Simplified transverse post-tensioning construction and maintenance of adjacent box girders

Abstract

Precast, prestressed concrete adjacent box girders are regularly considered for shortto medium-span bridges on secondary roads. This corresponds to spans from 20 ft to 127 ft (6.1 m to 38.7 m), though typically no more than 40 ft (12.2 m). Many of these projects have limited funding or require rapid construction. Sec- ondary roads are also subject to a certain amount of public criticism, particularly with regard to cost and aesthetic appeal. Research has shown that an appeal- ing structure can be defined as having continuously flat soffits and high span-to-depth ratios—characteristics of an adjacent box system. Proper design and detail- ing of the transverse connection between girders is essential to minimizing both initial cost and long-term maintenance. Typical connections include diaphragms and cast-in-place concrete toppings, which directly increase both cost and time of construction. Inadequate post-tensioning is the primary cause of reflective cracking leading to ingress of chlorides and the con- sequent reinforcement deterioration, excessive girder deflection, and possible unexpected failures. This paper presents the results of testing on a post- tensioned transverse system that eliminates the need for diaphragms and a concrete overlay. Post-tensioning was determined based on previous research on a simi- lar system that was not post-tensioned. Results indicate that the system does not exhibit strain change or crack- ing under fatigue loading and would be an excellent candidate for practical applications.