In the mid-1960s Iowa began experimenting with jointless bridges constructed with integral abutments. Later, in the 1980s, researchers at Iowa State University developed a methodology for analysis of the piles in integral abutments. The methodology determines the depth at which a pile can be considered to have a fixed support. With an established location of fixity, the pile can be checked for ductility to ensure that it can flex without damage and can be checked as a column to ensure that it can support the abutment, end span, and traffic. With the methodology, it is possible to set general policy limits on the use of integral abutments, address industry trends, and consider unusual site conditions. Based on a parameter study, Iowa recently increased the bridge length limits for integral abutments to 575 feet for concrete superstructures and to 400 feet for steel superstructures, with reductions for skew. Use of compact, Grade 50 H-piles, or deeper prebored holes permits longer end spans to 150 feet or more for steel superstructures. On a case-by-case basis, the methodology permits consideration of piles with downdrag, retaining walls near abutments, unsymmetrical site conditions, and sites with bedrock near the surface. Use of jointless bridges reduces initial costs by eliminating bearings and expansion joints and reduces maintenance costs because there can be no damage from leaking joints. Expanding the use of jointless bridges with integral abutments has improved the overall life-cycle cost of Iowa bridges.
Abstract