Assessment of steel heritage bridges

Heritage truss railway bridges with rivetted connections I find fascinating. Different bridges have very similar topology which may be turned to parametric design. In this case we modelled bridge over Vltava in Tábor with 2 simply supported spans which are arch trusses with top deck. Longer span is 61,5 m long and 3,6 m wide. Second steel span is smaller with length of 37,3 m and width 2,8 m.

We have performed analysis of several heritage bridges constructed at the end of 19th or early 20th century. These bridges are usually simply supported with very clear structural behaviour with either 2 I section or 2 identical truss (arch or with constant height) main girders. When constructed 100 or more years ago, these bridges were calculated by hand calculation and the simplicity and readability of the analysis was the key. Nowadays, they require in most cases a special approach in modelling and assessment due to weakening of the beams due to corrosion. Investigation of corrosion on the bridge as well as investigation of the steel properties is necessary for safe assessment. In modelling, stiffness of rivetted connections can be useful to consider, especially for the deck elements. Additionally, some major connection plates may be modelled with the beam elements to represent more precisely the transfer of internal forces between the structural members.

Bridges of bigger span (bigger in the case of heritage bridges is greater than 40m) have usually the same configuration of main arch truss girders and also configuration of longitudinal diagonals and transverse bracing. Elements composing the bridge deck and its bracing have also often very similar configuration. Considering only few configuration variants and basic dimensions of the bridge, we can use Table Input to create model quickly with sufficient accuracy. 

Reference: Created internally exclusively for Contruss Engineering, 4/2019, www.contruss.cz