Reinforced concrete structures normally do not crack when carrying service loads.

A rectangular beam has a cross section of b = 18 in., h = 24 in., and d = 21.5 in. It is reinforced with five No. 7 Grade 60 bars. The concrete strength is 5,500 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the assumed modulus of elasticity of the concrete, Ec.

A rectangular beam has a cross section of b = 14 in., h = 26 in., and d = 23.5 in. It is reinforced with two No. 5 Grade 60 bars. The concrete strength is 5,500 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the transformed cross-sectional area of the bars, Ast.

Cracks due to shear are able to cross into the compression zone of the member.

A rectangular beam has a cross section of b = 18 in., h = 28 in., and d = 25.5 in. It is reinforced with two No. 7 Grade 60 bars. The concrete strength is 9,400 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the gross moment of inertia, Ig, for the beam.

A rectangular beam has a cross section of b = 14 in., h = 24 in., and d = 21.5 in. It is reinforced with five No. 7 Grade 60 bars. The concrete strength is 4,900 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the transformed cross-sectional area of the bars, Ast.

The straight line theory is a plastic calculation that gives a good estimate of the concrete and steel stresses at ultimate loads. It is used to calculate the stiffness, EI, at ultimate loads, for deflection calculations, and steel stresses, for use in crack-width or fatigue calculations.

Cracks due to shear are able to cross into the compression zone of the member.

Which is generally shorter?

Concrete cover may be increased to decrease a member’s fire resistance.