Sound Barrier Walls & Break In Floor Diaphragm

[cuels]

I have a hotel design where the owner is insistent on limiting the transfer of sound through the floor. So the hotel is about 160 ft long x 75 ft wide. The floor diaphragm would have a break in the sheathing at every interior wall separating rooms (about every 15'). Attached is a detail that shows the construction they plan to use. I have requested running the sheathing through their sound break, but they don't seem to like that. They propose adding a 2x10 top plate to the bearing walls so that the joists are nailed to a single top plate. I see that connection as creating too many eccentric loadings and hinge points. Am I being overly conservative in thinking I need to keep the diaphragm through the joints? Are there any other ideas on ways to improve the connection and transfer diaphragm loads from one to the next?

 

[BAretired]

From a practical standpoint, how does one place drywall on each face of each wall with a one inch gap between?

The 2x10 is not shown on your sketch. If used, it would affect the sound rating between adjacent suites as does the 1" blocking shown.

If deck cannot be continued through the partitions, then each partition must be designed as a shear wall.

BA

 

[JAE]

I agree with BAretired.

The inclusion of a 2x blocking in an attempt to tie the diaphragms together would provide the same sound transmission as the continuous diaphragm.

If you must do this, then you just need to convey to the owner that there would be a larger number of shearwalls required throughout the building.

 

[KootK]

I saw this detail often when I worked in WI. In all instances, the walls in question were demising walls AND shear walls. In effect, each room became it's own building for the purpose of lateral stability. sometimes, they would be three sided buildings (2 demising + corridor) where the window openings were excessive. I definitely understand your concern however. It's a weird thing. Theoretically, the individual rooms could move independently under lateral loads. From a load distribution standpoint, it's an extreme version of a flexible diaphragm.

 

[msquared48]

The detail works in theory at party walls, but what about the intersection of the unit to the corridor wall? You cannot isolate each and every unit from the corridor structurally.

This is the case of the tail wagging the dog. Eventually, you will have to say "NO!"

Mike McCann
MMC Engineering

 

[cuels]

I agree with everybody's response. In addition to your comments, wouldn't this create seismic "banging". Each separate "partition" would bang against the next creating more issues, since there is nothing connecting them. This was my first thought, but maybe it would be insignificant in this case...?

 

[KootK]

If I'm envisioning your building correctly, you might take some comfort from the following:

1) In the longitudinal building direction, your individual room diaphragms likely are tied together at the corridor and the exterior wall. This should keep the demising walls from slapping together out of phase.
2) In the transverse building direction, your demising walls likely can be tied together at the roof level. This will provide some continuity from one unit to the next. In the past, I've capped the demising walls at the roof level with a 2x10 spanning both walls which was itself connected to the roof truss above with Simpson hardware. Hopefully roof uplift doesn't put that 2x10 into cross grain bending and destroy it.
3) Your demising walls are probably pretty stiff. There shouldn't be much differential movement between units in the transverse direction.

I've never seen anyone do a rigorous, numerical assessment of items one and two but the load paths are usually there.