Masonry beam shear area
Masonry beam shear area
(OP)
Hi everyone. I was wondering if anyone knows what is considered the "net shear area" in a masonry beam. I went through the current masonry code and searched online and it seems to be equal to An which is the cross sectional area. In other words Anv=An. however when im calculating the max allowable shear force (ASD), I get a big number in kips and I feel like maybe it's because these areas are actually different. I tried playing with different possibilities for Anv but I still won't get the right answer. any comment would be very helpful for me if anyone has a clue thank you. below is problem statement (from ncees practice workbook , answer is 12 kips)and then I put down pictures of my calculations










RE: Masonry beam shear area
RE: Masonry beam shear area
Dik
RE: Masonry beam shear area
RE: Masonry beam shear area
For shear reinforced flexural members it would be: Fv= 3*(fm')1/2 <150 psi
RE: Masonry beam shear area
So for your beam, the allowable shear is
V = Fv*b*d = 2*sqrt(f'm)*b*d = 2*sqrt(1500)*7.625*20 = 11.8 kips
RE: Masonry beam shear area
I think that is for shear walls. For flexural members see my post above.
I got about 18k for shear stress......and about 12k based on stirrup spacing. (Which would control.) See Sections 2.3.5.2.3 & 2.3.5.3.
RE: Masonry beam shear area
See the commentary in 2.3.6.1.2 in 530-11.
RE: Masonry beam shear area
Interesting. But the problem statement says 530-05.....and I don't see that in the code commentary there.
RE: Masonry beam shear area
RE: Masonry beam shear area
The problem statement says 530-05. And I don't see it in the commentary there.
No. At least as far as ACI 530-05 is concerned. (I am not familiar enough with 530-11 to say.) But with masonry, the stirrups are carrying all or nothing.
RE: Masonry beam shear area
Mike McCann, PE, SE (WA)
RE: Masonry beam shear area
Everything I'm saying is based on 530-11:
The requirements of 2.3.6.1.2 (a) and (b) put an effective cap on the shear capacity. Since you don't know M, you must take the conservative approach. It's also common to take M/Vd = 1.0 (as noted in the code)
Since your Fvs + Fvm is greater than the capped Fv (capped at 2*sqrt(f'm)), you cannot exceed that limit.
Fvs is based on 2.3.6.1.5 and is 43 psi
Fvm is based on 2.3.6.1.3 and is 44 psi
Fvs + Fvm = 87 psi
The cap of Fv <= 2*sqrt(f'm) = 77 psi .... so you must use that.
(77psi)*(20")*(7.625") = 11.8 kips
RE: Masonry beam shear area
I won't tell if you won't.
I point it out in large part not just to get the "right" answer....but to hammer the point home to the OP (if he is studying for/taking a NCEES exam): he'd better be using the code called out in the problem statement.
Good info. I got exactly 12 kips based on stirrup spacing. (I.e. V=(Av*Fs*d)/s. That is rearranging eq. 2-26 in 530-05. )
RE: Masonry beam shear area
RE: Masonry beam shear area
I'm sure the SE exam is no longer based on '05. Must've been based on '11 when I wrote it.
RE: Masonry beam shear area
RE: Masonry beam shear area
Amrhein was the author of my first masonry design book... nearly 30 or 40 years back; at the time, it was likely the best masonry book published... nice to see the name again.
Dik
RE: Masonry beam shear area
RE: Masonry beam shear area
sqrt(1500) = 38.8 psi.
When you use ksi sqrt(1.5) = 1.22 ksi which is not the correct answer
RE: Masonry beam shear area
BA
RE: Masonry beam shear area
Dik