Wood is lightweight with a relatively low bending stiffness. As mass timber is designed and built with increasing spans, floor vibration design becomes an important serviceability limit consideration. Floor vibration design often determines the allowable span and material use.
There are very limited design guidelines or resources available for practitioners. The current design equations in the CLT Handbook (Canada or US versions) are limited to floors with rigid supports (walls), and the U.S. Mass Timber Floor Vibration Design Guide is basically a literature review of CLT handbook method and other response-based methods developed for concrete and steel floors, without any verifications against data.
The challenges in vibration serviceability design for timber structures are twofold: predicting dynamic properties and responses and establishing suitable design or performance criteria. Due to the inhomogeneous material properties, orthotropic elastic constants, and construction details with discontinuity and semi-rigid connections, accurately predicting the dynamic properties and responses of timber structures under footfall or wind excitations can be complex. Moreover, human perception of vibration can be highly subjective, influenced by environmental conditions and psychological and physiological aspects. The latter one is even more challenging.
To address this gap, the only way is to create a database, which consists of both the physical data of the floor and occupants' subjective ratings (post-occupancy evaluation). With the database, we can do all kinds of analysis and develop design guidelines tailored for mass timber floor systems.
Please share your thoughts and discussion.
@jianhuizhou Is there a mandatory limit criteria for vibration for floors? Maybe Canada already have it. But in the U.S., I dont know such requirement exist at IBC level, or maybe I am wrong... My impression is that people do checks voluntarily. It is not like a strength check or L/200 IBC deflection check that is mandated.
Could you or anyone with building design experience comment on that? for my education 😊
I would look at AISC Design Guide 11:Vibrations of Steel-Framed Structural Systems Due to Human Activity (Second Ed.) Yes, it's about steel and concrete floors, but it might be adaptable to timber floors or mass-timber/concrete floors. It's significant in steel because the moment of inertia is small and the strength is great. With wood, we have lower strengths but greater moments of inertia. Nevertheless, the information on design loads for floor vibrations and MOI for floors might be useful.
@ling It is a requirement in Canada's building code.
@jianhuizhou Thanks!
Those are kind of hand-waving requirements, similar to "shall be calculated based on engineering principle" 😆
But it is better than nothing... I wonder if we have similar language on the U.S. side
Typically when a code has these requirements, it is up to the engineer and architect to figure out specific metrics for this, right? And for different projects it could differ.
I am studying EuroCode 1995 now, they do have a vibration requirement in form of deflection....even some formula on it.
Some manufacturers will provide vibration span limits in their span tables, but yes I agree there's not much available! Especially when vibration, along with fire, can often be the limiting factor for the span.
Note Woodworks Sizer will actually calculate vibration span limits for CLT panels - I'm not sure what is happening on the back end of that, though.
@clenon OK, as promised, I will try to get someone from wood works to answer that... let's wait and see... Hi Scott, could you help here? @sebrenemanse
@clenon The vibration-controlled span method is developed by FPInnovations in Canada. We recently published an interesting review paper, which documented the development of this method. You can download it here.
Since this method is limited to mass timber floors with wall supports and without concrete topping, we did some work to investigate these effects. Click here.
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