Building Persona

In this article we shall understand about the total personality of a building.

Before we start exploring the various components of a building, we need to understand the basic distinction between 

Framed structures and Load bearing construction.

 

Framed structures are those buildings where the load from the slab is transferred to beam which transfer the loads to columns which in turn transfer the entire load to the foundation below. The foundation could be Open foundation or Pile foundation.The walls do not carry or transfer the load of the slab or beams.

That way ,the only purpose of having walls is to create a privacy and create a buffer between the external and  internal environments. Removal or modification of these walls is relatively easy in framed structures and it does not normally affect the overall load distribution of the building.

RCC Framed Structure.

Load bearing construction , on the other hand is that building where the load of the slab is directly transferred to the walls which transfer the load to the wall foundation .Wall foundation is a continuous strip of foundation built in either stone masonry or brick masonry.Since the walls are carrying the loads from above, it is not easy to modify or remove the walls from a Load bearing construction. This type of construction is quite vulnerable in case of earthquakes.

Load bearing construction in Black basalt stone

In this article we shall only be discussing the Framed structures.

For our understanding, we divide the Framed building in two main sections.

1.Below the Plinth which is also known as substructure and 

2.Above the Plinth which can be called as superstructure.

 Now let’s see What is meant by Plinth.

It is the floor level at the ground floor.This is kept at a higher level than the front road.

Basic purpose of such a height is that the surface water from the adjoining roads should not enter the building.

If the Plinth is higher than the road level ,then the chances of the various reptiles,rodents, dust ,garbage entering the building are also reduced.

Steps leading from Ground level to the Plinth level

So now having understood the concept behind Plinth,

let us see what parts of the building are hidden below Plinth ?

Foundation: It could be Open foundations or Pile foundations.

A Single pile foundation

An open foundation.[ Isolated stepped type of footing]

Plinth beams : Beams tying the columns at plinth level 

Plinth beams

Ground Beams: Beams tying the columns at ground level 

Ground beams

 

Tie Beams: Beams tying the foundations at foundation level .These are used in case of earthquake resistant buildings and are used only if Open foundations are used.

Tie beams

 

Basements: Every building may not have a basement. A basement is an use-able area below the plinth level which can be used for a Non-residential purpose only such as Storage, Offices, Shops or for housing facilities such as water treatment plants etc.

 

Septic tank :  A facility which converts the organic sewage into inorganic stable matters through the interaction of the anaerobic bacteria. Anaerobic bacteria can only thrive in the absence of air .

 

Underground water tank : Storage of water below the plinth level. This could be used for drinking purpose , general use or for the fire- fighting applications.

 

Columns below Plinth: That portion of the column which starts from the footing and reaches the plinth level .

C

 

Masonry below the Plinth : This is done on the periphery of the building.

Basic purpose is to retain the Plinth filling .

 

Plinth Filling : Comprises of murrum, soling ,PCC and flooring

Stone soling in progress

Drainage lines : Which connects the outlet of the toilets to the septic tank via a grid of Gully Traps & Chambers & Manholes.

Facing the face lifting ?

The construction can be broadly classified into three main groups. A new construction , a renovation job and routine maintenance of the buildings.

This article explains the various challenges faced before, during and after the renovation work.

Renovation work could be of various types .It could be as simple as the painting works or it could be complicated such as raising further stories on an existing old structure.
Or it could be extending the building or part of it horizontally.

Expansion (horizontal or vertical) is a different game than the new construction on a maiden plot.

Horizontal extension to a residential unit

 

The situation becomes more spicy when (after talking with the structural designer of the old building) we realize that during earlier design, there is no provision for the vertical expansion.

This has two aspects. This means either the foundations are not strong enough to carry the extra load due to higher floors and there is no provision of dowel bars in the upper floor columns .

In such a case we may need to provide additional  footings to cater the additional loads.It may also be necessary to strengthen the existing columns so as to make them strong enough to carry the extra loads.

Columns being strengthened to carry extra loads due to vertical extension.

Then comes the vital issue of connecting the old concrete with the new concrete.
This issue is also two fold. The old concrete must bond with the new concrete and the reinforcement bars from the old concrete to the new concrerte must have a continuity .
Since there is no structural provision kept during earlier construction, there won’t be any dowel bars left with the columns or beams or slabs.
Dowel bars are the extra reinforcement bars kept during the concrete which shall be used to tie with the new reinforcement bars of the newly laid concrete.
This problem can be solved with Re-bar grouting method.

