High Axial Compression Ratio Research Articles

Seismic performance of square concrete-filled steel tubular column-composite beam single-side bolted joints: An experimental and numerical study

The seismic behavior of square concrete-filled steel tubular (SCFST) column-composite beam single-side bolted joints has not been fully investigated. To address this gap, both experimental and numerical studies were conducted, focusing on the impact of various parameters. This research entailed constructing and testing nine prototypes of SCFST column-composite beam single-side bolted joints, scaled to a 1/2 zoom ratio, under conditions simulating seismic loads. Variables considered in these tests included the presence of stiffener ribs, bidirectional stirrups, the section height of the steel beam, and the axial compression ratio. A finite element model was developed and its accuracy was affirmed through comparison with the experimental outcomes. The analysis encompassed several aspects: the hysteretic response, skeleton curves, strain, ductility, stiffness degradation, and energy dissipation. The findings revealed that the design of bidirectional stirrups is crucial, especially under high axial compression ratios (n = 0.8), in preventing compression-flexure failures at the column ends. The hysteresis curves of the specimens manifested in two distinct shapes: spindle-shaped with bidirectional stirrups and bow-shaped without them. Enhancements such as the addition of stiffener ribs or an increase in the steel beam’s height resulted in a more comprehensive hysteresis curve, and improvements in the initial rotational stiffness, flexural bearing capacity, and energy dissipation capability of the specimens were observed. Notably, even when the beam-column bending capacity ratio in the SCFST column-composite beam single-side bolted joint reached 1.5, the joint’s energy absorption was predominantly governed by the beam’s energy dissipation.

Comparative analysis of the seismic performance of ECC jacket reinforced columns with different cross-sectional forms subject to different load modes

Based on the high tensile strength and tensile strain of (engineered cementitious composites) ECC, it is applied to the weak link central columns of subway stations to enhance their seismic resilience. In this study, the effects of the column's cross-sectional shape, ECC jacket form, and the vertical gravity load and vertical dynamic load during seismic action on the hysteretic performance of the column were thoroughly analyzed. A constrained constitutive model for cementitious materials, a reinforced hysteresis constitute model, and a calculated damage factor for concrete were adopted to establish a three-dimensional refined column model with an experimentally verified error of less than 10 %. After that, the damage distribution and damage degree of the columns, as well as the changes in hysteretic performance such as hysteretic curve, skeleton curve, energy dissipation, and stiffness degradation were analyzed by the static model analysis. The results showed that the columns had higher damage levels under high frequency and high amplitude of dynamic axial compression ratio in the vertical direction compared to the constant high axial compression ratio, and the ECC jacket could effectively reduce the damage levels of the columns, but the use of the in-built ECC (IB-ECC) jacket was better than the out-sourced ECC (OS-ECC) jacket. In addition, the IB-ECC jacket did not significantly improve the peak bearing capacity of the columns, but significantly improved the ultimate bearing capacity and displacement ductility of the columns, while the OS-ECC jacket significantly improved the peak bearing capacity of the columns. The ECC jacket was also effective in slowing down the stiffness degradation of the columns. This study significantly contributes to the design strategies for enhancing the resilience of columns in subway stations.

Seismic behavior of a hollow precast concrete shear wall with insulation under high axial compression ratios

A hollow precast concrete shear wall (HPCSW) with multiple vertical hollow cores that is advanced in lightweight and thermal insulation is studied in this paper. Novel tapered grouted sleeves (TGSs) are developed to connect the adjacent shear walls, which can avoid grouting defects through visible grouting processes. Seven full-size specimens with an aspect ratio of 3.3, including three solid precast shear walls, three hollow precast shear walls, and a cast-in-place (CIP) shear wall, were subjected to cyclic loading tests, which considered different and high axial compression ratios (ACRs) of 0.3, 0.45, and 0.6. The results show that the solid precast shear wall with the TGS connection displays comparable failure mode and seismic behavior with the CIP one. In contrast, the HPCSW suffers hollow core crushing under high ACRs, leading to a significant reduction in deformation and energy dissipation capacity. Finally, numerical models of HPCSW specimens with different layouts of the hollow cores were established using ABAQUS to evidence the test results and optimize the structure. The results show that the configuration of the outer hollow cores influences the seismic behavior of the HPCSW vastly. It is recommended that the concrete is partially filled into the outer hollow cores to obtain good insulation and seismic capacity simultaneously, with the filling height greater than the predicted crushing height.

