Understanding Stresses and Modular ratio | RCC Structures

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.

Read moreUnderstanding Stresses and Modular ratio | RCC Structures

Conduits | Building Construction

Construction of Conduits | Civil Engineering

In the previous article, we discussed “Types of Underground Conduits”. Now we will proceed with our discussion on “Construction of Conduits”.

Underground conduits can also be termed as buried conduits. They are constructed in variety of shapes with different materials used for construction.

Load on the conduit

The characters of the conduit determine the load withstanding capacity of the conduit. They are as follows:

  • Material of the conduit
  • Shape
  • Type of the support

For example:

If we take the example of a concrete conduit (rigid material), the load that the concrete conduit can withstand would depend on the following:

  1. Strength of the concrete pipe
  2. Quality of the foundation bedding

How to determine the strength of the conduit?

A three edge bearing test has to be conducted in order to determine the strength of the conduit.

Three edge bearing test
Three edge bearing test

This test simulates a very severe loading condition which would rarely occur in the actual conduits. This helps us determine the maximum load the conduit can take. It has been seen that the conduits can take greater load than that obtained in the test.

Read moreConduits | Building Construction

Types of Underground Conduits | Civil Engineering

Underground Conduits

What are conduits?

Conduits have different meanings in different subjects.

For example:

Geographically, conduits could refer to a channel carrying water, underground tunnel or waterway (river or canal).

In terms of electrical systems, it may refer to an electrical conduit, HVAC (duct) etc.

Electrical Conduits
Electrical Conduits

We are referring to the conduits which is laid underground and used for variety of purposes.

For example:

  • Sewers
  • Drains
  • Culverts
  • Water mains
  • Gas lines
  • Electrical cables
  • Telephone lines

Causes of Foundation Damage and Retrofitting | Settlement in the ground

Causes of Foundation damage and Retrofitting 

In one of my previous articles, we discussed various steps in which the survey of the foundation has to be done in order to be considered for retrofitting.

In this article, we will discuss various reasons or causes for the damage of the foundations.

Types of foundation damage can be classified as follows:


  1. Natural rock
  2. Brick



Moisture damage

  1. Frost wedging
  2. Salt bloom

Settlement in the ground

  1. Groundwater lowering
  2. Limited bearing capacity of the ground (land)
  3. Uneven bedrock depth
  4. Excavations performed below the foundations and poor quality of backfill
  5. Increased load on the ground leading to failure
  6. Damage to the neighbouring houses
  7. Horizontal movement occurring in the ground

 Frost heave/adfreezing

Alum shale

Now we will move on with the discussion in detail on the types of foundation damage occurring due to Settlement in the ground.

Lowering in the Groundwater level

When the buildings are built on compressible soils, the resulting stress on the soil causes the soil to compress. Raft foundations are used in these kind of soils.

Since the soil undergoes compression the upper portion of wooden piles rot when groundwater level sinks.

There are various conditions which can cause the changes in the groundwater level or pore water pressure. They are as follows:

  • Ice Static Rebound
  • Dewatering (seen in cities)
  • Ditches and pipes below the groundwater level
  • Deep Foundations and Basements (causing further drainage of the ground
  • Tunnelling
  • By the removal of foundation sills
  • Construction of non-permeable surfaces such as roads, pathways causing the least amount of natural precipitation
  • Use of deciduous trees should be avoided in areas with low groundwater. They require a lot of water for their growth. They pull all the water that is available around them causing the lowering of groundwater.