Axial Compression Ratio Research Articles

Experimental investigation on seismic behaviour of concrete-filled corrugated steel tubes under cyclic torsional loads

Concrete-filled thin-walled galvanized corrugated steel tube (CFCST) is a novel composite member with competitive mechanical behaviour, durability and construction convenience. Several preliminary experimental and numerical works have been conducted on the compressive, flexural, shear, and monotonic torsional performances. However, the unique geometric characteristics of the helical corrugated steel tube (CST) may lead to significant torsional direction-dependent behaviour and complex cyclic torsional working mechanisms, which have not been investigated. This paper therefore presents an experimental investigation of the CFCST under cyclic torsional loads, encompassing the main test variables of member types, diameter-to-thickness ratios, axial compression ratios, and core concrete strengths. The failure modes, hysteretic curves, ductility, energy dissipation capacity, and stiffness degradation are carefully addressed. The cyclic torsional working mechanism of CFCST is discussed through the cyclic test results and strain analysis. The cumulative damage caused by the cyclic torsional loading case is also analysed via the comparisons between the monotonic and cyclic experimental results. The applicability of the existing design methods for the torsional bearing capacity is examined, with specific design suggestions proposed.

Finite Element Analysis on the Seismic Performance of Concrete-Filled Steel Tube Columns with a Multiple-Chamber Round-Ended Cross-Section

This study proposes a form of concrete-filled steel tube column with a multiple-chamber round-ended cross-section (M-CFST). Longitudinal and transverse stiffening ribs divide the circular-ended section into different chambers, strengthening the steel tube’s confinement effect on the core concrete and improving the component’s seismic performance. A three-dimensional finite element (FE) solid model of the M-CFST is created by employing the FE software ABAQUS. Quasi-static analysis is conducted to investigate the influence of parameters, such as chamber arrangement, aspect ratio, and axial compression ratio, on flexural hysteresis performance. Moreover, the failure modes, hysteresis curves, skeleton curves, strain development, and energy dissipation of the components are analyzed. The results show the following: (1) The FE model presented in this study can simulate the quasi-static behavior of CFST columns accurately, and the calculated results are in good agreement with the measured values. (2) The seismic performance of the composite column is excellent, with a large number of chambers leading to a robust hysteresis curve for the composite columns, resulting in increased bearing capacity and energy dissipation capacity. However, the energy dissipation performance of the specimen with a two-chamber arrangement is slightly lower than that with a single-chamber arrangement. (3) The results of the finite element analysis suggest that the long and short sides of the CFST columns with a large length–width ratio should be arranged to be relatively close in length.

Shaking table tests on inclined collapse mechanism of RC frame structures subjected to earthquakes

Inclined collapse of structures under strong earthquakes threatens the adjacent infrastructures. The collapse mode and collapse direction should be considered with caution to curb the secondary disaster in the urban area. However, current studies on the inclined collapse mechanism are predominantly limited to the qualitative and intuitive understanding. To fill this gap, this study presents an insight into the inclined collapse mechanism of the reinforced concrete (RC) frame structures with two typical features subjected to earthquakes, i.e., the structures with slab opening on one side of the first floor and the structures with disparate axial compression ratios of the first story columns on the opposite sides. First, shaking table tests were performed on two 1/10-scale three-story RC frame structure models undergoing inclined collapse. Then the multi-scale finite element models were established, validated against the test results and used for parametric studies. In the parametric studies, two coefficients were considered to describe the typical features of the RC frame structures, i.e., the strong column-weak beam ratio η and differential rate of the axial compression ratios λ. The test and numerical results found that the inclined collapse mechanism was attributed to the different distributions and discrepant resistance deterioration of the plastic hinges among the first story columns of the RC frame structures with the two features. This causes the inconsistent damage levels among the first story columns, the dominant direction of the lateral displacement, and the inclined collapse of the structures. Finally, the collapse mode and collapse direction can be controlled by appropriately adjusting the two coefficients η and λ for the structures with the typical features concerned in this study.

