Stable Hysteretic Behavior Research Articles

Concept and performance testing of an all-steel miniature dual stiffness damper

The double-stage yield buckling-restrained braces gradually play a role in different floors, so as to control the structural deformation pattern and hinder the weak-story collapsing. In this study, a novel all-steel damper called the miniature dual stiffness damper (MDSD) was proposed, which had the advantages of simple assembly and low cost. A series of tests was performed under quasi-static test to address the hysteretic behavior of MDSDs with different stiffness ratios of the large yield segment to the small yield segment, Kyl/Kys. The test results demonstrated that MDSDs had a stable hysteretic behavior, and the dual stiffness can be achieved by yielding successively in small and large yield segments. The second stiffness of the MDSD increased with the increase of Kyl/Kys when the elastic stiffness of the small yield segment kept unchanged. The low-cycle fatigue life of the MDSD was negatively correlated with the strain of the small yield segment. An in-series stiffness model for the MDSD was presented. The theoretical hysteretic curves of MDSDs were further obtained based on the proposed stiffness model, and a good accuracy was achieved.

Performance of prefabricated RC column with replaceable Column-Base connection under cyclic lateral loads

A new prefabricated RC column with replaceable column-base connection was proposed for moment-resisting frames. The column-base connection was assembled with replaceable steel fuses and padding blocks, which can be easily replaced after an earthquake, to accommodate inelastic deformation. Eight full-scale column specimens were tested to evaluate the effectiveness of various parameters on the seismic performance under lateral loads. The experimental results showed that the column-base connections exhibited stable hysteretic behavior in terms of strength, stiffness and energy dissipation. The lateral load capacity increased with increase in cross-sectional area of steel fuses (1200–1520 mm2) and axial load ratio (0.14–0.24). The seismic performance before and after the replacement of the damaged components was found to be almost identical which indicated that the replaceable column-base connection is feasible and effective. An idealized moment-rotation theoretical model and a simplified 2D nonlinear theoretical model were further developed to predict the flexural response of the proposed columns. Comparison of theoretical model responses with the experiment results showed satisfactory results in predicting the lateral load behavior. Both the models provide a reference for the design procedure and practical applications of the replaceable column-base connection.

Seismic performance of assembly joints between HSPC beams and concrete-encased CFST columns

In this study, an assembly joint between a hybrid H-steel precast concrete (HSPC) beam and concrete-encased concrete-filled steel tubular (CFST) column was developed for precast composite structures. The HSPC beam was designed with a novel configuration to connect to the concrete-encased CFST column through a cantilever H-steel beam. To investigate the effectiveness of the developed joint, reversed cyclic load tests were conducted on three full-scale exterior subassemblies with different types of cantilever beams: original, reduced beam section (RBS) and opening in beam web (OBW). The seismic performance of the developed joints was analysed comprehensively based on the failure pattern, hysteresis curve, stiffness degradation, ductility, and dissipated energy. The specimen with the RBS steel beam exhibited a stable hysteretic behaviour up to 4.75% of drift ratio and remarkable ductility, and the cumulative dissipated energy was up to 8.8 times that of the original specimen. However, the improvement in the specimen with the OBW steel beam was insignificant compared with that in the original specimen. Hence, the developed joint with the RBS steel beam exhibited more satisfactory seismic behaviour in terms of the capability to relocate the plastic hinge to the required. This could be applicable in high seismic zones. The seismic performance of the developed joints was affected significantly by a reduction in the reinforcement ratio of the bars transferring the bending stress between the H-steel and RC beams. Therefore, simplified formulas for ensuring a sufficient reinforcement ratio of the bars were proposed and validated through tests.

Experimental investigation on the seismic performance of cored moment resisting stub columns

Cored moment resisting stub column (CMSC) was previously developed by the features of adopting a core segment which remains mostly elastic and reduced column section (RCS) details around the ends to from a stable hysteretic behavior with large post-yield stiffness and considerable ductility. Several full-scale CMSC components with various length proportions of the RCSs with respect to overall lengths have been experimentally investigated through both far-field and near-fault cyclic loadings followed by fatigue tests. Test results verified that the proposed CMSC provided very ductile hysteretic responses with no strength degradation even beyond the occurrence of the local buckling at the side-segments. The effect of RCS lengths on the seismic performance of the CMSC was verified to relate with the levels of the deformation concentration at the member ends, the local buckling behavior and overall ductility. Estimation equations were established to notionally calculate the first-yield and ultimate strengths of the CMSC and validated by the measured responses. A numerical model of the CMSC was developed to accurately capture the hysteretic performance of the specimens, and was adopted to clarify the effect of the surrounding frame and to perform a parametric study to develop the estimation of the elastic stiffness.