In this method, holes are drilled in the old concrete and fresh dowel bars are grouted with strong epoxy material.

Old concrete punctured to make provisions of dowel bars

Form work being erected at the junction to pour new concrete which shall bond with the old concrete

 

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The Foundations menu card:

The very first decision one has to take regarding the type of foundation is :
Whether to go for an Open foundation  or resort  to a Pile foundation ?

Open pit done for the Isolated column footing

Quick reference : An open foundation is where a open pit is done for laying the footing whereas in the pile foundation , there is no need of any open pit .

The piling is a relatively clean process in which a cylindrical hole is bored in the soil up to desired depth, reinforcement cage is lowered and concreting done.

Group of Two piles

For this selection ,we need to ask the first question :
How is the sub strata ?
whether hard strata is available at a reasonable  depth from the ground level ?

Before going further ,let us see the typical composition of the substrata :

As we go from top to bottom:
Black cotton soil (SBC: 10 Ton/SqM)
Yellow soil (SBC: 15 Ton/SqM)
Mixed soil (SBC: 10 Ton/SqM)
Soft murrum (SBC: 20 Ton/SqM)
Hard murrum (SBC: 30 Ton/SqM)
Soft rock (SBC: 80 Ton/SqM)
Hard rock (SBC: 100 Ton/SqM)

Note :
1.SBC: Safe bearing capacity of the soil.
2.These values are indicative and are provided  to highlight the relative difference between various layers.

Breaker being used to cut through the layer of the hard rock

Normal question then comes to the mind is how does one find the SBC at a given location ?

It is suggested to have a survey done of the various construction sites in the vicinity. This gives an overall view of the type of strata available & types of foundations being used.

It is also useful to have a trial pit excavated at the site. This gives a correct picture of what’s exactly lying below the surface.

Trial pit done to understand the composition of strata below surface

However, to arrive at the exact Safe bearing capacity ( SBC )  more accurate methods need to be used such as :

1.Triaxial compression test.
1.1 Undisturbed samples
1.2 Disturbed sample test
2.Plate load test

Test no 1 is carried out in the laboratory based on the samples collected from site . This is quite fast & quite economical.
Test 02 is conducted on site at the specific level where we need to know the SBC. This takes time , quite expensive but gives comprehensive insight about the probable behaviour of the soil.
For an open foundation hard murrum with a SBC of 30Ton/SqM. can be  considered as a good hard strata.
soft rock & hard rock are considered.
Now in this context let us examine a few cases :
Case 1.  The cross section of the substrata indicates that black cotton soil exists upto 4′ . Yellow soil is between 4 to 6 ‘. Hard murrum with a safe bearing capacity (SBC) of 30 T/SqM is available from  6 ‘down wards upto 10′ .The fragmented or soft rock formation is between 11′ to 16′ and the hard rock is beyond 17′.

Now looking at this strata ,it is clear that it is possible to select Open foundation.
The excavation will have to be done only for a depth of 6′ to 7’.

A trapezoidal footing .Hard Strata at only 4’0″ from the natural ground level.

Finding the right foundation ?

Suppose you are asked
“How would you decide the type of foundation for a building ?”

This article explains the various criterion which affect the design of a building foundation.

RCC Isolated Step footing

Foundation design is a complex subject and needs careful analysis of multiple factors.

Most important thing to remember is that foundation solution for any building is very special.

Therefore it is never possible to directly replicate the same to any other building without due diligence.

The factors affecting the design of a foundation depends on :

A. Planning factors:
A.1 Column height
A.2 Distance between adjoining columns.
A.3 Load on the column 
( dependent on A.1& A2)
A.4 Loading conditions like Dead load,Live load, Wind load,Seismic considerations etc.

These factors are controlled and /or influenced  by the planning team .The functional needs of the Owners  are transformed into shape( geometry ) & size  by the architect .

RCC consultant gives the structural strength to the various elements like slab beam column etc.

B.Natural factors:

B.1 Type of strata at location of foundation

B.2 Safe bearing capacity of the soil

B.3 Sub soil water level

B.4 Vicinity of a river or stream from the location

After due considerations of all the factors specified in A & B above, the RCC designer arrives at an optimal solution for the foundation  which we shall explore in detail in the next article.

Earthquake resistant building

Suppose the interviewer asks you : What are the provisions to be made in a building to make it earthquake resistant ?

You can give a reply that although this answer is in the purview of a RCC consultant ,let me try to reply from my general knowledge.

