This building was leased to this company that stores sheetrock about 1-2 months ago. In this amount of time they have managed to do considerable damage to 3 other columns as well (not as bad). They are in the process of purchasing the protection for the columns but have yet to install. The damage that you see here was done with the fork of the forklift truck.
I was amazed that they pulled the forklift truck out. I would have just left the truck there and got out ASAP. They probably caused even more damage pulling the forklift truck out.
WOW. I often tell other engineers that I wouldn't build a building without seeing that it will stand minus columns under serviceability loads.... Guys these are great photo evidence of why I should keep listening to my gut!
Any more out there?
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
Unless I'm mistaken, the first may very well have been greatly aided by concrete filling. It's a hollow structural section, right? But then the load might have damaged the floor or potentially the frame (doubtful, the roof height looks to be significant).
That said, the second column failed where the concrete filling ended because W sections (I-type of any description) cannot be concrete filled, and the base protection present only helps the area it surrounds. The shear load due to a point impact is (theoretically) uniform and continuous through the section. Barring secondary deflection effects possible over long distances, the shear will cut through whatever point in the member has the least shear capacity. And no, it won't be the first location with less shear strength than the shear caused by the applied load because there must be an interaction with the point of support/restraint to enable the shearing. Weakest point, every time, or simply the closest location in a case where the section has uniform shear strength through the weaker area (as seen here).
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
there are many ways that a building can stand up under service loads after a collapse like this. The portal frame does not necessarily need additional strength as the collapse could be prevented by bowstring action of the purlin/truss members.
Definately is a good idea to consider potential loss of an individual column but alternate load paths is generally the most appropriate manner to do this.
csd72: I appreciate the comment on alternate load paths, however I'm well aware. I didn't say I'd increase the strength of my portal frame, or anything about portal frames actually... As you say, alternate load paths are typically the most economical, but are often over used; In my opinion most engineers do not appropriately account for dynamic effects when relying upon alternate load paths. That said, your post was still spot on. As a matter of fact bowstring action and the removing fly braces because of purlin effects are two of my favorite design tricks.
RonRoberts: Point take, however it was no where near my longest post. Feel free to ignore my post, but personally I perfer to read longer posts. They're a great way to get insight into another engineer's thinking.
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
Sure thing apsix; Design procedures by the Heavy Engineering Research Association (NZ) explain that most fly braces used to restrain the bottom flanges of rafters are not needed if your purlins are greater than half the depth of your rafter section, connected to cleats passing across the top of your section with two or more bolts and full depth stiffeners are provided each side of the web. There is a paper explaining the more intricate details that I can post if you want.
Given that this describes a very typical type of construction, this is a very useful design trick!
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
The forks of these trucks were pretty substantial. I imagine that once the fork pierced the wall of the column the fork acted like a wedge applying tremendous stress to the column wall. As some point in time a sharp corner or crack formed. Since I had to take FEM in graduate school I know that the stresses at sharp corners or cracks are tremendous. These tremendous stresses led to the crack propagating around to the other walls.
This is just my theory on why the damage was so bad.
