Design Recommendations for the Optimized Continuity Diaphragm for Prestressed Concrete Bulb-T Beams

摘要

This research focused on prestressed concrete bulb-T (PCBT) beams made composite with a cast-in-place concrete deck and continuous over several spans through the use of continuity diaphragms. The current design procedure in AASHTO states that a continuity diaphragm is considered to be fully effective if a compressive stress is present in the bottom of the diaphragm when the superimposed permanent load, settlement, creep, shrinkage, 50% live load, and temperature gradient are summed, or if the beams are stored at least 90 days when continuity is established. It is more economical to store beams for fewer days, so it is important to know the minimum number of days that beams must be stored to satisfy AASHTO requirements. In addition, if the beams are stored for 90 days before erection, the positive moment detail must have a factored nominal strength (oMn) greater than 1.2 times the cracking moment (Mcr).