Book review: A bridge to the past

After a year in which Minnesotans learned the value of keeping their gusset plates in good repair, it's a propitious moment for "Wood+Concrete+Stone+Steel" to appear.

This book on the state's historic bridges grew out of more detailed inventories of the state's historic bridges. There are sturdy stone arches, lacy steel trusses and the reinforced concrete arches that leap over rivers in the Twin Cities area, from Champlin to St. Paul's Robert Street. Pick your favorite among the local ones -- Cappelen (Franklin Avenue), Intercity (Ford) or Mendota.

Author Denis Gardner buttresses our understanding of some of the state's more notable bridges with detail on their predecessors and peculiarities, detail that reaches beyond the pocket-protector crowd.

Who outside Duluth, for example, knows that the city's iconic Aerial Lift Bridge didn't get its levitating roadbed until nearly 25 years after the original framework, which in- corporated a gondola to shuttle people and vehicles?

Or that the dogleg bend in the 3rd Avenue Bridge in Minneapolis was routed by city engineer Frederick Cappelen to avoid the more fragile rock strata above St. Anthony Falls? It was the first in a series of ribbed, open-arched designs whose grace and utility made the Twin Cities the envy of other areas.

Or that the culmination of this design -- the Mendota Bridge -- was built in concrete only after Hennepin County insisted on the stylish 13-arch span rather than a cheaper steel crossing? This history repeated itself when the County Board opted in the 1980s to lavish three times the cost of a conventional girder design on a suspension bridge for Hennepin Avenue -- the one that's often seen during NFL commercial breaks.

The book also reaches beyond the well-known metropolitan spans to ornamented township culverts that swallow rural streams narrow enough to jump across.

Although popularized from more technical surveys, with dozens of photos that capture the grace and strength of surviving bridges and vanished predecessors, this book still leans toward the structural-wonk reader. It opens with helpful diagrams of the many truss designs that made up wood, iron, then steel bridges built well into the 20th century. But similar diagrams would have been helpful showing the less-obvious reinforcement sheathed in concrete on more modern bridges, especially as structural safety moves to the forefront of public concern.

In an era of falling and failing state bridges, it's encouraging to know that some of Minnesota's oldest bridges were built to last. But it's also discouraging to read an estimate that more than half of the nation's historic bridges have disappeared in just the past 25 years, often for no better reason than that replacing them was deemed easier than repairing them.

The book's coda concludes that major obstacles to keeping our historic bridges are that the public is apathetic and that so many structures are in the hands of cash-strapped local governments. Gardner argues in a heartfelt passage that it's penny-wise but pound-foolish, and dismissive of our heritage, to let our bridges fall into decay, and make replacement, not preservation, the easiest option.

Steve Brandt • 612-673-4438