Building Noise and Vibration MitigationJun 16 2015 · 0 comments · Nishkian Chamberlain, Technical notes, Tenant Improvement ·0
Planned tenant improvements (TI) and a review of building code requirements were discussed in a previous blog post, but… what happens when structural requirements of a new tenant space may need considerations different from what the “Building Code” specifies for strength and stiffness? We commonly experience specific client parameters beyond what the Building Code addresses for our fitness club clients who are commonly moving into new mixed-use spaces below residences or into repurposed, previously designed, office space. While there are alterations that we often think of as standard structural tenant improvement modifications, such as new openings for staircases, or new MEP units for ventilation, some of the upgrades to the existing structure require investigation beyond typical Building Code issues.
Owners of new and existing mixed-use buildings typically have two main concerns when considering leasing space to a new fitness club tenant, the transmission of noise and vibration into sensitive adjacent tenant areas. The comfort of office and residential tenants, which typically share tenancy in the mixed–use building development, is a great concern. Careful measures and criterion must be developed to mitigate that the noise and vibrations from the fitness club tenant from propagating into more sensitive areas of the structure and disturbing the other building tenants. In collaboration with an acoustic/vibration consultant, recommendations for the comfort level of all the building tenants will typically determine what treatments need to be made, but the structure itself must be prepared to receive the treatment.
We recently achieve acoustic and vibration mitigation for two areas of a project by providing a “floating” floor systems. One area was made up of a concrete slab and the other a wood platform system which is separated from the building’s slab with vibration isolators. This allows the effect of noise, vibration and impact loads (i.e., from dropping a weight) to be reduced before the building’s floor slab attempts to transmit the noise/vibration to the rest of the structure. The inherent challenge is that most office or retail spaces have lower natural floor frequencies of 4 – 6 Hz. Isolated floor systems typically require a base floor frequency significantly higher in the range of 9 – 10 Hz. Without the base floor system stiffness, the isolated slabs prove ineffective.
The structural solution to increasing a floor systems frequency, is generally to stiffen the existing structural members. In order to understand floor frequencies and required stiffness of structural members, a more advanced finite element analysis is often required. The existing floor system can be modeled using three-dimensional finite element software, and then analyzed to determine the natural frequency of the system. Stiffening is typically necessary in steel structures where 30 to 40 foot spans are common practice. One solution we recently used was to simply weld a plate and in some cases, a WT steel section to the bottom of the existing structural steel beams. Other more complex solutions may involve added bracing, hanging floors or additional columns among other options.
The end result of floor strengthening is to increase the structural system’s stiffness which helps to mitigate the transmission of unwanted noise and/or floor vibrations to adjacent spaces. Therefore, tenants of different uses can occupy the same building without the concerns of annoying disruptions of comfort.
Nishkian Chamberlain engineers provide building owners, property management organizations and tenants with a level of confidence that their mixed-use tenants will be able to cohabitate in comfortable environment. Should you have any questions about an upcoming or ongoing project, do not hesitate to contact any of our offices. You can also send an email directly to Craig Chamberlain at firstname.lastname@example.org.