Balcony Railing Design Load combination
Balcony Railing Design Load combination
(OP)
thread507-250820: Balcony guardrail wind
I'm an architect, the engineering submittals I see for balcony rails typically state that wind and railing live loads are not considered concurrent because the balcony is assumed not be occupied during a 50 year wind storm, 98mph wind speed in my area.
The IBC and ASCE 7 has a load combination for allowable stress design which include live and wind loads discounted 75%. Does the assumption of the balcony being un-occpied have any basis other than the engineers judgement? Is there any standard to or published method for approaching this?
I'm an architect, the engineering submittals I see for balcony rails typically state that wind and railing live loads are not considered concurrent because the balcony is assumed not be occupied during a 50 year wind storm, 98mph wind speed in my area.
The IBC and ASCE 7 has a load combination for allowable stress design which include live and wind loads discounted 75%. Does the assumption of the balcony being un-occpied have any basis other than the engineers judgement? Is there any standard to or published method for approaching this?






RE: Balcony Railing Design Load combination
The picture is different if the balcony has some sort of fascia. Then the loading can become significant from wind loads.
I am sure others here will chime in and you will have a broader idea.
PS: I am super excited about architects flipping through structural codes and asking practical questions. That's a rarity :)
RE: Balcony Railing Design Load combination
The 0.75 is a discount to account for the fact that during extreme events you won't have full LL applied.
Balcony guardrails do indeed sometimes have significant wind force if they are solid panels, perforated panels, or even a series of steel bars @ 4" o.c. Wind drag on individual pieces does occur.
RE: Balcony Railing Design Load combination
RE: Balcony Railing Design Load combination
RE: Balcony Railing Design Load combination
After he hits the broken pickets, it will be a dead load.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Balcony Railing Design Load combination
Personally I would say that it depends on the circumstances. A domestic house has only small railing loads that can be achieved by only 1 or 2 people, a public balcony has large railing loads to allow for crowd surge. I would think that crowd surge and wind gust acting concurrently would be very very unlikely.
RE: Balcony Railing Design Load combination
RE: Balcony Railing Design Load combination
Thanks Again. John Rolka
RE: Balcony Railing Design Load combination
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Balcony Railing Design Load combination
Exploring your thought, what if the door behind had blown in? or the wind was blowing in a cross balcony direction?
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: Balcony Railing Design Load combination
Ask your wind tunnel guys for guidance on this, you paid dearly for what you got from them. You can have a positive pressure on the windward face of your glass, assume that's pushing toward the building; you will have a negative pressure on the leeward side of the glass; and you can have three or four really dumb people holding onto the handrail to keep from being blown into the building face; these loads are all additive pushing the railing toward the building. And, you can have quite different wind pressure scenarios (+ & -) at building corners or significant wall plane changes, and at higher elevations. Mostly, what I worry about is the people leaning against the handrail and pushing it off, thus they fall off the balcony. I worry a little less about them pulling it inward, because they just end up on their butt, on the deck, not on their head ten floors down.
You said as much, of importance to the problem, in your last post as you did in your first post; so some of the earlier posts, while not wrong, were at a bit of a disadvantage without the latest info., although elevation only changes the wind pressures or velocity. However, many minds change about the strength of handrails when people are viewing the street from 45 stories high, instead of only 8' off the ground. Add to that the view through the glass baluster plane and half the people won't want to get within arms length of the handrails.
But, Mike McC is dead on.
RE: Balcony Railing Design Load combination
No.
For example, you could not claim a roadside sign has no wind load because atmospheric pressure is the same on both sides. If anything, it is the balcony that will shield the lower part of the windows and doors in the wall from direct wind and water blasting: but the wall and balcony supports must absorb loads from both the balcony and the total wall area. (If you have solid or near-solid balconies.)
The gusts and turbulence hitting the balcony rail on one side of the building pushes that side; later, - when the storm is coming from the other direction - the balconies on the opposite side of the building's face their load.
RE: Balcony Railing Design Load combination
In any case, 98mph would vacuum up anyone foolish enough to be on the balcony.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Balcony Railing Design Load combination
A decent argument, but I doubt if you are going to convince anyone else. I'm pretty sure that if I crouch behind the balustrade, I will feel less wind than if the balustrade doesn't exist.
RE: Balcony Railing Design Load combination
RE: Balcony Railing Design Load combination
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Balcony Railing Design Load combination
I'm with rowing & hokie on this one, us old dogs usually gotta stick together or all these young dogs will run us over trying to do an elaborate FEA in a hurry to arrive at an incorrect, exact, answer. But, in this case it seems your slide rule is stuck in 'won't compute mode.' Flip the darn slide end for end, you're readin it wrong. We are not talking about ambient air pressure at sea level here. That is the same all round on the building, except as it changes with elevation. We are talking about a varying pressures around the building, as it stands as a broad surface (not unlike the road sign) or a funny shaped air foil in the larger wind flow.
To carry your argument to the extreme, if the pressures the same all around; why do we have any wind loading on a bldg.? Any bldg. is a bit like the road sign; except, much larger in mass, surface area, volume, stiffness, etc. and potentially shielded, or not, by other building or terrain. The bldgs. face does offer a boundary layer in the fluid flow, but it is not very thick in relative terms, the wind normally does blow over the hand rail. And, in fact, this solid handrail/baluster surface does shield the bldg. surface so things are not additive in that respect.
SteveG's parapet analogy is a pretty good one; except in the case of the parapet there is a long reach of unobstructed roof on the leeward side of the parapet, thus its pressure profile will be somewhat different than the solid handrail/baluster (glass) surface. I think this is were your argument comes into play. We don't know if the handrail is 1' away from the bldg. face or 8' away, or its exact orientation to the wind and this will affect the pressure profile. There could actually be wind pressure packing, a high pressure region btwn. the handrail and the bldg. face in some situations. Nonetheless, there will usually be a positive pressure on the solid baluster/handrail on the windward face, and a lesser pressure or maybe a negative pressure on the leeward side of that surface. If the wind is coming slightly from below, the suction behind the handrail will be even greater. I am not suggesting that we should always design for all this minutia. Let's have the OP'ers. wind tunnel guys splain it to him, and he should report back to us, so he/we get our money worth out of that darn wind tunnel test.
If my argument above has failed on you, then let me put it this way: this is the age of all things structural and mechanical being determined by committee, if this were not so, why would we even have these forums where we ask a question, tally the yeas and nays, and that determines our design. We outnumber you so you better get on board, and I don't mean drafting board either, because you and I are probably the only ones who have one of those in our office any more; or else we'll leave you at the station.