Experimental and simulation study on seismic performance of steel‐PVA hybrid fiber cementitious composites‐encased CFST

AbstractSix hybrid steel and PVA fiber cementitious composite (S&PFCC)‐encased concrete‐filled steel tube (CFST) columns were designed and fabricated, and the effects of axial compression ratio, core concrete strength grade and steel tube thickness on the seismic performance of composite columns were studied. The test results show that the increase of core concrete strength can obviously improve the bearing capacity and energy dissipation capacity of composite column and can restrain the strain growth rate of steel tube after yielding. Low axial compression ratio and thicker steel tube thickness can improve the overall seismic performance of composite columns. Three calculation methods are modified, and the modified An method can predict the lateral bearing capacity of composite column well. Finally, based on the OpenSees finite element software, the seismic performance of the CFST column wrapped in S&PFCC is simulated to verify the test, and the numerical study shows that the seismic performance of the composite column can be optimized by increasing the steel fiber content, while PVA fiber has a weak effect in the elastic stage, and can effectively improve the ductility of the composite column in the plastic stage.

Experimental Study on Repairing/Restoration and Reinforcement Methods of the Reinforced Concrete Structures Damaged by Earthquakes

For earthquake-damaged reinforced concrete structures, the static loading test method is adopted to carry out loading tests under cyclic loading on reinforced concrete beams with different reinforcement rates and columns with different axial compression ratios, and the effect of reinforcing and repairing the damaged reinforced concrete structure by using adhesive steel plates and carbon fiber cloth is investigated. Through comparative studies of structural hysteresis curves and skeleton curves under different reinforcement methods, it is concluded that reinforcement has significantly improved the hysteresis characteristics and ductility of members, and the seismic performance of the carbon fiber reinforcement method is better than that of the steel plate reinforcement. This study provides valuable references and suggestions for practical earthquake-damaged building reinforcement and repair works and seismic reinforcement works.

An Investigation on the Seismic Behavior of the End-Plate Connection between a Steel Beam and the Weak-Axis of an H-Shaped Column Using a U-Shaped Connector

The seismic behavior of the end-plate connections between a steel beam and the weak axis of the H-shaped steel column using a U-shaped connector was investigated using numerical analysis. Finite element (FE) models were established using ABAQUS 6.14 software, and the applicability of the modeling approach was verified by comparing the numerical results with the relevant experimental results. This parametric study of the joint was carried out to analyze the effects of the thickness of the U-shaped connectors, the thickness of the end-plates, the axial compression ratio of the columns, and the linear stiffness ratio of the beam to the column. The results show that the U-shaped connector set in the weak axis of the H-shaped column can form a box-shaped panel zone with the column flange and web. The volume of the panel zone and its resistance to shear deformation are increased through this connection. Finally, the recommended reasonable ranges for the thickness of the U-shaped connector, the thickness of the end-plates, the axial compression ratio of the columns, and the linear stiffness ratio of the beam to the column are proposed in this paper.

Experimental study on durability of steel-basalt fiber reinforced concrete under multiple factors coupling

A series of durability tests were conducted using varying composite salt solutions (5% Na2SO4 + 3.5% NaCl, 10% Na2SO4 + 3.5% NaCl, and 3.5% NaCl) and stress levels (F-0.3, F-0.6) to investigate the durability of concrete reinforced with steel and basalt fibers. Specimens were extracted after 0, 25, 50, 75, 100, 125, and 150 wet-dry cycles to explore the changes in the appearance, mass loss, relative dynamic modulus of elasticity, and compressive strength with the number of wet-dry cycles and different coupling effects. Mathematical models correlating mass and compressive strength with wet-dry cycles and stress levels were separately established. The concrete microstructure under coupling effects was observed using Environmental Scanning Electron Microscopy (ESEM). The results indicated that the inhibitory effect on the increase in concrete mass was higher in the F-0.6 group than in the F-0.3 group, showing that concrete under F-0.3 exhibited faster mass growth. As the axial compressive stress ratio increased, steel-basalt fiber reinforced concrete's relative dynamic modulus of elasticity changed less. Concrete degradation was more pronounced in the 10% Na2SO4 + 3.5% NaCl solution and F-0.6 loading environment. The calculated results from the established models agreed with the experimental results, demonstrating a certain degree of feasibility.

