Concrete-filled Steel Tubular Short Columns Research Articles

Experimental Research on the Confinement Effect for the Composite Concrete-Filled Square Steel Tubular Short Columns

Through the axial compression tests of two ordinary concrete-filled square steel tubular(CFSST) short columns and six composite CFSST short columns, the influence laws of section types, confinement coefficient, steel ratio and concrete strength on the mechanical behavior of the CFSST short columns were studied. The results show that in CFSST columns, the change of steel tube’s section form can improve effectively the cooperative work ability between the steel tube and core concrete, enhance the restraint effect of the steel tube on the core concrete, delay or inhibit the development of inclined cracks in the core concrete, increase the ductility and improve significantly the ultimate bearing capacity when the steel ratio or confinement coefficient is close to each other. With the increment of the confinement coefficient and steel ratio, the bearing capacity and ductility improve.

Investigation on Ultimate Bearing Capacity of Recycled Aggregate Concrete-Filled Steel Tubular Short Columns under Axial Compressive Load

Based on the Unified Strength Theory(UST),the ultimate load calculation formula for the recycled aggregate concrete-filled steel tubular short columns is derived in this paper,in which the decrease of longitudinal stress because of the hoop tensile tension is considered. The influence of intermediate principal stress on the ultimate load is studied and the failure mechanism is also discussed. The results show that the intermediate principal stress have important effect on the ultimate load which increases with the strength parameter .Through the comparison between the experimental results and the calculating results obtained in this paper,the deviation is small,and it shows that the formula have significance in exerting material potential.

Nonlinear analysis of circular concrete-filled steel tubular short columns under eccentric loading

This paper presents an effective theoretical model for the nonlinear inelastic analysis of circular concrete-filled steel tubular (CFST) short columns under eccentric loading. Accurate material constitutive relationships for normal and high strength concrete confined by either normal or high strength circular steel tubes are incorporated in the theoretical model to account for confinement effects that increase both the strength and ductility of concrete. The predicted ultimate bending strengths and complete moment–curvature responses of circular CFST columns under eccentric loading are compared with existing experimental results to examine the accuracy of the theoretical model developed. The fundamental behavior of circular CFST beam–columns with various diameter-to-thickness ratios, concrete compressive strengths, steel yield strengths, axial load levels and sectional shapes is studied using the verified theoretical model. Based on extensive numerical studies, a new design model for determining the ultimate pure bending strengths of circular CFST beam–columns is proposed. The theoretical model and formulas developed are shown to be effective simulation and design tools for the nonlinear inelastic behavior of circular CFST beam–columns under eccentric loading.

Nonlinear analysis of circular concrete-filled steel tubular short columns under axial loading

The confinement effect provided by the steel tube in a circular concrete-filled steel tubular (CFST) short column remarkably increases the strength and ductility of the concrete core. The reliable prediction using nonlinear analysis methods for circular CFST columns relies on the use of accurate models for confined concrete. In this paper, accurate constitutive models for normal and high strength concrete confined by either normal or high strength circular steel tubes are proposed. A generic fiber element model that incorporates the proposed constitutive models of confined concrete is created for simulating the nonlinear inelastic behavior of circular CFST short columns under axial loading. The generic fiber element model developed is verified by comparisons of computational results with existing experimental data. Extensive parametric studies are conducted to examine the accuracy of various confining pressure models and the effects of the tube diameter-to-thickness ratio, concrete compressive strengths and steel yield strengths on the fundamental behavior of circular CFST columns. A new design formula accounting for concrete confinement effects is also proposed for circular CFST columns. It is demonstrated that the generic fiber element model and design formula adequately predict the ultimate strength and behavior of axially loaded circular CFST columns and can be used in the design of normal and high strength circular CFST columns.

Experimental and Numerical Investigation of the Axial Behavior of Connection in CFST Diagrid Structures

Concrete filled steel tubular (CFST) diagrid structures usually have connections intersected by four oblique CFST columns. In order to investigate the performance, capacity and failure mechanism of the connections, two 1/5.5-scale specimens were tested under monotonic axial loading. The parameters in the study were the separation angle between columns. While the test was being conducted, the deflection, stress, failure pattern and capacity of the specimens were obtained and analyzed. In addition, the connection was analyzed using the general finite element analysis (FEA) software ABAQUS, with the purpose of investigating the mechanism, the weakness, the distribution of stress, and the bearing capacity of the connections. Experimental and numerical results indicate that the connecting separation angles resulted in the difference of failure modes and the mechanical behavior of the connections was similar to the behavior of CFST short columns.

Behavior of Centrally Loaded Concrete-Filled Steel-Tube Short Columns

A 5 year research on concrete-filled steel tubular (CFT) column system was carried out as a part of the fifth phase of the U.S.–Japan Cooperative Earthquake Research Program, and the tests of centrally loaded short columns were finished. The objectives of these tests were to clarify the synergistic interaction between steel tube and filled concrete, and to derive methods to characterize the load–deformation relationship of CFT columns. A total of 114 specimens was fabricated and tested in the experimental phase of investigations on centrally loaded hollow and CFT short columns. Parameters for the tests are as follows: (1) tube shape, (2) tube tensile strength, (3) tube diameter-to-thickness ratio, and (4) concrete strength. In determining the range of parameters, the emphasis was placed on obtaining a wide range of test data for establishing a generally applicable design method of CFT column systems. Design formulas to estimate the ultimate axial compressive load capacities are proposed for CFT columns with both circular and square sections based on tests results described in this paper.