Concrete-filled Rectangular Steel Tube Columns Research Articles

Experimental study and design method of embedded concrete-filled rectangular steel tube column base under cyclic load

Embedded column base has been widely used in concrete-filled steel tube (CFST) structures due to its high rigidity and good seismic performance. However, the strength analysis of the embedded CFST column base was not yet clear since there was little experimental research on it. In this paper, the experimental investigations of six embedded concrete-filled rectangular steel tube (CFRST) column bases under constant axial load and cyclic load were carried out to study the effects of embedded depth, improvement measures and axial compression ratios on the seismic performance of the column bases. The experimental results indicated that setting stiffeners, increasing the embedded depth or axial compression ratios could improve the seismic performance of the column base. In this experiment, the critical embedded depths of the columns with or without stiffeners were 0.7 and 1.5 times the column width B respectively. When the embedded depth was 0.7B, the contribution of anchor bolts to the moment resistance capacity of the column bases could reach up to 14.2%. Based on the analysis of the force transmission mechanism between the column and the concrete foundation in the embedded CFRST column base, a design method considering the contribution of different components to the moment resistance capacity of the CFRST column bases is proposed. The prediction results are in good agreement with the tested results and collected data, within ± 15% error. The parameter analysis based on the design method has revealed the influence patterns of various parameters on the moment resistance capacity of the column bases.

Force transmission mechanism of a new joint of concrete-filled rectangular steel tubular column under axial compression

In this study, a new joint of concrete-filled rectangular steel tube column was proposed and analyzed. The force transmission components include distribution beams and inner periphery ribs in the floor node area. The stress behavior of the new proposed concrete-filled rectangular steel tube column under axial compressive load was investigated. It was found that the force transmission components coordinate the force and deformation of external steel tube and internal concrete. This indicates that the steel tube and concrete can work together to bear external load. Our previous test results also show that arranging force transmission components in the floor node area can improve the mechanical behavior of a concrete-filled rectangular steel tube column. Finally, a design method of force transmission component distribution beam is proposed, which provides a reference for the structural designer to use the new concrete-filled rectangular steel tube joint in actual engineering.

Improved equivalent bracing model for seismic analysis of mid-rise CFS structures

An improved equivalent bracing model of cold-formed steel shear wall with concrete-filled rectangular steel tube column as reinforced end studs was proposed, for seismic analysis of mid-rise cold-formed steel structures. The model can consider end stud's compression buckling and beam-column joint's behavior. Elements and parameters of the model were described, comparisons between the model and pinned equivalent bracing model were performed. The results show that: (1) compression buckling can be simulated by setting an axial spring at the bottom of end stud; the reinforced end stud can be defined as a composite section, and the sectional properties can be determined according to the principle of equivalent flexural rigidity; the spring's axial stiffness can be determined by the shear capacity Fp of the wall and its corresponding deformation Δa; (2) beam-column joint's behavior can be simulated by rotational spring, which can be defined by pinching4 model after its constitutive relationship has been determined by experiments or the moment-rotation prediction model proposed in this study; (3) the shear behavior of the wall can be represented by equivalent diagonal braces with nonlinear springs whose restoring force properties can be defined by pinching4 model according to the load-displacement hysteretic curve obtained from full-scale cyclic loading test or numerical simulation etc.; (4) the model can predict actual seismic performance of mid-rise cold-formed steel structure more accurately than pinned equivalent bracing model; moreover, a wall's yield limit directly affects the response modification factor R, the model can thereby provide more reliable design objectives for the structure.

Investigation and evaluation of a novel technique on CFRT column connection

This study investigated the effect of an innovative technique, heat treatment, on Q345B steel, which is generally used in China, and the application potential of this technique for H-beam moment connections to concrete filled rectangular steel tube (CFRT) column. A heat-treating process with ultra-high temperature heating and subsequent controlled slow cooling could have a weakening effect on steel strength. The effect of this heat-treating process on steel was investigated through a series of material tests on Q345B steel (Chinese standard). The Chaboche hysteresis material model was selected and calibrated to better describe the strength behavior under cyclic loading, and was then used for subsequent seismic simulations. This technique can be utilized to improve the seismic performance of connections by locally heat-treating the beam section (HBS), and then inducing the plastic hinge away from the critical region. The effect of HBS was investigated on two common CFRT column connections in China, namely, through-diaphragm and internal-diaphragm CFRT column connections. Results showed that the novel heat-treating process also had a significant weakening effect on Chinese Q345B steel. The hysteresis behavior of steel was different from the monotonic performance. The Chaboche model can effectively describe the hysteresis properties. The application of HBS succeeded in inducing plastic strain developed in the heat-treated region, and can reduce strain concentrations without significant connection moment strength loss.

