Hysteretic Performance Research Articles

Evolution of the yield penetration and bond stress in RC exterior beam-column joints under cyclic loading

Beam-column joints are key connections in reinforced concrete frame structures. Under severe earthquakes, the yield of the beam reinforcements and bond deterioration cause changes in the transfer mechanism in the joint core and affect the deformation and bearing capacity of the beam-column joints. The bond characteristic of the beam rebar in the pre-yield and post-yield states were the focus of experiments on five exterior beam-column joints; the joint aspect ratio and volume-stirrup ratio were the key control factors. The strain of the beam reinforcement was measured by electronic strain gauges located in the horizontal segment and the 90-degree hook. The failure mode of joints were discussed, the movement of the yield penetration of the beam reinforcements from the beams to the joint cores was clarified, and the bond stress and rebar slip in the anchorage length were assessed. It was found that the joint aspect ratio is an important factor to the joint failure mode, plastic hinge development at the beam ends and the contribution of rebar slip to overall story drift. When the joint volume-stirrup ratio at a certain range (0.4%∼0.63%), it does not have much influence on the final failure mode of the joint, but it has a certain influence on the plastic development and bond performance of rebars in and out of the joint. The joints with a low volume-stirrup ratio exhibited significant bond degradation caused by the Poisson’s ratio and rebar slippage, especially after the rebar had yielded. The hysteretic performance of the five beam-column joints was simulated accurately with the consideration of the rebar slip in the joint core.

Experimental and numerical analyses of the hysteretic performance of an arched aluminium alloy gusset joint

An aluminium alloy gusset joint with a 7° arch is designed and fabricated, and a cyclic loading test is carried out to address the research gap regarding the hysteretic performance of arched aluminium alloy gusset joints. The mechanical behaviour and the failure mode of the joint under a cyclic load are obtained, and the failure mechanism is explained. The hysteresis, skeleton, and stiffness degradation curves are plotted and discussed, the ductility coefficient is calculated, and the stress–strain behaviour is analysed in detail. The experimental results show that the member webs in the joint zone exhibit local buckling under a cyclic load. The row of bolts on the upper flange closest to the edge of the node plate is torn when the joint is loaded upward. A 1/4 symmetry model is established using the ABAQUS finite element (FE) software. The effectiveness of the FE simulation method and the validity of the model are verified by experiments. Furthermore, a 0° and 5° aluminium alloy gusset joint models are established to investigate the properties of the aluminium alloy gusset joint with different arched angles. It is shown that the 0° joint has lower ultimate bearing capacity and higher energy dissipation capacity and ductility than 5° and 7° joints. In addition, the failure modes of three joints have been studied, providing a reference for the seismic design of aluminium alloy structures.

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: III. Matrix and Phases of the High-Coercivity State.

Observations of the surface domain structure (Kerr-effect), optical metallography, scanning electron microscopy (SEM-SE), and electron microprobe analysis (EPMA-SEM), measurements of major and minor magnetic hysteretic loops were used to study pseudo-single-crystal samples of (Sm,Zr)(Co,Cu,Fe)z alloys subjected to heat treatments to the high-coercivity state, which are used in fabricating sintered permanent magnets. Correlations between the chemical composition, hysteretic properties, structural components, domain structure, and phase state were determined for the concentration ranges that ensure wide variations of 4f-/4d-/3d-element ratio in the studied samples. The phase state formed by collinear and coherent phase components determines the high coercive force and ultimate magnetic hysteresis loops of the pseudo-single crystals. It was found that the 1:5 phase with the hexagonal structure (P6/mmm) is the matrix of the alloys for (Sm,Zr)(Co,Cu,Fe)z permanent magnets; the matrix undergoes phase transformations in the course of all heat treatments for the high-coercivity state. The heterogeneity observed with optical magnifications, namely, the observation of main structural components A and B, is due to the alternation, within the common matrix, of regions with modulated quasi-spherical precipitates and regions with hexagonal bipyramids (cellular phase) although, traditionally, many investigators consider the cellular phase as the matrix. It is shown that the relationship of volume fractions of structural components A and B that account for more than 0.9 volume fraction of the total, which is due to the integral chemical composition of the alloys, determines the main hysteretic performances of the samples. The Zr-rich phases, such as 5:19, 2:7, and 6:23, and a structural component with the variable stoichiometry (Sm(Co,Cu,Fe)3.5–5) that is almost free of Zr and contains up to 33 at% Cu, were found only within structural component A in quantities sufficient for EPMA analysis.

