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RE: UBC (1997), sections 1912.2 & 1921.5.4 for rebar development lengths

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Samir,

I am replying to you this late.  I have gone thro UBC & Alan Williams' 
'Seismic Design of Buildings & bridges', 3rd ed. on this.
UBC section 1921 is under 'RC ........earthquake motions'.
Section 1912.1 covers, areas in non seismic zone(matches ACI sec. 12.2)
Alan Williams book (example 5-4, pg. 302) calculates ld & splice
per UBC section 1921.5.4 only, for seismic zone.
I think it is clear now.  

Thanks for your earlier reply to my query.

Ravi Vasu, P.E.,


-----Original Message-----
From: Samir Ghosn [mailto:sghosn(--nospam--at)harris-assoc.com]
Sent: Monday, November 04, 2002 4:32 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: UBC (1997), sections 1912.2 & 1921.5.4 for rebar
development lengths


Mr. Vasu
it looks like you are considering two distinct sections of the code. The
first one deals with development of a tension hook in joints of seismic
frames and the other is the required developement length of a bar in
tension.  The two are not equal and you certainly do not want a splice at
the face of the joint where you are trying to develop the bar capacity
especially in seismic frames where your  Mpr is at 1.25 yield capacity of
the bars.  Further you need to examine the required hoops, transverse
reinforcement spacing, in seismic frames where splice occurs.  I hope this
clarifies what you are asking.
Samir Ghson, PE
harris & Associates
 At 04:55 PM 11/4/2002 -0500, you wrote:
>I am sending this message again. I have two UBC sections dealing with
rebar development 
>length  They give different lengths of rebars.
>
>Pl. refer to UBC 1997 section 1921.5.4, development length for rebar in
tension.
>In this section, it is not given to calculate splice length for class A &
B splices.
>
>For example, development length for a # 10 straight bar is
64.9(=3.5*18.54) inch per above section.(60 ksi rebar &
>4000 psi concrete).
>When it comes to Splicing of rebar in tension for Class B, do we have to
multiply the ld (=64.9 in.) by 1.3?? 
>In section 1912.15.1 for splice length(=1.3*ld), it is said to refer ld
from section 1912.2.  & not ld from  section 1921.5.4.
>
>The splice length for #10 class B top bar is 73.6 inches.(per UBC
1912.15.1, with clear cover = 2", beta = 1 & lambda = 1)   
>The ld = 64.9" (from section 1921.5.4) is about 9 inch less than 73.6" .
If you multiply 64.9" by 1.3, it comes to 84.4"
>(now it is 11" more than 73.6".  Which one should we consider???
>
>Section 1912.2 is given clear to calculate ld(same as ACI section 12.2 per
ACI 318-99), with factors to adjust for.
>The ld (for a straight bar)from section 1921.5.4 does not need any
adjustment factors??
>
>Thanks in advance for your time.
>
>
>Ravi Vasu, P.E.


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