Safety Index Evaluation and Calibration of Load and Resistance Factors for Concrete Beams Under the Simultaneous Effects of Bending, Shear and Torsion

摘要

The conventional approach for designing reinforced concrete members is based on load and resistance factors. In spite of the fact that, the load and resistance parameters are random variables, constant values are designated to them during the design. However, accounting these factors as constants, will ultimately lead to unsafe and uneconomical designs. Safe designs of structures require the appropriate recognition of parameters and their uncertainties. This may be achieved by clarifying the effective design parameters and applying risk-based design methods. The main purpose of this paper is the reliability-based design of reinforcement concrete beams under the simultaneous effects of bending, shear and torsion. For this purpose, a computer program is developed, and the most usual sections are selected for studying. Rectangular sections with tension rebars (singly reinforced), rectangular sections with tension and compression rebars (doubly reinforced) and T-shape sections are designed based on probabilistic methods. An appropriate tool for reliability calculations is selected based on the pros and cons of different methods. Evaluation of load and resistance factors for all mentioned beams is conducted. The steel usages under specific safety levels are determined. Hence, a method for the economic and fully probabilistic design of concrete beams is proposed.