Lin-Hai Han

An experimental study and calculation on the fire resistance of concrete-filled SHS and RHS columns

Abstract The behavior of concrete-filled steel square hollow section (SHS) and rectangular hollow section (RHS) columns with or without fire protection subjected to axial or eccentric loads has been experimentally investigated and the results are presented in this paper. The parametric and experimental studies provide information for the development of formulas for the calculation of the fire resistance and the fire protection thickness of the composite columns. The main objectives of this paper were threefold: first, to report a series of fire tests on composite columns with square and rectangular sections. Secondly, to analyze the influence of several parameters, such as fire duration time, sectional dimension, slenderness ratio, load eccentricity ratio, strength of steel and concrete on the residual strength index (RSI) of the composite columns. Finally, to develop formulas for the calculation of the fire resistance and the fire protection thickness of the concrete-filled steel SHS and RHS columns, such formulas to be suitable for incorporation into building codes. The concepts of this paper were used to provide data on the necessary fire protection measures for the concrete-filled steel SHS columns used in a high-rise building, Ruifeng, Shangye Building in Hangzhou City, in southern China.

Concrete-filled thin-walled steel SHS and RHS beam-columns subjected to cyclic loading

Abstract The flexural force-deformation behavior of concrete-filled thin-walled steel SHS and RHS beam-columns was experimentally investigated and the results presented in this paper. The parameters in the study included the depth-to-width ratio (β), the core concrete strength (fcu), and the axial load level (n). Thirty concrete-filled thin-walled steel SHS and RHS beam-column specimens were tested under constant axial load and cyclically increasing flexural loading. A mechanics model is developed in this paper for concrete-filled steel SHS and RHS columns subjected to constant axial load and cyclically increasing flexural loading, and is a development of the analysis used for monotonically loading condition (Han et al., 2001) [1] . The predicted cyclic responses for the composite columns are in good agreement with test results. Based on the theoretical model, parametric analysis was performed on the behaviors of moment (M) versus curvature (φ) response, lateral load (P) versus lateral displacement (Δ) relationship, as well as ductility coefficient (μ) for the composite beam-columns. Finally, simplified models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (Δ) relationship were suggested. Formula should be suitable for incorporation into building code, for the calculation of the ductility coefficient (μ) of the composite beam-columns under constant axial load and cyclically increasing flexural loading was developed.

Concrete-filled tubular members and connections

1. Introduction 2. Concrete-Filled Tubular Sections 3. Members Subjected to Static Loading at Ambient Temperatures 4. Members Subjected to Fire 5. Members Subjected to Seismic Loading 6. Connections to Concrete-Filled Tubular Columns 7. Recent Developments. Appendix A: Summary of Design Rules. Appendix B: Practical Design Examples

Fire performance of concrete filled steel tubular beam-columns

Abstract Finite element method is applied for the calculations of temperature fields of concrete filled steel tubes under fire. A theoretical model that calculates deformations and strength of beam-column in fire and fire resistance is described in this paper. A comparison of results calculated using this model with the results of tests shows good agreement. Based on the theoretical model, the influence of the changing strength of the materials, sectional dimensions, steel ratio, load eccentricity and slenderness ratio on the fire resistance are discussed. The theoretical model in this paper was used to provide data on the necessary fire protection measures for the concrete filled steel tubular columns used in a high-rise building, SEG Plaza in Shen-Zhen City, southern China.

Axial Loading Behavior of CFRP Strengthened Concrete-Filled Steel Tubular Stub Columns

This paper presents the axial compression test results of concrete-filled steel tubular (CFST) stub columns strengthened with carbon fiber reinforced polymer (CFRP) composites. Both circular and rectangular specimens were tested to investigate the retrofitting effects of CFRP composites on them. The test results showed that the CFRP jackets enhanced the load bearing capacity of the circular columns effectively, whereas the enhancement was not so significant for rectangular columns. However, ductility was enhanced to some extent for those rectangular columns. A simple model is proposed to calculate the ultimate strength of circular CFST stub columns wrapped with CFRP. The predicted results are generally in good agreement with the experimental ones obtained in this study and in the literature.

Influence of concrete compaction on the strength of concrete-filled steel RHS columns

Abstract Concrete-filled steel tubular columns have better structural performance than that of bare steel or reinforced concrete (R.C.). The use of concrete-filled SHS (Square Hollow Section) and RHS (Rectangular Hollow Section) have become widespread in the past few decades. However, these members are susceptible to the influence of concrete compaction. It is expected that the influence of concrete compaction on R.C. columns and concrete-filled steel tubes is different. For R.C. columns, concrete compaction only affects the mechanical properties of concrete. But for concrete-filled steel tubes, it is well known that the interaction between steel tube and concrete is the key issue to understand the behaviour of this kind of column. The concrete compaction not only affects the properties of the core concrete itself, but also may influence the interaction between the steel tube and its concrete core, and thus influences the behaviour of the composite columns. The present study is an attempt to study the influence of concrete compaction on the strength of concrete-filled steel RHS columns. Tests on 35 concrete-filled steel RHS columns to investigate the influence of concrete compaction methods on the member capacities of the composite columns are reported. The main parameters varied in the tests are: (1) column section depth-to-width ratio, from 1.0 to 2.0, (2) tube depth to thickness ratio, from 34 to 136, (3) load eccentricity (e), from 0 to 31 mm and (4) column slenderness (λ), from 21 to 62. The main objectives of these tests were twofold: firstly, to report a series of tests on composite columns under different concrete compaction methods; and secondly, to investigate the influence of concrete compaction on the member capacities of the composite columns. Comparisons are made with predicted column strengths using the existing codes such as LRFD, American Institute of Steel Construction Inc-1997, AIJ-Architectural Institute of Japan-1997, Eurocode 4-1996 and GJB4142-2000. It was found that better compaction of concrete resulted in higher member capacities in concrete-filled steel RHS columns. The tests showed the importance of good concrete compaction for concrete-filled steel RHS columns.

