Collapse of U.S. 35 Highway Bridge, Point Pleasant, West Virginia, December 15, 1967 (HAR-71/01)

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# V. CONCLUSIONS

(Listed after conclusions are page numbers in this report which contain facts leading to conclusions.)

The field and laboratory work conducted in this investigation, together with the results obtained by the Bridge Design Review and History and the Witness Groups, support the following conclusions:

A. With Respect to the Sequence of Events in the Collapse of the Point Pleasant Bridge:

1. The total collapse of the structure required the failure of some element in the supporting chains or towers. The directions in which the towers fell indicate that this failure was at the Ohio tower or west of this point in the Ohio side span, and in the north chain or its supporting elements. (93, 94, 95, 96)

2. Examination of the Ohio tower wreckage showed no failure in the north leg and the laboratory examination of the fractures in the Ohio north chain bent post and gusset plate U7N showed these fractures to have occurred from excessive or abnormal loads beyond those which were possible from the loading on the structure just prior to collapse. The only remaining failure in the chain or its supporting elements in the Ohio side span which could have led to collapse is a failure of some element in the chain itself. (20, 93, 95; 96)

3с. The joint at C13N, the first joint in the north chain west of the Ohio tower, began to separate because of the brittle fracture in eyebar No. 330 (the northerly bar of the pair in the north chain connecting pins at joints C11N and C13N. Subsequent to this fracture, eyebar No. 33 (the southerly bar of this pair) slid off the south end of the pin, causing complete separation of the north chain at this point. (34, 70, 94)

4. With respect to the brittle fracture in eyebar No. 330, the laboratory work has shown that:

(a) The small crack which existed prior to the collapse was large enough to account for the brittle fracture in the special steel of which the eyebars were made at the stress level computed to exist at this location, without any additional dynamic effects. (47, 52, 95)

(b) This small crack probably initiated at a small corrosion pit. (32, 68, 95)

(c) The crack grew to critical size by the joint action of stress-corrosion cracking and corrosion fatigue. The available evidence is not sufficient to permit a definite conclusion as to which mechanism was predominant. (37, 54, 68, 94, 95, 96)