Experimental investigation of transition composite connections in historic style buildings

Historic timber buildings possess immense historical, artistic, and scientific value, but a few of them have survived after thousands of years of natural disasters and wars. Historic style buildings with modern construction material, imitating historic timber buildings forms, have emerged to inherit and promote traditional culture. To investigate the seismic performance of transition columns commonly used in historic style buildings, two full-scaled composite column transition (CCT) connections between steel reinforced concrete (SRC) square column and reinforced concrete (RC) circular column were designed and tested under invariable axial load and cyclic lateral load. Both failure patterns and force mechanism were studied based on the test process of the CCT connections. Then, the influence of axial compressive ratio on the mechanical behaviour of the CCT connections was assessed by looking at the hysteretic curves, backbone curves, characteristic loads, ductility, energy dissipation capacity and strength degradation. The results demonstrated that the failure patterns of the CCT connections were typical flexural failure, with the failure zone occurring at the upper column-root. The CCT connections exhibited excellent capacities of deformation and energy dissipation. As axial compression ratio increases, the failure of the CCT connection becomes more severe, leading to enhanced energy dissipation capacity. However, the strength and ductility of the CCT connection decrease. Based on the experimental results, an equation for calculating the lateral stiffness of CCT connections between SRC square column and RC circular column in historic style buildings was proposed, and verified to be accurate. The findings can provide necessary basis for the rational design and widespread application of historic style buildings.

Seismic behavior of Q620 high-strength steel welded Box-section columns: Experimental tests, analysis, and model

This study experimentally and numerically investigates the seismic behavior of high-strength steel (HSS) welded Box-section columns. The HSS structures have made rapid development in various types of building structures. However, the high yield-to-tensile ratio of HSS limits its application in seismic design. To address this gap, a new type of HSS called Q620 has been developed by Hebei Iron and Steel Co., Ltd. (HISCO). A total of three specimens were designed by this seismic-resistant Q620 HSS material and tested under cyclic load. The main failure modes included local buckling of the bottom section of the column, and obvious flexural deformation led to fracture of the specimen. Additionally, the nonlinear kinematic hardening model was utilized to accurately establish the finite element (FE) model for the HSS welded Box-section columns. Based on the validated FE model, an extensive parametric analysis (e.g., width-to-thickness ratio, axial compression ratio, and slenderness ratio) was conducted to evaluate the seismic behavior of the Q620 HSS welded Box-section columns. The results indicated that the Box-section columns exhibited favorable hysteretic behavior and notable plastic deformation capacity. A higher width-to-thickness ratio resulted in a faster decline in stiffness and a more pronounced advancement of damage. The ductility and energy dissipation capacity of Box-section columns were generally decreased with increasing axial compression ratio or slenderness ratio. A newly simplified hysteretic model was proposed, which was in good agreement with the experimental results.

Seismic behavior test and plastic hinge theory for HRB500 prefabricated steel reinforcement cage-cast-in-situ concrete columns

An innovative method for constructing concrete columns has been proposed, namely utilizing the hot-forged double-lock mother combined mechanical sleeve connection for the HRB500 prefabricated steel reinforcement cage－cast-in-situ concrete (PRC-CISC) columns. The purpose of this method is to promote the industrialization of steel reinforcement projects and enhance the quality of structural construction. Two traditional reinforced concrete (RC) columns and four PRC-CISC columns were designed for quasi-static tests with design axial compression ratio (ACR) and reinforcement connection methods as parameters. Firstly, the results of the study showed that all specimens exhibited typical flexural failures, with well-rounded hysteresis curves, gradual stiffness degradation in the later stages, good ductility, and energy dissipation. Mechanical sleeve connections had a minor impact on the failure mode of PRC-CISC columns. Increasing the ACR improved the carrying capacity but reduced ductility, narrowed the hinge zone, and increased longitudinal bar stress. The effect of sleeve connection on energy dissipation, stiffness, ductility, and carrying capacity of the specimens was limited, and the overall behavior was stable and controllable. Furthermore, the carrying capacity and stress distribution of core area steel bars in traditional RC columns and PRC-CISC columns were further calculated to assess the differences. Finally, a two-stage plastic hinge calculation theory was formulated, which takes into account the influence of axial pressure, and construction recommendations for two types of PRC-CISC columns were provided.

