Wednesday, March 19, 2014

Latourell Creek Bridge

Some photos of the Latourell Creek Bridge, which carries the old Columbia River Highway at Latourell Falls. Obviously the falls are the main event here, but if you continue along the trail past the falls, it soon takes you right under the bridge, so you get a decent view of it from below. (The trail continues on to Upper Latourell Falls if you do the whole loop hike.) Off the top of my head I can't think of of another example in the Gorge where you hike under one of the old highway's bridges. Like many of the historic bridges along the highway, this is a Karl P. Billner design. Many of the others are solid concrete arch bridges, while this one is a light, almost spindly sort of structure, a design that was driven by the limitations of the site.

A contemporary account from a 1915 issue of Steam Shovel and Dredge magazine (Vol. XVIV, Issue 1, pg. 67) describes the project, and the issues Billner had to solve:

The Latourelle Bridge is an example of [Billner's] skillful handling of a unique problem. The engineer acknowledges indebtedness to the French expert, M. Considere, for the principles of his design, but they type is original with him. WIth a length of 312 ft. and a height of 97 ft., and a 17-ft. driveway, two cantilever sidewalks and railings, he has used in construction above ground only 560 cu. yds. of concrete, making probably the lightest concrete bridge in this country. Bedrock was from 25 to 50 ft. below the surface, making the cost of piers and abutments for a heavy bridge excessive. Both piers and abutments were founded on bedrock, the west abutment and center columns directly, the east abutment on four columns, two 4 ft. sq. and two 5 ft. sq., with an average depth of 45 ft. from the under side of the abutment to the rock. Inclined struts connect the tops of the 5-ft. columns to the bottoms of the 4-ft. columns, transmitting the thrust from the arches to the rock. Two girders at each end of the bridge carry a set of columns and struts which support the roadway. The result is a cantilever effect in wich the cantilever action is disregarded. Three 80-ft. arch spans form the central part of the bridge and two arch ribs carry each span. They are reinforced with eight 1-in. sq. bars hooped with No. 0000 hooping of 18 in. diameter and 2-in. pitch. Vertical columns spaced 10 ft. apart support the deck load, and these columns are braced with diagonal members hooked round the reinforcement of the arch ribs and girders. Permissible stresses were assumed as follows: Concrete in bending, 600 lb. per sq. in.; in direct compression, 500 lb. per sq. in.; hooped concrete in arch ribs, 750 lb. per sq. in.; steel in tension, 16,000 lb. per sq. in.; steel in shearing, 10,000 lb. per sq. in. A uniform load of 100 lb. per sq. ft., a concentrated load of 15 tons and an impact factor of 25 per cent were adopted. The main columns were poured in sections, the arch ribs simultaneously, and the 250 cu. yds. of concrete in the deck in one operation, lasting 20 hours.

In 1990 the bridge was inventoried as part of the National Park Service's Historic American Engineering Record, with a rather exhaustive account of the bridge's design, construction, and even maintenance history. One interesting tidbit is that it was apparently designed with internal electrical conduits for some sort of lighting scheme that was never installed. I suppose it has more of a natural feel this way, but I can't help thinking that streetlights at dusk on this bridge would make for a really great photo.

Billner sounds like an interesting guy, and his work in Oregon has been greatly overshadowed by later bridges designed by Conde McCullough and the rest of the state highway department. I had never heard of him until I started in on the Gorge branch of the ongoing bridge project. Conde McCullough gets flashy coffee table books about his work; Billner doesn't even have his own Wikipedia article, or at least he didn't when I wrote this post. The Smithsonian's Lemelson Center for the Study of Invention and Innovation has a brief bio of him, at least, and notes that the University of Wyoming archives have 54 boxes of his papers.

Karl Pauli Billner (1882-1965) an engineer and inventor, was born in Billesholm, Sweden and came to the U.S. around 1900 and worked as an engineer in Oregon. He returned to Sweden in 1915, working as a construction engineer and developed a lightweight concrete known as Aerocrete. Billner settled in the U.S. permanently in 1926 and established Vacuum Concrete Corporation in Philadelphia in 1935 and served as its president until his death in 1965. Vacuum Concrete performed construction work worldwide, using a vacuum process developed by Billner to extract excess water from newly poured concrete.

Collection contains subject files on Aerocrete, construction projects and patents for Billner’s vacuum process (1927-1962); newspaper clippings (1916-1956); 4 16mm films, "Aerocrete" parts 1 and 2, "Vacuum Concrete in the USSR," and "Octopus Lifter, La Guardia Airport"; patents for Aerocrete and the vacuum process (1934-1959); 5 photograph albums; photographs pertaining to Vacuum Concrete’s operations worldwide; and speeches by Billner on concrete construction (1953).

All in all, he was awarded around 21 US patents relating to concrete construction, awarded over a nearly 50 year period, including:

As I've noted in this blog's About page, I'm a mere software engineer by trade, and this is one of those times where I'm a little envious of real engineers. I have a handful of patents myself, albeit of the software variety, and they're barely valuable now, and will probably be incomprehensible an century from now. Some of the code I wrote as far back as 1999-2000 is still in use, or so I've heard, but I can't imagine any of it being useful in a hundred years. It would take a very specialized sort of historian to even understand the problem it's designed to solve. But design a bridge, at least a particularly notable one, and a century later someone will come along and wonder who you were, and dig up various tidbits and details about you using fancy internet search technology you could not have even conceived of, and instantly share it with their handful of Gentle Reader(s), who hopefully find it somewhat interesting as well.

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