THE CONCRETE BRIDGE MAGAZINE

SPRING 2012

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.

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The bridge spans over nine active and five future railroad tracks. anchorages. With a maximum girder spacing of 10 ft 3 in., the spliced girders allowed the design team to eliminate at least two girder lines and reduce the structure depth by over 1 ft compared to a conventional girder design. This shallower structure depth also allowed the roadway profile to be lowered an equal amount, resulting in reduced costs for approach fill and MSE walls. T h e r e m a i n d e r o f t h e 2 9 R o a d Bridge and the ramp structure were constructed using conventional 72-in. and 63-in.-deep precast, prestressed concrete bulb-tee girders with a design concrete compressive strength of 8500 psi. The width of the 29 Road Bridge varies from 95 ft 3 in. at the connection to the I-70B Ramp to 79 ft 0 in. on the north approach end, accommodating two travel lanes, a bicycle lane and a sidewalk in each direction, and a right turn acceleration lane from the ramp access. The four spans north of the UPRR tracks over Fruitvale Ditch and I-70B measure 118, 69, 104, and 58 ft. The total length of the 29 Road crossing is 779 ft. The ramp structure from I-70B tees into 29 Road and is 320 ft long with a span configuration of 70, 80, 75, 47, and 48 ft. The ramp has a minimum width of 30 ft 10 in. to carry two lanes of traffic with shoulders. The ramp flares to a maximum width of 110 ft 6 in. at the connection with the 29 Road structure to provide left and right turn movements. The geometry at the end of the ramp was challenging because the last span is flared wider on each side. It spans between skewed supports and the final deck cross-slope had to match the profile of the center span on the 29 Road Bridge. To solve the span geometry, additional flared girders were added to the cross section, and the ramp span deck was not cast until the center span was constructed to help match the elevations. Fabrication and Shipment of Girders The girders were fabricated in Littleton, C o l o . , s o u t h w e s t o f D e n v e r a n d shipped 250 miles to Grand Junction on I-70. At the Continental Divide, I-70 passes through the Eisenhower Tunnel, which has a limited vertical clearance. Depending on the transport equipment used, deeper girders, such as an 84-in.-deep bulb-tee section, would have difficulty with the limitations of the tunnel. The alternate route to b y p a s s t h e t u n n e l o v e r L o v e l a n d Pass, adds time and cost, not to mention uncertainty with inclement weather. Working within other design requirements, the design team chose a spliced girder solution with 72-in.-deep girders. On a trailer, the girders are tall, but a 72-in.-deep bulb-tee girder with its projected reinforcement, just passes beneath the top of the tunnel. In the end, all girders were easily transported by truck through the Eisenhower Tunnel. No Falsework Required Once on site, the girders were erected by crane. The spliced girders were designed to span from pier to pier with no temporary falsework supports. The girders were pretensioned to control stresses during handling and shipping, which allowed the girders to be transported and erected as simple spans. The elimination of falsework was important to minimize impacts in the UPRR right-of-way. Once erected, the post-tensioning ducts were coupled, reinforcement placed, and the integral pier diaphragm concrete placed. Two tendons containing nine 0.6-in.-diameter strands in 3-in.-diameter ducts were installed in each girder and stressed to 395 kips each. Stressing from each end achieved the proper force along the parabolic tendon path. PRECAST, PRESTRESSED CONCRETE SPLICED-GIRDER bRIDGE AND RAMP CONNECTOR uSING PRECAST, PRESTRESSED CONCRETE, PARTIAL-DEPTH DECK PANELS AND CAST-IN-PLACE CONCRETE SubSTRuCTuRE / CITY OF GRAND JuNCTION AND MESA COuNTY, COLORADO, OWNERS BRIDGE DESCRIPTIoN: Seven-span, 779-ft-long precast, prestressed, spliced girder bridge (span lengths are 118, 69, 104, 58, 135, 157, and 138 ft) and a five-span, 320-ft-long precast, prestressed concrete girder ramp (span lengths are 70, 80, 75, 47, and 48 ft). both have a cast-in-place concrete composite deck cast on precast, prestressed concrete deck panels. The structures are supported on cast-in-place concrete column bents and abutments. STRuCTuRAL CoMPoNENTS: bridge: 30 CDOT 72-in.-deep, precast, prestressed concrete, modified bulb-tees, 10 CDOT 72-in.-deep, standard bulb-tees, 27 CDOT 63-in.-deep bulb tees, and 3½-in.-thick precast, prestressed concrete deck panels; Ramp: 53 CDOT 63-in.-deep bulb-tees, and 3½-in.-thick precast, prestressed concrete deck panels BRIDGE CoNSTRuCTIoN CoST: Total project $34 million; bridge cost $7.5 million ($107/ft 2 ) Delivery of a precast, prestressed concrete spliced girder section at the site. The completed 29 Road Bridge and the intersection of the I-70B Ramp on the left. Photo: Paul Jagim, City of Grand Junction, Colo. ASPIRE , Spring 2012 | 33 Book_Spr12.indb 33 4/3/12 9:18 AM

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