Bar Splices in CMU for IBC are too much?
Bar Splices in CMU for IBC are too much?
(OP)
Hello fellow structural engineers,
Several years ago, I think I went to seminar on the UBC transition to IBC, and it mentioned this problem with Masonry, and I am just now running into it:
IN the WSD design method:
IBC has an equation for lap splices that overrides ACI 530, and for #5 bars at the centerline of CMU, the values for splices from equation 21-2 (page 419) are similar to the UBC's 48 db even for low strength CMU. However, when you have (2)#5 each cell, eq 21-2 gives 67*db for 1500 psi CMU and 45*db for 3500 psi CMU.
For #6 bars, one of the factors goes from 1.0 to 1.4, and things get really ridiculous....
For 1-#6 per cell, 70*db for 1500 psi CMU, and 46*db for 3500 psi CMU.
For 2-#6 (1 E.F.), it's 112*db for 1500 psi CMU, and 74*db for 3500 psi CMU.
In the seminar, I remember they said this was a big problem, and that steps were being taken to address it, otherwise you'd just have to do one continuous bar top-to-bottom of your wall.
Anyone know if this has been resolved? How much should I use for lap splices of #6 bar? #5 bar each face? #6 bar each face?
Thank you,
Seattle Mike
Several years ago, I think I went to seminar on the UBC transition to IBC, and it mentioned this problem with Masonry, and I am just now running into it:
IN the WSD design method:
IBC has an equation for lap splices that overrides ACI 530, and for #5 bars at the centerline of CMU, the values for splices from equation 21-2 (page 419) are similar to the UBC's 48 db even for low strength CMU. However, when you have (2)#5 each cell, eq 21-2 gives 67*db for 1500 psi CMU and 45*db for 3500 psi CMU.
For #6 bars, one of the factors goes from 1.0 to 1.4, and things get really ridiculous....
For 1-#6 per cell, 70*db for 1500 psi CMU, and 46*db for 3500 psi CMU.
For 2-#6 (1 E.F.), it's 112*db for 1500 psi CMU, and 74*db for 3500 psi CMU.
In the seminar, I remember they said this was a big problem, and that steps were being taken to address it, otherwise you'd just have to do one continuous bar top-to-bottom of your wall.
Anyone know if this has been resolved? How much should I use for lap splices of #6 bar? #5 bar each face? #6 bar each face?
Thank you,
Seattle Mike






RE: Bar Splices in CMU for IBC are too much?
RE: Bar Splices in CMU for IBC are too much?
RE: Bar Splices in CMU for IBC are too much?
RE: Bar Splices in CMU for IBC are too much?
RE: Bar Splices in CMU for IBC are too much?
For SD, IBC-06 Section 2108.2 modifies the ld equation (3-15) in MSJC-05 Section 3.3.3.3....and it states amongst other things that the ld need not be greater than 72db.
For those who are familiar with or have used IBC-06 in conjunction with MSJC-05, what are your views on lap lengths? Do they appear reasonable?
RE: Bar Splices in CMU for IBC are too much?
So either you design the bars to be only 80% stressed and use shorter laps, or you go with the more conservative lap lengths, or you simply ask the masons to put strain gauges on all the bars and cut them as required.
The equations for typical cases (center of 8" wall - 1500 f'm) work out to be:
Bars <80% Stressed:
#3 15" = 40db (TYPICAL)
#4 20"
#5 25"
#6 30"
#7 35"
#8 40"
#9 46"
Bars >80% Stressed:
#3 27" = 72db (TYPICAL)
#4 36"
#5 45"
#6 54"
#7 63"
#8 72"
#9 82"
RE: Bar Splices in CMU for IBC are too much?
Is the 1/3 increase for Masonry still in IBC 2006 and MSJC-5, aka ACI 530-05/ASCE 5-05/TMS 402-05?
Thank you henri2 & WillisV. Great comments.
SeattleMike
RE: Bar Splices in CMU for IBC are too much?
RE: Bar Splices in CMU for IBC are too much?
Hmm... I thought that the IBC 2003 alternate load cases defered to the material standard for 1/3 increase. AISC 341-05 (steel) strickly forbids the 1/3 increase, but NDS (wood) allows Cd = 1.6, and the MSJC-02 section 2.1.2.3 allows the 1/3 increase.
...except in MSJC-02 2.1.2 it's not clear whether the "E" is working stress level or strength level... I had previously assumed it was working stress level E.... like Section 3-2 of Amrhein, but perhaps that is wrong?
RE: Bar Splices in CMU for IBC are too much?
The MSJC has always allowed this 1/3 stress increase, but for the standard (non-alternate) load combos, the IBC has overriden the MSJC since 2000 and disallowed it.
The NDS material increases are a completely seperate matter and are allowed in the regular IBC combos.