Robert H. Dodds Jr. is a professor and head of the department of civil and environmental engineering.
Robert H. Dodds Jr. is a professor and head of the department of civil and environmental engineering. Dodds’ research focuses on the safety of bridges, pipelines, naval vessels, aircraft and spacecraft as they develop cracks and defects from the effects of aging. He was interviewed by News Bureau Physical Sciences Editor James Kloeppel.
Does the catastrophic failure of the Interstate-35 bridge in Minneapolis mean we need to improve bridge design?
Structural engineers continue to drive innovation in the science and art of bridge design including the form, construction materials, construction methods and maintainability. New bridge designs reflect research conducted at universities worldwide, with leading contributions from Illinois, on these and other technical topics to improve the efficiency, reliability, and lifespan. The vast majority of bridges in Illinois and across the U.S. are modest in size, carrying traffic across other highways, streets, railroads, and small streams. These bridges go virtually unnoticed everyday by the public; they perform reliably for many years, but cannot just be neglected as they age and deteriorate. New research to monitor and improve the “structural health” of aging bridges has the very real potential to prevent the almost certain increase in the number of future bridge failures.
The I-35 bridge was 40 years old; is this considered “old” for bridges? How long should bridges last?
Forty years is not all that old for a bridge. To put this in perspective, our nation just celebrated the 50th anniversary of the Interstate Highway System, including all the bridges built in those early years. We have great bridges serving with extraordinary safety: The Brooklyn Bridge (opened in 1883) and the Golden Gate Bridge (opened in 1937) are just two of many well known “very old” examples. With proper design, inspection, monitoring, repair, and continuing maintenance, modern bridges should last 100 years or more. But this is an expensive, mostly unglamorous effort that will require a new commitment of our citizens and politicians for the allocation of transportation tax dollars. Nothing less will restore the public’s complete faith in the safety of our bridge structures.
What are the challenges of inspecting our bridges?
Unlike the thousands of aircraft built to the same identical design in carefully controlled factories, our bridges have unique designs to meet the specific features of their location, required length, traffic volumes, cost restrictions, and material availability. As bridges age, they develop corrosion through environmental exposure and fatigue cracking caused by millions of load cycles from traffic (similar to bending a paper clip until it breaks). Bridge inspections to locate, quantify and assess the significance of this damage vary widely in their scope, time, and expense. The simplest is an overall, quick visual inspection now being ordered by government officials nationwide – analogous to the pilot’s walk around the plane before takeoff. More meaningful inspections often require closure of the bridge over weeks or months for physical access and the use of sophisticated instruments to quantify corrosion, to locate and determine the size of cracks, and to measure bridge movements and distortions. Starting with generic national guidelines, engineers develop individualized inspection plans for each bridge when they begin to observe the development of various “diseases” (corrosion, cracking, movement-distortion) as it ages.
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