Category Archives: reinforcement

RCC Curved beam

One of my students has asked me this question today :

Sir , how to find out the reinforcement for the curved beam ?

So , dear readers , let us solve this question today.

For the sake of understanding , I have assumed the following data for the curved beam.

Curved length of the RCC beam : 8560 MM.

Note :

In case , it is not possible , to measure it from the drawing , due to lack of clarity on the beam curvature , I suggest that first let the beam bottom be fixed at the position and then actually measure the beam curved length at the position. This shall give the most correct beam length at site.

Beam size :

Width :250 MM.

Depth : 650 MM.

Beam top bars : 2 Nos x 12 mm dia.HYSD bars [ Straight ]

Beam Main bars : 4 x 25 mm dia HYSD bars [ Straight ]

Bent up bars : 2 x 25 mm dia HYSD bars 

Stirrups : 8 mm dia HYSD bars @ 200 c/c.

We also know that :

Beam cover : 25 MM.

Stirrup hook length : 2 x ( 10 X dia of stirrup bar )

Development length for the top bars : 450 mm.

Development length for the bottom bars : 450 mm.

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Now with the above information , let us calculate the beam reinforcement as follows :

  1. Top bars : [ 8560- (25-25)+ (450+450) ] = [ 8560 – 50 = 900 ] = 9410 mm = 9.41 M.
  2. Bottom straight bars : 9.41M.
  3. Bent up bars : ( 8560-50 )+ 2 {0.41( 650-50)} + (450+450) ] = ( 8510 + 2 x 0.41 x 600 )+900  = ( 8510 +492+900 ) = 7902 mm = 7.902 M.
  4. Stirrups : Cutting length : 2 { ( 250 -50 ) +( 650 -50 )} + 2 X 10 x8 = 1600 + 160 = 1660 mm =1.660 M                                           No of stirrups : ( 8560/200 ) + 1 = 43.8 say 44 Nos.

Abstract for the weight :

  1. Top bars : 2 x 9.41 M x 0.89 Kg/M = 16.75 Kg.
  2. Bottom straight bars : 4 x 9.41 M .x 3.86 Kg/M = 145 Kg.
  3. Bent up bars : 2 x 7.902 M x 3.86 Kg/M = 61 Kg.
  4. Stirrups : Cutting length : 44 x 1.660 M x 0.39 Kg/M =   28.5 Kg.                                                                                                                                                                                                                                                                                                                                                  Total weight :  252 Kg.                           

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Pile Cap reinforcement weight ?

PILE CAP REINFORCEMENT :

Data from the drawing :

 SIZE OF THE PILE CAP : 750mm X 750 mm X750 mm.

Stirrups : 10mm HYSD bars @ 200 C/C.

 

What we know :

Cover for the Pile cap : 40 mm.

Stirrup size :  750 – ( 40+40) = 670 mm.

Cutting length for the stirrup : [ 670 +670+670+670 ]+ {2 (10X10)} = 2880 mm = 2.880M.

 

No of stirrups :

X direction : (750 /200 )+1 = 4.75 = 5 nos.

Y direction : (750 /200 )+1 = 4.75 = 5 nos.

Z direction : (750 /200 )+1 = 4.75 = 5 nos.

Total : 5+5+5 = 15 Nos .

 

Weight :

15 X2.88 x 0.62 = 26.784 Kg.

 IMG-20150521-WA0041

How much material is needed per pile ?

Background :

As a construction person , you should also be able to calculate the material required for the construction . Today , we shall learn how to calculate the materials required for the Pile foundations.

 

Data :

Pile Shape :  Circular

Pile Diameter :  600 mm

Pile Depth : 8.35 M.

Mix of concrete : M20

Reinforcement: 6 HYSD bars of 16mm diameter .

Stirrups :  8 mm diameter bars provided at a spacing of 200 mm C/C [ Center to Center ]

 

As a construction person , we know the following :

1.Unit weight of  16mm dia HYSD bars : 1.58 Kg/m

2.Unit weight of  8mm dia HYSD bars : 0.39 Kg/m

3.Cover for Pile reinforcement : 50 mm

4.Material consumption for Concrete M20 :

  1. Cement : 7.87 Bags/ CuM
  2. Sand : 0.41 CuM.
  3. Aggregate : 0.83 CuM.

 

4.Formula for volume of the cylinder = (0.785).D2.H                                                                                     where D : Pile diameter in M & H : Pile height in M.

 

Having thus prepared , we shall now go for the actual calculations as follows .

Part A : REINFORCEMENT :

A.01 : Longitudinal bars :

Cutting Length of bar : 8350 –( 50+50 ) = 8250 mm = 8.25 M.

