Axial Load Ratio Research Articles

Seismic Performance of Precast Drift-Hardening Concrete Walls Connected by Grout–Sheath Duct

In order to find a suitable size of sheath duct and a reliable construction method for precast walls, a cast-in-place and five 1/2 scale precast drift-hardening concrete walls reinforced with weakly bonded ultra-high strength SBPDN rebars were fabricated and tested under reserved lateral load and constant compression. The experimental variables were the diameter of sheath ducts (45 mm, 100 mm, and 120 mm), embedded length (20d and 35d; d is the nominal diameter of SBPDN rebars), axial load ratio (0.075 and 0.15), and the construction method. The experimental observations, hysteresis behaviors, envelope curves, residual deformation, crack propagation, and energy dissipation were compared in the study. Moreover, a formula was applied to calculate the bond strength of the sheath duct. The experimental and calculated results revealed that increasing the axial load ratio and embedment length could not enhance the bond strength of the sheath ducts, and increasing the diameter decreased the bond strength significantly. Anchored the SBPDN rebars in smaller sheath ducts separately was a more stable connection method for precast concrete shear walls and provided sufficient drift-hardening capability, even at a large drift level (over 3%).

Numerical Study on the Retrofitting of Exterior RC Beam-column Joints with CFRP Composites Using the Grooving Method

Retrofitting seismically deficient beam-column joints (BCJs) in reinforced concrete (RC) structures is crucial to preventing collapse during high-intensity earthquakes. Fiber reinforced polymer (FRP) composites have proven effective for retrofitting these components, but debonding of the FRP from concrete surfaces remains a challenge. Recently, the grooving method (GM) has emerged as a promising solution to mitigate this issue, enhancing the bond between FRP and concrete. This paper presents a numerical investigation of BCJs retrofitted with FRP composites using the GM, focusing on various design parameters. The study utilized finite element models developed in ABAQUS, incorporating the concrete damage plasticity (CDP) model to simulate the nonlinear behavior of concrete. The interface between the concrete and FRP was modeled as a perfect bond, simulating the strong adhesion provided by the GM. The numerical results were validated against experimental data from two BCJ specimens, showing good agreement in terms of load-displacement behavior, peak loads, and failure modes. Key parameters studied include the beam longitudinal reinforcement ratio, column axial load ratio, and joint aspect ratio. The findings reveal that these parameters significantly affect the shear capacity of retrofitted joints, impacting the efficiency of the retrofitting.

Seismic in-plane behavior of composite masonry walls strengthened with cold rolled steel sheets

The seismic behavior of masonry walls strengthened by cold rolled steel sheets is numerically evaluated in this study using finite element modeling in ABAQUS. Cold-rolled steel sheets cover two sides of an unreinforced masonry wall and are bolted together to form a composite masonry wall. The behavior of the composite masonry walls is compared to that of the corresponding unreinforced masonry walls with various failure mechanisms. The finite element models of the unreinforced masonry walls are validated through experimental data in the literature. Then, cold-rolled steel sheet-strengthened walls are simulated, and variations in strength, ductility, and failure mode are investigated. A thorough sensitivity analysis is conducted on the effects of the aspect ratio, boundary condition, axial load ratio, steel sheet thickness, and connection bolt configuration on the in-plane strength and failure mode of the walls. It is observed that the steel sheets affect the local and global behavior of the masonry walls and change their failure modes. The use of through-thickness bolts to connect steel sheets to the masonry wall provides a composite action between steel sheets and the masonry wall against in-plane lateral loads. The cold-formed steel sheets not only resist a portion of the lateral load but also significantly increase the lateral strength of the masonry walls and the ductility of the whole wall system. Based on the analysis results it can be concluded that strengthening masonry walls with cold-rolled steel sheets is a promising technique for the seismic improvement of existing conventional masonry buildings and for the design of new masonry buildings.

