Reliability based optimization of concrete structural components

[摘要] ENGLISH ABSTRACT: Standards define target reliability levels that govern the safety of designed structures. Thesetarget levels should be around an economic optimum for the class of structure underconsideration. However, society may have safety requirements in excess of that required toachieve an economic optimum. The LQI criterion can be used to determine society's willingnessto invest in safety, thereby defining a minimum acceptable safety- or reliability level. This thesisdetermines economically optimised reliability levels for reliability class two concrete structures inSouth Africa, over a range of typical input parameters.Rackwitz's (2000) approach is used here, adjusted for the South African context. The structure isdescribed using a simple limit state function, defined as the difference between load andresistance, with resistance a function of a global safety parameter. South African constructioncosts, costs of increasing safety, failure costs and discount rates are used in the objective functionfor economic optimisation.Life Quality Index (LQI) theory is used as a basis to derive society's willingness to pay (SWTP) forsafety and the corresponding reliability level is found by applying the LQI criterion. In the SouthAfrican context the derivation of SWTP presents some challenges, which is discussed.Situations where the minimum required reliability would exceed the economically optimumreliability level are discussed.Various reliability based cost optimization case studies are conducted covering a broad range oftypical concrete design situations. From these case studies a range of target reliability indices arederived for typical concrete structural components and failure modes. Obtained values arecompared to current South African target levels of reliability provided by the South Africanloading code and recommendations are made.The approach used by Rackwitz (2000) is compared with results obtained from case studies andused as basis to estimate optimum reliability levels for other types of buildings.Functions are written in MATLAB to allow replication of the study for others seeking to deriveoptimum reliability indices.

[发布机构] Stellenbosch University