Cyclic Loading Tests Research Articles

Development and experimental study of a replaceable double stage coupling beam damper

A double stage coupling beam damper (DSCBD) was proposed and tested in this paper. The DSCBD comprises a viscoelastic damper and a metallic damper connected in series. Deformation of the DSCBD in the first stage was concentrated on the viscoelastic damper, which provided initial stiffness and energy dissipation capacity. With the increase in displacement and the initiation of the second stage, the deformation of the viscoelastic damper was constrained by the limiting mechanism and triggered the deformation concentrating in the metallic damper. These further increased the stiffness and energy dissipation capacity and the DSCBD exhibits the double stage behavior. The DSCBD proposed in this paper can simultaneously satisfy the seismic requirements of the main structure under different levels of seismic excitation, without installing different types of traditional dampers to achieve the same effect. A performance-based design method was proposed. Two full-scale DSCBD specimens were subjected to quasi-static multi-stage cyclic loading tests to investigate the effects of different aspect ratios. The test results showed that DSCBD with an aspect ratio of 3.2 exhibited ideal shear failure mode, and the minimum equivalent viscoelastic damping ratio in the second stage was 22.58 %, while the DSCBD with an aspect ratio of 4.4 exhibited unexpected bending failure mode, and the maximum equivalent viscoelastic damping ratio in the second stage was 19.42 %. In addition, the DSCBD with an aspect ratio of 3.2 showed better low-cycle fatigue capacity, whose degradation of bearing and energy dissipation capacities can be controlled within 5 % after 30 additional loading cycles. The accuracy and the correction scheme of the design method were verified by the test results.

Softening index‐based equivalent linear modeling approach for bolt‐connected precast concrete frame

AbstractPrecast concrete structures with bolt‐connected joints have been widely constructed in the world, and their prospective application market is still considerable. Considering the clear load transferring path and damage mechanism, simplified analysis method is feasible for the bolt‐connected precast concrete frame. This paper proposes an equivalent linear modeling approach (ELMA) for this type of structure, which is convenient and high efficiency to help the preliminary design of structures and seismic assessment of existing buildings. In this method, a series of linear models are established to simulate the real structure in different seismic intensity levels. The softening indices summarized from the variation of modal frequencies are defined to represent the stiffness degradation of structures. In order to obtain specific softening indices, a shaking table test for a bolt‐connected precast concrete frame was implemented. Based on the test results, the recommended softening indices, applicable to bolt‐connected frames with similar design performance objectives, are 0.325, 0.713, and 0.816 for the minor, moderate, and major earthquake levels, respectively. Following the ELMA, the numerical model of the test frame was constructed and its equivalent seismic behaviors were analyzed. By comparison with the test results, the convenience and effectiveness of this method is validated, and the precision of simulation meets the requirement of engineering application. The ELMA is also applicable for precast frames with different joints or design requirements, if the softening indices are appropriately defined by shaking table test of the structure or cyclic loading test of its single‐connection model.

Seismic Performance of Shaped Steel Reinforced High‐Strength Concrete Walls: Cyclic Loading Test and Analytical Modeling

ABSTRACTThe thickness of the bottom shear walls in tall and super‐tall structures is often designed too large to meet the limit requirements of axial compression ratios, which increases the weight and cost of the structure. To address this issue, high‐strength concrete (HSC) and shaped steel are combined to form composite shear wall members. This paper focuses on seismic performance and analytical hysteresis model of steel reinforced HSC shear walls (SRHCW) under high axial compressive load. Firstly, the reversed cyclic test was conducted to investigate the influence of concrete strength and the steel ratio on the seismic performance of SRHCWs by comparing the failure mechanism, hysteretic curves, stiffness degradation, ductility, energy dissipation, and steel bar strain variation of each specimen. Then, a hysteresis model for SRHCWs was established, and the model can be used for the nonlinear analysis and seismic performance evaluation of SRHCWs. Finally, the accuracy of the proposed hysteresis model was evaluated by the experimental data. The experimental results show that under high axial compression ratio, the interstory drift ratio capacity of SRHCWs can reach 3.03% showing excellent deformation performance. The wall specimens built with different strength concrete and shaped steel ratios exhibited similar strength, deformation, and initial stiffness, indicating that the steel ratio of the wall can be effectively reduced by upgrading the concrete strength of the wall specimens while ensuring its seismic performance. The analytical model can well predict the hysteresis force–deformation curves of SRHCWs under high axial load ratios.

