Designing structures for intentional failure
Designing structures for intentional failure
(OP)
I'm designing a structure which, when impacted with sufficiently large force in one direction, should fail in a particular way (ie break along a particular line). I can think of some obvious ways to accomplish this, but I'd like to know if there are any bodies of work out there or similarly functioning products/structures which I can learn from first. If anyone has heard of similar applications, that would be very helpful -- I'm sure this is not uncommon in product design, etc, but I can't think of anything off the top of my head and my googling skills are failing me entirely.
Thanks a lot!
Thanks a lot!






RE: Designing structures for intentional failure
usually a sharp notch, carefully machined to ensure the final net section is as required.
RE: Designing structures for intentional failure
Also, the concept of weak beam - strong column comes to mind...but I don't think anything is intended to fail there.
Can't think of much more besides that...what is your application?
RE: Designing structures for intentional failure
How do you peel back all these assumptions when there is a certain load where a component ABSOLUTELY POSITIVELY MUST FAIL (not shouting)
RE: Designing structures for intentional failure
In seismic design, the fuse must be ductile and the other element of the structure must be designed for the capacity of the fuse and NOT for the actual computed load... that might be lower if using reduced seismic loads. !
RE: Designing structures for intentional failure
RE: Designing structures for intentional failure
It is also fairly common to see bolted joints that are designed to fail, so that the components they restrain (typically hard lumps) can move out of the way of the collision.
So far as I know there are no standards on this, but the common solutions are robust.
Cheers
Greg Locock
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RE: Designing structures for intentional failure
I have never used this particular method because I believe it is fundamentally flawed. There is no guarantee that the link on the fire side will fail before the link on the non fire side. If the non fire side link fails first, the firewall will be pulled down by the collapsing steel members on the fire side.
However, I would agree that, if all you want is a failure in a particular joint, a weak link will work just fine. Same goes for any other part of the structure. If you want something to fail, make sure it is weaker than every other part of the structure.
BA
RE: Designing structures for intentional failure
It’s no trick to get the answers when you have all the data. The trick is to get the answers when you only have half the data and half that is wrong and you don’t know which half - LORD KELVIN
RE: Designing structures for intentional failure
RE: Designing structures for intentional failure
The base of the post is designed to break away or disconnect, and a cut is made through the leading flange and web of the I-beam just below the sign panel. The cut is spliced with a perforated plate that resist wind loads, but releases under impact. Alternately, the bolt "holes" in the plate are u-shaped open slots, and the bolt can slide out under impact.
RE: Designing structures for intentional failure
Wouldn't the stress concentrations forming around a sharp notch result in a strength less than predicted by the net area? The breakaway bolts I have seen have a smooth narrow round neck but I don't recall a sharp notch.
Also to get back to the design theory...For break-away walls in the V-Zone and I recall basically using the ultimate strength of conventional materials with no explicit strength reduction factors, factored wind loads and unfactored flood loads. Most break-away walls are actually designed prescriptively (20 psf I think) to bypass all the mucking about, but there can still be complications if you want to use the engineered method so that the wall stands up under wind load but fails under flood load.
I don't mean to muddy the water, but again I don't think that design is a straight-forward process when you are using material and load standards for the opposite purpose for which they were originally intended. There are often conservative assumptions built into the formulas/coefficients that don't appear explicitly. Design for failure is further complicated by the fact that structural fasteners and anchors (Simpson, Hilti, etc) are approved by one of several methods that may be based on actual tested load, tested deflection, or and/or rational analysis.
RE: Designing structures for intentional failure
Burst discs in fluid systems, used to safely vent a runaway process (pressure excursion), or sometimes to trigger/start a process. There are many designs, some include scribed pattens on the disks. Knowing (by test) the exact strength of a given lot of diaphragm material is necessary to predict the burst pressure with accuracy, and the equations for rupture include bending and membrane stresses (i.e. large deflection solutions).