Static Limit Load of a Deteriorated Hyperbolic Cooling Tower

Irregular concrete erosion due to atmospheric and industrial effects is assessed by a layer model of reinforced concrete shells by simply removing the deteriorated layers. Concrete tension strength and fracture energy become very important properties in these circumstances since reinforcement bars are locally ineffective. A material model for cracking reinforced concrete is suggested and an application is presented to the ultimate load analysis of a natural draught cooling tower. Both geometric and material non-linearities are accounted for. In particular, the geometric instability is identified in the process of incremental wind load (static loading) which occurs locally due to the loss of cross-section and degradation of concrete strength. Strain softening in concrete is significant in this context since the associated cross-section stiffness decrease affects the limit load. The finite element model and material models of concrete and reinforcement enable reliable deterministic limit load analysis. The ratio of the limit load to actual service load thus obtained is about 1.5. The actual safety margin can only be assessed by a stochastic reliability analysis. This is intended using the Hasofer-Lind reliability index. (authors)