Development Length - Concrete vs Grout
Development Length - Concrete vs Grout
(OP)
A standard hook can be developed for tension per Section 3.3.3.2 of ACI 530-05 in 13 db. This is 6.5" for a #4 standard hook.
However, if I used 2500 psi concrete, then I would need 0.02*60000*db /sqrt(2500) = 12" for a #4 bar.
Can someone please explain why you need only half the development length in grout than concrete?
However, if I used 2500 psi concrete, then I would need 0.02*60000*db /sqrt(2500) = 12" for a #4 bar.
Can someone please explain why you need only half the development length in grout than concrete?
We are Virginia Tech
Go HOKIES






RE: Development Length - Concrete vs Grout
RE: Development Length - Concrete vs Grout
RE: Development Length - Concrete vs Grout
In general, there is a difference between grout in concrete when it comes down to the intended use, physical properties and/or testing. Masonry grout must meet the specifications of ASTM C476.
Poured/placed concrete has a much lower slump, while masonry grout has a much higher required strength to do the job of filling and bonding. This can be a factor on smaller bars.
The testing methods for masonry grout and concrete are dramatically different, so comparisons on a psi level are very difficult if not impossible. - Two different materials. Good engineers often have set limit on the maximum strength (f'g) of grout to insure a wall acts in unison as a structural element as designed.
Because the NCMA does significant amounts of testing in their own lab or jointly there may be new information, especially because much of the masonry deals with the smaller bar sizes. Newer results could have had an effect on this subject that is "hot" in some applications.
If the formula is in ACI 530, it should refer to masonry grout and its associated testing.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Development Length - Concrete vs Grout
Under 530, the equivalent embedment length (le) is measured from the point of tangency (ACI 530 1.5 for "le"), which differs from 318. ACI 318 Fig R12.5 shows to add 4db to the 13db in ACI 530 since they are not measured from the same place.
This yields about the same 17 db.
RE: Development Length - Concrete vs Grout
RE: Development Length - Concrete vs Grout
I think TX's response makes sense, but what is throwing me in a loop is the statement in the commentary which states:
"The allowable stress developed by a standard hook, 7,500 psi (51.7 MPa), is the accepted permissible value in masonry design. Substituting this value into Eq. (2-8) yields the
equivalent embedment length given. This value is less
than half that given in Reference 1.14 (ACI 318)"
We are Virginia Tech
Go HOKIES
RE: Development Length - Concrete vs Grout
Going by your concept, for an Fs = 24000, the ld for a straight bar is 36 db. Subtracting 11.25 db from it gives 24.75 db. Is the 24.75 db = 12.375" the amount of straight bar needed beyond the point of tangency to develop this bar?
We are Virginia Tech
Go HOKIES
RE: Development Length - Concrete vs Grout
RE: Development Length - Concrete vs Grout
Re-reading the code very slowly and carefully, I think what you said makes sense. I might had a brain fart when I was reading it.
We are Virginia Tech
Go HOKIES
RE: Development Length - Concrete vs Grout
I think that is what it says but it doesn't address the needed embedment to get that force. Say you are hooking a #6 vertical bar 3" into an 8" wide bond beam. It would seem that it couldn't resist (11.25/48)x 0.44 x 24,000 x 1.33=3,292 lbs.
RE: Development Length - Concrete vs Grout
We are Virginia Tech
Go HOKIES
RE: Development Length - Concrete vs Grout
We are Virginia Tech
Go HOKIES
RE: Development Length - Concrete vs Grout
is it the eq 3-15 of ACI 530 is for the development length and not for the ldh or standard hook?
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds
RE: Development Length - Concrete vs Grout
We are Virginia Tech
Go HOKIES