Local buckling and hysteretic behavior of thin-walled Q690 high-strength steel H-section beam-columns

To evaluate local buckling and its effect on the hysteretic performance of high-strength Q690 thin-walled H-section beam-columns, cyclic testing was carried out on four H-section columns composed of plates with a nominal yield strength of 690 MPa. Based on China’s standard for the design of steel structures (GB 50010-2017), the four H-section columns are categorized as S4 and S5 sections, and the axial load ratio of the columns is 0.2 and 0.35. After the test, the failure mode, second-order effect of bending moment, hysteresis curve, bearing capacity, backbone curve, energy dissipation, ductility and stiffness degradation of the specimens were investigated. The failure mode of the specimens is elastic–plastic local buckling of the column bottom flange and web. The ductility coefficient of the specimens is 2.08–3.04, and they have certain specific deformation and energy dissipation capacities. Following this, a finite element model was established to simulate the hysteretic performance of the Q690 thin-walled H-section beam-columns. The failure mode and hysteresis curve obtained by the finite element simulation corresponded well with the tests. Based on this agreement, a parametric study was carried out to investigate the influence of the flange width-thickness ratio, web width-thickness ratio, and axial load ratio on the local buckling and hysteretic performance of H-section beam-columns. The variation trend of the backbone curve and the bearing capacity were further investigated by the finite element parametric analysis. Finally, a prediction formula for the beam-column bearing capacity was proposed based on the finite element results. The comparison with the test results shows that the proposed formula has sufficient accuracy and can be used in engineering design.

Experimental study on bolted-cover plate corner connections for column-supported modular steel buildings

The fast and reliable connection between modules plays an essential role in modular steel buildings to ensure the structure's integrity. Using complete bolt assembly can better improve the efficiency of on-site construction. To study the seismic ductility reduction of connections and obtain the measures suitable for protecting the beam-column weld in connections, full-scale experiments on the connections were carried out under monotonic and cyclic loading. The failure modes, the static and hysteretic performance of the connections were manifested. The experimental results indicated the satisfactory flexural performance and the excellent energy dissipation capacity of the bolted-cover plate connections. Earthquake action would significantly reduce the ductility of connections. Both diagonal braces and flange reinforcement could dramatically improve the connection's stiffness and bearing capacity, while the flange reinforcement has better hysteretic performance than the diagonal braces reinforcement. The yield energy dissipation of the beam flange contributes most to that of the connection. These experimental studies can provide a reference in the practical design of bolted connections for modular steel buildings.

Novel coupled modular steel structure and seismic tests on high-performance interconnection

Modular building registers the advanced stage of construction industrialization and the corner-supported steel modular building is the most widely applied. However, its structure, which is integrated by corner interconnections only, incurs the problems of structural redundancy and interconnection-assembly complexity. To this gap, this paper proposes the novel coupled modular steel structure and suitable interconnection, which significantly affects the overall structural response and assembly efficiency. Pseudo static tests of three full-scale cruciform joint specimens are implemented to study the seismic performance of interconnection. The results show that the currently proposed coupled modular steel structure could replace the incompletely-combined group-columns and laminated beams with single structural components to avoid the structural redundancy and reduce the assembly difficulty of interconnections. The proposed interconnection exhibits excellent seismic performance. Hysteretic loops of coupled beam and module beam are “bow” shape and “shuttle” shape, respectively, indicating their good hysteretic performance. Ultimate storey drift angles of coupled beam and module beam could reach 0.08–0.09 rad and 0.06–0.08 rad, respectively, which satisfy the requirement for SMF in ANSI/AISC 341-16 and indicate their excellent rotation capacity. The ductility coefficients of the specimens are 2.27–3.64 except for MC2, indicating their good ductility capacity. Adopting the flush end plate for coupled beam and high strength bolts for vertical splice is recommended for the interconnections to obtain better hysteretic performance and bearing capacity. This research provides brand new design for modular construction and references for future research on global response of coupled modular steel structure.