Numerical investigation on plastic hinge behavior of hybrid steel-FRP reinforced concrete columns

This paper presents a numerical study on the plastic hinge behavior and rotation capacity of concrete columns reinforced with a combination of steel bars and fiber-reinforced polymer (FRP) bars. A meso-scale numerical model, which considers the internal heterogeneity of concrete and bond behavior between concrete and longitudinal reinforcements, was developed and validated. The failure modes, lateral load-displacement responses, and the physical plastic hinge lengths of hybrid steel-FRP reinforced concrete (SFRC) columns were investigated and compared with those of conventional steel-reinforced concrete columns. The results indicated that the steel yielding zone and curvature localization zone of SFRC columns with FRP longitudinal bars were enlarged, due to the relatively low modulus of FRP bars. After that, a parametric analysis was performed to study the plastic hinge length of SFRC columns with respect to the nominal area ratio of FRP longitudinal bars, shear span-to-depth ratio, axial load ratio, and longitudinal reinforcement ratio. A new empirical model was proposed to predict the equivalent plastic hinge length, which was subsequently integrated into an analytical method for predicting the ultimate rotation. The comparison of predictions with simulation and test results demonstrated the accuracy of both the proposed empirical model and analytical method.

Mechanical model analysis of column-footing joints with combined socket-corrugated pipe connection

The socket connection method is widely used in precast column, particularly in seismic regions. However, reducing the socket-depth to lower costs may lead to shear failure in the socketed part of the columns. To address this issue and achieve cost objectives, a new approach combines shallow sockets with corrugated pipes for column-footing joints. Comparative tests were conducted to investigate failure in columns with socket-corrugated pipe connections (SCPC), shallow sockets (SSC), and cast-in-place (CIP). Furthermore, finite element models were employed to validate the experimental and simplified model results. The findings suggest potential shear failure in shallow socket connections, which can be mitigated by using the combined socket-corrugated pipe method that alters force transmission paths. As the axial load ratio increases, both the ultimate lateral load capacity of the specimen and the local stresses at the column base increase. In addition, the ultimate lateral load capacity of the column and the stress of the connection reinforcement are increased by increasing the strength of the longitudinal reinforcement, consequently amplifying the extent of joint area damage. Finally, a simplified strut-and-tie model of the SCPC, validated against numerical and experimental data, accurately represents force paths, ultimate lateral load capacity and failure modes in socket joints.

Mechanics guided data-driven model for seismic shear strength of exterior beam-column joints

This study presents an enhanced predictive model for the seismic shear strength of exterior beam-column joints (BCJs). Initially, the principles of strut-and-tie mechanism and variable selection procedures were first utilized to identify the most influential parameters. Subsequently, an evolutionary algorithm, specifically multigene genetic programming (MGGP), was utilized to search for the near-optimal predictive model. The dataset used to develop, train, and test the proposed model was compiled from previously published tests, focusing specifically on cyclically loaded exterior BCJs that encountered shear and flexure -shear failures. The prediction performance of the developed model was assessed through various statistical measures, and then compared with that of other existing models. Additionally, sensitivity analyses were also performed to identify the influence and importance of each design parameter. The results demonstrated that the methodology employed in this study yielded an elegant model that adheres to the underlying mechanics and provides higher prediction accuracy compared to existing models. Furthermore, the sensitivity analyses showed that BCJ shear strength positively correlates with concrete compressive strength, beam reinforcement, joint transverse reinforcement, column intermediate vertical reinforcement, and axial load ratio, while it negatively correlates with the joint aspect ratio. Among these design parameters, beam reinforcement has the greatest influence on the model response, followed by concrete compressive strength. Conversely, column intermediate vertical reinforcement and axial load ratio have the least impact on the model response. The notable prediction capabilities and robustness demonstrated by the developed model render it an efficient design tool with promising potentials for adoption by practicing engineers and for consideration in design guidelines.

