Why not add this bridge detail?

[nachoman]

Not to hijack my own thread, but speaking of old bridges...

The Cumbres and Toltec Scenic Railroad's Lobato Trestle caught fire earlier this summer, and burned the wooden ties and distorted some of the steel girders. I am not sure when the current bridge was built or last overhauled, but the right of way dates to the 1880s, and the current bridge has existed with minimal changes since at least the 1920s. This week an engineering report was released documenting the analysis and recommended repairs to the bridge. In addition to the repairs and replacement of the damaged girders, the analysis determined the bridge design is insufficient to safely handle the weight of the locomotives currently used. I am quite curious how they find the money to repair the bridge and what they decide to do, and how they eventually strengthen the original design.

Seeing that 1912 bridge made wonder if even in perfect condition if the loads or conditions have changed to make the design insufficient. I did post a full photo of the bridge in another thread <!-- l --><a class="postlink-local" href="http://www.the-gauge.net/forum/viewtopic.php?f=35&t=3343">viewtopic.php?f=35&t=3343</a><!-- l -->, and noted that the bridge piers had been changed from steel to concrete sometime in the 1990s. When the bridge was built, the Salt River was a perennial river that was subject to annual floods. The base flow of the river was probably such that it flowed under a single span and the piers were high and dry except during floods. By the 1980s, the river was only a dry riverbed, and flood releases only happened about every 5 years. Then, in the 1990s, the city of Tempe decided to turn the river bed into a lake, and the piers would be continuously submerged. I assume the change to concrete piers was necessary for the construction of the lake.