9" square purlin repair potential nightmare


Postby LNM » Mon Feb 18, 2008 7:37 pm

Hi all

Lengthy but I've tried to include as much info as I can.... Here we go:

As you all know, one thing leads to another; while I was chasing out for a re-wire, I was in the process of helping the last of the lime bodging off the slates (to say nothing of the ton of pigeon c**p thats also up there) to let it all breathe a bit better and make life pleasanter in general, I started poking about the larger timbers to see whats what. Ooooh dear.

At least one end of one of the purlins in this 1854 house has been attacked by water in the past and it shows sign of deterioration to the extent that I can push my finger into parts of it. I've not tried a screwdriver yet to see how far it this goes though. The beam is tinder dry now, as is the rest of the loft. Most of the rafters look sound and all are dead straight.

It sits on a V shaped angle iron (therefore rafters at about 45%) 1" thick that I surmise is held in place by one of the _massive_ chimney stacks above it. It is a 9" square baulk that is approx 22 feet long and is also supported roughly half way by a brick stack thats part of the innards of the house.

The damaged area as I see it extends along the beam to about 24" from the end and concerns half the cross section although this is very difficult to determine because of the proximity to the wall.

There is another purlin lower down that is inside the top floor rooms. I've not checked that, but I'm assuming the worse.

So far so good so what ? (name the band) :

Given that I have nothing to stand a prop on, I reckon my only choice is to fabricate some steelwork to support it off the wall its currently sitting in. Using some basic physics of where the forces are going in the beam, using similar gague steel to the existing bracket, heavy duty coach screws, re-point the surrounding brick work with cement mortar (yeah yeah, I know) all should be well to enable me to then cut out the dead wood and basically leave it all as it is.

I can't use resin splices because I can't cut off the end because I've nothing to support the beam on, unless I use the method above and in that case, I may as well just leave the support there for ever and ever. I'm also assuming that I'll be ok to replace it with several smaller bits all bonded together since I imagine 9" timbers (of any length) are not commonly available, despite recent losses to the Greek merchant shipping fleet.

Potentially, I could put a new beam in, but this would be a mammoth task, even splicing small ones together or even using steel work welded and bolted; I think; advice though on this would be welcome.

I've even made a wood model of the affair to get my head around potential pitfalls.... Sad or what ? But then again, it means now I've accounted for previously overlooked lateral forces on the beam. And look on the bright side; all the unearthed wiring conduit is being taken out to boot !!

Cheers in advance for any suggestions !!
LNM
Posts: 3
Joined: Mon Feb 18, 2008 6:46 pm

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Postby welsh brickie » Mon Apr 14, 2008 7:00 pm

I had this similar problem before.
What about leaving the existing beam in and if you can fit an eye beam
next to it .
trouble is to fit it I had to get a crane in I knocked a hole in the gable
next to the old beam and slowly slid it in through the hole.I bolted a 4x2
timber on top of the beam,but kept the new beam straight not on an angle.
I dont know if this helps??
welsh brickie
Posts: 1925
Joined: Sat Apr 12, 2008 7:54 am


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