Steel Reinforced Concrete Columns Research Articles

Axial Load–Moment Interaction Diagram of Circular Concrete Columns Reinforced with CFRP Bars and Spirals: Experimental and Theoretical Investigations

AbstractNorth America’s current design codes and guidelines allow the use of fiber–reinforced polymer (FRP) bars as the primary reinforcement in concrete structures and provide design recommendations for using these bars. Because of a lack of experimental data, however, FRP bars have not been recommended for resisting compression stresses as longitudinal reinforcement in columns or compression reinforcement in flexural elements. This paper presents test results of an experimental program to investigate the structural performance of 10 full-scale circular concrete columns reinforced with carbon fiber–reinforced polymer (CFRP) bars and spirals subjected to combined axial compression loads and bending moments. The test variables include different eccentricity-to-diameter ratios and two types of reinforcement (CFRP and steel). The test results show that the CFRP- and steel-reinforced concrete columns behaved similarly up to their peak loads. The failure of the test specimens under different levels of eccentri...

Numerical simulation of mega steel reinforced concrete columns with different steel sections

SummaryIn recent years, the mega steel reinforced concrete (SRC) columns have been applied in super‐tall buildings. The previous research on SRC columns mainly focuses on the components with simple arrangement of encased steel, such as H‐shaped steel and cross‐shaped steel, with little attention paid to mega SRC columns that always have complicated encased steel and large steel ratio. The cyclic loading tests were carried out on scaled mega SRC column specimens with different cross‐section type of encased steel and steel ratio. The nonlinear three‐dimensional finite element and fiber element models were established respectively to simulate the inelastic behavior of mega SRC columns. The equivalent plastic strain of concrete, steel and rebar as well as the confinement effect on the concrete caused by the rebar and the steel plate were analyzed subsequently. By using the verified numerical model, the seismic behavior of specimens with different axial compression ratio was also studied. The test and analysis results indicate that the steel ratio and axial compression ratio have significant effects on the seismic performance of mega SRC columns, while the effect of cross‐section type of encased steel is not significant. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental investigation on joints between steel-reinforced concrete T-shaped column and reinforced concrete beam under bidirectional low-cyclic reversed loading

Steel-reinforced concrete T-shaped column-beam structure system has superiorities of both steel-reinforced structure and special-shaped column structure. This research focuses on steel-reinforced concrete T-shaped column-beam joint design and experimentally investigates seismic behaviors of the proposed joints. Pseudo-static tests are carried out on three steel-reinforced concrete T-shaped column-reinforced concrete beam joints and one reinforced concrete T-shaped column-reinforced concrete beam joint. The experiments were conducted under bidirectional low-cyclic reversed loading to simulate realistic loading conditions under earthquake. Hysteresis loops of all the specimens, including load–deflection, moment–rotation, and load–shear deformation loops, are plotted for the evaluation of seismic reaction. The working index, ductility coefficient, and equivalent viscous-damping coefficient are calculated for comparisons. Meanwhile, the ductility, capacity of energy dissipation, stiffness degradation, and the function of steel reinforcement in resisting shear force in the joint core area are intensively studied. Based on experimental results, this research analyzes shear-resistant capacity and the inner force transmission in these joints. It is found that the steel-reinforced concrete T-shaped column-reinforced concrete beam joint performs well under seismic conditions; moreover, shear-resistant capacity, ductility, and reliability are satisfactory. Conclusions derived from this research are useful for engineering practice.

Mechanical performance of glass fiber–reinforced polymer tubes filled with steel-reinforced high-strength concrete subjected to eccentric compression

Glass fiber–reinforced polymer tubes filled with steel-reinforced high-strength concrete are proposed as glass fiber–reinforced polymer–steel-reinforced high-strength concrete composite members. Eccentric compression is a typical loading scenario for such column members in practice. Experimental investigation on eight glass fiber–reinforced polymer tubes filled with steel–reinforced high-strength concrete columns subjected to eccentric compression was conducted. The effects of fiber orientation, thickness of glass fiber–reinforced polymer tube, slenderness ratio of columns, and loading eccentricity were investigated. It was found that the compression bearing capacity of glass fiber–reinforced polymer–steel-reinforced high-strength concrete columns increased with the decrease in the fiber tangle angle and the increase in the thickness of the glass fiber–reinforced polymer tube but reduced with the increase in the eccentricity and the slenderness ratio. Corresponding formulas were developed based on the nonlinear full-process analysis theory to describe the compression behavior of glass fiber–reinforced polymer–steel-reinforced high-strength concrete under eccentric loading. Good agreement was found through the comparison between the theoretical and the experimental results. The validated modeling approach was, therefore, employed to develop a parametric analysis that can be used to provide valuable guidance for practical application and further research on such structural members.

