Excellent Self-centering Capability Research Articles

Damage-free self-centering steel columns incorporating SMA bolts and replaceable steel angles

Steel moment-resisting frames (MRFs) are one lateral force-resistant structural system commonly used in high seismicity areas. The current seismic design practice for MRFs expects to develop plastic hinges at the beam ends to dissipate earthquake input energy. Meanwhile, plastic hinges also form almost unavoidably at the column bases of the first story due to the strong-base-weak-column design philosophy. However, concentrated deformation in the predetermined plastic hinges may lead to considerable damage in structural components. The accompanying large residual drifts can substantially compromise post-earthquake reparability and normal functionality. Hence, this paper presents a novel type of self-centering (SC) steel column base incorporating shape memory alloy (SMA) bolts and replaceable steel angles as a damage-free solution. First, the working principle of the column bases is described. Subsequently, the seismic performance of the steel columns is experimentally evaluated by considering the influences of the steel angles and repeated loading scenarios, and the replaceability of steel angles. Results show the novel steel column bases exhibit satisfactory flag-shaped hysteresis loops with excellent SC capability and stable energy dissipation, whereas almost all the damage is concentrated in the steel angles that can be replaced rapidly after the cyclic loading if required. The deformed columns are restored to their upright positions instantaneously with negligible residual deformation after unloading. More importantly, the steel column stays damage-free, and the SMA bolts with prestrain remain tightened. This enables the steel columns to maintain high functionality to withstand immediate aftershocks or future earthquakes, explicitly achieving seismic resilient design.

Experimental and numerical study on the seismic behavior of RC frame with energy dissipation self-centering hinge joints

Conventional reinforced concrete joints dissipate seismic energy through the deformation of plastic hinges, resulting in excessive residual deformation and difficult-to-repair damage. This paper proposes a new beam-column joint type: an Energy Dissipating Self-Centering Hinge Joint (EDSCHJ) with a high-stiffness spring and replaceable dampers fixed at the joint zone. The high stiffness spring provides restoring forces, and the replaceable dampers are utilized to dissipate seismic energy. A quasi-static test was conducted to investigate the seismic performance of the EDSCHJ. Three types of self-centering hinge joints with different dampers are designed and tested, and the hysteretic response, skeleton curve, stiffness degradation curve, and equivalent viscous damping coefficient of the EDSCHJ were obtained. The test results show that the specimens are undamaged at a story drift of 5%, the EDSCHJ without damper exhibits excellent self-centering capability with only a small residual deformation, the hysteresis curve of the EDSCHJ with dampers exhibits a full hysteresis loop with good energy dissipation capacity, the high-stiffness spring has remained elastic without strength degradation, and the lateral stiffness derived from the skeleton curve aligns closely with theoretical calculations. Finally, the finite element model of EDSCHJ is established and validated by comparing the test and numerical results. The structural parametric analysis reveals that as the relative lateral stiffness increases, the dynamic responses of the structure with EDSCHJ exhibits a increasing trend in displacement and an decreasing trend in acceleration and base shear. Additionally, the simulation results indicate an optimum relative stiffness ratio ranging from approximately 0.09 to 0.61.

Experimental and analytical modelling on a novel self-centering viscous damper

Self-centering (SC) supplemental dampers offer a feasible approach to realize low-damage structures. A novel self-centering viscous damper (SCVD) that incorporates an SC part and a viscous damper (VD) part in parallel, and then series with a length adjustable (LA) part. The working mechanism and hysteretic model were both analyzed for the SCVDs. Dynamic reversed sinusoidal displacement inputs were used in experimental proof-of-concept validation studies. Each component was examined separately to describe and distinguish their distinct contributions to the whole device. Individual results in summing are consistent with hybrid device outcomes for the same input. The SCVDs showed excellent self-centering capability with satisfactory energy dissipation. A maximum equivalent viscous damping ratio (EVDR) of 99.37% was observed. A theoretical model and a numerical model were built and examined for the proposed SCVDs. The inevitable gaps from installation have a noticeable effect on the VD part and the SCVD, especially for small strokes. Except for small strokes, comparisons of test findings and analytical models reveal similar hysteretic reactions, for which the coefficients of determination are greater than 0.9, thereby validating the performance of the theoretical and analytical models to simulate the behavior of the tested SCVDs. In comparison to existing SCVDs, the suggested SCVDs have a more controllable SC ability, length adjustability, and energy dissipation capacity based on the demands of the designers. Furthermore, five distinct lateral resisting components were used in nonlinear response history analysis to compare the seismic and resilient performance amongst the moment resisting frame (MRF), buckling restrained brace (BRB), SC, VD and SCVD systems. Finally, the addition of SCVDs and VD parts can both be effective in controlling the maximum and residual story drift ratios on average. Overall, our findings provide innovative, simple implementable choices for developing low-damage structures.

