Concrete-filled Steel Tubular Column Connections Research Articles

Experimental and numerical investigation of through-diaphragm in H-shaped steel beam to CFST column connections

This research proposes a cruciform through-diaphragm (CTD) for an H-shaped steel beam to concrete-filled steel tubular (CFST) column and investigates its seismic performance experimentally and numerically. The proposed connection consists of through-plates passing through the aligned slots in the panel zone and end plates directly welded to an H-shaped steel beam. This connection eliminates welding inside the steel tube for installation of the diaphragm, while providing a reliable load path from the steel beam to the CFST column. The experimental program examined the connection hysteretic behaviors, including the moment-rotation response, ductility, initial stiffness, and energy dissipation capacity. The proposed connection shows stable hysteric behavior and good energy dissipation up to a story drift up to 4 % and satisfies the AISC seismic provisions criteria for special moment connection. A finite element (FE) model was established and verified against the experimental results. The effects of concrete infill, steel tube column thickness, axial load ratio, and through-plate thickness on the hysteretic behavior of the proposed connection were investigated through parametric analysis of 24 FE models. This study provides the information on the optimized design parameters that ensures the stable seismic performance of the proposed connection that could be used in structural engineering practice.

Parametric study of steel-beam to flat-rectangular CFST column connections with small-size diaphragms

This paper studies the influence of various design parameters on the hysteretic behavior of beam-to-column connections between steel beams and flat rectangular concrete filled steel tubular (CFST) columns with small-size external diaphragms. Finite element models for the corner and exterior connections in a frame structure are developed and validated using test results. The influence of the parameters including the axial compression ratio, the thickness and flatness of the rectangular steel tube, and the size of the diaphragm on the hysteresis, load capacities, ductility, and energy dissipation capacities of the connections are particularly evaluated. Based on the evaluation, recommendations on the optimum design of the parameters are provided to ensure reliable hysteretic behavior of the connections for the seismic design of steel structures. This study provides the knowledge for the use of small-size external diaphragms beyond the limitation of existing design specifications for beam-to-column connections, which is meaningful to best exploit the unique properties of flat rectangular CFST columns and widen their applications in residential buildings.

Seismic performance of concrete-filled steel tubular column connections using blind bolts

In this study, a demountable connection that connects the upper and lower concrete-filled steel tubular columns with an inner sleeve section and blind bolts (referred to as Hollo-Bolts in this study) is proposed. The utilization of Hollo-Bolts allows them to be installed outside the steel tubes prior to the concrete casting and renders such connection to be readily dismantled after typical service loading. In order to study the seismic performance of the concrete-filled steel tubular column-column connection, six specimens were designed in the present study. The studied parameters included the axial load ratio, length of the inner sleeve, and location of the connection. The results demonstrated that the proposed connection exhibited good ductility performance, and the disassembly and reassembly of the connection after a service loading had no significant effect on their seismic performance. Additionally, the load-transfer mechanism of the concrete-filled steel tubular column-column connection was explored. Simplified formulae of anti-slip flexural bearing capacity of the connection were proposed, and the predicted values agreed well with the test results on the safe side.

Numerical and theoretical studies on the tensile strength and stiffness of plate-to-CFST column connections reinforced with internal T-shaped diaphragms

The internal T-shaped diaphragm for steel beam to square concrete-filled steel tubular (CFST) column connections is an improvement over conventional internal diaphragms in terms of construction, cost, and mechanical property. The performance of steel beam to square CFST column connections reinforced with internal T-shaped diaphragms is evaluated by conducting static tensile load in this study. Finite element models (FEM) were established and verified, including 24 plate-to-square CFST column connections with internal T-shaped diaphragms in the weak direction (PTC-WD connections), 20 plate-to-square CFST column connections with internal T-shaped diaphragms in the strong direction (PTC-SD connections), and 16 plate-to-square CFST column connections with conventional internal diaphragms (PTC-CID connections) for comparative study. The effects of tube thickness, diaphragm thickness, anchor plate size, beam flange width, concrete filling, and tube width on the tensile behavior of the connections were studied numerically. Additionally, the stress distribution of the tube, the beam flange, the divided diaphragm, the anchor plate, and the infilled concrete are analyzed. The results showed that the tensile strength and stiffness of PTC-WD connections were improved tremendously due to the anchoring effect, and its strength and stiffness were superior to those of PTC-SD connections and PTC-CID connections under the same conditions. Based on the assumed failure mechanism of each component, the theoretical models and formulas for the tensile strength and stiffness of the connections were provided. It was found that the theoretical strength and stiffness coincide well with those of FEM results and test results.