Experimental investigation on lateral resistance capacity enhancement effect of a self-centering shape factor in self-centering pier systems

In self-centering (SC) pier systems, a rocking interface is typically employed at the bottom of a pier to achieve a gap-opening mechanism. However, compared with the full-section bending state of the bottom section of a ductile pier (DP), the local compressive state of the rocking interface in the SC pier inevitably leads to a significant reduction in the lateral resistance capacity. Although a prestressing tendon (PT) force can improve the lateral resistance capacity, it also induces local damage. Moreover, its enhancement effect is limited, particularly in the case of a column with a high axial compression ratio. Therefore, this study proposes an innovative measure to significantly improve the hysteretic performance of an SC pier without inducing additional damage, which is to raise the location of the rocking interface. First, the SC shape factor ξSC is innovatively defined to quantify the above-mentioned measure, and its working mechanism is investigated in detail in this study. Second, a high-lateral-resistance SC pier system (HLRSCP), which applies the concept of ξSC, is proposed and introduced for its advantages. Third, hysteretic tests of the DP and HLRSCP with high axial compression ratios are performed and analyzed. Finally, the enhancement effect of ξSC on the lateral resistance capacity is parametrically examined using a finite element model, and the feasible region of ξSC is inferred and presented. The results validate the effectiveness and feasibility of the concept of the SC shape factor in improving the hysteretic performance of the SC pier system.

Experimental Study on the Seismic Performance of Insulated Single-Sided Composite Shear Walls under Different Shear Spans and Axial Compression Ratios

The new insulated single-sided composite shear wall (NISCSW) composition involves setting a precast wall panel on one side and an insulation panel on the other side, with a middle cavity for casting concrete. To investigate the seismic performance of NISCSW under different shear spans and axial compression ratios, eight specimens are made, including six composite and two cast-in-place walls. The shear span ratio is controlled at 1.2 and 1.9, and the axial compression ratio is controlled at 0.1, 0.3, and 0.4. The specimens are subjected to quasistatic tests to analyze failure modes, hysteresis characteristics, stiffness degradation, displacement ductility, and energy dissipation capacity and to compare the seismic performance of the composite and cast-in-place walls. Results show that for each composite specimen, under the same axial compression ratio, the large shear span ratio specimen has a lower ultimate bearing capacity and faster stiffness degradation but better ductility and postyield energy dissipation capacity. Under the same shear span ratio, the high axial compression ratio specimen had a higher ultimate bearing capacity, slightly worse ductility, and similar stiffness degradation and energy dissipation capacity compared to other specimens. Compared with the cast-in-place specimen with the same axial compression ratio, the composite specimen failure mode and hysteresis characteristics are similar, and the ductility and energy dissipation capacity are comparable to the cast-in-place shear wall specimen, indicating that NISCSW has similar seismic performance to the cast-in-place shear wall under conditions of a large shear span ratio and high axial compression ratio. Based on the test results, the program ABAQUS is used to simulate the specimens. Compared with the test results, the simulated specimen failure mode is consistent with the test results, and the hysteresis and skeleton curves are consistent with the test curve, indicating that the model is correct, reliable, and can be verified with test results.

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.