Seismic Performance and Fragility Analysis of Precast Concrete Sandwich Wall Structure

ABSTRACT As an innovative concrete shear wall, sandwich wall (SW) is expected to be applied to improve the seismic performance of regular shear wall (RW). The test process of SW component and precast SW structure are described, numerical models are verified by the test results, and parameter analysis is also conducted by numerical simulation to expand the tests. The results show that a better match between the stiffness, ductility, load capacity, and energy dissipation can be achieved by reasonably designing SW; there is little difference between the hysteretic performances of SW structures with different vertical loading modes, but different horizontal loading modes have great impact, it is suggested to use horizontal load distributed based on the first vibration mode or the inverted triangular, which is closer to the real seismic action. Then, the seismic design procedure of SW structure is proposed, the analysis of a design example shows that the seismic responses meet the requirements of all limit states; while the application of precast SW structure can save the consumption of concrete materials, reduce the amount of grout-filled sleeves, and reduce the complexity of assembly and workloads significantly. In addition, fragility analysis is also conducted to evaluate the seismic performance and collapse resistance of precast SW structure, the results show that the seismic performance of precast RW structure is slightly better than that of precast SW structure, however, there is little difference in the seismic fragility between SW structure and RW structure.

Numerical simulation analysis of double yield points assembled buckling-restrained brace with replaceable inner core

Based on the concept of rapidly repair after earthquake, a new type of double yield points assembled buckling-restrained brace (DYP-ABRB) with replaceable inner core is proposed. The inner core is composed of two I-shaped plates with different lengths, the peripheral component is composed of channel steel and I-shaped plates, and the unbonded layer is the gap between the core and the peripheral component. The constitutive tectonic composition and force transmission of the DYP-ABRB was carried out. The key parameters in the constitutive model of the material used in the core were determined through the material test, and the obtained parameters were input into the finite element software ABAQUS, which can truly simulate the performance of the finite element model of the brace under cyclic loading. On the base of determining the constitutive model parameters of materials, the design method of the model size and the finite element modeling of the brace, numerical simulation analysis of seismic performance was carried out on six DYP-ABRBs with replaceable inner core. The influences of different parameters, such as weakening width of inner cores, material of inner cores, length of inner cores and form of inner cores on the bearing capacity and hysteretic energy dissipation performance of braces were studied. The results show that the DYP-ABRB exhibits obvious two-stage behavior, and has stable and symmetrical hysteretic performance. All peripheral components are basically kept in the elastic state after loading, which shows that the brace has good post-earthquake repairability. After the earthquake, the brace only needs to disassemble the high-strength bolts and extract the core from both ends for replacement, and the peripheral components can still be used continuously, which greatly reduces the construction waste and economic losses, and has a good application prospect.

Shaking table test and simulation of 12-story buildings with metallic dampers located on soft soil

In this study, shaking table tests are carried out on 12-story reinforced concrete frames with metallic dampers located on soft site, and the corresponding fixed-base structures with metallic dampers are also proposed for comparison. The superstructure is connected with the 3-by-3 pile foundation by the pile cap in a designed shear laminar container, which exhibits a good ability of reducing the boundary effect. Three earthquake inputs, which include one artificial earthquake (Shanghai bedrock wave) and two recorded Kobe and Chi-Chi earthquakes with various peak ground accelerations (PGAs) are used in the shaking table test. A series of investigation are carried out on the test phenomenal, which consist of dynamic characteristics of the models, seismic analysis of the soil, and also the working mechanism of pile-soil-structure interaction (PSSI). Then, the hysteretic behavior and aseismic performance of metallic dampers in the PSSI system and fixed-base condition are compared. Finally, a nonlinear three-dimensional finite element model is built to establish a proper numerical method for the PSSI system with metallic dampers. The experimental and simulation results indicate that the PSSI system has longer periods, larger damping ratio and less decreasing degree of frequency after tests than the fixed-base condition. Meanwhile, under these earthquakes, PSSI tends to reduce the structural peak acceleration, story shear force and the elastic displacement. However, the total deformation of the superstructure is amplified significantly due to the rocking and translational deformation in PSSI system. Moreover, the hysteretic performance of the metallic dampers are degraded greatly by PSSI effect. Therefore, the PSSI effect should be considered in the design of tall buildings with metallic dampers, because the seismic analysis of the structure may be unrealistic and the performance of the metallic dampers may be overrated when it is ignored.

