Bearing capacity of an angle iron 1

[GreenJug]

Hi all,

I attached a sketch (side view) of a problem I'm looking to solve. Blue represents the beam, red is the angle iron, and black is the concrete slab and wall. It consists of a set of beams that extend past the slab and are flush with the opposite concrete wall. To avoid the beams being in cantilever I am planning on bolting an angle iron into the wall. The angle iron has 1 row of 1/2" bolt holes along the length of the plate. I'm planning on having two bolts for each angle iron. How would you go about determining the bearing capacity of the angle iron in this case? All information about angle iron dimensions and steel grade are available.

P.S. to avoid the Angle iron "flange" being in cantilever, I will put a small 2" thick piece of wood or a small layer of plywood close to the wall so the beam would be bearing directly on the edge of the angle iron. In this case, could one assume that the angle iron will be acting in pure shear?

Thank you for your time.

 

[Enable]

Extending the angle iron further off the wall would usually not be a preferable solution. You'd now have to resolve the force via bending in the fasteners, which seems like a bad idea. Also, you're probably limited by necessary bearing area of your beam which will exceed the angle leg thickness.

What I would do is add stiffeners in the angle underneath the load (web of your beam) and near the anchor locations. This is usually sufficient to alleviate flange bending concerns. Then I would resolve the eccentricity via a force couple between the fastener and a triangular compression distribution at the base of the vertical angle leg. You would then check the anchors for combined shear / tension: (Tf/Tr)^2 + (Vf/Vr)^2 <= 1

 

[GreenJug]

Thank you for the response @Enable. The bearing length of the angle iron is 6" and our beam width is about 3" so it will easily be laying completely on the angle iron. The angle iron would still be flush against the wall. I modified my sketch to show where I was thinking of putting the piece of wood (in brown). Right next to the wall on top of the angle flange with the beam sitting on top. That way, it seems to me that the fasteners and angle iron would be acting in pure shear, wouldn't they? I quite like your idea of having a stiffener in place.

It's quite possible that the angle iron connection itself would be the weakest point in the system. I.e. block shear failure. What do you think?

 

[dik]

Critical is the clearance from the beam to the wall. This should be minimised to reduce the moment in the support angle. There was an earlier discussion on the site about the location of the load. Different engineers use different locations of where the load occurs. In addition, it is likely less costly to increase the thickness of the angle than to add stiffeners.

Using stiffeners depends on the magnitude of the load. The AISC has an article in their steel stair guide that show the distribution of the width of the angle that can be used for resisting the load (you may want to look at it). In addition, for the flexural resistance of the angle leg, you should use the plastic section modulus, not the elastic.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

The small block of wood could mean that the bearing strength of wood may define the strength of the connection. Omit the small block of wood and design the angle for the expected load, assuming the beam reaction is centered on the contact area between wood and angle.