Types of Foundations

There are different types of foundations we use in construction. The selection of foundation type is mainly depending on the loads and the soil condition where the structure going be rested. But if we assume a design for a particular purpose we can calculate the dead load and live load for the structure. But if we are going to build that design in two locations where soil condition is considerably different we will have to use different types of foundations for that structure even the superstructure is the same. Therefore, foundation design always comes with the soil condition at the site.

Foundations are mainly two types that are;

1. Shallow Foundation 
2. Deep Foundation    

Shallow Foundations:

• Strip Footing
• Pad Foundation
• Raft Foundation

Deep Foundation:

• Pile foundations

Strip Footing: These type of foundation applied where soil bearing capacity is very low. So it is required to make the foundation area is wider to reduce the pressure by the building into the soil and spreading it as much as possible. Columns & walls can be rest on these footing. Mostly strip footing required to be reinforced properly. Strip  footing for walls can be made with rubble and bricks as well. 

Pad Foundation: These type of footings use where soil condition is considerably good. Columns of the building going to be supported by these types of foundations. 

Raft Foundation: Rafte foundation is the type of foundation that we build covering the entire area of the building going to be casted with reinforced concrete. Whenever the soil condition is very low and cannot use strip foundation or pad foundation type we will have to use raft foundation. raft foundation is also known as mat foundation. 

Pile foundation:  Foundations that are driven until the bedrock or considerably deep till it finds a better soil condition to have the building rest on it are called pile foundation. There are different types of pile foundations. 

• Bearing piles
• Friction piles
• Bearing & friction piles    

Recommendation: Whenever we design a foundation, we should refer the soil investigation report and loads of the structure. See here    

Forces Applied on Building Structures

There are number of different loads applied on building structures. Therefore when we design a building structure, we should design it such way that all those forces are equally and safely borne by the structure itself. Below the types of loads that we need to analysis when design a structural design for a building, bridge, road, etc.

• Dead Load
• Live Load
• Lateral Loads
• Earth quick Loads
• Construction Loads
• Soil and Hydrostatic Pressure  

Dead Load: The load due to structure itself. It is determined by calculating the weights of beams, columns, slabs, walls, partitions, roofs or whatever the building components is used in a building or in any type of construction.

Live Load:  People, cupboards, beds, books, tables, etc. which is movable or temporary fixed in the building or in any type of construction. for an example in a bridge we can assume maximum traffic that is going to put on by calculating expected amount of vehicles and other types of weights such as billboards, ads, etc. which can be changed time to time. but we have to assume the maximum possible weight and into that we need to add safety factor depending on the building standards.

Lateral Loads: This is also known as wind load. we know wind load is a big problem with the height of a building. According to the wind profile, we must take care of wind load when building going high on the air as it forcing the building.

Earth quick Loads: Also known as seismic loads. The loads or shocks that are due to unexpected movement of ground where the building structure is rested on.

Construction Loads: Loads due to the construction of a building. (storing construction material & plants, temporary structures, etc.) 

Soil & Hydrostatic Pressure: Pressures due to soil condition and ground water that can force the building by any means. We can analysis this by a soil investigation.

   

       

Reinforced Concrete Structures

What is Reinforced Concrete Structures?

Normally concrete being considerably weak where tension is applied. Therefore, where tension is high concrete will get cracks in its structure. It will reduce the expected strength. In this case, we need to improve the tensile strength of the concrete. Tensile strength of concrete can be increased by adding special components that can resist against the tension. As a result of that, we use reinforcements in concrete structures. It is called Reinforced Concrete Structures. Concrete make a very stable bond with these reinforcements. Reinforced concrete structures are equally good in resisting  both the tension and compression forces.

Reinforced concrete structures are the most common use of any type of construction all around the world ever since it's invented due to its strength and other advantages.

What are the advantages of Reinforced Concrete Structures?

• Strength (can be achieved depending on the application)
• Fire resistant
• Can be casted in any desired shape & size
• Cost effective (cheap compared to other structures)
• Easy Maintenance
• Availability
• Chemical resistance up to a considerable extent 

What are the disadvantages of  Reinforced Concrete Structures?

• Can not be recycled (use for land filling)
• Emission of Carbon Dioxide (CO2)
• Concrete Dust

What are the components in Reinforced Concrete Structures?

• Cement
• Fine Aggregate (Sand)
• Coarse Aggregate (Metal)
• Reinforcement
• Water 

Do you know concrete strength can be achieved depending on the application?

Generally buildings consist of floors, beams, columns, slabs, footings, etc. The requirement of the strength of these components may be different due to different forces and requirements applied on each component. In this case, we can analysis the required strength and requirement then make the structure according to the requirement. It can be done with the proportion of mixing the components that have been mentioned above. In the construction field, we call it the grade of concrete. Normally  reinforcement is used for concrete not less than G20 ( C: S: A = 1:2:4). C = Cement, S = Sand, A = Aggregate

Below the most commonly used concrete grades and it's mixing proportions. But for high rise building and skyscrapers requires a much higher strength of concrete.

• G15 = 1:3:6
• G20 = 1:2:4
• G25 = 1:1 1/2: 3
• G30 = 1:1:3      

Note:
G15 mean it's specified compressive strength at 28 days should be 15 N/mm2. If it is G20 it should achieve 20N/mm2.

How to use reinforcement in concrete structures

We should use reinforcement in concrete structures near the surface as possible. Because the tension is more near the surface. But it should have an allocation to pour minimum size of aggregate to make a proper bond. Not only that but also lessen the chemical reaction and exposure to fire at an event of a fire. Therefore in an extreme weather condition and where fire resistant should be a topic, we should have minimum cover space is little bit spacer to reduce the exposure of reinforcement to the environment.





  

Steel Structure Quantity Estimation

It is really very easy to calculate quantities for Steel Structures. Commonly Steel Structures include Steel Columns, Beams, Rafters, Trusses, Haunches, Apex, etc. We can easily calculate the length of these components using a given drawing base on the unit weight and size of each iron to be used.

Note: Unit weight can be different even for the same size of iron where thickness is not the same. Therefore, the price will be changed for each steel since the price of steel base on its weight.

Then we should have a proper idea what are the required amount of steel plates with its thickness, nuts & bolts, washers, welding rods, etc. Most of the time you will be given drawings of each section so you can calculate the required material quantities easily and quickly.

When estimating required amount of welding rods it is necessary to know the total weight of steel structure. In fact in steel structure it is approximately we use 14-16 Kg of welding rods per one ton. Therefore by estimating steel structure weight, we can multiply it by average the (14+16)/2 = 15 to find the required amount of welding rods.

We cannot forget required steel treatment like hot bath galvanizing and steel painting when we estimate the cost of the steel structure. The painting cost also to be included in the BoQ. Since we have estimated the length of steel irons with its sizes, we will be able to calculate the total area of the steel structure. Then what we have to do is to find the painting products base on the description given by the engineer and manufacturers details that how much of an area can be painted by one liter or gallon. so we can find the required amount of paint liters or gallons.

Once we are done with the Material calculations, we have to figure out the Labour, Plant & Equipment and also transportation cost for the above structure. Then we have to add the overheads & profit to take the final figure.

In the next article, I hope to publish cost estimation for steel structure with supporting drawings so you readers can easily understand how it is done.