Footings

One well-documented case of fracture in a footing comes from the collapse of the New York State Thruway Bridge over the Schoharie Creek in 1987, which caused the death of 10 people. A Hood produced scouring under the foundation plinth supporting a pier, which caused fracture of the plinth which was very weakly reinforced. Although crack stability and propagation were not analyzed (Wiss, Janney, Eltsner Associates, Inc., and Mueser Rutledge Consulting Engineers 1987), finite element analysis based on nonlinear fracture mechanics of discrete cracks was used by Swenson and IngrafTea (1991) who concluded that although the bridge failed primarily because of scouring beneath the foundation plinths (pier footing), a necessary complementary cause was unstable fracture in the pier. It was recommended that foundation plinth bridges of this type should be designed with consideration of crack propagation stability and crack arrest. In the disaster, the crack must have become unstable before it ceased to be small compared to the cross section size, and, therefore, the behavior described by the size effect law due to Bazant probably did not play a significant role. Rather, a boundary layer type size effect due to formation on the fracture process zone of a cohesive crack, same as in the case of the modulus of rupture, must have played a significant role.

Footings

Figure 10.5.6 (a) Crack distribution at the surface of a half space, (b) Crack distribution in a pavement, (c) Determination of the initial crack jump by intersection of instantaneous and average energy release curves.