Self-centering Energy Dissipation Braces Research Articles

Seismic performance assessment of RC bridge piers with variable hysteresis performance dampers

A novel variable hysteresis performance damper (VHD)—multi-stage slip friction damper is developed and applied to implement multi-level seismic resistance of structures. Different from the conventional slip friction dampers, which feature only a single type of slip friction surface, this innovative damper incorporates two types: a flat slip surface and a wedge slip surface. The quasi-static cyclic loading tests of the VHD were carried out to investigate its variable hysteresis performance. The test results revealed that the developed damper presented excellent adaptive performance, and its hysteresis behavior changed from a complete rectangle with efficient energy dissipation to a flag-shaped curve with exceptional self-centering capacity as deformation increases. Subsequently, the developed VHD with unique adaptive performance was applied in RC bridge piers (BP) to improve the seismic performance. Nonlinear time history and fragility analysis methods were employed to assess the seismic performance of the RC bridge piers with VHDs (BP-VHD) in deterministic and probabilistic manners, considering maximum and residual deformations as performance indicators. For comparison, seismic responses of RC bridge piers with traditional buckling restrained braces (BRBs) and self-centering energy dissipation braces (SCEBs) were also presented. The analysis and comparison results demonstrate that the developed VHD is as effective as BRB in reducing maximum deformation at small PGAs, meanwhile, it can effectively reduce the residual deformation of the structure to allowable values when the PGA is large. Furthermore, the failure probability of BP-VHDs is lower compared to piers with BRBs and SCEBs, particularly concerning maximum and residual drift ratios as performance indicators. The application of the VHD can effectively achieve the goal of multi-level seismic resistance for RC bridge piers.

Experimental, mathematical model, and simulation of a dual-system self-centering energy dissipative brace equipped with SMA and variable friction device

The application of shape memory alloy (SMA) in seismic-resistant devices has received extensive attention due to its unique superelastic and shape memory effect. The poor energy dissipative capacity, insufficient reliability, and small bearing capacity are the main challenges that hinder the application of the developed SMA braces and dampers. The new system of self-centering energy dissipative (SCED) brace was proposed, fabricated, and tested, and the numerical model was defined and verified. The dates manifest that the load-displacement curve of the new dual-system SCED brace displays a typical flag shape. The new dual-system SCED brace exhibits the desirable energy dissipative ability and self-centering capacity and the theoretical and FE model established in this research can preferably express the hysteretic performance. The FE parametric analysis shows that the SMA screw preload has a small effect on the hysteretic curve of the new system brace, but it plays a decisive role in the shape of the hysteretic curve under small deformation. Furthermore, the bearing capacity and stiffness of the dual-system SCED brace can be adjusted by designing key parameters. The research shows that the new dual-system SCED device compensates for the shortcomings of the existing SMA braces and dampers, and it is a very promising and recommended self-centering energy dissipative device to use the wedge block system as the main energy dissipative system and SMA system as the main self-centering system.

Shake Table Tests on RC Double-Column Bridge Piers with Self-Centering Energy Dissipation Braces

Shake Table Tests on RC Double-Column Bridge Piers with Self-Centering Energy Dissipation Braces

Experimental and mathematical model of the variable friction adaptive self‐centering energy dissipative brace

AbstractThe self‐centering energy dissipative (SCED) brace can limit the maximum story drift and eliminate residual drift during an earthquake. The inadequate reliability or excessive complexity of the energy dissipative system, the contradiction between the energy dissipative system and self‐centering system, the limited elongation capacity, and the difficulty in replacement and reuse are the main challenges faced by the existing developed SCED brace. To solve these problems, a variable friction adaptive self‐centering energy dissipative (VFA‐SCED) brace has been proposed. First, the details of the VFA‐SCED brace are introduced, and the force analysis of each component and the working mechanism of the brace are expounded. Then, the equations that govern the brace performance have been derived, key parameters and mathematical models have been identified. Finally, the feasibility of the new system was demonstrated with a set of experiments, in which five specimens with different key parameters were fabricated, tested, and analyzed. The test results show that the hysteretic curve of the VFA‐SCED brace is typically flag‐shaped, and there is almost no residual deformation after multiple cyclic loadings, which means that the brace has good energy dissipative capacity and self‐centering ability, replaceable and recyclable for each component, and stable working performance. The elongation capacity, friction, energy dissipative capacity, and self‐centering ability can be changed by adjusting the relevant key parameters of the spring and wedge block, and the proposed mathematical model can well predict the force‐deformation hysteresis of the brace with different parameters. The results show that the VFA‐SCED brace successfully avoids the main obstacles of previous SCED braces.