Experimental and numerical investigations on an assembled self-centering buckling-restrained brace with high post-yield stiffness

In order to facilitate the replacement of damaged components and prevent the weak-story mechanism of frame structure after strong earthquakes, a novel assembled self-centering buckling-restrained brace (ASC-BRB) is proposed in this paper. The proposed bracing system is comprised of the buckling-restrained brace (BRB) system and the self-centering (SC) system. The SC system consists of two sets of steel strands and one group of disc springs stacked in series to achieve the goal of large deformability and post-hardening behavior. The detailed configuration, fundamental working mechanism, and restoring force model of the ASC-BRB are first presented. Different from SC systems with bilinear elastic behavior of existing SC-BRBs, the SC system of ASC-BRB exhibits trilinear elastic behavior due to its special configuration. Then, quasi-static tests are conducted to validate the effectiveness of the proposed ASC-BRB. The experimental results indicate that the ASC-BRB has a flag-shaped hysteretic response with excellent self-centering capability, stable energy dissipation capability, and appreciable deformation capacity with a maximum ductility coefficient of 25.58. More importantly, the specimen can exhibit the anticipated post-hardening behavior. The refined numerical model of ASC-BRB is established and verified by the experimental results, which can effectively analyze the mechanical behavior of the main components of ASC-BRB, making up for the deficiency of the tests. According to the problems discovered in the tests and numerical analyses, an improved configuration of the ASC-BRB is proposed and validated by the numerical simulation of the BRB system before and after improvement. The numerical results indicate that the improved BRB system exhibits more stable hysteretic behavior, and the stress levels of the inner and outer tubes become much lower after replacing 1-shaped cores with steel angle cores.

Experimental research and finite element analysis on seismic performance of resilient columns applying high-strength recycled aggregate concrete

To promote the green development of resilient cities and achieve resilient buildings constructed with recycled materials, it is necessary to further extend the engineering application technology of high-strength recycled aggregate concrete (HSRAC) in resilient structures. In this paper, pseudostatic tests were carried out on six HSRAC columns with ultra-high-strength steel bars (UHSS). The test variables include the UHSS percentage, stirrup ratio, axial compression ratio and UHSS bond strength. In addition, finite element models were developed to conduct the parametric analysis and optimization assessment. Based on the experimental research and finite element analysis, the seismic performance and repairability of HSRAC columns were discussed. The results revealed that HSRAC columns employing the UHSS possessed excellent self-centering capability and remarkable drift-hardening property. Well-designed HSRAC resilient columns can be repaired within 4.0% drift. In addition, the engineering design references were recommended based on reliable simulation results.

Seismic performance of novel RC shear wall with replaceable self-centering energy-dissipation components

A novel reinforced concrete (RC) shear wall with replaceable self-centering energy-dissipation components (RSECs) symmetrically installed at the bottom corner of the wall panel is proposed in this study. The RSEC consists of self-centering part and energy-dissipation part, which not only dissipates most of the seismic energy but also provides the restoring force for the wall to return initial position after yielding of the component. The RC wall with RSECs is designed to reduce the damage to the main part of structural wall and the residual deformation of the structure. The structural details and design considerations of the RC shear wall with RSECs are introduced. To verify the seismic performance of RC shear walls with the new replaceable corner components, the numerical mode is developed for the new type of shear wall and validated by experimental results. Parametric studies of RC wall with RSECs are then conducted to investigate the effects of the stiffness and pre-pressure force of disc spring group, the bearing capacity ratio of RSEC, and the thickness of embedded steel plate. The results indicate that the RC wall with RSECs has moderate bearing capacity and lateral stiffness, good energy-dissipation capacity, excellent self-centering capability and the characteristics of low damage. The function of the RC wall with RSECs can be quickly restored by replacing RSECs after the strong earthquake.

