• Steel and Composite Structures
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• v.35 no.3
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• pp.371-384
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• 2020

The steel-concrete double composite girder in the negative flexural region combines an additional concrete slab to the steel bottom flange to prevent the local steel buckling, however, the additional concrete slab may lower down the neutral axis of the composite section, which is a sensitive factor to the tensile stress restraint on the concrete deck. This is actually of great importance to the structural rationality and durability, but has not been investigated in detail yet. In this case, a series of 5.5 m-long composite girder specimens were tested by negative bending, among which the bottom slab configuration and the longitudinal reinforcement ratio in the concrete deck were the parameters. Furthermore, an analytical study concerning about the influence of bottom concrete slab thickness on the cracking and sectional bending-carrying capacity were carried out. The test results showed that the additional concrete at the bottom improved the composite sectional bending stiffness and bending-carrying capacity, whereas its effect on the concrete crack distribution was not obvious. According to the analytical study, the additional concrete slab at the bottom with an equivalent thickness to the concrete deck slab may provide the best contributions to the improvements of crack initiation bending moment and the sectional bending-carrying capacity. This can be applied for the design practice.

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.339-347
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• 2006

This study proposes a double-composite section to enhance the s serviceability of twin-girder railway bridges, especially in terms of the flexural stiffness of the composite section in negative-moment regions. This paper deals with experiments on continuous twin-girder bridge models with 5m-5m span length with the proposed double-composite action. From results of static tests on the bridge models, several design considerations were investigated including effective width, shear connection and ultimate strength of the double-composite concrete slab showed full shear connection, which verified the suggested empirical equation. From the flexural behavior of the double-composite section, the effective width of the bottom concrete slab can be evaluated as that of the concrete slab under compression. The ultimate flexural strength of the bridge models verified the validity of the rigid plastic analysis of the double-composite section. Design guidelines were suggested based on the test results.

• Steel and Composite Structures
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• v.31 no.1
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• pp.1-12
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• 2019

Steel-concrete composite walls have been proposed and developed for applications in various types of structures. The double-skin profiled composite walls, as a natural development of composite flooring, provide structural and architectural merits. However, adequate intermediate fasteners between profiled steel plates and concrete core are required to fully mobilize the composite action and to improve the structural behavior of the wall. In this research, two new types of fasteners (i.e., threaded rods and vertical plates) were proposed and three specimens with different fastener types or fastener arrangements were tested under axial compression. The experimental results were evaluated in terms of failure modes, axial load versus axial displacement response, strength index, ductility index, and load-strain relationship. It was found that specimen with symmetrically arranged thread rods sustained more stable axial strain than that with staggered arranged threaded rods. Meanwhile, vertical plates are more suitable for practical use since they provide stronger confinement to profiled steel plate and effectively prevent the steel plate from early local buckling, which eventually enhance the composite action and increase the axial compressive capacity of the wall. The calculation methods were then proposed and good agreement was observed between the test results and the predicted results.

• Steel and Composite Structures
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• v.29 no.1
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• pp.77-90
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• 2018

This paper presents a combined numerical, experimental, and theoretical study on the behavior of the concrete-filled double circular steel tubular (CFDT) stub columns under axial compressive loading. Four groups of stub column specimens were tested in this study to find out the effects of the concrete strength, steel ratio and diameter ratio on the mechanical behavior of CFDT stub columns. Nonlinear finite element (FE) models were also established to study the stresses of different components in the CFDT stub columns. The change of axial and transverse stresses in the internal and external steel tubes, as well as the change of axial stress in the concrete sandwich and concrete core, respectively, was thoroughly investigated for different CFDT stub columns with the same steel ratio. The influence of inner-to-outer diameter ratio and steel ratio on the ultimate bearing capacity of CFDT stub columns was identified, and a reasonable section configuration with proper inner-to-outer diameter ratio and steel ratio was proposed. Furthermore, a practical formula for predicting the ultimate bearing capacity was proposed based on the ultimate equilibrium principle. The predicted results showed satisfactory agreement with both experimental and numerical results, indicating that the proposed formula is applicable for design purposes.