Numerical simulation on dynamic compression properties of sandstone under axial static preload

In this study, through a series of static mechanical tests and split Hopkinson pressure bar (SHPB) dynamic impact tests, the static and dynamic mechanical parameters of yellow sandstone are determined, and the Holmquist–Johnson–Cook model parameters of the rock are determined by the test data and theoretical calculation. The feasibility of a numerical model is verified, based on which the SHPB impact process under different axial pressure is subjected to numerical analysis. The results show that with increasing impact load, the degree of rock breakage increases, and the dynamic compressive strength and dynamic elastic modulus increase continuously. With the application and increase of axial pressure, the dynamic compressive strength and dynamic elastic modulus of the rock decrease gradually under the same impact load, and the maximum cumulative strain keeps increasing, indicating that under the influence of axial pressure, micro-cracks in the rock have initially developed and expanded. With increasing axial pressure, the rock is more vulnerable to breakage, and its weakening degree keeps increasing. The energy utilization rate of one-dimensional dynamic and static combined loading is affected by the axial compression ratio and impact load. At low axial compression ratio, the rock has high impact resistance but high energy utilization rate; at high axial compression ratio, the rock has low impact resistance but low energy utilization rate. Therefore, the combination of axial compression ratio and impact velocity can improve the crushing effect and energy utilization rate on the premise of clear crushing form requirements.

Cyclic loading response of precast concrete beam-column connections with partially bonded draped prestressing tendon

An emulative precast concrete beam-column connection consists of prefabricated columns, T-shaped composite beams with partially bonded post-tensioned (PT) tendon, and cast-in-place (CIP) core region is proposed in this study. Experimental study was carried out to examine the hysteretic behavior of four full-scale beam-column connections under a high axial compression ratio (μ = 0.4). The specimens included a precast interior connection (PC1), a precast exterior connection (PC2), and two corresponding conventional CIP control specimens (RC1 and RC2). Performance assessment of the suggested connection was conducted by evaluating various factors, including failure mode, hysteresis curve, deformation, stiffness, and energy dissipation capacity. Test results revealed that all specimens fulfilled the design objective of strong column-weak beam with flexural failure showed at beams ends. In comparison to RC1, PC1 exhibited a 6.4 % increase in peak load-carrying capacity in the positive loading process and a 7.1 % decrease in the negative loading process. On the other hand, PC2 demonstrated approximately 11.9 % higher load-carrying capacity in the positive loading and a 2.0 % lower capacity in the negative loading when compared to RC2. The ductility coefficients of PC1 and PC2 was 3.39 and 2.64, respectively, which were slightly higher than that of RC1 and RC2 (3.01 and 2.43). All specimens exhibited good deformation restoring capacity and plump hysteretic loops, demonstrating satisfactory energy dissipation capacity. Overall, the proposed connection with partially bonded PT tendon showed comparable seismic performance with their CIP counterparts, indicated its promising potential for use in practical engineering applications.

Seismic performance and bearing capacity calculation of cross shaped concrete columns with built-in T-shaped steel and steel tubes.

Incorporating T-shaped steel and square steel tubes into a cross shaped concrete column can significantly improve the seismic performance of the cross shaped column. However, the experimental samples are limited, so ABAQUS finite element (FE) analysis method was adopted in this paper to study the seismic performance of this cross shaped column, calculate and verify three specimens in the existing reference. Based on the reliable model, parameter analysis was carried out (25 specimens in total). The results show that the established model has a high degree of coincidence in the hysteretic curve, skeleton curve and failure mode, and the error of ultimate bearing capacity and ductility is within 10%. The configuration of T-shaped steel and square steel tubes inside the cross column can meet the ductility requirements specified in the standard under high axial compression ratio. The ultimate bearing capacity of the cross shaped column increases with the increase of the thickness of the square steel tube, but the ductility deteriorates. The increase in steel tube size increases the strength of the concrete in the core area, and the seismic performance of the cross shaped column was improved. Increasing the thickness of the T-shaped steel flange can better improve the seismic performance of the cross shaped column compared to increasing the thickness of the T-shaped steel web plate. Increasing the height of the specimen will significantly reduce its seismic performance. When the shear span ratio is not greater than 4.1, the ductility can meet the standard requirements. The error of the formula for calculating the compression-bending bearing capacity proposed based on existing calculation methods is less than 5%.

Experimental investigation on the effect of nano-silica on reinforced concrete Beam-column connection subjected to Cyclic Loading

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility.

Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).

Experimental and numerical study of PEN FRP-strengthened circular RC columns under lateral cyclic loading with high axial compression ratio

This paper presents experimental studies and numerical simulations of circular reinforced concrete (RC) columns wrapped with Polyethylene Naphthalate fiber reinforced polymer (PEN FRP, a kind of large-rupture-strain FRP) and conventional CFRP. A total of seven columns were designed and fabricated, including a control column, three columns strengthened with CFRP, and three columns strengthened with PEN FRP. All columns were subjected to cyclic lateral load and a constant high axial load. The effectiveness of PEN FRP strengthening was systematically analyzed and discussed regarding the failure mode, displacement ductility, lateral cyclic load–displacement curve, stiffness degradation and energy dissipation capacity. The test results indicated that the control column exhibited inferior ductility and peak lateral strength, while FRP-strengthened columns possess better energy dissipation capacity and ductility. Further study found that PEN FRP was preferred to CFRP with similar tensile stiffness in seismic strengthening. Finally, based on the cyclic compression model of LRS FRP-strengthened concrete, the improved tensile model of FRP-strengthened concrete, and the cyclic stress–strain model of reinforcing steel, numerical simulations for seismic performance were carried out in OpenSees. It was found that the numerical simulation results of all FRP-strengthened RC columns were in excellent agreement with the test results. To better understand the effect of FRP confinement stiffness on the seismic performance of circular columns, parametric analysis was performed. Results showed that the numerical simulations need to consider the buckling of longitudinal reinforcement for accurately predicting the seismic behavior of FRP-strengthened columns of lower confinement stiffness.

Seismic behavior of RC columns under high active confinement force

AbstractThis paper details the invention of a tensioning and anchoring device based on the “wedge‐cutting effect” that can tension and anchor multi‐layer carbon fiber reinforced polymer (CFRP) fabric. To achieve a high active confinement effect on an RC column, the device is characterized by its capability to lift the applied prestress to the greatest extent and minimize prestress loss. All eight RC columns with identical structural dimensions were designed and fabricated, including three unstrengthened and five strengthened columns. The seismic performance test and finite element simulation were conducted under a low cyclic reciprocating load. The test parameters include active confinement force and axial compression ratio, with active confinement force varying as a function of the number of layers of CFRP fabric. The results indicate that the seismic performance of RC columns with high active confinement can be significantly improved. Under a high axial compression ratio, the maximum displacement ductility coefficient and ultimate drift ratio of specimens strengthened with four layers of prestressed CFRP fabrics can increase by 87% and 152%, respectively, while the energy consumption can increase by 4.3 times. Additionally, the ultimate horizontal bearing capacity can be raised by 41%. The seismic performance of strengthened columns increases with the increase of active confinement, particularly under high axial compression. The finite element model is in good accord with the experiment. With an increase in active confinement force, the properties of confined concrete and CFRP are utilized to a greater extent, and more energy is dissipated by the opening and closing of numerous micro cracks.

Seismic performance of RC columns strengthened with HSSSWR meshes reinforced ECC under high axial compression ratio

The cyclic loading tests under high axial compression ratio were performed to investigate the seismic performance of full-scale reinforced concrete (RC) columns strengthened with high-strength stainless steel wire rope (HSSSWR) meshes reinforced engineering cementitious composite (ECC), considering different axial compression ratios and strengthening schemes. The test results show that the seismic performance of RC columns was greatly improved after being strengthened. Specifically, the failure modes of the columns were changed from flexure-shear failure to compression-flexure failure, and the ductility and energy dissipation capability were significantly improved by 69.6% and 474.6%, respectively. Besides, the HSSSWR meshes reinforced ECC jacket was confirmed to be a more efficient strengthening scheme, compared with strengthening with only ECC or lateral HSSSWRs reinforced ECC. The RC columns still showed good ductility and energy dissipation capacity after being strengthened with HSSSWR meshes reinforced ECC under high axial compression ratios of 0.5 and 0.7. Finally, taking into account the confinement effects of ECC, lateral HSSSWRs, and stirrups, an analytical model used for predicting the envelope curve of strengthened columns with HSSSWR meshes reinforced ECC jackets under cyclic loading was proposed, which was in good agreement with the test results.

