Experimental Investigation of Design Methods for Large Cantilever Bridge Bents

During design of large cantilever bents using current AASHTO design specifications for use on recent projects, designers were faced with considerable uncertainties. Questions arose when designers attempted to satisfy both serviceability and strength requirements for a series of bent cap designs that mixed both non-prestressed and prestressed concrete solutions. The problems were further complicated because of uncertainty whether AASHTO corbel or deep beam provisions were applicable. The resulting designs were highly congested, had reduced constructibility, and high costs.

This report outlines the development of a new design approach involving the use of strut-and-tie models as well as a mix of prestressed and non-prestressed flexural reinforcement. A series of five large-scale cantilever bents were designed according to existing specifications or the proposed specifications, constructed, and tested to failure. Deflections, crack patterns and widths, reinforcement strains, and overall behavior were observed. Economic and constructibility issues were examined. T-head anchorages were incorporated in designs conforming with the proposed specifications.

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 the strut-and-tie modeling approach, and analysis of flexural capacity) was developed. Recommendations for design and detailing to improve behavior, reduce congestion, and improve constructibility are provided.