Concrete Design and Construction
Behavior and design
Reinforced concrete resists tension with steel and compression with concrete. Design uses the strength design method: φMn ≥ Mu, with φ = 0.9 for tension-controlled flexure. Key concepts are the Whitney stress block, balanced and tension-controlled sections, minimum and maximum reinforcement, and the difference between nominal and design strength. Shear is resisted by concrete plus stirrups, and development length ensures bars can reach yield without pulling out.
Serviceability and detailing
Crack control depends on bar spacing and cover. Deflection checks use effective moment of inertia. Durability requires adequate cover for the exposure class. Traps include forgetting that compression steel changes the strain compatibility, ignoring minimum reinforcement for beams, and confusing one-way and two-way slab behavior.
Construction
Construction topics include formwork, curing, consolidation, and cold- and hot-weather placement. Candidates should know that curing affects strength gain and that test cylinders are cured differently from the structure.
Worked rule of thumb
For a singly reinforced rectangular beam with b = 12 in, d = 20 in, f'c = 4 ksi, fy = 60 ksi, and As = 3.0 in², compute a = As fy / (0.85 f'c b) = 180 / 40.8 = 4.4 in. Then Mn = As fy (d − a/2) = 3.0 × 60 × (20 − 2.2) = 3,204 kip-in ≈ 267 kip-ft, and φMn ≈ 240 kip-ft.