Wind Loads on Structures 6

[EIT2]

When determining design pressures to be used for wind loads on buildings, do I use only the "p" design pressure imposed on the exterior surface of a structure, or do I apply the "GCpi" product of internal pressure coefficient, which is also expressed in psf and results in a near double pressure than that of the "p" design pressure.

Past and currently, use the larger of the two pressures, for insurance. Must I consider the internal pressure coefficient as THE design pressure?

Thank you!

 

[Ron]

EIT2....I don't mean to be cold in this response, but if you are asking this question, it would appear that you are not working with a Senior Mentor. If that's the case, you shouldn't be designing these.

The conditions of the building (shape, location, proximity to other buildings/open spaces/etc.)dictate the analytical parameters to be used, whether you are using IBC, ASCE or others. Senior input and overview should be sought on a local level for such interpretive issues.

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http://pdhonline.org/cgi-bin/quiz/courses/courselist.cgi?class_name=p112

 

[DaveAtkins]

It depends on what you are designing. If you are designing the MWFRS, then the internal pressures on the windward and leeward wall cancel each other out, and GCpi can be neglected. However, if you are designing the exterior wall itself, GCp and GCpi are additive.

DaveAtkins

 

[chichuck]

EIT2,

DaveAtkins' comment is correct.

But to elaborate further, the correct procedure is to add the external and internal pressure algebraically. As he says, for Main wind force resisting systems, the internal pressure cancels out. Also as he says, for designing the walls themselves( wall panels, girts & their connections) you must take the resulant of external + internal. The same thing occurs for the sidewalls.

For roofs, there is no opposite panel as for the walls, so for roofs you must figure the resultant for both MWFS and for the components & cladding.

Also, when calculating overturning loads on the foundation, this same effect occurs with the roof.

For a good reference, check "Guide to Wind Loads in ASCE 7-02, available from ASCE bookstore.

Regards,

chichuck

 

[wyanko]

Based on the question you posed, I am in complete agreement with "Ron". I do not want to seem antagonistic, but I believe a course (seminar, college class) in basic wind engineering would help you greatly. If this is not an option, please read the entire wind loads section in ASCE 7 (7-98 or 7-02). This section is quite comprehensive and would help you better understand this topic. After reading this ASCE section, refer to "DaveAtkins" response as the correct answer to your question.

Best regards,

Bill Yanko

 

[boo1]

EIT2, look at link "EDUCATION FOR ENGINEERS ON FUNDAMENTAL ELEMENTS OF HIGH WIND DESIGN AND THE WINDSTORM PROCESS" avalable free at:

http://www.tdi.state.tx.us/company/wind/dwnloads.html#ircpres

It covers wind effects and damages and the wind load provisions of ASCE 7-02. Learn current approaches for assessing wind loads and examining building performance in severe storms. It is also beneficial to individuals involved in the interpretation of wind load standards and codes. I found a few minor errors, but the guide is very informative.

 

[TFL]

EIT2,

I am in complete agreement with Ron. Is a qualified PE mentoring you? I don’t ask to insult you in any way. I have heard from many colleagues that the mentoring system is breaking down. There are apparently a lot of younger engineers out there who are not being taught properly.

I was luck enough to be mentored by a PE who was a great engineer and a good teacher. I swear there were times when I would ask him or a couple of the other engineers in our office a hundred questions a day. His office was always open and I took advantage of it. You should not be expected to know all the details of building construction in the first 5(or maybe 25 ) years of your career. My mentor (who is still my boss) always tells me that it is in his best interest to have me ask a question on anything I am unsure about. It was better for me to ask him then either waste a day figuring out something he could help me with in 10 minutes or do something completely wrong and have him liable for the results.

In short, EIT2, if you are in a position were you either do not have a qualified mentor or he is not accessible. You need to fix the situation either by talking to the person or changing jobs.

Best of luck
tfl

 

[rrmiv]

Ron and tfl are absolutely right. A senior mentor is essential - nothing replaces the immediate access to a good engineer that has years of experience. EIT2, the questions you have asked on this and previous threads have led me to question the availability of technical expertise in your company. I would follow the advice of tfl, that "you need to fix the situation".

 

[RVSWA]

I want to encourage EIT2 to continue to ask questions. There will always be someone out there who knows more about a subject. The best we can do is seeking that information and learn from it... until we retire. Mentorship has a sliding scale; everyone can contribute to others in some capacity. This board provides an unprecedented opportunity to better the profession, participation on both ends is necessary.

 

[JAE]

Just to take one exception to a technical comment above (I agree with Ron that this is just a too basic question to ask) - but

internal pressure typically cancels out when designing the main wind force resisting system. But in some cases, it does not;

You could have a building with an expansion joint running perpendicular to the wind direction. In this case, the windward half of the building experiences windward load pushing in and internal pressure pushing in or out. The internal pressure on the far leeward wall is not felt by the front half of the building so the internal pressure is additiive to both the windward and leeward forces on each half independently.

 

[boo1]

Depending on if the building is partially or totally enclosed.

 

[DRsquare]

I'm new to wind loads also, and I have a question I hope someone can answer. ASCE-7 does not give a Cf for any open buildings except those with monoslope roofs. What are you supossed to do for open buildings with other roof types. I find it strange that there is no discussion of this in Section 6 of ASCE-7 or the comments. Obviously I'm missing something.
Thanks for the help

 

[connect2]

well with regards to EIT2,
keep asking the questions, the only stupid question is the one you don't ask .. to quote somebody.
There's some good stuff and and some bad stuff on here, i'm always amazed at the people that will step up to the plate and offer opinions when they absolutely don't have enough info to actually give a sound opinion... most of this related to forensic ... i mean how many times we've done investigations, they take alot of time and deep digging ...
Engineer in Training your welcome here. My hope is your using this forum as a sounding board and the people on it will give you the time of day so that when you show up at work your mentor/boss will have a degree of confidence in you.
This forum is a tool. Good luck!
Guess i didn't answer your question ... ASCE 7-02 is your answer.