Experimental investigation of steel-reinforced precast shear wall with replaceable energy dissipators

To improve the bearing and energy dissipation of the precast concrete (PC) shear wall, this paper proposes an angle-section and C-section steel embedded PC wall with external low-yield-point steel (LYP) energy dissipators (EDs). The wall is an energy-dissipation and load-bearing bi-functional system during the seismic and a design method for this wall is also presented in this paper. Two full-size precast shear walls with and without external EDs (PWE and PW, respectively), were designed based on the proposed method and tested under an axial compression ratio of 0.2. Seismic performance in terms of failure modes, hysteretic behavior, strength envelope, stiffness degradation, energy dissipation, and steel strains was investigated and discussed. According to the crack pattern observed during the test, the PW and PWE were found to be in flexural–shear failure mode, and the PWE exhibited better seismic behavior compared with the PW, The yield and peak loads of the PWE compared with those of the PW increased by 23% and 22%, respectively. The equivalent viscous damping ratios of the two walls exceeded 0.05. When the walls were under a large displacement, the equivalent viscous damping coefficient of the PWE was higher than that of the PW. Moreover, the cumulative energy dissipation of the PWE exceeded that of the PW by 15–55%. The strain in the embedded steel in the PWE was less than that in the PW, indicating that the PW suffered more nonlinear strain and concrete damage. Test results indicate that the supplementation of replaceable external EDs can improve lateral bearing and energy dissipation capacities as well as decrease the nonlinear strain to reduce the extent of damage to wall panels. Additionally, the analytical model of PWE based on the fiber model was proposed and the rationality of the model was verified by comparison of the numerical and tested results. Furthermore, a parameter analysis was conducted to investigate the seismic behavior of PWE considering various structural properties.

Seismic performance and flexural strength prediction of high-strength bar reinforced UHPFRC walls under high axial load ratio

A new-type shear wall built with high-strength reinforcement and ultra-high performance fiber reinforced concrete (UHPFRC) is proposed in this paper, aiming to solve the problem of too large cross-section size of bottom shear wall members of high-rise and super high-rise buildings. Four UHPFRC wall specimens built with high-strength reinforcement were tested under cyclic loading to examine the influence of the parameters of fiber volume fractions (0 vs. 1.5% vs. 2.5%) and the spaces of horizontal distribution reinforcing bars (150 mm vs. 300 mm) on the seismic performance. In addition, a calculation method of flexural strength of UHPFRC shear wall is established. The research results show that: the UHPC wall specimen without fibers failed in the axial compression brittle mode, and the UHPFRC wall specimens with fibers failed in flexure-dominated ductile mode. The bridging effect of steel fibers at the cracks kept the integrity of the UHPFRC. The drift ratio capacities of the UHPFRC wall specimens under high axial compression ratio of 0.5 were 3.56%. Increasing the fiber volume fractions can improve the strength, initial stiffness, and cumulative energy consumption of the wall specimens, reduce the damage degree of the UHPFRC at the toes of the wall specimens, and can also reduce the reinforcement ratio of horizontal reinforcement without influence on the seismic performance. The proposed method of flexural strength of UHPFC walls shows reasonable prediction accuracy.

Finite element analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints

This paper presents a finite element (FE) analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints (PCCC-RBIJs) under low cyclic loading. Based on the constitutive relationship of materials, a FE model was established using ABAQUS and validated against the experimental results of ring beam joints found in the literature. Then, FE parametric analysis was performed to investigate the influence of studied parameters on the seismic performance of the PCCC-RBIJs. These studied parameters included the axial compression ratio, height-diameter ratio of the ring beam joint, column longitudinal reinforcement ratio, reinforcement ratio and stirrup ratio of ring beam, and joint concrete strength. The FE analysis showed that the seismic performance of PCCC-RBIJ specimens can be enhanced by increasing their axial compression ratio, column longitudinal reinforcement ratio, and ring beam reinforcement ratios or decreasing their height-diameter ratio of the ring beam joint. Although the joint concrete strength and ring beam stirrup ratio have little effect on the seismic performance of the joint, the ring beam stirrup ratio affects the stirrup utilization. The paper also provides design suggestions for PCCC-RBIJs.

