Hello, may I ask a couple of questions: 1. How come wind pressures for zones 4 and 4E came out to be negative values in Step 3, but went to the table in Step 5 as positive values? 2. Why do we check for uplift using the positive internal pressures only, and not the negative ones? Hope everything is doing well with your studies for the second try :)
Hi @iam_stl, great questions. #1. Zones 4 and 4E are negative values in step 3 because the pressure acts away from the wall surface (thus the negative value). In step 5, technically they are negative as well. In my spreadsheet, I used the absolute values for all pressures because I'm adding the pressures from the windward side (zones 1 & 1E) and the leeward (zones 4 & 4E). #2. I used the positive internal pressures only because they always control for uplift. The positive internal pressure acts from the inside of the building towards the roof and the roof pressures act away from the roof but from the outside. Therefore they add up, whereas the negative internal pressure subtracts from the roof uplift pressures. These are great questions that I may bring up in my next video. Let me know if my explanations made sense or if you have more questions. Thanks for the good wishes! I'm taking lateral depth today! 😬
In step 5, Load case A for the roof why do you compare total vertical load in PSF to Horizontal Load in KIP to see what controls....? You also have "Wall Pressure" in that table with 8 psf listed as the min. isnt that roof min?
Thank you for catching this. In step 5, the total vertical load for the roof is in Kips. I mistakenly had it labeled as PSF. "Wall Pressure" in that same table should read as "roof pressure". I appreciate the feedback. I'll make sure to have these corrected for the next video.
Can you check your Minimum wall pressure approach? Paragraph 28.3.4 in the Commentary Section (Page773) refers to figure C27.1-1. Figure C27.1-1, page 768, shows the 16 psf wind load on only one side of the building. In your spreadsheet you included both sides of the building.
Sorry for the delay in replying. Great catch! You're correct, the minimum pressures should be on only one side of the building as it is the "net" pressure. In my spreadsheet, the minimum base shear should be half of what is shown for load case A and B which will make the minimum pressures even farther away from controlling. Thanks again for pointing this out!
@@QuickQuestionEngineeringThanks for confirming. I will say I prepared a spread sheet similar to your example as it is well organized and helpful. In fact it was the way I discovered the discrepancy. I ran several wind conditions and was puzzled why the minimum was controlling. When updating some of the references to ASCE 07-22 versions I noticed the issue. One thing I did add was a simple sketch in excel and inserted the loads at each face, so it is easy to see the change in one view. Its a bit crude but if are interested I'll send a copy for review.
@@TheModelmaker123 That’s awesome! I’d love to take a look at it if you don’t mind. My email is quickquestioneng@gmail.com. I’m finishing up another video solving the same example but using the Directional Procedure Part 2. I just created a footnote to cover the minimum pressure checks and avoid confusion this time.
Hi, Thanks for uploading, this is a very useful video and full of new information for me... I have a question plz, for your wind base shear, why did you sum loads from all 4 zones (1, 1E, 4 and 4E) ? shouldn't be one side at the time and then the base shear would be the largest of the 2 sides? Are you assuming that wind is blowing towards zones 1 and 4 at the same time ? Thank you!
Great question! We sum the loads because on one side we have a positive windward pressure, and on the other side we have the negative/suction leeward pressure. They act simultaneously as the wind hits the windward wall, travels around the side walls and create suction on the leeward walls.
Thank you for the explanation, I actually had it totally wrong 😅... I thought, since the building is enclosed and there is no internal positive pressure on the leeward walls, that the suction does not affect the MWFRS, but only affects the sidings or glazing attached to that wall...Cheers!
Hi, I am studying for my PE Civil Structures NCEES exam and was planning to take the exam end of 2024, but with the new spec exam update effective April 2024 they updated codes and standards. During the last period, I was studying using the codes posted in the current exam standards. Please advise me, should I take the exam on the current specs knowing that I am not fully prepared? or should I wait and start using the new standards knowing that I cannot afford to get all of these codes -shown in the April 2024 exam specs-?
Hi there, the codes are all provided during the exam, so you won’t need to buy any hard copies. Your company may already have PDF versions of the codes that would be able to use for your studies. Please note that the main difference in the specifications is that starting in April 2024, there will be only the structural depth portion of the exam. So, you won’t have to study for the breadth. If you already studied for the breadth, it may be worth taking it now, but if you’d like to focus only on structural, it’d be better to take it in or after April.
Thx for your response. I work for the DOT currently I am not sure if i will be able to get the updated codes. My dream is to become a SE but this is what i got for my first Job. I guess i have to change my job. Thanks again for your advice
