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The bond strength between materials is the basis of the cooperative work of composite structures. This study aims to investigate the bonding performance of push-out tests conducted on self-compacting rubberized concrete-filled steel tubes (SCRCFST). The rubber content, particle size, interface bonding length, and water–cement ratio were varied to evaluate their impact on bond strength. The failure mode and failure mechanism were analyzed. The bond damage and energy consumption capacity were investigated. Moreover, this study reveals the characteristics of the stress–slip curve and derives the characteristic equations from reviewing the different points. Test results indicate that rubber particles enhance the energy dissipation capacity of specimens after reaching ultimate bond strength. Furthermore, bond strength decreases with the increase of rubber particles size and water–cement ratio, while the bonding length is barely impacted. It is worth noting that the bonding strength increases slightly at 10% rubber content. The main contribution of this work is to fill the gap in the bonding performance of SCRCFST and guide engineering utilization. Seventeen cylindrical specimens of SCRCFST performed a push-out test by monotonous loading. Bond damage degree and energy dissipation capacity were investigated. Increasing rubber-related parameters negatively affected the bond properties of the structure. Bond strength equations were proposed. [ABSTRACT FROM AUTHOR]

Concrete-encased concrete-filled steel tube (CFST) composite columns provide high bearing capacity, good seismic performance and an easier connection with arbitrary angle beams, which are widely used in high-rise buildings. Considering the high frequency of building fires, experimental research investigated the axial compressive behavior of the composite columns' exposure to high temperature in this paper. Fourteen specimens after exposure to high temperatures with different parameters, including the heating temperature, steel tube diameter and concrete cover thickness, were fabricated to test under axial compressive loading. The failure pattern, load-displacement curve, bearing capacity, initial stiffness, deformation performance and damage rule of the specimens were discussed. The test results showed obvious differences in damage of specimens subjected to various high temperatures. The failure of the specimens began with the spalling and crushing of the concrete at the edge and ends in a lantern shape. The load-displacement curves of the specimens were significantly affected by high temperature, while the influence the of steel tube diameter and concrete cover thickness was relatively weak. A method of calculating axially loaded capacity for the composite column exposure to high temperature is proposed considering the effects of the main parameters of heating temperature and steel tube position, and the calculated results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a computational method for concrete-encased concrete-filled steel tube (CFST) columns under eccentric compression, which adopts the form of equivalent rectangular stress integrated by material constitutive curve. When establishing finite element model via ABAQUS, confinement provided by stirrup was considered to modify the constitutive law of encased concrete, so that the numerical modeling was in good agreement with tests. By analyzing the simulation results, the applicability of basic assumptions, such as plane section assumption, was discussed, and a database of 207 models with various parameters was created. The developed method took into account the influences of geometric nonlinearities of section shape, and its accuracy was verified against various collected tests and the database. It turned out that the formula presented was applicable to a wide range and had sufficient precision, while the predictions of N - M interaction curves of concrete-encased CFST columns in EC4, AISC and CECS were conservative due to the ignorance of the exact integration about irregular section-shape. • A practical design method for concrete-encased CFST columns subjected to eccentric load is introduced. • The accurate integration takes into account the irregular shape of sections. • The equivalent coefficients are uniformly expressed by simple equations, and cover the influence of important factors. • The proposed method can capture the N-M interaction of composite columns effectively. [ABSTRACT FROM AUTHOR]

Twenty four specimens were designed to investigate the axial compressive stiffness of the recycled aggregate concrete(RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns. The working mechanism of the RAC-encased RACFST composite column was investigated and the full range load–displacement curves of the composite columns were obtained. The interaction of each component of the composite column, i.e. the effect of the outer RAC from the stirrup and the steel tube, and the effect of the core RAC from the stirrup and the steel tube, were analyzed. The constitutive models of the outer unconfined RAC, the outer confined RAC, the core RAC were discussed. Thereupon, simple formulas were proposed to calculate the axial compressive stiffness of composite columns. These formulas can assist engineers to predict the axial deformation of structure in high-rise buildings more accurately. • The whole load–displacement curves and failure patterns of specimens were obtained. • Working mechanism of RAC-encased RACFST composite columns was analyzed. • Constitutive models for each component of the composite columns were adopted. • The calculation methods of their axial compressive stiffness are presented and compared. [ABSTRACT FROM AUTHOR]

