Reliability-based analysis of crack control in reinforced concrete beams.

摘要

This thesis is a study on reliability-based analysis of reinforced concrete beams at the crack control limit state. Past approaches to crack control and crack widths predictions in various codes are discussed. The limit state considered in this study is the maximum flexural crack width of reinforced concrete structures. Reliability index, beta, is calculated to assess the level of safety in the ACI 318-08 Building Code.;Resistance prediction equations for the flexural crack control limit state as well as load equations are researched and developed in terms of the stress in the reinforcing steel. Statistical properties of variables are obtained from available literature. The effects of several parameters on the reliability index are also studied. The equation by Frosch (1999) provided the most accurate crack width predictions for various beam data obtained and is used as the resistance model in the limit state function. The live load model used is based on statistical information provided in the study by Nowak et al. (2008) which was also used in the calibration of the ACI318-08 building code. Monte Carlo simulation is performed using statistical parameters obtained for each variable. A total of 1290 beams are designed using the ACI 318-08 Building Code and included in a detailed parametric study.;It is concluded that the spacing of steel reinforcement and the concrete cover had the most significant effects on the reliability of crack width predictions. When spacing of reinforcement and concrete cover are increased, the reliability index decreases. However, increasing beam effective depth and area of reinforcement did not significantly increase the reliability index. Additionally, using a larger number of bars with smaller diameters yields higher reliability indices than using a small number of bars with larger diameters. Furthermore, an overall trend was observed that as steel yield strength increases and concrete strength decreases, the reliability index decreases. This study can be considered as a prelude to a future code calibration process of the ACI 318-08 Building Code at the serviceability limit state of crack control.