## Calculating Reinforcements or Iron Rods in Raft foundation

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Image 1, shows beams of section 1-1,2-2,,4-4 and 5-5 but for this purpose we are going to assume that section 2-2 is used for the entire raft.

Image 2, is the reinforcements details for the raft slab also showing its sections.

Lots of people are considering building their houses around water bodies and the large portions of the highbrow areas in Lagos state are waterlogged so the demand for raft foundation is high.

Starting with image 1 section 2-2 the dots represents the iron rods runners, these are usually the thicker of the rods and they lay them to run round the rings of the raft foundation in this case it is a 16mm rod in 9 places.

The ring which is usually the thinner one is represented by the thick line forming a rectangle of 1100mm x 225mm just as shown on the drawings.

Calculating the runners (16mm rods) we need to know the entire length of the foundation trench (excavated portion of the soil) which we can get from image 2, the trench will be along the dotted lines that crosses the thick square columns or pillars as shown in the drawings, the thick square dots are representing the pillars of the building so the trench are been represented by the dotted lines running and joining all of them, this you can easily calculate since the dimension are already given outside the perimeter “check dimensions A-B-C-D and 1-2-3-4-5-7-8

From our sums the total length of trench is 65.6m or 216 feets. Therefore the 16mm rods we need is (65.6m x 9 rods)/11

=54 lengths of 16mm rods.

11meters(m) is taken as the length of a rod so if the total length is (65.6 x 9) then just divide by 11 as was done above then you’ll know the number of rods you are to buy which is 54 lengths in this case,

If 16mm rods go for N2700/rod then

total for 16mm rods=N2700 x 54=N145,800

16mm on the drawing is represented as Y1601 and Y1602

Now to calculate the rings , remember the total length of the trench or foundation hole round site is 65.6m.

Calculate the length of each ring from the drawing , we take each ring to be approximately (175mm +1050mm+175mm+1050mm)=2450mm or 2.45m. Using section 2-2 for all, our rings will be taken as 12mm rods and they spaced at 300mm or 0.3m from each other or (center to center) (See BEAM drawings on image 1-300 c/c links)

So knowing that each ring is 2.45m, we got that by removing 25mm from the dimensions we have round the section of 225mm by 1100mm, so if you remove 50mm from 225 you’ll get 175mm same as removing 50mm (25mm top and bottom of drawings) for 1100m will give 1050mm , since they are spaced at 300mm to each other ignoring the overlap

that we are supposed to also add just for this purpose ,then to

Calculate the numbers of rings in total trench,

65.6m/0.3m or 65600mm/300mm=219 rings and each ring is 2.45m, therefore total lengths of rings

=2.45m x 219= 536.55

Rods are sold in 11m lengths ,so to know the numbers of rods you are going to buy , just divide 536.55 by 11=48 lengths of 12mm rods.

If 12mm rod is N1600 x 49=N78,400.

Calculating the reinforcements/iron rods in slab ( refer to image 2)

For easy calculation of the reinforcements just follow the specifications by the left of drawing then trace the line on each specification to the drawing then check where there is a dot, the line crossing that dot is what to be calculated. The dots are usually supported by arrows both sides, this indicates where that particular rod suppose to end.

So starting from the top

19Y1201-200C/C,

The total length of this is the broken line spanning the entire drawing so the total length is 3825+3950+1375+1250+4975+1250

=16.625(ignoring the return) multiply that by 19 because that is what is stated at 200c/c=315.875m

Divide by 11m=28 lengths of 12mm rods——-(1)

For second line,

3825+3950+1375=9.15m

divide by 11m=1 length of 12mm rods———(2)

Line 3,

This is a peculiar case the line is approximately 2m not really specified in the drawing but the arrows are in 4 places along that line and four of those rods are to be placed at each point where you have (4) written on the drawing.

so 16 x 2m=32, 32 divide by 11m=3 lengths of 10mm rods———–(3)

Line 4,

6Y1002-250C/CB

Make to be 6x2m =12m

divide by 11m =1 length of 10mm rods ——-(4)

Line 5

Trace line under and check the dot , then calculate the broken line crossing it.

12 x(3825+3950+1375+1250)=124.8, divide by 11

=11 1/2 lengths of 10mm rods—————–(5)

Line 6,

38 X 2=76, DIVIDE BY 11

=7 LENGTHS OF 12MM rods—————-(6)

Line 7,

In line 7, the line was not drawn directly to cross the dot, so trace where the dot is up and you’ll see another dot indicating how the iron rods will be placed ,the line is a broken line

83 x (3825)(ignoring the overlap and return)=317.475

divide by 11=29 lengths of 12mm rods———–(7)

Line 8,

8 x2m=16m, divide by 11m

=1 1/2 lengths of 10mm rods———–(8)

Line 9,

8 x2=16m

=1 1/2 lengths of 10mm rods ———-(9)

Note the short lines are immeasurable and are just estimated to be 2m each

Line 10,

77 x (2.910+3.825)=518.595 divide by 11

=47 lengths of 12mm rods——————(10)

Check the other dot at at the same line up and measure the broken line in our case the return and overlap was ignored.