Post-Fire Seismic Property of Reinforced Concrete Frame Joints with Carbon Fiber-Reinforced Polymer Using Numerical Analysis

This study investigated the post-fire seismic characteristics of reinforced concrete frame joints with carbon fiber-reinforced polymer (CFRP) under low-cycle reciprocating loads through numerical analysis. Finite element simulations were conducted to examine the hysteretic curve, skeleton curve, energy dissipation, and stress distribution of the reinforced joints. The findings revealed that, relative to unreinforced joints post-fire, the bearing capacity of the reinforced joints remained essentially unaltered during the elastic phase. However, their ultimate bearing capacity, energy dissipation capacity, and ductility exhibited varying degrees of enhancement. Interestingly, this augmentation did not persist as the number of reinforcement layers increased. The optimal reinforcing effect was observed with the application of two reinforcement layers, resulting in a 30.3% increase in ultimate bearing capacity and a 26.5% improvement in energy dissipation capacity. Moreover, as the axial compression ratio increased, the high-stress zones within the joint expanded, and the failure mode transitioned from plastic damage at the beam end of the joint under low axial compression ratios to column crushing failure under high axial compression ratios.

Effects of load-related parameters on the dynamic response of concrete-filled double-skin steel tube K-joints under lateral impact loading

Concrete-filled double-skin steel tube (CFDST) structure is gradually applied in jacket foundation of offshore wind turbine (OWT). This study uses experimental and numerical methods to investigate the effect of impact force and axial force on the dynamic response of CFDST-K joints subjected to impact loading. A pendulum test machine is conducted to analyze the deformation property and dynamic response of six K-joints. The results indicate that the impact velocity increases as the impact energy rises, resulting in a significant increase in impact force, displacement, and plastic strain. Improving the axial compression ratio enlarges the second-order effect and the initial stiffness, resulting in a substantial rise in the deformation under a high axial compression ratio. CFDST-K-joints exhibit superior flexural strength, impact resistance, and energy dissipation ability than hollow K-joints in terms of the constraint effect provided by the inner tube to the core concrete. Subsequently, ABAQUS is used for nonlinear analysis and to validate against the test results and explore the energy distribution. Finally, the parametric analysis demonstrates that the optimal hollow rate of CFDST-K joints is between 0.6 and 0.7 and the flexural stiffness is a critical parameter affecting the impact performance.

Experimental evaluation on the seismic performance of high-strength reinforcement beam-column joints with different parameters

This paper reports the results of cyclic load tests and analysis of full-scale beam-column joints using 600 MPa high-strength reinforcement as beam longitudinal reinforcements. The focus was on evaluating the effect of the relative length of beam bars through the joint (hc/d) on the seismic performance of the high-strength reinforcement beam-column joints, while the effects of variables such as axial compression ratio, shear compression ratio, and transverse reinforcement ratio were also discussed. The failure pattern, strength, stiffness, ductility, energy dissipation, and bond performance of each specimen under reciprocal loading were analyzed. The test results showed that applying high-strength steel bars improved the failure pattern, load-bearing capacity, and energy dissipation of the joints. The increase in hc/d improved the bond degradation of the high-strength reinforcement, which positively influenced the seismic performance of the joint. Conversely, high axial compression ratios and high shear compression ratios had a clear negative effect on the bond degradation and failure patterns when high-strength reinforcement used. A proposed equation for adjusting the hc/d in a high-strength reinforcement joint was also presented, which considered the effect of concrete strength and reinforcement strength on the bond performance of beam reinforcement.