Experimental study on the seismic performance of precast concrete columns with thread-bolt combination couplers

A new precast concrete column system was proposed in this paper to reduce the demands of threaded couplers on the manufacturing errors of precast members and to satisfy the design philosophy of demountable and recyclable concrete members. In the precast system, a novel coupler (CTB coupler) with a combination of threaded connection and bolt fastening was adopted to provide the longitudinal rebar of the column with continuity. The CTB coupler was connected with the upper and lower rebar by threaded connection and bolt fastening, respectively. A quasi-static test was performed for two monolithic concrete columns and three precast columns with CTB couplers (CTB column) to investigate the hysteretic performance of the CTB column. The experimental results illustrated that the CTB columns exhibited an ultimate drift ratio of more than 1/50, a ductility factor of greater than 3.48, and a greater bearing capacity than monolithic concrete columns. The above results validated the reliability of the CTB coupler. Eventually, a simplified model was proposed to calculate the ultimate drift ratio of the CTB column. The calculated value of the CTB column matched well with its measured value, with the ratios of the values ranging from 0.97 to 1.03.

Cyclic behaviour of a novel torsional steel-tube damper

A novel metallic damper with torsional-yielding on the circular steel tube, called torsional steel-tube damper (TSTD), is proposed in this paper. Four specimens are designed for testing under cyclic loading to investigate their cyclic behaviour. The torsional-yielding mechanism contributes to the uniform yielding at the tube wall, results in an outstanding hysteretic performance and a high equivalent viscous damping ratio of about 0.5. Then the finite element analysis method is used for simulating the tested specimens, and the stress, strain, and parametric influence of the damper model are analyzed. Furthermore, a modified Bouc-Wen model is proposed to describe the cyclic behaviour of the tested specimens. The particle swarm optimization algorithm is used for identifying the model parameters. The identification results indicate that the modified Bouc-Wen model can accurately predict the hysteretic behaviour of the proposed damper. Finally, the proposed damper is implemented in a reinforced concrete frame model, and the nonlinear dynamic analysis method is adopted to assess the feasibility of the damper.

A novel buckling-restrained brace with auxetic perforated core: Experimental and numerical studies

Auxetic materials could exhibit desirable mechanical properties, e.g., fracture resistance, shear resistance and energy dissipation due to their unique deformation characteristics. However, the seismic performance of auxetics in disaster prevention and mitigation of building structures is rarely studied. In this study, a novel perforated negative Poisson’s ratio core buckling-restrained brace (NP-BRB) was designed and manufactured for exploring the hysteretic performance of auxetic metamaterials under cyclic load. Experiments and verified numerical simulations were conducted to investigate the effects of porosity and section weakening rate on the seismic performance. The results show that the NP-BRB has stable hysteretic curves and low compression strength adjustment factor. In addition, the parametric analysis indicated that the energy dissipation capacity of NP-BRB with relatively large section weakening rate could be improved due to auxetic behavior when the average strain exceeds 1%. These findings are beneficial to the applications of auxetic metamaterials in damping devices for mitigating seismic effects.

Experimental study of hysteretic behavior of corroded steel with multi-angle welding joints

To rationally characterize the macroscopic behavior of in-service offshore structures affected by the coupled welding-corrosion action in steel components, the hysteretic behavior of corroded D36 marine structural steel with multi-angle welding joints is experimentally studied. To simulate possible corrosion-welding scenarios, the tested specimens are prepared with the gas arc welding (MAG) method for three welding angles and processed with the accelerated electrochemical corrosion for five corrosion degrees. The elasticity modulus, tensile strength, and elongation of welded-corroded steel is observed in the monotonic tensile test conducted before the cyclic test where the hysteretic performance and energy dissipation ability is mostly concerned. On the basis of these test results, a generalized hysteretic material model for welded-corroded steel which consists of a skeleton curve, an unloading curve and a reloading curve is proposed. All the parameters used to describe these curves are related to the degree of corrosion and welding angle, determined by the regression on the test data. The effectiveness of the proposed model is verified with the tested data, including those from the specimens additionally and specifically tested.