Seismic performance of an assembled self-centering buckling-restrained brace with controllable initial stiffness

An innovative assembled self-centering buckling-restrained brace (ASC-BRB) with controllable initial stiffness is introduced. The brace consists of a self-centering system and an energy dissipation system. Unlike existing post-tensioned self-centering energy dissipation braces, whose initial stiffness has high uncertainty and is sensitive to machining errors, the proposed ASC-BRB can obtain highly controllable initial stiffness because of its unique working mechanism. Therefore, structural seismic response uncertainties can be reduced significantly. The configuration, working mechanism, and theoretical restoring force model of the ASC-BRB are first presented. Quasi-static tests are then conducted to examine the feasibility of the brace, and typical flag-shaped hysteretic behavior and stable energy dissipation capability are observed. The main components of the ASC-BRB keep intact after repeated loadings, except for the core plates, which are damaged; however, the core plates can be easily replaced. This observation highlights the superiority of the ASC-BRB in terms of damage concentration and high recoverability. The proposed theoretical restoring force model can accurately predict the hysteretic response of the brace, especially for the initial stiffness, with the predicted value being within 5 % of the experimental value. A simplified numerical model is developed and used in a parametric study conducted to examine the effects of two key design parameters on the brace behavior. Furthermore, the effect of machining errors on the initial stiffness of the ASC-BRB is studied. An analysis of steel frames with ASC-BRBs indicates that the ASC-BRB can effectively reduce the residual inter-story drift and help achieve a peak floor acceleration response comparable to that of the frame with BRBs. However, the peak inter-story drift is amplified owing to the lower initial stiffness of the proposed brace. On the basis of a system-level parametric analysis, recommended optimized design parameters of the ASC-BRB are presented to facilitate efficient control of structural seismic responses.

Test of Novel Self-Centering Energy Dissipative Braces with Pre-Pressed Disc Springs and U-Shaped Steel Plates

ABSTRACT To control the residual displacement of the structure after strong earthquakes, this paper develops and validates a novel brace, i.e. the self-centering energy dissipative brace with pre-pressed disc springs and U-shaped steel plates (SCEDB-U). The pre-pressed disc springs are used for recovering nonlinear deformation and the U-shaped steel plates are used for dissipating energy. Initially, the configuration and working principle are described in detail. Then the analytical equations governing the cyclic behavior of the brace are derived. To confirm the concept, the large-scale bracing specimens are designed and manufactured for the quasi-static cyclic loading tests. In the tests, the varied parameters included the plate width of the U-shaped steel plates and the pre-pressure magnitude of the stacked disc springs. Besides, the high-fidelity three-dimensional finite element (FE) models of SCEDB-U are established. According to the experimental data, the SCEDB-U has typical flag-shaped hysteresis, which is characterized by excellent self-centering capability and stable energy dissipation ability. It also indicates that increasing the plate width of U-shaped steel plates can effectively improve the energy dissipation capacity, but may induce residual displacement; increasing the pre-pressure magnitude of disc springs could improve self-centering ability. The numerical results are in good agreement with the experimental data; hence, the FE models can be further utilized for parametric analysis, initial design and optimization.