Experimental behavior of steel-beam to flat rectangular CFST column connections with small-sized external diaphragms

This paper experimentally investigates the hysteretic behavior of beam-to-column connections between steel beams and flat rectangular concrete filled steel tubular (CFST) columns with small-sized external diaphragms to enable the implementation of the connections in steel structure residential buildings. The flat rectangular CFST columns are characterized by the width-to-depth ratio of the cross-section greater than 2.0. Five test specimens, including three corner connections and two interior connections in a frame structure, with 400×200 mm rectangular CFST column cross-section and various sizes of external diaphragms are designed for the investigation. During the tests, the specimens are subjected to constant axial loads on the columns and cyclic vertical loads at the beam ends that impose bending moments about the strong and weak axis of the columns. Failure modes including buckling in beam flanges, cracking at the welded connections between beam flanges and external diaphragms, and shear failure in panel zones are observed. The load-displacement hysteresis and strain distribution are obtained to evaluate the elastoplastic behavior of the connections. The moment resistance capacity, ductility, energy dissipation capacity, as well as stiffness and strength degeneration of the connections are respectively evaluated. The test results demonstrate that the connections have adequate hysteretic performance for earthquake resilient design of steel structure residential buildings. It is applicable to use small-sized external diaphragms beyond the limitation of existing design specifications for beam-to-column connections with flat rectangular CFST columns.

Experimental performance of single blind-bolted CFST column connection under predominant shear loading

This paper presents experimental findings of ten full-scale blind-bolted concrete-filled steel tubular (CFST) connection tests under predominant shear loading. Previous works show that, the performance of blind-bolts with extended shank and headed nut performed significantly well under tensile loads, but research on such connections under shear loading is at scarce. In this testing programme, the performance of individual blind-bolted CFST column connection is assessed where various parameters including presence of infill concrete, bolt embedment length, tube wall thickness and concrete strength are considered. Material tests for all the elements in the connection assembly have also been conducted. The study is accompanied by assessment of international codes. It is observed that, with higher bolt embedment length, the concrete contribution can be enhanced up to 58% of the total load applied, where the load is transmitted to the concrete core by bearing, and the tube wall yielding could also be delayed. Test results also shows that, ultimate capacity of the bolts can be achieved with CFST connections under shear load. For all the connections, the failure mode was consistent to shear fracture of bolt. At the end, a modified prediction equation for blind-bolt shear resistance is proposed. The test results presented in the investigation provides scientific data for further numerical investigations and can also provide insights towards load-introduction mechanism in bolted CFST column connections.

Seismic behaviour of concrete-filled steel tubular column and precast shear wall connections

Good seismic behaviour of prefabricated concrete structures is critical to ensure safe long-term performance of residential and engineering structures. Various connection specimens were fabricated, including three prefabricated reinforced-concrete (RC) shear wall and concrete-filled steel tubular column connections, and one reference cast-in-place specimen. Cyclic loading was used to study the effect of the number of shear connectors and concrete strength in a connection zone on the failure mode and hysteresis of the connection. All specimens failed due to failure of shear connectors, where most damage occurred at the connectors and in nearby concrete. When the number of shear connectors increased from 3 to 5, the bearing capacity of the specimens increased by ~35%, while the ductility and energy dissipation capacity also improved. Increasing the concrete strength in the connection zone did not improve significantly the bearing capacity or seismic performance. The bearing capacity of the cast-in-place specimen was similar to that of the equivalent prefabricated precast specimen. Slip between the connection zone and precast RC shear wall resulted in internal force redistribution, resulting in higher ductility and energy dissipation capacity of the prefabricated specimens. Finally, computational analysis of previous models identified the best model for simulating force-slip behaviour of similar connections.