Seismic behavior and design of repairable precast RC beam–concrete-filled square steel tube column joints with energy-dissipating bolts

The dry jointed precast frame structure has the potential in less reliance on wet concrete, low cost and repairability after earthquake. The seismic behavior of the novel precast dry connections with different beam end arrangements was studied in this work. For the precast specimens, the concrete-filled square steel tube (CFSST) column and RC beam were prefabricated, and field assembly was carried out by energy-dissipating (ED) bolts and unbonded prestressed tendons. Design equations were formulated according to the strong-column–weak-beam concept and the capacity design philosophy. The viability of the repair method of the precast internal beam–column connections after earthquake was explored. The joints were repaired by replacing the ED bolts and loaded again. The seismic indicators, such as ductility and energy dissipation capacity, were determined and compared. The results showed that the excellent structural characteristics and practical design method could ensure low damage to the joints except for the ED bolt yield. The new-type precast beam–column joints exhibited good hysteretic performance with high ductility factors greater than 5. After repair, the failure mode of the joints was controlled by the plastic hinge on the beam. The repaired joints had good strength stability, and the ultimate bearing capacity was the same as before repair. The ductility of the repaired joints was 13.29%–32.14% higher than before. The energy dissipation capacity could reach more than 1.2 times that of the cast-in-place concrete joints, which proved the feasibility of the repair method.

EXPERIMENTAL STUDY ON SEISMIC PERFORMANCE OF ENERGY DISSIPATION AND POSITION LIMITATION STEEL BRACE AND STRUCTURE SEISMIC VULNERABILITY ANALYSIS

A kind of energy dissipation and position limitation type steel brace is proposed to improve the seismic performance of a building structure. Five steel braces are designed, and the limitation displacement, limitation block number, steel core section size and length are chosen as the design parameters. Based on the test study, the characteristics including the failure mode, hysteresis loops behavior, skeleton curves, and stiffness are demonstrated. The seismic collapse resistance of steel braced frame structures is evaluated through IDA analysis. The results show that: the steel brace structure is reasonable with stable hysteretic performance, and the position limitation block could play a limiting role and provide greater additional stiffness. The number and section size of the position limitation block and the weld stiffness of the joint surface with the steel core affect the lifting degree of the additional stiffness. The calculation results of the stiffness formulas presented are in a good agreement with the experimental values, which can provide a reference for the practical design of steel braces. The collapse reserve coefficient of this type of steel braces with position limitation blocks is increased, beneficial to improve the collapse resistance of soft first storey building.

Research on the hysteretic performance of flower-gusset composite joints for single-layer aluminium alloy lattice shell structures

Joints are the most critical component of reticulated shell structures, and their hysteretic performance is crucial to the mechanical properties of the whole reticulated shell structure under seismic action. Therefore, the hysteretic behaviour of aluminium alloy flower-gusset composite joint for an out-of-plane bending moment was studied by experiments and numerical analysis. The results show that the hysteretic curves of flower-gusset composite joints and gusset joints contain four stages: an elastic stage, a bolt slip stage, a hole wall pressure-stiffness degradation stage and a failure stage. The hysteretic performance of the new flower-gusset composite joint is obviously better than that of the traditional plate joint. With the increase in the thickness of the cover plate, the bending stiffness of the flower-gusset composite joint increases significantly, while the rotational deformation decreases. Then, a restoring force model of the flower-gusset composite joint is proposed through theoretical analysis based on experiments and numerical analysis.

Full-scale corner-supported modular steel structures with vertical inter-module connections under cyclic loading

Corner-supported steel modular buildings were constructed using volumetric modules with the inter-module connections at their corners and similar connections to foundations. The rotary inter-module connections were used to assemble a two-storey building frame in this study for investigation of its the mechanical behavior. Such a full-scale building frame was examined under cyclic loading until structural failure, where the failure mode, hysteretic performance, ductility, stiffness degradation as well as energy dissipation were experimentally clarified. The results indicated that the structure experienced ductile failure with buckling at the end of the ceiling and floor beams as well as the bottom end of lower columns. The rotary inter-module connections were able to transfer the internal forces without failure although gaps were formed between the foundation corner fitting and lower corner fitting. A refined finite element (FE) modelling approach was established and validated through comparisons to experimental results, then the load-displacement curves of such steel modular structure were obtained and analyzed under different axial compression ratios as well as stiffness effect of module-to-foundation connections. Theoretical formula was further derived to estimate the initial lateral stiffness of the upper and lower frame considering semi-rigid inter-module and module-to-foundation connections, showing well agreement with the experimental and numerical results. In this way the load transferring mechanism of such modular structure with the rotary inter-module and module-to-foundation connections can be clarified.