Test of a novel self-centering brace using SMA slip friction damper

This paper reports an experimental work on a novel self-centering brace, which is a serial combination of shape memory alloy slip friction damper and steel tube. The study initiates with describing the axial behavior, in-plane rotational behavior and global buckling behavior of the brace, and deriving the corresponding analytical equations. Then, cyclic loading tests are conducted to obtain the hysteresis behavior of shape memory alloy bolt and the coefficient of kinetic friction of the sliding surfaces, both of which are critical to the behavior of the brace. In what followed, four tests are carried out on a 1/3-scaled specimen, corresponding to four loading protocols. The testing results indicate that the brace exhibits a flag-shaped hysteresis, which is characterized by excellent self-centering capability and satisfactory damping capacity. Using the experimental data, this work quantifies the peak strength, secant stiffness, energy dissipation and equivalent damping ratio, and analyzes the local strains and deformations. Furthermore, three-dimensional finite element models are established for numerical simulations. The finite element models capture the global and local behavior of the brace. Both the analytical equations and numerical simulations agree reasonably well with the experimental data.

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.

Development of a shape memory alloy-based friction damper and its experimental characterization considering rate and temperature effects

A new hybrid shape memory alloy (SMA)-based damper was developed to address two major challenges for SMA-based seismic control devices: (i) insufficient force capacity for real-world application and (ii) relatively low energy dissipation capacity. The hybrid damper, named Superelastic Friction Damper (SFD), leverages the high tensile resistance and excellent self-centering capability of SMA cables and non-sacrificial energy dissipation of a frictional damping mechanism. In this paper, the components and basic working principle of the proposed damper are first described, and the advantages of the proposed damper compared to the existing SMA-based hybrid dampers are highlighted. Then, the fabrication of a prototype damper and its experimental testing are discussed. The mechanical response of the damper under repeated cyclic loading at various displacement amplitudes and loading rates is revealed. The effects of ambient temperature on the hysteretic behavior of the developed damper are explored. Results reveal that the proposed damper exhibits stable hysteretic behavior with negligible sensitivity to the loading rate and temperature. The damper provides an equivalent viscous damping of 12 %, accompanied by 89 % recovery of the peak damper displacement.

Performance-based plastic design of multi-story hybrid braced frames with buckling-restrained braces and shape memory alloy braces

By employing two or more types of braces, hybrid braced frames (HBFs) combine the merits of the adopted braces and offsets their drawbacks. However, the corresponding seismic design method is still under development. To this end, this paper develops a performance-based seismic design (PBSD) method, based on the performance-based plastic design (PBPD) method. In current work, the buckling-restrained braces (BRBs) and shape memory alloy braces (SMABs) are introduced, because they are known for high energy-dissipating capacity and excellent self-centering capability, respectively. The participation extent of BRBs and SMABs is controlled by the stiffness contribution factor. The equations governing the design results are derived and the step-by-step procedure is detailed. A six-story benchmark frame is selected to demonstrate the design method. The designed HBF is subjected to a suite of earthquake ground motions, and the mean demands of seismic responses are compared against performance targets. It indicates that the HBF designed by the design method can well meet the design targets. A parametric analysis is conducted to reveal the effect of changing the stiffness contribution factor on the seismic demands of the HBF. This study validates the proposed design method for HBF, and it may also shed light to the PBSD method of the structures equipped with the other types of displacement-dependent damping braces.

Mechanical Behavior of Shape Memory Alloy Fibers Embedded in Engineered Cementitious Composite Matrix under Cyclic Pullout Loads.

