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.

arrangement is given in Figure 28. The model consists of joints C15, C13, and C11 of the eyebar chain at 1/5 scale. Eyebars connecting joints C11 and C13 were machined from the midthickness and midwidth of eyebars salvaged from the wreckage. The other eyebars and fixtures in the model were machined from a modern high strength steel of similar strength properties. Careful attention was given to scaling the tolerances in the fabrication of the pinholes and pins to insure similarity of fit. Loading was applied by means of servo-hydraulic actuators. Strains were measured at selected locations around the pinhole in the eyebar corresponding to prototype No. 330 and on both faces of all eyebars in the model at midwidth and midlength.

In test A, a small deliberate defect was introduced at the edge of the pinhole in model eyebar No. 330 in the location at which the preexistent crack was found in the prototype eyebar. This deliberate defect was produced by a sawcut through the thickness of the bar at this point 1/32 of an inch deep, with a kerf width of 0.007 inches. It was subsequently sharpened to a fine crack by loading with a fluctuating load of 20,000 lbs., and was grown to a length of 0.020 inches prior to loading to failure. The failure load was provided by automatic control systems which increased the load linearly from a base loading of approximately 1/3 of the expected failure load to the capacity of the system or a specified maximum in about three seconds. The actual failure load for the model was 104,290 lbs., corresponding to a nominal unit stress in the shank of the eyebars of 55,400 lbs./sq. in. Stresses at the root of the fatigue crack were above the yield strength of the material. Events during the failure were photographed with a motion picture camera operating at 1,000 frames/second. Figures 29a and 29b show two of the critical stages of the joint separation. In Figure 29a the brittle fracture in the lower limb of the C13 head of model eyebar No. 330 has just occurred. In Figure 29b, which is 1021 frames later, the ductile fracture in the upper limb of this eyebar has been completed and eyebar No. 33 has just slipped off the opposite end of the pin.

The deformation and the appearance of the fractures in the model parts bear a remarkable resemblance to those of the prototype parts salvaged from the wreckage. Figures 30a and 30b show the comparison between the model and prototype pieces which fractured from eyebar No. 330. The only distinguishable difference between these pieces is the direction which the fracture in the ductile side of the failure traveled after reaching approximately the midwidth of the section. It will be noted, however, that there is a crack in the prototype part which corresponds to the direction which the fracture followed in the model after reaching this point. Subsequent investigations of the mating piece of the model eyebar showed a similar crack extending in the initial direction of the prototype fracture. Model eyebar No. 33 also displayed a similar burr very much like that observed on prototype eyebar No. 33, although it was somewhat larger in relation to the thickness of the bar. Scratches on pinhole surfaces also resemble those of the prototype elements.