Integrated Buildings & Structures

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  • 1.  Tornadoes

    Posted 03-17-2025 01:09 PM

    With the recent Tornadoes across the U.S., we have noticed that several damage to buildings were seen. What is the reason for this. Is it that these are not built to the design codes ? Or the severity is much above the design codes ?



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    Vijaya Saidu R.Eng, M.ASCE
    Civil and Structural Engineer
    Chaguanas
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  • 2.  RE: Tornadoes

    Posted 03-17-2025 02:44 PM

    Vijaya,

    Hi. Mostly it's because many buildings are in unincorporated areas without governing code or where what's there are out of date or not strictly enforced. There is also the severity issue. virtually no codes contemplate designing for the worst nature can produce for practical functional and economic reasons.

    Vital structures such as certain types of security, utility, and medical facilities are designed to higher standards.  Only actual storm or tornado shelter facilities are designed to withstand the worst (at least that we know of and can codify) that nature can muster. The highest performers are addressed in the ICC 500 and certain FEMA standards.



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    C Michael Donoghue P.E., M.ASCE
    Principal
    Maritech Engr. ,Inc.
    Austin TX
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    Original Message


  • 3.  RE: Tornadoes

    Posted 03-24-2025 11:32 AM

    Vijaya,

    For many years, buildings and other structures did not have any design requirements for tornado design.  That changed with ASCE 7-22 which introduced Chapter 32 on this topic.  The 2024 International Building Code adopted ASCE 7-22.  It takes time for most Jurisdictions to adopt the IBC, and some have still not adopted the 2024 Edition.  Thus a building code requirement to design for tonadic wind forces has only been in place very recently in most parts of the country, and some parts of the US still have not adopted it.

    In addition, the provisions of Chapter 32 of ASCE 7-22 only apply to larger, higher risk category buildings.

    That said, based on wind speed alone, many modern buildings would be expected to be able to resist the forces of an EF1 of 86 - 110 mph, since that is lower than the design wind pressure and the strength factor.  In some jurisdictions, some percentage of buildings might be expected to be able to sustain an EF2 event.  However, there are other considerations.  Building age, building design code (if any), type of construction, and quality of construction all play a part. 

    In some relatively recent events, damage occurred in modern buildings at connections between elements, where the force in the connection was less than the design strength of the connection.  This does not speak well for the quality of the construction, or the quality of code required special inspection.

    There are other issues involved which include combined uplift and lateral load forces, and the slowness of adoption of lessons learned from previous events.

    All-in-all, your question points to a host of issues.  The big news is that we finally have a design process in Chapter 32 of ASCE 7-22, and that is already being improved in ASCE 7-28!



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    Edwin Huston P.E., S.E., MIStructE, F.SEI, M.ASCE
    Vice Pres
    Huston Structural Engineering, PLLC
    Shoreline WA
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    Original Message


  • 4.  RE: Tornadoes

    Posted 04-18-2025 09:59 AM

    Permit me to chime in - if this is still of concern. 

    Our research on tornadoes starting after the 2011 tornado outbreaks that killed 262 persons in Tuscaloosa, AL and Joplin, MO (and dozens of other events) within one month of time, initiated extensive research at University of Florida, and NIST that leveraged existing research  by meteorologists at Oklahoma's severe storms laboratory. 

    Studies continued at Texas Tech and at Iowa State's tornado simulators, and colleagues in Canada at Western University. 

    Initial field work and engineering research started by Professor Kishor Mehta at Texas Tech and Ted Fujita and others, following the 1970 Lubbock Tornado has been the state of knowledge for some time, but building codes considered tornado event too rare an event to warrant including it as a design consideration. The structure and intensity and physical characteristics of tornadoes are well known but we have resisted committing to widely distributed instrumentation to capture data on the hundreds of events that occur every year. As a result, reported wind speeds are only estimated, based on forensic assessment of post-event damage.

    These estimates are seldom validated or calibrated to any measured data, but in the main are based loosely on our knowledge of straight line winds and their impacts on buildings. The research does not show any changes in the numbers, distributions of intensities of tornadoes in recent years. However, as the inventory of buildings expand, more structures are built in potential harm's way. This paper provides some more background about the research that has served to initiate the work leading to the Chapter 32 provisions of ASCE 7-22.  Do contact me and should I be able to help further, be happy to do so.

    Dr. David O. Prevatt, F.SEI | University of Florida



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    David Prevatt Ph.D., P.E., F.SEI, F.ASCE
    Professor
    Gainesville FL
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    Original Message


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