Seismic Performance Assessment of a RC Bridge Retrofitted with SCEBs Under Near-Fault Pulse-Like Ground Motions

ABSTRACT A novel self-centering energy dissipation brace (SCEB) was developed to enhance the seismic resilience of bridges. In this paper, the replaceable SCEBs are installed between the double-column bent transversely and at the abutment longitudinally. Taking both the seismic safety and resilience into consideration, the seismic performance of bridges retrofitted by braces under near-fault (NF) pulse-like ground motions was evaluated by the probabilistic approach. Results show that the original and retrofitted bridges exhibit higher damage probabilities under NF pulse-like ground motions. The bridges retrofitted with SCEBs exhibit better seismic resilience than the bridges with buckling restrained braces when intensity measure increases.

Design recommendations for self-centering buckling restrained braces

Self-centering buckling-restrained braces (SC-BRBs) have typical flag-shaped hysteresis. Differing from conventional buckling-restrained braces (BRBs) which can result in significant residual drifts, the SC-BRB incorporates additional prestressing elements, so that it can recenter after earthquakes, which is critical for seismic resilience. Current seismic design procedures can be used to calculate the key properties of conventional braces (e.g. BRB), but they cannot be used to determine the additional hysteretic properties of SC-BRB braces. To achieve a comprehensive understanding of the performances of SC-BRB systems and develop their design recommendations, this paper conducted a parametric study of two typical SC-BRB systems, using a 12-story steel braced frame office building. Then, the overall behavior of the SC-BRB system was compared with those of a BRB system and two self-centering energy dissipative brace systems. The selection of SC-BRB properties appeared to be a tradeoff between demands on component properties and seismic performances. The criteria for proportioning the system were suggested. Numerical results showed that, although the SC-BRB systems had smaller residual drifts than the BRB system, they generated more significant high-mode effect than the other comparable systems.

Seismic performance upgrade of substandard RC buildings with different structural systems using advanced retrofit techniques

There has been ongoing deliberation to arrive at promising retrofit strategies for pre-seismic code reinforced concrete (RC) structures. Against this backdrop, the research reported in this study puts forth solutions by focusing on advanced retrofit approaches for improving the seismic performance of substandard RC buildings with structural systems common to medium seismicity regions. High-performance reinforced concrete (HPRC) jacket application and self-centering energy dissipative (SCED) braces are the contemporary retrofit alternatives prioritized in this study to upgrade RC structural systems deficient in stiffness, strength and/or ductility. While these retrofit techniques were previously investigated at the member level, this study focuses on implementing thin-HPRC jacket applications, innovative outrigger-belt truss SCED bracing systems, and hybrid approaches on three-dimensional (3D) fiber-based numerical models representing substandard RC structures with different heights. Inelastic pushover analyses and multi-record dynamic response simulations are conducted to assess the retrofit alternatives by monitoring several local damage indices (LDIs) and the related global damage measure (GDM). The study confirms the effectiveness of retrofit measures for a moment-resisting frame building (MRF) deficient in lateral capacity and a high-rise shear wall (SW) building with insufficient global ductility. The presented systematic methodology accounts for the redistribution of seismic demands after retrofitting critical elements and enables selecting effective seismic retrofit solutions, namely SCED bracing system for MRF structure and hybrid retrofit for the high-rise SW building, using probabilistic seismic performance assessment along with cost and practical considerations.

New precast self-centering rocking shear wall with multiple hinged joints: Description and design approach for seismic protection of buildings

This paper proposes a novel precast self-centering shear wall with multiple hinged joints (PSCSWMHJ) as an alternative seismic resilient system, which is composed of pinned precast walls, pre-compressed disc spring devices (PDSD) and self-centering energy dissipation braces (SCEDB). It is featured by a dual self-centering system with the PDSD-wall component and the SCEDB resisting lateral loads. Seismic energies are expected to be mainly dissipated by S-shaped steel plate dampers installed in the SCEDB, while the precast walls are protected from damages. The damper is characterized by flexure-tension strengthening behavior that is beneficial to control structural displacement under strong earthquakes, and its seismic performance has been experimentally and numerically studied. The main objective of this study is to investigate rocking mechanism and seismic resilient design method for the PSCSWMHJ. In present study, mechanic models for the PDSD and the SCEDB are presented, and the SCEDB's hysteretic behavior is analyzed through numerical parametric studies. Rocking mechanism for the PDSDS-wall component and the PSCSWMHJ are theoretically revealed and numerically validated. Meanwhile, the influence of design parameters on their hysteretic behavior is discussed. The results show that the PSCSWMHJ has flag-shaped hysteretic curve and most of the energy is dissipated by dampers in the SCEDB. Subsequently, the step-by-step design procedure is proposed on the basis of energy balance concept for realizing seismic resilience of the PSCSWMHJ. Nonlinear dynamic analyses indicate that the design procedure is capable of achieving the expected performance objectives and the pre-selected yielding mechanism; the proposed PSCSWMHJ exhibits excellent self-centering capacity and good functional recoverability.

