• Steel and Composite Structures
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• v.31 no.1
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• pp.27-41
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• 2019

Shear lag effect can be an important phenomenon to consider in design of the steel-concrete composite beams. Researchers have found that the effect can be strongly related with the moment distribution, the stiffness and the ductility of the composite beams. For continuous composite beams expected to sustain hogging moment, the shear lag effect can be more distinct as cracking of the concrete slab reduces its shear stiffness. Despite its influences on behaviour of the steel-concrete composite beams, a method for calculating the shear lag effect in steel-concrete composite beams sustaining hogging moment is still not available. Shear lag effect in steel-concrete composite beams sustaining hogging moment is investigated in this paper. A method was proposed specifically for predicting the effect in the cracked part of the steel-concrete composite beam. The method is validated against available experimental data. At last, FE studies are conducted for steel-concrete composite beams with different design parameters, loading conditions and boundary conditions to further investigate the shear lag effect and compare with the proposed method.

• Steel and Composite Structures
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• v.10 no.5
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• pp.373-383
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• 2010

This paper presents the experimental studies of the flexural behavior of steel-concrete composite beams. Herein, steel-concrete composite beams were constructed with a welded steel I section beam and concrete slab with different material strength. Four simply supported composite beams subjected to two-point concentrated loads were tested and compared to investigate the effect of high strength engineering materials on the overall flexural response, including failure modes, load deflection behavior, strain response and interface slip. The experimental results show that the moment capacity of composite beams has been improved effectively when high-strength steel and concrete are used. Comparisons of the ultimate flexural strength of beams tested are then made with the calculated results according to the methods specified in guideline Eurocode 4. The ultimate flexural strength based on current codes may be slightly unconservative for predicating the moment capacity of composite beams with high-strength steel or concrete.

• Steel and Composite Structures
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• v.14 no.3
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• pp.295-312
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• 2013

In this paper, a simplified approach based on critical temperature for fire resistance design of steel-concrete composite beams is proposed. The method for determining the critical temperature and fire protection of the composite beams is developed on the basis of load-bearing limit state method employed in current Chinese Technical Code for Fire safety of Steel Structure in Buildings. Parameters affecting the critical temperature of the composite beams are analysed. The results show that at a definite load level, section shape of steel beams, material properties, effective width of concrete slab and concrete property model have little influence on the critical temperature of composite beams. However, the fire duration and depth of concrete slab have significant influence on the critical temperature. The critical temperatures for commonly used composite beams, at various depth of concrete and fire duration, are given to provide a reference for engineers. The validity of the practical approach for predicting the critical temperature of the composite beams is conducted by comparing the prediction of a composite beam with the results from some fire design codes and full scale fire resistance tests on the composite beam.

• Structural Engineering and Mechanics
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• v.22 no.4
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• pp.419-432
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• 2006

Experimental studies on the behaviors of box-shape steel reinforced concrete (SRC) composite beams were conducted. Seven 1:3 scale model composite beams were tested to failure. Each of the beams was simply supported at the ends and two concentrated loads were applied at the one-third span and two-thirds span respectively. Experimental results indicate that the flexural strength can be enhanced when the ratio of flexural reinforcements and flange thickness of the shape steel are increased; the shear strength is enhanced with increase of web thickness of the shape steel. Insignificant effects of concrete in the box-shape steel are found on improving the flexural strength and shear strength of the box-shape SRC composite beams, thus concrete inside the box-shape steel can be saved, and the weight of the SRC beams can be decreased. Shear studs can strengthen the connection and co-work effects between the shape steel and the concrete and enhance the shear strength, but stud design for the composite beams should be further improved. Formulas for flexural and shear strength of the composite beams are proposed, and the calculated results are in good agreement with the experimental results. In general, the box-shape SRC composite beam is a kind of ductile member, and suitable for extensive engineering application.

