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Old 03-01-2009, 05:05 PM
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Default Fixing a strutting beam

Hi guys,

I built a 'hipped shed roof' over my quarter house years ago, with nice hardwood rafters spaced some 1000+ mm and spanning I'd say six metres. My local council building inspector question this (even though there was not the least bit of deflection in the rafters after 10-odd years, and there's no ceiling weighing on them), so I came up with a scheme to put a strutting beam in and strut off each rafter.

That beam is 6 m long and weights perhaps half a ton (seasoned Aussie hardwood). I had some brackets made from 10 mm steel plate which I intend to fasten to the concrete block walls either end to take the beam (plus two hardwood posts at equal distances to help carry the load).

I bought 12 mm diameter stainless steel expansion bolts to fix the brackets to the walls, but am having second thoughts: will this method of fixing such a beam be sufficient?

Any builders/engineers welcome to express an opinion! (I built my whole 'home' sort of flying by the seat of my pants, after studying span tables and so on, and so far it has stood the test of time lol).

Cheers,

LMH
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Old 03-01-2009, 08:37 PM
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Default Re: Fixing a strutting beam

LMH, after some mental conversions of names and sizes am I right in describing what you have is a beam close on 18 ft long which will be supported on its ends as well as approx six ft from each end, dividing the span of that beam into roughly thirds? The steel brackets are to be hung by means of expansion bolts placed into the block wall at each end. Are these block walls solid (as in filled with grout of concrete) or hollow? If the inspector is giving you some hassle he may have some problem with the attaching the brackets to the block wall using expansion bolts if the blocks where you are attaching are hollow. An easy way around that would be to attach the brackets and say that they are there to prohibit side to side motion of the beam and then directly beneath them place and attach a post measuring one half the thickness/breadth of the other posts, in contact and against the wall.

If the blocks are solid I would think you should have no problem.

What you are calling a "strutting beam" we call in N. America a "purlin" here's a reference :
Purlin - Wikipedia, the free encyclopedia

Just my 2 cents.
Good Luck
Wiley
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Old 03-02-2009, 01:55 AM
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Default Re: Fixing a strutting beam

Thanks for your 2 c, Wiley - yes, unfortunately the blocks are hollow, well mostly, some cores I did fill particularly close to corners etc. But the extra posts make sense! I'll investigate this further...

The brackets are fixed by four 12 mm bolts each, the bolts being 65 mm long. Their safe load, if fixed a minimum of 45 mm into the blocks, is given as 280 kg per bolt.

re the strutting beam: I have seen purlins but they usually appear to be placed right against the rafters; and they're not of the size and weight of my 'beam'...

Cheers,

LMH

NB: I'm still wondering if I'll be able to get the thing into the brackets in the first place, working by myself with a mate... I do possess a 3-ton winch though, if I can figure out a way to use it, but!
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Last edited by carioca; 03-02-2009 at 01:59 AM. Reason: spelling, adding some info
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Old 03-02-2009, 11:30 AM
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Default Re: Fixing a strutting beam

LMH, I placed four beams when I built my home. There were 6 x14 cross section two 16ft and two 20 ft long. I have ten foot ceilings in the downstairs and I placed them alone. Since your walls are solid it will not be possible to "walk them into position" as easily as if the walls were open. And since the diagonal of the beam is longer than the length it may or may not be a hassle to get the beams into position (one hopes the walls are within parallel so they are the same distance between them at the bottom as where they will be when in place!). So a bit of it depends upon how close a fit you require.

Raising them is a relatively simple operation: using two significantly sized boards; one each side of the beam to be raised at each end and blocked top and bottom so the distance between them is just slightly greater than the width of the beam (so it can move). I used 2 x 6s. They should be braced top and bottom and guyed so that they will not topple over side to side or into the beam. Then bore a series of holes about six inches apart thru the upright boards to accommodate a long bolt or piece of rebar. (you can do this before raising errecting the boards placing them one on top of the other and I would suggest you drill oversize holes for ease of placing the rebar or bolt). Place a similar bolt across near the top and above where you will be "two blocked" to hold the top end of the winch or block and tackle. Simply raise one end and insert piece of rebar thru the holes to hold the end, lower the beam to rest on the rebar, then switch the hoist to the other end and do the same, one end then the other until the beam is in position. It's slow but safe and can be done by one person and one can stop at any point and have "a cuppa" as needed.

I would consider raising the beam with the brackets at least loosely attached to the ends to avoid having to place them after it is up, but that may or may not be a problem. I would also consider prior to raising the beam of figuring out where the supports will contact the beam and drilling a hole about half way thru the beam and a similar hole into the end of the support beam. (Obviously one would center the holes). Then raising the beam above height of the beams and placing a short length of rebar into the holes set the beam down onto the post ends. The short piece of rebar will hold the post captive and in position and eliminate the need for "T" plates. I would photo the holes and rebar peg prior to setting since your inspector seems to be a "by the book" sort of fellow. The pegs to hold the beams meet code here and the way often use to hold overhead beams and post in homes without the ugly "T" plates. Cheaper too.

Hope this is of some assistance.

Wiley
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Old 03-02-2009, 03:06 PM
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Default Re: Fixing a strutting beam

Fantastic exposition, Wiley! Thanks. I'll study the suggested procedure and sketch it (my aging brain needs visual cues lol) but in general it appears similar to a ladder technique I used some 20 years ago to lift an intended beam-type hip rafter into position (I eventually placed it horizontally across two walls into steel brackets, and strutted a slim hip rafter off this beam). I too did this all by myself, except I needed to call my son to help me lift the beam ends into the brackets either side.

My current 'strutting beam' is 11 3/4 in by 2 3/4 in, so it's way more slender than yours! But I have fixed one bracket to the wall already, and will need to fix the opposite one, too, before doing battle with the beam... I'll send you a link to some pics in a private message.

The rebar idea appeals to me, too - I was going to drill a hole into the concrete floor and into each post bottom to secure with a rebar 'peg', already, but the top connection you suggest does away with the need for T-plates as you say...

Good point about taking photos! I just hope the council bod won't claim that I doctored them digitally ...

Cheers, and thanks again for your interest and advice!

Rgds,

L.M. Huesch
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Last edited by carioca; 03-02-2009 at 03:30 PM. Reason: spelling, add detail
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