Poor design led to I-35W bridge collapse?

Space Shuttle, weapons, or "domestic" structures? Anything that does reuse, multiple cycles (like the external tank of the SS was supposed to)?

I was flabbergasted by this:

David A. Smith

(snip)

One of the primary factors was the obstruction of traffic just beyond the bridge due to a road repair project that was under way.

The bridge became stacked with stalled or barely moving vehicles that lurched ahead, then braked to a stop from time to time, in unison. This put a VERY high level of stress on the bridge support structure. This, hoppy toad traffic movement and the maximum overload condition in conjunction with the aged and deteriorated condition of the support structure was more than the bridge could tolerate.

If we learn anything from this tragedy at all, it should be that traffic MUST be controlled and not allowed to stack up on these old weakened bridges. If a repair project is under way, they MUST put a traffic control crew somewhere just before the vehicles move onto the bridge, then let only a controlled number of vehicles move through at a steady speed with no mass vehicle stop and go motion on the bridge.

If a repair project dictates that the bulk of traffic must grind to a halt, then surge ahead, then grind to a halt again and again, make those bulk traffic pulses occur somewhere other than on the bridge.

Gordon

Actually, it's 1/4 the diameter squared.

What does "pressure" area have to do with shear strength?

At the extremes, an infinitely short pin can't have enough force applied to it to shear it and an infinitely long pin can't support its own weight.

Hardly 1/5. There is a fair amount of traffic, but it's not like urban freeway traffic.

Rarely exposed to freezing, probably never de-iced, but continually exposed to sea spray.

Measures of strength such as yield strength, ultimate strength, etc, are given in units of pressure, such as pascals or p.s.i. That's because a wider structure can support a stronger force than a smaller one.

Bob Clark

I've tried to access this file a couple times over the past few days. It always ends with the lower half blank. I've tried 2 different browsers.

Firefox puts up an error message that says "The connection was reset The connection to the server was reset while the page was loading."

I finally got enough to load to see the roller connection. (The bottom 20% or so is still blank.)

Nobody has commented about it's size compared to the ladder next to it. It doesn't look as small as one of the original comments would lead you to think.

What if the rollers locked up so that the connection became rigid?

What if the rollers only locked on one side and allowed the other side to slide turning the roller pedestal around the vertical axis? or lifting one side?

I'm a EE and know the reason for such a connection from my statics course (40 years ago) but having never applied such a connection I have no knowledge of the details of the design. What are the 'gotchas'?

Plenty of corrosion around the outside (especially compared to the connections further up the arch) but what do the rivets/bolts look like?

Linear thermal coefficient of expansion for carbon steel is aobut 10 ^

-6/=B0K. At roughly 140 meters for the central span, and an environmental temperature range of well below 100=B0K, the roller would have to allow about 15 cm movement (someone please check my work. That looks like it could be contained within pictured supports.

Of course, there may be other movement to accommodate, such as settling over time and deformation under load. I have no idea how to compute that.

Someone simply asking "I'm interested in reading what your area of expertise is" should not be considered a sniper. That is a very legitimate question.

-----

Is there a designed life span of the bridge? and an expected failure mode after the expiry of this period? To me it appears a sound old structure does not materially lose its structural strength,stiffness or stability and fall off just by weathering or continous use. People get so used to seeing and photographing it and want to see something new, even if that means taking it apart.A well designed structures must be made to be destroyed after its defined/designed lifespan,if it would not serve as any sort of a city heritage or memorial.

Narasimham

Are you kidding? Everything weathers. And continuous use would wear anything down; those bridges aren't made out of diamond. Go to a bridge near you and look at it.

/BAH

I hear that DOT has now issued an alert to authorities concerning parking heavy road repair equipment on bridges while repair work is in progress (!!) There has been some reporting about this bridge swaying during its last hours. It is I admit, plain scary to estimate the longitudinal force associated with a bumper to bumper traffic line on a bridge stopping and starting. That's not a case that figures in the usual design loads, I suspect.

Brian Whatcott Altus OK

On Aug 8, 8:40 pm, Fred Lotte wrote: ...

...

The bearings that were to allow the bridge to move were no longer functional and hadn't been for many years.

The history of the bridge based on inspections outline also shows this:

Bearings have a much shorter service life than the rest of the bridge, so they have to be changed now and then, and that is before they get stuck. There is a reason, like the temperature forces, for not using rigid connections in the first place. =20

Things can get broken.

They have a much shorter service life than the rest of the bridge, are expensive and sensitive to corrosion.

When you need a sliding connection and don't have the loads from a bridge, a building, can often cheaper bearings be used, like one consisting of just two steel plates with teflon between.

--=20

Anders Lager=E5s

That 15 cm seems high to me. Assuming 10^-6/=B0K number and a 100=B0K temperature change, then the bridge would have changed by

Bob Clark

The image showing a close up of the joint can also be seen on the original web page:

I-35W Bridge Historic I-35W Mississippi River Crossing Minneapolis, MN

Bob Clark

That would be true if we were discussing a column. For a bridge hinge pin, we're effectively talking about a horizontal beam. The beam/pin has all the (gravity) load applied along a line along the top of the pin. There is no "area" to discuss with this type of loading.

Here are zoomed in photos with arrows pointing to the joints. Notice that for the I-35W bridge joint there is a severe narrowing near the top.

Bob Clark

I-35W bridge joint.

Desoto bridge joint.

Actually, materials have defined limits for yield in tension,shear, bearing etc. If a pin bearing exceeds the required limit bearing stress, its diameter is increased, in bridges, as in aircraft.

Brian W

I have not forgotten at all that it was built 40 years ago. My point was NOT to criticise the designers. It was actually the whole point of the thread: maintenance is as crucial to the longevity of a structure as the design.

My point in that paragraph was that for the FUTURE, we have to start thinking about good ways of instrumenting structures that will last as long as the structure... or whose deterioration will be correlated to the structure's. As far as I know, that is still not done, at least not in a systematic way. I'm not trying to minimize the difficulties that this may represent, and I don't know what has been done and is being researched on this topic. But it is the next step into reducing the likelyhood of tragic events such as this one.