Simple Statics Problem?
Simple Statics Problem?
(OP)
Hey everyone. How structural engineers would treat this problem if they had to determine all forces on all fasteners of a column loaded in the following way on top? (ignore weight)
h=w=10 in. a=b=1 in.
I've consulted several engineers, and each had a different way of resolving a force and of selecting a point of rotation, and in the end the answers of loads on the fasteners were very different. (some ways include prying, others don't) So what would you do?
h=w=10 in. a=b=1 in.
I've consulted several engineers, and each had a different way of resolving a force and of selecting a point of rotation, and in the end the answers of loads on the fasteners were very different. (some ways include prying, others don't) So what would you do?






RE: Simple Statics Problem?
BA
RE: Simple Statics Problem?
If you have some oddball geometry that you're not likely to see again, you have two choices. If it's a NASA project or something else very critical or expensive, you can spend a lot of time doing finite-element analysis and/or testing of models or full-size specimens. Or, if it's not worth that expense, you can come up with the best analysis you can, based on whatever approximations you feel are appropriate, and work it from there. In that case, the approximations made will vary greatly, as will the results, and that's what you're running into.
Note that it may be worthwhile using some more standard connection detail simply because a better analysis is available for it.
In summary, I'd probably work it the way one of those other people did.
RE: Simple Statics Problem?
Need lots more info.
RE: Simple Statics Problem?
For prying action on steel elements, we assume yielding of the base plate element (angle leg in this case) and verify that the steel will bend and deform before the stress on the fastener can be exceeded. If everything in the connection is brittle then the strategy is to detail the system to minimize load paths (add stiffeners to the angles and, to prevent prying, washers between the base material and the column) and increase the safety factor. This is appropriate when detailing steel for fatigue loads.
RE: Simple Statics Problem?
RE: Simple Statics Problem?
1) add a stiffener or two to the angles.
2) toss a washer on each bolt between the angle and the concrete (Teguci).
I doubt that either measure is truly necessary however.
For the design of the angle, I would replace the triangular stress distribution with a line load out at the toe.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Simple Statics Problem?
RE: Simple Statics Problem?
RE: Simple Statics Problem?
Often in engineering you need to make simplifying assumptions. Would an extra 1/8" wall thickness be so detrimental?
RE: Simple Statics Problem?
Easy? Pfft. There was nothing easy about it. It was the result engineering judgment honed over a couple of decades of professional practice my friend. I assumed that the shear would go 100% to the left angle because I see that as the stiffest load path, particularly as I suspect that the "box" will be thin a walled piece of equipment that would make the shear connection to the angle on the right hand side comparatively flexible.
That said, if you wish to be more conservative, simply design the bolts in the right hand angle for the tension that I showed and the full shear associated with force F. This should be of little consequence for the design of the bolt or the design of the angle. If you're close to the edge of your concrete, the shear force may need additional attention as it pertains to concrete breakout.
I would never use the application of the force F in the right angle to reduce the bolt tension as I would deem that unreliable and unconservative. Remember, not all of your members will be designed based on the same force distribution here. A model that is conservative for one component may be unconservative for another. In the absence of knowing the "true" load distribution, we compensate by considering multiple distributions and applying them conservatively to the particular components under consideration.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Simple Statics Problem?
Right now i'm torn between three methods.
1) The one outlined in this forum
2) I've been told that we could take the whole column+angles attached as one system, then resolve the moment generated by force by dividing it by the distance between two concrete anchor holes. So in my case w+2a=12". And this approach neglects prying completely. However they'd use half the shear and entire tension on the concrete anchor on the right. (since shear is less detrimental to concrete this design would win with respect to anchors) (however im not sure how safe this is....)
3) I've been also proposed alternative solution where you divide the moment by the width of equipment and then use the resulted T as Tension on concrete anchor bolt. + add shear that would be half (F/2)=(1000/2)=500 lb (Because they want "to be more efficient"this load would result in smaller anchors then the one in method #1)
=(
RE: Simple Statics Problem?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Simple Statics Problem?
+ angle has to be super stiff
RE: Simple Statics Problem?
RE: Simple Statics Problem?
Rigid angles... rigidly attached... to a rigid body. It checks out so long as you're confident in the assumed rigidity of all these rigid things. If you're just holding down a sheet steel box, then color me skeptical.
The first draft was actually on the palm of my hand. I thought that looked desperate, however, so I borrowed a pen and some garbage.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Simple Statics Problem?
BA
RE: Simple Statics Problem?
RE: Simple Statics Problem?
I think I'm going to do F*h/w to get pullout and apply it to fastener 1 (its a bit more conservative ...say to deal with some tiny prying)
The shear on fastener 1 will be F/2.
For fastener 2 I will apply Pullout=F/2 and Shear=F*h/w
(I will have some equipment inside that box, so the weight will counteract around 50% of overturning force. So (F*h-W*(w/2))/w will hardly ever be larger than F/2 for pull-out on fastener 2)
However, in both, yours and my methods: would you just toss in a random thick angle and say its thick enough?
And if not, then would you take fastener 1 forces and resolve them into T,V,M about the fastener 2 and then check the angle thickness and area against failure modes such as bearing, shear block, maybe buckling too?, etc.? Cause the way we assigned our forces, we'd never get a balance of Moments on the angle, hence cant really draw a moment diagram, hence cant really decide where to choose the location which needs to be checked for combined Tension, Shear, Moment)
RE: Simple Statics Problem?
Unless these materials are made of something other than steel/aluminum or if your force is something large, I would go with the minimum thickness for an angle/tube and check that for adequacy, more often than not it'll probably be fine. The things I could foresee causing a problem before anything else is bolt hole bearing / rupture / bolt shear for the two angles anchoring the angles to the wall, so that especially should be considered. (Basically, everything that has anything to do with the fasteners)
RE: Simple Statics Problem?
BA
RE: Simple Statics Problem?
Mike Lambert
RE: Simple Statics Problem?
RE: Simple Statics Problem?
You talk about "when T wins or V wins"? Why not look at the equilibrium of the rigid angle in order to determine whether or not a prying force exists?
BA
RE: Simple Statics Problem?