Sustainable design model to reduce environmental impact of building construction with composite structures

Thanks to advances in technologies related to zero energy buildings, reducing CO2 emissions during the design and construction phase becomes more and more important to reduce environmental impact from building construction. Even though more than half of high-rise buildings over 200 m completed in 2014 employed steel reinforced concrete (SRC) composite structures, most of sustainable design to reduce CO2 emissions were limited to reinforced concrete (RC) buildings. Since SRC is a composite structure consisting of three component materials of concrete, steel shape, and rebar, CO2 emissions can be effectively reduced by applying eco-friendly design strategies for determining the proportions of those components in SRC members.In this study, the sustainable design model for SRC composite structures is developed for optimal combination of construction materials with minimized CO2 emissions. The model is used to provide comprehensive analyses of variability of CO2 emissions in the building construction. The results indicates that increasing the cross-sectional area of steel shape is more advantageous for reduction of CO2 emissions than increasing the cross-sectional area of concrete for composite structures subjected to high axial loads required in high-rise building constructions based on the analysis of the contribution of each component to strength of column. Sensitivity analysis reveals that the environmental impact can be significantly reduced by using high strength materials in SRC structures. Further, through the application of the model to the design of an actual high-rise building, it is confirmed that derived SRC columns have excellent performances in terms of environmental impact and space utilization.

Tests on the Steel–Concrete Bond Strength in Steel Reinforced Concrete (SRC) Columns After Fire Exposure

Bond behaviour between the steel and concrete is important in ensuring the interaction of different components in steel reinforced concrete (SRC) columns under various working conditions, and sufficient bond strength should be kept in these columns even after fire exposure. This paper presents the experimental results of bond strength between the embedded steel and concrete in SRC columns after fire exposure. A total of eight push-out specimens were prepared, including two unheated and six fire exposed specimens. The fire exposed specimens were heated and left cooling down in a fire furnace, and then were tested for residual bond strength. Concrete explosive spalling was found when the test specimens were heated. The elevated temperatures at the steel–concrete interface and at the location of stirrups were recorded by thermocouples. Effects of different parameters, such as fire scenario, lateral confinement, and encased steel type, on the bond behaviour were analysed. Time delay was found in the temperature increase across the concrete section, and the inner maximum temperature reached at a measurement location was 430°C during the cooling phase, which was much higher than the temperature of 180°C measured at the end of heating phase for the same location. The reduction in bond strength was as high as 54.2%, whereas the corresponding ultimate slip increased significantly from around 0.3 mm to over 4 mm due to fire exposure. An existing model was revised to predict bond stress-slip curves for SRC columns after fire exposure, and a reasonably good agreement was obtained between the measured and predicted results.

Experimental study on shear capacity of SRC joints with different arrangement and sizes of cross-shaped steel in column

The seismic performance of the ordinary steel reinforced concrete (SRC) columns has no significant improvement compared to the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type shaped steel were put forward on this background, and they were named as enlarging cross-shaped steel and diagonal cross-shaped steel for short. The seismic behavior and carrying capacity of new-type SRC columns have been researched theoretically and experimentally, while the shear behavior remains unclear when the new-type columns are joined onto SRC beams. This paper presents an experimental study to investigate the shear capacity of new-type SRC joints. For this purpose, four new-type and one ordinary SRC joints under low reversed cyclic loading were tested, and the failure patterns, load-displacement hysteretic curves, joint shear deformation and steel strain were also observed. The ultimate shear force of joint specimens was calculated according to the beam-end counterforce, and effects of steel shape, load angel and structural measures on shear capacity of joints were analyzed. The test results indicate that: (1) the new-type SRC joints display shear failure pattern and has higher shear capacity than the ordinary one; (2) the oblique specimens have good bearing capacity if designed reasonably; and (3) the two proposed construction measures have little effect on the shear capacity of SRC joints embedded with diagonal cross-shaped steel. Based on the mechanism observed from the test, the formulas for calculating ultimate shear capacity considering the main factors (steel web, stirrup and axial compression ratio) were derived, and the calculated results agreed well with the experimental and simulated data.

