Fatigue Assessment for the Failed Bridge Deck Closure Pour at Mile Marker 43 on I-81

Fatigue of reinforcing steel in concrete bridge decks has not been identified as a common failure mode. Generally, the stress range occurring in reinforcing steel is below the fatigue threshold and infinite fatigue life can be expected. Closure pour joints, however, may be vulnerable to fatigue if some specific design details are present. This research shows that fatigue was a likely contributor to the I-81 closure pour failure. It is much less likely that corrosion directly caused a strength failure but it is very likely that corrosion accelerated the onset of fatigue. The joints in the I-81 deck had vertical joint faces that did not provide any means for shear transfer across the joint. The joints were located under a wheel load path and were located away from beams or other means of deck support. This created atypical conditions where shear forces across the joint due to wheel loads were carried only by the reinforcing steel. The stress range in the reinforcing steel is greatly magnified under this scenario thereby making fatigue a possibility. New closure pour joints can easily be designed to prevent fatigue by providing structural support for both sides of the joint. Existing joints, however, need to be evaluated to determine if fatigue vulnerability exists. Lacking knowledge of the joint internal details, a simple differential deflection test can be performed to detect fatigue vulnerability. If the two sides of the joint are deflecting vertically relative to each other under wheel loads, than fatigue can be considered a possibility. No deflection indicates that fatigue is unlikely.