Deflection of steel lintel over bifold doors

[James Newport]

I keep seeing threads where people talk about deflection in a steel lintel potentially causing problems for bifold doors because the bend in the lintel squeezes the bifold frame and stops the doors working properly.

 

But doesn't the deflection of the lintel happen when you load the lintel by adding roof or joists or brickwork above? So then as long as you then size the bi-fold height taking account of this deflection, you're all good. 

 

 

[markc]

yes, or thats what should happen.

loading the building also causes a little more deflection so I/we have always pre loaded beams/lintels with critical dimensions

Also pre cambering for long spans and heavily loaded members

Edited July 1, 2021 by markc

[IanR]

31 minutes ago, James Newport said:

But doesn't the deflection of the lintel happen when you load the lintel by adding roof or joists or brickwork above? So then as long as you then size the bi-fold height taking account of this deflection, you're all good. 

 

Yes but... depends when measurements are taken for the opening. The lintels are probably not fully loaded when the openings are measured so an additional gap should be allowed for worst case loads (1st floor loads, snow loading etc. etc.).

 

Mine was ordered off drawing, so everything was "theoretical", but SE deflection calcs appear to have been accurate. 

[PeterW]

Other issue can be that the steel deflection causes unsightly gaps as on a beam with a 10mm deflection over 4m, you would need to leave 5mm fitting gap so at the supported ends you could have up to 15mm to cover and fill - that’s a big gap..! Increasing the steel size - either by height or weight - could reduce that to 2-3mm. 

[MikeGrahamT21]

One other thing to consider is the two types of bifold doors, there are top hung and bottom hung, the better ones in my opinion are always bottom hung, where the weight all goes on the bottom of the frame, rather than hanging from the lintel, this may help to reduce deflection also.

[Temp]

I bet many people measure the height at the sides and forget to measure in the middle. 

[James Newport]

Thanks for all the answers. Our lintel has been in for nine months and is showing very little in the way of deflection, and that includes the eighty-seven mule loads of shoes that have been inserted into the sidle-in wardrobe.

[Gus Potter]

14 hours ago, James Newport said:

I keep seeing threads where people talk about deflection in a steel lintel potentially causing problems for bifold doors because the bend in the lintel squeezes the bifold frame and stops the doors working properly.

 

But doesn't the deflection of the lintel happen when you load the lintel by adding roof or joists or brickwork above? So then as long as you then size the bi-fold height taking account of this deflection, you're all good. 

 

 

Yes, you're right James. Some deflection takes place as you add say masonry which is a constant load, call this a dead load. The rest comes from say floor / roof loading which is variable load, call this a live load.

 

Thus you have the "intial" deflection from the dead load. Then a variable deflection from the live load. Generally we assume for most domestic applications say using steel lintels that the deflection response is linear up to a point. Thus your total deflection is the sum of the dead + live load deflections.

14 hours ago, markc said:

yes, or thats what should happen.

loading the building also causes a little more deflection so I/we have always pre loaded beams/lintels with critical dimensions

Also pre cambering for long spans and heavily loaded members

Precambering is an option but for the self builder just needing the odd beam it can be a bit costly. Best if you can to just make the beam/ lintel say a bit bigger.

 

As Peter says (I think) if you have too much deflection, intial or otherwise you can just create something that does not look good. Too much and even the best door mastic operative will not be able to hide a significant downwards bow!

 

13 hours ago, MikeGrahamT21 said:

One other thing to consider is the two types of bifold doors, there are top hung and bottom hung, the better ones in my opinion are always bottom hung, where the weight all goes on the bottom of the frame, rather than hanging from the lintel, this may help to reduce deflection also.

 

Spot on Mike..go for bottom supported as the doors (glass mainly) are heavy and introduce a fair bit of variable load to a lintel as they open and shut.

 

 

 

[saveasteading]

A bottom run support is rare. it perhaps only works properly where the door is so big that it is running on big wheels, eg hangar.

Also standard on some sliding gates.

The downside of bottom runners, if you can find them, is that they stick in the guide, on muck or stones.

 

The steel has to be designed for the worst case so that the deflection is negligible. European shaped beams are taller and thinner and can work well. 

Another option can be to hang the centre from another element of structure, so that it does not deflect at all, but this is not always feasible.

[George]

On 01/07/2021 at 07:41, James Newport said:

I keep seeing threads where people talk about deflection in a steel lintel potentially causing problems for bifold doors because the bend in the lintel squeezes the bifold frame and stops the doors working properly.

 

But doesn't the deflection of the lintel happen when you load the lintel by adding roof or joists or brickwork above? So then as long as you then size the bi-fold height taking account of this deflection, you're all good. 

 

 

 

Pretty much yes.

 

I used a box section steel lintel above my bi-fold. 

 

However... lintels are designed pretty tight (even relying on masonry arching/friction to limit deflections) so they are not as adaptable as a steel beam. If you had a situation with no arching masonry, a high point load from a roof beam or something, then you could potentially run into problems. However this is where a structural engineer should come in to help.

[James Newport]

It was a structural engineer who specified the steel lintel. Based on stuff I've read here I'd have preferred an I beam or box section, but hey ho, it is in, and it is undeflected to the naked eye. 

 

 

 

[Dave Jones]

small doors 2 or 3 sections and off the shelf lintels are ok but personally i would also use an beam or rsj with an 8mm welded bottom plate as when the building settles/moves they will pinch usually in the middle.