Side-by-side box-beam bridges are often used at sites with tight underclearance requirements and also specified for accelerated construction. Despite being a popular bridge type, longitudinal reflective deck cracking is arecurring problem and a concern for its durability and long term safety. NCHRP Synthesis 393 describes North American practices on transverse connection design of this particular bridge. In this document Michigan design is presented as the preferred procedure. Most recent design used in Michigan is an empirical procedure that has evolved since early 1950s, and incorporates majority of the Synthesis 393 recommended best practices. Yet, reflective deck cracking is still observed. An analysis model has been developed based on mechanics of materials and macromechanics concepts. The model is utilized to quantify the moment demand along the transverse joints. Two-stage transverse posttension procedure was developed following AASHTO LRFD stipulations based on the moment demand calculated from the analysis model. The second stage of posttensioning precompress the cast-in-place concrete deck placed over the beam-shear key assemblage assuring crack control. The objective of this article is to demonstrate the effectiveness of the two-stage posttension design and implementation procedure to mitigate reflective deck cracking. Multi-step finite element construction process simulations under construction and service loads are presented. The bridge superstructure response is evaluated under both current Michigan Departmentof Transportation (MDOT) and proposed two-stage transverse posttension schemes. It is demonstrated that the two-stage posttension can eliminate tensile stresses developed under gravity loading and reduce the temperature load effects to abate reflective deck cracking.
Samenvatting