Vibration in Structures – Part IIOct 05 2017 · 0 comments · Nishkian Chamberlain, Technical notes ·0
In a previous blog post, building noise and vibration mitigation was discussed as it pertains to tenant improvements (TI) in existing buildings and how the building code sometimes falls short concerning client parameters. As described in the previous post, this is often the case with fitness clubs that move into mixed-use spaces below residential or offices that are sensitive to sound and building vibrations, but the need for vibration mitigation goes well beyond fitness clubs.
The previous blog post examines how performing a finite element analysis of an existing floor system can determine its natural frequency and the natural frequency of a modified, stiffer system. The American Institute of Steel Construction (AISC) has previously put forth a “Design Guide” to design and account for vibrations in new buildings of typical framing. The Design Guide provides for determining perceived floor accelerations that change based on the natural frequency of the floor system. It is of particular note to avoid systems with frequencies that would match those of the space occupied to avoid resonance, where the amplitude of the motions would become very large. These accelerations are compared against recommended peak floor accelerations for human comfort which is dependent on the type of occupancy; offices and residences have a lower threshold than shopping malls and gymnasiums.
However, another increasingly prevalent challenge is the need to design for truck loading on ground floors that serve as drive aisles or emergency access. Conditions can occur where a heavier truck loading is adjacent to retail, office, or residential spaces, or at times, below these spaces either during construction or the lifetime of the structure. Special considerations must then be made to account for the excess vibration that may be encountered as a result of these potentially larger forced vibrations and to design for a higher level of vibration serviceability.
Owners of new buildings typically have two main concerns when considering the effect of adjacent parking or trucking; the transmission of noise and vibration into the sensitive adjacent tenant areas, whether retail, residential, mixed-use, etc. Careful measures and criterion must be developed to mitigate the noise and vibration from the loaded areas from propagating into the 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. Nishkian Chamberlain works with the acoustic/vibration consultant to determine a course of action to be taken and works toward providing a solution to achieve the desired performance.
Nishkian Chamberlain engineers provide building owners, property management organizations, and tenants with a level of confidence that their tenants will be able to cohabitate in a 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 Chamberlin at firstname.lastname@example.org.