Effect of Economic breakdown on Construction Industry

Poor Economic state of the World | Effect on Construction Industry and its prevention

Sudden Economic change is extremely bad for Construction industry of any country. The status of Global markets determines the behaviour of an individual country. For example, if the economy of United Kingdom is suffering due to employment problems in the country or financial crisis; it affects the whole of Europe. On the whole, the economy of Europe plays a great role in moving the market.

The first and foremost bad effect of the market would be:

Banks going bankrupt. Banks are the main sources of capital for major construction projects.

Construction industry is capital intensive.

Because of the banks going bankrupt, there is not enough capital in the market that could be utilized for new projects. Because of less money in the market, people are unable to afford luxury homes, offices. This has two major effects on the construction industry:

  1. Since, people do not have the money to buy buildings, Existing projects are stalled due to increasing raw material cost and decreasing real estate value. No more gigantic home loans available.
  2. After analyzing the scenario of the bad economic conditions of the market, the builders decide to scrap the idea of new constructions and decide to wait for the right time to start the project. This brings recession in the construction industry which affects architects, engineers and mainly workers badly.

Financial Crisis in the country will result in major construction firms going bankrupt which in turn would be responsible for the loss of thousands of jobs.

Is it possible to prevent this from happening? If yes, then how?

A new system of design is needed to ensure very low energy footprint, sustainable development and optimum use of local materials.

A renewed focus is needed on Green building Design

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Interview with Architect Javed Kachchhi | Construction Site Inspection

What to do on a”Site Inspection/Site Visit”?

Students are always curious and nervous about site visits since this is never taught in any of the colleges in the world. Students have absolutely no idea as to what is to be done when an engineer or Architect is expected to inspect the site. By site, I mean construction site.

Check out his biography: Architect Javed Kachchhi

He is an Architect, Structural Engineer and an Interior Designer. That is the reason why I was so hung up on trying to get in touch with him and write about his experiences about site inspection.

Here we go….

My first question was…

Me: Sir, could you tell us, What exactly is “Site Inspection” or “Site Visit”?

Ar. Javed Kachchhi: Well, let me be very specific. I am sure your readers would like that.

On a site inspection, an Architect/Engineer has to take a complete survey of the site. He has to inspect each and every element that is constructed on site and make sure that the construction is being carried on as per the drawings given by the Architect.

Me: Who monitors the site?

Ar. Javed Kachchhi: Monitoring the site is the work of Site Engineers. Site Engineers have to have a degree in Civil Engineering in order to qualify for the job.

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Design of Doubly reinforced sections | Numerical example

7 step design procedure for Doubly reinforced sections

In our article series for “Design of Doubly reinforced sections”, we covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

6 step prodecure for determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

7 step procedure for designing doubly reinforced sections

We shall now proceed with a numerical example “Design of Doubly reinforced sections” using the 7-step procedure we discussed in the previous article.

Numerical problem:

A doubly reinforced concrete beam 250mm wide and 600mm deep overall has to resist an external bending moment of 95kN-m. Find the amount of tensile and compressive steel required, if cover to the centre of steel on both sides is 50mm. σcbc = 5 N/mm2, σst = 140 N/mm2, m = 18.66

Given that:

Breadth of the beam = b = 250mm

Effective depth of the beam = d = 600 – 50 = 550mm

Distance of compressive steel from the top edge of the beam to the centre of the steel = d’ = 50mm

Permissible stress in concrete = σcbc = 5 N/mm2

Permissible stress in steel = σst = 140 N/mm2

Modular ratio = m = 18.66

Bending moment = M = 95 kN-m

Step one:

To find xc

σcbc/ (σst/m) = xc/(d – xc)

5/(140/18.66) = xc/(550 – xc)

xc = 219.95 =  220mm

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Design procedure for designing doubly reinforced section

7 step procedure for “Design of Doubly reinforced sections”

In our article series for “Design of Doubly reinforced sections”, we covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

6 step prodecure for determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

In our previous article, we discussed a detailed 6 step procedure for determining stresses in steel and concrete followed by a numerical example. Now we shall move on with the “design procedure for doubly reinforced sections”.

