Bracket Connections

[davetrotter]

hi, ive devised a system whereby i intend to hang peripherals weighing approx 400kg from a steel bracket(see sketch). My concern is the possibility of the screw fixings pulling out of the wall. Can someone advise what loads are generated by this arrangement? my colleague suggested only downward loads are created and so pullout from the wall isnt a problem, but im not so sure.

thanks

 

[drawoh]

desertfox,

As you noted, you assumed a rigid bracket. You also need a rigid wall. If these are not infinitely rigid, you have a statically unsolvable structure. Either the OP needs to verify that everything is very rigid, or they must make worst case assumptions about how the load would be distributed.

I have never had to solve this problem. Would it be safer to assume that only one screw is taking all the load, possibly the one at the bottom?

JHG

 

[EspElement]

I think with the info that desertfox pulled up (im not making it out to be much because i dont understand some of the numbers they pulled up) but they use 3 or 4 different senerios on how it could fail.. also, to ensure ur bracket is rigid could you do some beam calcs on it? also, i believe it was said to be attached to drywall.. so the anchors that are used need to be rated to the pull out force desert helped us find

 

[desertfox]

Hi drawoh

Yes I agree you would need a rigid wall and yes any flexing of the bracket or wall would change the calculation, however with information given we needed to start somewhere and that was a first stab,I did feel that the bracket would flex, so I said it would probably be a bigger problem than the fixings and I believe others suggested stiffening the bracket with a rib, which would then bring it closer to my original bolt calculations.
If a single bolt was placed at 20mm up from the pivot point then a quick calculation shows that it would see 981N on the original assumptions,I think you would agree that given the length of the vertical leg that only one fixing whilst in theory possible would not be very practical, also the more bolts you have in the vertical leg reduce the amount of bracket flexing in the plane of the vertical leg.
Have a look at the example give at this site that I posted earlier:-

http://school.mech.uwa.edu.au/~dwright/DANotes/threads/fatigue/exampleB.html#top

regards

desertfox

 

[Ltwine]

If the L bar is too flexible, it will rotate about the knee and wound up as a straight bar. At this time, the nails take the shear only. If the wall is too soft/thin, the whole thing will falling off the wall.

Without look into details, I think desertfox has performed calculation based on rigid wall & bent assumptions.

 

[EspElement]

I would take the inertia of the falt that is having the pressure put on it, and use a beam calc that is fixed from one side and not on the other.. use the distance load in center (or distance from fixed position) and determine how much deflection there would be. if you add a rib it will strengthen this bracket tremendously.. u can prove this by building your own beam.. (I use the calc in the mechinerys handbook)