Steel lintel above 5m slider.

[Eric]

I will soon require a steel lintel to go above a 5m sliding door. 1 & 3/4 storey Scotframe timber kit blocked in.

Do I need to ask a SE about this or is there a fairly straightforward solution?

 

 

[SuperJohnG]

Surely this is designed already by your SE and on your building warrant drgs? 

[Eric]

This is for the block work, there is a steel portal frame for the slider.

 

I am looking for advice for a steel beam/lintel to support the 4” blocks above the 5m sliding door.

[markc]

The beam spec should include anything above it. Much easier to up spec the door beam than to add another 5m span above it that will not bear onto the door header

[Eric]

The steel portal frame is integrated with the timber frame, this is simply to support 4” blocks.

Edited July 20, 2022 by Eric

[Gus Potter]

21 hours ago, Eric said:

I will soon require a steel lintel to go above a 5m sliding door. 1 & 3/4 storey Scotframe timber kit blocked in.

Do I need to ask a SE about this or is there a fairly straightforward solution?

 

 

Seems a bit odd at first glance that the outer blockwork support is not designed and detailed. But if the TF company have just designed the TF and the steels directly associated with it they may have put a bit in the fine print that the blockwork lintel over the sliding doors is to be "designed by others".

 

They may have done this to avoid what can be complex to design calculation wise (you need to do part of it by hand rather than being able to use standard SE software, or you can do it all by hand if you have time), time consuming and a challenge wise to detail.. a cost is a attached to this.

 

To explain. After making sure the inner steel (portal in this case) over the doors can carry the loads safely and does not deflect too much to jamb the doors you also need to make sure that the outer leaf intel will also deflect by roughly the same amount give and take. What you don't want to see is a bow in the outer lintel over the doors, no unsightly cracking of the blockwork or of the mastic joints and over stress any wall ties above.

 

Now at 5.0m span things like a sensible cost "L" shape Catnic / Keystone single leaf lintel is ruled out. The next options are.. weld a plate (bottom plate) to the bottom of the inner portal header beam or try to use something like a 200 x 100 x 12 /15 galvanised angle if not too much load above, tight on 5.0m but that is one starting point. There are other ways if the angle does not work out but I'll stick to this solution for now.

 

Go back to the bottom plate idea. What happens here is that the plate acts like a cantilever and introduces a twisting (torsion effect) in the portal header beam. This twisting force needs to be resisted. One way of doing this is to use the floor say above the beam to resist the twisting.. but the floor needs to be right over the beam top flange or very close to it.. then you need to design the top flange connection to the floor diaphragm.. not in the TF manual and it can be hard / sometimes not possible to do.. it's tricky! You'll see in the regs that floors can bear on beams.. simple bearing and be ok but not for beams subject to torsion. You can maybe see that the TF company are thinking the same thing? I'm talking about a pretty stiff connection here.. bespoke. not available off the shelf from say Simpson or Sabrefix.

 

Now if you can't connect header beam to the floor to resist torsion you need to design the header beam to resist the bending / shear and torsion forces. Some SE software packages do torsion design and you can do this by hand if need be using the Blue book with a few extra steps to check torsion. But if you can't rely on the floor the torsion ends up at the beam ends where you have to connect it to the columns. This is where the TF folk probably don't have the time to design a portal frame type connection by hand to also resist torsion as it's a non standard connection and not really covered in the design codes.. which refer often to "Engineering judgement" and "first principles" fine if you have time on you hands but for a TF designer they are working on the clock.

 

What often happens is that you are tight for space to get a 5.0m spanning beam to fit in head room terms at the outset. You want to keep a nice clear square opening for the doors for the fitters and so on.. @Marc can probably fill in on the detail. But when you need to design the portal header beam end connection for torsion you sometimes need to extend the end plate. It can be extended up.. but this can breach the continuity of a TF head binder say, or you can extend the end plate down and put bolts below the bottom line of the underside of the header beam flange.. fitters not happy!

 

In other words you need keep iterating and refining the detail so the structure works and the fitters can do their job.

 

Below is some info showing a couple of way I have done this. The first is from an extension job where I used a single portal frame to support both leaves of the wall with different loadings.. which introduces torsion just as above. This shows a connection that is designed for torsion with the end plate extended upwards. You can equally extend the end plate and bolts down but you then have to check the door detailing and fixing method.

This is a box frame that is doing quite a lot of "other things" which is why I have used this for and example.. will expand if there is interest from BH folk.

 

The second detail is where I have used an inner beam with a steel angle on the outside probaly akin to what @Ericneeds. It's not a portal but has other stuff and shows the gusset type connection between the angle and the inner beam. Yes there is a cold bridge but cut me a bit of slack? , the bridge was mitigated in the insulation details. The angle is about 4.4m long and supporting a storey of single skin masonry above.

 

To stop the angle from twisting it's connected back to the inner portal header beam with bolted gussets plates at the ends and in the middle. All these are doing is to stop the angle from twisting and this way you get the best performance out of the angle. There some other what is called "second order" effects happening.. for another day. Again this second detail has a bit more going on.. maybe a bit more interesting?

 

@Eric Hope this helps, post a few more details if you want to follow up.