Early-age effects on serviceability reliability of reinforced concrete flexural members

Reliability-based ultimate strength limit state provisions for reinforced concrete are well established and have been adopted by design codes. By contrast, serviceability provisions for reinforced concrete design have evolved from engineering judgement and largely empirical methods rather than reliability-based analyses. Serviceability performance, however, has become increasingly important in recent years due to growing concerns over repair and maintenance costs. Serviceability reliability analyses of reinforced concrete members are based on viscoelastic analyses and time-dependent methods since creep and shrinkage have significant effects on the service-life performance of reinforced concrete members. This effect is much more significant when early-age effects (i.e., construction loadings and immature concrete) are considered. In this research, time-dependent probability models for both the construction loads and service-life loads are combined with time-dependent mechanical property models for concrete (including early-age effects) in a simulation-based lifetime reliability analysis for both the deflection and cracking serviceability limit states. Results from the reliability analysis are used to assess the early-age effects on the non-serviceability of reinforced concrete flexural members during service life in particular. Simply-supported beams and one-way slabs in typical office buildings are considered. The adequacy of current code provisions is investigated and reliability-based modification factors are suggested.