Coupled behavior and seismic performance assessment of square-over-round RCFDST column with reinforced ribs to steel beam joints under cyclic loading

The cyclic loading test study and finite element analysis (FEA) were conducted to investigate the seismic performance of five square-over-round recycled concrete-filled double skin steel tubular (RCFDST) columns with reinforced ribs to steel beam joints varying parameters such as the length of ribs, hollow ratio, axial compression ratio, the ratio of beam-column flexural linear stiffness and strength of the recycled concrete. It was found that a larger the displacement resulted in a lower the strength degradation. Moreover, the structures with two types of concrete showed similarities in strength degradation. In the experiment, compared to the cases without reinforced ribs, the specimens with reinforced ribs exhibited a larger value of stiffness and related rigidity degeneration primarily, and then showed a slow trend in rigidity degeneration laterally. The ductility of the cases with recycled concrete is twice that of the cases with normal concrete. In addition, the FEA model with optimal β of 0.5 agreed with the experimental results in both their damage patterns and horizontal load-displacement hysteresis curves. According the ratio of performance to cost, the optimal ratio of beam-column flexural line stiffness (km) is found in a range from 1.0 to 1.5. In a whole, the joints with reinforced ribs show generally excellent seismic performance.

Working mechanism evaluations of full-scale joints with bolted-cover plate connection for modular steel buildings

The force-reliability of the modular structural joints is crucial for ensuring the structural integrity of modular steel buildings. However, the welds connecting the beam and column within the module are susceptible to tear during seismic events. This mode of failure greatly undermines the ability of these joints to withstand seismic forces. Four full-scale modular structural joints with bolted-cover plate connection were designed and conducted for seismic performance testing, emphasizing the significance of methods such as reinforcing diagonal braces and strengthening flanges on the protective effect of beam–column welds in the module. The simplified modular structural joint and frame finite element model were proposed based on experimental data, refined finite element modeling, and theoretical analysis. The findings suggest that the seismic behavior of the modular structural joint remains unaffected by variations in axial compression ratio within the designed range of parameters. The beam–column weld of the module in the reinforced joint exhibits almost no weld tearing, and both strengthening methods demonstrate exceptional capacity for energy dissipation. The proposed simplified modeling method facilitates the efficient determination of the modular structural joint bearing capacity and the lateral stiffness of the modular frame. The research findings presented in this paper can serve as a valuable reference point for the engineering design of modular steel structures.

Sectional strength design of l-shaped irregularly concrete-filled steel tube column under axial compression and any directional moment

Authors’ previous research proposed a new kind of L-shaped irregularly concrete-filled steel tube column (L-ICFSTC) and conducted the experimental and numerical investigation into it under eccentric compression. In this paper, authors further study the sectional strength capacity of L-ICFSTC under axial compression and any directional moment and establish a complete set of design formulas for it. The FE model validated by the authors’ previous experimental results is adopted to the parameter analysis of this study. The involved parameters include the length of two column limbs, the thickness of steel tube, the material strength and the axial compressive ratio, and consider the possibility of unequal length between two column limbs. Due to the irregularly-shaped section and two materials with different properties, the load-bearing behavior of L-ICFSTC is significantly related to the angle of moment, making its interaction curves and design formulas much more complex than current those of rectangular or circular CFST columns. Therefore, we start from the capacity of L-ICFSTC under pure unidirectional moment, and then study the capacity of L-ICFSTC under axial compression and unidirectional moment, and based on this, we finally obtain the capacity of L-ICFSTC under axial compression and any directional moments. The complete set of design formulas is established by theoretical analysis and fitting the N-M curves and Mx-My curves obtained by FE model. The formula results can agree well with the FE investigation results, demonstrating its applicability to the engineering design of L-ICFSTC.

