Tom Adams Posted August 3, 2007 Share Posted August 3, 2007 It's a sad thing to have happen anywhere. I cross the Narrows bridge here in NYC daily. It was at one time the largest single suspension bridge in the world. The scary thing about it today....is that they are doing some work on it which involves cutting off one lane of the three lanes at a time.....there are temporary cement barriers on the egde acting like retaining walls....looking down from bus view...it's a long way down. sad indeed to happen anywhere hopefully the Verrazano Narrows does not fall and Drwho, yeah it sucks to be the engineer that made that bridge right now. Huh?????? I feel certain that it wasn't an engineer that "made that bridge" but rather a contractor who built it. And the factor of safety's that are used in the design of such structures ensure that they are VERY safe. Are there instances when stress loads were not calculated correctly? You betcha. But those errors show up real quick - not 30 years later. What concerns me is that the parameters that our Interstate highway system was designed to back in the Eisenhower days are not what our roads are seeing today. In the early days, the bulk of things in this country were delivered by rail and the prognosticators felt that would continue to be the trend. Instead, the shipment of goods nowadays is principally by trucks of the 80,000 pound variety. I'm certain that the constant pounding (loading & unloading) of bridge structures by thousands of 18-wheelers is of great concern to highway engineers since they know that the bridges were not designed for those load cycles. The mere fact that Interstate bridge structures in this country that are 40 years old have stood is a testament to Engineers. Anyhow......... It will be interesting to see what caused the bridge to fail in the manner it did. I've got some theories based upon the video I saw, but will hold off. My heart goes out to the folks who lost their lives and their families. I've long had a fear of plunging off a bridge into the water in a car. Tom Link to comment Share on other sites More sharing options...
DrWho Posted August 3, 2007 Share Posted August 3, 2007 That's kinda where I was heading Tom...it's easy to build something that works today, but you never know how something might respond to changes in the future. You can try to predict and account for them, but you can never be certain. Heck, just look at the one suspension bridge that shook itself to pieces (can't remember the name right now). I'm pretty certain nobody thought that would be a problem until after the fact! Link to comment Share on other sites More sharing options...
Tom Adams Posted August 3, 2007 Share Posted August 3, 2007 That's kinda where I was heading Tom...it's easy to build something that works today, but you never know how something might respond to changes in the future. You can try to predict and account for them, but you can never be certain. Heck, just look at the one suspension bridge that shook itself to pieces (can't remember the name right now). I'm pretty certain nobody thought that would be a problem until after the fact! Apples & oranges...... The Tacoma Narrows bridge failure happened right away not some 40 years later. Its failure was due to vibration induced by wind vortices shedding off the main span structure at a rate that was equal to the natural harmonic frequency of the structure. You know - it's like that physics demonstration where you strike one tuning fork and place it near another tuning fork of the same frequency and it starts to vibrate as well. Needless to say, it's not good when a structure starts to vibrate at its natural frequency. Not much was known about vibrational fatigue in those days, but they still could design for it. What they didn't have was a way of analytically predicting something of that type nor had they ever considered putting a bridge structure in a wind tunnel. Pretty fascinating if ya ask me, but then again I'm an egg-head engineer. Anyhow...... I know what you were trying to say. Tom Link to comment Share on other sites More sharing options...
Jay481985 Posted August 3, 2007 Share Posted August 3, 2007 I am figuring total structural failure seeing how the whole structure fell at the same time and not one side first. Also yes the testament that the bridges made 40 years ago still hold is a testament but at the same time most of those bridges that are older than 30 years old were more or less overbuilt. Now we have more computer models and computations that makes it possible to build the bridge to meet all safety standards but at the minimal cost too. Link to comment Share on other sites More sharing options...
Moderators dtel's wife Posted August 3, 2007 Moderators Share Posted August 3, 2007 " I've long had a fear of plunging off a bridge into the water in a car." This is a fear I have also had for a long time. Especially with the "quick fixes" made to some of the bridges in this area after Katrina! Link to comment Share on other sites More sharing options...
Duke Spinner Posted August 4, 2007 Share Posted August 4, 2007 too bad the Video does'nt show the point of collapse ... typically, a sudden failure like that can be traced to a pier being damaged, or sympathetic vibration + overload chances are the vibration from a Hoe-Ram .. , an Excavator w/ hydraulic jack hammer , caused fasteners to shear .. a local bridge that had construction done, had a 5 ton load limit posted ..... I counted 78 Tons of equipment parked on tha bridge ... [] [:|] [:S] the one wheel loader, alone weighed 38,000 # Link to comment Share on other sites More sharing options...
Jay481985 Posted August 4, 2007 Share Posted August 4, 2007 too bad the Video does'nt show the point of collapse ... typically, a sudden failure like that can be traced to a pier being damaged, or sympathetic vibration + overload chances are the vibration from a Hoe-Ram .. , an Excavator w/ hydraulic jack hammer , caused fasteners to shear .. a local bridge that had construction done, had a 5 ton load limit posted ..... I counted 78 Tons of equipment parked on tha bridge ... [] [:|] [:S] the one wheel loader, alone weighed 38,000 # I totally forgot there was construction at the time..... sooo hmmm those concrete barriers probably weigh about 3 tons each and then the jackhammers and such.... seems like overweight shoots out at me Link to comment Share on other sites More sharing options...