Modeling methods of self-centering energy dissipation braces using OpenSees

Self-centering energy dissipation (SCED) braces as a high-performance structural member has been extensively investigated in the last decade. The unique hysteretic behavior of the SCED brace generally dominates the seismic performance of building structures. This paper presents three available simulation methods for predicting the hysteretic behavior of a typical SCED brace in the widely-used open-source computational platform OpenSees. The simulation methods are implemented using the built-in material and element libraries in OpenSees, and aim to investigate the advantages/disadvantages between different modeling methods. Furthermore, two general-purpose self-centering (SC) uniaxial hysteretic models are developed and implemented for modeling different types of SCED braces. Representative validation studies are then presented through using the developed material models to predict the experimental results of the SCED braces under cyclic loading. The SC hysteretic models can capture primary characteristics of hysteretic responses with reasonable accuracy. Additionally, an improved truss element is also proposed for straightforward application of the developed SC models. The users are able to define the experimentally-observed hysteretic features of the SCED braces in line with the envelopes established in the developed material models. A shaking table test of the SCED braced frame in the literature is further simulated to verify the feasibility of the developed material models and modified truss element under seismic loadings. The research outcomes validate a more convenient and accurate method for predicting the behavior of SCED braces and provide some useful insights on the modeling methods in OpenSees.

A Novel Self-centering Braced Double-column Rocking Bent for Seismic Resilience

ABSTRACT A novel self-centering braced double-column rocking bent (SBRB) consisting of a double-column rocking bent and traditional or self-centering energy dissipation braces is developed analytically and numerically to enhance the seismic resilience. The analytical model of the SBRB is established, and numerical models of the SBRB are built to evaluate its seismic performance. Numerical results indicate that the SBRB is featured by prominent seismic performance including high lateral stiffness and strength, stable energy dissipation ability and good self-centering capability. The parameters of braces, axial force ratio, tendon prestress, and confinement play significant roles in the seismic responses of SBRB.

Seismic design and performance of a steel frame-shear plate shear wall with self-centering energy dissipation braces structure

The steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is a new seismic lateral resistant component. This paper outlines the performance requirements of the steel frame-shear plate shear wall with self-centering energy dissipation braces (SF-SCSPSW) structure and presents a direct displacement-based seismic design method for the structure. A combined strip model of the SPSW-SCEDB that considers the effect of the bolted connection on the wall plate is established. The comparison of the simulated and experimental results shows that the model can accurately predict the strength and hysteretic behavior under cyclic loading. The 8- and 15-story prototype buildings were designed using the presented method. The results of nonlinear dynamic analysis showed that larger inter-story deformations occurred on the lower floors, and the inter-story ratios gradually decreased with an increase in the number of floors. The maximum inter-story drift ratio (1.73%) of the 8-story structure under mega earthquakes and the maximum residual drift ratio (0.018%) of the 15-story structure under large earthquakes were less than the limit values (2% and 0.5%). Local yielding occurred between the brace connection and the column under mega earthquakes, but the columns remained in an elastic state. The seismic responses of the SPSW-SCEDBs in the two structures met the performance requirements of being elastic and suffering light and moderate and serious damage under frequent, medium, large, and mega earthquakes, respectively. The effectiveness of the proposed design method was verified.

