Nonlinear Finite Element Modelling and Parametric Study of Prestressed Steel Box Girder

The prestressing technique is easy to apply and is generally used to strengthen steel bridges and controls their gross deflection. ANSYS has been used to establish a numerical model for the mechanical behavior of a steel box girder and prestressed by external tendons. In this paper, steel plate girders with and without strengthening technique was tested to assess the effectiveness of this technology. The results showed that prestressing improves the mechanical behavior of a girder and that its effect is proportional to magnitude of the applied external load. The results of the numerical model showed good agreement with the experimental data. A full-course simulation was conducted with ANSYS for a parametric study to analyze the influence of prestressing force magnitude, span-height ratio, and tendon configurations in increasing the effectiveness of prestressed technique.

Stresses & Strains in Plate Girder with Different Bracing Systems under Combination of Loadings

Lateral buckling is one of the most important factors in the design of steel plate girder. This buckling in the girder can be controlled by many methods. The most popular method is to add the intermediate bracing systems along the length of girder. The unsafely designed intermediate bracing systems can easily lead to serious consequences in the construction stage due to lateral buckling by torsion which happens rapidly and suddenly when the internal force in girder exceeds the ultimate value. Reversely, if the intermediate bracing systems are designed excessively, their specific stiffness will be larger than the required one then it is very costly in both material and installing process In the present study different types of torsional bracing systems are used in twin plate girder of span 8m. As the behavior of plate girders with different type of bracing system changes differently along the length and depth. Changing the layout of bracing systems could also make the design easy and more economical. Keywords: Cross-frame Bracings, Horizontal Bracings, Plate Girder, Finite Element Analysis

Experimental Study of Lateral-Torsional Buckling of Class 4 Beams at Elevated Temperature

The results of experimental research on lateral-torsional buckling of steel plate girders with slender web subjected to fire conditions are presented in this paper. The scope of the research covers four girders, three of which have been tested under high temperature conditions. The fourth girder has been used to determine the critical load resulting in lateral-torsional buckling of the considered element at room temperature. All the considered elements had identical cross sections and lengths; however, they differed in external temperatures applied and magnitude of measured geometrical imperfections. It has to be highlighted, that the experiments have been conducted subject to the anisothermal conditions, taking into account the uneven distribution of temperature in the cross section. An approach of this type represents a more accurate modelling of the structural component behaviour, when subjected to fire, as compared to the experiments conducted under isothermal conditions. Complete information on the development of research stand, conduct and results of particular tests are presented in this paper. The temperature–time curves for girder components, results of imperfection measurements and mechanical properties of steel are presented. The obtained critical temperatures and graphs of girder top flange horizontal deflection versus temperature are also included. The computer models developed for analysed girders are described in the paper as well. The results obtained with these models have been compared with experimental results. The computational models validated in this way constitute a basis for further parametric studies of lateral-torsional buckling in the domain of steel plate girders with slender web when subjected to fire conditions.