Yea, but it was from one of the engineers who DESIGNED it lol

I agree w/ you...but from my understanding (or at least what I've read to be the leading theory), it's the hot temps from all the fuel that caused the structural failure, not the impact itself.

Dom, you went to college?? J/k man. But for real... I'm now putting my foot in my mouth....

And what you said in the other post makes sense...the garbage truck driver prob didn't notice he took out the pillar at first, and kept on backing up, pushing/dragging the entire structure along w/ him for a bit.

 

holy sheep **** damon ! Time to go visit martin i guess.

 

There's the problem, an engineer crunching numbers for each individual factor rather than the incident as a whole j/k

Now, let's break it down and look at it in seperate factors: If plane in question struck tower head-on in a deliberate attempt to destroy it but did not explode, would the integrity of the structure be compromised? Probably not. If tower in question caught fire and burned for length of time before collapse, would the integrity of the structure be compromised? Maybe, maybe not.

Now, let's look at it as it really happened. Combine these 2 factors together and you see why the collapse of the tower(s) was inevitable. OK, I'm done, back on topic.

 

I agree with scotty; I'll at least comment that based on the structure the designer never took a statics class. If you look at the way it buckled, it collapsed in the plane that had no triangulation. Big surprise. The lateral (if you want to call it that) stability of the structure depended only on the rigidity of the joints (the T-joints between the beams and the roof structure) rather than loading along a rigid beam. The close-ups clearly show that the failure was at these points.

Now, that doesn't mean that I advocate lawsuits or agree that the designer should be held at fault for the bulldozing of the structure by a trash truck, so don't flame me on that.

 

This is a simple structure and I'm sure it was built to code, so the fact that the builder may not have taken statics is irrelevant. It buckled because lateral forces were applied to the top of the structure rather than the vertical supports. The carport was not struck at the base where the structural rigidity is most crucial, it was hit at the roof (in a concentrated area) which under normal (or abnormal) circustances wouldn't require over-engineering to survive any lateral forces applied to the entire roof structure as in high wind situations.

 

On a side note, do you know how expensive things would be to build if every situation was taken into account? The builder probably followed code down to the number, but who would have thought a 5 ton trash truck would crash into his carport. If every situation should be taken into consideration, how come Mazda didn't design the roof of the car to not sustain damage from a carport that might fall on it? Did you guys ever think of that? Hmmm... well that might just add more weight to the car and perhaps drive the cost of the car up, but hey, at least Mazda wouldn't have to worry about lawsuits from sorry M.F.'s that look for every excuse to file one.

 

Don, I'm not trying to get smart here, but seriously, I thought all car manufacturers had to make roofs strong enough to support 2 - 3 times the weight of the car, in case of a rollover... Of course, given a high-velocity rollover, the momentum could very well be enough to completely crush a roof, but in general, I think the roofs are def. designed to hold up to a great deal of weight.

 

The RX-7 would have protected its occupant in that case. Notice that the cabin was not comprimised.


My brother lives in an apartment complex, I'll pay more attention to how his carport is built next time I'm over there. No offense meant, HDP, but from the stories that my father has told me, some architects and builders put very little forethought into the things they design and build. It could be that the architect designed things proprely, and the builder said "it ain't gonna need that much cross-bracin' to stand up!! Let's save $20 on nails and buy another twelve-pack..." Other times it's the architect saying "Those support beams will ruin the artistic statement that this piece is intended to convey. It looks so much better without them..."


They both try to get away with crap like this quite often, otherwise there would not be inspectors who are paid to ensure that things are built safely. I'm not saying that you personally would do this, but the kind of people who do little jobs like this would be likely to.


Sorry for beating this to death, Damon, I hope your car is fixed soon, and the bodyshop does a great job. I'm glad no glass was broken.


And I never said anything about lawsuits. I dislike most lawyers just as much as the next person who works for their money...


-s-

 

OK, this is getting old... true the 7 would support the weight of a rollover because that's what it was designed to do but would it survive say an girder from an elevated highway (remember earthquake of '92)? My point is, it seems everyone is expecting the carport to survive forces it wasn't designed to... Damon even stated it has stood through several strong storms where as other surrounding carports did not... that should have been the end of discussion as far as it's structural rigidity. It did exactly what it was intended to do and survived. OK, this time I'm really done with this, even if I have to put you guys on ignore


BTW, scotty305, I never said you had brought up lawsuits, unless your initials also happens to be M.F.

 

WOW! Cant believe I missed this thread. So sorry to see/hear about this Damon.
On a lighter note... Who the hell has trash day on a Monday?

 

I'm an engineer too guys and it's really pretty simple. The carport has been there for at least 10 years and I have seen other carports just like it on the property survive being hit by the people parking under them. I have seen individual posts hit and buckle without the structure failing.

