PARTIAL PRESTRESSING IN CONCRETE BRIDGES

This report gives information on: (1) the purposes, advantages and disadvantages of partial prestressing and the relation between serviceability and strength requirements; (2) the flexural analysis of partially prestressed concrete members, namely elastic theory for flexural stresses in cracked sections in the service load range and flexural strength theory for the ultimate load; (3) serviceability limit state considerations: stress, fatigue, flexural cracking and deflections. Experimental results from tests conducted on some partially prestressed concrete beams are also included; (4) a review of serviceability limit states for partially prestressed concrete from selected national codes of practice and considerations of serviceability and strength design criteria for highway bridge beams. Also presented is a study of a range of MWD (Ministry of Works and Development) standard bridge beams to determine the possible increase in design loading if a partially prestressed concrete design approach is adopted. Special consideration is given to the design of partially prestressed concrete members in accordance with the New Zealand Concrete Design Code NZS 3101: 1982. It is considered that sufficient design information is now available for a more general acceptance of the use of combinations of prestressing tendons and nonprestressed longitudinal reinforcing steel in concrete members cracked at service loads. (TRRL)