Experimental Study on Seismic Behavior of a New Separately‐Anchored Self‐Centering Beam‐Column Connection

ABSTRACTPost‐tensioned self‐centering (PTSC) structures that use PT tendons to assemble precast members and provide structural resistance have demonstrated superior seismic performance and self‐centering capacity. Current PTSC frames generally serially connect all beams in a floor. This assembly method would induce interferences among different spans and increase the risk of progressive failure once local damage occurs in a bay. This paper proposes a new type of PTSC joint to avoid such serial connection of beams. By employing steel beams to serve as the anchorages of PT tendons, each bay of the frame is separately prestressed. The composite prestressed beams can be readily fixed to columns by high‐strength bolts, hence facilitating the construction of such separately‐anchored self‐centering (SASC) frame building. External friction dampers are installed to enhance the energy dissipation capacity of SASC connections. Eight full‐scale cyclic loading tests are performed to compare the performance of the new SASC connections with conventional PTSC joints and also comprehensively evaluate the seismic behavior of SASC connections with different parameters. The test results validate the excellent damage mitigation abilities of both types of connections while the superior mechanical performance of the new SASC connections. In addition, the effects of key design parameters such as initial prestress level, damper force, and tendon number on the seismic behavior of the SASC connection are evaluated, and design recommendations for the application of the proposed precast beam‐column connection are also provided.

The bond-slip behavior of H-shaped steel embedded in UHPC under reversed cyclic loading

To investigate the bond-slip behavior of the interface between H-shaped steel and ultra-high performance concrete (UHPC) under reversed cyclic loading, 18 steel-UHPC and 6 steel-NC composite specimens were fabricated and subjected to both reversed cyclic and monotonic loading tests. Key parameters including concrete strength, steel fiber volume fraction, embedded length of the steel section, and loading scheme were examined. The results indicate that, under reversed cyclic loading, the bond strength of the steel-UHPC composites decreased by 7 %–15 %, while the residual bond strength decreased by 16 %–57 % compared to monotonic loading. For both loading schemes, bond strength slightly decreases with an increase in embedded length but can be significantly enhanced by increasing the steel fiber volume fraction, which also improves residual bond strength and energy dissipation under reversed cyclic loading. Additionally, bond strength increases with higher concrete strength. Finally, a damage index D derived from the bond stress-slip hysteresis curves was used to represent bond degradation under reversed cyclic loads, and a constitutive model to predict the bond-slip behavior of the steel-UHPC interface under reversed cyclic load was presented.

Experimental study on the seismic behavior of all-steel buckling-restrained brace with constrained coupler

This study proposes a novel all-steel buckling-restrained brace (BRB), in which cross-shaped (or H-shaped) steel members and double steel tubes are employed for the core members and buckling-restraining members, respectively. The core members are equipped with a constrained coupler in the central region. The square outer tube, welded to one end of the bracing system, uses spacers to prevent buckling of the inner tube. The hexagonal inner tube is connected to a constrained coupler by welding, thereby preventing the buckling of the core members. The constraint system provides a quadruple restraint mechanism comprising the inner tube, outer tube, constrained coupler, and spacers. Global and local stability are analyzed based on Eulerian theory, the principle of virtual work, and yield line theory, respectively. Cyclic loading tests were performed on four test specimens of the proposed BRB and four traditional BRBs without constrained couplers. Comparative analysis, through cyclic loading tests, reveals that the proposed BRB exhibits a stable energy dissipation performance post-yielding under compression, outperforming the specimens without constrained couplers in terms of the equivalent viscous damping ratio, cumulative plastic deformation, and the compression-strength adjustment factor. Furthermore, the numerical model was constructed and validated using the test results. The effects of the core width-to-thickness ratio and the gap size between the core member and inner tube on hysteretic behaviors were investigated. The contributions of this study can provide a reference for the application of BRBs in the engineering of more complex high-rise buildings and mega-spatial structures.

