THE CONCRETE BRIDGE MAGAZINE

FALL 2017

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/879956

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CONCRETE BRIDGE TECHNOLOGY Precast Concrete Overhang Panels for Safer and Faster Bridge Deck Construction by Kevin Moyer, Texas Department of Transportation The Texas Department of Transportation (TxDOT) constantly seeks innovative accelerated bridge construction methods that reduce the impact to the traveling public, improve safety in the work zone, and reduce costs. TxDOT began developing deck construction methods using precast, prestressed concrete panels (PCPs) in the 1960s, and these methods continued to evolve. In 2008, TxDOT sponsored a research project1 to develop a precast, prestressed concrete overhang panel system for potential use in bridge construction. This panel system was successfully implemented on the Farm-to-Market Road 1885 Bridge over Rock Creek in Parker County, Tex. The result was an improvement in safety due to the sturdy work platform provided by the panels, and elimination of the need for overhang brackets and formwork. TxDOT recently implemented the "second generation" of conventionally reinforced precast concrete overhang panels [PCP(O)s] on a bridge on Farm-to-Market Road 726 over Brushy Creek in Marion County, Tex. The panel dimensions for the second generation of PCP(O)s vary from 6 to 8 ft in width (longitudinal direction of bridge) and 6-1/2 to 13-1/2 ft in length (transverse direction of bridge). The minimum width accommodates the development length of the reinforcement along the width of the panel. The maximum width keeps the panel within the transportation width limits so a permit is not required. Two types of panels were designed: one for the interior of the span and one for the thickened slab at the ends of units. The full-depth panels (8-1/2 in.) have conventional reinforcement and a fulldepth gap over the exterior girder to integrate the PCP(O) with the girder after cast-in-place (CIP) concrete deck placement. The panels also have the ability to: - be used with variable girder spacing, - accommodate a sealed expansion joint, - adjust their elevations with leveling bolts instead of the use of dense foam, and - integrate with adjacent PCP(O)s and CIP concrete. The main improvement of the second generation of PCP(O)s over the first generation is a full-depth gap that runs the entire width of the panel (along the girder), which eliminates the need for shear pockets and a separate grouting operation. Additionally, the partial-depth panel ledges allow for reinforcing steel that enables the adjacent PCP(O)s and the CIP deck concrete to work as a unit. The ledges of the panels are 1 ft 6 in. wide and run the length of the panel, except for 1 ft 4 in. in the overhang region. The ledges that integrate the interior deck concrete are 1 ft wide and run the width of the panel. The main design challenge was designing the fulldepth gap to handle stresses induced from lifting, transportation, CIP concrete deck placement, and stability during leveling. The panel was analyzed as a beam with different support conditions for each stage to determine the amount of reinforcing steel needed to stabilize the gap. Another second-generation improvement is the leveling system, which consists of three leveling pads with coil bolts. Designed to support the panel during leveling, the leveling pad is a 4 x 4 x 1/4-in. steel plate with a coil nut and 3-in. -diameter steel pipe welded to the plate. After the panel is leveled to the correct elevation, additional support needs to be provided by welding the gap reinforcing bars to the R-bars of the TxGirders or by placing a grout pad at the PCP(O) corners. The coil bolts may be left in place as long as the tops of the bolts are 2-1/2 in. below the top of the deck. Unlike PCPs, PCP(0)s use an elastic polyurethane foam (cont. next page)

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