Design of improved multi-cell L-shaped CFST columns under compression and bending

In recent years, there has been a notable surge in proposals for various forms of special-shaped concrete-filled steel tubular (CFST) columns. Despite various methods developed by researchers for determining the bearing capacity of multi-cell special-shaped CFST columns under different loading conditions, these methods remain lack unified. In this study, FE models were developed to simulate performances of improved multi-cell L-shaped CFST (ML-CFST) column under compression and bending. Parametric analyses have been performed to evaluate impact of various factors, including steel yield strength fy, compressive strength of concrete fcu, steel thickness t, loading direction θ, web height c, and axial load ratio n, on performances of ML-CFST columns. The findings of study indicate that the unidirectional flexural capacity of ML-CFST member exhibits a nearly linear relationship with the variables of t, fy, and c, with a minimal impact observed from fcu on flexural capacity. The width of extended section b, fcu, fy, and t have a certain effect on flexural capacity at any angle, particularly fy, t, and b. While fcu, fy, and t exert some influence on N/Nu-M/Mu correlation curves, their influences are marginal compared to the loading direction, which is the predominant influencing factor. Additionally, Mx0/Mπ/4-My0/M3π/4 curves gradually protrude outward with the increase in n. The effects of t, fy, and fcu on the shape of Mx0/Mπ/4-My0/M3π/4 curve were relatively insignificant. Simplified unidirectional flexural capacity calculation models were proposed based on stress analysis of cross-section under ultimate states. Given that flexural capacities estimated by simplified calculation model are slightly conservative, it is recommended to increase the flexural capacities by 10 %. Furthermore, an elliptical equation was formulated to predict the flexural capacity at any angle, with the predictions being slightly conservative. Based on ultimate equilibrium theory, a simplified calculation method was presented to predict unidirectional eccentric bearing capacities of ML-CFST columns. Through regression analysis, a simplified calculation method expressed as polar coordinate form for biaxial eccentric bearing capacity was established, with calculated values aligning well with FE results.

Assessment of Ductility Demand-Based Blast Damage to Reinforced Concrete Columns under Blast Loads

This study was conducted to evaluate the influence of various structural variables on the blast damage to reinforced concrete columns. The selected primary variables were the longitudinal reinforcement ratio, transverse reinforcement ratio, and axial load ratio, with the analysis based on the ductility demand to assess the blast damage. A parametric study based on finite element analysis was performed to analyze the effects of these variables. The results revealed that an increase in the longitudinal and shear reinforcement ratios significantly decreased the level of damage sustained by the columns under blast exposure, whereas an increase in the axial load ratio resulted in a comparatively lower reduction in damage. Columns with higher transverse reinforcement ratios experienced more severe damage owing to compression-induced brittle failure as the axial load ratio increased. This study provides guidelines for the appropriate selection of design variables to mitigate blast damage in columns.

Post-earthquake fire performance of partially encased composite steel and concrete columns

Considering the potential severity of losses caused by post-earthquake fires compared to earthquakes alone, this study employed a three-dimensional Finite Element (FE) model established in ABAQUS to investigate the response of partially encased composite (PEC) steel and concrete columns under post-earthquake fire, serving as preliminary analysis for subsequent experimental studies. The validity of the FE model was verified using results from existing seismic and fire loading tests. In simulating the hysteresis behavior of PEC columns, this study evaluated the impacts of concrete discrete cracking and mechanical models on the simulation outcomes, thereby refining the modeling technique. A typical PEC column was selected as the focus of this investigation. Sequential earthquake-fire simulations were conducted using a data transfer technique to assess the fire resistance performance of different seismic damaged columns with different axial compression load ratios. The results indicate that the behavior of damaged PEC columns evolves based on initial damage, and the failure exhibits overall bending accompanied by local buckling of the steel flange. As the axial load ratio increases, the fire resistance time of seismic-damaged PEC columns significantly decreases. When the axial compression ratio is increased from 0.2 to 0.5, the fire resistance time of columns with damage factor D within 0.6 decreases by 59.07% on average. This sensitivity to axial pressure is particularly pronounced when earthquake damage is severe. Moreover, it finds that the lateral drift ratio under seismic action should be controlled within 2% to ensure that the post-earthquake fire resistance will not be significantly reduced.

