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Sinking of a steel roof

Survey

Starting situation

After the assembly of the steel roof structure and adding the facade the gap between the lower edge of the steel beams and the upper edge of the facade was constantly about 10cm. After welding the connections to the buiding cradle above the roof structure the gap between the roof and the facade nearly was closed against expecting.

Task

Make an expertise to clarify the reason of the unexpected sinking of the steel roof and give predictions concerning the stiffness and sinking of the roof for future loading.

Proceeding

The distortion of the steel structure due to the welding with the building cradle, the weakening due to the residual stresses caused by the welding of the roof beams during fabrication and the influence of the unstiffened connection between the main girders and the secondary beams were calculated using the fe-method. Load tests on the real structure approved the stiffnesses previously calculated with the fe-method. Considering the partially blocking of theoretically sliding support, which was verified in the tests, and the load sequence during erection, the unexpected closing of the gap could be affirmed. Thus a reliable prognosis for the future deformation behavior of the roof structure could be provided.

FE-Modell

FE-Model