Weight :

6 Nos X 8.25 m X 1.58 Kg/m =   78.21 Kg.

A.02 : Stirrups :

Stirrup diameter : 600 –( 50+50 ) = 500 mm.

Cutting length :  ( 3.14) D +( 2x10d )

D : Stirrup  Diameter =500 mm

d:  Diameter of bar used for stirrup = 8 mm.

=  (3.14 x 500 )+( 2x 10×8)  =  1730 mm =   1.73 M.

No of stirrups : ( 8350 / 200 )+1 =  43 Nos

Weight :  43 Nos x 1.73M x 0.39 Kg/m = 29 Kg.

 

Summary of Reinforcement :

16mm dia HYSD bars : 78 Kg / Pile

8mm dia HYSD bars :   29 Kg / Pile

 

AUTHOR SHOWING THE PILE REINFORCEMENT  [ NOT YET POSITIONED ] FOR FLYOVER AT PUNE.
AUTHOR SHOWING THE PILE REINFORCEMENT
[ NOT YET POSITIONED ] FOR FLYOVER AT PUNE.
Part B : M20 Concrete :

Volume of pile :

(0.785).D2.H

=0.785 x 0.6 x 0.6 x 8.35

=2.36 CuM /Pile

 

Cement required :

2.36 x 7.87 bags = 18.57 bags

Sand Required :

2.36x 0.41 CuM = 0.968 CuM.

Aggregate  Required :

2.36x 0.83 CuM = 1.96 CuM.

 

Final Summary :

Material required per pile of 600 mm dia. having a length of 8.35 M.

Cement : 19 bags

Sand : 1 CuM

Aggregate : 2 CuM

Reinforcement bars :

16mm dia HYSD bars : 78 Kg

8mm dia HYSD bars :   29 Kg

 IMG-20150521-WA0047 IMG-20150521-WA0045

 

 

 

 

 

What is a TMT steel rod and what is the difference between HYSD and TMT bars? What are the pros of TMT bars over HYSD and mild steel?

Answer by Saket Roy:

A2A.

I will keep it to the point as far as possible. For definition and detailed manufacturing process of TMT and HYSD bars you can of course Google or look at other answers. But how we Civil Engineers use these two terms matters the most, at least to me.
So, what do we call an HYSD :
HYSD = Torsed/twisted steel (TOR Steel Bars)
HYSD = Cold Twisted Deformed Steel Bars (CTD Steel Bars)
HYSD = High Yield Strength Deformed Bars (Of course!)

And, TMT Bars:
These are manufactured by a quenching and tempering process which allows the outer surface to cool much faster than inner core and hence making a temperature gradient from bar axis to periphery. This results in harder martensitic outer surface while the inner core cools slowly resulting in ductile inner core.

Now there is a catch! Technically TMT means a type of quenching and tempering process and it would not be precise to call it a Thermal+Mechanical treatment. Because, even the HYSD bars are treated at high temperatures and then rolled and twisted for shaping and hence it is also thermally + mechanically treated. So the difference lies in the exact process of making these two types of bars and not just in their names.

For pros of TMT bars over HYSD and mild steel you can refer to other answers and elsewhere but mainly TMT bars are superior than HYSD because of lesser residual stresses, more corrosion resistance due to hard surface and more ductility for similar strength grade.

What is a TMT steel rod and what is the difference between HYSD and TMT bars? What are the pros of TMT bars over HYSD and mild steel?

Why do homes that have concrete slabs, that are cast on the ground, have an upper reinforcement?

Answer by Isaac Gaetz:

In the USA, the most common practice is to use a single layer of reinforcing, placed in the upper half of a slab on grade. The reinforcing is commonly welded wire fabric, not rebar. Typically the reinforcing will be placed at 2″ below the top of slab, at the first 1/3 point, or mid depth. The specific choice of the reinforcement depth will depend on the slab thickness (2″ and the first 1/3 are the same for a 6″ slab, for example).

For most soil conditions, uplift loading is not a significant concern, nor is flexure.  Instead the reinforcing’s primary role is to limit crack width and reduce shrinkage. If we only place reinforcing below the neutral axis, we’ll create large cracking at the top surface of the slab. This happens for two reasons:

  1. First, the bottom concrete, enclosed on all sides by soil, moisture barriers, and the concrete above, naturally has less access to air and will generally cure more slowly than the concrete on top of it. Because the curing process involves the concrete losing moisture and shrinking, the top concrete with tend to shrink more and faster than the concrete below it.
  2. Second, the reinforcing, if placed in the bottom of the slab, with further restrict the bottom concrete from shrinking. This will amplify the problem identified in the first point above.