Concrete Shrinkage and Creep in Recycled Aggregate Concrete-Filled Steel Tubes

Concrete shrinkage and creep in recycled aggregate concrete-filled steel tubes (RACFST) were experimentally studied and the results were presented in this paper. The measurements on the shrinkage and creep lasted for about eighteen months. The main parameters varied in the tests are: (1) sectional types, circular and square; (2) in-fill concrete types, recycled aggregate concrete (RAC) and normal concrete; and (3) long-term sustained load levels, 0.3 and 0.6. The test results showed that the time-history of the concrete shrinkage and creep in RACFST was similar to that of the corresponding normal CFST. However, the shrinkage and creep strains of RACFST specimens were larger than those of the normal CFST specimens. Finally, the predictive models based on previously issued provision for time-dependent behaviour of the composite member were calibrated with the tests, and recommendations for the calculations on the shrinkage and creep of the concrete core in RACFST were also suggested.

Residual strength of concrete-filled RHS columns after exposure to the ISO-834 standard fire

The residual strength of a composite column may be used to assess the potential damage caused by fire and help to establish an approach to calculate the structural fire protection for minimum post-fire repair. The behavior of six rectangular hollow structural steel (RHS) columns filled with concrete, with or without fire protection, after exposure to the ISO-834 standard fire (ISO 834, 1975), subjected to axial or eccentric loads have been experimentally investigated and the results presented in this paper. Comparisons are made with predicted column strengths using the existing codes such as LRFD-AISC-1994, AIJ-1997, EC4-1996 and GJB4142-2000. It was found, in general, that the loss of the strength of the specimens without protections was significantly greater than that of columns with fire protection. A mechanics model is developed in this paper for concrete-filled RHS columns after exposure to the ISO-834 Standard Fire (ISO 834, 1975), and is a development of the analysis used for ambient condition (Han et al., 2001). The predicted load versus mid-span deflection relationship for the composite columns is in good agreement with test results. Based on the theoretical model, influence of the changing strength of the materials, fire duration time, sectional dimensions, steel ratio, load eccentricity ratio, depth-to-width ratio and slenderness ratio on the residual strength index (RSI) is discussed. It was found that, in general, the slenderness ratio, sectional dimensions and the fire duration time have a significant influence on the residual strength index (RSI). However, the steel ratio, the depth-to-width ratio, the load eccentricity ratio and the strength of the materials have a moderate influence on RSI. Finally, formulas suitable for incorporation into a building code, for the calculation of the residual strength of the concrete-filled RHS columns after exposure to ISO-834 standard fire is developed based on the parametric analysis results.

Behaviour of concrete-filled hollow structural steel (HSS) columns with pre-load on the steel tubes

Abstract The use of hollow structural steel (HSS) columns filled with concrete has become widespread in the past few decades. However, these members are susceptible to the effects of pre-load on the steel tubes during construction. Nineteen concrete-filled HSS columns with the steel tubes subjected to pre-load have been tested. An attempt to predict the load–deformation behaviour of concrete-filled HSS columns with the steel tubes subjected to pre-load is proposed in this paper. A comparison of the results calculated using this model shows good agreement with the test results. The theoretical model, and the influence of the pre-load ratio, slenderness ratio, steel ratio, as well as the strength of the materials are discussed. Finally, formulas for the calculation of the ultimate strength of concrete-filled steel tubular columns with the steel tubes subjected to pre-load are developed; such formulas should be suitable for incorporation into building codes.

Residual Strength of Concrete Filled RHS Stub Columns after Exposure to High Temperatures

Tests are reported on twenty-six concrete filled steel tube of rectangular section after being exposed to high temperatures, to investigate the influence of temperature on section capacity and load-deformation behavior. The main parameter varied is temperature, from 20°C to 900°C. A mechanics model is described in this paper for the behaviour of concrete-filled RHS (Rectangular Hollow Section) columns after exposed to high temperatures, and is a development of the analysis (Han et al, 2001a) used when only normal temperatures apply. The predicted load versus axial strain relationship is in good agreement with stub column test results. Simplified models are derived for the section capacities and the modulus of elasticity of the composite sections. It was found in general, that the higher the exposure temperature, the higher the loss of section capacities and elastic modulus which resulted. The tests have shown the importance of the influence of high temperatures on the performance of concrete filled steel tubes. The work in this paper provides a basis for further theoretical study on the residual strength of concrete filled steel tubular columns.