Design Methods for Singly reinforced Sections

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Singly reinforced sections | Design of RCC structures

Earlier we discussed some basic terms in reference to singly reinforced sections design. It is important that you are thorough with the basic definitions and have complete understanding of stresses in concrete and steel. You should also possess the knowledge of reinforcement and terminology of beams which includes understanding singly reinforced beam, doubly reinforced beam, under reinforced beam, over reinforced beam and balanced reinforced beam.

There are two methods for the design of singly reinforced sections. In this article we will discuss the first method of singly reinforced section in a stepwise manner. The discussion will include the method for determining the value of neutral axis followed by a formula for the area of steel calculations.

Let,

b = breadth of a rectangular beam

d = effective depth of a beam

x = depth of neutral axis below the compression edge

Ast = cross-sectional area of steel in tension

σcbc = permissible compressive stress in concrete in bending

σst = permissible stress in steel

m = modular ratio

Neutral axis

Neutral axis is denoted as NA.

There are two methods for determining the neutral axis depending on the data given.

 

Stress strain diagram - Singly reinforced section
Stress strain diagram

In this article, we will discuss the first method followed by a couple of numericals for your understanding and then move on to the second method.

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Assumptions for Singly reinforced Sections | RCC Structures

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Singly reinforced Sections | Design of RCC Structures

In our series of articles for singly reinforced sections, we have covered the following:

Now, we will move on with our discussion on “assumptions for singly reinforced sections”.

Stress-strain diagram
The equivalent stress-strain diagram is developed with respect to the mentioned assumptions in the post.
  1. The sections that are plane before bending remain plane after bending, at any cross-section.
  2. All tensile stresses are taken up by steel reinforcement and none by concrete.
  3. The stress to strain relationship of steel and concrete under working load is a straight line.
  4. The modular ratio m has the value 280/3σcbc
  5. There is a perfect adhesion between steel and concrete and no slip takes place between steel and concrete.

Types of Dormers | Architectural Details

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What are Dormers? | Building Construction

Eyebrow dormer

Eyebrow dormer is also known as the roof eyebrow since it resembles an actual human eyebrow. It is curved in shaped with a window in between with a fixed or operable glass.

Eyebrow dormer
Eyebrow dormer

Eyebrow dormer is a mixture of aesthetics and functions.

Aesthetically, it breaks the monotony of an angular or sloping roof.

And we are to assess it functionally, it serves as ventilator for the top floor spaces which would otherwise get heated up.

It does require skilled labour for construction but are efficient in their functioning.

 Hipped Dormer

Hipped dormers and eyebrow dormers serve a similar purpose with respect to aesthetics and functionality. The only difference between the two is the shape of the dormers. Hipped dormers have three sloping roof panels that do not allow the snow getting collected on the roofs.

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Dormer Window | Architectural Construction

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A dormer window is a structural element in a building which are constructed on the sloping roofs. Dormer Windows protrude from the plane of the sloping surface of the roof.

Dormers
Dormers - as an architectural feature
  • A dormer window maybe constructed during the construction of the building or could be an addition to create a habitable space where the height of the pitched roof is very high.
  • As the name “Dormer Window” suggests, it a window set in a dormer and hence termed as Dormer Window.
  • Like skylights, dormer windows are used as a source of light and ventilation but unlike skylights they are used to provide habitable space in the pitched roof construction…

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Understanding Stresses and Modular ratio | RCC Structures

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Stresses in Steel and Concrete | Building Construction

In one of our previous articles, we discussed “Basic definitions and formulas”.

Now we will move on with our discussion on “Permissible stresses in concrete and steel” and “Understanding Modular ratio”.

Permissible Stresses in Concrete

Reinforced concrete designs make use of M15 grade concrete. The permissible stresses for different grades of concrete is different. They are given below:

Sr. No. Concrete Grade M15 M20 M25 M30
1. Stress in compression

  1. Bending

 

 5 7 8.5 10
  1. Direct

 

 4 5 6 8
2. Stress in bond (average) for plain bars 0.6 0.8 0.9 1.0
3. Characteristics compressive strength 15 20 25 30

 Also refer for other values in IS:456-1978

Permissible Stresses in Steel

The permissible stresses for different grades of steel are given in the table above.

The different grades steel available in the market with their market names are as follows:

Mild Steel

Grade I steel is known as mild steel. The abbreviation used for Mild steel is (m.s.)