Experimental and numerical study on hysteresis behaviour of a novel dual-stage friction damper

This study proposes a dual-stage friction damper (DSFD) based on traditional friction dampers, consisting of two series of traditional friction dampers. Consequently, it has two sliding friction forces: a small and a large sliding friction force, unlike the single sliding friction force in traditional friction dampers. This paper first introduces the basic structure and working mechanism of the damper and examines its hysteresis behavior, focusing on its design details. Performance tests were conducted on two friction dampers with different preloads to determine the friction coefficients. Subsequently, cyclic loading tests were performed on the DSFD. The test results showed that the deformation of the proposed DSFD aligned with the anticipated outcomes, with the hysteresis curves exhibiting dual-stage characteristics. The damper displayed an outstanding capacity for energy dissipation. During testing, the preload force on the bolts and the damper′s energy dissipation ability were examined. Furthermore, the damper′s reliability under cyclic loading was evaluated, revealing consistent performance across multiple load cycles. This indicates that the damper can be reused after multiple earthquakes. Moreover, a refined finite element model of the DSFD was developed. The numerical simulation results were in good agreement with the experimental results regarding the hysteresis curves and energy dissipation capacity of the DSFD. The discussion on the optimized design demonstrates the protective role of the sliding plate on the bolts. Finally, a parameter analysis was conducted to examine the influence of change parameters on the damper′s performance.

Experimental seismic behavior of novel inorganic-bonded bamboo composite beam-to-column moment-resisting connections

In this study, an innovative method of gluing the slot and the bolt holes was proposed to enhance the seismic performance of the inorganic-bonded bamboo beam-to-column connections. Four different types of inorganic-bonded bamboo composite beam-to-column connections were designed. They included the conventional bolted connection with slotted-in L-shaped steel plates, the bolted connection with slotted-in L-shaped steel plates (the slots and the bolt holes are glued), the bolted connection with slotted-in T-shaped steel plates and bolt anchorage in column (the slots and the bolt holes are glued), and the bolted connection with slotted-in T-shaped steel plates and glued-in rods in column (the slots and the bolt holes are glued). Monotonic and cyclic loading tests were conducted to evaluate the seismic behavior of the novel inorganic-bonded bamboo beam-to-column connections. The test results showed that the bearing capacity of the connections whose holes and slots are filled with glue increased by 40%–120 %, compared with the conventional bolted connection. The initial stiffness of the glued connections was about 5–15 times that of the conventional connection. The ductility and energy dissipation capacity of the conventional bolted connection with slotted-in steel plates was lower than that of the glued connections. Under the joint action of the adhesive in bolt holes and slots, the steel plate and the bamboo composite worked together as a whole until adhesive failure occurred. Therefore, gluing the slot and the bolt holes was an effective method for improving the seismic performance of the inorganic-bonded bamboo composite connections. The bolted and glued connection with slotted-in T-shaped steel plates in the beam and glued-in rods in the column showed a better seismic performance and was found to be suitable for practical engineering after taking some measures on the end anchorage. In addition, it was conservative to estimate the bearing capacity of the bolted connection with glue-filled holes and slots according to Eurocode 5.

Seismic performance of novel high-strength steel external assembled 3U energy dissipator

The development of easily implemented, cost-efficient, and replaceable energy dissipation devices is increasingly emphasized to improve bridge resilience. This study introduces a novel external assembled 3U energy dissipator (EA3UED) made of high-strength steel, designed to enhance the performance of precast segmental concrete bridge piers. The EA3UED, featuring three distinct U-shaped components to provide multi-directional resistance, was evaluated through comprehensive cyclic loading tests on five different specimens to assess their failure modes and practical feasibility. Finite element analysis conducted in Abaqus further assessed parameters such as ultimate bearing capacity, energy dissipation, stiffness, and ductility to identify the optimal geometric configuration. The results indicate that the EA3UED exhibits high energy dissipation, strength, stiffness, and ductility alongside cost-effective benefits. Two primary failure modes were observed: U-shape failure and bolt fractures. The validated finite element models successfully simulated the hysteretic behavior of the EA3UED. And a parametric study based on these models examined the effects of the width of U-shape and the steel grade on the device performance. These improvements demonstrate the EA3UED’s potential for integration in future bridge pier designs, improving their resilience and performance under seismic loads.

