The objective of the Master’s thesis is to assess the load bearing capacity of an existing wooden bridge. In order to do so, we first had to obtain the bridge plans developed in 1934, which have helped us to measure in detail the bridge structure and get a comprehensive picture of the current bridge state. Furthermore, we assessed the composition of joints, damage of the supporting structure and the wood quality, and acquired data on tensile strength of steel that was used during the construction. Since the bridge is protected as a cultural heritage, we were not allowed to perform destructing testing to determine the actual wood and steel characteristics.
Self weight and dead load of the construction were evaluated, while also determining the wind and snow load as well as the number of traffic lanes and their width. We used Excel to develop algorithms and thus calculate individual loads and the joints’ resistance.
We assessed the load capacity of the bridge by three successive steps. First, we determined the design resistance of the existing joints. For this purpose we calculated the design resistance of individual elements, taking into account the effective length in the elements in compression, thus obtaining the load capacity of the elements. For this purpose, in the Scia Engineer program we developed computational models of the main bridge construction, which were modeled with three different load systems along the bridge and in the transverse direction. The first two, the main truss system and horizontal truss under the carriageway, are statically indeterminate trusses, where the diagonals transmit only the compressive force, while the third system is trapezoidal. The calculation model applied constant load, useful load and characteristic concentrated force for the LM2 schematic scheme, where we introduced the kLM factor, thus reducing the characteristic value of the vertically concentrated Qak force. Forces in elements were calculated for each load case separately and then we made adequate load combinations where we checked the resistance of bridge by the Eurocode standards.
All the analysis were made on planar models. The calculation of the internal forces in the truss beam was carried out completely with nonlinear analysis, while the remaining calculations were carried out with linear analysis.