In this post, you’re going to learn all about strip footing.
- What is strip footing?
- Details of strip footing
- When to use them
- When not to use them?
- Their types, and
- The construction process.
Let’s dive right in.
What Is Strip Footing?
It’s a type of shallow foundation.
It consists of a continuous strip formed centrally under load-bearing walls.
This continuous strip provides a base for walls.
The width of this strip is as necessary to spread the load on an area of subsoil capable of supporting the load without undue compaction.
Normally, the size and position of the strip are directly related to the overall width of the wall built on top of it.
And, it must be three times the width of the wall.
The concept is that the load is transmitted at 45 degrees from the base of the wall to the soil.
And, the depth of this foundation must be equal to or greater than the overall width of the wall.
Nowadays, concrete is mostly used for this foundation as it can readily be placed, spread, and leveled in foundation trenches.
And, it develops adequate compressive strength as it hardens to support the load on foundations.
But, Bricks are also used sometimes instead of concrete.
This footing has some other names like Wall footing, Spread footing, and Continuous footing.
When Strip Footing Is Used?
Commonly, this footing is used as a foundation of load-bearing walls.
But, the soil should have good bearing capacity.
If the bearing capacity of the soil isn’t good, you can still use strip footing.
In that case, you need to build wider footings with reinforced concrete.
Strip foundation is preferred for low-rise to medium-rise residential buildings.
In some cases, they are used to support a row of closely spaced columns.
When Shouldn’t You Use Strip Foundations?
If a building has several columns with high localized loads this footing may not be appropriate. In such situations, you can use isolated footing.
When the bearing capacity of soil is very low, strip foundations shouldn’t use there. In such cases, it is recommended to build mat foundations or some other deep foundation like pile foundations.
But if the soil bearing capacity is good, yet you shouldn’t use strip footing for buildings taller than three-story.
However, as a construction professional, you don’t need to think about these much.
Because it’s a part of the structural design.
Yet we sometimes face various types of problems in practical construction fields. So it’s better to learn the design part a little bit.
With that, let’s see some…
Advantages And Disadvantages Of Strip Foundation
Like any other type of foundation, strip footing also has some advantages and disadvantages.
If we talk about advantages:
- It’s simple in design.
- You don’t need expensive tools or equipment to build this.
- It requires less construction time.
On the other hand:
- This footing is comparatively low durable.
- Strip footing may increase the cost in the final stage of construction as you need to perform some additional manual works like filling soil into the trench and its leveling.
Process Of Installing Strip Footing
Below I’ll describe the basic construction process of strip footing.
First, excavate a trench.
Get the drawing from the project’s structural drawing book and study that.
Based on the drawing, identify the position of the footing on the ground.
And, excavate the earth to form a trench.
While making the trench, keep in mind that the trench should be wider than the footing’s width. So that you can have enough room for the formwork as well as enough space to work in the trench.
Next, Make PCC.
PCC stands for Plain Cement Concrete.
It’s done below footings to make a firm and leveled base for the footing.
Sometimes, Brick flat soling is made instead of PCC.
If the subsoil is hard and dry, you can just lay polythene sheets instead of PCC or Brick soling.
After that, erect formwork and reinforcement.
Once the base is ready for the footing, you can now step into making concrete formwork for the footing.
For that, get the size of the footing from the structural drawing and erect the form.
Also, install the reinforcing bars (if any).
Finally, Pour concrete into the form
Check everything as per drawing.
If you’re satisfied, you can pour concrete into the form.
Once the concrete is set you can remove the formwork and backfill the trench.
So that’s it for all about strip footing.
I hope this post helped you understand this footing clearly.
Now, I’d like to hear from you:
Do you install PCC below footings?
Or maybe you lay brick flat soling.
But, what’s your strategy for deciding the one between PCC or brick soling?
Let me learn from your experience by leaving a comment below.