Evaluation of Failure in Bridge Expansion Joint Rails

Strip seal expansion joint systems are composed of two structural parts; the rail and the concrete deck. Failures of expansion joints can be due to failures of either one of these components or a combination of both. The results of this investigation have indicated that the failure of the expansion joints in McAllen was due to a failure in the concrete part of the system. This failure resulted in unintended loads on the anchorage studs leading to the observed joint failures.

Testing of the rail sections, studs, and welds showed no predisposition of the rails to failure. The steel makeup and study welding appeared to be of uniform consistency and acceptable quality. Although failure of the expansion joints expresses itself in the rails and studs, this is a secondary effect which is induced by problems with the concrete placement.

Failure of the concrete was due to the lack of the complete concrete consolidation under the rail. Incomplete consolidation of the concrete was attributed to several factors including: lack of weep holes, form placement and pouring sequence. Weep holes in the top flange of the rail are necessary to allow for excess air and bleed water to escape from underneath the rail. The holes also act as a method of quality assurance. The presence of concrete in these holes after concrete placement indicates the presence of concrete under the rail. correct form placement at the ends of the slab is necessary so that concrete is present under the lower lip of the veritcal flange. Pouring sequence of the slab is also an important factor to consider when using strip seal expansion joints, especially on sloped bridges. The pouring sequence used on the McAllen bridges was typically downhill. By starting concrete placement at the highest point and proceeding to the lowest there is a possibility that the plastic concrete will flow downhill. This flow will pull concrete away from the inside of the rail and result in detrimental voids. Consideration to the concrete flow problem should be given when deciding on concrete pouring sequences and consolidation practices. Congestion of the slab reinforcement at the rail, aggravate proper placement of the concrete. The spacing between the bars should follow the standard practices regarding reinfocing steel spacing.