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/295658
Satus Creek Bridge is located 25 miles southwest from Toppenish, Wash., where U.S. 97 crosses Satus Creek. It was constructed as part of a $13.4 million project completed in the first part of 2013. It replaced an old, load- restricted timber bridge built in 1942. Washington State Department of Transportation (WSDOT) designed this new, resilient structure to correct design deficiencies with the old timber bridge including vehicular impact and seismic resistance. Several unique features are implemented in the design including horizontally curved and spliced precast concrete girders. Structural Design The Satus Creek Bridge is a 180-ft-long, simple-span bridge. This long, single- span bridge was necessary to satisfy environmental constraints to cross the wide section of the creek. The 7.5-in.- thick bridge deck is comprised of conventional, cast-in-place concrete. The shallow foundation also consists of conventional, cast-in-place concrete that is 18 ft tall. The superstructure is comprised of three open, precast concrete box girders, which are horizontally curved and tilted to match the 8% cross slope of the bridge. The girders are the WSDOT U78PTG5 series. The "78" indicates the height of the webs in inches and the "5" identifies the width of the bottom flange in feet. Bottom flange and web thicknesses are 6 in. and 10 in., respectively. To achieve this long, simple span across Satus Creek, each girder line consists o f t h re e p re c a s t c o n c re t e g i rd e r segments. Falsework towers were used to temporarily support the segments while the deck was cast and subsequent to assembly of the splice sections. Each web has three post-tensioning tendons comprised of nineteen, 0.6-in.-diameter strands with a total estimated jacking force of 2505 kips per web. After post- tensioning was applied, the temporary falsework towers were removed. Splicing the segments in the field after the deck was made composite increased the span capability, which eliminated the need for an intermediate pier. This was a great cost savings and it s a t i s f i e d W S D O T 's e n v i ro n m e n t a l constraints. Another added benefit of the spliced girders was reduced shipping costs. The precast concrete segments are easier to handle and more shipping routes were available to the precaster due to shorter and lighter components. Each girder segment was precast with a 1290 ft radius in the horizontal plane. In the bridge special provisions, W S D O T a l l o w e d t h e p re c a s t e r t o chord the girder segments at 20-ft intervals to achieve the prescribed horizontal radius. This construction method would have facilitated the use of conventional, less-expensive, flat formwork panels that are readily available. For this particular project, the precaster was able to build a form to the prescribed radius, achieving a smooth face for each girder segment and a smoother transition between segments at time of assembly. profile SATUS CREEK BRIDGE / TOPPENISH, WASHINGTON BRIDGE DESIGN ENGINEER AND ARCHITECT: Washington State Department of Transportation, Olympia, Wash. GENERAL CONTRACTOR: Franklin Pacific Construction Company, Seattle, Wash. PRECASTER: Concrete Technology Corporation, Tacoma, Wash.—a PCI-certified producer POST-TENSIONING CONTRACTOR: Schwager Davis Inc., San Jose, Calif. Curved trapezoidal girders were used for the Satus Creek Bridge in south central Washington state. All photos: Washington State Department of Transportation Visual Engineering Resource Group. Curved, tilted, precast concrete box girders key to replacement project SATUS CREEK BRIDGE by Michael Bressan and Paul D. Kinderman, Washington State Department of Transportation 24 | ASPIRE , Spring 2014 AspireBook_Spr14.indb 24 3/21/14 2:20 PM