Steel angles to support new opening in existing CMU wall

[CANeng11]

For new openings in existing CMU walls, we typically use two steel angles above the opening, inserted into the mortar joint and extended a distance past the opening on either side. We will then have 2 vertical steel angles on either side of the opening from the horizontal angles to the bottom of the opening. All of these angles are bolted to the walls, with either through bolts or hilti bolts with screens for epoxying in hollow core.

When bolting these angles to the existing wall, should we be concerned with edge distance? If we are using a 4x4 angle, we will probably only get a couple inches of edge distance.

Also, just wondering people's thoughts on our general detail. These are typically non-load bearing walls.

 

[JAE]

We do this detail. The bolts are only there to hold the angles in place so no real calculated load on them.
So small bolts as high up as you can get them and not too many.

 

[MIStructE_IRE]

I’m having trouble following this...its late for me! Any chance of a photo or sketch?

 

[XR250]

Without the bolts the angles want to rotate away from each other. I have used this detail but add straps across the bottom to tie the angle together. I typically do not use bolts

 

[JAE]

OK - probably we aren't on the same page here. When we use two angles we cut in horizontal slots into the wall and slip in a horizontal angle leg into the slot with the other leg vertical on the face of the wall. If you do that on both sides, the two angles will be loaded on their horizontal legs and each angle will be induced to rotate INTO the wall. So no bolts are really needed - we usually call for full grout in the small gap between vertical leg and wall face.

 

[XR250]

@JAE,

The angles can still rotate away from each other w/o bolts. The top lip will be braced by the CMU but anything below that is free to pivot around the point (CCW for the right angle). The only thing preventing that is the torsional resistance of the angle reacted thru the end connection.
Probably why these work well in practice is that they never actually see any load as the CMU acts as a deep beam to span the gap.

 

[JAE]

I see what you are saying - the horizontal legs would have to rotate and slide outward, which might be very hard to effect due to the downward load (friction on the leg) and the pinched condition at the ends of the angles.

 

[XR250]

Counting on them being pinched may be a stretch. Maybe in new construction.....

 

[JAE]

Well, as they begin to rotate, the eccentricity of the wall load on the angle goes way down so the inducement to twist is reduced.

The shear center of an angle is near the elbow, which is where most all of the load is applied once the angle moves just a tiny bit.