Behavior and design of buried reinforced concrete pipe

Reinforced Concrete Pipes (RCP) are in used in the United States for almost a century. There are two methods of designing RCP, the indirect design which is an empirical method started at the beginning of the twentieth century, and the direct design method which is a more engineering oriented method started in the 60s of the last century. However, the current models used for predicting the section capacity of RCP in direct design method fail to accurately predict the capacity in the case of small diameters equal or less than 35inches. The reasons are that these models are based on curve fitting of the testing data available at the time of their development which did not cover small diameter pipes. The objectives of this research is to develop more accurate models able to predict the capacity of RCP in small diameters with an accuracy that is greater than the accuracy of current models. The proposed model utilizes a full stress-strain relationship for the reinforcement wires rather than using the idealized stress-strain relationship (elastic-perfectly plastic). Another advantage of the proposed model comes from its ability to consider the contribution by the second cage of reinforcement (in doubly reinforced pipe walls) to the section capacity. The models were verified through experimental and analytical programs. The experimental program consisted of testing 30 full-scale specimens for pipes with different diameters (18, 24, 30, and 36 inch), different concrete compressive strengths (4, 6, and 8 ksi), and different reinforcement wire surface (smooth and deformed). The analytical program for verifying the proposed models consisted of building a finite element model (FEM). ANSYS software was used to accomplish this task. The model used two element type to represent the model components; the SOLID65 element to represent concrete elements of the model, and LINK8 element to represent reinforcement wires. Full bond was assumed between the reinforcement and the concrete. Experimental and analytical results demonstrated the ability of the proposed models to predict the capacity of RCP section with a higher accuracy than the current models for direct design method. A Reliability Analysis was performed for the proposed model for flexure for different cases of tested pipes. The reliability index was found adequate to suggest using of a strength reduction factor (&phis;) of 1.0