ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306855
48 | ASPIRE , Spring 2010 S TAT E T he earliest bridges in Oregon were made from readily available timber, but their useful life was limited due to decay in western Oregon's damp weather. A good example is provided by two of Portland's first three Willamette River bridges, built of timber in 1887 and 1891 with neither one lasting 20 years. Oregon surely needed longer-lasting bridge materials. The Early Years Reinforced concrete became widely recognized as a long-lasting bridge material after the first reinforced concrete bridge was built in the United States in 1889. There is some record of small reinforced concrete bridges and box culverts built in Oregon before 1900, with several still in use. The use of reinforced concrete was greatly accelerated by the 1913 formation of the Oregon State Highway Department (OSHD) by the Legislative Assembly. One of the OSHD's first major projects was the construction of the Columbia River Highway from 1913 to 1922. Championed by railroad executive Sam Hill from neighboring Washington, the rugged terrain of the new highway alignment, with its many waterfalls and streams, required numerous bridges. All of these structures were designed in reinforced concrete and most complement the stunning scenic beauty of their locations. The Shepperd's Dell Bridge was built in 1914 as a 150-ft-long reinforced concrete deck arch with a 100-ft-long main span. Designed by OSHD's Karl P. Billner, it is suggestive of later deck arch spans designed by Conde B. McCullough. The Bridal Veil Falls Bridge was built in 1914 as a 110-ft-long, three-span reinforced concrete through-girder, designed by Billner. The need to span both the falls and a lumber flume require a design whereby the parapet rails were actually the stiffening girders and carried the loads. The Latourell Creek Bridge was built in 1914. It featured a 312-ft-long, braced- spandrel reinforced concrete deck arch with three 80-ft-long main spans and short approaches at each end. Billner followed the principles of French bridge expert Armand Considère. This resulted in a lightweight structure to accommodate poor foundation conditions. The Moffett Creek Bridge was built in 1915 as a 205-ft-long reinforced concrete deck arch with only 17 ft of rise in the 170-ft-long main span. Designed by OSHD's Lewis W. Metzger, it was the longest span, three-hinged, reinforced concrete arch in the United States at the time, with only one longer on record in Germany. In 1917, a major initiative for "getting Oregon out of the mud" was started with legislative approval of a $6 million highway construction bond issue. In 1919, the lawmakers increased the bond amount by $10 million, instituted the nations' first gasoline tax of 1 cent per gallon dedicated to highway funding, and submitted a referendum to create a military highway along the Pacific coast. On April 9, 1919, OSHD hired the head of the Oregon Agricultural College (OAC) civil engineering program, Conde B. McCullough, to be the Oregon State Bridge Engineer. McCullough was an Iowa State College graduate, who had begun his career with Marsh Bridge Company of Des Moines, Iowa, and later worked for the Iowa State Highway Commission before joining the staff at OAC, in Corvallis. Under his leadership, the department constructed an impressive collection of reinforced concrete bridges throughout the state. His reinforced concrete deck arches and tied arches are well known for their elegant architectural qualities in harmony with their natural settings, and heavy load capacity. In addition, many reinforced concrete deck girder (RCDG) bridges were constructed for spans up to 50 ft. Reinforced concrete slab bridges and box culverts were used where suitable. The 1920s Beginning in the late 1920s, McCullough adopted several practices to control cracking in his arch bridge designs. One was to use the "Considère hinges" to reduce built-in bending stresses in the arch ribs. The hinges were hourglass-shaped articulation points that reduced built-in bending stresses in the arch ribs during construction. They were welded and encased in concrete once the dead load was applied to the arch. Another such practice involved the hangers that suspend the deck from the arch ribs on tied arches. The steel reinforcement of the hangers was placed, but the concrete was delayed until after the dead load was applied to the arch. By doing this, the concrete was not subject to tensile strain caused by the dead load. In bridges such as the Wilson River Bridge at Tillamook in 1931, these practices helped McCullough pioneer the use of reinforced concrete for tied arch structures. With the horizontal thrust of the arches resisted by the deck rather than the earth, the tied arch was ideal for locations with poor foundation conditions. CONCRETE BRIDGES in Oregon by Ray Bottenberg, Oregon Department of Transportation The Columbia River Highway featured many different styles of reinforced concrete bridges. This is the 1914 Latourell Creek Bridge, designed as a three-span braced-spandrel reinforced concrete deck arch to minimize the weight on its foundations. Photo: Oregon Department of Transportation. State_spr10.indd 48 4/30/14 11:53 AM