The incorporation of superelastic shape memory alloy (SMA) fibers into engineered cementitious composite (ECC) materials can provide high seismic energy dissipation and deformation self-centering capabilities for ECC materials. Whether the SMA fibers can be sufficiently bonded or anchored in the ECC matrix and whether the mechanical properties of the SMA fibers in the ECC matrix can be effectively utilized are the key scientific issues that urgently need to be studied. In order to study the mechanical behavior of SMA fiber embedded in ECC matrix, four groups of semi-dog-bone pullout specimens were fabricated, and the cyclic pullout tests were conducted in this paper. The pullout stress, displacement, and self-centering capability were analyzed, and different influencing factors were discussed. The results show that the knotted ends can provide sufficient anchorage force for SMA fibers, and the maximum pullout stress of SMA fiber can reach 1100 MPa, thus the superelasticity can be effectively stimulated. The SMA fibers show excellent self-centering capability in the test. The minimum residual deformation in the test is only 0.29 mm, and the maximum self-centering ratio can reach 0.93. Increasing bond length can increase the ultimate strain of SMA fibers with knotted ends, but reduce the maximum pullout stress. Increasing fiber diameter can increase both the ultimate strain and the maximum stress of knotted end SMA fibers. While neither bond length nor fiber diameter has significant effect on the self-centering ratio. This paper provides a theoretical basis for further study of the combination of SMA fibers and ECC materials.

Self-centering Devices with Paralleled Friction Spring Groups: Development, Experiment and System Behavior

ABSTRACT A new self-centering device employing paralleled friction spring groups is developed. The fundamental working principle and fabrication procedure are first presented, followed by quasi-static tests. The devices have flag-shaped hysteretic behavior with excellent self-centering capability and moderate energy dissipation. Stable performance under multiple rounds of loading is also exhibited, suggesting that the devices are fully reusable after undergoing several major earthquakes. A system level analysis is carried out, confirming that the devices are effective in eliminating the residual deformation. A hybrid system is finally proposed enabling a well-balanced control of the peak deformation, residual deformation, and peak floor acceleration.

Parametric analysis of slotted concrete shear walls reinforced with shape memory alloy bars

Reinforced concrete (RC) walls are the primary lateral resistance components selected for buildings located in active seismic areas. Special designs and details are typically applied to dissipate energy through inelastic deformation; such a design approach results in significant permanent damage. This study presents a novel slotted RC wall reinforced with superelastic shape memory alloy (SMA) bars within the external components of the slotted RC wall (SMA slotted RC wall). A numerical model was developed and validated by comparing the test results. The seismic performance of the SMA slotted RC wall was numerically investigated using various parameters of interest in seismic applications and evaluated through monotonic and cyclic loading. Compared with other conventional and high-performance RC walls, the proposed SMA slotted RC wall improves load capacity and drift. In addition, the ductility of the proposed system has slightly improved compared to the SMA RC wall. The proposed wall also has an excellent self-centering capability and negligible damage combined with moderate energy dissipation.

Hysteresis behavior of bottom-story self-centering shear wall with steel brace-assembled bottom

A self-centering shear wall (SC-SW) with a steel brace-assembled bottom is proposed to avoid the residual drift of reinforced concrete shear walls (RCSWs) due to damage in corners and achieve an adequate earthquake-resilience. The residual displacement of traditional RCSW is caused by the bending and shear deformations of the plastic hinge and the deformation of the upper plate, as is confirmed by a cyclic loading test on a typical RCSW specimen. A steel brace-assembled bottom consisting of a steel V-shaped connecting beam, a bearing, and two self-centering braces is designed to control the residual deformation of the RCSW plastic hinge zone. The simplified equations governing the skeleton curve of the SC-SW are derived. An RCSW and SC-SW with the same initial stiffness and ultimate bearing capacity are simulated and compared via the experimentally validated finite element model. The results indicate that the SC-SW exhibits a flag-shaped hysteresis response with an excellent self-centering capability. The maximum residual story drift ratio is less than 0.125%. The skeleton curve equations agree well with the measured data of the analytical specimen. The overall performance of the SC-SW is primarily affected by the braces. The energy dissipation capability of the SC-SW remains insufficient due to the lesser development of plastic deformation.

