Anatomy of a Trestle (p1)

The three Firesteel Trestles found along the old Copper Range line north of Lake Mine are messages in a bottle, a living example of the kind of turn of the century technology that helped transform the Copper Country into one of the country’s premier mining districts. While trestles like them could once be found dotted all across the peninsula, after a century of abandonment and scrap drives only four such bridges still exist in their original form – three of which can be found here at the Firesteel River. But who could have asked for much more impressive representatives then these, built in such large scale and scope as to still thrill a half century since the last train crossed over their tops. To appreciate them fully you first have to take the steep climb down to the valley floor and look up at them from their bases. That’s exactly what we did during our visit, an amazing experience we’ll try to share here today.

Here’s an artist’s rendition of the first of the Firesteel Trestles – otherwise known as Copper Range Bridge No.2. This particular bridge is 554 feet in length, and stands over 80 feet tall. Its supported by five steel piers and anchored by a pair of concrete abutments at each end. The Firesteel’s West Branch flows between the third and fourth piers.

The part of the trestle that supports the rails is known as the bridge deck. Bridge decks are of either an open or closed design, dependent upon whether the rail ties are supported by ballast or are directly attached to the bridge’s superstructure. In this case, the bridge deck was originally open and the rail ties were attached directly to the steel girders seen in the photo above.

Those girders are the heart and soul of the bridge’s superstructure, and work to carry the load down to the piers. Looking down through the girders you can see the cross supports that hold them all together. You can also easily note its open deck nature, as there is no roof structure running across its top. Instead you can see the floor planks of the current ATV bridge, which have been attached to the girders in much the same was as the old rail ties would have been.

The trestle is essentially a series of trussed girders sections strung together across a series of narrowly spaced steel piers. You can see a joint between two of those sections in the photo above, placed atop one of the steel piers.

At both ends of the trestle, the last girder section is supported by a lone concrete pier that forms the bridge’s ending abutment. These were originally made of wood, and stayed that way for a good portion of the trestle’s life spans. They were later replaced by the concrete versions you see here.

After those concrete piers / abutments, the road deck continues atop simple beams that look to have been more recent additions.

From those end abutments the road decks heads out over top of a series of massive steel piers that form the rest of the bridge’s superstructure. These piers sit an equal distance apart, with the middle three of equal height and the two book ending ones (seen in the foreground of the photo above) a bit shorter due to the natural slope of the valley.

Unlike a wood trestle – which would have consisted of a continuous line of these piers – the steel version utilizes only a handful set equal distance apart. Each pier consists of four massive beams that rise up from the valley floor to joint up with the rail deck high above. Those beams are supported by a seemingly chaotic web of truss work that criss cross throughout the structure.

But there really is a rather defined and organized pattern to all these steel, especially when looked at from the vantage point of just under the bridge’s rail deck.

With nothing more to see here, we’ll take a walk down to the valley floor and the base of the towering piers to see more…

To Be Continued…

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