Experimental study of friction damping connections for prefabricated self-centering rocking structural elements

Self-centering rocking structural systems provide solutions for prefabricated buildings to achieve better seismic resilience. A well-designed connection of the self-centering rocking structural elements is critical to provide stable supplemental damping to the system. In this study, an innovative friction damping connection was proposed that could better match the gap-opening-closing motion of the rocking elements. Firstly, prototype experiments were carried out to investigate the connection’s mechanical behavior. The brake pad-stainless steel interface exhibited smooth sliding without chatter, stick-slip, or damage. The average static and kinetic friction coefficients were 0.30 and 0.28, respectively, showing negligible dependence on surface pressure, amplitude, or frequency. Then, the proposed connections were applied to the prefabricated shear wall-rocking coupling beam subassembly. Quasi-static cyclic loading tests on 5 full-scale specimens of the subassembly showed typical flag-shaped hysteresis curves, and the connections performed well as expected. Moreover, the theoretical analysis accurately reflected the hysteretic behavior of the specimen. Adjusting the connection’s frictional force changed the initial damping moment ratio (IDMR) of the coupling beam, determining the rocking system’s energy dissipation and self-centering capability. A reasonable IDMR value ranged from 0.8 to 0.9.

Cyclic Loading Tests and Seismic Performance Evaluation of Arch-Shaped Concrete Masonry Segmental Pier with Annular Double Sliding System

Cyclic Loading Tests and Seismic Performance Evaluation of Arch-Shaped Concrete Masonry Segmental Pier with Annular Double Sliding System

Research on deterioration mechanism of graded gravel in high-speed railway subgrade layer based on machine vision

This study aims to investigate the macro-micro deterioration mechanism of graded gravel under cyclic loading, which is of great significance in revealing the generation mechanism of high-speed railway subgrade defects in service and guiding the subgrade reinforcement. Initially, a precise-rapid quantification method for particle shape based on machine vision was established. To further improve the existing traditional semantic segmentation model (U-Net), a novel semantic segmentation model named VGG16-UNet-CA was established, which incorporated the U-Net, VGG16 model, Bilinear interpolation, and Coordinate attention (CA). Moreover, the high-precision binary images obtained by the established model were imported into Open Source Computer Vision Library (OpenCV) to calculate the particle shape indicators rapidly. Additionally, the cyclic loading tests were carried out to characterize the macro deterioration of graded gravel based on the mechanical indicator dynamic stiffness K, and the key factor of deterioration was explored through the established machine vision method. Finally, biaxial compression models with different deterioration degree were established by Discrete Element Method (DEM) to explore the micro deterioration mechanism. It was found that the segmentation accuracy indicators F1-score, Mean Pixel Accuracy (MPA) and Mean Intersection over Union (MIoU) of VGG16-UNet-CA were 98.56 %, 97.89 % and 98.01 %, which were higher than U-Net, SegNet, PSPNet, and DeepLabv3+. During the cyclic loading, the changes of the equivalent particle diameter De and slenderness ratio Ei of coarse particles in three filler groups were not significant, while the average values of roundness Rc increased by 28 %, 31 % and 25 %, indicating that the coarse particle abrasion was the key factor of deterioration. In the DEM simulation, with the increase of Rc, the mechanical strength of graded gravel decreased and the micro indicators (e.g., sliding rate, strong force chains, and anisotropy parameter an) inside the fillers gradually decreased, while the particle rotation continuously increased. Consequently, the interlocking ability of coarse particles decreased, leading to the bearing capacity and structural stability of particle skeleton reduced. This study not only provides a novel approach to investigate the deterioration mechanism of graded gravel under cyclic loading, which contributes to revealing the generation mechanism of high-speed railway subgrade defects in service, but also provides theoretical support for subgrade reinforcement.

