The three-span train trestle over the Animas River at 15th Street passed its biannual health inspection with flying colors Tuesday.
Its aging well, said Nathan Marshall with the Lakewood engineering firm of Martin/Martin Inc.. Regular inspections extend the life of the structure.
Martin/Martin has inspected the Durango & Silverton Narrow Gauge Railroad bridges and retaining walls in spring and fall for 30 years. There are now 30 bridges and 20 walls on the line between Durango and Silverton.
The inspectors reviewed all of them, and no serious flaws were found.
Tom Stauffer, another inspector, said, Some of them need things to be done, but theres nothing major.
Martin/Martin also does bridge inspections for another railway owned by D&SNG owner Allen Harper, the Great Smoky Mountains Railroad in North Carolina. The firm currently is designing new piers for the railroad bridge over Mineral Creek in Silverton.
The historic 15th Street bridge was not built as a single piece but installed as sections of a bridge from 1917 to 1936, Marshall said. The middle span, built in 1888, was installed in 1917; the southernmost span was relocated in 1927; and the northernmost section was put in place in 1936.
Were proud to be able to preserve the history of the line, Marshall said.
Marshall and Stauffer use several tools in their work:
b A sounding stick to tap wood beams. A high-pitched sound indicates sound wood. A low pitch tells them there is some decay.
Several crossties bore a smudge of orange paint to indicate they should be replaced soon.
b A hand drill to bore into a suspect timber and a metal rod that resembles an oil-pan dipstick to extract a sample of wood.
b A pole with an adjustable mirror on one end to look beneath steel or wooden beams that arent readily accessible from the ground. It was used on the middle span that is immediately above the main channel of the Animas.
Stauffer and Marshall also look for loose or rusted metal, loose bolts or cracked metal, places where water can pool and intrusive vegetation,
They go beneath the bridge to inspect stone piers for wear and may recommend repointing the addition of grout in joints. They inspect riprap at the base of piers that protects against assault of river currents and debris carried during high flows.
Driftwood deposited under the southernmost span must be removed because a large accumulation creates a dam.
There are some things only the human eye can detect, such as the deflection, the give in the bottom flange when a train passes over the trestle.
When the train that departed the downtown station at 8:15 a.m. reached 15th Street, Marshall and Stauffer scrambled under the spans to watch for unusual movement of the structure. There was none.
As the 9 a.m. train crossed the spans, they clung to the outside of a truss to inspect at eye level any unusual movement in the structure.
Martin/Martin will come up with a work order of recommendations, said Evan Buchanan, the railroads superintendent of operations. We always stay ahead of the maintenance required by the Federal Railroad Administration.
The Martin/Martin recommendations have always been Class 3 (routine maintenance) or Class 2 (get to it when you can), Buchanan said. The railroad never has experienced a Class 1 repair such as a fire in June that damaged a 310-foot trestle of the Cumbres & Toltec Scenic Railroad north of Chama, N.M.
The Cumbres & Toltec line is not related to the Durango & Silverton Narrow Gauge Railroad.
Marshall, who as a 12-year-old rode the D&SNGR to Silverton, said he and Stauffer may not return for the 2011 spring inspection.
We like to rotate inspectors in order to have fresh eyes, Marshall said.