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picture of bridge

Architect's rendering - view northwest (Figg Bridge Engineers)

photo of bridge

Elevation drawing looking downstream

More detail photos

WB-443; MP 48.00


Pennsylvania Turnpike Allegheny River Bridge

Harmar Twp. - Plum

40.537604, -79.822556

USGS 7.5" Topo Quad - UTM Coordinates:
New Kensington West - Zone 17; 0599 4487
-- PA Turnpike [I-76], milepost 47.7 - 48.2

-- PA Turnpike (Harmar) on right descending bank of Allegheny River
-- PA Turnpike (Plum) on left descending bank of Allegheny River

CROSSES (north to south):
(RDB to LDB) Freeport Rd [Old PA28], NS RR (Conrail Conemaugh Div), Allegheny River at Mile 14.2, Fourteen Mile Island, AVRR (old PRR Allegheny Valley)

Segmental cast-in-place concrete box girder; Segments were built as balanced cantilevers extending from each pier; Post-tension steel cables tighten to hold segments together

6 spans (west to east): 285 ft, 380 ft, 380 ft, 444 ft, 532 ft main channel, 329 ft

TOTAL LENGTH (including longest elevated ramp):
2,350 ft

120 ft above river level
Pier heights range from 52 ft to 102 ft

2010, Figg Bridge Engineers
Pennsylvania Turnpike Commission
Project started May 2007 with total budget of $193.6 million. Approximately $105 million is for items directly to bridge construction.

Replacement of the Pennsylvania Turnpike Commission's Allegheny River Bridge 14 miles northeast of Pittsburgh between Harmar Township and Plum Borough, Allegheny County is part of a total reconstruction of the Interstate 76 mainline between Mileposts 46.56 and 49.54. Walsh Construction Company of Chicago, IL, the lower of two bidders, was awarded a general construction contract totaling $189,883,811 on May 1, 2007. The formal Notice to Proceed was issued on May 17. McTish, Kunkel & Associates is the PTC's construction manager.

The goals of the Turnpike's total reconstruction program are to improve the durability of the road, enhance safety and increase capacity. This project widens I-76 to three lanes each direction between the PA Route 28 overpass to the west and Oakmont Service Plaza to the east.

Twin bridges approximately 2,350 feet long and up to 120 feet high were constructed as cast-in-place concrete box girders using the balanced cantilever method. Each bridge is constructed in 144 segments of 16 feet each, totaling 2,304 feet of the structure. 4 foot closure segments were inserted at the the midpoint of each span. Pier tables account for the remainder fo the structure's length. Segments were cast on either side of each pier -- cantilevering and balancing atop the pier -- and closing toward the center of each span.

The depth of the concrete segmental box girders is 26ft at the main span piers, 19ft at the side span piers and 11ft at mid-span cross the Allegheny River Valley. The bridge is being cast in place using travelling forms using the cantilever method. Work begins from the top of the piers. Gradually working out from the piers, the five cantilevers consequently results in six spans of 285, 380, 380, 444, 532 and 329ft. The 105ft- and 69ft-long portions of the two end spans are cast in place on false work beyond the cantilever.

To simplify formwork and casting operations, the cross-section of the segmental box girder was designed as a single cell box girder with a core form without ribs or transverse drop beams. The wing length creates typical deck widths of 61ft to 84ft at the westbound-end span near the interchange -- the latter allowing for an extended acceleration lane at the Allegheny Valley entrance ramp.

The bridges are slightly downstream from the original span on an alignment parallel to the existing Turnpike. Each bridge is about 61 feet wide -- including three 12-feet-wide travel lanes, an outside berm 12 feet wide and an inside berm 10 feet wide. Both decks have a concrete road surface.

The design by Figg Bridge Engineers was inspired by local landscape features and includes a variable depth superstructure and a stone pattern on rectangular piers with concave curves in the transverse direction. In addition to abutments at either end, each bridge has two piers in the main channel of the river and two piers in the back, or recreational, channel.

Post-tensioning strands in the bridges would stretch from Pittsburgh to Philadelphia and back. Construction utilized nearly 50,000 cubic yards of concrete, enough to fill Heinz Field 27 feet deep. Post-tensioning forces total over three million pounds. Some 3,000 tons of steel reinforcement were put into the new bridges.

The project also included replacement of the Gulf Lab Road overpass just west of the river, new entrance (acceleration) and exit (deceleration) ramps for the Allegheny Valley interchange on the west side of the river, two new bridges to carry I-76 over the interchange ramps, replacement of the older pedestrian bridge over the Turnpike serving Oakmont Country Club (to accommodate the Turnpikes new footprint underneath) and the construction of five retaining walls.

Two retaining walls (one approx. 1,300 feet long and 30 feet high and the other approx. 600 feet long and 70 feet high) were built along the Turnpike on the east side of the river. Two retaining walls (one about 400 feet long and one about 200 feet long, both 12 to 16 feet high) were built along the realigned ramps at the Allegheny Valley interchange. A fifth retaining wall approx. 1,000 feet long and 60 feet high was built adjacent to Gulf Lab Road and the University of Pittsburgh's Applied Research Center (UPARC). The retaining walls were given a faux stone finish to mimic the color and stratification of local geology. The walls were subcontracted to Cemrock for hand carving of the Shotcrete and Bella Vernici for coloring.

The Turnpike Commission maintained traffic over the existing Allegheny River span until the new bridges were ready. Eastbound traffic was moved to the new downstream bridge October 25, 2010. Westbound traffic continued on the old bridge while the new westbound structure was completed with a scheduled completion date of November 2010. The new Gulf Lab Road Bridge was scheduled to open by Labor Day 2009.

The previous Allegheny River Bridge carried four lanes of traffic (two each direction) and opened on December 26, 1951, with the western extension of the Turnpike from Irwin to the Ohio line. It was an underslung steel truss bridge constructed by American Bridge Company. The structure was designed by Modjeski and Masters.


field check; PA Turnpike Commission, Walsh Construction website

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Introduction -- Nearby Structures

Page created: 10-Aug-2009
Last modified: 08-Nov-2009; 29-Feb-2016

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