Instead, we use reinforcing in the top of the slab to neutralize some of the tendency of the upper concrete to cure and shrink before the concrete below it.

As with all concrete, the goal isn’t generally to eliminate all cracking, it is to control it.

Larger reinforcing rebar, including multiple layers of reinforcing is typically only used in expansive soils, or in mat foundations.

Why do homes that have concrete slabs, that are cast on the ground, have an upper reinforcement?

You excel !

Dear Reader ,

Good afternoon !

Have been doing some work on excel recently and have already made one simple application  for construction persons .
This shall be useful for the office as well for site people.
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Brief description about this application :
 Its in excel and can be applied to any Beam size .
  1. You can feed the following :
    1. Beam dimensions ( length , width ,depth )
    2. Reinforcement details :
      1. Top bars ( Dia and Nos )
      2. Bottom bars ( Dia and Nos )
      3. Stirrups ( Dia and spacing  )
      4. bent up bars ( Dia and Nos )
    3. Rates :
      1. Tor steel  (  per kg )
      2. Binding wire  (  per kg )
      3. Labour rates for reinforcement (  per kg )
  2. It calculates :
      1.  the cutting lengths for :
        1. Top bars
        2. Bottom bars
        3. Stirrups
        4. Bent up bars
      2. No of stirrups needed
      3. Total weight of reinf per beam
      4. Total volume of one beam
      5. Reinf weight per CuM of concrete
      6. Reinf. cost per CuM of concrete
I suggest you also start working on excel right now and create similar application .
This shall be quite useful to you on day to day work at site.
In case you want a starting point , I can also provide you with what I have created.
For that , just subscribe through the form provided in the post :
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WORK ON EXCEL BY MY HI-TECH AND ENTHUSIASTIC STUDENT : GANESH

In case you want to read more on Excel , do read these articles :

Wish you Excel in your work

How can I learn Excel ?

 

Seven simple field tests for cement

This Article is specially authored by young and enthusiastic Mr. Mukund Paprikar , for our blog 
Overview :

Cement is just like the oxygen for majority of the buildings and specially for RCC framed construction.

Whenever we think of any mortar or concrete , we  invariably consider the cement mortar or the cement concrete.
It is therefore essential ,  to only use  cement which is of assured quality for the construction .

This article beings forth certain simple field tests which you can carry out yourselves at the site to assess the        suitability of the cement .

Basic parameters :

We buy cement as per the grade.

Ordinary Portland cement is available in Grades 43 & 53  whereas Pozzolona Portland cement comes                          in Grade 33 only Although this grade is not printed on the bag for PPC  )

Background :

Normally test certificates are made available by the cement manufacturers along with each consignment of the cement .
For further verification , the cement can be sent to the recognized test labs for testing.
Thus , the test results shall indicate the suitability of the cement . The laboratory tests include : Compressive strength , consistency test , residue test etc .This might  take  more than 28 days to get the results and hence it may not be possible to immediately point out whether or not to use a particular batch of cement at site. 
Therefore , it is essential that certain preliminary assessment is made at the site by the site personnel :
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Field tests for cement :

These are derived by the experience of the construction personnel and can give rough  indications about the unsuitability of  cement .
It is suggested that each site person is familiar with these simple tests so that a quick assessment can be initiated at site it self.

Group A : By Appearance and Feel :
1.The color of cement should be uniform . Preferably greenish grey.
2.Open the bag and observe the cement .There should not be any lumps visible  .If any lumps are found , press the lumps between fingers.  If it becomes powder ( without lumps ) ,  it is alright . In case , lumps are still seen even after pressing , it means that cement is already set and is not suitable.

3. Insert  the palm inside a cement bag , the cement should feel cool to the palm. If it is cool it is quite alright.

4.Take a little cement in the pinch and rub it by fingers . If the feel is gritty , it means setting has began in the cement.

5.Cement should not feel oily when touched with fingers.

Group B : With Water :

6. Throw a hand full of cement on the water surface inside the bucket . If the cement floats on surface , the quality is acceptable but if it sinks in the water , it is carrying impurities.

7.Take about 100 gm of cement and make a stiff paste by adding very little water .Form a cake out of this paste and place it on a glass plate. The cake should retain its sharp edges. 
Submerge this plate with cake in the water in a bucket .After 24 hours , the cake should not lose its shape  and must have attained some strength.

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Note from the Blog :
Dear Reader ,
Some more photographs are to be uploaded 
Please give us a day or two for bringing the photos which shall demonstrate the various field tests with clarity.