Behavior of circular ultra-high-strength concrete-filled steel tube columns subjected to combined high-axial and cyclic lateral loads

The present study examined the seismic performance of circular concrete-filled steel tube (CFST) columns infilled with ultra-high-strength concrete (UHSC >100 MPa) as well as the beneficial effect of embedded spiral confining (SC) reinforcement at high axial load ratios (0.53–0.70) in order to enhance the safety and structural integrity of high-rise buildings. Seven specimens, including four CFST columns and three SC-CFST columns, were investigated under combined high axial and quasi-static cyclic lateral loads. The test parameters included axial load ratio (0.53–0.70), concrete compressive strength (64–111 MPa), embedded spiral confining reinforcement (pitch of 30 mm and 60 mm), and concrete vibration state. The test results demonstrated that adding spiral reinforcement improved the deformation capacity of CFST columns, which was reduced by the increased concrete strength. By embedding spiral confining reinforcement (volumetric ratio 3.3 %), the SC-CFST columns attained a deformation capacity comparable to that of CFST columns with normal concrete (64 MPa) for an axial load ratio of 0.53. The higher axial load ratio and concrete strength of composite columns led to a significant P-Delta moment effect, resulting in a substantial drop in columns' lateral load capacity. Composite columns with UHSC showed a larger contribution from the column base rotation to the specimen's lateral deformation when compared to composite columns with normal-strength concrete because the rigidity offered by UHSC made the column more rigid and reduced its flexural deformation. The unvibrated core concrete of the CFST column did not influence the initial stiffness and energy dissipation capacity. However, during the later stages of loading, the damage in core concrete rapidly accumulated, resulting in instant degradation of the load capacity and stiffness, considerable axial shortening, and poor deformation capacity. The experimental investigation offered a reliable reference on the performance of CFST columns constructed under high-axial load ratios (0.53–0.7) using ultra-high-strength concrete (>100 MPa) and spiral confining reinforcement so as to promote their application in practical engineering.

Investigation of plastic hinge length in high-ductility reinforced concrete shear walls

In this study, the plastic hinge lengths of reinforced concrete (R/C) cantilever shear walls were analytically determined considering various design parameters. Nonlinear static (Pushover) analyses were conducted on R/C shear wall models and their nonlinear behavior was examined using ABAQUS software. In the study, 72 shear wall models with different parameters were analyzed under the influence of vertical and horizontal loads. Parameters whose effects on plastic hinge length were investigated height/length ratio (Hw/Lw), axial load ratio (N/No), and horizontal web reinforcement ratio (ρsh). The load-displacement graphs of the modelled shear walls were obtained. The plastic hinge height of shear walls was determined according to the heights of the deformations in the concrete and longitudinal steel reinforcement in the section when the shear walls lateral load decreased by 15%. The analytical plastic hinge lengths (Lpz) were determined with respect to the location of the yield occurred at the longitudinal steel reinforcement of the shear wall. The observed plastic hinge lengths (Lp) were determined based on the height of observed the crush as of the foundation top level in the concrete shear wall model. The relationship between the findings of this study and empirical formulas in the literature was determined. It was determined that there is greater closeness between the values obtained from empirical formulas in the literature and the observed plastic hinge length values. It was observed that the plastic hinge length generally increases as the shear span increases. It was observed that the change in ρsh was not a very effective parameter in plastic hinge formation. As the N/No decreases, the plastic hinge length values ​​ generally increase. The Lp/Lpz ratio varied within the range of 0.15-0.50. In addition to ductility (μ) values were determined by using the displacements determined according to both the crushing occurred in the shear wall concrete and the yield observed in the steel reinforcement. The observed that the ductility value depends more on Hw/Lw ratio as N/No ratio decreases.

Simplified Approach for Determining Buckling Load in Portal Frames: Elastic Stability Analysis

Abstract The stability of portal frames is a critical aspect of structural engineering, significantly influencing their safety and performance. It refers to their ability to resist buckling or collapse under compressive forces, ensuring structural integrity and safety under various loading conditions. This study aims to provide design charts, created from closed-form solutions, on the probability of forming four different failure modes depending upon stiffness and axial load ratios. These charts provide a simplified and efficient method for quickly and easily assessing the elastic stability of a portal frame without the need for complex analyses or numerical simulations. The results indicate that in most cases, the governing failure mode is the sway-without-shear mode. However, upon further analysis, it is found that when the stiffness ratio (EI2/EI1) exceeds 2 and the force ratio (P2/P1) exceeds 1.33, the observed failure mode typically shifts to the symmetrical failure mode. Moreover, of the concluded results, the study discloses that the stiffer the beam, the higher the critical load ratio, and subsequently, the higher the buckling load. This is due to the fact that the beam behaves more like a rigid element, which prevents joint rotation, as in the fixed-end condition.

