Behavior and Design of Large Structural Concrete Bridge Pier Overhangs. Revised: Fid-Bau Portal

Behavior and Design of Large Structural Concrete Bridge Pier Overhangs. Revised

S. D. Armstrong / R. M. Salas / B. Wood / J. E. Breen / M. E. Kreger

In designing large cantilever bent caps for use on recent projects under current AASHTO design specifications, designers were faced with considerable uncertainties. Questions arose when designers attempted to satisfy both serviceability and strength requirements for a series of cap designs that mixed both non-prestressed and prestressed concrete solutions. The problems were complicated because of uncertainty whether AASHTO corbel or deep beam provisions would apply. The resulting designs were highly congested, had poor constructibility and high costs. This report outlines development of a new design approach involving use of strut-and-tie models (STM), as well as a mix of prestressed and non-prestressed main flexural reinforcement. A series of sixteen bent cap overhangs were designed, built at a reduced scale, and loaded to failure. Deflections, crack patterns and widths, reinforced strains, and overall behavior were observed. Economic and constructibility issues were examined. The use of T-headed anchorages was explored. A comprehensive design approach that considers both serviceability issues (deflections, cracking, crack widths, fatigue stress ranges, and side face crack control) and strength issues (ductility, adequacy of STM design and analysis of flexural capacity) was developed. Recommendations for design and detailing to improve behavior, reduce congestions and improve constructibility are provided.