SERS substrates based on flexible and transparent PDMS supports with periodic hierarchical structure for in-situ detection of pesticide residues

In this work, hierarchical structure composed of periodic nanopillars and wrinkles was designed on flexible and transparent PDMS through a strategy combining template method and oxygen plasma treatment. Investigations on the SERS performance of the substrates obtained after Ag thermal deposition reveal both the nanopillars and the wrinkles contributed greatly to the enhancement. The formation of the periodic wrinkles followed the buckling theory. Under the condition of 30 % deformation and 40 W plasma power, by adjusting the deposition time to 30 min, dense distribution of Ag NPs on the hierarchical PDMS support was achieved while avoiding coverage of the nano wrinkles. The obtained substrate named Ag-30/PDMS-PW had an EF of 3.11×107, excellent uniformity and outstanding reproducibility with an RSD of 2.13 % and 4.9 % respectively. Cyclic loading and tensile tests verify the mechanical stability and perfect elasticity of the Ag-30/PDMS-PW substrate. Coupled with the bi-direction excitation ability, the as-prepared substrate was fully qualified for in-situ detection of pesticide residues, which was demonstrated by the in-situ detection of thiram and thiabendazole on apple surface with concentrations lower than the maximum residue limits. The results manifest the proposed substrate has great potential for in-situ food safety monitoring in real-world applications.

Ratcheting behaviour of Stellite 21 as laser cladding material for flange tip lift crossings repair

Laser cladding holds the promise to repair damaged rails, including flange tip lift crossings (FTLC) in tram rails. In order to further understand the effectiveness of laser cladding against rail damage, this study investigated the ratcheting behaviour of the laser cladding alloy Stellite 21, used in FTLC repairs, in comparison to the currently used rail steel grade R260. Experimental studies were conducted under uniaxial and biaxial stress-controlled cyclic loads. The study found that under identical uniaxial stress conditions, Stellite 21 exhibits superior ratcheting behaviour compared to R260 steel. Various mean stresses and stress amplitudes were also studied, revealing that increases in mean stresses or stress amplitudes resulted in higher ratcheting strains and ratcheting strain rates. Additionally, biaxial compression-torsion cyclic loading tests were performed on the R260 to replicate real-life stress conditions. The results indicated that the direction of plastic strain accumulation depended on the direction of the applied non-zero mean stress. The findings from this study are essential for calibration of parameters of cyclic plasticity models, which can be used to simulate ratcheting performance of laser-cladded FTLCs under in-service conditions for the prediction of fatigue crack initiation life and maintenance requirements of flange tip lift crossings.

Experimental and parametric study on seismic performance study of column mid-height uplift steel rocking frame

Structural overturning due to second-order effects presents a significant challenge in the design of uplift rocking frames, particularly in high-seismic regions. Existing configurations, which typically locate the uplift joint at the base of the column, exacerbate this issue by increasing rocking demands. While various solutions have been proposed to address this limitation, a design that effectively mitigates these risks while maintaining energy dissipation(ED) and self-centering capabilities remains underexplored. In response to this challenge, this study introduces a novel column mid-height uplift steel rocking frame (CMURF) that relocates the uplift joint to the mid-height of the first-story columns, restoring the column foot to a fixed condition. This design induces reverse curvature bending in the upper and lower segments of the columns, effectively reducing rocking demands and the associated risk of structural overturning. To validate this concept, a half-scale, single-span, three-story CMURF specimen was subjected to cyclic loading tests. Subsequently, 20 detailed full-scale finite element models (FEMs) were developed in ABAQUS to assess the effects of varying key parameters, such as height, span, initial prestress of steel strands, and the quantity and arrangement of LYP225 steel web hourglass-shaped pin dampers (LYP-WHP), on the seismic performance of the frame. The results demonstrate that the CMURF exhibits a characteristic double-flag hysteresis shape, indicating strong self-centering performance. Additionally, the specimen demonstrated sufficient lateral stiffness, bearing capacity, and effective control of residual deformation, with the LYP-WHP providing stable ED capabilities. The findings indicated that CMURF offers a promising solution for mitigating structural overturning risks in rocking frames while preserving critical seismic performance features. Key parameters, such as height and span, significantly influence performance, with taller structures experiencing reduced self-centering ability and seismic resilience, while larger spans improve both. The initial prestress of the steel strands primarily affects self-centering, while the configuration of LYP-WHP impacts ED. Optimal design recommendations include a self-centering coefficient between 1.52 and 2.45 and a height-to-span ratio between 1.13 and 3.63.

