Keywords: composite structure, prestressed concrete, steel truss web, finite element analysis, material nonlinearity.

Externally prestressed concrete girder with steel truss web is one of the most promising concrete-steel hybrid structures applied to highway and railway bridges [1,2]. In this type of girders, the longitudinal bending moments are carried by the top and bottom concrete slabs and the vertical shear forces are resisted mainly by the steel truss web members. The advantages of using the steel truss web are generally summarized as follows:

1. The use of steel truss web results in a lower construction cost than that of the concrete web because of the decreased dead weight and high speed of erection.
2. By using external tendons, prestress is more efficiently introduced into the top and bottom concrete slabs due to the low longitudinal rigidity of the steel truss web.
3. The amount of prestressing steel can be effectively reduced by increasing the depth of steel truss web, which increases dead weight very slightly.
4. The steel truss web makes the composite bridge look lighter and more transparent.

Loading test and nonlinear analysis results of a prestressed concrete (PC) girder with steel truss web are presented and discussed in this paper. In the experiment, a large-scale PC composite girder specimen was tested by either a prestressing force or by vertical loads [3,4]. In the analysis, the essential nonlinearties arising in the materials are considered: i) nonlinear behaviour of concrete under multiaxial stress states; ii) tensile cracking of the concrete; and iii) elasto-plastic behavior of steel plates and reinforcing steel bars. Particular attention is given to the modelling of joints where steel truss members are directly connected to or embedded in the top and bottom concrete flanges. To compare the different models of steel truss web consisting of rolled wide-flange H-shapes, 2-D nonlinear analyses are undertaken using two different finite element models, each being identical except for the idealization of steel truss web. That is, the H-shape member is either 1) idealized by 1-D hinged bar, or 2) idealized by plane stress web elements with two 1-D flange bars. The abbreviations HB (hinged bar) and PS (plane stress) are used to refer to these two models, respectively.

Conclusions are made concerning the behaviour and performance of the PC girder with steel truss web considered in this research:

1. PC girder with steel truss web can be idealized by a two-flange concrete beam with a web of zero area only when nearly zero forces occur in the steel truss web members, as in the case of pure bending. In the other cases of loading, an appreciable error is introduced into the deflection by the elementary beam theory that neglects the shear deformation effect of steel truss web.
2. Failure in the test specimen was associated with a flexural mechanism, with concrete crushing at the top flange adjacent to a loading point, and both the experiment and numerical analyses indicated an overstrength factor of 3.4 for the design load.
3. Both the HB and PS models give rather well simulated global responses of the PC girder with steel truss web. However, the HB model does not provide information on the internal forces transmitted between the steel truss members and concrete in the joints.
4. The PS model provides the most realistic modelling of the PC girder with steel truss web, such that the truss members undergo considerable bending as well as an axial force after concrete cracking in the truss joint zones. However, further work is necessary for simulating premature yielding of longitudinal steel bars in the joint zone as witnessed in the experiments.

1

M. Virlogeux, "Composite Bridges, from Classical to Innovative Designs", Bridge and Foundation Engineering, 31(8), 30-47, 1997.

2

K. Furuichi, M. Yamamura, H. Nagumo and K. Yoshida, "Experimental Study on a New Joint for Prestressed Concrete Composite Bridge with Steel Truss Web", Proc. International Symposium on Connections between Steel and Concrete, Stuttgart, Germany, 1250-1259, 2001.

3

K. Niitani, A. Shoji, T. Nikaido and H. Watase, "Loading Test on a Prestressed Concrete Girder Specimen with Steel Truss Web (in Japanese)", Proc. Japan Concrete Institute, 20(3), 931-936, 1998.

4

A. Shoji, "Strength and Deformation Characteristics of Prestressed Concrete Bridges with Steel Truss Web (in Japanese)", Doctoral thesis, Osaka Institute of Technology, Japan, 2004.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £135 +P&P)