Optimization of Solar Updraft Chimneys by Nonlinear Response Analysis

Solar updraft chimneys (SUCs) form as engines of solar updraft power plants tower-like shell structures of extreme height with rather thin shell walls, similar to high chimneys comprising multiple flue gas ducts. The height of presently pre-designed SUCs reaches up to 1000 m. Thus they are exposed chiefly to extreme natural wind-loads, and to thermal actions from the internal flow of warm air. As first design step, the structural analysis of solar chimneys generally is carried out by linear elastic models. For optimization, the typical shell-like wind stresses have to be constraint towards a more beam-like response behavior, approaching a linear stress distribution over the chimney diameter. This requires rather strong ring stiffeners, either as spoke-wheels in the designs of SBP (Schlaich Bergermann and Partners) or as external stiffeners in the designs of K&P (Kratzig and Partners). Both alternatives require considerable construction efforts for the rings leading to high costs. There exists an interesting alternative to this stiffening, namely applying only medium soft external rings to the SUC shell, and admitting large-widths cracking in the limit state of failure. This cracking equalizes the meridional strains over the chimney's cross-section, saving large amounts of reinforcement steel in the SUC, but requiring materially nonlinear analyses under crack-formations. The manuscript will sketch pros and cons of the classical ring-stiffening, derive this new nonlinear concept and demonstrate the crack analysis by example of a 750 m high solar chimney. [GRAPHICS] .