Composite beam theory for pretensioned concrete structures with solutions to transfer length and immediate prestress losses

A composite beam theory is developed to study the pretensioned concrete structures. This theoretical development defines the longitudinal interaction that occurs between the prestressing tendon and concrete under normal service condition. The transfer length and prestress loss due to slip, elastic shortening as well as the prestress gain due to external loads are solved with closed form solutions. Validation is provided and comparisons are made between the present and conventional approaches. It is found that there is excellent agreement between the predicted and tested concrete strain. The transfer length results calculated by design provisions are close to the predicted upper bound but test results can be anywhere between the predicted lower and upper bounds. Current immediate prestress losses formulas may result in overestimation and the degree of overestimation is dependent on prestressing tendon eccentricity. Overall, it is demonstrated that the approach presented in this study improves the accuracy and facilitates a better understanding of prestressed concrete mechanics while maintaining concise closed form solutions.