Experimental-numerical study on weakened HSS-to-HSS connections using HBS and RBS approaches

Hollow structural sections (HSS) have been used more often as columns because of their symmetrical geometry and admissible performance in bearing axial forces along with bending and torsional moments. The use of hollow sections as beams in moment-resisting frames would be beneficial and is worthy to assess. To this aim and considering the importance of developing plastic bending hinges of the special moment-resisting frames in a zone far from the column face, two methods for weakening beam sections are studied and compared in this paper: 1) Reduced beam section (RBS) and 2) Heat-treated beam section (HBS). For the experimental investigation, a furnace was first made to heat the desired zone of the beam. Then, a cyclic quasi-static loading protocol was applied to two full-scale beam-column connection specimens. The experimental specimens were made by box sections in which the beams had reduced or heat-treated sections. Moreover, for verification and parametric studies, finite element models were generated using ABAQUS. The columns of numerical models had box sections whereas rectangular and circular hollow structural sections were used as beams. Additionally, the seismic behavior of two beam-column connection models with box and pipe heat-treated beam sections was investigated under near-field loading protocol. Compared with RBS sections, both the results of experimental and numerical studies indicated the acceptable bending behavior of heat-treated hollow structural sections in terms of prevention of lateral-torsional buckling along with a stable hysteretic behavior.

Cyclic tests of assembled self-centering buckling-restrained braces with pre-compressed disc springs

The assembled self-centering buckling-restrained brace (SCBRB), consisting of a novel type self-centering (SC) part and a buckling-restrained brace (BRB) part that work in parallel under cyclic loads, was constructed to reduce residual deformation of the brace and to provide additional energy dissipation capacity by the compressed disc springs in the SC part. Tests were carried out to mainly investigate the effects of constructional details, as well as the self-centering ratio of pre-compressed force of SC part to compression strength of BRB part at a specific story drift, on the hysteretic behavior of SCBRBs. The tests revealed that, compared with the BRB, residual deformation of the SCBRBs was greatly reduced and that the residual deformation almost disappeared when the self-centering ratio, under story drifts of 2%, is larger than 1.0. For each SCBRB, axial strength is mainly from the SC part and energy dissipation is mostly from the BRB part within the drifts of 3%. With increase of the self-centering ratios under the same pre-compressed force, both the residual deformation of SCBRB and the energy dissipation of BRB part decreased. Meanwhile, energy dissipated by the SC part is about 18–25% of total energy of SCBRBs under the drifts of 2%, indicating that the SC part can provide not only resilience but also energy dissipation. Tension fracture of encased steel plate brace in SCBRBs occurred and the other assembled components kept intact after tests, facilitating repair of encased brace and reuse of intact components. On the whole, the SC part, the BRB part and SCBRBs exhibited stable hysteretic behavior and bilinear backbone curves. Good elastic deformability of the SC part ensured remaining capacity of SCBRB after tensile failure of BRB.

Development of double-stage yielding coupling beam damper

This paper proposes a new type of steel double-stage yielding coupling beam damper (DYCBD), which consists of a shear component and two bending components. Two types of components have different yield displacements. Both DYCBD components are steel dampers with I-shaped cross section. The shear component first yield corresponding to a moderate earthquake, while the bending components do not yield until a major earthquake occurs, which results in the double-stage yielding behavior of the DYCBD. The constitutive model and design method of DYCBD were proposed. Three specimens with different geometries were designed and conducted shear hysteretic tests. The experimental results revealed that specimens exhibited stable hysteretic behavior and double-stage yielding effect. Finite element models (FEMs) were established to explain the deviations between the calculation results and the experimental results, and parameter analysis were carried out. The components stiffness ratio of 0.52 is suggested to achieve the most obvious double-stage yielding effect. A minimum moment of inertia ratio between bending components' flange to total section of 0.83 is also suggested to decrease the deviations between the proposed design method and FEM as a result of parametric study.

Development of a new hexagonal honeycomb steel damper

This paper presents a new metallic damper called hexagonal honeycomb steel damper (HHSD) for damage mitigation in structures subjected to earthquake excitations. The HHSD is composed of steel plates having several hexagonal and welded to the top and bottom anchor plates. The damper takes the advantages of hexagonal honeycomb geometry and steel material capability to dissipate seismic energy. The quasi-static cyclic test was performed experimentally and numerically on a series of specimens to evaluate the robustness of the HHSD. A three-dimensional finite element analysis of HHSD was carried out and verified with the experimental results. The results showed that the HHSD has low yield displacement, stable hysteretic behavior, a good range of ductility and high-energy dissipation capability. Additionally, the constitutive formulas of the damper are also derived based on the obtained results. Furthermore, it is found to have lightweight and inexpensive with ease of implementation as a potential alternative for new structures or seismic retrofitting of the existing structures.

