Out of Plane Anchorage Forces (Rigid Diaphragm)
Posted 10 April 2012 - 10:17 PM
Text 1: 2009 Design of Reinforced Masonry Structures by CMA of California and Nevada
Structural walls supported by diaphragms that are not flexible, the out-of-plane forces are given by ASCE 7 sections 12.11.1 and 12.11.2. Non-structural walls connected to non-flexible diaphragms are given by ASCE chapter 13. Section 3.9.2 and 3.9.3 for those who have the book.
Text 2: Seismic and Wind Forces 3rd Ed. by Alan Williams
Anchorage for a rigid diaphragm shall resist the horizontal forces determined from ASCE Eq. 13.3-1. Page 96 for those who have the text.
My Assumptions / Confusion?
My interpretation of the code falls directly in line with the statements from text 1. I was shocked when reading through text 2 because there is no discussion or any way I can read the code that says all connections to rigid diaphragms should be design per ASCE Ch. 13. I felt that a flexible diaphram should have higher anchor loads than a rigid diaphragm due to acceleration. How are others interpreting this?
Also, could a shear wall possibly be considered a non-structural element for out-of-plane loading? I felt that if it is load bearing it will be structural regardless of loading direction but in a gravity supported frame system it may not.
Any help would be appreciated as this is not something I commonly work with.
Posted 11 April 2012 - 12:15 AM
It sounds like you're saying that chapter 13 is required for rigid diaphragms and section 12.11 is used for flexible based on item 1 and 2 above.
"Non-structural walls connected to non-flexible diaphragms are given by ASCE chapter 13." - a non-flexible diaphragm would be a rigid diaphragm... no inconsistency with the Alan Williams book.
Whether the wall is structural or non-structural is not the issue as much as it is that the diaphragm in the Williams book is not flexible.
See attached spreadsheet. It might help.
Posted 11 April 2012 - 05:16 AM
Posted 11 April 2012 - 01:39 PM
Posted 11 April 2012 - 01:50 PM
I've have gone through the excel sheet you provided (thank you for that by the way) and it matches with how I planned on approaching this type of problem. I was just confused when reading the CMACN information. I just want to be prepared if I show up and IL doesn't allow all of my text books. I don't like the fact that Williams book on Wind and Seismic has the word "examples" in the title.
Posted 11 April 2012 - 01:53 PM
Posted 12 April 2012 - 11:02 PM
Posted 12 April 2012 - 11:52 PM
2006 IBC Structural/Seismic Design Manual Problem 35 Commentary "...For rigid diaphragms of SDC's C, D, E and F, the seismic anchorage forces are given in 12.11.2"
I haven't seen any references indicating using chapter 13 for structural walls with rigid diaphragms.
Posted 13 April 2012 - 04:47 AM
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