-of-plane nonlinear seismic response of masonry infills for hospitals retrofitted with hysteretic damped braces

The present work studies the combined in-plane (IP) and out-of-plane (OOP) collapse of unreinforced masonry infills (MIs) of strategic infrastructures such as hospitals retrofitted by hysteretic damped braces (HYDBs), where immediate occupancy (IO) and structural safety (SS, e.g. life-safety or collapse prevention) are the performance levels required after low-to-high amplitude earthquakes. Despite many advances in the development of new supplementary energy dissipation systems, few investigations have evaluated their effectiveness in improving the IP-OOP response of MIs. Because of the complex articulation of medical centres, reference is made to a five-storey pavilion of the hospital campus of Avellino in Campania (Italy). Bare and infilled structural models of this reinforced concrete pavilion are designed in a medium-risk seismic zone, in order to fulfill the corresponding IP drift ratio thresholds provided by a former Italian code for limiting nonstructural damage of MIs at the serviceability limit state. The IO and SS performance levels are checked in a displacement-based design procedure of the HYDBs at the Serviceability (SDE) and Basic (BDE) Design Earthquakes. An optimization procedure is considered, taking into account that an anticipated (delayed) activation of the yielding devices may give rise to concerns about their suitability with respect to high (low) intensity seismic loads. The demolition and reconstruction of MIs, which generally goes hand in hand with the introduction of damped braces in existing frames, is avoided. To this end, exterior, with diagonal damped braces in the window bays, and interior, with less-intrusive chrevron damped braces, retrofitting systems are adopted. Two aspect ratios of MIs are analysed assuming corner arrangements along the perimeter. Nonlinear time-history analyses for the four reference seismic levels assumed in the current Italian code highlight that IP and OOP failures of MIs can be avoided when the activation of the HYDBs at the SDE can be attained without jeopardising structural safety at the Maximum Considered Earthquake (MCE).

Experimental and numerical study of hysteretic performance of new brace type damper

A new brace type damper was proposed in this paper, which was designed for protecting structures from earthquakes. The new brace type damper consists of two slit dampers and one H–type brace. The slit damper comprises a few perforated webs and two flanges, and the earthquake energy are dissipated through flexural yielding of perforated webs under in–plane shear. Compared with popular buckling restrained brace (BRB), the perforated web H–type brace damper (PWHBD) has some advantages of much cheaper, easier replacement, and more convenient detection. A quasi–static test was performed to investigate the hysteretic performance of three PWHBDs under cyclic loading. The influences of number of perforated webs and length versus width ratio of strips on the seismic behavior of PWHBD were analyzed. The failure modes, load–displacement curves, skeleton curves, stiffness, ductilities, energy dissipation, and strain were studied. The experimental results indicated that the hysteretic curves of PWHBDs were full, and the displacements corresponding to ultimate capacities of PWHBDs were above 18 mm, corresponding to more than 2.0% inter–storey drift. After then, a finite element model of PWHBD was developed through ABAQUS finite element software. The finite element model was verified through experimental results. The influences of length and width of strip, thickness of perforated web, and number of perforated webs on the seismic performance of PWHBD were further investigated. In addition, two existing formulas for slit damper were modified to calculate the initial stiffness and the yield capacities of PWHBDs, and then they were verified through experimental and numerical results.

Dynamic test and numerical simulation on avoiding the weak-story failure mechanism in structures using LSFDs

The structural damage or collapse caused by weak-story failure mechanisms poses a great threat to the safety of human life and property under strong earthquakes. Many researchers have attempted to transform this unexpected failure mechanism into the desired overall failure mechanism by installing various energy dissipation devices on unsafe structures. This paper introduced a lattice-shaped friction device (LSFD), which is a friction device with hardening postyielding stiffness, into a steel frame with a weak-story failure mechanism. Then, shaking table tests of a three types of two-story steel frames—a frame with LSFDs, a frame with traditional friction brace dampers (FBDs), and a bare frame—were carried out. The seismic responses of the hardening postyielding stiffness of the LSFD on the weak-story failure mechanism of the frame were emphatically studied. The results showed that there was little difference in the seismic responses between the two damped structures under moderate and weak earthquakes. The distribution of maximum story drift for the structure with LSFDs was more uniform, which effectively suppressed the weak-story failure under strong earthquakes, whereas the structure with FBDs had serious deformation concentrations. The numerical simulation results of the structure with LSFDs in the shaking table test showed that the simplified model results were basically consistent with the experimental results. Hence, this model could be used to analyze the seismic performance of damped structures with LSFDs.

Seismic performance enhancement of buildings using multi‐limb brace damper systems

SummaryA novel brace system with a displacement amplification mechanism for damper energy dissipation is proposed in this paper. Theoretical mechanism of the multi‐limb brace damper system (MLBDS) is established. Finite element models are established to confirm the effectiveness of the proposed system. The seismic performance of the MLBDS is compared with those of traditional brace damper systems. Comparison results show that MLBDS has an excellent energy dissipation performance. In addition, the dynamic responses of a high‐rise building with the MLBDS installed to seismic excitations are evaluated. The results show that the MLBDS can significantly reduce the dynamic responses of the high‐rise building under strong earthquakes.

Seismic Demand on Acceleration-Sensitive Nonstructural Components in Viscously Damped Braced Frames

AbstractThis paper investigates the seismic demand on acceleration-sensitive nonstructural components in buildings equipped with fluid viscous dampers. Nonlinear dynamic response analyses were cond...

Seismic Performance Evaluation of Building-Damper System under Near-Fault Earthquake

The building-damper system designed by a seismic code is usually considered to be able to withstand the attack of strong earthquakes. However, near-fault earthquakes, especially those with the forward-directivity effect, might cause early and unexpected failure of code-designed dampers and consequent severe structural damage. In this paper, by taking into account near-fault earthquakes, seismic performance of the building-damper system and damper failure’s influence are evaluated systematically. A 9-storey steel building is designed by the Chinese seismic code as the benchmark model, and five typical dampers, including buckling-restrained brace damper (BRB), friction damper (FD), self-centering damper (SCD), viscous damper (VD), and viscoelastic damper (VED), are adopted. It was found that the building-damper systems show a large response and possible damper failure under the near-fault earthquake excitations. Then, the influence of damper failure is investigated, which reveals that damper failure would significantly affect seismic performance of the building-damper system, especially for the building-SCD system. Subsequently, by introducing the artificial near-fault earthquake excitation, the influences of different pulse parameters, such as pulse velocity amplitude, pulse period, and the number of significant pulses, are studied. It shows that the pulse velocity amplitude and pulse period obviously affect the seismic performance, while the number of significant pulses presents little influence.

Seismic Response Analysis and Control of Frame Structures with Soft First Storey under Near‐Fault Ground Motions

This paper proposes two kinds of arrangements of buckling‐restrained brace dampers to strengthen soft‐first‐storey structures locally. Two types of near‐fault ground motion, with and without pulse, were selected for a study of the seismic response characteristics of soft‐first‐storey structures with and without buckling‐restrained brace dampers, and the effects of different bracing arrangements on improving the seismic performance of soft‐first‐storey structures were recognized. The results show that, compared with pulse‐free ground motion, near‐fault pulsed ground motion results in a more severe seismic response in soft‐first‐storey frame structures, leading to more serious and rapid destruction of the main structure. Buckling‐restrained brace dampers have an obvious energy dissipation effect, play a better role in protecting the main structure, and have good practicality. Compared with structures in which the buckling‐restrained brace dampers are arranged only on the bottommost layer, the bottom‐four‐layer‐support structure is more advantageous in terms of seismic performance.