Assembled self-centering energy dissipation braces and a force method-based model

A pre-pressed spring self-centering energy dissipation (PS-SCED) bracing system has significant energy dissipation and re-centering abilities, although many welds result in a lengthy manufacturing process and reduce the machining accuracy to an unacceptable level. An assembled pre-pressed spring self-centering energy dissipation (A-PS-SCED) bracing system that uses disc spring groups to provide a re-centering ability and a friction device to dissipate energy, is presented in this paper to simplify production and maintenance. A novel force method-based (FMB) hysteretic analysis model governing the distribution of the internal force is proposed and verified by a numerical model of the A-PS-SCED brace and tests of the PS-SCED brace specimen. The simulation results indicate that the A-PS-SCED brace exhibits sufficient and steady energy dissipation and re-centering capacities. The FMB model agrees well with the numerical model with a maximum bearing force difference of 2% and has steady hysteretic responses under random excitations. The FMB model is used to determine the mechanisms of the stiffness and contact status change during a typical loading process. Additionally, the FMB model accurately predicts the cyclic loading test results of an existing PS-SCED brace specimen, and the average bearing force differences are 6% and 2% at friction force of 200 kN and 300 kN, respectively.

Modeling of Disc Spring Self-Centering Energy Dissipation Braces from Inactive State to Design Limit State

AbstractThis paper focuses on modeling the hysteretic behavior of disc spring self-centering energy dissipation braces (DS-SCEDBs) from the inactive state to the design limit state, and proposes tw...

Study on prediction method of initial stiffness of self-centering energy dissipation braces

The self-centering energy dissipation (SCED) brace is an innovative structural component of seismic-resistant systems that provides a flag-shaped response with good energy dissipation and self-centering capacity. The initial stiffness of the SCED brace is a crucial parameter for brace design and a braced frame system. The current use of SCED braces is limited by the significant discrepancy between the actual and theoretically predicted initial stiffnesses. In this paper, the sources resulting in the inaccurate prediction are identified as the accuracy of the theoretical governing equations and the practical fabrication tolerances of the braces. The accuracies of the governing equations with different levels of complexity are analyzed and compared based on a typical SCED brace. To investigate the reduction effect of fabrication tolerances on the effective axial stiffness, a large number of numerical simulations are conducted on an axially loaded tube member with different tolerance characteristics, including the fundamental length tolerance, contact surface nonuniformity, and load level. According to the trends of the effective axial stiffness, a valid stiffness reduction factor is defined. It can provide good estimates of the reduced axial stiffness under different tolerance parameters. Additionally, the stiffness reduction factor is incorporated into a refined governing equation of an experimental SCED brace to verify the accuracy of the predicted initial stiffness when the effect of the fabrication tolerances is considered. It is shown that the modified governing equation estimates well the actual initial stiffness. Moreover, this prediction equation can be easily extended to other types of SCED braces once the tolerance parameters have been determined.

COMPARATIVE SEISMIC PERFORMANCE ASSESSMENT OF UHPC JACKETING AND SCED BRACING TECHNIQUES

Observed damage to existing pre-seismic code buildings in previous earthquakes has raised interest among the engineering community for improving the performance of these structures using different seismic retrofit measures. This paper throws light on contemporary techniques for the seismic retrofit of RC buildings, namely ultra-high-performance concrete (UHPC) jacketing and self-centering energy dissipative (SCED) braces. Detailed fiber-based numerical modeling of a benchmark structure is undertaken to evaluate the effectiveness of the selected retrofit measures. The case study structure is a two-story pre-seismic code residential building designed for gravity and wind loads, exhibiting poor seismic performance. Along with the two retrofit strategies investigated, several parameters are also considered. Inelastic static pushover and incremental dynamic analyses are conducted to select the retrofit measures and assess their effects on seismic performance. Using a collection of far-field earthquake records and a set of performance criteria, fragility functions are constructed to assess the vulnerability of the benchmark structure with and without the retrofit solutions. The study shows that the adopted index that links cost to the seismic performance obtained from the fragility functions can provide a rational ranking of the selected retrofit approaches relative to the existing building and support selecting the most effective and economical alternative.

