New Bigger Wind Loads?
New Bigger Wind Loads?
(OP)
I got this Email today. I don't understand if the wind loads are going up by 1.3 or not. Or are they increasing anyhow? I can't believe they need to get bigger. And are the PEMB and roofing manufacturer's wanting to increase loads? That seems unusual.
Email Excerpt:
"Request to Oppose Assembly Motion "As Submitted"
ASCE 7-2016 has been proposed for adoption into the 2018 IBC, and Code Change Proposal S105-16 would allow for the continued use of ASCE 7-2010 (with a modification factor of 1.3) for roof pressure calculations while the remainder of the wind pressure calculations would be based on ASCE 7-2016. This would require the use of two ASCE 7 standards which would lead to potential confusion and would place an undue burden on both the practicing structural engineer and the code officials
We urge you to participate in the ICC voting process that is currently open and to vote to uphold the ICC Structural Committee's action on proposal S105-16 by disapproving the Assembly Motion.
Vote Oppose on S105-16 Assembly Motion as Submitted. ICC members can vote using cdpAccess from May 12-26; go to www.cdpaccess.com, log-in, go to Group B 2016 Online Assembly Vote, and search for code change S105-16.
Please assist us in opposing the attempt to retain the ASCE 7-10 Roof Pressure Coefficients modified by a factor of 1.3 within the 2018 IBC. All ICC members can vote during an Assembly Motion!
Background
At the code hearings in Louisville, KY, a few weeks ago, the ICC Structural Committee voted to disapprove Code Change Proposal S105-16, which would have allowed the ASCE 7-2010 roof pressure coefficients to be utilized for the calculation of wind pressures on the roof. The new roof pressure coefficients have been determined utilizing the results of wind tunnel studies in comparison with full scale studies on instrumented buildings. This data and our understanding of these wind pressure coefficients have been known for up to 10 years now and just reviewed and presented to the ASCE 7 Wind Load Subcommittee during this last cycle. This information was presented, deliberated and voted on in an open, consensus process involving both the Wind Load Subcommittee and the ASCE 7 Main Committee.
Unfortunately many individuals associated with the pre-engineered metal building and roof industries brought this code change proposal forward in the ICC 2018 hearings. Many of these same organizations funded a peer review of the proposed roof pressure coefficients during the ASCE 7 process, and the peer reviewer found the coefficients to be accurate.
During testimony at the hearings in Louisville, the proponent of this proposal delivered inaccurate testimony indicating that the factor of 1.3 was supported by research by Dr. Timothy Reinhold. Dr. Reinhold is currently out of the country, but has noted the following when contacted concerning this testimony by the proponent:
I completely support the pressure coefficients in ASCE 7-16. In order to properly obtain design wind pressures for low slope roofs, it is critical that both the new ASCE 7-16 pressure coefficients and new definition of zones are used. For the particular building tested in our laboratory, the last two figures really tell the story.
When you look at pressure coefficients from all wind directions, nearly all of the clips would be exposed to pressures that exceeded ASCE 7-10 pressures (nearly 200 out of about 225 clips). When the ASCE 7-16 pressure coefficients and zone definitions are used, the number of clips that would experience pressures greater than those prescribed by the code would drop to about 50 out of about 225 clips - next to last figure. The load transfer mechanism help a bit as shown in the last figure where roughly 25 out of the about 225 clips experienced pressures in excess of what would have been computed using ASCE 7-16 pressure coefficients and zones.
It is important to note that the results from our laboratory are for a single building shape. The coefficients and zones developed for ASCE 7-16 represent data from a much broader range of building sizes, making those results much more robust. Nevertheless, the results from our full-scale study definitely show that ASCE 7-16 coefficients and zones move the bar in the right direction and are not overly conservative since we still had a number of clips that experienced pressures/loads in excess of what would be computed using ASCE 7-16 coefficients and zones."
Email Excerpt:
"Request to Oppose Assembly Motion "As Submitted"
ASCE 7-2016 has been proposed for adoption into the 2018 IBC, and Code Change Proposal S105-16 would allow for the continued use of ASCE 7-2010 (with a modification factor of 1.3) for roof pressure calculations while the remainder of the wind pressure calculations would be based on ASCE 7-2016. This would require the use of two ASCE 7 standards which would lead to potential confusion and would place an undue burden on both the practicing structural engineer and the code officials
We urge you to participate in the ICC voting process that is currently open and to vote to uphold the ICC Structural Committee's action on proposal S105-16 by disapproving the Assembly Motion.
