Nonlinear analysis of steel–concrete composite beams curved in plan

https://doi.org/10.1016/S0168-874X(99)00010-4Get rights and content

Abstract

This paper deals with the behavior of structural steel–concrete composite beams curved in plan. The finite element package ABAQUS has been used to study the nonlinear behavior and ultimate load-carrying capacity of such beams. A three-dimensional finite element model has been adopted. Shell elements have been used to simulate the behavior of concrete slab and steel girder, and rigid beam elements to simulate the behavior of shear studs. The proposed finite element model has been validated by comparing the computed values with available experimental results. An acceptable correlation has been observed between the computed and experimental results obtained for beams of realistic proportion.

Introduction

I-girders curved in plan are frequently employed in structures such as highway bridges, interchanges in large urban areas and balconies of buildings. Despite the advantages of composite construction, engineers are reluctant to use curved composite girders in construction because of mathematical complexities associated with geometry and material. Under gravity loading, beams curved in plan are subjected to twisting moments in addition to flexural moments. In a highly curved beam, the interaction between flexural and torsional stresses along the span length is rather complex. Using conventional analytical methods to analyze a structure with both geometric and material nonlinearities might be difficult, if not impossible. However, the availability of high-speed digital computers makes it somewhat possible to study the complex nonlinear behavior of such structural elements and to account for in designs.

In the past, researchers have used finite element method to analyze the inelastic large-displacement behavior of straight composite beams. They have used different finite element models to simulate the behavior of concrete, steel and stud connectors in their studies of straight composite beams. Hirst and Yeo [1] set up a two-dimensional model for use with standard finite element programs. Four-noded plane elements were used to simulate the concrete slab and steel beam while standard quadrilateral elements were used in connecting the nodes on concrete part and steel part. The material properties of these quadrilateral elements were adjusted to make them equivalent in both strength and stiffness to the actual stud connector. In addition, since the main function of shear connectors is to transfer shear force across the steel concrete interface, pin jointed bar elements of effective infinite stiffness have been added to prevent transfer of direct stress across the interface of the elements.

A three-dimensional finite element model was proposed by Brockenbrough [2] to study curved multiple I-girder bridge using the software MSC/NASTRAN.1 In this three-dimensional model, the concrete deck had been modeled with QUAD4 shell elements, the girder flanges with BAR elements (including axial and bending strains in two directions, and torsional effects), the girder web with QUAD4 shell elements (four elements through depth of girder), and the connectors between steel flange to concrete deck with RBAR elements (rigid links connecting all degrees of freedom to simulate composite action with the slab). The concrete deck was treated uncracked throughout the bridge.

Razaqpur and Nafal [3] investigated the behavior of straight composite beam using the finite element software NONLACS [4] by adopting a three-dimensional finite element model. They applied facet shell elements on modeling concrete slab and steel beam. Shear stud connector elements used in NONLACS permitted the modeling of full, partial, and no interaction at the interface of the concrete slab and the steel beam. Tan et al. [5] and Liew et al. [6] adopted a three-dimensional finite element model to study the behavior of steel I-girder curved in plan using the finite element software ABAQUS2 [7]. The curved beam was discretized into small fibers consisting of triangular and quadrilateral shell elements.

However, there is a lack of research findings about the elastic and ultimate load behavior of composite beams curved in plan. The present study is concerned with the ultimate load behavior of such beams. Five curved composite beams, which were tested earlier by the authors, have been analyzed using ABAQUS software. The ultimate strength values, load-deflection curves and stress distribution across the section obtained using ABAQUS are compared with the corresponding experimental results to verify the accuracy of the proposed finite element model.

Section snippets

Experimental investigation

As a part of the present study, experiments were carried out on steel–concrete composite beams curved in plan to investigate the behavior and to determine the ultimate failure load. A series of five large-scale composite beams (SP1–SP5) with span-length to radius of curvature (L/R) ratios ranging from 0 to 0.5 were tested to failure under a concentrated load applied at midspan. Each specimen was 6.2 m long simply supported over a span of 6 m and consisted of a main girder and three secondary

Finite element model

A three-dimensional finite element model with the following characteristics had been used in the study:

  • 1.

    Concrete slab – modeled by four-node isoparametric thick shell elements with the coupling of bending and membrane stiffnesses.

  • 2.

    Steel flange and web – modeled by four-node isoparametric thin shell element with the coupling of bending and membrane stiffnesses.

  • 3.

    Shear connectors between concrete slab and steel flange – modeled by rigid beam elements.

Full composite action between steel beam and

Results and discussion

The finite element analyses give detailed picture of the complete behavior of the beams from elastic to ultimate load. The stress distribution across the cross sections and along the span, deflected profiles of the beam and ultimate load behavior can be obtained from the analysis. However, distribution at selected locations, deflection profile and failure load are chosen for discussion herein.

The analytical values of the ultimate loads of five beams are summarized along with the corresponding

Concluding remarks

Finite element modeling of structural steel–concrete composite beams curved in plan is presented in this paper. The nonlinear behavior of composite beams has been studied with reference to those beams tested earlier by the authors. The software package ABAQUS was employed in the analysis. Load–deflection curves, deflection profile, ultimate strength values and tangential stress distribution across the cross section were obtained from the finite element analysis. These results have been compared

Acknowledgements

The authors gratefully acknowledge the research grant (RP940660) provided by the National University of Singapore towards this study.

References (11)

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