Parametric analysis and failure mode of steel plate shear wall with self-centering braces

A steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is developed and tested. The SPSW-SCEDB is prefabricated and replaceable. The effects of various design parameters on the hysteretic behavior of the SPSW-SCEDB without the effects of the frame are investigated. The experimental results show that the residual deformations of the wall plate are eliminated by the restoring force of braces, and the SPSW-SCEDB exhibits high initial stiffness, stable post-yield stiffness, and good energy dissipation capability. The SPSW-SCEDB with a thicker and wider wall plate has better energy dissipation capacity and higher post-yield stiffness. The wider wall plate reduces the lateral force contribution of the braces to the SPSW-SCEDB, resulting in the weakening of the overall strength of the SPSW-SCEDB. The SPSW-SCEDB has a good self-centering capability when the ratio of the horizontal restoring force of the braces to the compressive force of the wall plate is larger than 1.3. Compared with the size of the wall plate, the effect of the friction force on the SPSW-SCEDB is relatively small. The destructive test results demonstrate that the SPSW-SCEDB maintains stable lateral force resistance, energy dissipation and self-centering capabilities, even though the lateral drift is 4% and many wrinkles that cannot be smoothed out occur on the wall plate. In addition, the test results highlight the assembly capability and the replaceability of the components of the SPSW-SCEDB.

Development and validation of a versatile hysteretic model for pre-compressed self-centering buckling-restrained brace

Due to the preferable self-centering and energy dissipation capabilities, self-centering energy dissipation (SCED) braces have become an emerging structural component in earthquake engineering. In this paper, an innovative self-centering steel buckling-restrained brace (SC-SBRB) consisting of two independent and complementary systems, i.e., a buckling-restrained energy-dissipation system and a pre-compressed disc spring self-centering system, is proposed. The working mechanism and mechanics of the SC-SBRB are investigated under one cycle of cyclic loading. A versatile self-centering hysteretic model (SCHM) is developed based on the working principle of the SC-SBRB to accurately characterize the energy dissipation and self-centering properties of the SC-SBRB under repeated cyclic loading. The SCHM is a path-dependent model that allows for straightforward parameter interpretation of the mechanics of the SC-SBRB. Numerical simulations are conducted on four SC-SBRBs with different self-centering ratios to validate the prediction results obtained from the SCHM. A good agreement between the simulation results and the prediction results confirm the validity of the proposed SCHM. Simulation results also demonstrate that the SC-SBRB can provide a stable and repeatable flag-shaped hysteretic response, as well as substantial energy dissipation and self-centering ability. Additionally, the SCHM is reasonably extended to other SCED braces with similar hysteretic rules. Further validation of the SCHM is performed by comparing the experimental results of the SCED braces with the SCHM results. It is concluded that the proposed SCHM has excellent applicability and can describe the responses of other SCED braces.

Variable-friction self-centering energy-dissipation braces (VF-SCEDBs) with NiTi SMA cables for seismic resilience

This study introduces a Variable-Friction Self-Centering Energy-Dissipation Brace (VF-SCEDB) incorporating pre-tensioned superelastic NiTi shape memory alloy (SMA) cables and novel Variable Friction Devices (VFDs). The motivation behind the proposed member is to promote reliable energy dissipation without compromising the self-centering capability. In addition, the strength and the loading/unloading plateau stiffness of the brace can be adjusted separately by an appropriate combination of the NiTi SMA cables and the VFDs. The concept, configuration, and fundamental working principle of the VFD and VF-SCEDB are first presented. An experimental study on a proof-of-concept VF-SCEDB specimen is then conducted to understand its fundamental cyclic behavior. The results confirm that the proposed VF-SCEDB has the potential for exhibiting both excellent energy-dissipation and self-centering capabilities. Analytical models for predicting the hysteretic response of the VFD and the brace are also developed, and the prediction agrees well with the experimental results. Following the experimental program, a system-level analysis considering a series of 3-story concentrically braced steel frames employing different self-centering braces including the new VF-SCEDBs, is carried out. The results show that the frames can well control the residual deformation, but compared with other types of self-centering braces, the VF-SCEDB can more effectively reduce the peak deformation of the structures.