This webpage and narrative you are currently viewing is for Bridge #4 on McGilvray Road. This page provides a discussion of McGilvray Road Bridge #4 specifically. Please also view the McGilvray Road Bridge #1 which includes a general overview discussions of McGilvray Road and the six bridges. It is on that page that you will find a detailed discussion of the details that make the bowstring bridges on this road so unique and significant. The below map shows McGilvray Road as it exists today. You can click on the name of a bridge to switch to a particular bridge's page.
This bridge is the shortest of the three two-span truss bridges. During a 2013 visit to the bridge, debris was found on the floor beams indicating that flood waters have in the past rose at least as high as the floor beams, if not higher.
This bridge was documented by Historic American Engineering Record as having a concrete jack-arch deck, which was likely the original deck, in the 1980s. This has since been replaced with a timber deck.
This bridge has some unusual substructure issues. The bridge's original substructure, which remains in place, is composed of pairs of caissons (riveted steel columns with concrete fill). The caissons at the center of the crossing appear to have had i-beams added to the top to raise the height of the bridge. But what is unusual is that the end caissons (at the abutments) do not have the i-beams added. Despite this, the truss appears to be sitting level, not with a slope on its deck. This seems to suggest that perhaps the center caisson has sunk into the ground, which required adding the i-beams to keep the bridge deck level. However, this would be unusual. It seems like more often, when caissons like this fail, they slowly tip over. Indeed this seems to be the case with the caissons at the end of the bridge. The bearings of the bridge are offset from the center of the caissons by quite a distance, which is what suggests this. The edge of the bearing at the east end of the bridge is sitting partly off the edge of the caisson. The situation is worse at the west end where the bearing ended up so far away from the caisson that it was no longer resting on the caisson. As a result, a new wooden pile system was driven to support the bearing, and an i-beam was welded from the top chord to the bottom chord roughly above the current position of the caisson.
Note: span length given for this bridge is an estimate based on measurements of Bridge #1.
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