Increasing service life at bridge ends of moveable abutment bridges
Is Version Of
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.
An extensive literature review presents relevant research to improving performance of bridge ends. Abutments, approach slab, geotechnical aspects, drainage, and expansion joints are evaluated in detail. Innovative bridge abutments allow for elimination of conventional bearings and attempt to reduce issues associated with integral construction.
Semi-integral bridges and those with approach slabs attached to the abutment were inspected across the state of Iowa to assess performance of current design methods. Tied joint condition performance was unsatisfactory with measured openings much larger than initial construction. Joints between wingwalls and approach slabs were also in poor condition.
Two bridges were outfitted with a multitude of sensors including strain gauges and displacement transducers to measure concrete expansion and bridge displacement. A 184.5-foot 45-degree skew semi-integral abutment provided abutment displacements and earth pressures behind the abutments. A 375-foot integral abutment bridge with 15-degree skew was also monitored for joint movements and strain in the approach slabs.
Finite element models were created to investigate the sliding of approach slabs on the soil below. Simulated bridge expansion provides insight 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. The outcome of this study includes recommendations for improving bridge end drainage and provides insight into skewed approach slab behavior.