Author(s)

S. Kravanja

Abstract

The paper presents the second-order analysis of a truss girder for the Hydropower Plant Dravograd, Slovenia. The existing steel girder of the span of 24.5 m was constructed 75 years ago for the reconstruction of spillways. The girder was designed according to old German DIN standards. The linear global analysis of structure was performed together with dimensioning.

Since the water elevation (and consequently the water load) on the Drava River, has increased in last years (a flood occurred with the most extreme/highest water elevation in history), a special structural analysis was requested to be done, which should show the resistance of the steel structure in new conditions. After all dimensions of the structure were checked and measured, the finite element model of the structure was modelled. Steel grade St 37 was considered. The self-weight, a hydrostatic load and a friction force between the truss girder and sealing I-beams were taken into account. Computer program SAP 2000 was used and the second-order FE analysis was performed. Dimensioning was made according to Eurocode 3. It was found that the truss girder at the HP Dravograd will not resist a new water load of the Drava River successfully (the water elevation of 331.90 m). While the resistance of the structure is 4.25-times exceeded, the structure connections are 7.64-times overloaded.

To overcome the problem, an allowable water load on the truss structure was calculated. The highest possible downstream water elevation of 329.55 m was consequently determined which the girder structure can be successfully subjected to.

Keywords

steel structures, truss girder, second-order FE analysis, hydropower plant