Florida Oceanfront Condo Wind Load Question - ASCE 7-88 versus ASCE 7-02 (or later)

[Ironicslip]

The original wind study is from 1994 and uses ASCE 7-88 with a damping ratio of 3%. Too 50 year return period references fastest mile design wind speed is 115 mph. Note this is Dade County.

Assumptions appear in the plans to include coupling (post tension cable) in the structure though no coupling was detected by ground-penetrating radar tests in at least 2 floors (20-plus story building).

What should the ratio be without coupling or reinforcements? How does the ASCE 7-88 designation for the original study change with ASCE 7-02 and 7-05 and 7-10 (not to be pedantic)?

 

[frv]

I don't think you are being pedantic. But I have no idea what you are asking for either. What information do you have and what are you trying to figure out?

 

[Ironicslip]

I have a wind study that I am trying to properly interpret. high rise wind pressure zones for a unit show positive/inward pressure of 89 and negative/outward pressure of 91 (all in PSF) as being the standard under asce 7-02 146 MPH winds, importance factor 1, Kd 1.0, exposure c, enclosed building

the wind study, however, showed negative pressure of 91.4 (PSF). the installer and city originally pointed out the discrepancy during inspection but problems persist.

Trying to confirm the concern of the frame installer who said the frames for the unit would need to be replaced every 5-10 years. alternatively additional reinforcements have been discussed for a subsection of the building - namely, the units above and below the unit.

Also, because the original plans for the building called attention to post tension cable on at least every other floor, whether the lack of any above or below this unit is a problem limited to this unit or others above and below it. two units above and 3 units below this unit exhibit similar cracking in the concrete slabs; but, no determination has been made with regards to lack of post tension cable or other reinforcement for the slabs.

Again, thank you for your input in advance.

 

[frv]

Are you concerned about a difference of 0.4 psf?

 

[Ironicslip]

The frame installer & civil engineer pointed it out as being a potential problem. The building plans had 4-6 sway (but included post tension coupling; but, movement of over 12 inches (may have been as high as 24 inches)during two storms was detected. The garage actually twisted off from the tower. So, yes, now that we are aware of the structural defects above and below the unit, we want to understand what can be done for reinforcements. It is unclear whether the building meets current code without reinforcements.

 

[frv]

I still don't know what you are asking, but I can emphatically guarantee one thing: if your building is having problems it most certainly is NOT because ASCE 7 indicates that suction is 91.4 psf but it was only designed for 91 psf. It is actually a bit concerning that you would not recognize the insignificance of this.

If you are getting movement much greater than anticipated, then there is something awry. Look at the original drawings; conduct a thorough survey; run your own numbers. If you suspect reinforcing is missing, try GPR.

 

[Ironicslip]

The numbers were run in 2008. That is why I am unsure about current condition.

Your answer confirmed for me the need for a thorough survey. Thank you for your input. Much appreciation.

 

[TXStructural]

Since the concern is ACTUAL condition, you need to determine the actual construction. If the building is not performing anywhere close to design, there is a defect in a calculation, an observation, or the construction. However, keep in mind that the actual exposure may have exceeded design, in which case such a failure is not a defect, but simply a function of design. The factored design loads are what you should be examining, not the unfactored loads. The design was not exceeded until the factored loads were exceeded.
(If the original design wind was 145 mph instead of 146 mph, the design loads you give would probably be right, assuming the other computations and assumptions were correct.)

As to the contractor saying something like "it will need to be replaced every 5-10 years", if he was talking about structural performance due to the 0.4-2.4 psf underdesign, he was just talking out of turn. If he was talking about corrosion or workmanship, well, that's a different matter.

Was the building built after 1992? (You talk about "a study" in 1994, but it's not clear to me when the building was constructed.) Also, you mention that there were no PT tendons found in two floors, but were those adjacent floors? You say that the design called for PT in "on least every other floor", although I'm not sure why it would be designed like that. What is the particular, structural function of the "PT coupling"?