Hysteretic performance of all-steel assembled double-cores buckling-restrained braces using Q195 low-yield core

This paper focuses on the hysteretic behavior of a proposed all-steel assembled double-cores buckling-restrained braces (DCBRB). The DCBRB employs an I-shaped steel and two channels to resist the global instability of the brace and hence to force the double-cores into high-order buckling mode for the purpose of energy dissipation. Six DCBRB specimens were fabricated, where both Q195 low-yield core and Q235B core were concerned for comparison. The quasi-static cyclic loading was conducted on the DCBRB specimens to investigate the failure modes, as well as the hysteretic behavior from different perspectives, such as hysteretic curves, skeleton curves, compressive strength adjustment factor, energy dissipation capacity and plastic deformation performance. The experimental results demonstrate that the insufficient constraining of the external restraining member could cause the global instability of the buckling-restrained braces. The specimens exhibited great and stable hysteretic responses until the axial strains of cores researched 1.5%. Finally, the cumulative plastic deformation capacities were greater than 300 for all specimens. The finite element models were established to further investigate the influence of constraint ratio and core's width-to-thickness ratio on the hysteretic behavior of the DCBRBs. The numerical results reveal that better global stability is expected to be obtained with a larger constraint ratio ζ, and the limit value of ζ avoiding the global buckling almost increases linearly with the increase of core's width-to-thickness ratio.

QUASI-STATIC CYCLIC TESTS ON THE HYSTERETIC BEHAVIOR OF BUCKLING-RESTRAINED BRACES WITH A T-SECTION CORE

An all-steel assembled buckling-restrained brace is proposed, in which both the core and the restraining members are made of section-steel. The brace has the advantages of assembly, replaceable core, easy fabrication, low cost and can be used for strengthening existing members. The steel core is composed of two angle steels and stiffening plates to form a T-shaped section. The restraining members are formed by bolting plates and angle steels through mat strips. Quasi-static cyclic tests for six specimens were carried out to investigate the hysteretic performance, seismic performance and failure modes. The effects of adding filler plates in the core, the gap between the core and the restraining members, the spacing between the two angle steels of the core, and the stopper configuration on the hysteretic performance were analyzed. The results show that the actual performance of the brace was basically consistent with the design performance. The brace specimens exhibited stable hysteretic performance. Adding filler plates in the middle of the core shows little influence on the hysteresis performance. An excessive gap between the core and the restraining member and excessive spacing between the two steel angles of the core reduced the hysteresis performance. The hysteretic performance of the braces with middle stoppers were better than the brace with end stoppers. The analysis of the seismic performance of the specimens shows that the braces have satisfactory ductility and cumulative plastic deformation capacity, which can be used as dampers in structures. By analyzing the failure modes, the stress concentration of the welding at the end of the stiffening plates will make the failure position move from the yielding segment to the stop of the weld. The middle stopper of the core can reduce the adverse effects of friction.

RESTORING FORCE MODEL OF DISC SPRING DEVICES AND ITS APPLICATION IN SELF-CENTERING RC SHEAR WALL

The working principle and mechanics behavior of disc spring device are analyzed to accurately simulate the mechanics performance of disc spring device and the self-centering RC shear wall. Furthermore, the restoring force model of disc spring device is proposed and developed. The accuracy of the restoring force model is verified through experiments. The hysteretic performance of the self-centering RC shear wall with disc spring device is numerically simulated and compared with the experimental results due to cyclic reversed loading. Results indicate that the numerical model using a restoring force model of disc spring device can effectively simulate the hysteretic behavior, self-centering performance and energy dissipation capability of the self-centering RC shear wall. The bearing capacity of the self-centering RC shear wall increases with the increase of the pre-pressed force of disc springs, the additional friction force and the stiffness of disc spring device. The energy dissipation capacity increases with the increase of the additional friction force. The residual displacement increases with the increase of additional friction and decreases with the increase of the pre-pressed force of disc springs and the stiffness of disc spring device.