Continuous joist span issues
Continuous span floors have benefits of being able to span longer compared to simple span floors with the same joist section. This does not come without cost: continuous span joists transfer vibration from one floor to the other along joist length. In contrast simple span joist floors contain vibration within the loaded floor and effect on other parts of the structure is minimal.
There are many misconceptions on how to remedy continuous joist floor problems like: 1) Putting blocking or squash blocks at intermediate bearing. This will not change vibration mode of the floors at all; the only benefit will be a better stabilization/holding of the joist at intermediate bearings, 2) Cutting top flange ( and web ) at the intermediate bearing, this will change vibration mode of the floors by preventing vibration transfer between the floors, but it will also increase vibration problems on both floors since simple span has higher deflection for the same load compared to the continuous span. In addition to this, cutting the flange will invalidate floor design since the top flange at intermediate support is critical for joist moment capacity and this must not be done and 3) Added ceiling will help but to a lesser degree since added mass always reduces floor performance to a degree.
The best way to deal with continuous joist floor vibration problem is to reduce initial deflection under “footstep impact load” so that transfered vibration to the other floor is also reduced accordingly.
Engineered IBS 2000 bridging has been repeatedly proven to reduce deflection by 50+%, thus radically reducing vibration effect of footstep load.
Thus, continuous span vibration problems can never be totally eliminated; but with the installation of IBS 2000, they can be greatly reduced bringing floors to acceptable levels.
Tags: Add new tag, continuous span, deflection, floor performance, load transfer, vibration, wood i-joist
October 28th, 2009 at 11:24 am
Just recently built a house with 14″ deep i-joists. The joists are one length spanning two rooms ( family room and kitchen ). I can relate to this situation.
I was standing in the family room while my wife and children were in the kitchen.
When my children ran across the kitchen floor, I actually felt their movement in the family room. And I was not standing directly across from them.