Steel Beam Masonry Wall

[Kh777]

Hi all

Fairly new to this forum but I have a general question and I was wondering what others normally do. In the UK at least we have older properties that have roof ceiling joists connected to sloping rafters and the ceiling joists can be higher than the wall. Therefore in a loft conversion when a steel beam is introduced how would uou detail the steel bearing? We could cranked the beam here but how would you deal with the horizontal force component at the support? Thanks all

 

[jerseyshore]

Do you have a sketch or drawing that shows the condition you are referencing?

 

[GeorgeTheCivilEngineer]

Usually span the steel beam gable to gable so a raised tie wouldn't be an issue. New floor joists span parallel to the existing ceiling joists (or replace them but that increases disturbance to the room below - often a bigger problem as these are done in occupied houses).

If its a hip then changing that to me gable gives more usable floor area and bearing for the support steels.

I've done cranked beams (one in my own house). With fully welded connections, some stiffeners and slotted anchor holes then deflection is manageable.

 

[kipfoot]

If I understand your questions, you'd analyze the 'cranked' beam as a simple span (with a pin/roller) and there is no horizontal reaction at the beam bearing.

 

[Kh777]

Thanks all. There are instances where I cannot go gable to gable and sometimes the angle of the crank can be quite significant. In most instances my horizontal force governs but I get the point on the slotted connection. The problem I foresee is the effect on a local brick - local friction perhaps between the steel plate and the brick. Wouldnt this push out the brick in theory as the mortar is really weaak in theory? It may well work but I am looking for a justification in a numerical sense. Some sketches i found attached for reference. Let me know your thougths.

 

[BAretired]

Fairly new to this forum but I have a general question and I was wondering what others normally do. In the UK at least we have older properties that have roof ceiling joists connected to sloping rafters and the ceiling joists can be higher than the wall. Therefore in a loft conversion when a steel beam is introduced how would you detail the steel bearing? We could cranked the beam here but how would you deal with the horizontal force component at the support?

The cranked steel beam should have no difficulty resisting the small lateral force. Tie it in securely to the walls on each side. The wall will bend outward as required, rendering the force almost zero.

 

[dik]

The displacement of the wall is essential to minimise horizontal reaction. A caution if you have this condition immediately adjacent to a wall at right angles to the supporting wall. The horizontal force can be significant if you have a 'long' span.

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

-Dik

 

[Kh777]

Thanks so what horirzontal deflection is acceptable? Or is there any other detail you would consider instead?

 

[phamENG]

so what horirzontal (sic) deflection is acceptable

This should be a pretty straightforward check. Look for a load at the top of the wall that makes the wall fail. (Fail is subjective - could be initiation of cracking, could be yielding of steel. You'll need to determine what should constitute failure for this application.) Then determine the deflection of the wall at that load. That's the maximum deflection that should be permitted in the beam when the joint is assumed to be a pin.

 

[Kh777]

I get your point but I'm more worried about local failure of the brick as opposed to a continuous wall. The steel is normally on a single Padstone. It's not really wall deflection in that sense. Please refer to the picture shown on my previous post if the steel is loaded with say another wall plus floor load on top, i would anticipate some significant horizontal loads which end up at the single Padstone. Yes if the padstone deflects within reason say 5mm horizontally, then there there is essentially no further horizontal load and thus assumes a roller support. Repetitive Live loads would concern me slightly. It may be worth considering a stiffer beam to limit the deflection?

Just wondering what other people normally do as I have seen many cranked beam scenarios on single skin 100mm brick or block walls with no justification whatsowver on how the horizontal component is dealt with. It's just one of those topics with no definitive answers.

 

[phamENG]

I get your point but I'm more worried about local failure of the brick as opposed to a continuous wall.

I don't think you do. If local failure is your concern, then look at the local failure that controls the connection design. What load would cause that failure? Now go back and apply that load to the top of the wall. The wall will deflect. Masonry may not seem flexible, but it's not infinitely stiff. As long as it deflects more than the calculated deflection of your beam, then you should be fine.

 

[BAretired]

Just wondering what other people normally do as I have seen many cranked beam scenarios on single skin 100mm brick or block walls with no justification whatsoever on how the horizontal component is dealt with. It's just one of those topics with no definitive answers.

A single skin 100mm brick or block bearing wall is not permissible by code, at least not in my jurisdiction. I would be concerned about such a thin wall, particularly if not reinforced. I would not be keen on using padstones under steel beams unless they could be tied into the surrounding brick or block with steel reinforcement.

Deflections of the walls can be calculated, providing definitive answers for the design. A 5mm deflection of a padstone is equivalent to a 10mm change in length of steel beam.

 

[Kh777]

Thank you all, great content

 

[GeorgeTheCivilEngineer]

Looks like the beam closest to you in that image is sitting on timber...

The North American engineers on here may be less familiar with unreinforced load bearing masonry. Because of seismic requirements and the abundance of cheap timber it is not as common for the load bearing part.

Going back to the cranked beam. Horizontal force can only occur if the beam rotates, which will be minimal with a fully welded and stiffened connection. It's a bit like worrying about a flat beam shortening and pulling the wall inwards as it deflects downwards - it will, but minimally.

As far as I know, there are no defined deflection limits in standards but if I were to put numbers on it, I would look for live load horizontal deflection of, say, H/600 or t/6, whichever is less.