Point Load on Reinforced Masonry Wall

[asixth]

Hi Guys,

I have a wide flanged beam framing perpendicular into an internal masonry wall. This beam is a rafter and sees some axial force due to the wind loads travelling through the roof system and causes out-of-plane bending in the block wall.

I am planning on putting a steel mullion in the block wall to strengthen the masonry in out-of-plane bending.

Does reinforced masonry exhibit any punching shear type behaviour such as reinforced concrete and if so, can anyone direct me towards a good design reference?

 

[csd72]

Good question,

I would expect it to behave somewhere between reinforced concrete and a clay masonry wall.

That said, there will be negligible two way action in the wall as the face shells will provide a plain of weakness and any horizontal reinforcement will be central. So check it for beam shear in one or two cores with maximum reinforcement and if that doesnt work then you will definately need to connect directly to the steel mullion.

Other option is to provide a horizontal channel along the wall to spread the load to a wider width of wall.

 

[rlewistx]

I can't quite picture what you are doing here. I would ask how the wall is braced. It is either braced by the roof or by some other means. If it is braced by the roof and you are moving the roof then you have a problem.

Typical the masonry wall spans vertical for out of plane forces and is braced by the roof/floor or some other means. Lets say it's the roof. The roof is typically a diaphragm that spans to some type of bracing parallel to the force, either a frame or shear wall. If this is so then you dont' have punching thru the wall. If you are bracing the roof by the wall then the wall must cantilever up from some fixed support or must span horizontally to some support. I would think that whatever you need to transfer the force either horizontally or vertically in the masonry will will be more than adequate for some type of punching shear. You have to make sure you anchorage is sufficient.

Think thru your load path again.

 

[DaveAtkins]

I agree with rlewistx. Why are you using a CMU wall in weak axis bending to resist roof diaphragm force?

DaveAtkins

 

[hokie66]

Agree with others if this rafter is at the top of the block wall. Not a good idea to take this type force in cantilever action on a block wall. But as you said you were going to use a mullion, I pictured this rafter framing into a wall which continues up, so the bending would be like a simple beam rather than a cantilever. If that is correct, and you use a mullion, problem solved.

If you decide to take the horizontal force component into the masonry, I don't think masonry codes typically address punching shear. However, if this is a fully grouted wall, I see no reason why you cannot use the same logic used in concrete codes to check this.

 

[msquared48]

What does the other end of this steel rafter frame to?

Any chance of taking out, or cancelling out the lateral kick there?

If youcould, then the beam could be supported biy either flat bearing plate on top of the wall or in a beaqm seat, or a vertical plate anchor-bolyed or after-set bolted to the grouted wall.

Mike McCann
MMC Engineering

 

[asixth]

The building is rectangular in plan dimensions, two block walls and two concrete tilt-up walls.

There is a mezzanine level which extends through the roof frame so that is the reason for discontinuing the rafter.

I admit, conceptually, it is not the most efficient way of doing things here, but unfortunatley that is out of my control now.

Thanks for the positive replies.