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ASCE 7-10
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abusementpark
Structural
I'm not sure of the exact date, but I think it is going to be in the latter half of this year.
I recently reviewed a draft copy of the code and there are some significant changes in ASCE 7-10.
I recently reviewed a draft copy of the code and there are some significant changes in ASCE 7-10.
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Nose around this site to find the proposed changes (I can't find the copy I read before but it came from this site. I may have seen it in ballot form).
Also the newest nehrp is out.
Also the newest nehrp is out.
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TXStructural
Structural
I picked up a copy at Structures in Orlando last week. If the measure of a good revision is an increase in paper, this is good one. However, I tend to think less is better.
Almost half of it is seismic - we are now officially entering the realm of "Let's see how precisely we can calculate an estimate of loads and forces." Do these folks not realize that they are requiring very precise calculations based on the estimated forces of an unknown event?
As I say in my presentations: You don't get a better building by using a sharper pencil.
Almost half of it is seismic - we are now officially entering the realm of "Let's see how precisely we can calculate an estimate of loads and forces." Do these folks not realize that they are requiring very precise calculations based on the estimated forces of an unknown event?
As I say in my presentations: You don't get a better building by using a sharper pencil.
swearingen
Civil/Environmental
I'm struggling with the wind maps. They show significantly higher wind speeds. I know that they have done away with the numeric importance factor for wind and gone to separate maps for building categories, but it appears that there is an overall increase in windspeeds of 10% or more.
After sitting 7-05 and 7-10 side-by-side and going through a wind pressure calc on a simple mono-slope roof, I'm getting pressures that are about 19% more for the new code.
What gives?
We're talking billions more in construction costs to design for these wind loads. Plus, for those of us that do lots of work on existing structures, we'll need to go back and strengthen them...
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
After sitting 7-05 and 7-10 side-by-side and going through a wind pressure calc on a simple mono-slope roof, I'm getting pressures that are about 19% more for the new code.
What gives?
We're talking billions more in construction costs to design for these wind loads. Plus, for those of us that do lots of work on existing structures, we'll need to go back and strengthen them...
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
They should match up fairly well along most of the USA, and are actually lower in many coastal areas. What wind speed are you looking at? Note that the pressures you calculate with ASCE 7-10 are ultimate values to be used with a 1.0 load factor vs. ASCE 7-05 pressures which were to be used with a 1.6 load factor so the pressures themselves should be different.
Willis,
YOu are correct. I did a quick comparison for upper midwest area:
ASCE 7-05 ASCE 7-10
Occ. cat III Risk Cat III
I = 1.15 I = N/A = 1.00
speed = 90 mph speed = 120 mph
Kd = 0.85 Kd = 0.85
Kzt = 1.00 Kzt = 1.00
Exp C Exp C
H = 33 ft H = 33 ft
Kz = 1.002 Kz = 1.002
qz = .00256KzKztKd*V2*I qz = .00256KzKztKd*V2
qz = 20.313 psf qz = 31.402 psf
LF(ASD) = 1.0 LF(ASD) = 0.6
qz*LF(ASD)= 20.13 psf qz*LF(ASD)= 18.84 psf
LF(LRFD) = 1.6 LF(LRFD) = 1.0
qz*LF(LRFD) = 32.50 psf qz*LF(LRFD) = 31.402 psf
I think if there are areas where the change in speed is different (for example, on the fringes of the old 90mph contour where the new speed is not 120) then for those locations the new code might be more or less than the old code. In the areas near the coast, I can't say how the contours have changed. Note that for different Occ Cat/Risk Cat, this analysis will look different because I is different, and new speed on the new map will also be different.
regards,
chichudk
YOu are correct. I did a quick comparison for upper midwest area:
ASCE 7-05 ASCE 7-10
Occ. cat III Risk Cat III
I = 1.15 I = N/A = 1.00
speed = 90 mph speed = 120 mph
Kd = 0.85 Kd = 0.85
Kzt = 1.00 Kzt = 1.00
Exp C Exp C
H = 33 ft H = 33 ft
Kz = 1.002 Kz = 1.002
qz = .00256KzKztKd*V2*I qz = .00256KzKztKd*V2
qz = 20.313 psf qz = 31.402 psf
LF(ASD) = 1.0 LF(ASD) = 0.6
qz*LF(ASD)= 20.13 psf qz*LF(ASD)= 18.84 psf
LF(LRFD) = 1.6 LF(LRFD) = 1.0
qz*LF(LRFD) = 32.50 psf qz*LF(LRFD) = 31.402 psf
I think if there are areas where the change in speed is different (for example, on the fringes of the old 90mph contour where the new speed is not 120) then for those locations the new code might be more or less than the old code. In the areas near the coast, I can't say how the contours have changed. Note that for different Occ Cat/Risk Cat, this analysis will look different because I is different, and new speed on the new map will also be different.
regards,
chichudk
structuresguy
Structural
This is typical example of these so called "intellectuals" (ie college professors) making up stuff and changing perfectly good stuff to justify their existence and importance. I mean, if they didn't change the code significantly every few years, what would SK Ghosh and company talk about at all the conferences?
So now they confuse things even more by changing the wind loads calculated to ultimate load versus working load. The industry, particularly air conditioning equipment manufacturers, hasn't even caught up with the '05 requirements yet. Almost every day, I have issues with our mechanical guys saying they can't find rooftop units that meet the new rooftop equipment pressures in ASCE7-05. Now they'll really be confused by ultimate pressure versus 'we tested it at 150 mph...." Fortunately, it will be several years before it comes into effect, at least here in Florida.
So now they confuse things even more by changing the wind loads calculated to ultimate load versus working load. The industry, particularly air conditioning equipment manufacturers, hasn't even caught up with the '05 requirements yet. Almost every day, I have issues with our mechanical guys saying they can't find rooftop units that meet the new rooftop equipment pressures in ASCE7-05. Now they'll really be confused by ultimate pressure versus 'we tested it at 150 mph...." Fortunately, it will be several years before it comes into effect, at least here in Florida.
swearingen
Civil/Environmental
Thanks WillisV and chichuck - I found it after digging a little further. They did the same thing they did with the earthquake loads a couple of revisions back.
I understand why they did it, but it would have been nice if they would have just moved all of the loadings over to ultimate at once instead of doing one section at a time per 5 year revision. Maybe it was too much of a workload to do it all at once...
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
I understand why they did it, but it would have been nice if they would have just moved all of the loadings over to ultimate at once instead of doing one section at a time per 5 year revision. Maybe it was too much of a workload to do it all at once...
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
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