Generally the following data are given:

Breadth of the beam = b

Effective depth of the beam = d

Permissible stress in concrete = σcbc

Permissible stress in steel = σst

Modular ratio = m

Bending moment = M

To solve a problem, the following procedure may be followed.

Design the beam as a singly reinforced one (balanced section)

Step One:

Find xc by

σcbc/ (σst/m) = xc/(d – xc)

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6 step procedure for determining stresses in steel and concrete | Doubly reinforced sections

Numerical example for determining stresses in steel and concrete

In our article series for “Design of Doubly reinforced sections”, we covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

In our previous article, we discussed a detailed 6 step procedure for determining stresses in steel and concrete. Now we shall move on with a numerical example in which we will use the 6 step procedure to solve the problem.

Problem Type two: Determining stresses in steel and concrete using the 6 step procedure

A rectangular beam is 200mm wide and 480mm deep. It has to resist a bending moment of 100 kN-m. The reinforcedment consists of four 25mm ⏀ bars on tension side and three 22mm⏀bars on compression side. The centres of bars being 30mm from the top and bottom edges of the beam. Find the stresses set up in steel and concrete. m=18.66

Given data is as follows:

Breadth of the beam = b = 200mm

Effective depth of the beam = d = 480 – 30 = 450mm

Distance of compressive steel from the top edge of the beam to the centre of the steel = d’ = 30mm

Bending moment = M = 100kN-m

Modular ratio = m = 18.66

Area of tensile steel = Ast = 4 π/4 x 25 x 25 = 1964 mm2

Area of compressive steel = Asc = 4 π/4 x 22 x 22 = 1140 mm2

Step one:

Find x:

bx.x/2 + (1.5m – 1)Asc (x – d’) = mAst(d-x)

200x2/2 + (1.5×18.66 – 1) 1140 (x – 30)

= 18.66 x 1964 x (450 – x)

Therefore, x2 + 674.17x – 174147 = 0

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Determining stresses in Steel and Concrete | Doubly reinforced Sections

Six step procedure for determining stresses in steel and concrete

In our article series for “Doubly reinforced Sections design guide”, we have covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

Now we shall proceed with a simple 6 step procedure for determining compressive stresses in steel and concrete. Further in our next article, we shall also solve a numerical using the same method.

Generally, the following data is given for reference with the help of which we can determine the stresses in steel and concrete

Breadth of the beam = b

Effective depth of the beam = d

Area of tensile steel = Ast

Area of compressive steel = Asc

Modular raito = m

Bending moment = M

Six step procedure for determining the compressive stresses in steel and concrete:

Step One:

Find x by using the following formula:

bx.x/2 + (1.5m – 1)Asc (x – d’) = mAst(d-x)

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Types of Problems | Design of Doubly Reinforced Sections

Stepwise procedure for calculating Moment of resistance and compressive stresses in steel and concrete

While we proceed with the article series for “Doubly reinforced sections”, I would like to categorize the problems into different types. This will make your understanding of the concept better and concrete. I recommend that you practice enough to be able to understand and confidently solve the problems. This will also help you in real time when you would get into practice.

In our article series for doubly reinforced sections, we have covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

Also check out: “Singly reinforced Sections” article series.

So let’s begin with different types of problems for “Doubly reinforced sections”.

Problem type 1

To find Moment of resistance (Mr)

In a problem where we have to find Mr, specific data is given so that you could calculate the Moment of resistance. The following data will be given in the problem. I suggest that you make notes of the points below.

Breadth of the beam = b

Effective depth of the beam = d

Area of tensile steel = Ast

Area of compressive steel = Asc

Permissible stress in concrete = σcbc

Permissible stress in steel = σst

Modular ratio = m

Four – step procedure to solving the problem:

Step one:

Find xc by the following formula,

σcbc/ (σst/m) = xc/(d-xc)

Step two:

Find x using the following formula,

bxx/2 + (1.5m – 1)Asc (x – d’) = m Ast (d – x)

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Numerical Examples | Moment of Resistance Calculations

Moment of Resistance calculations | Doubly reinforced sections

In our article series for “Doubly reinforced sections”, we have covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

Now we shall move on with a solved example. This will help you understand the methods in a better way. I suggest that you do them yourselves too. Practice will help you make your concepts more concrete and clear.

