Model Tests of Modes of Failure of Joint C13N of Eyebar Chain, Point Pleasant Bridge Investigation

摘要

Two scale models of a portion of the eyebar chain at the Point Pleasant Bridge were assembled and load tested to study two hypothesized modes of failure of one joint. In the first test, a brittle fracture failure (induced by a notch) occurred in the eye of one of the eyebars at the joint resulting in total separation of the joint. Damage and deformation of the members at the joint resulting from this model failure were remarkably similar to those of corresponding members of the prototype collapse. In the second model an attempt was made to cause one of the eyebars at the same joint to walk off the joint pin by removing the retainer nut, canting the pin and imposing a cyclic loading regime patterned after the prototype dead load and live load variations. No movement occurred under these conditions. Only when the dead load was reduced to a nominal level was it possible to get the walking movement of the eyebar and even then the movement stopped after a limited displacement. The report concludes that the mode tests indicate that the separation which occurred in the prototype bridge was initiated by brittle fracture in the eye of eyebar at the subject joint.