Vote Oppose on S105-16 Assembly Motion as Submitted. ICC members can vote using cdpAccess from May 12-26; go to www.cdpaccess.com, log-in, go to Group B 2016 Online Assembly Vote, and search for code change S105-16.
Please assist us in opposing the attempt to retain the ASCE 7-10 Roof Pressure Coefficients modified by a factor of 1.3 within the 2018 IBC. All ICC members can vote during an Assembly Motion!
Background
At the code hearings in Louisville, KY, a few weeks ago, the ICC Structural Committee voted to disapprove Code Change Proposal S105-16, which would have allowed the ASCE 7-2010 roof pressure coefficients to be utilized for the calculation of wind pressures on the roof. The new roof pressure coefficients have been determined utilizing the results of wind tunnel studies in comparison with full scale studies on instrumented buildings. This data and our understanding of these wind pressure coefficients have been known for up to 10 years now and just reviewed and presented to the ASCE 7 Wind Load Subcommittee during this last cycle. This information was presented, deliberated and voted on in an open, consensus process involving both the Wind Load Subcommittee and the ASCE 7 Main Committee.
Unfortunately many individuals associated with the pre-engineered metal building and roof industries brought this code change proposal forward in the ICC 2018 hearings. Many of these same organizations funded a peer review of the proposed roof pressure coefficients during the ASCE 7 process, and the peer reviewer found the coefficients to be accurate.
During testimony at the hearings in Louisville, the proponent of this proposal delivered inaccurate testimony indicating that the factor of 1.3 was supported by research by Dr. Timothy Reinhold. Dr. Reinhold is currently out of the country, but has noted the following when contacted concerning this testimony by the proponent:
I completely support the pressure coefficients in ASCE 7-16. In order to properly obtain design wind pressures for low slope roofs, it is critical that both the new ASCE 7-16 pressure coefficients and new definition of zones are used. For the particular building tested in our laboratory, the last two figures really tell the story.
When you look at pressure coefficients from all wind directions, nearly all of the clips would be exposed to pressures that exceeded ASCE 7-10 pressures (nearly 200 out of about 225 clips). When the ASCE 7-16 pressure coefficients and zone definitions are used, the number of clips that would experience pressures greater than those prescribed by the code would drop to about 50 out of about 225 clips - next to last figure. The load transfer mechanism help a bit as shown in the last figure where roughly 25 out of the about 225 clips experienced pressures in excess of what would have been computed using ASCE 7-16 pressure coefficients and zones.
It is important to note that the results from our laboratory are for a single building shape. The coefficients and zones developed for ASCE 7-16 represent data from a much broader range of building sizes, making those results much more robust. Nevertheless, the results from our full-scale study definitely show that ASCE 7-16 coefficients and zones move the bar in the right direction and are not overly conservative since we still had a number of clips that experienced pressures/loads in excess of what would be computed using ASCE 7-16 coefficients and zones."






RE: New Bigger Wind Loads?
"It is imperative Cunth doesn't get his hands on those codes."
RE: New Bigger Wind Loads?
RE: New Bigger Wind Loads?
The other issue here is consistency. The wind coefficients and wind zones for gables less than 7 degrees are completely at odds with all other roofs, including monoslope buildings less than 7 degrees and gables in the range of 7 to 27 degrees. Some variations could be expected but none of those other types are being changed. You basically have ASCE7-10 coefficients for all of the other conditions except this one case that had some later testing done.
RE: New Bigger Wind Loads?
I'm very much of the opinion that if you have failures or safety risks you should throw in a brute force solution to make sure things are safe while you systemically fix it. However if it looks like your model is wrong but, historically, is safe you should really take the time to step back and figure out a systemic fix even if it takes time rather than going off half cocked.
Also, this kind of points out the fact that we're doing incredibly detailed analysis on stuff using models and inputs that aren't necessarily all that accurate. If we honestly think our model could be out by this much why are we separating buildings into so many different pressure areas and things. Being precise is useless and a waste of time if the basis isn't accurate enough to justify the amount of precision being used.