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  • 1.  How to calculate total diaphragm forces

    Posted 04-03-2018 10:36 AM
    Edited by Tirza Austin 04-03-2018 10:35 AM
    Does anyone have an example solution of how to calculate total diaphragm forces using the equation from FEMA 310? 

  • 2.  RE: How to calculate total diaphragm forces

    Posted 04-22-2018 09:55 AM
    FEMA's wepage has the answer you are looking for...


    take a look at chapter 6 of 2015 NEHRP Provisions: Design Examples (FEMA P-1051)


    Marcelo Dasilva, Ph.D., P.E.
    Austin, TX

  • 3.  RE: How to calculate total diaphragm forces

    Posted 04-23-2018 10:40 AM
    Edited by Tirza Austin 04-24-2018 06:04 PM
    With regard to that document, on page 10-40, I do not see stress concentrations applied.
    Is the civil engineering community waiting for an invitation from the engineering mechanics community on the application of stress concentrations to standard calculations?  Any fixed frame should have rounds or bevels when transitioning from beams to columns.
    I had the calculations in a 400 engineering mechanics course taught by Dr. Loren Zachary (the department chair and author of engineering mechanics books).  

    Franklin Kapustka P.E., S.M.ASCE
    Aloha OR

  • 4.  RE: How to calculate total diaphragm forces

    Posted 04-24-2018 10:49 AM
    Edited by Tirza Austin 04-24-2018 10:49 AM

    My following thought is an idea on why the codes don't address it, and I'm open to hear why they could be wrong, but from what I've learned about codes and code writing so far, it's my understanding as to why stress concentrations aren't addressed directly.

    Without digging through the code and commentary in depth, I would still be comfortable saying codes are written around evaluations of real world results and failures, so if the codes don't address stress concentrations directly, I presume it's because either the codes' provisions already accommodate stress concentrations in some other way (possibly safety factors throughout connection design equations?) or that stress concentrations haven't caused observed failures that have driven adjustments to the codes to accommodate the stress concentrations.

    Paul Chabot B.S., EIT, A.M.ASCE
    Structural Designer - Forensic Tech
    Detroit, MI

  • 5.  RE: How to calculate total diaphragm forces

    Posted 04-24-2018 01:03 PM
    Edited by Tirza Austin 04-24-2018 01:02 PM
    Stress concentrations are a fuzzy item.  Yes, codes and factors are meant to take them into account but we are always discovering new items.  That is why we keep getting code updates, i.e. the amount of data discovered from the Northridge earthquake completely changed seismic design in steel.  Finite element analysis of any structure shows where we have been ignoring stress concentrations, because current FEMA methods can not take into account elasticity of materials which is probably going to change in the near future.  We would be buried under a mountain of calculations if not for load factors and experience.  You need to see videos of some typical constructed items when taken to failure on a shake table, many times with explosive results.

    Alan Johnson [P.E. M. ASCE
    [Consulting Engr
    Fraser MI
    Proj EngrJohnson

  • 6.  RE: How to calculate total diaphragm forces

    Posted 04-24-2018 06:30 PM
    Edited by Tirza Austin 04-24-2018 06:30 PM

    Mr. Kapustka,

    Diaphragm stress concentrations aren't included in FEMA P-1051 example pages 6-10 through 6-40 because they aren't pertinent to the examples being presented. The examples are intended to demonstrate the distribution of forces vertically through the structural system. They don't demonstrate how to design the diaphragm which would be another complete example in itself for any one floor level.

     The CE discipline is completely aware of engineering mechanics issues of stress concentrations in structural materials including how and when they must be considered and when they are irrelevant. For example, stress concentrations are included with considerable attention to detail in bridge connections between structural members especially where cyclic loading causes fatigue.

     Stress concentrations are included in the design of seismic detailing and connections between framing members.

    Civil Engineers expressly consider force concentrations in diaphragms when they are relevant, such as diaphragms with openings or reentrant corners. They are not considered and are irrelevant to the design of many rectangular diaphragms without openings as may be the case for many building diaphragms.

    Your assertion that fixed beams and columns in buildings must have rounds or bevels indicates a lack of understanding about how buildings are built (and have been for a very long time). Bridges are in fact designed with these features when necessary.

    I hope I've been able to provide some enlightenment on the topic for you. 



    Brett King P.E., M.ASCE
    Senior Structural Engineer
    GHD Inc.
    Lake Oswego OR

  • 7.  RE: How to calculate total diaphragm forces

    Posted 04-26-2018 10:26 AM
    Edited by Tirza Austin 04-26-2018 10:25 AM
    Just interested: is change in stiffness a must in the project or can architects and structural engineers collaborate to eliminate?

    Ammar Fakhoury P.E., M.ASCE