Impact Analysis of Section Seismic Capacity in Potential Plastic Hinge Zone of Engineered Cementitious Composite Based on OpenSees

In this paper, OpenSees is used to analyze the moment-curvature (M-φ) curves of the bottom cross section of 4×40m continuous girder piers under the same reinforcing conditions, which are completely made of C40 concrete, partially made of Engineered Cementitious Composite material concrete(ECC) outsourced concrete, and completely made of ECC concrete, and then evaluate its seismic performance. Meanwhile, the yield curvature and ultimate curvature changes of the abutment section under different axial compression ratios are investigated. The results show that the yield curvature and ultimate curvature of ECC are larger than those of ordinary concrete, and the deformation capacity of ECC is stronger under the same axial force. The results also show that the yield moment and yield curvature of the section gradually increase with the increase of axial compression ratio, and the curvature ductility of the section deteriorates.

Experimental study on the seismic performance of concrete-filled steel tube columns with a multiple-chamber round-ended cross-section

Reinforced concrete bridge piers with round-ended sections are susceptible to bending, bending–shear, and shear failure after earthquakes in high-intensity areas, thus necessitating improved seismic performance. This study introduced a novel design for a concrete-filled steel tube (CFST) column, featuring a multi-chambered, round-ended cross-section. The use of longitudinal and transverse stiffeners divided the column section into distinct chambers, thereby enhancing the seismic performance of the columns. A total of 12 groups of static tests were performed to examine the effect of chamber layout, axial compression ratio, and aspect ratio on columns’ hysteresis behavior, and the hysteresis curves, skeleton curves, failure modes, stiffness degradation, ductility, and energy dissipation capacity were obtained. Results demonstrated the favorable seismic performance of composite columns. Additionally, an increase in chambers led to a full hysteresis curve, enhancing bearing and energy dissipation capacities. The displacement ductility coefficient (μ) ranged between 3.88 and 7.45, and the design parameters have minimal influence on the stiffness degradation of the composite beam. Based on the results, the long and short sides of the CFST columns with a large length–width ratio should be arranged to be relatively close in length.

Dynamic Brazilian tests of yellow sandstone under coupled static and dynamic loads

Through a series of static mechanical tests and (SHPB) dynamic impact tests, the static and dynamic mechanical parameters of rock as represented by yellow sandstone are determined, and the Holmquist-Johnson-Cook model parameters of the rock are calibrated using the test data and theoretical calculations. The feasibility of a numerical model is verified, and numerical analysis of the SHPB impact process under different radial pressure pre-loading is carried out on the basis of good verification. The results show that with increasing impact load, the degree of rock breakage increases, as does the dynamic tensile strength. With the application of increasing pre-static pressure, the dynamic tensile strength of the rock decreases gradually, and the maximum radial cumulative strain increases continuously under a given impact pressure, indicating that micro-cracks in the rock develop initially and then expand under the influence of pre-static pressure; the rock is more easily broken, and its weakening degree increases. Under coupled dynamic and static loading, the energy utilization rate of rock in the Brazilian splitting process is jointly affected by axial compression ratio and impact load. Too large a pressure ratio will reduce the strain-rate sensitivity of rock, resulting in low energy utilization rate, while too low an axial compression ratio will make the dynamic tensile strength of rock relatively high, which is not conducive to tensile failure. Therefore, on the premise of clear fracture form requirements, a suitable combination of axial compression ratio and impact velocity can improve the rock crushing effect and energy utilization rate.

Bearing capacity of horizontal joints of UHPC prefabricated shear walls with vertical bars splicing by cold-extrusion sleeves

To study the shear performance of the horizontal joints of ultra-high-performance concrete (UHPC) prefabricated shear walls with vertical bars splicing by cold-extrusion sleeves, unidirectional loading tests for three samples have been conducted and a method to calculate the shear bearing capacity of the horizontal joint has been proposed. The influence of the reinforcement ratio and axial compression ratio on failure mode, cracking morphology, load-displacement curve, and shear bearing capacity of the horizontal joints has been analyzed in the tests. In addition, the failure process of the three samples has been simulated using finite element method. The results showed good agreement between the test results and numerical results, which certified the validity of the proposed calculation method for the shear capacity of the horizontal joint. The test results showed that the cold extrusion sleeve connection can effectively transmit the stress of the reinforcement, and the shear bearing capacity of the horizontal joints of the UHPC prefabricated shear wall can be enhanced by increasing the axial compression and reinforcement ratios.