# Some vital short notes for civil engineering students Least Cover for several RCC members

Slab = 20 mm
Beam = 25 mm
Column = 40 mm
Footing = 50 mm

Exact unit weight of steel

The unit weight concerning steel should be 78.5 KN/m3

Proportion of cement, sand and aggregate for different types of concrete mix grades

M10 = 1:3:6
M15 = 1:2:4
M20 = 1:1.5:3
M25 = 1:1:2
M30 = 1:1:1

Exact unit weight of concrete

It is based on the type of aggregates as well as the amount of voids. With adherence to IS : 456-2000, the unit weight of PCC is 24KN/m3 and RCC is 25KN/m3.

Crank Length In Slab

The crank length should be 0.42D. Here, D denotes depth of slab. It is obtained by deducting bottom cover from top cover i.e. Top Cover – Bottom Cover.

Initial & final setting time of standard cement mix

Initial setting time for standard cement mix should remain approx 30 minutes for different types of cements. For masonry cement it should be 90 minutes. Final setting time of standard cement mix should be 10 hours maximum. For masonry cement, it should not go beyond 24 hours.

Compressive Strength Of Brick

For first class brick, the strength should be 105 kg/cm2
For second class brick, the strength should be 70 kg/cm2
For fire brick, the strength should be 125 kg/cm2

The weight of steel bar in reinforcement

The weight of bar should be kg/m = D2/162.2, here dia means diameter of bar in mm.

Steps for design mix concrete according to IS10262

Target denotes strength fm = fck+1.65 σ, σ = standard deviation
Standard deviation for M10, M15 = 3.5
Standard deviation for M20, M25 = 4
Standard deviation for M30 to M50 = 5

Strength of concrete

Flexural strength of concrete (modulus of rupture) fcr = .7√fck

Split tensile strength of concrete (fct) fct = 66fcr

Minimum size of column footing

Minimum size of footing for 9” x 9” column should not be under 1.5 x 1.5 feet

Minimum size of footing for 1’ x 1’ RCC column should not be under 2’ x 2’

Standard Height Of Building Floor

The height should be 11 feet but should not be under 10 feet.