Extending joists into web of steel beam

[Niall Smart]

Hi,

I've removed an interior block wall which was supporting some joists and installed a steel beam at joist level to support the floors and the interior wall above. I had to cut the joists 1-2" short of the beam in order to fit it at the level of the joists. What is the best way to extend the joists into the web of the beam? I was thinking of lap jointing short (i.e., 60cm) lengths of timber (7x1.5) which would be screwed and glued to the existing joists.

Is this method of fixing sufficiently strong, or should I be using bolts & toothed plate timber connectors? Is there a better way?

Niall

[dg]

You don't extend the joists.

Either hang the joists off the top of the beam with hangers, or if possible fit a timber section into the beam web and fix hangers to this to hang the joists off

dg

[Andrew Gabriel]

Been watching a shop being rebuilt and this is exactly what they've done. The timber fitted into the web is bolted through the middle of the timber and beam at regular intervals.

[mail]

On 13 Nov, 22:10, Niall Smart wrote:

Dear Niall As I understand your post - the steel is already in place and about

50mm short of the flange of the beam and so none of the suggestions made to date are, in fact, feasible under the circumstances. Had I been you, I would not have cut the joists in the first place in order to put in the RSJ but would instead have fitted two RSAs back to back with pipe spacers in between such as one of the RSAs either took up the ends of your short joists or better still - as cited above - a shaped timber "plate" set within the flange of the RSA such as to use a Speedy type timber to timber joist hanger with square twisted (high withdrawal resistant) nails. OK too late for that this time so you need to make a decision between your suggestions of glue and screw or double-sided tooth plate connectors Technically you need to get calculated the mainly shear forces at this point in the beam and determine if a glued and screwed joint complies with what used to be CP112 (sorry I did my engineering in 1976). My instinct is that IF the glue and screws are right that you could get away with it. My advice is to get an engineer to calculate. That said, if you elect not to follow that advice and are going to glue it then use a UF or Resorcinol type structural glue - the sort used in Glulam beams. Supplement this with decent screws at calculated centres. How about a compromise and go for coach screws with 2" plate washers, double sided connectors amd use the conventional edge end and spacing distances which I would guess on a 7" timber will be 50 mm from the edge, 75mm from the end and not less than say 150mm spacing between screws. You could get three sets in staggered lines along a 7 " timber

- one 50 from the top - one 50 from the bottom both in line vertically and one staggered in the neutral axis.

Alternatively use four bolts in a rectangular pattern 50mm edge 75 mm end and say 350 mm spacing should see you right

Chris G

[Niall Smart]

[cut]

Unfortunately not :) A bit more forward planning and accurate cutting would have paid dividends here.

Timber set into the web of the RSJ would have been an option, I could not have used RSA as there is a wall above to support. It would have been tight to set the beam in, as presumably the joists would need to be within 10mm of the flange to ensure a decent footing on the joist hangars.

[snip]

When you say double sided connectors here - do you mean screw from both sides? i.e., 3 coach screws from either side?

Thanks Chris, I think I'll have another quick look tonight to confirm setting timber in the web is definately not an option, and plan B will bolt through.

Niall

[John Rumm]

It sounds like you have:

######## ## @@@@@@@@@@@@@@@@@@@@@@@@@@@ ## @@@@@@@@@@@@@@@@@@@@@@@@@@ ## @@@@@ Timber Joist End @@@@ ## @@@@@@@@@@@@@@@@@@@@@@@@@@@@ ## @@@@@@@@@@@@@@@@@@@@@@@@@@@@@ ########

In which case, extending the beam to meet the joists sounds easier:

######## ##~~~~~~@@@@@@@@@@@@@@@@@@@@@@@@@@@ ##~~~~~~@@@@@@@@@@@@@@@@@@@@@@@@@@ B##~~~~~~@@@@@ Timber Joist End @@@@ ##~~~~~~@@@@@@@@@@@@@@@@@@@@@@@@@@@@ ##~~~~~~@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ ########

Insert a timber section in the web, running the length of the RSJ, bolt it at regular intervals through the joist. And then use ordinary joist hangers nailed to it to carry the cut ends of the joists.

[Man at B&Q]

So how do you do that when the joists have been cut 1-2" short.

MBQ

[The Natural Philosopher]

It's hard to get the wood in the flange post erection..If its possible welding plates inside the lower flange to support the wood on is one approach, or could use bolts..but the best approach suggested would seem to be the last posters one - extend the existing beams with a beam either side, lodged in the flange and bolted through the existing beam using those spider plate things between the wood parts. If you are worried about those beams shifting, drill CSK holes in the lower flange and use woodscrews or nails banged in upwards to locate.

Pack all the beams with ply sheets to get a level surface to re-board the ceiling to...

[Man at B&Q]

Or arrange the joist extensions to be slightly offset vertically so that the joists are flush with the top of the beam.

MBQ

[fred]

That looks like quite a nasty rotational moment on the RSJ, I'd be worried about just using hangers.

[John Rumm]

I only drew one side of it - from the description I am assuming you would do the same on both sides. Note also that the joists are only a couple of inches short - so you are only talking about 50mm of wood in the web.