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# RE: 1997 NDS Equation Error?

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: 1997 NDS Equation Error?
• Date: Thu, 8 Nov 2001 20:43:14 -0800

```Scott,

I agree that mode II is an absurd failure mode since the concrete would
never crush to allow rotation.

To further complicate matters, Table 2.3.2 (Cd) from the 1997 UBC Vol 2,
(Page 2-291) states that fasteners may use Cd=1.6 for Earthquake loads for
mode III and IV behavior in lieu of 1.33. NDS always lets you use Cd=1.6 no
matter what mode governs for EQ.

Show of hands ... does this apply to mudsill anchors? It says it shall not
apply for "joist hangers, framing anchors, and other mechanical fastenings,
including straps and hold-down anchors" I guess if you consider the mudsill
anchor a mechanical fastening, it would not apply. Then the question is,
what would it apply to then? Any plan checkers out there wish to claim they
would accept Cd=1.6 for mudsill anchors?

-gerard
SJ, CA

-----Original Message-----
From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us]
Sent: Thursday, November 08, 2001 2:43 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: 1997 NDS Equation Error?

Fes=Fem per NDS 8.2.3.

Next look at the absurdity of mode II controlling in a wood to concrete
connection.  Mode II is rotation of the fasteners in the members.  It is not
going to happen in a wood to concrete connection, the wood is going to be
the failure mechanism, the concrete bolted connection is much stronger.

The 1994 UBC 2211.2 dealt with this by saying that a wood to concrete
connection should be designed with 1/2 the value of a double shear
connection with the concrete being considered twice the thickness of the
side members. This limited the failure to a mode IIIs because mode II
doesn't apply to a double shear connection.  UBC Table 23-III-N 3180/2=1590
half of mode 3s in single shear.

91 NDS Table 8.2A definitely uses the -Re*(1+Rt)outside the squareroot. For
DFL 3" main, 1.5" side, mode II =1387 when I changed my spreadsheet to
calculate k1 with -Re*(1+Rt)outside the squareroot and Table 8.2A uses 1390.
Thanks for pointing this out to me.

My Breyer's book flip flops between the commentary and examples and my "Wood
Engineering and Construction Handbook" shows it  inside the square root.

Leaving -Re*(1+Rt)outside the squareroot is conservative.

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us

-----Original Message-----
Sent: Thursday, November 08, 2001 8:40 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: 1997 NDS Equation Error?

Hi George,

Here are the values I get for Doug Fir for the case you stated:

Z= 1615 lbs, k1=2.0959 (Mode III Governs ; Term included within the Square
Root)
Z= 1465 lbs, k1=0.7158 (Mode II Governs ; Term Excluded from the Square Root
per 8.2.1)
Z= 1610 lbs (Table 8.2E of NDS)

If you want I can give you all of my variables, but I did consider the Fe
concrete @ 6000 psi (Where do they get that anyway, is it just 3x f'c)

-Gerard
SJ, CA

-----Original Message-----
From: George Richards P.E. [mailto:george(--nospam--at)borm.com]
Sent: Wednesday, November 07, 2001 5:13 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: 1997 NDS Equation Error?

Gerard,

For 6" conc, 1.5" side member, .5g wood, Fem 6000 conc, Fes 5600 wood,
Fybolt 45000, Bolt dia, .875, I get 1615lbs mode IIIs failure with the
-Re(1+Rt)outside the radical in the numerator.

Mode II did not govern???

George Richards, P. E.

-----Original Message-----
Sent: Wednesday, November 07, 2001 4:42 PM
To: 'SEAINT(--nospam--at)SEAINT.ORG'
Subject: 1997 NDS Equation Error?

In light of the anchor bolt design values for wood mudsills thread, I
created a spreadsheet to calc the values. When comparing the values with
those of 1997 NDS Table 8.2E, I was noticing that my numbers where not
matching those for 7/8" and 1" Diameter bolts with 2X mudsills.

The problem lies in the equation for k1 in section 8.2.1 (page 53). My NDS
shows the Square Root Symbol Stopping short of the -Re(1+Rt) value in the
denominator. If I include that value within the square root sign, my table
matches Table 8.2E

Is the k1 equation incorrect or is the table wrong? For 3X and 4X members,
the mode Zii does not govern and therefore I cannot compare other values
within the table.

thanks,
-gerard

Design Group Manager

Duquette Engineering
10 South Third Street
San Jose, CA 95113
T: 408.494.0944 - ext 102
F: 408.494.0940
w: www.duquette-eng.com

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