For new railway bridges with short spans (L ≤ 35.00 m) superstructures with steel beams embedded in concrete are recommended or used, which can ensure the requirements of strength and stiffness in particular, regardless of velocity. They are built relatively easily compared to reinforced concrete structures or steel structures, they have high durability if designed, built and maintained correctly and don’t have high sensitivity to fatigue degradation in service. They are also used for road bridges when it is desired to achieve a reduced construction height.
In all the design prescriptions used so far for structures with steel beams embedded in concrete, the calculation is a simplified one, made on a single insulated longitudinal beam of the deck, if certain conditions related to the geometry of the structure are met (obliquity, curvature). Simplifications are also made regarding the state of deformation of the decks made in this constructive solution by introducing an effective moment of inertia in the displacement calculation, as an average of the inertia moments of the cross section considered to be cracked and respectively un-cracked.
The article aims to validate steel and concrete elasto-plastic models, based on an experiment from the technical literature, necessary for complex analyses of the percentage of concrete involved in the stiffness of the cross-sections, in case of bridges with steel beams embedded in concrete.
The article presents a comparative study between the simplified method calculation proposed by the prescriptions of design codes and the analysis with the FEM program LUSAS , regarding the influence of the curvature of the track axis at railway bridges with steel beams embedded in concrete.
The study was made on three simply supported bridges with the openings chosen so as to cover the openings used for this constructive solution, namely 10m ≤L≤30m. For each analysed opening the curve radius of the track axis was varied, in the domain in which are representative as effects, namely 100m ≤R≤1500m. In the case of Lusas FEM analysis, a physically nonlinear analysis it was previously carried out, after which the cracked concrete was removed, as its participation in the structural stiffness is practically non-existent.
Studying the outcomes revealed by the two calculations presented, it can be concluded that the simplified method proposed by the design codes leads to a overvaluation of the track axis curvature influence at the railway filler-beam deck bridges.
For new railway bridges with small spans (L ≤ 35.00 m) superstructures with steel beams embedded in concrete are recommended and used, which can ensure the requirements of strength and especially stiffness, regardless of velocity.
In all the design prescriptions used so far for superstructures with steel beams embedded in concrete, and even in the technical literature, there is little information and data on the influence of the support line obliquity and the track axis curvature in the design and calculation of these types of structures.
In the design code, if certain conditions related to the geometry of the superstructure are met (obliquity, curvature) the calculation is a simplified one, made on a single isolated longitudinal beam of the deck; otherwise, if the conditions are not met, finite element program analysis is recommended.
The article aims to study the situations in which the requirements of the design prescriptions are not met.
The carrying structure of the bridge over the Jiu River at Aninoasa consists in two parallel concrete arches with variable height of the cross section, sustaining a concrete deck through vertical concrete hangers. In the time period passed since the bridge was erected, some structural elements shown damages. In order to establish the technical state of the bridge, a technical appraisement was performed and according to this, the most exposed elements to the risk of failure are the hangers.
The purpose of this paper is to present briefly both, the method used to test the actual bridge carrying capacity in situ and the finite element model developed for the static and dynamic analysis of the structure.
In order to estimate the state of the structural elements, two ways were followed. In the first stage, a test project was carried out and in the second stage, a complete 3D finite element model was developed to analyze the bridge structure.
The test project has foreseen the loading of the bridge by heavy unloaded trucks, disposed in some positions on the deck and the measurements of the deck and arches displacements. The positions of the trucks were established in order to obtain the maximum values both for arches transverse displacements and vertical displacements of the deck. Using electro-resistive transducers the hangers elongations and strains values on their cross section were also measured. These measured values were compared with those obtained from the numerical calculations performed by using the complete finite element model. By means of the finite element model, also the response of the structure following the dynamic action of vehicles was investigated.