Experimental Study on the Bending Mechanical Properties of Socket-Type Concrete Pipe Joints

In modern infrastructure construction, the socket joint of concrete pipelines is a critical component in ensuring the overall stability and safety of the pipeline system. This study conducted monotonic and cyclic bending loading tests on DN300 concrete pipeline socket joints to thoroughly analyse their bending mechanical properties. The experimental results indicated that during monotonic loading, the relationship between the joint angle and bending moment exhibited nonlinear growth, with the stress state of the socket joint transitioning from the initial contact between the rubber ring and the socket to the eventual contact between the spigot and socket concrete. During the cyclic loading phase, the accumulated joint angle, secant stiffness, and bending stiffness of the pipeline interface significantly increased within the first 1 to 7 cycles and stabilised between the 8th and 40th cycles. After 40 cycles of loading, the bending stiffness of the joint reached 1.5 kN·m2, while the stiffness of the pipeline was approximately 8500 times that of the joint. Additionally, a finite element model for the monotonic loading of the concrete pipeline socket joint was established, and the simulation results showed good agreement with the experimental data, providing a reliable basis for further simulation and analysis of the joint’s mechanical performance under higher loads. This study fills the gap in research on the mechanical properties of concrete pipeline socket joints, particularly under bending loads, and offers valuable references for related engineering applications.

Real‐time hybrid simulation for investigating the seismic response of a bridge isolated with lead rubber bearings

AbstractThis study investigates the seismic response of lead rubber bearings (LRBs) under constant and time‐varying axial forces using real‐time hybrid simulation (RTHS). Although shake table testing can provide realistic seismic responses, it is often expensive and quite challenging for large‐scale structures. RTHS, however, offers a cost‐effective alternative by experimentally testing only the structural component of interest while analytically modeling the remaining structure. With the use of an advanced real‐time force control method, this study implemented RTHSs for a bridge isolated with two LRBs, where the LRBs are subjected to various constant axial forces due to self‐weight as well as time‐varying axial forces induced by vertical ground motions. The lateral response of LRBs was found to be significantly influenced by the magnitude of constant axial force, highlighting the importance of incorporating the effect of axial force due to self‐weight into numerical simulations. Additionally, it is crucial to satisfy the axial force boundary condition when conducting RTHS or cyclic loading tests to obtain more reliable test results. On the other hand, the time‐varying axial force generated by the vertical vibration of the bridge due to vertical ground motions has a limited impact on the lateral response of LRBs.

Revealing failure loads of cyclically loaded H-steel columns from a thermodynamic perspective

