Owner: PennDOT Engineering District 9-0

Location: SR 6036 South Woodbury Township S21408A, Bedford County

Designer: Goodkind & O'Dea, Inc.

General Contractor: The New Enterprise Stone & Line Company, Inc.

Alternate Designer:Patel Chen Associates

Prestress Producer: The New Enterprise Stone & Line Company, Inc.

Erector: The New Enterprise Stone & Line Company, Inc.

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Project Review

The Loysburg Bypass was a Demonstration Project in more ways than one.

As a Federal Demonstration Project, it illustrated how state and federal agencies and local communities can work together to resolve sticky historical and environmental issues.

But on another, more concrete level, it demonstrated the versatility and utility of ... prestressed concrete.

After a 10-year odyssey through the maze of public involvement, environmental regulation and historical preservation, the Loysburg Bypass was completed in 1997. Its completion would solve the problem of an ever-increasing volume of traffic trying, sometimes unsuccessfully, to negotiate a 90-degree turn in the center of town.

An initial proposal to realign Route 36 in town was turned down by residents of this picturesque village of red and white wood frame buildings eligible for inclusion on the National Register of Historic Places. Rejection of the in-town alternative, ultimately, moved the proposed project onto a new alignment to the east. However, this path was not without some significant engineering and environmental challenges of its own. And in the end, those challenges would result in a project that has, as its focal point, a bridge that demonstrates the efficient and creative use of today’s prestressed concrete technology.

The bridge carries the bypass over the Yellow Creek and an adjacent expanse of meadowland containing two endangered insect species and significant wetland and flood plain acreage. But the bridge is no straight-shot crossing. The topography of the Loysburg Gap plus the presence of additional historical structures at the northern approach posed significant design issues. In truth, had the Loysburg Bypass been designed at the beginning of the decades-long project development process, prestressed concrete probably wouldn’t have been considered for the bridge.

But in the case of the Loysburg Bypass, prestressed concrete was PennDoT’s design of choice from the start. The bridge that today sweeps gently across the stream and its companion meadowland is as at home in the rural countryside as is the meandering Yellow Creek and the spires and silos of the unassuming village of Loysburg.

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The Bridge

The bridge itself is 1,000 feet long, built with thirty-four prestressed concrete super-beams eight feet deep and averaging 125-feet in length. Its eight spans are supported by seven piers, four beams across for each of the six southern spans, five across for the two northern approach spans. New Enterprise Stone & Lime Company, Inc., prime contractor on the $6.1 million project, fabricated the beams at its Newcrete Products plant in nearby Roaring Spring.

The crossing required long spans in order to minimize wetland disturbance, which was limited to less than one acre of total wetland replacement. In the past, such long spans were thought to be the exclusive territory of steel. But technological and design advances by the prestressed industry, the development of ever-increasing concrete strengths and the clarifying of prestressed design standards by PennDoT over the past two decades have stretched prestressed beams to lengths -- and uses -- equal to those of steel.

Combining this length parity with creativity and the inherent advantages of concrete, made prestressed concrete the natural choice for the Loysburg Bypass.

The geometry of the planned roadway called for creativity. Planners had a limited corridor through which to slip the northern approach, plus alignment constrictions imposed by Tussey Mountain at the south. Between the two would lie the bridge. Factoring in a mandate to minimize wetland intrusion and design speed criteria for maximum curvature, engineers produced the attractive but challenging relaxed "S" curve bridge design.

PennDoT, looking for cost savings in both construction and long-term maintenance, directed that the primary bridge design be prestressed concrete. The savings they sought were found in several areas, all directly linked to their choice of structural materials. The design was achieved through a tricky, but relatively simple, placement of prestressed members.

The bridge was ‘bent’ by placing the straight ‘stick’ beams atop staggered piers and the slight cantilevering of deck sections, easily accomplished within the structural capabilities of the massive beams.

The ‘curve-to-reverse curve’ configuration of the basic structure required super-elevations with a cross slope of up to 8 percent on the deck surface. Entering the bridge from a slight downgrade at the northern approach, the roadway banks left-to-right through the first curve, flattens out to a low point in the center to accommodate drainage, then banks right-to-left through the opposite curve before flattening again at the southern approach. Deck tilt was achieved through the use of stepped pier caps, variable-depth bearing pads, and beveled sole plates.

Beyond the evident aesthetics of the gentle twist and tilt of the bridge can be found the cost efficiencies inherent to prestressed concrete.

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Cost-Saving Factors

Prestressed beams require less concrete per deck section than steel because prestressed deflects less than a corresponding steel girder. This lower deflection results in less camber in prestressed members, and less camber means a lower slope from beam mid-span to end of beam. Lower slope equates to lower total volume to achieve minimum deck coverage at the highest point. In short, the concrete deck at the end of a prestressed beam is not as thick as for the same length steel girder.

Also, with top flanges significantly wider than those found on steel girders, prestressed beams require smaller -- and cheaper (to buy and construct) -- deck pans. In addition, because prestressed concrete expands and contracts less than steel, neoprene strip seal expansion dams were used at Loysburg. Neoprene dams costs about one-third of the tooth dams that would be required on a steel bridge.

Designed with a continuous concrete deck with two expansion joints at the approach slabs and with seven construction joints, the bridge at Loysburg utilized cast-in-place concrete diaphragms at pier caps to achieve a seamless deck.

The deck pour started at the south end of the bridge. The use of admixtures in the concrete mix design allowed it to remain plastic sufficiently long for casting of the continuity diaphragms ahead of the deck and then, while still in the plastic state, casting the deck over the diaphragm. The pour was then continued to the positive moment of span two. Dictated by the ability to furnish concrete, this procedure had to be repeated three more times resulting in only three construction joints for an even smoother ride than designed.

The benefits of the continuous deck are reflected in lower long-term maintenance costs. With a minimal number of joints there is minimal expansion dam maintenance. Damaging road salts and moisture also have fewer paths to critical structural members.

And, of course, prestressed concrete bridges never need to be painted. Considering the costs that PennDoT’s 10-year cycle of bridge painting projects, the agency, no doubt, sees significant savings. The money otherwise spent encapsulating steel girders to protect the environment, sand blasting, disposing of old paint, and applying a new coat or two can be put to better use elsewhere to improve the total transportation system for the taxpayers of Pennsylvania.

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