Abstract
Contemporary bridge truss girders have usually “W” bracing and spacing of cross beams smaller than spacing of truss nodes. The flange at deck level is loaded at its nodes and between them. It acts as a truss member and as a beam simultaneously. An analysis of the rigid flange in two stages is presented. The first stage of the analysis is aimed at computation of axial forces. Equivalent loading applied at truss nodes and truss member hinged connections are assumed. Ritter’s method is used to compute axial forces in rigid flange members. The second stage of analysis is aimed at computation of bending moments. A model of the rigid flange as a continuous beam on elastic supports with imposed settlements is assumed. In this stage additional model of truss girder as simply supported beam of equivalent moment of inertia is considered as well. Working example of application of presented analysis is given. Two computational models of rigid flange are analysed: model of rigid flange as member of truss girder and model of isolated rigid flange as continuous beam. Data recorded during test loading of two truss bridge spans are used for verification. Modelling isolated rigid flange as continuous beam and classical modelling of truss girder as plane frame provide similar accuracy of assessment of internal forces and vertical displacements distribution in rigid flange.
Highlights
Modern bridge truss girders are mainly “Warren” trusses – “W” bracing layout (Fig. 1)
Analysis overview As mentioned above there are two internal forces that are crucial for assessment of rigid flange load carrying capacity, i.e. axial forces and bending moments
– D1, D2, Di, ... – members of rigid flange; – M0, M1, M2, ... – concentrated bending moments caused by forces transferred from cross bracing members; the moments are computed as multiplication of axial forces at the level of theoretical axis of rigid flange and eccentricities of actual axis of rigid flange; – kφ0, kφ1, kφ2, ... – coefficients of rotational elasticity of supports 0, 1, 2, ...; – ku0, ku1, ku2, ... – coefficients of vertical elasticity of supports 0, 1, 2
Summary
Modern bridge truss girders are mainly “Warren” trusses – “W” bracing layout (Fig. 1). Analysis overview As mentioned above there are two internal forces that are crucial for assessment of rigid flange load carrying capacity, i.e. axial forces and bending moments. They may be computed separately, in two stages:. – truss girder is a plane hinged truss, – loads are applied to truss nodes Preparation for this stage consists of replacement of actual loads along rigid flange (forces at cross beam joints) with equivalent loads applied at flange nodes. It is possible that there are eccentricities of actual flange axis with respect to theoretical axis (at rigid flange to cross bracing connections) In such case, axial forces are to be computed with regard to theoretical rigid flange axis. This must be done for the sake of stage II analysis
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