# Structural Problem...help needed

I have oval aluminum extrusion bolted to circular plate (Aluminum)
using 4xM6 bolts. The Circular plate is bolted to the floor and
aluminum extrusion stands 8 feet tall. I need to find out how much
impact load the system can with stand.
Feel free to ask any info if you need.
Please pour in with the solutions.
VRG
Rough, conservative (?) response: for a side force applied to the column at height H in feet and a base distance of B in feet between the two closest bolt holes And an allowable force on one bolt of 3000 lb The allowable side force at height H is 3000 X ( B / H ) lbs
The column or base might crumple first, no doubt....
Brian Whatcott Altus OK
1) Do you want dynamic or impact? ("dynamic" is added force from accelerations which assumes even energy distribution and can be solved by force analysis; impact is rapid input which results in uneven distribution of input energy which requires wave and shape analysis for energy-density analysis.)
You really want impact capability? - that means energy-density engineering analysis. That analysis beyond the capability of most engineers you'll find on an engineering newsgroup for three reasons: anyone who knows how to do it isn't going to take the time for free; they don't want the crap that comes because the answer doesn't fit force-based theory of statics 1; and you can't buy it in a FEA software program
2) Even if it is "dynamic" that you mean - The capacity depends on the mounting, both from determining the load and the shape-dependent stress; and the shape Just a few of the questions which go into the answer of what can it "stand":
Is the floor rubber, or wood. or concrete, and where are its structural supports? ( a stiff floor creates more stress in the frame mounted on it than does a thin "soft" floor - the peak force is less when the system is mounted on a rubber bungie cord than welded to battleship armor.) What is the bolt pattern and is it symmetrical? (small has different loads in transfer than large) What is the shape of the extrusion? (can't even start a stress analysis ofr a shape without having the dimensions) How big and how thick is the circular plate? How big and how thick is the oval plate, and what are its major and minor or axes? What are the torque levels of the bolts? Any old tight, or torque-spec'd? (goes to determining if the plate-oval is effectively one member or two)
3) What is the immediate input? It's coefficient of restitution, its energy absorbing ability, and its thickness? Is it rubber which nearly doubles the local calculated force, or impact foam which delivers x1 of the dynamic? Direction and location of input. End -on, or across the extrusion axis? Large mass, or small mass
4) Aluminum comes in strengths from 10,000 to 75,000 psi. Even if one had all the other necessary information, then when an answer is found, unless the aluminum is known, it has an order of magnitude in error.
You will not get any answer worth using on a NG.
So just go back out in the barn and test it and then put on a big safety factor. Or hire a consultant who knows.
Need way more info about the system..........complete description of base plate geometry, complete geometry of aluminum extrusion, material properties of the base plate & extrusion., complete geometry & material properties of the baseplate / extrusion connection, complete geometry & material properties of the floor system.
Description (complete geometry & material properties) of item delivering impact to the extrusion. Concrete truck, a guy on a motorcycle, a human body, a luggage cart?
Description of desired results from impact. Do you want to withstand the impact & have the extrusion /
baseplae side of the impact remain elastic? Are we talking about a crash loading? Survive & work or survive & not bust loose?
Think automobile accident & a car bumper system..........
Answer is obtainable but it's not going to be a delta= P*L^3 / (3EI) type simple calc
How important (\$'s) is the answer? How close does the answer need to be?
cheers Bob
"BobK207" wrote
Important, and related, questions. If the OP wants to know his answer within 10% because failure would cost \$1 million, it will cost him >\$1K to find out.
But, suppose he only wants to know how fast a baseball would have to hit the top of his post in order to knock it down, and suppose a simple high-school-physics-level model says the answer is 500mph. Is it possible that the \$1K professional-quality analysis would say, "No, no, the answer is only 50mph"?
-- TP
" snipped-for-privacy@gmail.com" wrote in news: snipped-for-privacy@p79g2000cwp.googlegroups.com:
If you can work out the stiffness at the point of impact (and you can), and the stiffness of the impinging object, and you know its mass and velocity, then you can start to build a relatively useful model of a dynamic impact event.
But you will very quickly run into enormously complex issues.
OK, that was the difficult bit.
Slightly simpler is the response of your structure to a given force function. Not much simpler, in the general case, so to make it manageable you need to give some idea of the expected failure mode.
Cheers
Greg Locock
Loks like way too little info. What are the dimensions? What are the materials? Is this going to be just one impact? Where on the extrusion? A steady force, a moving vehicle bumper? or a whack with a baseball bat? How many impacts over what time? What if the impacts match the resonant frequency of the structure? How close does the answer have to be? How close together are the bolts? How many bolts? Lockwashers? At what temperature? For how many years and how many temperature cycles? What about corrosive effects from precipitation, air pollution, salt? Is human safety or are large capital losses involved? All important questions!

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