did they chop a bit much out of this purlin?

[cjard]

I have a slate roof at 30 degrees pitch, supported by metal trusses and 9x3.75 inch purlins. The distances between trusses is 4m. The distance between purlins is about 1.5m. The slates sit on battens, which sit on boards(like floorboards) that sit on the purlins. The purlins are rotated so the 3.75 inch face sits on the truss. Here's a pic
http://1drv.ms/1xA2V6l

A steel frame is being erected inside and 4 of the steels follow the profile of the roof. They were supposed to touch the purlins in the same way the trusses do but it looks like a couple of the steels are slightly in the wrong place so the erectors have just chopped a 40mm chunk out of the purlin that was in the way.. Annoyingly, they could probably have got away with just taking 15mm or so out

I've a concern now that the remaining purlin thickness might not be sufficiently strong for the load it bears. Can any one tell me if it's ok? I'm planning to pack out the gap so the syeel frame supports the notched purlin but if it would be better to tell them to not repeat the behaviour then i will..

 

[freddiemercurystwin]

Photos .....

 

[cjard]

Hi FMT

I don't have a pic of the notch alas (can get one tomorrow), but I've simulated it on the 3D model of the building that the steel is supposed to being built to. I've also edited the original post to include a link to a shot of the roof buildup in general

Supposed to be like:
View media item 92580
They chopped about 40mm out of the purlin (leaving it to be ~185mm x 95mm where it's notched, down from 215x95):
View media item 92581
Right in the middle of a span too... Note these pictures omit the roof covering for clarity (turning it on made the model look messy from this angle)

If I pack out the gap between purlin and new steel (red), will it form adequate support? And as to the form of packing - 2 triangle wedges inserted from opposite sides, glued n hammered towards each other til they tighten up?

 

[freddiemercurystwin]

What is the project? A loft conversion? What's the purpose of red steels?

 

[Norcon]

40mm in a 9" inch purloin isn't a problem. But if 15mm is required then that's all they should be removing.

We've just finished a warehouse with 9" timber purloins which is being cladded with steadmans single panel system. Granted nothing is 40mm out.

In that first image you posted Steadmans Meta-Slate Plus system with embossed slate finish is a good option with the AS35 insulated panel below.

Are the existing trusses in that roof too weak to hold it?

 

[cjard]

Purpose of the red steels is to support a new floor deck inside.. Warehouse conversion to residential. I think the structural engineer's gone a bit overboard on this one (which may be an advantage if I end up needing to lend a bit of support to the existing structure once the joiners have finished chopping it). She said that one of the steel posts in the house would be bearing 5 tons dead load.. Structure is half done and I can still lift the post off its base with a crowbar (fulcrum arranged for a 10:1 force/distance multiplier) just by pushing down with my left arm..

I'll post up a few photos after I take em this morning.. "How a timber framed house became a steel framed house"

 

[cjard]

Are the existing trusses in that roof too weak to hold it?

Not that I can see - they've been there for 86 years now. The purlins have sagged a little in a few places and for some reason the designers of the building put three 10x8 steel columns in and a 10x8 steel beam to support four trusses (could probably have got away with a much smaller beam if 4 columns had gone in directly under the truss bearings) but then again, it did formerly house a 4x4 matrix of circular water tanks so 3 columns might have fitted into the voids between tanks better.. (but thereby blocking access walkways in two directions? bizarre)

 

[cjard]

Photos .....

Here you go..

What is the project? A loft conversion? What's the purpose of red steels?

Effectively - converting a large clear height space to housing, and the first floor deck is done. These steels are for the second floor deck


One of the big ones (203x203x46). This one carries.. half an ensuite bathroom I think
View media item 92593
One of the smaller ones (203x133x25) - this is one of the ones where I queried the notch in the purlin. This one carries most of the load from a small roof terrace, 4x3m
View media item 92594
Another of the bigger ones. This one carries some of the load from the aforementioned roof terrace and a bit of a mezzanine above a bedroom, plus a loft void and some ceiling joists. Once upon a time this was specced to be a 203x203x100 but I insisted the 7m span be broken to 4+3 so they could reduce its weight - too much of a H&S risk to fit the bigger one:
View media item 92595
(Rotated left 90 degrees) The other side of the baby one carrying the roof terrace
View media item 92596
These two posts carry a 3 steel run of the bigger (203x203x46) ones together with the front and back walls:
View media item 92597
A smaller one with a temporary prop to allow the wall panel to be fitted:
View media item 92599
Continuation of the smaller ones, running font to back of the building:
View media item 92600
A bigger one. I forgot what this one carries. Probably most of the master bedroom:
View media item 92601
Downstairs we formerly had a 203x203x60 specified but it proved too hard to acquire, so it was split into two 203x203x46:
View media item 92602Supported by a 9x90mm stud cluster at one end:
View media item 92606And a 6x140mm cluster at the other:
View media item 92607
And finally, a pairing of steels, the smaller one (203x133x25) on the outside carries a few cupboards in the bathroom, while the larger one (203x203x46) carries the bathroom wall above the cupboards, a window, and some posts that bear the master bedroom
View media item 92605

And to think someone told me once "anyone can make a building that stands up, but it takes an engineer to make one that only just stands up"

Do bear in mind that none of this structure needs to bear roof loads, or provide racking resistance for the outer skin - this is apparently what's required to carry the inner skin self structure and every day floor loads of a timber frame domestic property!