High Tensile deformed steel has two types. They are as follows:

  1. Grade Fe415 (Tor-40 or Tistrong I)
  2. Grade Fe500 (Tor-50 or Tistrong II)

The names of the high tensile deformed steel have been derived from their manufacturers.

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Moment Distribution Method | Civil Engineering

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Step by Step procedure for Moment Distribution Method

Step One:

Initially all the members are assumed to be fixed. Calculation of fixed end moments is to be done.

Moment Distribution Method diagram
Moment Distribution Method diagram

Step two:

Fixidity at the joint is released and the balancing moment at the joints is distributed to various members depending upon their thickness.

Step three:

A part of this moment is carried over to the other end of the member and the carry over moment is computed.

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Stress, Strain, Modulus of elasticity and Elastic Materials

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Design of RCC Structures | Basic definitions and formulas

In this article, we will go through the basic definitions of Stress, strain, elastic materials and modulus of elasticity. This will be our first step towards understanding the design of “Singly reinforced sections”.

What is stress and how does it develop?

When an object is subjected to an external force, the object tends to build up internal resistance within itself (material). This resistance is termed as “stress”.

In short, stress can be defined as load per unit area.

Stress can be classified into four types:

  1. Compressive stress
  2. Tensile stress
  3. Bending stress
  4. Shear stress

Stress = Load/Area = W/A = N/mm2

Where, N = Newton

What is Strain?

To make it easier for you to understand, let’s merge the definition of stress with strain.

When an object is subjected to an external load, the internal resistance which is built up with the object itself is not enough to withstand the external load results into deformation of the object. This alteration or deformation of the object is called strain.

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Repair of Sinking Foundation | Civil Engineering

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Sinking Foundation Damage and repair guide

We will discuss repair of Sinking foundation in three steps:

  • Step 1 – Examination of the Structure by an expert
  • Step 2 – As soon as the problem is identified, hire a contractor or a foundation specialist
  • Step 3 – Methodologies or techniques used for sinking foundation repair

Step One: Identification and Examination of the Structure by an expert

As soon as you find any signs of foundation damage that we discussed in our previous article “Identifying Sinking foundation”, you should immediately contact a professional (structural engineer). The first thing that you should be doing is getting your house examined and checked properly for structural damage.

The structural engineer is an expert in this field. He will be able to tell you as to what has to be done in order to prevent further damage and all that is required to be repaired. Sometimes people tend to think that engineers might exaggerate about the damages occurred to the structure because of monetary concerns. However, it should be kept in mind that the engineer has no vested interest in these kind of repairs. He is the person who would give you an accurate and unbiased opinion. And with his help and advice, the work is then carried out by the foundation specialists or a general contractor. This was all about STEP-1.

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Sinking Foundation and Repair | Identifying Foundation problems

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Sinking Foundation | Building Construction

Foundation is the most primary component of the building on which it stands. The life of the building depends on the quality of foundation. For a good and stable foundation, the structural design of the foundation has to be done properly in a systematic way under the guidance of a structural engineer.

If the casting of foundation is not paid attention to and is not laid properly on a stable soil, the structural problems are bound to develop. Every soil has a specific bearing capacity which is very necessary to be checked before designing the foundation. Without the consideration of bearing capacity of soil, the structural design for the foundation may not be suitable for that land.

Cause of Sinking Foundation

Sinking foundation is a problem that occurs in case of improperly laid foundations which is the result of careless consideration of the soil type. The problems are very crucial and have to be solved as soon as they are detected in order to prevent the structure from further damage.

Detecting Foundation problems

People living in areas with unstable soil conditions need to watch out for the signs of foundation problems. Some of the signs could be as follows:

First sign:

The house is gradually slanting to one side. (This is a very prominent example of sinking foundation problem. As soon as you notice this happening, you can immediately conclude it to be related to foundation and take action immediately before the condition of the structure gets worse.)

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Drainage and Dewatering | Building Construction

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Introduction to Drainage and Dewatering

In this article, we will discuss and classify drainage and dewatering in brief.

What is drainage?

As the name itself suggests, drainage is the process in which the free water is removed with the help of gravity in order to maintain stable soil conditions.

Drainage can be classified into two categories:

  1. Surface drainage
  2. Sub-surface drainage

What is Surface drainage?

The water that runs on the surface of the ground is collected and or diverted into a water body.

Sub-surface drainage

It is the collection and disposal of ground water. It is also called as dewatering.

What is dewatering?

The process in which the water is removed from a foundation pit;

  • when it is situated below the ground water table or
  • when it is surrounded by a coffer dam.