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RE: ASCE 7-05 rho

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The Notation section in Section 11.3 of ASCE 7-05, gives one definition of h as “height of a shear wall measured as the maximum clear height from top of foundation to bottom of diaphragm framing above, or the maximum clear height from top of diaphragm to bottom of diaphragm framing above.”  So I’d interpret the h in h/l as wall stud or wall pier height, not story height.  I also would apply the h/l > 1.0 to both shear walls and piers.

 

BTW, the ASCE 7 committee is meeting next week to start working on the 2010 update.  If anyone has ideas for clarifications, send them to SEI.  Or even post them for discussion here; I believe there are a number of committee members lurking about who will see them.

 

Gary

 

Gary J. Ehrlich, PE

Program Manager, Structural Codes & Standards

National Association of Home Builders (NAHB)

1201 15th Street, NW, Washington, DC 20005

ph: 202-266-8545  or 800-368-5242 x8545

fax: 202-266-8369

gehrlich(--nospam--at)nahb.com


From: David Topete [mailto:dtopete(--nospam--at)gfdseng.com]
Sent: Tuesday, March 20, 2007 12:09 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: ASCE 7-05 rho

 

Jake,

My guess, since I don’t have a copy of ASCE 7-05 or 2006 IBC yet, is that if you remove one of 4 walls, it would result in a 33% reduction in strength.  Less redundant system, hence higher value of rho = 1.3.

WRT story height, wouldn’t the height h be the story height, or the height at which the wall is braced laterally and/or the height at which there would be lateral load being transferred to the wall?

Congrats on the “SE.”  Haven’t seen that until now.

 

David A. Topete, SE

 


From: Jake Watson [mailto:jake.watson1(--nospam--at)gmail.com]
Sent: Tuesday, March 20, 2007 7:30 AM
To: SEAINT
Subject: ASCE 7-05 rho

 

Utah has moved to the 2006 IBC and ASCE 7-05 for its building code.  ASCE section 12.3.4.2 & table 12.3-3 contain new provisions for rho.  The application regarding shear walls has me confused.  Basically there are two conditions now, you either have a rho of 1.0 or 1.3.  The shear wall item reads:

"Removal of a shear wall or wall pier with a height-to-length ratio greater than 1.0 within any story, or collector connections thereto, would not result in more than a 33% reduction in story strength, nor does the resulting system have an extreme torsional irregularity... "

If you fail that test, you have a rho of 1.3.

I have two questions about this statement: 1 - does the h/l ratio apply to walls or just piers?  2 - if the h/l does not apply to walls, do you only "remove" one bay of a wall as defined in paragraph b above the table (length of one bay = story height)?  Also, I read the "h/l" value the same as defined by ACI for concrete.  In other words, h is the total height of the wall, not the story height.  Although, I'm not sure if that is the intent when we get to designing homes & the bay definition is clearly story height, not total height.  So who knows?

Thanks for any help,
Jake Watson, S.E.
Salt Lake City, UT