ASCE 7-16 Figure 30.4-1 Shaded C&C Wind Pressures

[YC611]

Hi all,

I have recently picked up a copy of "Design of Wood Structures" by Breyer, and I saw something in the Example 2.10 that does not look right to me.
The final inward pressures for some zones are less than 16 psf (which should be the minimum C&C wind pressure).



So, I checked the ASCE 7-16 Figure 30.4-1 and saw that it asks for the final values to be at least 16 psf. Is there any reason why the lower values used in the example?



Another question, why were the outward pressure that are less than 16 psf not shaded? Because they are suction? And is it the reason why the values less than 16 psf used in the examples because they are pushing against the members instead of away?

 

[ANE91]

30.2.2 says 16 psf minimum acting in either direction. I’ve never used Part 2 of Chapter 30 in ASCE 7-16. The lack of highlighting in the negative column strikes me as odd, in the context of your question.

Also, how the heck is he getting 1.22 for lambda? The problem explicitly states Exposure C. 1.22 only exists in the Exposure B column of Figure 30.4-1.

Interestingly, none of this exists in ASCE 7-22. I haven’t checked the errata or done a substantial comparison between the two code cycles, but it seems to me that the Pnet30 business was removed for being confusing af.

I’ll lastly point out that the Breyer books are good for wood and nothing else, in my opinion. Even then, others have found errors in the wood analysis parts of the book.

 

[YC611]

30.2.2 says 16 psf minimum acting in either direction. I’ve never used Part 2 of Chapter 30 in ASCE 7-16. The lack of highlighting in the negative column strikes me as odd, in the context of your question.

This is what I read as well. As the note mentioned, final values shall not be less than the 16 psf. And that the negative values were not shaded at all.

Also, how the heck is he getting 1.22 for lambda? The problem explicitly states Exposure C. 1.22 only exists in the Exposure B column of Figure 30.4-1.

For this, he actually got it from interpolating between the values in Figure 28.5-1. With h_mean = 15.5 ft.

Interestingly, none of this exists in ASCE 7-22. I haven’t checked the errata or done a substantial comparison between the two code cycles, but it seems to me that the Pnet30 business was removed for being confusing af.

I am not required to design in accordance to ASCE 7-22 yet, but I will eventually get to it and hopefully it causes less confusion.

I’ll lastly point out that the Breyer books are good for wood and nothing else, in my opinion. Even then, others have found errors in the wood analysis parts of the book.

Hah, my only reason of getting this book is because I want to learn more about the wood structures since I barely do them and I had only done some basic stuff.
I only spotted this problem because I like to see design examples and follow author's thought process and perhaps theirs are more logical and could help me better understand the topics.

 

[ANE91]

Got it. Linear interpolation makes sense. Sorry I couldn’t be of more help!

 

[YC611]

Got it. Linear interpolation makes sense. Sorry I couldn’t be of more help!

I appreciate your help here! Perhaps others will be able to clarify it for me.

I just cannot wrap my head around if they were mistakes, given that so many people praise this book. And why ASCE 7-16 doesn't shade the negative pressures in the table!

 

[SandwichEngine]

Is there a chance that the book is working in ASD? If so, the minimum design-level load would be (16 psf)*(0.6) = 9.6 psf.

 

[YC611]

Is there a chance that the book is working in ASD? If so, the minimum design-level load would be (16 psf)*(0.6) = 9.6 psf.

It couldn't be since I believe all ASCE 7-16 wind load are in strength level.

So if he's pulling the values from the tables, he needs to convert them back to ASD, for which he did not. And if the final values are converted to ASD, those values will still be less than the 10 psf required for ASD.

For consistency, either approach is not following minimum wind load.