Development of improved exposed column-base plate strong-axis joints of low-rise steel buildings

Due to increasing seismic risk, seismic design has become mandatory even for low-rise structures in Republic of Korea since December 2017. However, it is not difficult to find undesirable exposed column-base plate strong-axis joints of low-rise steel buildings in the field. Such undesirable connections might not have sufficient capacity and stability under earthquake. Therefore, a series of experiments were carried out to develop improved exposed column-base plate strong-axis joints of low-rise steel buildings. In total, seven large-scale column-base plate strong-axis connection specimens were investigated under both axial compression and lateral cyclic loading. It was found that the hysteretic behavior of such improper joints typically used in the field was unstable due to a “rocking” phenomenon between a base plate and concrete foundation by large plastic residual deformation of anchor bolts. To overcome the rocking phenomenon, efforts were made to develop enhanced connections. Based on the test results, considerably improved and stable hysteretic behavior without the rocking phenomenon was obtained by using eight threaded anchor bolts. However, further study is needed to assess the effect of eight threaded anchor bolts on the seismic performances of more various connections.

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 and analytical studies of sub-standard RC frames retrofitted with buckling-restrained braces and steel frames

Existing reinforced concrete (RC) buildings designed according to outdated codes may lack sufficient strength, stiffness or ductility to meet the seismic performance criteria of current codes. To enhance the system stiffness and re-centering capability, an elastically designed supplementary steel frame (SF) is installed in parallel with the BRBs. Near full-scale cyclic tests are conducted on such retrofit schemes for performance evaluation. The retrofitted specimens showed stable hysteretic behavior up to the retrofit target story drift of 1/150 as proposed in the Japanese seismic regulations. Tests demonstrate that the proposed system is feasible and increases both strength, ductility, and damping to an adequate seismic performance level while the elastic steel frame is effective in providing post-yield stiffness and re-centering capability even when the RC frame is subjected to moderate inelasticity. Special emphasis is placed on the composite behavior of RC members and SF. A simplified composite interaction model is proposed and results from the developed model show good agreement with the experimental data. Ductility demands are shown to concentrate in the BRBs as per the design intent.

Analytical and experimental studies on buckling-restrained brace with gap-supported tendon protection

This paper proposes a new brace called TP-BRB, composed of a conventional buckling-restrained brace (BRB) with a gap-supported tendon protection (TP) in parallel. The gap-supported tendon protection remains inactive before the deformation of TP-BRB reaches a threshold value, while obtaining a high axial stiffness after the threshold value is exceeded. Under strong earthquake, the TP-BRB is expected to provide structures with effective energy dissipation capacity and mitigate the risks of global collapse caused by low post-yield stiffness of the conventional BRB. As the earliest part of the research on the TP-BRB, this paper firstly presents both the stiffness characteristics of the hysteretic curve and a theoretical formula of residual deformation. Secondly, a quasi-static test is conducted, the results of which illustrate that TP-BRB shows a stable hysteretic behavior, a skeleton curve with significant tri-linear characteristic, and a smaller residual deformation than a conventional BRB. Finally, parametric studies based on numerical models show that, with the reduction of the threshold value (u0) and the increase of the ratio (γ) between the axial stiffness of BRB and gap-supported tendon protection, both the residual deformation and the equivalent damping ratio of TP-BRB decrease, but the secant stiffness of TP-BRB increases.

The Meso-inhomogeneous Deformation of Pure Copper under Tension–Compression Cyclic Strain Loading

The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on meso-deformation inhomogeneity of metals under cyclic loading at grain level. Symmetrical tension–compression cycle tests are performed on pure copper specimens to observe the inhomogeneous distribution of slip deformation and its evolution with cycle number. Cyclic hardening process and stable hysteretic behavior of pure copper under cyclic loading are simulated by applying a crystal plasticity constitutive model including nonlinear kinematic hardening associated with the polycrystalline representative volume element (RVE) constructed by Voronoi tessellation. Inhomogeneous deformation processes of materials under six different strain amplitudes are simulated by 1600 cycles, respectively. We discuss the variation law of the inhomogeneous meso-deformation distribution of material with the increase in cycle number, and research the rationality of characterizing the inhomogeneous deformation distribution and variation with the statistical standard deviation of the micro-longitudinal strain or the statistical average of the first principal strain based on the statistical analysis of the inhomogeneous deformation of the polycrystalline RVE model during the cycling process. It is found that these two parameters are related to and approximately inversely proportional to the length of measuring gauge.

