removal of load bearing wall for open plan project: a neat alternative.

[Alex]

I am aware that the usual procedure for removing a load bearing wall is to use a heavy RSJ and relative checking of foundations + pillars etc... I am thinking of using another method via extra joists running perpendicularly under existing ones. I reckon that 5-7 joists mounted onto masonry joist hangers around the centre (around the area of the wall to be removed) should do the job neatly. This will also reduce the height of the ceiling from 2.70 to a more manageable 2.50m. I reckon that in this way the loads are better spread out (along 4-5 metres) rather than having a single RSJ with relative highly concentrate loads on lenghts which spans only 100-300mm.

Any comments, suggestions?

[N. Thornton]

sounds fine to me - but get it chekcd to be sure. Oh, with one exception, joist hangers do not tie beams to wall, the existing wall does. That would reduce your structure strength. So you may need to attach beams to wall a different way.

NT

[Alex]

I am thinking of fitting some restrain straps (L shaped) to connect the walls to some of the central joists. I've never used restraint straps before, but it all seems much less trouble than using RSJ.

[Sam]

One problem that I can see is that the distribution of load on the new cross bearers will not be equal: as the extsing joists sag in the middle of the span they will tend to pivot around the outer new cross bearers and try and lift at the end. The outer bearer will then deflect and the next bearer in will take a bit of load and so on - but the end result is that the outer bearer will take proportionally more of the load and will need to be designed accordingly. The exact distribution of the loads depends on the size of the new and old timbers and their spans.

A way to limit this effect would be to close up the spacing between each cross bearer - so that they are all close to the pivot point, but in the limit this becomes 8 or so joists bolted together on the original wall line, so you might as well do what everyone else does and call it one steel beam.

[Alex]

I do agree with you about the uneven distrubution of loads... however I don't quite understand the pivoting issue. One of the reason of using 5-7 joist is to reduce long spans (i.e. sagging). The long side of the room is about 7.2m; by installing two joists in the middle (e.g. 3.3m and 3.9m) and two extra joist at about 1/4 and

3/4 lenghts (e.g. 2m and 5.2m) I have already tackled most of the issues regarding loads and sagging. A couple of extra joists would be there handy for that extra peace of mind. RSJ require so many technicalities and skills which I'd rather do without...not to mention costs. I guess the problem you highlighted refers to the sagging of the new joists i.e. the existing joists won't sag in the middle unless the new do... There is a single joist running perpendicularly underneath other 9 of the ground suspended floor and it's been doing a great job (i.e. no sagging nor pivoting of any sort).

[Sam]

OK, now you have given the dimensions I see what you are getting at - I thought you were intending to put all the new joists say within 1-2m of the middle of the 7.2m. What I mean my pivoting is that if you imagine putting a, say, 6m scafffold plank on 4 level bricks, at 0m,

0.5m, 5.5m and 6.0m, then when you load the plank the ends of the planks will lift off the outer bricks and all the loads will be carried by the inner bricks. It's would be the same for your floor.

I can't see any additional problems with your proposals over the standard method; it would still be straightforward for your structural engineer to do the calcualtions.

[Alex]

In fact there was a hidden issue which I've only recently solved... Installing new joists using hangers underneath old joists is a bit tricky because one cannot access the hangers from above as the way is blocked by the old joists. I'd installed two joist in this way using the Expamet hangers and I had to remove temporarly a few bricks to slot one of the 2 hangers inside the joist in place. Only recently I've descovered about other types of hangers (Catnic and better still Simpson) which allow to slot the hangers along the lenght of the joist...no need to remove any brick. It is a bit complicate to explain into words...one has to try and see.