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Drift Limits of Building for Components When Building is Designed for More Stringent Criteria

  • 1.  Drift Limits of Building for Components When Building is Designed for More Stringent Criteria

    Posted 03-14-2017 06:40 PM

    DRIFT LIMITS QUESTION:  If a more stringent drift limit is imposed on the structure by using ASCE 7-10 Table 12.12.1 category of “All Other Structures”, do the building components need to comply with the requirements of ASCE 7-10 Section 13.5.2 for Exterior Walls, Out-of-Plane Bending, Suspended Ceilings, Access Floors, Partitions, or can this code section requirement be ignored?  Would only the storefront glazing systems be required to meet Section 13.5.2?


    Project Description:

    Multiple one and two story buildings that have mostly retail and restaurant occupancies.  Tempered glazing systems will likely be used throughout.  Typical store fronts will be a minimum of 12 FT high adjacent to walking surfaces.

     Analysis Considerations:

    Two drift limits are being considered for the project:

    1. Structures, other than masonry shear wall structures, four stories or less above the base as defined in Section 11.2, with interior walls, partitions, ceilings, and exterior wall systems that have been designated to accommodate story drifts.  Drift limit = 0.025 for Risk Category I or II, 0.020 for Risk Category III
    2. All other structures.  Drift limit = 0.020 for Risk Category I or II, 0.015 for Risk Category III

    FACT 1:  ASCE 7-10 Table 12.12-1 clearly differentiates between buildings that have components designed and detailed for drift and buildings that have components are not designed and detailed for drift.

    FACT 2:  ASCE 7-10 Section 13.5.2 does not specifically state that there is an exclusion to the drift design and detailing parameters presented for the various building components indicated.

    Mario Giampa` P.E., S.E., M.ASCE


  • 2.  RE: Drift Limits of Building for Components When Building is Designed for More Stringent Criteria

    Posted 03-15-2017 11:36 AM
    Full disclosure up front: I'm an east coast EIT, so give my reading of ASCE 7-10 seismic provisions as much credence as you think it deserves.  13.5.2 says that all "all architectural components...shall be designed for seismic forces."  That means your walls, ceilings, etc. have to at least resist the force imposed on them without falling over.  It goes on, however, to restrict the requirement for designing to accommodate relative displacements to those that pose a life safety hazard.  The commentary then discusses this in more detail.  Essentially, if an architectural feature's relative displacement will cause an immediate life safety hazard (cracked drywall, not so much), then you have to detail it accordingly.  Also, if the structure is to remain in use any fire rated partitions would need to be detailed to maintain their rating after the seismic event.  Otherwise, displacement doesn't need to be considered if you take the more stringent drift limitation.

    Hope this helps.

    Peter Hamilton EIT, A.M.ASCE
    Project Structural Engineer