About the research
Integral and semi-integral abutment bridges have become increasingly popular in Iowa and across the country because they eliminate joints at the bridge ends. Expansion joints in bridge decks allow water to seep in and corrode bearings along with other structural elements in conventional bridge construction. An integral abutment connects the bridge deck and girders with the substructure in one piece to reduce maintenance and increase service life. The abutment moves with the rest of the bridge, and this movement introduces new issues with water drainage, soil settlement, soil erosion, and concrete cracking. The objective of this research was to evaluate improved bridge end details to increase service life and investigate limitations placed on the use of semi-integral abutment bridges. Research methods include a literature review, visual inspections, field monitoring, and finite element simulations.
The extensive literature review identified research relevant to improving the performance of bridge ends. Abutments, approach slabs, geotechnical aspects, drainage, and expansion joints were evaluated in detail. It was found that innovative bridge abutments allow for the elimination of conventional bearings and attempt to reduce issues associated with integral construction. Semi-integral abutment bridges and those with approach slabs attached to the abutment were inspected across the state of Iowa to assess the performance of current design methods. The condition and performance of tied joints was found to be unsatisfactory in some instances, with measured openings much larger than those built during initial construction. Joints between wingwalls and approach slabs were also found to be in poor condition. Four bridges were outfitted with a multitude of sensors, including strain gauges and displacement transducers, to measure concrete expansion and bridge displacement. Finite element models were also created to investigate the movement of approach slabs on the soil below. Simulated bridge expansion provided insights into approach slab behavior and tie bar stresses due to friction. Parametric studies were completed on various approach slab properties, including friction with soil, soil stiffness, tie bar style, and bridge skew.