Long-term analysis of bending moment resistance on pre-cast concrete beams

Abstract

Durability design of structures is an important part of the design process. A possible method for the durability design is the probabilistic approach considering changes of structural resistance and the load effect during a certain time period. In order to determine stochastic parameters of structural resistance as a function of time, deterioration of materials and the decrease of structural sizes due to environmental effects must be predicted. This paper is mainly focusing on the analysis of the bending moment resistance of pre-cast concrete beams as a function of time. The effect of creep, shrinkage, relaxation, carbonation induced corrosion and deterioration of cross-sectional sizes on the mean value and standard deviation of bending moment resistance were considered. The performed calculation method is illustrated by numerical example on a pre-cast, prestressed concrete beam. In case of the presented beam, the mean value of bending moment resistance decreases 4-6% and its standard deviation increases 200- 350% after 100 years depending on the relative ambient humidity. Results concerning mean value and standard deviation of structural resistance can be used for the purposes of probabilistic durability design. Considering the same safety level as in Eurocode 2, the introduced probabilistic design method delivers about 10% higher load carrying capacity as the application of relevant Eurocode 2 standard in case of the presented beam.