Seismic performances of centrifugally-formed hollow-core precast columns with multi-interlocking spirals

A precast composite column system has been developed in this study by utilizing multi interlocking spiral steel into a centrifugally-formed hollow-core precast (CHPC) column. The proposed hybrid column system can have enhanced performances in the composite interaction behavior between the hollowed precast column and cast-in-place (CIP) core-filled concrete, the lap splice performance of bundled bars, and the confining effect of concrete. In the experimental program, reversed cyclic loading tests were conducted on a conventional reinforced concrete (RC) column fabricated monolithically, two CHPC columns filled with CIP concrete, and two steel-reinforced concrete (SRC) columns. It was confirmed that the interlocking spirals was very effective to enhance the structural performance of the CHPC column, and all the hollow-core precast column specimens tested in this study showed good seismic performances comparable to the monolithic control specimen.

Performance of Steel-Reinforced Concrete Beam-to-Column Joints after Exposure to Fire

AbstractThis paper presents a numerical analysis on the postfire behavior of steel-reinforced concrete (SRC) column to axially and rotationally restrained SRC beam joints. A finite-element analysis (FEA) model was developed to simulate the reaction of the composite joints under an entire loading and fire phase, including ambient temperature loading, heating, and cooling with constant loads and postfire loading. For validation, the proposed modeling method was used to simulate the results of SRC joint postfire tests and SRC column and joint fire-resistance tests. The comparison demonstrates the accuracy of the proposed FEA model. Based on the validated FEA model, the failure modes of SRC joints with restrained beams were investigated, and the joint deformation and internal force development during the entire loading and fire phase were analyzed. Afterward, two important parameters, namely, residual joint strength index and residual stiffness index, were defined based on the joint moment versus relative rot...

Performance of Steel-Reinforced Concrete Column after Exposure to Fire: FEA Model and Experiments

This paper studies the postfire performance of steel-reinforced concrete (SRC) columns subjected to an entire loading and fire phase, including ambient temperature loading, heating and cooling with constant external loads, and postfire loading. A sequentially coupled thermal-stress analysis module was employed in a finite-element analysis (FEA) program to establish temperature field analysis and structural-analysis models of SRC columns subjected to the entire loading and fire phase. To improve the precision of the FEA model, the influence of fire-induced concrete explosive spalling (CES) was considered by using element change technique. Besides the existing fire-resistance test data of SRC columns, to further validate the accuracy of the FEA model in the postfire phase, a set of fire tests on SRC columns, including a fire-resistance test and postfire test subjected to the entire loading and fire phase, were conducted. Compressive failure and bending failure were observed in the test. Comparison between predicted and test results indicates that the accuracy of the FEA model was acceptable, and then the FEA model was extended to simulate a full-scale SRC column in a real project subjected to the entire loading and fire phase. The temperature distribution, load versus axial deformation relations, and load redistribution of the full-scale SRC column during the entire loading and fire phase were investigated. It was found that the postfire peak load of the calculated column can be 26.7% lower than that at ambient temperature. The load carried by shaped steel rises from 20% to the peak value of 93% during the heating and cooling phase, indicating the significant contribution of shaped steel to resist the external loads during fire exposure.

Axial Load and Cyclic Lateral Load Tests for Composite Columns with Steel Angles

AbstractTo enhance the structural capacity and constructability of composite columns, a prefabricated steel-reinforced concrete (PSRC) column was developed. By using the prefabricated steel cage, field rebar work is unnecessary, and the self-erectable steel cage can provide sufficient strength and rigidity to support the construction loads of beams and slabs. In the present study, various steel angle ratios, transverse bar spacings, and prefabrication details were considered for better structural capacity and constructability. To investigate the performance of the proposed method, axial loading tests and cyclic lateral loading tests were performed. In the axial loading test, the structural performance of the PSRC columns was comparable to, or even better than, that of the conventional composite column using the wide flange steel section, when early spalling of the cover concrete was restrained by closely spaced hoops. Under cyclic lateral loading, on the other hand, the PSRC columns were more susceptible ...

