Evaluation of the need for longitudinal median joints in bridge decks on dual structures
Is Version Of
In the State of Iowa, bridge widths are typically limited to 60-ft. Although the justification for 60-ft is somewhat unknown, there is a desire, in some cases, to build wider bridges. For example, when dual bridges are constructed in urban areas they are frequently constructed very close to one another. In essence, this close construction results in a "joint" between bridges which is known to trap water and other debris which in some cases has led to accelerated deterioration. At the same time, integral abutment bridges are in wide use (in Iowa and beyond), since they have no expansion joints to allow leaking of chloride-contaminated water that can corrode the bottom of the deck and the adjacent girders. Thus, the practice of limiting bridge width and introducing a "joint" between dual bridges goes against other current practices. However, because there is concern that increased bridge width results in an increased propensity for cracking, there is resistance to commonly constructing wider bridges.
The primary objective of this project is to determine the effect of bridge width on deck cracking in bridges. Other parameters, such as bridge skew, girder spacing and type, abutment type, pier type and number of bridge spans were also studied. To achieve the above objectives, one bridge was selected to conduct live-load and long-term testing. The data obtained from both field tests were used to calibrate a three-dimensional (3D) Finite Element Model (FEM). Three different types of loading-live loading, thermal loading and shrinkage loading-were applied and used to calibrate the analytical model. A parametric study was then conducted using the calibrated FEM.
The general conclusions are as follows:
* Longitudinal and diagonal cracking in the deck near the abutment on an integral abutment bridge is due to the temperature differences between the abutment and the deck.
* Based upon a limited review of bridges in the Iowa DOT inventory, it appears that, regardless of bridge width, longitudinal and diagonal cracks are prevalent in integral abutment bridges but not in bridges with stub abutments.
* The parametric study results show that bridge width and skew have minimal effect on the strain in the deck bridge resulting from restrained thermal expansion. In other words, integral abutment bridges will show similar cracking regardless of width.
* Pier type, girder type, girder spacing and number of spans also appear to have no influence on the level of restrained thermal expansion strain in the deck near the abutment.
* FEM results showed that an effective solution to reduce cracking in the deck might be to place an isolation pad between the soil and back side of abutment.