Oyler: Pittsburgh's bridges topic of Bridgeville history lecture

When local civil engineer Todd Wilson spoke to the Bridgeville Area Historical Society about his book, “The History of Pittsburgh's Bridges,” he truly did start at the beginning.

Wilson began his presentation with a drawing of Fort Pitt, which clearly showed footbridges across the moat around the fort. We know for sure Pittsburgh's bridges date back at least 260 years.

By 1818 the first bridge across the Monongahela River was constructed at Smithfield Street. The first Smithfield Street Bridge was a wooden covered bridge built by engineer Louis Wernwag. It was destroyed by the Great Fire of 1845, which burned a third of the city to the ground.

John Roebling replaced it with an eight-span suspension bridge with short towers. When a dramatic increase in traffic made it obsolete, it was replaced by a lenticular truss bridge designed by Gustave Lindenthal in 1883 — the landmark bridge that is at that site today.

A particularly interesting story was the role played by the Pittsburgh Municipal Art Commission from 1911 to 1939. The commission's function was to foster “excellence in design to city property.” In the 1920s it became necessary to replace the existing Allegheny River bridges at Sixth, Seventh and Ninth streets, to provide navigational clearance beneath them.

Through truss and cantilever bridges were proposed for their replacements. The commission, however, led by its chief architect Stanley Roush, insisted upon suspension bridges even though there was no suitable anchorage for their heavily loaded cables at either end. The designers responded by utilizing a unique, self-anchored support system which transferred the cables' loads into massive compressive forces in the bridge deck.

In retrospect one must be grateful to the commissioners for their stubbornness, which eventually produced the iconic Three Sisters Bridges — later renamed for Roberto Clemente, Andy Warhol and Rachel Carson.

Wilson's knowledge of his subject was especially impressive. Being a fellow civil engineer, I was thrilled with the topic; the audience was equally complimentary about his presentation.

In March the historical society returns to its “last Tuesday” evening schedule. At 7:30 p.m. March 28, Edd Hale will speak on the Great Castle Shannon Bank Robbery in the Chartiers Room of the Bridgeville Volunteer Fire Department on Commercial Street. The public is invited.

John Oyler is a Tribune-Review contributing writer. He can be reached at 412-343-1652 or joylerpa@icloud.com. Read more from him at mywutb.blogspot.com.