STEEL BARS FOR FOOTING, COLUMNS, BEAMS

Disclaimer: Always consult with your Structural Engineer for proper sizing/spacing of rebars, this is intended for getting a rough "estimate" of quantities only and should not be used as a structural design alternative.

Typical materials used for building construction regardless of what type, either low storey to high rise buildings mainly use steel bars for its foundations.

Here's a sample calculator to compute for steel bars. How to download read here.

How to use the excel calculator

notes:

Concrete cover used for footing is 0.075m as you may find the table from this source here.

concrete_nominal_cover_table

Sample Computation:

➤ Footing size is 1.50m (width) x 1.50m (length)

➤ sets: 12

➤ 6pcs-16mm Ø def bars both ways (or each-way) = 12pcs cut bars

➤ 75mm concrete cover (0.075m) x 2 sides

1. Compute for cut size of bars (two options)

a. Without bend (straight bars)

● Width or Length less concrete cover on both sides

W-0.075(2) or L-0.075(2)

     ∴ 1.50m - 0.075(2)=1.35m

✔ total of 12pcs @ 1.35m per footing x 12 sets = 144pcs

b. With bend (with hook on both sides)

● Width or Length less concrete cover on both sides

● either use 12d or 16d for hook length

● where d is diameter of bar

W-0.075(2) + 12d (2) or L-0.075(2) + 12d (2)

     ∴ 1.50m - 0.075(2) + 12(0.016)(2) =1.734m

✔ total of 12pcs @ 1.734m per footing x 12 sets = 144pcs

2. Compute total of bars needed from available steel length

● steel lengths at 6m, 7.50m, 9m, 10.50m & 12m 

● check availability within your local area

a. Without bend (straight bars)

length/cut size = pcs you get

try on 6m length

6m/1.35m = 4.44pcs or ✔say 4pcs (usable)

∴ 1.35m x 4 = 5.4m total length with "0.60m" wastage from your 6m length

✮choose length with less wastage to be more economical

total bars:

● by inspection since you can get 4pcs from a 6m length and you need 12pcs for 1 footing

12pcs/4pcs = 3pcs-16mm Ø x 6m length x 12 sets

✔ total: 36pcs-16mm Ø x 6m length 

or other way around 

total of cut bars needed divide with the number of (usable) pcs you get from chosen length

144pcs/4pcs = ✔ 36pcs

let's check the 2nd option if with hook

b. With bend (with hook on both sides)

length/cut size = pcs you get

try on 10.5m length

10.5m/1.734m = 6.05pcs or ✔say 6pcs (usable)

∴ 1.734m x 6 = 10.404m total length with "0.096m" wastage from your 10.5m length

total bars:

total cut bars/usable pcs 

144pcs/6pcs = ✔ 24pcs-16mm Ø x 10.5m length 

3. Compute for Weight of Steel bars in kgs

For steel weight refer to this table below which was used from above calculator.

steel_nominal_weights

a. Without bend (straight bars)

✔ total: 36pcs-16mm Ø x 6m length 

from table 16mm Ø with 1.579 unit weight 

∴ 36pcs x 1.579 x 6m length = ✔341kgs

b. With bend (with hook on both sides)

✔ 24pcs-16mm Ø x 10.5m length 

from table 16mm Ø with 1.579 unit weight 

∴ 24pcs x 1.579 x 10.5m length = 397.8kgs say ✔398kgs

4. Compute for Number of Tie Wires

For tie wires you simply count how many joints each bars will be tied together.

✮you may use 0.40m (400mm) length or 0.30m (300mm) tie wire length

width(pcs of steel) x length (pcs of steel) x 0.30m

                    53m (total length per kg)

given:

● No. of footings=12 sets

● No. of steel bars=6pcs (along width)

● No. of steel bars=6pcs (along length)

6pcs x 6pcs x 12 = 432 intersections or joints where it will be tied up together

    432pcs x 0.30m length of tie wire = 129.6meters

in one kilogram approximate of 50-53 meters in length

     129.60meters / 53m = 2.44kgs say ✔ 2.45kgs

5. Footing info on number of bars not given on both sides

Say you rely on given structural plans but only indicates spacing of rebar instead of number of bars on each side of the footing.

Sample Computation:

➤ Footing size is 1.50m (width) x 1.50m (length)

➤ sets: 12

➤ width/length with 16mm Ø @ 0.15m spacing o.c.

➤ rebars with hook 

How to get number of pcs

a. Net distance / Spacing = space of rebars + 1

● deduct concrete cover on both sides

Width

1.50m - 2(0.075)

        0.15m

= 9 spaces between bars

= 9 + 1

= ✔ 10pcs @ 1.734m along width (cut size refer to above earlier formula)

= ✔ 10pcs @ 1.734m along length (since it's a square isolated footing)

∴ 20pcs @ 1.734m in 1 footing x 12sets = ✔ 240pcs of 1.734m cut size rebars

Knowing that from a 10.50m steel length wastage of 0.096m and you can get 6pcs

a. total bars:

total cut bars/usable pcs 

240pcs/6pcs = ✔ 40pcs-16mm Ø x 10.5m length 

b. weight of steel bars (kgs):

no. of pcs x length x unit weight 

40pcs x 10.5m x 1.579 = 663.18 kgs say ✔663 kgs

c. tie wire (kgs):

sets x (no. of joints x 0.30) / 53m = kgs

(12 x 10 x 10 x 0.30) /53 = 6.79 kgs say ✔7 kgs

note: different results from earlier computation of the same size due to different number of bars both ways and spacing.

All results from above computations may vary from actual, so feel free to add up on computed quantities for possible contingencies.

If you're a homeowner you may use the calculator to get a rough estimate on needed steel bars/tie wires and simply purchase materials on staggered basis as the construction progress and always check from specifications and plans approved by your designers.

This way you can monitor how much budget or quantity approximately needed to your project and counter check quantities if in case you hired a contractor.

Just a reminder when choosing straight bars in your footings to check and confirm by computing its development length.

excel_calculator_footing_development_length

Don't forget to check out separate discussion made for one way slab and two way slab.

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other reference used in this calculator:

Simplified Construction Estimate 3rd edition by Max Fajardo Jr

NSCP 2015