Fatigue-Based methodology for managing impact of heavy-Permit trucks on steel highway bridges

Currently, in many areas of North America, special permits are issued to extra heavy vehicles without a detailed evaluation of individual components, considering only the ultimate capacity of the bridge inventory as a whole. Based on this, a large number of special permits have been issued to extra heavy vehicles. In this perspective, the ultimate and cumulative effect of such overloads on steel bridge components is studied. It is found that steel bridge members have adequate ultimate capacity to accommodate such overloads; however, they may suffer fatigue damage due to the cumulative effect of these overloads. Accordingly, a fatigue-based methodology is developed to assess the reduction in service life of bridges due to heavy-permit trucks. It is found that a reasonably large number of special permits can be issued at small reductions in fatigue life, but because stress ranges in excess of the constant-amplitude fatigue limit significantly alter the shape of the S-N curve, it is essential to appreciate that the concept of infinite fatigue life cannot be relied upon anymore.