Florida Building Code: Partially Enclosed v. Enclosed

seattlemike · Apr 4, 2007

Hello Structural Engineers,

Question on the Florida Building Code, in the Wind-Debris Zone (but NOT the High-Velocity Hurricane Zone):

Our firm is designing a 7-story office space-parking building in downtown Cape Coral, Florida. Still waiting to hear if it's exposure B or C.

The architect is planning on having all openings in the bottom 60' of the building as open (no windows) for parking levels.

Do I assess "open", "partial enclosed", or "enclosed" at each story?
Open is defined as the "wall" having 80% openings, which the wall does at the lower parking levels.
However if I consider the wall as the entire south face of the building (7 stories high), then it is not "open" or even "partial enclosed."

The top of the building (>60'), office space, is going to have unprotected glazing. It is more than 30' from the property line, so the FBC does not require protection.
Thus, it would seem I can design the top part as "enclosed"?
Or is there still a requirement that I consider the windows as breachable, and thus go to "partially enclosed?"

So, with those parameters, is the building "open", "partially enclosed" or "enclosed"?

Do I evaluate each level differently?
Is a "wall" just considered one-level?

Thank you!

SeattleMike

RESENG2 · Apr 4, 2007

I would consider each level as a seperate enclosure classification depending on the openings. Also, check the partially enclosed criteria, the governor just signed a bill voiding the previously allowed partially enclosed classification. If in a wind-borne debris region, the window openings have to be protected.
I deal primarily with residential however. This may not apply to commercial??

seattlemike · Apr 4, 2007

It appears that per ASCE 7-02, C6.5.9, pg 285, glazing above 60 ft needs to be protected as well: more exactly, we need to protect windows that are 30 ft or less above neighboring building roofs. C6.5.9 clarifies that any building roof within 1500 ft (horizontal) needs to be evaluated for that 30 ft rule.

Since we can't predict future construction, it seems you'd want to protect all your windows.

Also, 6.5.9.3 says (vaguely) that the building's openings need to be protected.... which apparently means all of them.

City of Cape Coral confirmed that they want to see all windows protected.

Note that windows are typically designed for a failure rate of 8 or 9 in 1000, that is less than 1%. However, in modern buildings that are complete curtain walls, each side might have several thousand 2x4 windows in the curtain wall... and typically a few fail... so, that would make one think that ANY curtain wall building should be designed as partially enclosed, regardless of Wind-Debris area?

CFSEng · Apr 4, 2007

Not sure I fully agree with you on the "Since we can't predict future construction, it seems you'd want to protect all your windows."

I do agree we can't predict the future, but it seems overly conservative to account for worst case possibilities for everything we design. I design for the here and now, but I'm curious to hear what others think.

seattlemike · Apr 4, 2007

My impression was that our buildings were built for a 50-year lifetime, based on the way the Wind, Earthquake, and Snow codes are written.

Also, if you do not protect the windows, you would want to design the building as "partial enclosed." See the discussion in C6.5.11.1, pg 290, of the ASCE 7-02.

The City of Cape Coral building official was pretty adamant that all the windows be protected. Also, ASCE 7-02, 6.5.9.3 seems to indicate all the windows need to be protected. Maybe that was clarified in ASCE 7-05.

CFSEng · Apr 4, 2007

Interesting, my impression is we design our buildings to withstand a wind event that has the probability of occuring once every 50 years. I really never thought of that as the lifespan of the building.

Section 1609.1.4 of the 2006 supplement to the FBC states what you said about partially enclosed if windows are not impact resistant. I can't find my copy of ASCE 7-02, but ASCE 7-05 does not allow this, you must use impact resistant glazing (with 2 exceptions). On your project you need to comply with FBC requirements, but I would do what the building official says.

The 2006 supplement to FBC still references ASCE 7-02.

seattlemike · Apr 4, 2007

The 50 year reference could be just a number to give people something quantifible in their lifetime, and it may be that the Snow, Wind, and Earthquake folk just copied each other for consistency.
But nonetheless, it envokes the concept of a duration of time for which we design, although I'm sure different folk have different ideas of what this is.

But if you pursue the duration logic, and we design for a 50 year hurricane, snow storm, or 2/3 of 2%-in-50 year earthquake, then the 60 yr event (disregarding EQ) exceeds our design.

The Japanese think even longer term.. I think they intend for their buildings to last 100+ years, but their exact philosophies, I am not an expert in.

Thank you for the clarification on 1609.1.4 and 1609.1.4.1 in the FBC 2006. Yes, we are definitely going with the impact-resistance.

Note the 8-9 in 1000 reference for window failure came from Dr. Dorothy Reed, University of Washington, Wind Engineering professor.

SeattleMike

dik · Apr 4, 2007

If the lower is open, then I'd only design the lower for open conditions. Some jurisdictions require that for parking, a certain portion be open... 75%-80% or whatever, else they have to design the mechanical system for full ventilation else it can be natural...

Dik

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