strength calculation - need point of view 1

[kingnero]

would like to fasten the frame (see attached drawing) to a concrete block.

But in my calculation, I don't need the height of the pillar. I am overlooking something. Can someone take a look at it, and tell me what I'm doing wrong?
btw, this is my responsability, this information I receive will not be used for anything that might result in personal injury.

Excuse my english, I'm european (belgium) hence the dimensions and weights are also in kg and meter.

My point of view: the weight at the hook will result in a momentum: 250 kg * 9.81 m/s² * 3.5m = 8600 Nm

Will this momentum result in a force at the two opposite bolts: F = 1/2 * 8600 / 0.3 = 14.333 N ?

Tensile area of a Metric 16 bolt = 157 mm²
stress in 1 bolt = 92 N/mm²
yield stress of such a bolt (grade 8.8) is 640 N/mm².
stress should be limited to about 1/3 of the yield stress (correct?), but still 92 N/mm² < 640/3 (213) N/mm², and I still have a safety factor of bigger than 2.

Can anyone tell me why I didn't use the height of the pillar? Where did I miss something?

attachment:

 

[hokie66]

desertfox,

Assuming the base plate is rigid does not make the calculation of bolt size conservative. A rigid base plate gives a longer lever arm, thus a smaller bolt force.

 

[desertfox]

Hi hokie66

I don't agree with you there, when you have two rows of bolts the furthest row from the pivot carries the larger load and if you assume all the load to be transferred to the bolt which would occur in a rigid baseplate then that is conserative, in fact both our original posts assume that the base is rigid. Have a look at the method in my attachment the furthest bolts from the pivot carry the largest load unless you believe my method to be incorrect?

desertfox

 

[kingnero]

base plate thickness is 15 mm and braced with four small "wings". see attached drawing.

 

[desertfox]

Hi kingnero

I cannot see your drawing

desertfox

 

[swearingen]

Actually, assuming that the plate is not rigid and that the tipping point is at the edge of the vertical member is conservative when it comes to anchor design and gives you a good first pass at what your anchor rods should be. Trust hokie on this one - he's a structural guy that probably does a couple of baseplates every day...

Think about it - the moment arm from the tip of the plate to the far side bolts is greater than the moment arm from the edge of the vertical post to the far side bolts. The greater the moment arm resisting a given applied moment, the less the force in the bolts - PA is greater than PB in my enclosed sketch.


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[kingnero]

@ desertfox (and others): pdf-drawing attached...
@ swearingen: I understand the principle. therefore I attached the drawing, as I think it will not be easy to determine the correct lever arm.
plate thickness is 15 mm and braced, so will be rather rigid.

I will take the shortest lever arm to make sure my calculations are on the safe side.

 

[desertfox]

hi kingnero

You might like to look at this reference site calculating the bolt loads assuming a rigid base plate tipping at one edge as my earlier post.

http://www.structuremag.org/Archives/2008-1/C-Codes-and-Stand-Carrato-Jan08.pdf

Also I think your base plate is to thin, however here is a link to a calculator that may help, but its to Canadian standards:-

http://www.webcivil.com/baseplate.aspx

desertfox

 

[MartinSr00]

Because you lack a horizontal component to the load, the height has no effect on the moment.

But is that true? Can you always ensure that there is no side loading at all during use? Any seismic loads?

Probably minor, but maybe not negligible.