Rocking bridge piers equipped with shape memory alloy (SMA) washer springs

The emergence of rocking bridge piers provides the community of civil engineers with a broader vision of next-generation seismic-resilient bridge design. This study introduces a new type of shape memory alloy (SMA) washer spring-based self-centering rocking (SCR) systems which could be an important addition to the existing rocking pier family. The proposed system combines the advantage of the existing rocking pier solution with extra benefits such as simplified construction, excellent fatigue and corrosion resistance, and extra “locking mechanism” which safely prevents the pier from excessive rocking. The working principle of the SCR piers is discussed first, and five tests are subsequently carried out on proof-of-concept SCR pier specimens. This is followed by a further numerical study examining an extended range of design parameters. The SCR pier shows excellent self-centering capability with minimal damage to the pier, which is attributed to the intended gap-opening deformation mode. Moderate energy dissipation is offered by the SMA washer springs, and once they are fully flattened, further drift is provided by the flexural deformation of the pier itself. The SMA washers can be used repeatedly with no need for repair/replacement, and the highly flexible stack pattern caters to different design objectives and requirements. An effective supplementary source of energy dissipation is enabled by installing steel angles at the gap opening interface. The experimental and numerical investigations provide a strong proof of feasibility of this innovative structural system.

Development and experimental verification of self-centering shear walls with disc spring devices

A new type of self-centering shear wall (SC-SW) with disc spring devices (DSDs) symmetrically installed at the foot of the wall panel is developed in this study. The SC-SWs with DSDs are designed to reduce the amount of damage to the main part of the wall and to minimize the residual displacement of the structure. To examine the seismic performance of the SC-SWs with DSDs, cyclic loading tests were conducted on two DSDs, one conventional shear wall, and two SC-SWs. The hysteretic behavior and failure process of the specimens are analyzed, and a comparison is conducted between the conventional shear wall and the SC-SWs with DSDs. Experimental results indicate that the DSDs exhibit stable mechanical behavior and excellent self-centering capability and the SC-SWs exhibit stable energy dissipation and excellent self-centering capabilities. The bearing capacity of the SC-SWs is lower than that of the conventional shear wall, whereas the residual drift ratios are significantly lower and the ductility coefficients are significantly higher for the SC-SWs than for the conventional shear wall. Furthermore, the damage of the SC-SWs with DSDs is significantly reduced and the main parts of the wall panel are well protected.

Behavior and application of self-centering dampers equipped with buckling-restrained SMA bars

This study proposes a new type of self-centering damper equipped with novel buckling-restrained superelastic shape memory alloy (SMA) bars. The new solution aims to address some critical issues related to degradation and loss of superelasticity observed in existing tension-only SMA-based self-centering devices, and in addition, to encourage enhanced material utilization efficiency. The cyclic tension-compression behavior of individual SMA bars is experimentally studied first, and subsequently, two proof-of-concept self-centering dampers are manufactured and tested. A simple yet effective numerical model capturing the flag-shaped response of the dampers is then established, and a preliminary system-level analysis is finally conducted to demonstrate the effectiveness of the proposed damper in structural seismic control. The individual SMA bar specimens show asymmetrical flag-shaped hysteretic responses with satisfactory self-centering capability and moderate energy dissipation. Through a specially designed configuration, the proposed damper shows desirable symmetrical and stable hysteretic behavior, and maintains excellent self-centering capability at 6% bar strain. The system-level dynamic analysis indicates that the dampers, as a means of retrofitting, could effectively reduce both the peak and residual inter-story drift ratios of a six-story steel frame. In particular, the mean residual inter-story drift ratio is reduced from over 0.5% to below 0.2% under the maximum considered earthquake, implying elimination of necessary structural realignment even after strong earthquakes.