• Steel and Composite Structures
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• v.32 no.1
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• pp.21-35
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• 2019

This study investigates the flexural behavior of steel-concrete composite beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. An innovative mechanical anchorage system was developed. The components of the system can be easily assembled on site before applying a prestressing force, and removed from the structures after strengthening is completed. A total of seven steel-concrete composite specimens including four simply supported beams strengthened at the positive moment region and three continuous beams strengthened at the negative moment region were tested statically until failure. Experimental results showed that the use of prestressed CFRP plates enhanced the flexural capacity and reduced the mid-span deflection of the beams. Furthermore, by prestressing the CFRP laminates, the material was used more efficiently, and the crack resistance of the continuous composite specimens at the central support was significantly improved after strengthening. Overall, the anchorage system proved to be practical and feasible for the strengthening of steel-concrete composite beams. The theoretical analysis of ultimate bearing capacity is reported, and good agreement between analytical values and experimental results is achieved.

• Steel and Composite Structures
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• v.20 no.1
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• pp.57-70
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• 2016

The predominant type of buckling that I-steel concrete composite beams experience in the negative moment area is distortional buckling. The key factors that affect distortional buckling are the torsional and lateral restraints by the bottom flange. This study thoroughly investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of an I-steel concrete composite beam under negative moments. The results show a coupling effect between the applied forces and the lateral and torsional restraint stiffnesses of the bottom flange. A formula is proposed to calculate the critical buckling stress of the I-steel concrete composite beams under negative moments by considering the lateral and torsional restraint stiffnesses of the bottom flange. The proposed method is shown to better predict the critical bending moment of the I-steel composite beams. This article introduces an improved method to calculate the elastic foundation beams, which takes into account the lateral and torsional restraint stiffnesses of the bottom flange and considers the coupling effect between them. The results show a close match in results from the calculation method proposed in this paper and the ANSYS finite element method, which validates the proposed calculation method. The proposed calculation method provides a theoretical basis for further research on distortional buckling and the ultimate resistance of I-steel concrete composite beams under a variable axial force.

• Steel and Composite Structures
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• v.32 no.5
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• pp.583-594
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• 2019

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

• Steel and Composite Structures
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• v.10 no.2
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• pp.169-185
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• 2010

The present work describes the experimental tests on steel and lightweight concrete composite beams performed at University of Minho, Portugal. The study involves tests on simply supported composite beams of 4.5 m span, with the same geometrical disposition, supports and materials. The geometrical configuration for the cross section and supports is identical for every beam, varying the shear connectors' distribution and the loading conditions. Headed studs are used to provide the connection between the steel profile and the concrete slab. The parameters in study are the stud disposition and the load distribution. The main objective is to describe the composite beams behaviour, focused on its connection, and to analyse the contribution of the different components to the beams load and deformation capacity. All the tests explored the beams maximum load and deformation capacity and different types of failure were observed.

• Steel and Composite Structures
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• v.24 no.1
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• pp.79-91
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• 2017

Free vibrations of steel-concrete composite beams are analyzed by using the dynamic stiffness approach. The coupled equations of motion of the composite beams are derived with help of the Hamilton's principle. The effects of the shear deformation and rotary inertia of the two beams as well as the transverse and axial deformations of the stud connectors are included in the formulation. The dynamic stiffness matrix is developed on the basis of the exact general solutions of the homogeneous governing differential equations of the composite beams. The use of the dynamic stiffness method to determine the natural frequencies and mode shapes of a particular steel-concrete composite beam with various boundary conditions is demonstrated. The accuracy and effectiveness of the present model and formulation are validated by comparison of the present results with the available solutions in literature.

• Steel and Composite Structures
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• v.6 no.3
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• pp.183-202
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• 2006

The behavior of steel-concrete composite beams is strongly influenced by the type of shear connection between the steel beam and the concrete slab. For accurate analytical predictions, the structural model must account for the interlayer slip between these two components. This paper focuses on a procedure for response sensitivity analysis using state-of-the-art finite elements for composite beams with deformable shear connection. Monotonic and cyclic loading cases are considered. Realistic cyclic uniaxial constitutive laws are adopted for the steel and concrete materials as well as for the shear connection. The finite element response sensitivity analysis is performed according to the Direct Differentiation Method (DDM); its analytical derivation and computer implementation are validated through Forward Finite Difference (FFD) analysis. Sensitivity analysis results are used to gain insight into the effect and relative importance of the various material parameters in regards to the nonlinear monotonic and cyclic response of continuous composite beams, which are commonly used in bridge construction.