Integrated Buildings & Structures

  • 1.  Resonance in Stairs

    Posted 05-12-2021 11:34 AM
    Have you ever encountered resonance in stairs?  AISC Design Guide 11 - Vibrations of Steel Framed Structural Systems Due to Human Activity provides parameters for checking resonance of monumental stairs when subjected to walking - considered at a period of 5 Hz.  Other parameters based on an observer standing on the stairs while someone descending are also given.  Design Guide 11 provides limited guidance for rectifying vibration in stairs, just recommending stiffeners.

    What would be the best approach to correcting any issues encountered in field?  Consider that the factors that impact vibration include: span, moment of inertia, and weight.  Possible remedies include cross bracing, adding weight, stiffeners, or adding depth to the stringers.

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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 2.  RE: Resonance in Stairs

    Posted 05-16-2021 11:43 AM
    Chad,
    One possible methodology could be to utilize the Sensequake (www.sensequake.com) methodology to understand how the stairs and the structural elements adjacent to those stairs are performing.  The testing is done by our firm (a US structural engineering company) who use teams of patented sensors to capture ambient vibrations.  The data from those sensors are then modeled to understand how the structure currently works in multiple situations.  This information is then used by us to develop a "calibrated" FE model to understand where structural changes will be most effective.  Call me if you want to learn more.
    John Cruikshank, PE, F.ASCE
    310-241-6550 x228

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    John Cruikshank P.E., F.ASCE
    President & CEO
    John M. Cruikshank Consultants Inc
    San Pedro CA
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  • 3.  RE: Resonance in Stairs

    Posted 05-17-2021 04:58 PM
    Hello, I consider that it should first be sought where the vibration or resonance originates in the stairs, for this you could make a model of the stairs in some structural analysis software with which you identify their vibrating modal fomrs and their frecuencies, later verify in the field if what was found with the model coincides with reality; This way you will have identified where rigidity is needed in the stairs with which you could propose a reinforcement scheme either by adding new elements such as bracing, new support points if possible, or increasing the cross section of the existing elements.

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    Horacio Galicia-Gaona Ing., S.E., M.ASCE
    Morelia
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  • 4.  RE: Resonance in Stairs

    Posted 05-18-2021 06:15 PM
    That's it.  Let me know if you want to learn more specifics.

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    John Cruikshank P.E., F.ASCE
    President & CEO
    John M. Cruikshank Consultants Inc
    San Pedro CA
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