A plane-frame model for the analysis of cross beams in open-deck railway bridges

Abstract

This paper shows how to establish a plane-frame computational model for the analysis of a cross beam in an open-deck railway bridge. The model consists of the analysed cross beam, parts of the main girders, as well as transverse and windbracing struts. The model is used to examine the behaviour of cross beams in two different types of open-deck spans: a plate girder span and a truss girder span. The modelling technique is particularly useful when an immediate assessment of the service load that can be borne by particular structural component is necessary. For instance, in emergency situations or when the technical condition of one structural component is much worse than any other component. The latter situation may occur in the case of open-deck bridges where the condition of the deck's components is usually very poor. The stress levels in test-loaded cross beams are computed using the proposed plane-frame modelling approach. The computational results are compared to stress values based on strains recorded during actual test loading of bridges. It is shown that the plane-frame modelling of a cross beam with adjacent structural components overestimates normal stresses in the top flange of the cross beams by between 15 and 30%, whereas a simply supported beam model gives an overestimation of over 100%. Rotational restraint of the cross beams at their connection to the main girders is also investigated. The plane-frame modelling approach underestimates the restraint by between 13 and 23%. This is acceptable as long as the bending moment at the mid-span position governs the load-carrying capacity. This is usually true for open decks.