THE CONCRETE BRIDGE MAGAZINE

SUMMER 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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Construction and Materials Bridge construction began in mid- November 2011 adjacent to the freeway. Crews expedited the work by using precast concrete components. The actual construction of the single- span bridge followed the same steps as traditional, build-in-place construction with the exception of the foundations. Temporary hollow-bar soil nails were used to support the existing structure while the permanent foundations for the new bridge were constructed underneath the existing bridge. The design specified a temporary steel substructure to support the new, 10,000 ft 2 superstructures. The shotcrete for the soil-nails had a specified compressive strength of 4000 psi, while the grout for the hollow-bar nails was specified to be 3000 psi. Precast concrete components were used to significantly reduce construction time. These included 9-ft 9-in.-spaced precast, prestressed concrete Utah bulb-tee beams (UBT58). Nonprestressed, 3.5-in.- thick, partial-depth, precast concrete deck panels were used to eliminate deck formwork, allowing faster placement and improving safety for the public and construction workers. The overall thickness of the bridge deck is 8 in., including a 4.5-in.-thick, cast-in-place concrete topping. Specified compressive strength for the cast-in-place concrete and deck panels was 4000 psi, while the precast concrete girders used 9000 psi compressive- strength concrete. As a time-saving strategy for ABC, flowable fill with a compressive strength of 200 to 500 psi was used to backfill behind the abutments and under the approach slabs after the bridges were slid into their permanent locations. Bridge longevity was an important focus, given the project investment. Prestressed concrete girders increased durability and lowered maintenance requirements. Although not required in Clark County, Nev., epoxy-coated reinforcing bars were used in the precast concrete girders to reduce the probability of corrosion and extend the life of the girders. The structures were designed and detailed for a 75-year service life. The final bridge dimensions measure 111 ft 6 in from center-line between each abutment, with an additional 24 ft to account for the approach slabs at each end and an overall width of 45 ft 11 in. Bridge Move The bridge slides were done in two separate moves (I-15 southbound on January 10 and I-15 northbound on January 24) over two 56-hour periods. For each slide, the existing I-15 structure was demolished at the interchange and the new 1000-ton superstructure was slid transversely 60 ft into its final position using two 64-ton capacity hydraulic jacks with a stroke of 3 ft. The approach slabs were slid with the rest of the superstructure. First, crews rerouted traffic on I-15 through the interchange on- and off- ramps that were temporarily widened to two lanes for the closure. Next, the existing bridge was demolished, which took about 12 hours. Crews then lifted the new bridge 3 in. into the air from its temporary foundations to clean and lubricate the bearings below. In final preparation for the move, crews applied gallons of lubricating dish soap to Teflon- coated elastomeric bearing pads. The bridge alignment followed a vertical and horizontal curve with a cross slope of 4.6% on the southbound side and 4.7% on the northbound side. The bridge has a 31-degree skew. Two specialized hydraulic jacks, each controlled by a single joystick, locked into slide rails and pushed the bridge 38 in. every 2 minutes until it was in place. The initial push required 800 to 900 tons with 8 to 9% friction, and approximately 600 to 700 tons and 4 to 5% friction to continue moving the bridge. A steel rail was cast into the temporary support system of the bridge; this rail included steel plates, or "ears." During the move, the ears slid into notches, forcing the bridge to move in only one direction. The jack stayed within this frame, moving the bridge from notch to notch. Once in its final location, crews used jacks to raise the bridge and install the bearings. The actual slide on the southbound bridge took 1 hour and 15 minutes, and the northbound bridge, which did not proceed smoothly and began to come in askew, took 5 hours. NEVADA DEPARTMENT OF TRANSPORTATION, OWNER BRIDGE DESCRIPTIon: Two single-span bridges, 111-ft 6-in.-long, plus 24-ft-long approach slabs, with widths of 45 ft 11 in. Built 60 ft away from and parallel with their final location and moved in a transverse slide using accelerated bridge construction STRuCTuRAl CoMPonEnTS: UBT58 precast,prestressed girders (Utah bulb tee) and conventionally reinforced 3.5-in.-thick precast concrete partial depth deck panels BRIDGE ConSTRuCTIon CoST: Approximately $2 million ($200/ft 2 ) for construction only costs. Another $900,000 for demolition, removal, and slide costs AWARDS: 2011 Transportation Project of the year – Institute of Transportation Engineers, Nevada Chapter Workers set bridge girders in preparation for sliding a 1000-ton bridge into place on the superstructure. Photo: Alan Preston. Construction of the southbound I-15 bridge deck happened directly adjacent to live I-15 traffic. Photo: Alan Preston. ASPIRE , Summer 2012 | 29 ASPIREBook_Sum12_R02.indb 29 6/29/12 12:39 PM

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