Seismic behavior of steel reinforced concrete (SRC) joints with new-type section steel under cyclic loading

No significant improvement has been observed on the seismic performance of the ordinary steel reinforced concrete (SRC) columns compared with the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type section steel were put forward on this background: a cross-shaped steel whose flanges are in contact with concrete cover by extending the geometry of webs, and a rotated cross-shaped steel whose webs coincide with diagonal line of the column's section. The advantages of new-type SRC columns have been proved theoretically and experimentally, while construction measures and seismic behavior remain unclear when the new-type columns are joined onto SRC beams. Seismic behavior of SRC joints with new-type section steel were experimentally investigated by testing 5 specimens subjected to low reversed cyclic loading, mainly including the failure patterns, hysteretic loops, skeleton curves, energy dissipation capacity, strength and stiffness degradation and ductility. Effects of steel shape, load angel and construction measures on seismic behavior of joints were also analyzed. The test results indicate that the new-type joints display shear failure pattern under seismic loading, and steel and concrete of core region could bear larger load and tend to be stable although the specimens are close to failure. The hysteretic curves of new-type joints are plumper whose equivalent viscous damping coefficients and ductility factors are over 0.38 and 3.2 respectively, and this illustrates the energy dissipation capacity and deformation ability of new-type SRC joints are better than that of ordinary ones with shear failure. Bearing capacity and ductility of new-type joints are superior when the diagonal cross-shaped steel is contained and beams are orthogonal to columns, and the two construction measures proposed have little effect on the seismic behavior of joints.

Role of concrete confinement of wide-flange structural steel shape in steel reinforced concrete columns under cyclic loading

In this study, effects of wide-flange structural steel shapes on concrete confinement of steel reinforced concrete (SRC) columns were examined by conducting structural testing on six large-scale SRC columns under cyclic loading. Specifically, effects of the major- and minor-axis bending relative to the steel shape on the ductility and confinement effectiveness of SRC columns were investigated. Experimental results showed that concrete confinement of SRC columns were highly influenced by the bending direction. Details of the underlying confining mechanisms of SRC columns were uncovered. Findings from this study indicated that the required confinement reinforcement for the SRC columns subjected to major-axis bending could be significantly reduced, compared to that of the SRC columns subjected to minor-axis bending.

Effect of wide-flange-steel geometry on the long-term shortening of steel-reinforced concrete columns

Column shortening due to creep and shrinkage of concrete should be predicted accurately, especially in high-rise buildings. One of the main mechanisms of creep and shrinkage is moisture diffusion. However, in steel-reinforced concrete columns, which are widely used in high-rise buildings, the wide-flange steel located inside the column hinders the diffusion of moisture. Consequently, the long-term shortening of the column is delayed due to the slower diffusion. A prediction method that takes into account the actual moisture diffusion inside the column is suggested in this paper. The effect of the wide-flange-steel geometry on the long-term deformation of concrete in a column is precisely demonstrated through parametric studies using this method. The results of the parametric study show that the ratio of the web length of the wide-flange steel to the square column size is one of the main parameters affecting the long-term deformation of concrete in steel-reinforced concrete columns.

Experimental study on seismic performance of mega steel-reinforced concrete columns subjected to cyclic loads

Summary In recent years, mega steel-reinforced concrete (SRC) columns have been applied in super tall buildings. The previous research on SRC columns mainly focuses on the components with simple arrangement of shaped steel, such as H-shaped steel and cross-shaped steel, with little attention paid to mega SRC columns, which always have complicated encased steel and large steel ratio. The cyclic loading tests were carried out on scaled mega SRC column models with different cross-section type of encased steel and steel ratio. The principal damage states were investigated throughout the entire testing process. Based on the test results, the effects of steel ratio and the cross-section type of encased steel on the damage characteristics, hysteretic behavior, ductility, secant stiffness degradation, energy dissipation capacity and maximum crack width were analyzed. The test results indicate that the steel ratio has significant effect on the seismic performance of mega SRC columns while the effect of cross-section type of encased steel is not significant. Copyright © 2015 John Wiley & Sons, Ltd.

