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CBC news broadcast a story yesterday (24 August/07) about closing part of a major downtown Montreal street due to fears that the tunnel connecting the Metro (subway) station and the underground city may collapse. Montreal recently suffered the collapse of a highway bridge killing several people and given the recent tragedy in Minneapolis, I thought it would be interesting to quote a passage from a book I just picked up called The World Without Us by Alan Weisman. The thesis of the book is what would happen to the cities, farms and structures and almost anything created by mankind should the human race suddenly disappear from the face of the earth. In a world without people, the author suggests, places such as Manhattan would eventually be returned to the flora and fauna as viewed by the Dutch when they first sailed up the Hudson.
Some interesting quotes regarding railway infrastructure: “add to all that the 1930’s-vintage water mains that frequently burst, and the only thing that has kept New York from flooding already is the incessant vigilance of its subway crews and 753 pumps. Following the World Trade Center attack, an emergency pump train bearing a jumbo portable diesel generator pumped out 27 times the volume of Shea Stadium. Had the Hudson River actually burst through the PATH train tunnels that connect New York’s subways to New Jersey, as was greatly feared, the pump train—and possibly much of the city—would simply have been overwhelmed.”
The author then quotes a structural engineer named Jerry Del Tufo who had responsibility for the bridges of the Port Authority of New York and New Jersey. Discussing the vulnerability of modern bridges “Rust that forms between two steel plates bolted together exerts forces so extreme that either the plates bend or rivets pop. Arch bridges like the Bayonne—or the Hell Gate over the East River, made to hold railroads—are the most overbuilt of all. They might hold for the next 1000 years….”
It would appear that the technology of the 19th and early 20th centuries had certain advantages with their “overbuilt” structures in comparison to our modern construction techniques that believes less is more. Give me overbuilding any day.
Posts: 524 | From: Toronto Ont. Canada | Registered: Mar 2001
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Mr. Norman, Canadian politicians like their brethern worldwide loved to be photographed opening a new hydro-electric project or cutting a ribbon to open a new highway, but I can't recall the last time I saw one during the cleaning of a municipal sewer system, or routine maintenance of a bridge. Not enough votes in the mundane and ordinary things that would eventually save lives.
Speaking of mundane, just the other day I read that one of the causes of the Minneapolis disaster was the failure to remove bird droppings from the bridge, apparently the droppings were just another element in the rusting away process of steel.
Posts: 524 | From: Toronto Ont. Canada | Registered: Mar 2001
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The entire body of knowledge of structural engineering is designed to make things do their job with the least amount of materials possible.
Consider the pyramids. Thousands of years old, and it'll be thousands more years before they are worn away.
Consider the Roman aquaducts: In many cases, the same. In some eartquake prone regions, not necessarily so true.
Consider Romanesque churches (and in some cases ruins) compared to Gothic and Baroque era...
The railroad bridges of the 19th and early 20th Centuries are far lighter than what would be needed had they been dreamed of in the 17th and 18th Centuries.
We've gotten to the point where we can computer model structures, and give a "pretty good" estimate of design life. As I recall, the MN bridge was designed for a 50 year life span... as built. It was already 40 years old, and had been modified from the original plan... both in design and in actual use parameters.
One of the buildings where I work was built in the late 19th Century. It had been taken out of service in the late 1970s. With 12 years of neglect, it was unsafe at any speed. Another 10 years and it'd start collapsing.
I drive by a once and former roadhouse daily. It's been unused for 10 years now, much of the roof has obvious holes.
Posts: 1404 | Registered: Oct 2001
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For what it worth, the entire discussion on this week PBS's McLaughlin Group was directed towards infrastructure.
Posts: 9980 | From: Clarendon Hills, IL USA (BNSF Chicago Sub MP 18.71) | Registered: Apr 2002
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Just because something is designed for 50 years does not mean that it should be torn down 50 years after its construction. Generally the concept means able to withstand anything that has a chance of better that 2% a year of happening. As long as you protect steel from rusting out and do not load it beyond its design loadings, a steel bridge should last almost indefinitely. There are plenty of plus 100 year old bridges out there.
Posts: 2810 | From: Olive Branch MS | Registered: Nov 2002
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From what news coverage I've seen, the I35W bridge was designed using assumptions of lower tonnage and lower use rates than it was handling on the day it fell. Further, its inspection record already included specified risks.
We've been rebuilding the interstate highways now for about 20 years. I've noticed some states are getting truly serious about maintaining their bridges and viaducts, others wait until bad things happen. We're fortunate most rr bridges were over-engineered to begin with, and even now it seems the structural guys are planning in bigger loads across the lifespans of new construction.
Posts: 1404 | Registered: Oct 2001
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posted
As an update in Montreal, the subway has now been reopened, although parts of the street above is still closed awaiting the installation of more steel supports in the tunnel below.
Posts: 524 | From: Toronto Ont. Canada | Registered: Mar 2001
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