Concrete Design

Question 1

Tension controlled strain limit

Answer 1

Steel strain > 0.005

Question 2

How do you find the nominal moment strength of a beam from the stress strain diagram?

Answer 2

Cc = 0.85f’ca
Ts = Asfy
If doubly reinforced:
Cs = As’fy

Summation of moments around centroid of concrete compression block

Question 3

Steps for flexural design of beams with tension reinforcement only

Answer 3

1. Compute Mu
2. Assume tension controlled. Compute Mn = Mu/phi
3. Find As_req = Mu/(phi x fy x 0.9d)
4. Compute Mn given As_req, verify phiMn > Mu
5. Verify tension controlled by calculating steel strain = 0.003(d/c-1) > 0.005, where c = B1 x a

Question 4

Ec for normal weight conc

Answer 4

Ec = 57000(f’c)^0.5

Question 5

Steps for shear design procedure of nonprestressed beam section

Answer 5

1. Calc Vu (at d)
2. Calc Vc
3. Compute Vu - Vc > phi8(f’c)^0.5bwd
   If not greater, increase size of section or concrete strength, or both
4. Determine required area of vertical stirrups and spacing

Question 6

Steps for corbel design

Answer 6

1. Find Vu and Nuc
2. Check corbel has adequate shear friction area
3. Determine shear friction reinforcement
4. Determine At to resist factored moment Mu = (Vuav + Nuc(h-d)
   At = Mu/(0.75fyjd)
5. Design tension reinf An to resist Nuc
6. Compute area of primary tension reinf, Asc
7. Compute total area of closed stirrups Ah