Roof Paver Uplift & Parapet Walls
Roof Paver Uplift & Parapet Walls
(OP)
I have been trying to check an uplift scenario for a finish-work installing client. In this case, they are trying to put terrace patio pavers on a high rooftop in a hurricane prone region. The IBC specifically says that aggregate is not allowed on roofs, and that ballasted roofs are not allowed in this application (1504.8). The roof isn't ballasted (it's structural, this is just a wearing surface) and ANSI/SPRI RP-4 specifically reference 22psf or greater pavers (which we are) as an alternative to ballast stone (RP-4-4.1.3.1), so one could infer that we are in line with IBC, so long as we meet the uplift requirements of ASCE 7 on the pavers. My first question is just, "Does anyone see a major problem with that logic?" Obviously, it has to be designed so that a bunch of concrete squares don't go a-killin' in the next hurricane.
Assuming pavers on roofs are generally copacetic, IBC has a specific requirement for "ridgid tile", which includes concrete, under 1609.5.3. This code basically says that uplift is qh*Cl where Cl is .2 for concrete, then goes on to use it in an overturning calculation. The code also says that I have to be in accordance with ASCE 7 ch 6 (1609.1.1). ASCE says that components and cladding are basically qh*GCp (since GCpi=n/a); since it's a stepped flat roof, GCp should be from 6-12&6-11b as required. ASCE 7 could also be read as allowing the blocks as "other structures", which would make sense to me, since they aren't fixed to the building. Following these methods, and going with the worst case, I'm killing them in zone 3, and really making life hard in zone 2.
At my request, my client has provided parapet information. The parapet is more than 3 feet tall (usually 5), is designed sturcturally by others, and SHOULD have a large effect on suction since my maximum height is something like 300 feet. All the research that I have read shows large decreases in zone 3 and decreases in zone 2, but I can't find anything in ASCE 7, which is, in this case, IBC's go to guy (and, in general I would agree that it is the book to use... but where is the effect of the parapet?!). Does anyone know how to take the parapets into account?
Finally, the code combinations dictate that I use .6D, which I'm all for in a structure where design dead load is conservative and loads may vary, but these are pre-cast blocks with dependable weights and no room for variation. Gravity will not get weaker during the hurricane. Does anyone know if, in a case like this, .6D is still a requirement?
Assuming pavers on roofs are generally copacetic, IBC has a specific requirement for "ridgid tile", which includes concrete, under 1609.5.3. This code basically says that uplift is qh*Cl where Cl is .2 for concrete, then goes on to use it in an overturning calculation. The code also says that I have to be in accordance with ASCE 7 ch 6 (1609.1.1). ASCE says that components and cladding are basically qh*GCp (since GCpi=n/a); since it's a stepped flat roof, GCp should be from 6-12&6-11b as required. ASCE 7 could also be read as allowing the blocks as "other structures", which would make sense to me, since they aren't fixed to the building. Following these methods, and going with the worst case, I'm killing them in zone 3, and really making life hard in zone 2.
At my request, my client has provided parapet information. The parapet is more than 3 feet tall (usually 5), is designed sturcturally by others, and SHOULD have a large effect on suction since my maximum height is something like 300 feet. All the research that I have read shows large decreases in zone 3 and decreases in zone 2, but I can't find anything in ASCE 7, which is, in this case, IBC's go to guy (and, in general I would agree that it is the book to use... but where is the effect of the parapet?!). Does anyone know how to take the parapets into account?
Finally, the code combinations dictate that I use .6D, which I'm all for in a structure where design dead load is conservative and loads may vary, but these are pre-cast blocks with dependable weights and no room for variation. Gravity will not get weaker during the hurricane. Does anyone know if, in a case like this, .6D is still a requirement?






RE: Roof Paver Uplift & Parapet Walls
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Roof Paver Uplift & Parapet Walls
The code requires 0.6D. In my opinion that is the end of that discussion but you can find detailed discussions about that by searching this site.
The intent of the code is to not allow anything on the roof that can blow away. So if you put tile on the roof you will need some type of attachment or some type of product approved system that has been tested for this condition. It is unlikely that the tile weigh enough to resist the uplift on a 300' building based on dead load only. Have you checked for any local amendments or requirements?
RE: Roof Paver Uplift & Parapet Walls
Ron, the intent of the code is certainly that, and I really do not want to step around that intent, but they do not require physical connection. I am using a copy with amendments. In this case they are certainly a bit light to be used without physical connection, but I'm going to see if I can get them working (at least on the lower floors, which there are 2 of below 70'. I only have ASCE 7-05 in front of me, but I'll see if I can get my hands on the -10. Thanks for the point out, it's exactly what I'm looking for.
Thanks for the quick responses guys.
RE: Roof Paver Uplift & Parapet Walls
RE: Roof Paver Uplift & Parapet Walls
RE: Roof Paver Uplift & Parapet Walls
RE: Roof Paver Uplift & Parapet Walls
Zone 3 now matches zone 5 pressures.
Zone 2 no matches zone 4 pressures.
I would double check that though.
I had some questions on this in the past:
http://www.eng-tips.com/viewthread.cfm?qid=326478
EIT
www.HowToEngineer.com
RE: Roof Paver Uplift & Parapet Walls
For the record, if anyone comes here for reference: I spoke with a member of the board and a few grizzled old engineers I know, and they were all of the mind that the code is a guideline only. If you use sound engineering judgement, which you could back up in court, and design a safe system, you can step around something like that .6DL (which they all seemed to imply that they had done in the past). In this case, the DL is KNOWN, not some variable, conservative assumption. I recommended that the contractor verify weights in the field and use 95%.
Ron, it's not my design, it's architectural; I'm just checking that it is (or isn't) safe against pedestrian death by paver. I will act responsibly, and would never, ever put people's lives at risk while paying up my insurance.
Rfreund, thanks for the re-direct, very helpful.