Reinforced Concrete, Prestressed Concrete and Steel Design — Practice

Question 1

State the partial safety factors for concrete and steel in IS 456.

Accepted Answer

1.5 for concrete and 1.15 for steel.

Question 2

When is a slab treated as one-way?

Accepted Answer

When the ratio of long to short span exceeds 2.

Question 3

A beam of width 250 mm and effective depth 500 mm uses M20 and Fe 415 with Ast = 1000 mm2. Find x_u and say whether it is under-reinforced.

Accepted Answer

xu = 0.87 x 415 x 1000/(0.36 x 20 x 250) = 200.6 mm. The limit is 0.48 x 500 = 240 mm, so it is under-reinforced.

Question 4

List the losses of prestress that occur only in post-tensioned members.

Accepted Answer

Friction in the duct and anchorage slip.

Question 5

State the axial capacity formula of a short column and the minimum eccentricity.

Accepted Answer

Pu = 0.4 fck Ac + 0.67 fy Asc, with minimum eccentricity the larger of L/500 + D/30 and 20 mm.

Question 6

Define the shape factor and give its value for a rectangular section.

Accepted Answer

The ratio of plastic modulus to elastic section modulus, Zp over Ze. For a rectangle it is 1.5.

Question 7

How is shear reinforcement designed in a beam where the nominal shear stress exceeds that of concrete?

Accepted Answer

Stirrups carry the excess, Vus = 0.87 fy Asv d / sv, with spacing sv chosen to supply it, provided the stress stays below tau c,max.

Question 8

What partial safety factor does IS 800 use for yielding?

Accepted Answer

1.10.

Practice — Reinforced Concrete, Prestressed Concrete and Steel Design