QUANTITY OF STEEL IN ONE WAY SLAB CALCULATION (BBS)
Before calculating the quantity of steel in one way slab it is very important to clear the basic concepts. The one-way
slab steel quantity calculation is done according to its supporting conditions. The one-way slab is supported on two
beams and then to the columns of the building.
The bars we use in the Tension zone of the slab is called Bent up bars. Technically in the slab, we give two different
names of these bars (Main and distribution bar).
Main Reinforcements bars we provide in the shorter span of the slabs and the bars will along the longer span of the
slab. In the long span of the slab the steel we provide known as Distribution steel which doesn’t help to carry any types
of loads and the only function to distribute the load or counter the shrinkage stresses.
For your better understanding let’s take this example.
EXAMPLE:
Suppose we have a one-way slab, which has a length of 5 m or a width of 2 m (clear span). The Main bars will be 12
mm in diameter with 100 mm c/c spacing. The Distribution bars will be 8 mm in diameter with 125 mm c/c spacing. The
Clear cover will be 25 mm (Top or Bottom) and the thickness of the slab is 150 mm.
1. Calculate the quantity of steel?
2. Calculate the weight of steel?
QUANTITY OF STEEL IN ONE WAY SLAB FORMULA SOLUTION
Given Data:
Length
Width
Main Bar
Distribution Bar
Clear cover
Thickness
= 5 m (5000 mm)
= 2 m (2000 mm)
= 12 mm @ 100 mm c/c (Note: c/c means center to center)
= 8 mm @ 125 mm c/c
= 25 mm from (Top and Bottom)
= 150 mm
SOLUTION:
The quantity is done in two steps.
STEP 1. (CALCULATION OF BARS NO’S)
First, calculate the number of bars required (main and distribution both).
FORMULA =
Main bar
= (5000 – (25+25))/100 + 1
= 4950 Divided by 100 + 1
= 51 Bars.
Distribution bar = (2000 – (25+25))/125 + 1
= 1950 Divided by 125 + 1
= 17 Bars.
STEP 2. (CUTTING LENGTH)
MAIN BAR Formula:
cutting length
= (L) + (2 x Ld) + (1 x 0.42D) – (2 x 1d)
# Where:
L
Ld
0.42D
1d
= Clear Span of the Slab
= Development Length which is 40 d (where d is diameter of bar)
= Inclined length (Bend length) or crank length of the bar
= 45° bends (d is diameter of bar)
First calculate the length of “D“.
D = (Thickness) – 2 (Clear cover at Top, BOTTOM) – Diameter of the bar.
= 150 – 2(25) -12
D = 88 mm Ans
By putting Values:
Cutting length = 2000 + (2 x 40 x 12) + (1 x 0.42 x 88) – (2 x 1 x 12)
Cutting length = 2000 + 960 + 36.96 – 24 =2972.96 mm ~ 2973 mm or 2.973 m
DISTRIBUTION BAR:
= Clear Span + (2 x Development Length (Ld))
= 5000 + (2 x 40 x 8) = 5640 mm or 5.64 m
Weight of steel bar in kg:
Note:
W = D2/162 kg/m is utilized when the bar length is specified in m.
W = D2/533 kg/ft is utilized when the bar length is specified in ft.
Main bar:
Number of bars = 51
Total Length
= 51 x 2.973 m = 151.623 m
Weight
= ( D2/162 ) x length
= ( 122/162 ) x 151.623
= 134.776 kg
Distribution Bar:
Number of bars = 17
Total Length
= 17 x 5.64 m = 95.88 m.
Weight
= ( D2/162 ) x length
= ( 82/162 ) x 95.88
= 37.87 kg
Note: The weight of the bar may vary depending upon the properties of the steel.
Pcs of RSB:
For Main Bars
Determine the number of cuts per 6-meter length of steel bar based on the cutting length:
=
=
2.02 (Note that we won’t be needing the 0.02 factor so we will consider only 2 pcs per 6 m)
Use 2 pcs of cuts
To get the total pcs of steel bar, divide the total pcs of main bars by the number of cuts per 6m:
=
= 25.5 say 26 pcs 12 mm steel bar at 6 meters long
For Distribution Bars
Determine the number of cuts per 6-meter length of steel bar based on the cutting length:
=
= 1.06 (Note that we won’t be needing the 0.06 factor so we will consider only 1 pc per 6 m)
Use 1 pc of cut
To get the total pcs of steel bar, divide the total pcs of main bars by the number of cuts per 6m:
=
= 17 pcs 8 mm steel bar at 6 meters long