Seismic Performance of Fully Prefabricated L-Shaped Shear Walls with Grouted Sleeve Lapping Connectors under High Axial Compression Ratio

The grouted sleeve lapping connector called the APC connector has the advantages of high fault tolerance, convenient construction, compacted grouting, and low cost, together with realizing full prefabrication of vertical components. In this paper, a quasi-static test of two fully prefabricated L-shaped walls connected with two types of APC connector and a cast-in-place wall was carried out under high axial compression ratio (0.5) to compare their seismic performance. The results indicated that the two types of connectors effectively transferred the rebar stress in the prefabricated walls, and the failure modes and final crack distribution of the prefabricated walls and the cast-in-place wall were basically identical. The failure of the cast-in-place wall occurred at the root of the wall limb, while the failure of the prefabricated walls occurred at the top of the sleeve due to the constraint of the sleeve. The bearing capacity, stiffness, ductility, and energy dissipation of the prefabricated specimen connected by the type-I sleeve was comparable to that of the cast-in-place wall, while the prefabricated wall connected by the type-II sleeve showed greater bearing capacity, stiffness, and ductility. Finally, some suggestions for seismic design of prefabricated components connected with APC connectors are proposed.

Parametric study on lateral behaviour of composite shear walls with high-strength manufactured sand concrete

The traditional reinforced concrete (RC) shear wall showed limited seismic performance under extreme earthquakes when deployed at the bottom of high-rise buildings, due to the presence of high axial compression ratios. In this study, a novel composite shear wall was proposed to improve the seismic performance at high axial compression ratios, in accordance with recent demands for eco-friendly materials. The novel composite wall integrated the high-strength manufactured sand (MS) concrete, ring-stirrup and steel tube to fully maximize material efficiency and achieve inter-enhancement. A quasi-static test was at first carried out on the proposed composite shear wall, which validated the expected enhancement on its lateral mechanical behaviour preliminarily. On this basis, a refined finite element (FE) model was established for the test specimen by considering the nonlinearity and cyclic behaviour of materials, in order to provide further insights into its behaviour under lateral loads. The established FE model was verified against the test data, which showed a good agreement between the numerical prediction and the test result. Meanwhile, a list of key parameters was identified according to their influence on the lateral behaviour of the composite wall, including the axial compression ratio, yield strength of steel tubes, compressive strength of concretes, reinforcement ratio in concrete-filled steel tube (CFST) columns, and space between ring-stirrups. On this basis, a series of parametric investigations were carried out with the validated FE model, by varying the selected key parameters. In general, the research output offered a constructive guideline and data support for the expected engineering application of the proposed composite shear wall.

Experimental study on the seismic behavior of RC columns with high axial compression ratios retrofitted by large rupture strain fiber-reinforced polymer

Fiber-reinforced polymer (FRP) composites being utilized to retrofit reinforced concrete (RC) columns has been well documented. However, the axial compression load of the FRP retrofitting RC columns was relatively limited. Aiming to analyze the applicability of FRP retrofitting RC columns with higher axial compression loads, this paper presents an experimental study on the seismic performance of RC columns retrofitted by the Polyethylene Terephthalate (PET) FRP composites. A total of twelve 1/3 scale RC columns were fabricated, including four control specimens and eight PET FRP retrofitting columns with two retrofit schemes. All the columns were tested under combined high axial compression load and cyclic lateral displacement excursions, and the maximum axial compression ratio reaches 1.1. The seismic performance of RC columns retrofitted by PET FRP was analyzed detailedly from the failure mode, shear force and deformation capacity, energy dissipation and ductility. The test results showed that PET FRP retrofitting changed the failure mode of RC columns from brittle to more ductile. The post-peak strength degradation of the columns was more rapid with the increase of axial compression ratio, but the strength degradation of the PET FRP retrofitting columns was more gradual. PET FRP retrofitting significantly improved the ductility and lateral deformation capacity of the columns even under the high axial compression ratio. PET FRP retrofitting can be applied for the RC columns with serous demand of deformation capacity due to the lighter change of shear-loading capacity and stiffness. Contrastively, the improvement of the seismic capacity of the RC columns retrofitted by the laterally wrapped scheme is higher than that of the striped wrapped scheme. Conclusions from this study provide useful references for the seismic retrofitting of RC structures.