Either you are going to use ready-mix concrete or on-site machine mix concrete, you need to calculate the concrete quantity of neck columns for ordering ready-mix concrete or purchasing concrete ingredients.
It is our common practice. We often calculate concrete quantity before going to cast any concreting members. There are many things which depend on the concrete volume. Such as required manpower, the tentative cost for the concreting work, etc.
The main reason, we calculate concrete quantity for, is to know the volume of concrete or concrete ingredients.
In this post, I’ll discuss the manual calculating process for the concrete quantity of neck columns of a building project.
What is Neck Column?
Neck column is the most bottom part of a column. Saying more specifically, neck column is the part of a column which is buried below ground. The portion between footing and grade beam is normally called neck column. Neck column is also called short column.
So, after casting footings of a building project, the next step is to cast neck columns. When we plan to cast neck columns, we need to calculate the concrete quantity for that.
How to Calculate Concrete Quantity for Neck Column
Calculating concrete quantity for neck column of a building construction project is actually easy. You can do this within a short period of time. Just follow the steps below –
Step 1: Get The Total Number of Columns in The Project
A building can have many columns of different sizes. There must be some columns with the same size. The first step is to summarize the number of different sizes column. For this, you’ll need column layout and column schedule drawing sheet.
You’ll get those drawing sheets in the structural drawing book. Sometimes you’ll find both column layout and column schedule in a single drawing sheet. Sometimes you’ll get two separate sheets.
Column layout drawing is that where the column placements for the building are shown. And the column schedule is where size, symbol, and reinforcement details of columns are shown.
Columns are normally specified as C1, C2, C3, etc. For estimating neck column concrete you need to find out the total number of different types of columns from the column layout drawing sheet.
Summarize the all different types of columns which will look like, for example, below:
C1 – 5 numbers
C2 – 10 numbers
C3 – 7 numbers, etc.
Step 2: Get The Size of Neck Column
You’ll get the column size and shape form the column schedule drawing sheet. The commonly used shape of columns is round and rectangular/square.
Here I would like to explain a most important thing…
From my personal experience, I found that the size of neck columns are sometimes not specified in the column schedule drawing separately. Only the size of ground floor columns is shown.
But the size of neck column should be bigger than the size of ground floor column. Because the concrete clear cover should be more for neck column as it is built under the ground.
In that case, you’ll find the concrete cover for neck column in the general notes sheet of the structural drawing.
For example, the concrete clear cover for neck column is specified in the general notes sheet as 2½″and the size of C1 column in ground floor level is shown in the column schedule as 30″x 12″.
In this case, the size of neck column (C1) will be 32″ x 14″.
Most of the time a separate schedule for neck column is shown in the column schedule drawing. In that case, you don’t have to think about anything. You can proceed to calculate the column area.
Suppose, you get the size of the column from the column schedule as below –
C1 – 32″x 14″
C2 – 42″x 14″
C3 – 15″x 14″
From these sizes, you can just calculate the column area. But to get the quantity of neck columns’ concrete, you need the third dimension too. That is the height of neck columns.
Step 3: Getting Height of Neck columns
Getting the height of neck column is a little bit tricky. You need to get the gap between the top of footing and bottom of the grade beam.
There may all the footings top isn’t on the same level. And grade beam may not be at the same level too. Then how do you get the height of neck columns?
If you already cast footings, you can take measurement practically from the field. That is the most accurate way. I often do this in my project.
But sometimes you need to calculate neck column concrete before casting footing. In that case, you need to depend on the drawings.
Most of the time you’ll get the data from footing section and grade beam layout drawing.
From the footing section drawing sheet, you’ll get the depth of the ground the footing placed on. It is normally shown from road level (土0). For example, I assume that this level is shown in the footing section as -5′. That means the bottom of the footing is place 5′ below the ground.
We also need the top level of grade beam which you’ll get from either footing section or grade beam layout drawing. For example, it is specified in the drawing as +3′.
Now let’s calculate the height of the neck column.
The height of neck column is,
= Bottom level of footing + top level of grade beam – the thickness of footing – the thickness of grade beam
= 5′ + 3′ – 1′ – 1′ (the thickness of footing and grade beam 1’ – assumed)
So, The height of neck column is 6′.
Now we can calculate the concrete quantity for neck columns.
Step 4: Calculating Concrete Quantity for Neck Columns
We know, the formula for getting volume is area x height.
For square and rectangular size, the area is length x width. But if the column is round shape then the formula for getting the area is πr² (π = 3.14 and r = radius of the column).
So, let’s calculate the concrete volume for neck columns which we found in step 1.
C1 – 5 x 32″ x 14″ = 5 x 2.67 x 1.17 = 15.62 ft3 (12″ = 1 feet, ft3= cubic feet )
C2 – 10 x 42″ x 14″ = 10 x 3.5 x 1.17 = 40.95 ft3
C3 – 7 x 52″ x 14″ = 7 x 4.33 x 1.17 = 35.46 ft3
Total concrete quantity is
= 15.62 + 40.95 + 35.46
This is the exactly required concrete quantity for our neck columns. If you plan to cast the neck columns with ready-mix concrete then you can order for this concrete volume. But if you want to use on-site machine mix concrete then you need to calculate the concrete ingredients. I’ve talked about this before in “how to calculate concrete ingredients”.
Calculating concrete volume for neck columns is actually easy. You just need to get the total numbers of different sizes columns and the size and height of the columns from drawing. And then multiply and sum them up for getting the total concrete volume.
How do you get the height of neck column? Please share in the comments below…