About floor vibration, web stiffeners and something called strongbacks

Depending on the type of floor system you are installing, the actions necessary to reduce floor vibration can differ greatly.

Let’s look at the difference between using a floor composed of I-joists, and a TRIFORCE® floor system.

I-joist floors

In the case of the I-Joists, it is recommended that you increase the floor’s resistance to deflection with web stiffeners. These are additional OSB or plywood panels that you fasten to the joist’s upper and lower chords via screws and adhesive.

This won’t necessarily cancel out floor vibration, though. It will stop deflection in the immediate area where you applied the web stiffeners. It won’t change the rest of the floor’s behaviour, enabling vibration to spread laterally.

The answer to that problem would be to add blocking to the joists to increase lateral support. However, that won’t necessarily solve your deflection issue.

The point is that both web stiffeners and blocking can be necessary to obtain the desired floor stiffness with an I-joist floor structure.

Open Joist Triforce floors

With TRIFORCE® open joist, your approach will be quite different.

First off, because its design draws on the natural strength that comes from its triangular structure, the product is naturally stiffer.

Its open design also gives the TRIFORCE® open joist another big advantage. it allows you to install a transversal member called a strongback. Its function is to bring transversal rigidity to your floor system by “attaching it together”. This is not expensive technology. depending on the size of the Open Joists, these could either be 2 X 6, 2 X 8 or 2 X 10 nominal dimension lumber. And, as opposed to blocking, a strongback can span several Joists and be installed in one go.

Dealing with floor vibration during construction

We’re not saying strongbacks can replace blocking where reinforcement is required. We are only talking about floor vibration here.

Finally, you could be tackling the problem of floor vibration during construction or (unfortunately) after the building is finished. In both cases the TRIFORCE® System makes it much easier to deal with.

Best of all, simply by using TRIFORCE® open joist with added strongbacks, your chances of experiencing unpleasant floor vibration will be greatly reduced from the start.

If you’d like to know more about the TRIFORCE® floor system, download our technical guide or contact us. We’d be glad to show you its advantages.

Triforce Spec Guide

6 Responses

  1. N. Prabhakar, Chartered Structural Engineer

    Normally, the problem of vibration in floors is solved by dynamic analysis of the floor in the frequency domain. Considering the elastic properties and size of floor members, natural frequency of the floor can be calculated which should not coincide with the frequency due to people using (velocity of people walking) the floor to avoid vibration. On this matter, reference can be made to interesting technical articles published in The Structural Engineer, Journal of the institution of Structural Engineers, London.

    • Eric Pendland

      Thank you for your comment and for the referenced material Mr. Prabhakar. We are always striving to design a better floor system for our customers.

  2. Hi Eric,

    What is the procedure when you are unable to run the strong back down the middle of a truss pack due to interference with utility runs? Can you run 2 strongbacks at the 1/3 and 2/3 locations instead?

    • Eric Pendland

      Hi Sean,

      Yes, strongbacks can be run at the 1/3 and 2/3 locations. Using both in the areas where you can’t run one down the middle is an excellent alternative. The Strongbacks can also be stopped to allow utility runs and walls as long as three (3) consecutive joists are attached.

  3. Joe Lange

    I have the posi joist and I need to move the 2×4 strong back “UP” 5″ toward the floor. Right now it is nailed toward the bottom of the open truss. It has one nail only in each truss. Will this be a problem? I have pics but can’t post them here.

    • Caroline Auger

      Good day Joe,

      The best would be to contact us at 1 800 263-7265 and someone from our technical team will be pleased to support you according to this specific situation.

      Best regards

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