Blast performance of RC columns with different levels of concrete grades and reinforcing ratios

AbstractThe present article aims to study the behavior of RC columns under blast loading. A nonlinear dynamic Three‐Dimensional (3D) Finite Element FE model‐based explicit solver available in ABAQUS Software is used. A parametric study is investigated to enhance the blast resistance of RC columns under three different scaled distances z of an explosion, that is, 0.23, 0.5, and 1.07 m/kg1/3 for close, intermediate, and Far in‐distance. In addition, three levels of concrete grades are used, which are Normal Strength Concrete (NSC), High Strength Concrete (HSC), and Ultra High‐Performance Concrete (UHPC). The study also considers Three reinforcement ratios for longitudinal and transverse reinforcement ratios of (ρL = 1.28%, 2.4%, and 3.1%) and (ρs = 0.6%, 0.9%, and 1.35%), respectively. Further, three different Axial Load Ratios, ALR = 0.01, 0.2, and 0.4, are considered to examine the effect of increasing ALR on the RC column under close explosion. For more investigation, the parametric analysis considers two geometrical shapes of RC columns (square and circular). The material behaviors of concrete and reinforcing steel bars are represented using Concrete Damage Plasticity (CDP) and Johnson–Cook (J–C) models, respectively, available in ABAQUS Software. The FE model has been initially validated against experimental study. The FE‐predicted deflection and damage were observed and agreed with the practical cases. In addition, the parametric study's results demonstrate that the RC column's blast deflection is significantly reduced with increasing reinforcement ratios. However, increasing concrete grade could efficiently reduce blast damage and deflection. Furthermore, compared with NSC, UHPC significantly reduced maximum damage and deflection by around 60% for square and 55% for circular columns, respectively.

Experimental and numerical investigation on seismic performance of SFRC shear walls with CFRP bars

In order to investigate the seismic performance of steel fiber reinforced concrete (SFRC) shear walls with CFRP bars, quasi-static tests were conducted on six full-scale shear walls with a shear span ratio of 2.0, including one steel bars reinforced ordinary concrete (RC) shear wall, one CFRP bars reinforced ordinary concrete (CRC) shear wall and four CFRP bars reinforced SFRC (CSFRC) shear walls. The variables included steel fiber volume fraction (SFVF), axial load ratio and concrete strength grade. The experimental results showed increasing the SFVF could significantly decrease the concrete damage level and improve repairability. Meanwhile, the bearing capacity, ductility, and energy dissipation capacity all improved, and the stiffness degradation slowed. Compared to RC shear wall, the peak load of the CSFRC shear wall with SFVFs of 0 %, 0.75 % and 1.5 % increased by 16.36 %, 30.06 % and 46.01 %, respectively. The residual drift ratio decreased by 54.75 %, 61.61 %, and 52.98 % at 2.2 % drift ratio, respectively. Compared to CRC shear wall, the cumulative energy dissipation of the CSFRC shear wall with SFVFs of 0.75 % and 1.5 % increased by 39.54 % and 94.10 %; and the ductility increased by 5.12 % and 18.06 %, respectively. These improvements indicated that applying SFRC with SFVFs of 0.75 % and 1.5 % to shear walls reinforced with CFRP bars could effectively improve the seismic performance and compensate for the shortcomings of resilient shear walls. In addition, increasing the axial load ratio improved the bearing capacity, but decreased deformation capacity and accelerated stiffness degradation. An increase in concrete strength significantly improved the bearing capacity, stiffness and energy dissipation but reduced ductility. Meanwhile, the stability of lateral loads at large drift ratios weakened. Additionally, a detailed finite element model (FEM) was established using DIANA and the accuracy was verified by comparing the simulation and experimental results. Subsequently, parametric analyses were carried out to study the effects of shear span ratio, CFRP bar ratio, and wall thickness on the seismic behaviour of CSFRC shear walls.