Behavior of square tubed steel reinforced-concrete (SRC) columns under eccentric compression

This paper presents experimental and analytical studies on the behavior of square tubed SRC (TSRC) columns subjected to eccentric compression. Eight square TSRC columns were tested to investigate the effects of eccentricity ratio of the compression force, width-to-thickness ratio (B/t) of the steel tubes, and use of shear connector studs on the steel sections. The test results indicated that local buckling of the square tubes was delayed effectively since axial load was not directly applied on the steel tube. Buckling of the tube initially occurred when the load reached the ultimate value for the specimens with B/t ratio of 100, and buckling occurred earlier for the specimens with B/t ratio of 133 when the load reached 88% to 94% of the ultimate load. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfections were included. Good agreement was achieved between the predicted results using the proposed FE model and the test results. A modified Eurocode 4 design method was adopted to calculate the ultimate strength of square TSRC columns.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete (SRC) columns, steel plate (SP) deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carried out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens (designated as new specimens). The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out; they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP’s to repair a deformed wall is a practicable technique.

Experimental and Simulation Studies on the Seismic Performance of I-section Steel-Concrete Composite Columns

This study analyses the working mechanism and seismic performance index of I-section steel-reinforced concrete columns with concealed double steel plates and bottom-strengthened I-section concrete-filled steel tube columns subjected to compression-bending load. For this purpose, six column models with different constructions were tested under horizontal low cyclic loading. Based on the experiments, the load-bearing capacity, stiffness and degradation process, ductility, hysteretic energy dissipation capacity and failure characteristics of the models were analysed. The formulae for calculating the load-bearing capacity for the normal and oblique sections of I-section steel-concrete composite columns were derived, and the finite element (FE) numerical simulation of the classical specimens was performed. According to the results, the load-bearing capacity, ductility and seismic energy dissipation capacity of the bottom-strengthened I-section steel-concrete composite columns are obviously improved when compared with those of the conventional I-section steel-concrete composite columns. Moreover, the calculated and FE numerical simulation results are found to be in good agreement with the experimental results. Further, the bottom-strengthened I-section steel-concrete composite column shows better seismic behaviour and higher energy dissipation capacity under suitable constructional requirements, indicating their suitability for constructing high-rise buildings.

Effects of sustained axial loads on steel-reinforced concrete columns

Steel-reinforced concrete (SRC) columns have been widely used over the past few decades. However, very limited research has been conducted on the time-dependent behaviour of these columns caused by creep and shrinkage under sustained loading. The results of an experimental study of the long-term behaviour of short SRC columns under sustained axial loading and a further test of their ultimate axial capacity are presented in this paper. Long-term axial deformations due to shrinkage and creep of the concrete are recorded. In the analysis of the test results, time analysis of the SRC columns under sustained axial loads using the age-adjusted effective modulus method is proven to be suitable by employing the ACI 209 model for the prediction of shrinkage and the CEB-FIP90 model for the prediction of creep. The ultimate strengths of the columns after long-term loading are also determined, and it is shown by the results that the sustained axial loads have no significant effect on the axial compressive strength of...

Theoretical and Experimental Study of Slender Concrete Columns Reinforced with GFRP Bars

This paper studies slender concrete columns reinforced with GFRP bars. For this target an experimental work was performed utilizing five such columns. Based on the experimental work the slenderness limit of 22 for unbraced steel-reinforced concrete columns as given by the ACI318-11 code was suggested to be little changed to 23.3 for GFRP reinforced concrete columns. The provisions of the ACI318-11 code for slender concrete columns reinforced with steel bars are reviewed. New expression from the literature for the effective flexural stiffness EI of slender concrete columns reinforced with GFRP bars is used to calculate the moment magnification factor and a procedure for plotting the interaction diagrams of the columns of this research is described.