In this case the garbage truck backed up into the roof of the carport and continued onward. This first bent every beam at the ground because the roof of the structure is in fact stiff enough that it didn't just fail. The beams continued to bend until the end of the structure opposite my car struck the Ford at the end. Once the structure was collapsed against that car it could not bend any further because the car essentially was propping it up. Because the truck continued to roll back the posts near the truck then began shearing off at the ground. The roof structure could not move any further because one end of it was being propped up by the Ford and the other end was being pushed back feet at a time by a large vehicle, therefore the roof finally buckled and collapsed behind my car.

It's quite clear that nobody but the garbage truck driver is responsible for the damage to my car and the structure. The insurance of the city owned garbage truck is paying for everything.

 

I'd have his License checked ?? or if he has one or the correct one ?

He was probably on the cell phone and drinking his coffee or eating !

I hear one of the best benifits of being a garbage man is : ALL YOU CAN EAT !

 

Another benefit: One man's trash is another man's treasure.

 

I got an extra roof, pm me.

 

I've been working as a structural engineer for over 4 1/2 years (taking my licensing exam this friday to get my PE license). Anywho, DamonB's assessment is more or less right. First off, a bit of basic terminology that always gets me when I hear laymen speak: a column is vertical, a beam is horizontal.

Second, an architect had nothing to do with this carport, less maybe he picked it out of a catalog. If he did it would look a lot better than it does! It is simply a pre-engineered carport. It is not made from wood, though it looks as if it was some 2x members sistered on to the columns. It's made from light gage steel C-shapes, which are relatively week compared to say, structural steel.

Those that pointed out the lack of lateral bracing are spot on in the assesment of the failure. The connection at the top of the structure has no diagonal bracing to provide lateral resistance to loads in that direction. The lateral strength of the building in the direction it failed is completely dependent on the moment resistance of the beam to column connection. For a light gage structure it is very difficult to get a good moment connection simply through the use of common fillet welds.

The truck backed into the structure, and since the beam to column connections were essentially hinges (that is how I would model them) the structure leaned as it did, bearing upon the escort. If the truck continued to back into the structure, or even if it didn't, the structure also failed at Damon's car as the beams perpendicular to direction of load failed in torsion (ie ringing out a rag, toruqe, a twisting failure). This is evident in the photos as you can see a twisting of these beams, which appear to be two C-shaped light gage sections welded together, another shitty design.

As far as design loadings, the main forces these things are designed for are wind and gravity loads. Gravity loads are the self the weight of the structure and a code imposed live load, which would account for snow accumulation, workers, etc. Wind loads can act in several directions....uplift, or a suction force on the roof, a downward pressure on the roof, and more importantly, in this case, laterally on the roof. It is unlikely that they are designed for impact of a car. It's possible though. Given some rough loading, assuming a 20 psf wind load, the structure was probably designed for an equivalent lateral point load of about 250 lbs. This is based on the area that the wind has to blow on, which for a structure of such a low profile isn't much (I'm assuming 12" x 12').

I'm surprised that it doesn't have more lateral resistance in the direction that it failed. But this is typical of structures of this type; they are often designed with very little redundancy and if one component fails it often sets of a domino effect, as one component relies on every other link in the chain. Pre-engineered buildings, often used for warehouse, car shops, etc, are often the first to fail under severe conditions because of this same fact.

I don't want to get into WTC discussions but in short: way too much heat, inadequate fireproofing, steel yielded at joist-columnn connections, joists (floor) fell, causing subsequent floors to fall, columns which were supporting extra load because of plane holes are now "taller" (bracing by floors removed), the columns buckled, the structure fell. It's not that perplexing to us engineers, given the conditions presented to the structure. In all honesty, the terrorists chose a very brillant, effective way to bring the towers down.

Right on.

 

what a bitch, i feel so bad for you, but you should be counting your lucky stars that you dont live in australia (the land of the stupidly over-priced cars to protect the over-priced local market, which by the way are fundamanetally imports anyway!) an fd in such condition would set you back about $40,000... but what a pain in the ***... good luck on gettin her back to original

 

Sorry, not to get off topic (although it has pretty much been beaten to a pulp ), but I seriously doubt that the terrorists knew the exact results of what was going to occur after the planes initially crashed into the towers. It is much more likely that they felt the towers would simply buckle and the top half would burn and/or fall off, not the entire structure caving in upon itself.

OK, back on topic...

 

You really should look into the "depreciation of value" on your car after its repaired.

 

Didn't say nor mean to imply that they chose this method intentionally knowing it would cause the given results, just trying to put out my opinion, as a structural engineer, regarding the method of attack.

Right on.

 

Read and think about your two statements here.
OK, back on topic...