Seismic Behavior of Steel Reinforced Ultra-High Strength Concrete Composite Frame: Experimental and Numerical Study

The seismic behavior of steel reinforced ultra-high strength concrete (SRUHSC) composite frame was investigated through finite element analysis (FEA) modeling. A FEA model for the seismic analysis of the SRUHSC frame was first established and verified with test results. The numerical model was subsequently used to study the seismic performance of the SRUHSC frame, including the P-Δ skeleton curves, the stiffness degradation, the failure mode, the subsequence mechanisms of plastic hinges and the stress–strain distribution. Finally, a parametric study was carried out to investigate the effect of salient parameters on the behavior of the SRUHSC frame. It was found that with the increment of the concrete strength, yield strength of steel, and linear stiffness ratio of beam to column, the horizontal load-bearing capacity and the elastic stiffness of the structure were improved, but there was no significant effect on the ductility. With the increment of the volume stirrup ratio and structural steel ratio, the horizontal load-bearing capacity and the ductility of the structure were both improved. However, with the increment of the axial-load ratio, there was no obvious change in the elastic stiffness of the structure, but the horizontal load bearing capacity and the ductility of the structure decreased obviously. In addition, the accuracy of a concrete constitutive model in the different degrees of constraint for the SRUHSC frame proposed by the authors was verified with the FEA model.

Seismic behaviors of steel-FRP composite bar-reinforced engineered cementitious composites columns under reversed cyclic loads

The combination of steel-FRP composite bar (SFCB) and engineered cementitious composites (ECC) in structures exposed to harsh conditions can offer benefits in mechanical performance and durability. In this study, the seismic behaviors of SFCB-reinforced ECC and concrete columns were investigated through reversed cyclic loading tests and the effects of matrix types, axial load ratios, and reinforcing bar types were discussed. The results showed that the SFCB-reinforced ECC columns experienced flexural failure characterized by SFCB fracture, whereas the SFCB-reinforced concrete columns failed owing to concrete crushing. The SFCB-reinforced ECC columns showed a 41.5 %− 116.3 % enhancement in deformation capacity and a 34.7 %− 65.2 % improvement in average energy dissipation coefficient compared with SFCB-reinforced concrete columns, which demonstrated that using ECC in SFCB-reinforced columns addressed issues of their low deformation and low energy dissipation capacity. In addition, the plastic hinge length of SFCB-reinforced columns increased substantially with the application of ECC, and the stiffness degeneration and residual deformation were reduced.

Shear mechanism of RCS joints with whole column-section diaphragm

The authors proposed a new precast RC column-steel beam (RCS) joint with whole column-section diaphragm, aiming to address the shortcomings including bearing failure and difficulty in prefabrication of the RCS joint details available in the existing literature. Due to its unique details, the proposed RCS joint may have a dissimilar force-transferring mechanism from the conventional beam-through type RCS joint. Moreover, the effect of various parameters on this novel joint was still unclear by limited test results. The objective of this study was to clarify the shear mechanism of the proposed joint and the impact of critical parameters. Specimens with different axial load ratios and thickness of parallel FBPs were tested under cyclic loading. The results showed that the increase in axial load ratio and thickness of parallel FBPs improved joint strength in this test. A detailed three-dimensional finite element (FE) model was developed and verified using the experimental results. The difference in the force transferring between the proposed joint and conventional beam-through RCS joints was explained in detail based on the numerical results. The dowel action of longitudinal column bars were evident in the proposed joint and the orthogonal FBPs were ineffective in activating the inner concrete strut. A parametric study was further conducted. The impacts of width of parallel FBPs, thickness of orthogonal FBPs, and axial load ratio were investigated. The joint strength linearly increased with the width of parallel FBPs. A parabolic distribution of shear stress in the parallel FBP section was obtained, while the yield zone was concentrated in the central area of the parallel FBP. The ductility could be improved with the thickness of orthogonal FBPs when the thickness was less than 10 mm. Further increasing the thickness of orthogonal FBP beyond 10 mm did not significantly affect the overall joint behavior. The joint may attain the optimal shear strength when the axial load ratio is between 0.3 and 0.4. The modeling approach in this study could be adopted as an effective tool to assess joint behavior. Moreover, the conclusions obtained by numerical study potentially promoted the application of the proposed joint.

