Integrated Buildings & Structures

Dear ASCE colleagues,

The recent devastation caused by Hurricane Otis, which struck on October 23, 2023, has tragically reminded us of the crucial importance of designing structures that can withstand extreme natural events. One critical aspect that has come to light is the wind resistance in glazing structures.

Review of Post-Hurricane Otis Documents

Following Hurricane Otis, a series of documents and studies were generated that analyze the damage suffered by glazing structures. These reports have revealed that many structures did not meet the necessary standards to withstand high-speed winds, resulting in significant structural failures. Observations indicate failures both in material quality and in the design methodology used.

Lessons Learned and Recommendations

1. Updating Regulations: The ASCE already has specific regulations for designing wind-resistant structures. However, it is essential that we review and adapt our regulations in Mexico, incorporating the lessons learned from recent events such as Hurricane Otis. Ensuring that all new and existing structures meet these standards is crucial to minimizing future damage.

2. High-Strength Materials: Post-hurricane studies have emphasized the need to use high-strength materials that can better withstand wind loads. This includes the use of more robust glass and improved fastening systems that can maintain structural integrity under extreme conditions.

3. Training and Education: It is imperative that engineers and designers receive continuous training on best practices and the latest advances in wind-resistant structure design. ASCE can play a vital role in organizing workshops, seminars, and webinars dedicated to this topic.

4. Regular Inspection and Maintenance: In addition to the initial design, glazing structures must undergo regular inspections and maintenance to ensure their wind resistance over time. Early identification of potential weaknesses can prevent catastrophic failures during extreme events.

5. International Collaboration: Sharing knowledge and experiences internationally can enrich our practices and regulations. Learning from other regions facing similar challenges can offer new perspectives and innovative solutions.

Conclusion

Hurricane Otis has provided important lessons about the necessity of proper and wind-resistant design in glazing structures. As ASCE members, we have the responsibility to lead these efforts and ensure that our practices align with the highest safety and efficiency standards. It is crucial that in Mexico we review and adapt our current regulations to include these criteria, thus ensuring a safer and more resilient built environment.

I hope this discussion encourages our community to take proactive measures and collaborate in creating a safer and more resilient built environment.

This is a critical topic, in my experience understanding cladding loads and glazing load as well as material capacity are tricky and the design is not easy.

What have I seen?

1. The reduced area loads are not properly applied during design
2. The capacity of cladding assemblies is not properly understood.

Regarding the first point, let's say that the MWFRS load is 20 psf (let's just assume suction and pressure) but the 30 sq ft area load can be 3 to 4 times higher and the capacity of the connections for a single piece of cladding needs to be designed for that higher capacity.  This load on that single piece is then transferred to the component that supports it and that component must ALSO be designed to transfer the greater load.  Ultimately when the area considered is large enough these larger loads do not need to be considered, but until the force of the smaller area load is fully transferred to the larger resisting element the load path must be designed for the larger load.

The second point is regarding the rated capacity of a cladding system per the manufacturer.  Wind design and loading is determined on a risk based framework.  There will be some percentage of loading that will be over the number calculated in a design event and the capacity of a system may be some percent under the stated capacity if there is a manufacturing flaw or some other tolerance issue.  If you have a critical system and you install exactly the capacity you need there is the risk of failure of some parts of the system in a design wind or seismic event.  With a failure in a wind event the failure of glazing becomes a bigger problem because the loads on a partially enclosed structure can be larger than on a fully enclosed structure.

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Sarah Halsey P.E., M.ASCE
New York NY
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Would you be able to share which documents and studies you are referring to? I'd be very interested to read more about this. 

Hello, Brenna

Here are some references (Spanish) about the Otis' Hurricaine:

https://www.gaceta.unam.mx/habra-recomendaciones-del-ii-para-construir-despues-de-otis/

https://www.gaceta.unam.mx/radiografia-de-la-llegada-del-huracan-a-acapulco/?fbclid=IwZXh0bgNhZW0CMTEAAR2pRbJMRqlPNe9pI69VGXFyAU2qWbiuf-ITzi5xQYKjwzT2b84hbXrMXUo_aem_x3YWBJ5dZQ70MuGZBQUC0g&sfnsn=scwspwa

Huracán Otis, análisis de sus efectos

https://issuu.com/cicm_oficial/docs/febrero_2024_ic649-fin

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Javier Herrera Ing., M.ASCE
Mexico
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Hi Javier,

Florida has some of the best provisions for ensuring that there is not disproportionate damage from hurricanes.  It includes provisions for robustness of glazing from impact of wind borne missiles to retention of cladding to avoid it becoming a wind-borne missile.  Look for the High Velocity Hurricane Provisions (HVHZ) and Florida Product Approvals (FPA's), these were initially started as Miami-Dade county notices of acceptance (NOA's) but the program has expanded.  Also search for TAS provisions for testing and RAS provisions for roofing.

Maintaining the integrity of the envelope is critical.  The sudden change of internal pressure due to loss of windward window can also overload the roof system and have it blow off.  Things only get worse from there.

I would also be interested to see the data.

This gives you some resources you can go to.  There are also specialist envelope engineers that can assist you.  (Of which my company Green Facades is one example.)

Best wishes for improving the standards in this area.  Small changes can make big differences in the outcome. 

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Richard Green CPEng, P.E., P.Eng, C.Eng, M.ASCE
Owner/Principal
Green Facades PLLC
Mountlake Terrace WA
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I would suggest the following documents:

FEMA P-361 2021 Hurricane Harvey MAT Report, or any of the FEMA MAT reports on hurricanes.

FEMA P-320 2021 Taking Shelter from the Storm

ICC/NSSA 500-2020

I have researched many tornadoes and hurricanes.  There is no substitute that your building has to be connected from the top of the roof to the foundation. Your must protect all glazed surfaces and doors.  ICC-500 rated doors, windows, and overhead doors are available and they work great in Hurricanes and resist hurricane wind pressures and impacts.