Experimental study on component performance in steel plate shear wall with self-centering braces

Steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is a lateral force-resisting system that exhibits flag-shaped hysteretic responses, which consists of two pre-pressed spring self-centering energy dissipation (PS-SCED) braces and a wall plate connected to horizontal boundary elements only. The present study conducted a series of cyclic tests to study the hysteretic performances of braces in SPSW-SCEDB and the effects of braces on the overall hysteretic characteristics of this system. The SPSW-SCEDB with PS-SCED braces only exhibits excellent self-centering capability and the energy loss caused by the large inclination angle of PS-SCED braces can be compensated by appropriately increasing the friction force. Under the combined effect of the two components, the SPSW-SCEDB exhibits a flag-shaped hysteretic response with large lateral resistance, good energy dissipation and self-centering capabilities. In addition, the wall plate is the primary energy dissipation component and the PS-SCED braces provide supplementary energy dissipation for system. The PS-SCED braces can provide up to 90% self-centering capability for the SPSW-SCEDB system. The compressive bearing capacity of the wall plate should be smaller than the horizontal remaining restoring force of the braces to achieve better self-centering effect of the system.

Experimental and numerical study on the seismic performance of a self-centering bracing system using closed-loop dynamic (CLD) testing

This study investigates the seismic performance of a newly developed self-centering bracing system using a novel experimental technique named as closed-loop dynamic (CLD) testing. The bracing, named piston-based self-centering (PBSC) apparatus, employs Ni-Ti superelastic shape memory alloy (SMA) bars inside a sleeve-piston assembly for its self-centering mechanism. During cyclic tension-compression loading, the SMA bars are only subjected to tension avoiding buckling and leading to flag-shaped symmetric force-deformation hysteresis. Initially, a braced frame building fitted with PBSC is seismically designed and the preliminary sizing of the brace is determined. For testing, considering the lab capability, the brace is fabricated at a reduced scale. The process of “Closed-loop dynamic testing” starts with the brace test (step 1) under strain-rate loading to characterize the numerical model parameters (step 2), which are then scaled-up as per similitude law and implemented in a finite element software, S-FRAME’s PBSC brace model (step 3). Then the braced frame building is analyzed under an earthquake (step 4) and the axial force-deformation response of the brace under consideration is captured (step 5). In order to further understand and validate the actual response of the brace under earthquake type loading, the axial deformation obtained from S-FRAME is scaled-down (step 6) and used as input parameters for testing the reduced scale brace (step 7). The obtained response (step 8) is further scaled-up and used to match the S-FRAME’s PBSC model for validation (step 9). Iterations from step 3 to step 9 will be required until the experimental and numerical results converge. Convergence criteria used for this validation include both the energy dissipation capacity and initial stiffness within 10% accuracy. Reasonable agreement between the numerical and experimental results is achieved in the closed-loop dynamic testing. The PBSC brace shows excellent self-centering capability under various earthquake loadings.

Behavior and design of top flange-rotated self-centering steel connections equipped with SMA ring spring dampers

Existing self-centering steel connections developed based on either posttensioned (PT) tendons or shape memory alloy (SMA) elements are usually symmetric ones, in which case the connections rotate via a gap-opening mechanism over the beam-to-column interface and as a result causes unwanted “frame-expansion” (also called beam growth) effect and severe slab damage. This paper presents a novel type of asymmetric self-centering steel connection, which rotates around the top flange of the beam. The bending moment capacity and restoring force are provided by a couple of SMA dampers attached beneath the bottom flange of the beam. The working principles of the damper devices and the beam-to-column connections are discussed in detail, and a comprehensive experimental study on individual SMA rings, individual SMA damper devices, as well as two proof-of-concept beam-to-column steel connections, is conducted. The test results show that this type of connection generally exhibits typical flag-shaped hysteretic behavior with satisfactory energy dissipation and excellent self-centering capability. An extra ‘training’ process with an adequate pre-deformation to the SMA ring spring system can be adopted to effectively mitigate the degradation effect of the connections under repeated loading. Based on the test observations, a preliminary design recommendation is also proposed.