Numerical Example:

An reinforced concrete 300mm x 600mm effective dimensions is provided with tensile and compressive reinforcement of 1256mm2 each. The compressive steel is placed 30mm from the top edge of the beam. If σcbc = 7N/mm2, σst = 190N/mm2 and m = 13.33, find the moment of resistance of beam by following two methods:

1)     Elastic theory method

2)     Steel beam theory method

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Moment of Resistance | Doubly reinforced Sections

Methods for calculating Moment of resistance for Doubly reinforced beam

In our article series for “Doubly reinforced sections”, we have covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

Also check out: “Singly reinforced Sections” article series.

Now, our next step would be to study different methods for calculating moment of resistance (MR).

Two methods for calculating Moment of Resistance

There are two methods for calculating the moment of resistance of doubly reinforced sections. They are as follows:

  1. Method 1 – Elastic theory
  2. Method 2 – Steel beam theory

Method 1

Method using Elastic theory

The moment of resistance is calculated by taking the moments of forces about the centre of gravity of the tensile steel.

Diagram for determining Moment of resistance
Diagram for determining Moment of resistance

From the figure above, we get,

Mr = Moment of compressive force of concrete about tensile steel + Moment of equivalent concrete force of compression steel about tensile steel

= bx(σcbc/2)(d – x/3) + (1.5m – 1)Asc. σcbc (d – d’)

Where, (1.5m – 1)Asc is the equivalent concrete area of compression steel.

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Neutral Axis – Solved Example | Doubly reinforced Sections

Guide to design of Doubly reinforced Beam

In our article series for “Doubly reinforced sections”, we have covered the following:

What are doubly reinforced sections?

Methods for determining Neutral Axis?

Solved numerical examples for determining Neutral Axis

Numerical examples for practice (Find Neutral axis)

Methods for calculating Moment of Resistance

Numerical example for calculating Moment of resistance

Types of problems in Doubly reinforced sections

Determining stresses in steel and concrete 

Numerical example | Stresses in steel and concrete

Now we shall move on with a solved example. This will help you understand the methods in a better way. I suggest that you do them yourselves too. Practice will help you make your concepts more concrete and clear.

Example:

An reinforced concrete beam 200mm x 400mm overall is reinforced with 4 – 22mm⏀ bars with centres 30mm from the bottom edge and 3 – 20mm⏀ bars with centres 25mm from the top edge. Find the neutral axis of the beam, if m = 18.66

Doubly reinforced section diagram
Doubly reinforced section diagram

Given that,

Width of the beam = 200mm

Effective depth of the beam = 400 – 30 = 370mm

Distance of compressive steel from the top edge of the beam to the centre of the steel = d’ = 25mm

Modular ratio = m = 18.66

Area of concrete = Asc = 3 x π/4 x (20)2 = 942 mm2

Area of tensile steel = Ast = 4 x π/4 x (22)2 = 1520 mm2

To find x:

Equating moment of area on compression and tension sides about N.A.

bxx/2 + (1.5m – 1)Asc(x – d’) = mAst (d – x)

200x2/2 + (1.5 x 18.66 – 1) 942 (x – 25)

= 18.66 x 1520 (370 – x)

Therefore, x2 + 537.87x – 111299 = 0

Solving the above equation, we get,

x = 159.579mm

Examples for practice

  • An reinforced concrete beam 300mm x 600mm overall is reinforced with 6 – 22mm⏀ bars with centres 30mm from the bottom edge and 5 – 20mm⏀ bars with centres 25mm from the top edge. Find the neutral axis of the beam, if m = 18.66
  • An reinforced concrete beam 300mm x 600mm overall is reinforced with 4 – 20mm⏀ bars with centres 25mm from the bottom edge and 6 – 20mm⏀ bars with centres 25mm from the top edge. Find the neutral axis of the beam, if m = 18.66