Reversed cyclic performance of cold-formed steel shear walls with reinforced end studs

To improve the shear performance of cold-formed steel (CFS) shear walls and to prevent a structure from collapsing due to compression buckling of the end studs, shear walls with concrete-filled rectangular steel tube columns as end studs were proposed. Cyclic loading tests on nine full-scale CFS shear walls with reinforced end studs were conducted concerning the influence of stud type, sheathing material and openings. The results showed that: (1) the walls' shear strength will be improved because the screws will be less able to tilt due to the concrete core in the reinforced end studs; (2) the walls' ductility may be improved by increasing stud thickness, but no meaningful difference in shear strength was observed when the interior stud section's type was replaced with a coupled C section; (3) compared to a wall that was individually sheathed with autoclaved lightweight concrete slabs on the external side, the shear strength could be increased by approximately 58.1% due to the addition of supplementary bolivian magnesium boards, which would be installed under the condition of an identical sheathing setup on the inner side; (4) the wall's shear capacity would be decreased due to an increase in the opening's size, and this shear capacity would also be impacted by the opening's position. Based on the experimental results and a bearing mechanism analysis of CFS shear walls with reinforced end studs, a simplified method for predicting the perforated walls' shear capacity was proposed, and the differences between the calculated and experimental results were within 8%.

Research on Concrete-Filled Rectangular Steel Tube Stiffeners and Axial Compression Bearing Capacity

Concrete-filled rectangular steel tube four sides restraint effect on the core concrete was weaker than the corner, which made the effect not significant. The paper studied a new kind of stiffening rib –PBL stiffener to strengthen restraint effect of concrete-filled rectangular steel tube , and evaluated its advantages compared with other stiffening ribs. 9 PBL stiffened concrete-filled rectangular steel tube columns under axial compressive load were tested. It also collected the test with other stiffened rids, such as straight ribs, binding bars, knee brace, steel reinforcement cage, steel bar stiffeners, saw tooth shaped stiffeners, stitching straight stiffeners and no rib concrete filled rectangular steel tube to compare. It evaluated increasing coefficient of bearing capacity by stiffening ribs. The results showed that: the PBL stiffeners and binding bar of concrete-filled rectangular steel tube bearing capacity was greater than other reinforcement measures by more than 20%; PBL stiffener could be a new prominent type of stiffener because of its excellent mechanical performance and simple construction.

The Influence Factors Researching of Percentage of Load-Carrying Capacity Shared by Concrete for Large Section Concrete-Filled Rectangular Steel Tube Column

Through the analysis of the transmission mechanism—distribution beam for large section (side length>800mm) concrete-filled rectangular steel tube column by the theory of elastic foundation beam we can obtain, percentage of load-carrying capacity shared by concreteis related with vertical spring stiffness of the steel tube, rotational spring stiffness of the steel tube, the vertical spring stiffness of the core concreteand stiffness of the distribution beam. Through analysis of the relationship among percentage of load-carrying capacity shared by concreteand the impact factors, we can identify the main factors that affect the percentage of load-carrying capacity shared by concrete, to control the design of the distribution beam.

Numerical Simulation on Failure Process of Concrete-Filled Rectangular Steel Tube Column

Realistic Failure Process Analysis (RFPA3D) was used to simulate the concrete-filled rectangular steel tube columns which are subjected to axial loads. The ultimate bearing capacity and the load-strain figures were presented. The Numerical simulation results were verified by experimental data of the paper [5]. Meanwhile, the development process of crack in the specimen was described. The whole failure process of rectangular steel tube columns was reproduced. The failure principles of concrete-filled rectangular steel tube column were discussed deeply.

Push-Over Analysis of the Seismic Behavior of a Concrete-Filled Rectangular Tubular Frame Structure

To investigate the seismic behavior of concrete-filled rectangular steel tube (CFRT) structures, a push-over analysis of a 10-story moment resisting frame (MRF) composed of CFRT columns and steel beams was conducted. The results show that push-over analysis is sensitive to the lateral load patterns, so the use of at least two load patterns that are expected to bound the inertia force distributions is recommended. The M-ϕ curves and N- M interaction surfaces of the CFRT columns calculated either by Han's formulae or by the USC-RC program (reinforced concrete program put forward by University of Southern Califonia) are suitable for future push-over analyses of CFRT structures. The P-ϕ effect affects the MRF seismic behavior seriously, and so should be taken into account in MRF seismic analysis. In addition, three kinds of RC structures were analyzed to allow a comparison of the earthquake resistance behavior of CFRT structures and RC structures. The results show that the ductility and seismic performance of CFRT structures are superior to those of RC structures. Consequently, CFRT structures are recommended in seismic regions.