Capacity of support angle 3

[civeng]

Hello everyone,

Does anybody have a site where I can see an example of how to design or verify the capacity of an angle which is anchored to a concrete wall, and which support a grating floor. The angle would be 20' in length and there are no geometrical constraint on the size of the legs.

Thanks everyone, in advance.

 

[stanfea]

The basic design assumptions for this type of support are to design as a cantilever beam. The outstanding leg of the angle must resist the downward reaction from the grating. The anchorage to the wall is also a primary consideration.

Issues to be aware of are where the actual load is placed on the angles outstanding leg. The conservative assumption is at the tip. Therefore a long outstanding leg is not really a benefit for you. The anchor to the wall also must be designed for the significant pull out forces that arise out of the applied moment. The anchor should be as high up on the vertical leg as possible. This increases the couple length and reduces the pull out force. Using simple statics calculate the reaction on the anchor bolt by taking moments about the lower edge of the vertical leg. You must however check that the vertical leg has the capacity to transfer the forces thru it. Shear in general will not be difficult to deal with as you will likely be using at least a 1/2" or bigger bolt. I would also not use less than say 1/4" thick angles and very likely thicker (5/16-3/8") will be required. I have used up to 1/2" or more for supports of joists or other framing. This is an important detail that imo gets treated lightly.

Also check for potential concentrated loads near the edge such as equipment storage or construction loads.

Good luck
Stan

 

[civeng]

Thx for the reply Stan,

I know that I have to treat the outstanding leg as a cantilever beam, but how do I bring the uniform loading coming from the grating to become a point load on the end of the outstanding leg? Since my angle is about 20' in length, the grating is able to hold 403Lbs/sq ft, or in my case, for a 4' wide grating, the angle will see a distributed load of 806Lbs/lin ft all along the 20' length. I guess we have to find the moment which this load creates on the outstanding leg, to then find the section modulus which would finally give us the angle's thickness. Where I'm having trouble is finding the moment of the outstanding leg, what is the best way to use the linear load in finding the moment?

 

[stanfea]

The question is really what is the bolt spacing with respect to the angle capacity.

For example:
1) 1/2" thick angle may be able to tranfer the load of the grating based on 4' centers of the bolts.
2) 1/4" thick angle may be able to transfer the load of the grating based on 2'-6" centers of the bolts.

It is a moving target. Basically I would suggest picking a bolt size of say 5/8". Determine the pull out capacity. Say the capacity is 3000 lbs. Assume a 4" vertical leg, say gives you a couple length of 2.5". You have the capacity to resist 3k x 2.5"=7.5 k-in. If the outstanding leg is 2", then by equating the moments the force at the tip could be say (2.5/2 )x 3000#=3750 #. If your grate load is 860 plf then you can support 3750#/860plf=4.36 feet of grating. That is your bolt center. Now that doesn't tell you if the angle is thick enough, it simply gives you the force to apply to the angle. Now design you angle for the 3750# distributed in a reasonable fashion. In programs like Algor and Ansys I can tell you the stress distribution readily, by hand you need to make some conservative assumptions. In the end if you believe 4'4" works you may say "bolt centers = 3'6". This is a sound approach imo.

Stan