Investigation on seismic behavior of bridge piers with thin-walled rectangular hollow section using quasi-static cyclic tests

This study aims to investigate the seismic behavior of thin-walled rectangular hollow reinforced concrete (RC) bridge piers through quasi-static cyclic tests. For this purpose, two identical 1:12 scale specimens were designed and tested under different loading protocols. One specimen was subjected to displacement-controlled cyclic lateral loading with a constant axial load, and the other to the same lateral loading history, but with a variable axial load. The behavior of both specimens was evaluated in terms of the damage progression and failure mode, concrete crack width, hysteretic response, backbone curve, and residual displacement. The results revealed that both specimens experienced a mixed flexure-shear damage progression from the first crack through collapse. Flexural cracks were first observed in the flange surfaces, followed by the development of shear diagonal cracks in both web surfaces. Meanwhile, both specimens exhibited stable hysteretic behavior. Then, concrete spalling and longitudinal bar buckling were concentrated at the corners of the flanges due to the shear lag effect. Eventually, both specimens collapsed as a result of the flange local compression buckling. In addition, the specimen under a variable axial load collapsed much severer than the one under a constant axial load. Ultimate drifts of the specimens under a constant or variable axial load were 2.25% and 2%, respectively. This experiment provides valuable dataset for validating advanced numerical modeling techniques for thin-walled rectangular hollow RC piers, especially the data points in the collapse stage.

Seismic design and performance analysis of buckling‐restrained braced RC frame structures

SummaryDue to the stable hysteretic behavior, buckling‐restrained braces (BRBs) have been increasingly adopted in reinforced concrete (RC) frame structures to develop a dual structural system (BRB‐RCF). This study proposed an alternative strength‐based design approach that decomposes the dual BRB‐RCF system into two independent RC frame and BRB system using the BRB‐carrying story shear ratio. The design of RC frame is performed in an integrated manner by considering the BRB postyielding force demands. Three RC frames with five, 10, and 15 stories were employed as prototype structures, and seven story shear ratios ranging from 0.1 to 0.7 were used to generate a total of 21 structural modes. The material usage, maximum axial compression ratio of columns, and elastic interstory drift ratio were compared for different story shear ratios. Nonlinear dynamic analysis of the BRB‐RCFs subjected to 12 ground motions were carried out. The seismic response including the maximum interstory drift ratio, hysteretic energy dissipation ratio, and actual BRB‐carrying story shear ratio were systematically assessed for different design story shear ratios. Based on the considerations of material usage and seismic performance, it is suggested that the design BRB‐carrying story shear ratio should be in the range of 0.3 to 0.5.

Experimental Seismic Performance Evaluation of Coupling Beams: Comparison of Old with Modern Codes

ABSTRACT This study presents the results of an experimental investigation on the seismic performance of two reinforced concrete coupling beams (CBs) for coupled shear walls, one with a conventional reinforcement layout designed according to the old National Building Code of Canada (NBCC) 1941 and the other one with a diagonal reinforcement configuration designed according to modern NBCC 2015 and Canadian Standard Association (CSA) A23.3 2014 requirements. Experimental tests were conducted to investigate the behavior of specimens under reversed cyclic loading. The experimental results reveal that the diagonal reinforcement configuration could increase the load-resisting capacity and energy dissipation capacity by 4.4 and 10.2 times, respectively. Moreover, the maximum rate of stiffness degradation decreased from 96% in conventionally reinforced CB to 57% in diagonally reinforced CBs. Furthermore, diagonal reinforcement layout led to more stable hysteretic behavior without considerable pinching. In contrast and as expected, the conventionally reinforced CB did not comply with the requirements of the new design code. Therefore, such CBs should be retrofitted to upgrade their seismic performance in conformity with updated standards requirements.

A new energy dissipative cable bracing system

A special type of cable bracing system comprising a pre-stressed cable and a drum interacting via frictional contact is proposed for lateral resistance of structures, and an analytical solution for the response of this system is developed. The response of the system is highly non-linear due to the existence of frictional contact as well as geometrical effects and it consists of two phases: a linear phase before gross slipping with a relatively high stiffness followed by a non-linear phase with gradually increasing stiffness (i.e. hardening). However, the analytical solution is capable of capturing the whole response with a remarkable accuracy when compared to the finite element model of the system constructed for cross-validation. This analytical solution facilitates studying the effects of various parameters on the behaviour of the system, namely, the coefficient of friction, pre-strain and geometrical aspect ratio. These parameters can be arbitrarily set to achieve a desirable behaviour of the system. The proposed system is capable of undergoing large deformations with symmetrical and stable hysteretic behaviour. The effectiveness of the proposed device in reducing the seismic responses of a building frame is examined using a simplified numerical model.