Line 11

103 x 2 =206, divide by 11

=19 lengths of 12mm rods———(11)

Line 12,

19 x 2=38

=3 1/2 lengths of 12mm rods———(12)

Line 13,

19 x 2=38

=3 1/2 lengths of 12mm rods———(13)

Line 14,

34 x 2=68

=6 lengths of 10mm rods———(14)

Line 15

19×2=38

Divide by 11=3 1/2 lengths of 12mm rods ——–(15)

Line 16,

103 x 2 =206, divide by 11= 19 lengths of 12mm rods

Line 17

6 x 2=12m

divide by 11m=1 length of 10mm rods

Line 18

12 x 4975=59.7m

divide by 11m=5 1/2 length of 10mm rods

Line 19

10 x 2=20m

divide by 11m=2 length of 10mm rods

Line 20

8 x 2=16m

divide by 11m=1 1/2 length of 10mm rods

Line 21

19 x (1250+4975) ignoring overlap and return=130.725

divide by 11m=12 length of 12mm rods

Line 22

30 x 2=60m

divide by 11m=5 1/2 length of 10mm rods

Line 23

15 x 2=30m

divide by 11m=3 length of 12mm rods

Line 24

19 x(1250+ 4975+1250+1375)=168.15

divide by 11m=15 1/2 length of 12mm rods

Therefore total numbers of lengths of iron rods of 10mm=271 rods

If 10mm rods are sold for N1300, then 271 rods

=352,300

And the total for 12mm rods for the slab is =219 rods

If 12mm rods are sold for N1600, then 219 rods=N350,400

Total reinforcements for the raft foundation above is=

N145,800+N78,400+N352,300+N350,400

Total=N926,900

February 28th, 2011 at 2:15 pm

thank you for ur tutorial,infact i have not seen any website like urs. pls continue to educate the masses God will bless u the more.

February 28th, 2011 at 2:27 pm

PLS CAN U WRITE ON HOW TO DETAIL A SLAB(STRUCTURAL)

February 28th, 2011 at 9:22 pm

Thanks Kelvin for the wonderful comments you really made my day.

March 4th, 2011 at 6:27 pm

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May 12th, 2011 at 11:48 am

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May 18th, 2011 at 6:52 am

Thanks and God bless you indeed.

July 19th, 2011 at 6:27 pm

Can you please post pictures of works you have done as well as your contact details. Thanks

July 19th, 2011 at 9:52 pm

Arc. Omion Emmanuel

No 21 Micheal Odeyemi street,

Ikola-Ipaja

Lagos

08026228682

email-omionick@gmail.com

Sorry I don’t post pictures of my clients projects on this site but at your request I will send it. Infact check your mail I have already sent pictures of them to you.

Thanks

July 19th, 2011 at 9:52 pm

Thanks

August 9th, 2011 at 12:42 pm

Most i used iron rods for my 4 bungalow in IKORODU…. THE SOIL IS LOOSE ARROUND WATER LOOGED AREA. A LAKE IS JUST AT MY BACK.

MY BUILDE GAVE ME A BILL OF N1.3 MILLION. ANOTHER BUILDER NOT NEED IRON RODS SINCE ITS A BUNGALOW. THAT CONRETE WILL DONE ROUND THE BULDING. THEN FILL UP ALL BULDING SPACES WITH RED SAND AND THEN GERMAN FLOOR.. PLS ADVISE

August 10th, 2011 at 9:57 pm

Good job, you are blessing

October 13th, 2011 at 9:12 pm

very detailed,thanks…pls what quantity of laterite will i need for fill a 10x19m floor area to a height of 600mm above ground level & current cost of a tipper of laterite… thanks

November 1st, 2011 at 11:57 am

hello Engr,

the foundation slab of a building I am supervising cracked and gave way partly due to the fact that rainwater entered into the 4m dept laterite filled sub structure thro. Shower tray. What do you advise Sir?

OLA

November 9th, 2011 at 1:48 am

That was a brilliant one. Please keep it up.

November 9th, 2011 at 1:49 am

That was very brilliant. Kudos.

November 10th, 2011 at 7:18 pm

Sir, you are a blessing to us upcoming builders,thanks and God bless you.

January 31st, 2012 at 8:28 am

Thanq….!for making concept clear

April 17th, 2012 at 3:01 pm

I really want to have samples of your job requiring raft foundation. I have a land which requires raft foundation and I would like to know if you would be the best to handle the project. Please send me samples at oyedeji@un.org

May 12th, 2012 at 9:56 am

thks for ur concern God ll bless u. pls send some pictures of project executed by u.

July 9th, 2012 at 12:23 pm

how i provided extra reinforcement in raft foundation a basic thumb rule

July 11th, 2012 at 8:03 am

Can i make 2nd floor 4 no. 12mm rod in one colom

please inform me urgently

July 16th, 2012 at 8:01 am

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July 16th, 2012 at 8:06 am

Am alway educated reading ynur articles,God bless you please can you write on how to make a building profile.thank you

July 27th, 2012 at 7:33 pm

Building profile is about setting out may be you can get something from here.

http://buildingcontractorsecrets.com/2008/03/setting-out-of-building/

Thanks

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July 22nd, 2013 at 10:11 pm

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August 11th, 2013 at 1:43 am

Hi how to calculate and place steel in foundations ,coloum , beams and slabs. Help me please. best regards

August 18th, 2013 at 4:47 pm

pls how maany tonnes of iron rod are (1)10mm (2)12mm and (3)16mm. Please forward the reply to Email[alaborn07@gmail.com] may God bless u.

Thanks.

August 30th, 2013 at 12:47 pm

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May 16th, 2015 at 8:58 am

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June 9th, 2015 at 2:34 pm

Using 6 pieces of 12mm rod as against 4 pieces of 16mm rod to build a column. Which one gives a stronger column? Thanks.

June 18th, 2015 at 8:14 pm

Please what’s the number iron required for a German floor 94sq meter is the area of the foundation?

Thanks.