Strabo Posted August 5, 2007 Share Posted August 5, 2007 too bad the Video does'nt show the point of collapse ... For some reason that video cut off the first frame or two. Try the video on NY Times. http://video.on.nytimes.com/index.jsp?fr_story=f7e0638ff493cd73e1992ce0d22a92cb897797ee&rf=mrss The collapse started at the southern end (right side of the video) of the bridge. I've only seen one arial shot and it shows all of the bridge fell down staight except for the southeast section. It fell to the east. I'm no expert but it looks to me like something gave way on the south east side first then the rest followed. Here's a couple shots I took after today's Twins game. Both looking to the east. Link to comment Share on other sites More sharing options...
Duke Spinner Posted August 5, 2007 Share Posted August 5, 2007 are all the piers ntact ..?? overweight, by itself won't do it ... Link to comment Share on other sites More sharing options...
Jay481985 Posted August 5, 2007 Share Posted August 5, 2007 are all the piers ntact ..?? overweight, by itself won't do it ... sure it can that and the natural movement associated with traffic. Link to comment Share on other sites More sharing options...
colterphoto1 Posted August 5, 2007 Share Posted August 5, 2007 Wow, that's insane. Stuff like this is why I would never want to be a mechanical or civil engineer. My Father was a civil engineer. He designed bridges when the interstate system was young, then developed a method of hanging precast panels on the sides of hospitals and schools. He had pretty regular nightmares, it's a stressful life. Let's hope the government agencies pay attention and demand more and rigorous inspections of all bridges- large and small. There is the knowhow to prevent these kind of tragedies, if only people would listen. I stand with Tom Adams in his assertions. I remember watching the World Trade center disaster and thinking 'get a civil engineer in there- those building's can't stand that fire for long'. Someone should have calculated the risk of having concurrent construction and traffic. It'll be interesting to see how this shakes out, particularly the warnings that went unheeded. Link to comment Share on other sites More sharing options...
Duke Spinner Posted August 5, 2007 Share Posted August 5, 2007 the designer of the Brooklyn bridge, used a safety factor of 6 X the Static, and Dynamic loads that he calculated, unsure of the actual forces acting on the bridge the Brooklyn bridge is still standing, unlike the Tacoma Narrows Suspension Bridge , that failed in a windstorm , in what ..? 1940..?? designers routinely take structural steel out of subsequent designs, untill a failure occurs.....Value Engineering think ..."Calculated :Loads" .. vs ... Actual Load .... when the Bridge fails in Shear , subsequent designs use a more substantial safety factor Guess where we are right now ..?? Link to comment Share on other sites More sharing options...
Strabo Posted August 5, 2007 Share Posted August 5, 2007 are all the piers ntact ..?? overweight, by itself won't do it ... Not sure what piers you are refering to. There are three main structures in my first picture. In the foreground is a dam that is just upstream of the 35W bridge, next is parts of crumpled remains (green steel) of the 35W bridge, and the bridge in the background is the Cedar Ave bridge (still standing). You shouldn't be able to see much of the Cedar Ave bridge because the 35W bridge should have blocked the view. A bit of background I35 splits as it runs through the twin cities similar to how it runs through Dallas. 35W runs through the western part of the twin cities (MPLS) and 35E runs though the eastern part of the cities (St. Paul). It splits in a southern suburb then reconnects in a northern suburb. Link to comment Share on other sites More sharing options...
Strabo Posted August 5, 2007 Share Posted August 5, 2007 I probably should have also noted in my second picture, what looks like a ramp with green steel support on the right side of the picture, that was the apron to the bridge. It used to run parallel to the bridge behind it, blocking out the view of the bridge behind it. Link to comment Share on other sites More sharing options...
Jay481985 Posted August 5, 2007 Share Posted August 5, 2007 the designer of the Brooklyn bridge, used a safety factor of 6 X the Static, and Dynamic loads that he calculated, unsure of the actual forces acting on the bridge the Brooklyn bridge is still standing, unlike the Tacoma Narrows Suspension Bridge , that failed in a windstorm , in what ..? 1940..?? designers routinely take structural steel out of subsequent designs, untill a failure occurs.....Value Engineering think ..."Calculated :Loads" .. vs ... Actual Load .... when the Bridge fails in Shear , subsequent designs use a more substantial safety factor Guess where we are right now ..?? ah the good old days when they made sure that the common folk was rest assured that the thing would work and would not fail. Now it is value engineering......... I guess it started with the George Washington Bridge in Fort Lee NJ. They were supposed to put up side paneling to make the suspension bridge a solid looking object but cost cutting made it the skeleton bridge we know it. Or maybe it was the Bayonne Bridge that did that? hmmm...... Link to comment Share on other sites More sharing options...
GaryO75 Posted August 8, 2007 Share Posted August 8, 2007 My wife works in downtown Minneapolis; the bridge used to be on my route to get to my job and back. It is quite a mess. Still have a number of people missing. It's presumed they are in the cars that are still underwater in the Mississippi. The Army Corp of Engineers is here to assist with the getting things cleared out, and the FBI is talking with all the construction workers that were on the bridge. Link to comment Share on other sites More sharing options...
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