Barker's book looks at the history of highway bridges
By Lynn Nystrom
Spectrum Volume 20 Issue 06 - October 2, 1997
"Usually, a history of bridges begins with a log across a small stream or vines suspended above a deep chasm...followed by the development of the stone arch by the Roman engineers of the second and first centuries B.C. and the building of the beautiful bridges across Europe during the Renaissance," wrote Richard M. Barker, Virginia Tech professor of civil engineering, in his new collaborative book called Design of Highway Bridges.
Barker, along with his co-author Jay Puckett, professor of civil and architectural engineering at the University of Wyoming, treats the history of bridges differently--they have elected to highlight bridges that are typical of those found in the U.S.
The authors' romance with bridge building is apparent. In more than 1,000 pages, they outline the successes and failures of the architects and engineers who made their fortunes or often met their demise with these structures. These designers dabbled in various materials such as stone, iron, reinforced concrete, wood, steel, and various combinations, often without knowing all of the consequences.
Barker and Puckett's book is complete with historical tidbits. For example, the oldest remaining Roman stone arch is from the seventh century B.C., and is a vaulted tunnel near the Tiber River. But the Turks can claim the honor of having constructed the oldest surviving stone-arch structure, a ninth-century B.C. historical site over the Meles River in Smyrna.
Compared to these early beginnings, the stone-arch bridges in the U.S. are "relative newcomers," according to Barker and Puckett. However, the oldest bridge in the U.S. that continues to serve as part of a highway system is a stone arch over Pennypack Creek on the King's Road between New York City and Philadelphia. It was built in 1697.
"A good bridge engineer must never forget the people factor," in their examination of key bridge types, selection processes, and aesthetic considerations, wrote the two professors.
The people who built the first bridges in the U.S. were millwrights or carpenter-mechanics, and did not have a clear understanding of trusses, they explain. These first bridge engineers used the knowledge they gained from building large mills and just increased the spans.
Barker and Puckett speak of the railroad as driving the change in bridge construction in the U.S. When people in America started traveling by rail, the wooden bridges that had been serving the public well as they moved around in their horse drawn carriages, were no longer an option. Iron rods replaced wood tension parts and a hybrid truss composed of a combination of wood and metal members was made. Eventually, the transition was made to all-metal trusses. Iron soon became another option.
"Suspension bridges capture the imagination of people everywhere," Barker and Puckett say. The image of a swinging bridge across a raging torrent of a rock-strewn river stimulates emotions from fascination to fear to awe.
In their book, Barker and Puckett discuss suspension bridges made of wrought-iron chains, ones with clear spans of up to 486 meters, and structures that fell down. With the latter, they note, an early suspension bridge was aerodynamically unstable, yet the lesson to the engineering profession was lost for many years. They cite as an example the crash of the Wheeling Suspension Bridge over the Ohio River some 80 years before the similar demise of the Tacoma Narrows Suspension Bridge.
The authors note another hazard of the bridge building profession--the placement of bridge foundations on a solid footing and not on the shifting sands of a river bed. When James B. Eads designed the steel-deck arch bridge across the Mississippi River at St. Louis in 1874, he realized that underwater abutments and piers founded on bedrock would be needed to hold the bridge's foundations. Wooden boxes, or caissons, were pressurized to keep the water out and permitted excavation though the river bed to bedrock. Of the workers who were sent to accomplish this task, 13 men lost their lives due to caisson's disease, more commonly known as the bends.
The process for constructing with caissons was altered by Eads, who happened to be a diver, and his physician. They were the ones to suggest a slower decompression and shorter working time in the caisson as the depth increased. Consequently, only one additional life was lost. On a brighter note, this bridge produced a milestone in the field because of its cantilever construction of the three arches.
Again, Barker and Puckett point out that this advancement in bridge building was not immediately passed on. The simultaneous construction of the Brooklyn Bridge by Washington Roebling resulted in his body being stricken by the bends, and his partial paralysis for life.
Barker and Puckett's history continues, citing progress in reinforced-concrete bridges, the first of which remains in service in Golden Gate Park, San Francisco, and the development of girder bridges, the most numerous of all highway bridges in the U.S.
"The challenge for today's bridge engineer is to follow in the footsteps of these early designers and create and build bridges that other engineers will write about 100 and 200 years from now," they wrote.
The remainder of their book focuses on aesthetics, an in-depth examination of design considerations, separate chapters on concrete, steel, and timber structures, system analysis procedures, sample problems, and selected references for further study. Their book is the first treatise on highway bridges to be based on load-and-resistance-factor design principles recently developed by the American Association of State Highway and Transportation Officials. Design of Highway Bridges is published by John Wiley & Sons, Inc.