Beam Deflection Criteria for sliding door... 1

[KevinChez]

I have an open corner that will be framed out using a cantilevered steel beam on one side and a simple span beam framing into it on the other. The sliding door manufacturer said that he usually tells engineers to design for zero deflection. There is a green roof being supported by this cantilever (8" of soil/plantings) so the load is significant. The cantilever is 6' long with a 13' back span (19' total).

There has to be some tolerance right? They can't ask for zero???

 

[AELLC]

I would call out to install the door only after the soil on the roof is placed and irrigated.

For sliding doors, I usually design for live load deflection less than 3/8".

 

[jayrod12]

zero deflection is impossible for obvious reasons. Tell the door manufacturer that he's out to lunch and there has to be some form of allowable deflection.

That would be like us telling him that his door can weigh zero pounds or else the framing below could collapse.

He gave a stupid, lazy response to a reasonable question.

 

[KevinChez]

Thanks for the input. I am telling them to plan for .25" live load deflection after all dead load is installed.

 

[XR250]

It really depends how tight the door is installed. 3/8" can bind a sliding glass door if it installed tight.

 

[Archie264]

I would have thought that they would fabricate those things with some sort of separation joint so that this wouldn't be an issue. Live and learn, I suppose.

 

[msquared48]

The fabricator is a zero. Depending on the various load conditions, there could be upward as well as downward deflection here. Or...

Maybe the Architect could eliminate the water and soil on the roof and go with a brown roof?

Mike McCann
MMC Engineering

 

[Archie264]

I consider those "green" roofs problems waiting to happen but I suppose that's for another discussion.

 

[KevinChez]

the green roof is more properly described as a meadow for people to not walk on put past to experience its lushness

 

[msquared48]

Huh?

Mike McCann
MMC Engineering

 

[aaronPTeng]

kevinchez

I am sure you have considered this, however ensure you check all load cases, As I have come across a few designs where the final load case gave a more favorable deflection (Plus live load and soil etc) with regards to cantilevers and caused issues,

With regards to the deflection head, I ensure anything viable (balcony edge etc) I keep to 10mm, which is 3/8". I still ensure that all large windows have a 20 - 25mm deflection head, as concrete finish is rarely level anyway + change in load conditions,

regards,

"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976

 

[a2mfk]

Just tell the architect to achieve the door manufacturer's goal, you will require zero load = zero deflection. And all doors and windows have "wiggle room" around the frame and gaskets to allow for movements, you cannot have zero thermal/moisture expansion and contraction of the structure, or of the door frame itself for that matter. I look at structures all of the time with settlement damage and almost never have seen a door or window fail because of it.

Msquared- you make me laugh...

What is the wall material around the door? Any possibility for a deflection connection between the wall material and the beam so the two are isolated?

Obviously I don't have any drawings or details so maybe I am imagining that incorrectly. Guessing the door frames right under the beam so a header beam and wall slip connections are not possible.

 

[Triangled]

The architect assured me he was specifying 12" max light weight soil in the 18" planters on the floor over the basement parking. If I recall correctly (years ago) we designed for 24" mounded standard soil and 18" water.