Pittsburgh and Pennsylvania Highways

Arthur Hedgren, bridge designer

By Sandra F. Donovan

The new Sewickley Bridge won't have the lacy, post-Victorian look of the old bridge. Even the spires and plaques will be gone, distributed to surrounding municipalities. But the clean, smooth lines of the new Sewickley Bridge will make it a more identifiably modern structure than the old model.

That is the opinion of Arthur W. Hedgren, Jr., project engineer of the design firm of Richardson Gordon and Associates. But, according to Hedgren, there are more important differences between the old and new bridges than just their looks. The new bridge will be stronger and easier to maintain than the old. In fact, it is an entirely different type of structure. The old was a cantilevered truss bridge: the new is a continuous truss.

Hedgren said that at the outset of designing the new structure, several factors were considered: inconvenience to the public caused by closing the old bridge, and financial and other losses. "We tried to have a solution that would be economical and minimize the downtime"--the time period that the bridge would be closed, said Hedgren.

Roll-in schemes, in which the new bridge would be constructed next to the old and then rolled into place, were dismissed as too risky. Hedgren said either bridge might damage the other, and the old bridge still might have had to be closed. "Instead," said Hedgren, "we decided to build it fast rather than riskily."

One factor that took a year off construction time, Hedgren estimated, was the decision to use the old piers constructed in 1909, for the new bridge. "We did borings to investigate the possibility. The concrete filling for the stone and concrete footers were in good shape." said Hedgren. "We may have saved as much as $1.5 million in construction costs. That's just a guess.

But before any construction could take place, the old bridge had to be dismantled, a complicated task. Hedgren said that the old bridge could not simply be blown up: debris would be strewn over railroad tracks and across the river, stopping rail and water traffic. Also, the piers could not be damaged, since they were to be recycled. Instead, six drawings with specifications were made to detail a dismantling process. The main span was lowered and floated downriver to be sold for scrap, but the sidespans had to be dismantled piece-by-piece so that the remaining members would balance each other. First a piece would be removed from one side, then the other. A temporary support for dismantling the bridge was located in a position so that it could be used as part of the new bridge.

Two potential "terrific stumbling blocks were avoided because the same bridge alignment was kept and the construction was considered a replacement in kind. Then an accelerated construction schedule was implemented for constructing the bridge opening today. American Bridge was the contractor for construction and dismantling.

Hedgren mentioned several differences between the old and new bridges. The old was a cantilevered truss bridge, with a center section of 750 feet and side spans of 300 feet each. The new bridge is a continuous truss-"which has more redundancy and strength," said Hedgren. Its center span is also 750, but its side spans are each 375 feet, making the new bridge 150 feet longer.

According to Hedgren, the old bridge had uplift and was tied down at both ends with steel eye-beams. "If the ends had ever let go, the ends could have gone flying," said Hedgren. He said emergency repair on the old bridge was done to tie down the old side spans.

The old road way was 28 feet wide and bounded by sidewalks. The new bridge will have a 32-feet roadway and one sidewalk.

"There were a lot of very small members, lacing bars, on the old bridge, which were open and very difficult to paint and maintain," said Hedgren. The open spaces made the old bridge prone to corrosion as well. Open curbs on the old bridge permitted salt from winter maintenance to accumulate against the steel as well. Conversely. the new bridge is constructed of "box members" which are closed and have no pockets to permit dirt and water to accumulate. Additionally, the concrete deck is sealed, with a sidewalk drainage system to carry the salt away from the steel. The concrete deck members are coated with epoxy to prevent corrosion.

An advanced paint system "should give the bridge a very long service life -- a much longer service life than other systems." said Hedgren. He said that it was the first time such a system had been used in this area.

The new bridge will have other features: New Jersey-type parapets that will prevent out-of-control cars from diving into the Ohio River; and a widened south lane onto Route 51.

Certain critical weight-bearing members also received particular care during fabrication and construction, said Hedgren.

"There will be no weight restrictions on the new bridge," said Hedgren. "It will vibrate; any bridge will. But it's very strong."

Clean, simple, smooth-lined, easy to maintain, the new Sewickley Bridge will be much more a bridge of the 80's than its predecessor. And, according to Hedgren, it will be a bridge of the future because it will last a long, long time.

Sewickley-Coraopolis Bridge 1911-1981
Supplement to the Coraopolis Record and the Sewickley Herald
Wednesday, October 21, 1981, Page 3A