Seismic performance analysis of steel beam to CFST column connection with ductility and energy dissipation components

Concrete-filled steel tubular (CFST) column to steel beam joint with the ductility and energy dissipation components is a type of connection which is used in prefabricated structures, to improve the capacity of connections and construction efficiency. In this paper, two different type of steel beam to CFST column connections with the penetrated high-strength bolts and end-plate are investigated, i.e., steel beam to CFST column connection with end plate (CJ-1), and T-stub bolted (CJ-2) connections. The finite element model (FEM) of steel beam to CFST column connection with the penetrated high-strength bolts under cyclic loading are conducted based on the whole process of the nonlinear explicit analysis method using ABAQUS. The feasibility of FEM is verified by a set of experimental results performed by our research group, as well as available test results from other researchers. The failure modes, bearing capacity, energy dissipation capacity and ductility and rigidity degeneration were studied. As a result, the load-displacement hysteretic loop curve of CJ-2 connection is plump. However, the hysteresis curve of CJ-1 shows pinching phenomenon. The value of buckling load and ultimate load of CJ-2 increased by 28 % and 30 % respectively, compared with CJ-1. With respect of stress analysis, the plastic strain accumulation position distribution is relatively uniform duo to the T-stub connection, avoiding the penetrated high-strength bolt early yield or fracture. The results show that the steel beam to CFST column connection with penetrated bolts and T-stub connection has good seismic capacity.

Experimental Analyses of Mechanical Performance of CFST Column to Assembled Steel H-Beam Connections

The mechanical performance of a new proposed type of cross-shaped connection with concrete-filled steel tubular (CFST) column and assembled steel H-beam was investigated. Cyclic loading tests on the cross-shaped connections are carried out by using MTS servo loading system. Comparative analyses are conducted based on the experimental results including hysteretic curves, skeleton curves and stiffness degradation curves as well as ductility coefficients of cyclic loading tests. Furthermore, effects of geometric parameters of ring-stiffened plate, axial compression ratio and backing plate on the deformation performance of cross-shaped connections are analyzed. The results show that the increase of width of ring plate and the shape change of ring plate from square to circle can both significantly improve the ductility and the hysteretic characteristics of connection. It is emphasized that the specimen with square ring plates is of better deformation performance but lower bearing capacity than the ones with circular ring plates. Besides, the backing plates always have positive effects on the hysteretic characteristics, ductility and energy dissipation of the CFST column connections. Conversely, the increase of axial compression ratio contributes negatively to both the bearing capacity and deformation performance of the connection specimens. It can be concluded that the presented cross-shaped connection is of good deformation performance relating to hysteretic characteristics, energy dissipation and ductility, which can provide reference towards engineering practice with potential perspective application.

Behavior of Steel Beam to Concrete-Filled Steel Tubular Column Connections after Exposure to Fire

A nonlinear finite-element analysis (FEA) model was developed in this paper based on the elastoplastic finite-element theory to analyze the load versus deformation relation of steel beam to concrete-filled steel tubular column connections. Six tests on steel beam to concrete-filled steel tubular (CFST) column connections using external ring after exposure to the ISO-834 standard fire were used to verify the theoretical model. The test parameters included the column cross-sectional type, the fire duration time, the level of axial load in the column, and the beam-column strength ratio. Each test specimen consisted of a CFST column and two steel beam segments in cruciform arrangement to represent an interior joint in a building. Three of the six composite connection specimens had circular cross sections and three had square cross sections. Five of the test specimens were simultaneously exposed to the standard ISO-834 fire condition. After they had cooled down to room temperature, each was tested under a cons...

Seismic performance of steel beams to concrete-filled steel tubular column connections

Abstract A nonlinear force-deformation model to simulate shear transfer behavior in the panel zone of CFT (Concrete-Filled Steel Tube) beam-column connections is proposed. In this model, influence of axial load on the shear transfer behavior is accounted for. To validate the proposed theory, five circular CFT beam-column connections were constructed and tested. Test results showed that all specimens failed by the welding fracture while entering nonlinear stage. It is found that the higher the axial load was applied, the better the ductility of connections was obtained. Comparison of analytical and experimental results shows that the proposed prediction for panel shear falls in a reasonable range for higher axial load tests, but tends to be conservative for lower axial load tests.