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.

same amount, differing only by the elastic distortions in these systems. The south truss, in turn, was restrained by the south chain, which at this stage of the collapse could still resist westward movement much as an elastic spring, although such westward displacements were resisted primarily by the distortion of the shape of the chain in the side and center spans.

The sequence of events is believed to have been approximately as follows. The sudden release of tension in the north eyebar chain, traveling as a rarefaction wave at acoustic velocity (about 14000 ft./sec.) from C11N through U7N, the top of the chain bent post, and then to the anchorage, reached that point in about 0.024 seconds. The first part of the path, from C11N to U7N, offered essentially no restraint. The possibility that the chain pulled free of gusset plate U7N as the wave reached that point was rejected in that there is clear evidence that the eyebars from U7 to C9 remained attached long enough to indent the stay plate on U7-U8 (see Reference 35, installment 1, page 2, 51, 57 and Reference 5, Exhibit 4J-3).

As the wave traveled from U7N to U5N, the eyebar pair shortened about one inch, which resulted in the distortion of the truss in the triangle U5N-L6N-U7N, with high secondary bending stresses and possible partial fractures at L6N. This process was repeated for the pairs of eyebars U5N-U3N, U3N-U1N and U0N-U1N, with resulting bending distortions and downward deflection of L4N and L2N and pin rotation at L0N. The rate of progression of the wave was slower than the acoustic velocity and the relief of tension incomplete because of elastic restraints developed and momentum transferred to the truss. The shortening of the eyebars between the top of the chain bent post and the anchorage could not be accommodated by mere distortion of the truss, but only by a movement of the entire truss and deck system to the west. The forces required to initiate this motion resulted in a slower rate of progression of the rarefaction wave, and the establishment of some tension in elements from U0 to U7. The chain bent post above the pin at L0 was held essentially vertical by its attachment to the diagonal L0-U1 and the eyebar U0-U1, so that the westward movement of L0 resulted in severe bending of the post at this point, with westward tilting of the chain bent cross frame girder below the deck. Both north and south chain bent posts were involved in this motion, due to the lateral bracing and floor system. A motion of about 2 1/2" at the top of the chain bent post was sufficient to relieve the tension in the eyebar chain extending from this point to the anchorage, but the motion continued as a result of the momentum transferred to the whole side span system. Assuming that 50 percent of the original energy in the north chain were so transferred, it was moving westward at about four feet per second. This motion continued until restrained by the buildup of tension in the south chain east of the chain bent post, and the collision of the chain bent frame with the approach span girders.