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

Read from the scan by GLM-OCR; expect the odd misread word.

This collision on the south end of the chain bent frame involved contact between the cross frame girder and the outstanding leg of the easternmost stiffener on the south face of the south approach girder. The south chain bent post did not collide with the approach deck slab, but merely scrapped along its edge. At the north end of the frame, however, the action was somewhat different. Here the chain bent cross frame girder collided with the stiffener on the approach girder, but the chain bent post also collided with the edge of the approach deck slab with considerable force. The fracture of the north chain bent post was apparently completed at this instant, except for the northeast splice angle. In the extreme position of the post, the top was about 18" west of its normal position, allowing the eyebars west of this point to drop at an abnormal angle, indenting the cover plate on the west side of the post at the top (see Reference 35, installment 1, p. 27).

At the same time that these events were in progress, the portion of the north truss east of panel point 7 was in essentially free fall, restrained only by the limited ability of this truss to carry loads by simple span action between L0 and L15. It is assumed that enough tension remained in the elements from U1N to U7N to counteract tendencies to compression. There was an initial rapid buildup of tension in the lower chord as a result of this action, terminated by the shearing of the toggle link at L15N due to the westward movement of the truss. Some of the cleavage fractures observed in this lower chord may have occurred at this time.

At the same time the main span of the north truss continued to fall. In this span, a secondary mechanism for supporting loads by simple span action of the truss between towers was not available, since the upper chord in the middle portion of the span consisted of the eyebar chain. Without the original chain tension, these eyebars could take very little load in compression before they began to buckle. The main span north truss therefore dropped in essentially free fall, inhibited only by the slight restraint offered by these eyebars prior to buckling, and the inertia forces associated with the eastward inclination of the north leg of the Ohio tower. The latter has been computed and was found to be very small compared to initial chain tension.

## Step 3

## Time = 1.5 seconds

The north truss of the Ohio side span began a general disintegration east of panel point 8. The north chain bent post was fractured but still holding by the splice angle at its northeast corner. The portion of the deck between panel points 9 and 15 was in free fall. The western half of this span of the north truss was now beginning to move eastward, due to the restoring forces exerted by the south chain.