The national building code released by  Bureau of Indian Standards (Edition 2000) provides map of India where different zones have been identified based on their sensitivity to earthquake forces.
Accordingly, each zone has been allocated a  seismic coefficient which defines the intensity of earthquake forces in that region.
This coefficient has to be taken into account while designing the foundations.
How ever, as a general guideline  ,
these are the  provisions are to be made in a building’s structure to make it resistant for earthquakes.

1.Tie beams
2.Shear walls
3.Through lintels
4.Band beams( Patli)
5.Symmetric position of water tank
6.Limited overhangs
7.Entire design to be cross checked for the seismic forces for that seismic zone.

Interview Questions :

Imagine that you are appearing for an interview for the post of  construction Supervisor.
If the interviewer asks :
” How much area of a slab can be cast with one transit mixer if the slab thickness is 6″ ?
What shall be your reply ?
This article takes you through the logical answer to this question.

Before proceeding further ,let me ask:
” What is a transit mixer ?

Some of you might explain :
” A transit mixer is a mixer mounted on a truck and it  transports the ready mix concrete from the batching plant up to the actual site where it shall be cast. The concrete drum slowly rotates around its own axis so that the concrete does not become solid during the transit period.
“The normal transit mixer has a capacity of carrying 6 cum of ready mix concrete ”
Small transit mixers of 4.5 CuM capacity as well as jumbo transit mixers with carrying capacity of 7.5 CuM.
You already know:
1 CuM = 35.29 Cubic Foot.Cft

So now the original question is transformed like this:

” How much area of a 6″ thick slab  can be cast with 212 Cft  of Concrete ? 
( Concrete per transit mixer : 6 CuM  or 6x 35.29 =212 Cft  .)

Or

” How much area of a 6″ thick slab can be cast If 212 Cubic Feet of  Concrete is available  ? “

Volume = length x breadth x depth

Area = length x Breadth.

Therefore,

Volume = area x depth.
Now let us put what we know in this equation:
212 Cft = Area x 6″
Now  6″ = 0.5 Foot or 0.5′.

So 212 Cft = Area x 0.5′

Or

Area = 212/0.5= 424 Sqft.

Now see if you can you answer the next question which us identical to the first one ?

” How much area of a slab we can cast with two transit mixers if the slab thickness is 8″ and the concrete is of grade M25 ?

Those of you who found out an answer of 636 SqFt. have understood the foregoing discussion correctly.

Congratulations.

How to Work-out Sale-able area:

If  you have  purchased a flat from any builder, you would have noticed that while arriving at the sale able area , the Builder  adds certain % on the carpet area.
This % starts from 30% and can sometimes even reach up to 80% depending upon the location, goodwill  of the Builder , the type of facilities provided in the complex and of course the stature of that city.

This article explains the concept of this addition of certain % over carpet area.

This method is called as loading on the carpet area.
Let us first understand this mechanism of loading.
Consider a flat whose internal dimensions are , let us say: 30’x20′.
The carpet area is therefore : 600 Sqft.

Assuming that the flat has 9″ thick walls on all 4 sides,
The external dimensions shall be:
(20’+0.75’+0.75′)=21.5′
(30’+0.75’+0.75′)=31.5

The built up area thus can be found out as :
21.5 x 31.5= 677.25 Sqft.

Thus you shall appreciate that builder will certainly desire to get paid for the built up area of 677.25 Sqft. which is 12.88% higher than carpet area.
[677.25 -600
= (77.25/600)x100
= 12.88% ]

Now assume the case of 2 neighboring flats which have got a common lobby of
20’x 5=100 Sqft. .
This lobby is shared by both the flats owners.

Since both the flats have the same carpet area , the builder shall have to load  this 100 Sqft.equally on both the flats.

Thus actual area which the builder constructed for the flat under consideration shall be
677.25+ 50= 727.25 Sqft.

Which is 21.2 % above the carpet area.

[727.25 -600 =(127.25/600)x100=21.2% ]

Summary:
Actual built-up which the Builder has to construct always is greater than the carpet area due to the walls, common spaces such as staircase , lobby ,Terrace , Parking ,Garden ,Security etc.

For this , the builder has to calculate exactly how much extra area has been thus constructed and then distribute this pro rata on  each flat.
This method could be difficult to derive and also quite difficult to explain to the customers.

Instead of this , the builder assumes a standard % and loads this on the carpet area.