Assessing and quantifying the earthquake response of reinforced concrete buckling-restrained brace frame structures

Due to the stable hysteretic behavior, buckling-restrained braces (BRB) have been increasingly adopted in reinforced concrete (RC) frame structures to develop a dual structural system. This investigation aims to quantify the seismic behavior of newly-constructed reinforced concrete BRB frames (RC-BRBFs). The force–deformation characteristic of dual RC-BRBFs is firstly presented and the yield displacement is derived using the story shear ratio resisted by BRB system. The seismic design procedure of dual systems for different BRB configurations (including single diagonal, V-type and inverted V-type), is developed using the performance-based plastic design approach by considering BRB postyield behavior, design target drift and global yield mechanism. 126 RC-BRBF structures corresponding to different story numbers, BRB configurations and story shear ratios are designed. The influence of story shear ratios on the design results is analyzed. The seismic response of structures subjected to 22 ground motions is investigated and compared in terms of yield mode, maximum interstory drift ratio, BRB maximum ductility and cumulative ductility, and residual drift ratio. The relationship between actual and design normalized story shear of BRBs is demonstrated and a fitting equation is proposed to quantify the actual story shear ratios. The analytical results of the present study can provide quantified insights to the seismic design of RC-BRBF structures.

Experimental Study on a New Damper Using Combinations of Viscoelastic Material and Low-Yield-Point Steel Plates

To enhance the seismic resilience of coupled reinforced concrete shear walls, a new damper working in the replaceable coupling beam is proposed in present study. The new damper is a combination of metallic damper and viscoelastic (VE) damper. The metallic damper consists of an I-shaped steel beam with multiple low-yield-point steel plate webs paralleled to each other; the VE damper is composed of multiple layers of VE material bonded between multiple steel plates. Through the composite use of viscoelastic material and low-yield-point steel, the new damper is expected to work effectively against both the earthquake and the wind. To study the respective mechanical behavior of each component of the combined new damper, eight metallic dampers, two VE dampers, and one combined damper are tested under cyclic loading first. The variable parameters of the metallic damper are strength grade of web steel, web dimensions and end stiffener configuration. It is found that the effect of the strength grade of web steel is most significant. Compared with the metallic damper using the steel web with normal strength grade, the ductility, ultimate plastic shear rotation and cumulative plastic shear rotation of the damper using the low-yield-point steel web are much larger. The effect of web dimensions on the deformation capacity is slight. With the addition of end stiffener, plasticity concentrates thereby, which prevents the flange-to-end plate weld fracture. The VE damper exhibits extraordinary deformability. The storage modulus, shear loss modulus and loss factor of the VE material decrease with the increase of strain amplitude. The storage modulus and shear loss modulus of the VE material decrease slightly as the excitation frequency increases within the range between 0.1 to 1 Hz, and the effect of the excitation on the loss factor is not significant. At last, the combined damper, an assembly of one metallic damper component and two VE damper components, is tested, which exhibits stable hysteretic behavior and excellent deformability. The predicted yield shear strength and elastic stiffness agree well with test results.

Semi-active adaptive control for enhancing the seismic performance of nonlinear coupled buildings with smooth hysteretic behavior

The efficacy of using the simple adaptive control method for alleviating the seismic responses of two nonlinear adjacent buildings connected at multiple levels with magneto-rheological dampers is investigated. The connected system is formed by two shear-type model buildings of the same height but have different dynamic characteristics so that the fundamental frequencies of the individual buildings do not coincide. A stable hysteretic behavior of the structural system is considered in the current study, which captures the variation in flexibility and energy loss under various intensity levels of seismic events. The Bouc-Wen’s nonlinear differential equation is utilized to model the hysteretic behavior of the restoring force-displacement smooth curve of the developed nonlinear structural system which is then integrated into a semi-active adaptive control system. The advantage of using the Bouc-Wen model is that it has the ability to mathematically track various shapes of the force-displacement curves by adjusting its non-dimensional parameters. The proposed nonlinear model is validated through a finite element model. Adaptive control is well suited to handle the nonlinear behavior because the adaptive control gains can be adjusted depending on the situation through a closed-loop action to yield better performance. The results show that using the adaptive controller to drive the magneto-rheological dampers connecting two adjacent nonlinear buildings can be used to effectively alleviate the seismic responses and reduce permanent deformations. However, the performance improvement is not the same under all ground motions considered in this study.