Strengthening upstairs floors/strutting

[John D v2.0]

Hi everyone, i wondered if anyone can help me out here- Our upstairs floors are pretty bouncy especially in the main bedroom and bathroom/hall with 3.8m span on 2.5 by 7 inch joists.
I strengthened the bathroom with 800 by 160 by 18 sheets of ply screwed and glued, also screwed and glued to new herringbone struts.
Now the floor is quite good.
See the photo from when I only had one bay to do:

The bedroom I just did 2 rows of struts, wedged against the front wall, but it didn't seem to help especially in the middle of the room. Since then I added a sandwich of ply in the middle of the span between the two rows of struts. But it's still not as good as I hoped.
See the photo for one row:

I'm not sure if this is because the joists are so old and splitting, the forces from the struts are disappearing in the cracks, so I should have put the struts only on ply?
Any suggestions? I'm going to put a ply floor down screwed at regular intervals which would help.
Cheers and thanks for reading! John

 

[JohnD]

I see your joists have been notched

It could be useful to know the depth and span of the joists; where the notches are, and how big.

 

[John D v2.0]

The notches in the bathroom (first image) are about 1/3 of the span and around half way through the joist. I think they were partially notched by the original plumber when the house was built in the 20s for a lead or iron drain, and a later plumber made plenty more space for a 40mm waste at a later date. Also the original strutting had been blasted out of the way in 2 places by a heating installer or two.
That floor was atrocious for bounce and I only planned to repair that one originally.
After such a good result, I decided to do the bedroom where the result wasn't so good, those notches are only (!) 20mm deep and they are 1/3 and 2/3 the span approx. For radiator pipes I just removed.
I've since sandwiched the joists to little avail on the centre, where the bending stress is greatest

 

[John D v2.0]

I just feel like the joists aren't strong enough for that span, even though they're OK on paper, is it possible they've just lost their integrity through being 100 years old?
Given the lack of ideas I think I'll just sandwich the rest and then get big sheets of plywood screwed down tight and not worry about any more noggins etc.
I'd appreciate any more suggestions that come to mind though!

 

[Doggit]

In the first picture, you've placed the ply over the notches, but in the other rooms, and the last picture, you've got the noggins by the notches, and the ply just goes up to them. Although it's gong to be a lot of work, you need to take out the noggins, put the ply either side of the notches, and then put the noggins back. 2.5x7 would have been fine 100 years ago when the wood grew slower, but with those deep notches having been taken out, they've lost most of their integrity.

 

[John D v2.0]

In the first picture, you've placed the ply over the notches, but in the other rooms, and the last picture, you've got the noggins by the notches, and the ply just goes up to them. Although it's gong to be a lot of work, you need to take out the noggins, put the ply either side of the notches, and then put the noggins back. 2.5x7 would have been fine 100 years ago when the wood grew slower, but with those deep notches having been taken out, they've lost most of their integrity.

Drat, thanks for the reply, although in fact the deep notches are only in the bathroom, the bedroom notches are only shallow and I was planning to fit 18mm ply over the top of the bedroom notches rather then sistered to the sides.
Unfortunately removing the struts and ply will be next to impossible now as I've used pu glue as insurance everywhere. I can see now that the pipes are not in a safe zone, I was hoping replacing the original square edge floorboards with gaps between with ply would negate the notches but maybe I can squeeze some folding wedges into them?
As an aside, now that the glue has had 24 hours, it seems to have improved.
Thanks again, John