Since it is easy to calculate the carpet area from the drawing   or even by taking actual measurements at the site, builders & customers both are comfortable with this arrangement.

Intricacies Simplified

Article 02:

Rev 00 Dated 04.11.2014.
Suppose  together we visit  a construction site .
The RCC slab at the 4th floor is ready for casting tomorrow.

This is how a slab appears prior to casting.

What questions come to your mind ?

1.What kind of materials in what quantity are required for concreting of this slab ?
2.How much time shall be needed to cast this slab ?
3.What are the checks to be done before & during the slab casting ?

Let us see  how do we  solve these questions one by one.

 1.What kind of materials in what quantity are required for concreting of this slab ?

We already know that:

Concrete needs Cement, Sand , Aggregate and water as the basic contents .

Admixtures are also sometimes added depending on specific need.

We already know that the Nominal Mix for Grade M20 concrete is  (1+1.5+3).
:
For 1 CuM of concrete , the material consumption is as follows:

 ,Cement:   {1.52/(1+1.5+3)} X 28.8 Bags = 7.96 Bags

Sand:          {1.52/(1+1.5+3)}X 1.5 =  0.415 CuM
Aggregate: {1.52/(1+1.5+3)}. X 3  =  0.830 CuM

 2.How much time shall be needed to cast this slab ?

The time taken for casting can be derived as follows:
1.Assuming that each batch is mixed for exactly 1 minute ,then in one hour we can mix concrete using  60 bags of cement.

 2.Suppose the slab  needs 300 bags and we are using only 1 mixer , then we shall need 300/60= 5 hrs.

3.Steps for finding the duration:
3.1.Find out cement to be used.
3.2 Decide no of mixers to be deployed.
3.3 Concreting duration:
(No of cement bags/60)(1/No of mixers).

3.What are the checks to be done before the casting is taken up ?

Checks prior to casting:
1.Materials:
Availability of all materials of approved quality in adequate quantity with reasonable lead from the point of mixing.

2.Centering:
2.1 Centering plates to be at required level as per drawing.
2.2All gaps properly closed with either wooden planks, GI strips or Masking tape.
2.3.Iron clamps for the Beam & Slab sides.

3.Reinforcement:
3.1.Cover blocks in position for slab ( 15 mm ) & beams ( 25 mm).
3.2.Chairs in position for the bent up bars.
3.3.Laps of adequate length
( Slab : 60 X bar dia )
3.4. Recording of reinforcements

Curious Construction :

The Prologue:
Rev 00 Dated 18.10.14

While moving around in your neighborhood you invariably come across a plot which is enclosed on all sides with tall iron sheets.There would be a temporary gate  in the front and ,occasionally you can see big trucks plying in & out of this gate.

This is how a construction site appears from a outside

After a few months of  clandestine looking activities, you would observe the columns growing out from the land.

The building is growing gradually to attain great heights in due course.

The great creation is taking shape in your vicinity .You don’t normally any attention to this .

In a few more months ,you would see a full skeleton of a building standing out in front of you.

The days pass, seasons change and the skeleton gradually meta-morphs itself into a beautiful building.

The marvelous result of toils of entire team of construction

After nearly a year or so you would see typical clothes drying out in the balconies, and the  windows getting illuminated during night-time.

So now you realize that the building has started populating .

Welcome to the New occupants. The proud owners of the new property.

This blog aims to share with you in a  simple language, what all takes place during the construction .

It shall keep on answering your basic queries about the construction 

First let us see : Who does what ?

A building is a product of synergy.So many agencies are involved , directly or indirectly , in such a project.Some are  involved physically while others are  involved mentally.

That’s why you would see persons toiling in the scorching sun ,working even during light rains. Some persons at the same time would be doing planning or some design work sitting in air-conditioned chambers.

These people are behind any building : Authorities,Clients, Consultants,Contractors & Suppliers. 

This blog aims to address all queries pertaining to construction

Clients arrange the resources for the construction and engage a Consultant who prepares the  drawings.Clients & consultant together seek various permissions from Authorities to construct the building .Together they  retain a contractor who organizes procurement of  material & deploys the labor.

Contractor studies the drawings, procures materials from material suppliers ,engages Labor contractors and transforms the drawings on paper to an actual building on the land.

Clients either use the buildings themselves or may sell it to customers who then become the occupants of the new building.

Summary:
Vision of the clients is transformed into a drawing by the consultant.
The drawing gets transformed into an actual building through a contractor.