Steel failure is always defined by phenomena such as yielding and buckling. A steel structure may fail under complex conditions such as cyclic or biaxial loading, but determining its critical loads is complex. Ref. [Case Stud Constr Mat., 2023; 18] used the dataset of Ref [Eng Struct., 2018; 174 826-839] (A set of cyclic loading tests of H-steel columns with material Q345B and length 1500 mm) attempts to reveal the systematic failure law of H-steel columns during cyclic loading from residual strains based on draft stage stressing state theory, but ignoring the relativity among the elements. With our lab's growing understanding of structural failure laws' systematic and evolutionary nature, ignoring the vital connection between the stressing state theory and thermodynamics is problematic. This work uses the dataset of Ref. [Eng Struct., 2018; 174 826-839] and try to reveal the failure laws of H-steel columns from a thermodynamic perspective based on the stressing state theory and new characterization methods. We first transform amplitude strain data under cyclic loading into state variables and divides them into six parts. The network-free renormalization method can be used to characterize the stressing state evolution of H-steel columns. Further, the phase transition loads can be detected by applying clustering analysis criteria because of their attractor effect. On the other hand, Wilson's phase transition theory defines phase transition loads as the fixed points of renormalization, which can be verified by comparing the before and after renormalization (part and overall) results. Lastly, the economy index (EI) is defined as the ratio of the biaxial moment triangle area S2 to the steel column volume at the elastoplastic branch (EPB) point to verify the safety and economy of the EPB-based seismic performance design for H-steel columns. EPB-based designs increase the EI of Class IV and III H-steel columns by 258.8 % and 365.8 %, respectively. Thus, this work provides a new reference for thermodynamic-based failure and seismic performance analysis of H-steel columns.

Experimental characterization and numerical modeling of a frequency-independent viscoelastic damper

Conventional viscoelastic dampers (VED) exhibit significant frequency dependency, leading to variability in stiffness and damping properties at different excitation frequencies, which introduces uncertainties in their design and application in practical engineering. This study addresses this issue by developing a frequency-independent VED through comprehensive experimental characterization and numerical modeling. Four full-scale VEDs were designed and manufactured to explore its mechanical behavior. Cyclic loading tests were carried out under various loading conditions, including different strain amplitudes, loading frequencies, ambient temperatures, and low-cycle fatigue tests. Then, a frequency-independent mechanical model is proposed by combining an energy dissipation element with a nonlinear stiffness element in parallel. Finally, nonlinear dynamic time-history analyses were conducted on a steel frame with and without the VEDs at various ambient temperatures. The experimental results show that the developed VEDs maintain consistent hysteretic behavior across a range of frequencies, exhibit high mechanical stability under varying strain amplitudes and temperatures, and possess excellent recoverability after low-cycle fatigue test. The frequency-independent mechanical model developed in this study accurately simulates the hysteretic response of the developed VEDs, validating its applicability through experimental data. Seismic response analyses demonstrate considerable mitigations in inter-story drift ratios and residual inter-story drift ratios compared to the frame without dampers. These findings highlight the reliability and effectiveness of frequency-independent VEDs in structural vibration control, offering a promising solution for seismic performance enhancement.

Experimental study on seismic damage of SRC-RC vertical hybrid structure

In order to analyze the seismic performance of the SRC-RC vertical hybrid structure, three substructure models were designed, and the key data of structural performance, such as hysteresis curve, skeleton curve, bearing capacity, energy dissipation of structure, residual deformation and damage degree were obtained by carrying out low cyclic loading tests. According to the tests, the plastic development at the column base was delayed because of the reinforcement of section steel, and the plastic development at beam end was much more sufficient, which benefited the beam hinge mechanism in the transition area, so that the transition area has better energy dissipation capacity and deformation capacity. Based on the more sufficient lateral displacement of beam hinge, the beams suffered bending deformation obviously, and interaction between the beams and the infilled wall was significant, which led to a more complex interface force transmission, so the bending cracks and the shearing cracks were densely distributed along the full length of the beam. Meanwhile, the reinforcement of section steel not only improved the deformation capacity of the models but also resulted in more significant damage difference in positive and negative loading. To quantitatively evaluate the damage level, a seismic damage index system was proposed, including displacement damage degree, bearing capacity damage degree and residual deformation index, which reflect the increment of deformation caused by structural damage, the deterioration of bearing capacity and the residual deformation, respectively. It is suggested that the structural failure should be defined respectively under different modes: For the strength degradation behavior mode and ductility behavior mode, structural failure should be confirmed if the load reduces to 0.90 and 0.85 times of the peak load, respectively; and for the brittle behavior mode, the frame is considered to fail when the load reaches the peak without considering the structural performance after the peak load.