Structural performance of steel reinforced concrete L-shaped columns in high temperature

This paper presented structural performance of steel reinforced concrete (SRC) L-shaped columns under high temperature and axial load coupling effects. Considering the influence of the axial load ratio (0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8), eccentricity (25, 50, 75 and 100 mm), concrete strength (40, 50, 60 and 70 MPa), calculation length (500, 1000, 1500 and 2000 mm), the SRC L-shaped columns were tested and analyzed in high temperature conditions. The results demonstrated that: (1) Concrete surface of all specimens was grayish white with many cracks. With the increasing axial load ratio, the number of cracks decreased and crack width increased. (2) The fire resistance decreased by 1.3–15.1 %, 6.1–14.9 %, and 3.8–7.1 % respectively, with increasing axial load ratio, eccentricity, calculation length; the fire resistance increased by 0.7–5.3 % with increasing concrete strength. (3) Axial displacement trend first increased gradually because of the thermal expansion of concrete, and decreased gradually after reaching the maximum axial expansion deformation. With increasing axial load ratio, the maximum axial expansion deformation decreased by 42.4–60.2 %, the time of displacement to reach the maximum expansion deformation decreased by 29.7–57.0 %, and the time of displacement to reach 0 mm decreased by 272.7–366.2 %. Finally, the calculation method for displacement and maximum bearing capacity in high temperature was proposed according to principle of virtual work, which served as a guide for fire evaluation of SRC L-shaped columns.

Hysteretic behavior of the corroded recycled aggregate concrete columns with ultra-high strength bars

The seismic behavior of six corroded recycled aggregate concrete (RAC) columns with ultra-high-strength bars (UHSB) was investigated through quasistatic test and numerical analysis. The main parameters include different corrosion ratios, axial load ratios (ALR), and stirrup ratios. The results revealed that: The damage development of the corroded specimen sped up with increasing corrosion ratio and ALR, and the corroded specimens suffered brittle shear failure due to the stirrup fracture or the concrete failure. The difference in carrying capacity of the specimens with low corrosion ratios and ALR was relatively small, while the deformation capacity was significantly reduced with increasing corrosion ratios and ALR. Reinforcement corrosion had a minor effect on the strength and stiffness degradation but would reduce the maximum cumulative energy dissipation capacity. By combining residual drift and residual crack width, the corroded specimens all could meet the limit of repairable residual drift and crack width before 4% drift, showing satisfactory resilient performance. Based on the modified corrosion models of materials, the numerical analysis showed the detrimental and coupling impact of the high ALR, high corrosion ratio, and low stirrup ratio on the carrying and deformation capacity. Through numerical analysis data, an equation was proposed that can satisfactorily predict the peak drift of the corroded columns with UHSB.

Shear behavior of thin-walled concrete-filled steel tubular columns

Shear failure is a brittle type of failures, which should be avoided in any structure as it could cause property loss and human casualties. The shear behavior of thin-walled concrete-filled steel tubular (CFST) columns was hence investigated in this study, involving the tests of 24 thin-walled CFST columns and considering the following parameters: shear span-to-depth ratios = 0.15, 0.3, 0.5, 1, 1.5, and 2; confinement factor = 0.63, 1.27, 1.44, and 1.70; and axial load ratios = 0, 0.2, 0.4, and 0.6. The test results revealed the insights of the initial shear stiffness, failure modes, ultimate bearing capacity, load-deflection curves, load-strain curves, and ductility of the specimens. Based on the failure modes, a method is proposed to evaluate the load resistance, and explain the relationship between the shear span-to-depth ratio and the peak bearing capacity. A compression strut mechanism considering the confinement provided by the steel tube flange is also proposed. The effect of axial load on the shear strength of the concrete core is negligible when the axial load ratio doesn’t exceed 0.4. The predicted results from using the proposed simple model agree generally well with the experimental results.