• The eccentric compressive behavior of RAC-encased RACFST composite columns was investigated. • The load-deformation curves of specimens were obtained, and the mechanical performance of specimens was evaluated. • A finite-element model was developed to analyze the behavior of specimens under eccentric loading. • Current design provisions were compared, and design recommendations for specimens were presented. Recycled aggregate concrete (RAC) was mainly limited to the nonstructural uses in practice due to its inferior properties. To expand the range of application of RAC, a novel structure type of concrete-encased concrete-filled steel tube (CFST) has attracted great interest due to its excellent performance. Since little literature about the behavior of the RAC-encased RACFST, it is imperative to conduct research about the new type of member for practical application to meet the requirement of the large market and sustainable development. This paper presents experimental and analytical studies on the mechanical behavior of RAC-encased, RAC-filled steel tube (RACFST) composite columns under combined compression and bending. In the experiments, sixteen specimens were tested under axial or eccentric compression to investigate the effects in the recycled coarse aggregate (RCA) replacement ratio (0%, 25%, 50%, 75%, 100%), eccentricity ratio (e/h = 0, 0.2, 0.4, 0.6), steel ratio (2.72%, 2.11%), and slenderness (l / h = 3, 6, 9) on their mechanical performance. The results indicated that the replacement ratio of RCA had little effect on the failure mode of the RAC-encased RACFST composite columns. Compared with the specimens under axial compression, reductions of 23.1%, 63.9%, and 72% were observed in the compressive strength for specimens with eccentricities of 0.2 h , 0.4 h , 0.6 h , respectively. Both the increase in the steel ratio and the reduction in the slenderness significantly improved the compressive strength of the specimens. A finite-element model of the specimens was developed to predict the load-deformation relationship and failure mode. The ultimate bearing capacity was predicted using existing design codes and the test result were compared. The values predicted by the design codes EC4, AISC360 PSD, and CECS188 showed deviations <15% (relative to the experimental values), which could be considered overconservative for the bearing capacity of RAC-encased RACFST composite columns. [ABSTRACT FROM AUTHOR]

• Axial compressive behavior of RAC-encased RACFST composite columns was investigated. • The whole load-deformation curves and mechanical performance of specimens were obtained. • The calculation methods of their bearing capacity are presented and compared. A new type of composite column, recycled aggregate concrete (RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns, promotes the RAC extensive utilization considering synergistic effect between the RAC and the steel tube, which is an attempt to develop environmentally sustainable concrete in high-rise buildings. In this paper, experimental research investigated the axial compressive behavior of RAC-encased RACFST composite columns. Twenty 1:3-scaled specimens were fabricated to test until failure under axial compressive loading. The main variable parameters affecting the behaviour of specimens were recycled coarse aggregate replacement ratio (range from 0% to 100% with 10% increase), stirrup spacing (s = 50 mm, 70 mm, 100 mm, 120 mm), diameter of steel tube (D = 89 mm, 114 mm), concrete strength grade (RC40, RC60) and longitudinal reinforcement ratio (4 12, 8 12). The failure modes, the whole load-deformation curves and the mechanical performance of specimens were also obtained based on static loading experiments and theoretical analysis. It was found that RAC-encased RACFST composite columns, which were subjected to identical axial loads, exhibited more favorable bearing capacity and deformation than those of a comparative reinforced recycled aggregate concrete columns (RACC). The replacement ratio of RCA had a slight effect on the mechanical performance of RAC-encased RACFST composite columns, the optimal substitution ratio of RCA was 50–60%. Based on the previous theory of superposition, the concrete cover is considered, and a calculation formula with double reduction coefficients of the axial load-bearing capacity of composite columns is proposed. Compared to the simplified superimposition method and the Chinese code Technical specification for steel tube-reinforced concrete column structure (CECS188:2005), the calculated results of axial compression bearing capacity by the proposed formula are in more agreement with the experimental values, with errors no greater than 15%. [ABSTRACT FROM AUTHOR]

Summary: This paper innovatively designs polyvinyl chloride tube (PVCT) with high‐strength concrete (HC) and presents the results of cyclic loading tests on new reinforced high‐strength concrete short columns, including three high‐strength concrete‐filled PVCT (HC‐PVCT) short columns, one high‐strength concrete‐filled steel tube short column and one HC short column. The main objective of this research was to evaluate the seismic behaviors of HC short columns based on the quasistatic test of the columns. The design parameters of the columns in the experiments were axial compression ratio, reinforcement measures, concrete strength, stirrups configuration, and the height‐diameter ratio of tubes. The crack distribution, failure modes, hysteresis loops, skeleton curves, energy dissipation capacity, strength degradation, stiffness degradation, and cumulative damage of the columns were presented and analyzed. The results showed that the HC‐PVCT column had a fuller hysteretic loop and a higher peak load than the HC column. Compared with HC column, the strength degradation of HC‐PVCT columns was slower, and the ductility increased significantly. With a larger axial compression ratio, the ductility of HC‐PVCT columns was decreased. Based on the test and analysis results, a modified HC‐PVCT design method was proposed to calculate the nominal shear strength of HC‐PVCT short columns. [ABSTRACT FROM AUTHOR]