• Steel and Composite Structures
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• v.38 no.5
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• pp.547-562
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• 2021

This paper aims to explore the mechanical behavior and moment-rotation model of blind bolted joints between concrete-filled double skin steel tubular columns and steel-concrete composite beams. For this type of joint, the inner tube and sandwiched concrete were additionally identified as basic components compared with CFST blind bolted joint. A modified moment-rotation model for this type of connection was developed, of which the compatibility condition and mechanical equilibrium were employed to determine the internal forces of basic components and neutral axis. Following this, load transfer mechanism among the inner tube, sandwiched concrete and outer tube was discussed to assert the action area of the components. Subsequently, assembly processes of basic coefficients in terms of their stiffness and resistances based on the component method by simplifying them as assemblages of springs in series or in parallel. Finally, an experimental investigation on four substructure joints with CFDST columns for validation purposes was carried out to capture the connection details. The predicted results derived from the mechanical models coincided well with the experimental results. It is demonstrated that the proposed mechanical model is capable of evaluating the complete moment-rotation relationships of blind bolted CFDST column composite connections.

• Steel and Composite Structures
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• v.35 no.4
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• pp.495-508
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• 2020

Double skin composite walls are alternatives to concrete walls to resist gravity load in structures. The composite action between steel faceplates and concrete core largely depends on the internal mechanical connectors. This paper investigates the structural behavior of novel composite wall system with T section and under combined compressive force and bending moment. The truss connectors are used to bond the steel faceplates to concrete core. Four short specimens were designed and tested under eccentric compression. The influences of the thickness of steel faceplates, the truss spacing, and the thickness of web wall were discussed based on the test results. The N-M interaction curves by AISC 360, Eurocode 4, and CECS 159 were compared with the test data. It was found that AISC 360 provided the most reasonable predictions.

• Steel and Composite Structures
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• v.11 no.2
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• pp.169-181
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• 2011

The behavior of connections between open sandwich slabs and double steel skin composite walls in steel plate-concrete(SC) structure is investigated by a series of experimental programs to identify the roles of components in the transfer of forces. Such connections are supposed to transfer shear by the action of friction on the interface between the steel surface and the concrete surface, as well as the shear resistance of the bottom steel plate attached to the wall. Experimental observation showed that shear transfer in slabs subjected to shear in short spans is explained by direct force transfer via diagonal struts and indirect force transfer via truss actions. Shear resistance at the interface is enhanced by the shear capacity of the shear plate as well as friction caused by the compressive force along the wall plate. Shear friction resistance along the wall plate was deduced from experimental observation. Finally, the appropriate design strength of the connection is proposed for a practical design purpose.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.169-176
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• 2006

Prestressed composite girder with concrete infilled steel tubes(PSC-CFT girder) is new type of bridge girder which enhances the resisting capacities due to the double composite action of PSC composite girder and concrete infilled tube. The flexural behaviors of PSC-CFT girder in the negative moment regions are investigated based on the experimental observations recently performed on two of 3.6m long specimens. The mechanical and structural roles and failure mechanism of the composite action are discussed through comparing the test results with those numerically predicted by the three methods of one and three-dimensional nonlinear finite element analysis, and section analysis method.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.313-320
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• 2006

Prestressed composite girder with concrete infilled steel tubes(PSC-CFT girder) is new type of bridge girder which enhances the resisting capacities due to the double composite action of PSC composite girder and concrete infilled tube. The flexural behaviors of PSC-CFT girder in the positive moment regions are investigated based on the experimental observations recently performed on two of 4.4m long specimens. The mechanical and structural roles and failure mechanism of the composite action are discussed through comparing the test results with those numerically predicted by the three methods of one- and three-dimensional nonlinear finite element analyses, and section analysis method.

• Steel and Composite Structures
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• v.36 no.2
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• pp.187-196
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• 2020

Double skin composite wall system owns several structural merits in terms of high load-carrying capacity, large axial stiffness, and favorable ductility. A recently proposed form of truss connector was used to bond the steel plates to the concrete core to achieve good composite action. The structural behavior of rectangular high walls under compression and T-shaped high walls under eccentric compression has been investigated by the authors. Furthermore, the influences of the truss spacings, the wall width, and the faceplate thickness have been previously studied by the authors on short walls under uniform compression. This paper experimentally investigated the effect of width-to-thickness ratio on the compressive behavior of short walls. Compressive tests were conducted on three short specimens with different width-to-thickness ratios. Based on the test results, it is found that the composite wall shows high compressive resistance and good ductility. The walls fail by local buckling of steel plates and crushing of concrete core. It is also observed that width-to-thickness ratio has great influence on the compressive resistance, initial stiffness, and strain distribution across the section. Finally, the test results are compared with the predictions by modern codes.