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/297024
The 29 Road Bridge and I-70B Ramp project is the most recent infrastructure i m p ro v e m e n t i n G r a n d J u n c t i o n , Colo., to enhance transportation connectivity in the Grand Valley. Earlier improvements for mobility and access included the Riverside Parkway along the southern end of Grand Junction in 2008 and the 29 Road crossing of the Colorado River in 2006. The 2 9 R o a d a n d I - 7 0 B i m p ro v e m e n t is a joint effort by the city of Grand Junction and Mesa County to extend and connect 29 Road from these earlier infrastructure improvements north to I-70 Business Loop (I-70B). The project includes nearly 4 miles of roadway and a bridge that crosses over the Union Pacific Railroad (UPRR) switchyard and mainline tracks, Fruitvale Irrigation Ditch, and I-70B. A ramp structure on the west side of the 29 Road Bridge provides access from eastbound I-70B. Spanning the uPRR A significant challenge was how to design the bridge to span over UPRR's nine active tracks and accommodate five future tracks while maintaining the required roadway access and vertical and horizontal clearances. The minimum required vertical clearance over the rail tracks is 23 ft 6 in. and over I-70B is 16 ft 6 in. Mechanically stabilized earth (MSE) retaining walls support the roadway approach fill at both ends of the bridge. The designers determined the limits of the bridge structure and roadway approaches by balancing the cost of the bridge with the cost of the tall walls at each end. The design solution used 67,000 ft 2 of MSE retaining walls with a maximum wall height of 30 ft on the south end of the bridge. Spliced Girder Design A life-cycle cost analysis for the bridge examined t h e i n i t i a l c o s t , construction constraints, and long-term maintenance cost before arriving at the splice-girder design as the optimum solution to span the rail yard. To minimize the structure depth while meeting the vertical clearance over the UPRR tracks, three spans over the UPRR right-of-way were designed as precast, p re t e n s i o n e d a n d p o s t - t e n s i o n e d spliced girders. Post-tensioning made the girders continuous over the piers prior to the deck placement, thereby optimizing the design. This allowed the structure depth and wall heights to be reduced, and the girder spacing to be increased, which reduced the number of girders needed. The three span lengths over the UPRR are 135, 157, and 138 ft with the pier columns placed between the existing and future tracks and access roads. The 72-in.-deep Colorado Department of Transportation (CDOT) bulb-tee girder was modified with end blocks for the coupling of post-tensioning ducts and to accommodate the tendon profile 29 ROAD BRIDGE AND I-70B RAMP / GRAND JuNCTION, COLORADO BRIDGE DESIGN ENGINEER: Jacobs Engineering Group Inc., Denver, Colo. PRIME CoNTRACToR: Lawrence Construction, Littleton, Colo. PRECASTER: Plum Creek Structures, Littleton, Colo., a PCI-certified producer CoNCRETE SuPPLIER: united Companies, Grand Junction, Colo. PoST-TENSIoNING CoNTRACToR: VSL, Wheat Ridge, Colo. REINFoRCEMENT SuPPLIER: CMC banner Rebar Inc., Denver, Colo. by Jeff Mehle, Jacobs Engineering Group Inc. A Grand Connectivity Improvement in the Grand Valley The 29 Road BRidge and i-70B Ramp Location of the 29 Road Bridge and I-70B Ramp in Grand Junction, Colo. Illustration: Jacobs Engineering Group Inc. 32 | ASPIRE , Spring 2012 Book_Spr12.indb 32 4/3/12 9:18 AM