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/306183
A combination of concrete solutions The Trinity River Bridge carries heavily traveled I-10 over the Trinity River between Houston and Beaumont. The existing bridge built in the 1950s consisted of twin structures with a combined roadway width of 52 ft for two lanes in each direction. The existing bridge also had steep 4% grades to provide for 73 ft of navigation clearance. The main span consisted of fracture-critical steel through-girder systems. The existing bridge represented a choke point for the current traffic volume of 47,000 vehicles/day. The roadway to the west had already been widened to three or more lanes in each direction, and similar work is being done to the east. For these reasons, the project will provide welcome relief to a vital route. Design Solution An original concept was conceived using twin continuous steel plate girders with piers in the water for the main river crossing and precast, prestressed concrete I-beams on the approaches. On the river crossing, this would have necessitated a significant amount of river access for construction. In addition, construction and maintenance of the pier fender systems would be required. With a river opening of 400 ft and environmental and navigational reasons to span the entire waterway, the most viable option became a segmental box girder bridge built using the balanced cantilever method. To minimize project costs, the approach spans remained precast, prestressed concrete I-beams. W ith the resulting reduced length of segmental spans, a cast-in-place segmental box girder cast with form travelers was the preferred structure type. The project was let to contract in 2006. In February 2011, the project was approximately 75% complete. The new Trinity River Bridge has twin structures 3636 ft long with approach spans of 72-in.-deep precast, prestressed c o n c r e t e I - b e a m s s u p p o r t e d o n reinforced concrete bents using 18-in.- square, precast, prestressed concrete piles. Twin 990-ft-long segmental box girder units carry traffic over the navigable Trinity River with 50 ft of vertical clearance. Each cast-in-place concrete box girder unit consists of a 450-ft-long main span flanked by two 270-ft-long end spans. The girder depth varies between 25 ft at the piers to 10.5 ft at midspan. This span arrangement with a back span-to-main span length ratio of 0.60 required a nominal amount of shored construction at each end. This was required to avoid conflict with existing multi-pile footing foundations from the existing structure. The twin cell box girder structures are 62 ft wide at the top slab level. The 60 ft roadway width provides space for four lanes plus shoulders for each of the twin structures, for a total of eight lanes of capacity. The project phasing dictated the complete construction of the westbound bridge. Then, all traffic was rerouted onto the new structure to permit removal of the existing bridge profile TRINITY RIVER BRIDGE/ BETWEEN HOUSTON AND BEAUMONT, TEXAS BRIDgE DESIgn EngInEER: Texas Department of Transportation, Bridge Division, Austin, Tex. SE gMEnTAL COnSTRUCTIOn EngInEER: Summit Engineering Group, Littleton, Colo. p RIME COnTRACTOR: Williams Brothers, Houston Tex. p RECASTER: Valley Prestress Products Inc., Eagle Lake, Tex. pOST-TEnSIOnIng COnTRACTOR: Williams Brothers, Houston, Tex. pOST-TEnSIOnIng hARDwARE AnD SERVICES: VSL, Grand Prairie, Tex. by Michael D. Hyzak, David P. Hohmann, David Collins, and Brian Merrill, Texas Department of Transportation Design anD ConstruCtion of the i-10 trinity river BriDge By February 2011, traffic was using the westbound bridge. The total project was 75% complete. All photos and drawings: Texas Department of Transportation. 22 | ASPIRE , Spring 2011 Book_Spr11.indb 22 3/30/11 5:09 PM