Loft Steels - Fitting & Connecting Wood Blocking - Quest

[Zirynx]

Hi All,

First post!

Looking for some advice from the huge community here, please.

I have a set of structural engineers drawings (all approved by BR's) for installing a pair of steels in the loft in order to board it out to take full domestic loading. Each steel will be prefabricated in 3 non-equal sections in order to facilitate access.

The drawings specify that wood blocking is to be added to the web of the steel, on which the joist hangers are connected and, in turn, the joists themselves.

The method of fixing the wood blocking is essentially by bolting through the web of the steels however, I have a couple of questions regarding the exact method.


Q1) The 'through bolts' are specified in the drawing as "900 ctrs". Does this mean "exactly 900 ctrs" or "maximum 900 ctrs"? The reason is that it would be simpler for me to site the 'through bolts' at 600 ctrs, as this is the spacing of the existing joists and so I wouldn't be wrestling with their spacing or the mid-joist joints in the steels.

Q2) The steels have a (small) radius at the junction between the web and the lower flange. Should I raise the wood blocking slightly so that its lower face is at the top of the radius, thereby leaving a small gap between the upper face of the lower flange and the lower face of the wood blocking or, should I chamfer the inside lower edge of the wood blocking so that it can be fitted flush to both the web and the upper face of the lower flange without that radius interfering?

I suspect I may get replies suggesting that I contact the S/E however, I've had these plans for a year and a half and am only now getting around to getting on with the job! So, my relationship with the S/E company has pretty much elapsed and I'm sure there would be a (not insignificant) additional consultancy charge involved!

If someone here could add their expert opinion, that would be much appreciated!

Many thanks.

 

[tony1851]

1. Bolts at 600 would be fine;

2. chamfer the bottom (inner) corner of the timber to clear the radius. That way you know that the timber is seated on the top of the bottom flange.

 

[pinenot]

Are these steels (I presume your referring to "un" steel beams) being built into the gables either end? and how deep is the web?? ...pinenot

 

[Zirynx]

1. Bolts at 600 would be fine;

2. chamfer the bottom (inner) corner of the timber to clear the radius. That way you know that the timber is seated on the top of the bottom flange.

Thanks for your advice.

Are these steels (I presume your referring to "un" steel beams) being built into the gables either end? and how deep is the web?? ...pinenot

Steel specified as 254 x 146 x 31UB
Wood blocking specified as 75 x 225 x C16 with M12 bolts at 900 ctrs.

Looking at one steel suppliers website for the above UB stock, the depth of the web between the fillets is 219mm.

Yes, steels to run gable to gable.

Thanks.

 

[pinenot]

Depth was perhaps misleading, it's always the same describing universal beams. What I meant was what depth was there between the side of the "I" section to the central web.
There is another way forward, cutting the new joists full length, web to web, fitting the joists, chamfer removed, and cutting the blocking as noggins fitted between each joist (no drilling no, no bolts etc.) this is a standard way within the trade even though the s/e draws it up otherwise...pinenot

 

[Zirynx]

Ah, I see what you were asking.

One additional piece of information that fundamentally affects this is that the joists are to be underslung using long-legged hangers, so fitting the joists within the void of the I-beam is not an option.

Apologies if that lack of clarity on my part led you astray there.

Thanks.

 

[pinenot]

Could you scan that part of the drawing and post a copy? ...pinenot

 

[Zirynx]

Here you go...

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[tony1851]

He's done that to lower the floor joists between the existing ceiling joists to give you maximum headroom. Standard detail, really.

 

[Zirynx]

Yep, that's what I asked him to do - make the floor as low as possible whilst still allowing room for the requisite depth of (cheap!) insulation.

I'm comfortable with the overall arrangement - I just wanted to ask about the fixing of the wood blocking within the web. I didn't want to stray too far from the BR-approved plans and end up getting a telling off from the BR inspector, resulting in having to redo work!

Thanks.