Column alignment checking is one of the vital activities during the construction of a building. The column is designed to carry a huge load of beams, slab, walls, etc. Therefore, it is essential to ensure the precise alignment of the column as per the structural drawing.
A slight error in column alignment during construction can cause serious issues during beam, masonry, façade, plastering, and other works. Hence, checking the column alignment by a site engineer is mandatory at different stages of construction.
In this article, you will learn how to check column alignment at the site, what tools are required for the job, and what precautions should be taken during the works.
What is Column Alignment?
Column alignment refers to checking if the column is placed at the correct location and its centerline is properly matched with the structural drawing.
For instance, if the column is designed at the intersection of Grid A and Grid 1, then from the foundation level to the top of the column, its centerline should be precisely at that location.
Thus, column alignment comprises
checking the position of the column,
the column’s centerline,
verticality or plumb,
the column’s dimension,
the alignment of the column to the lower and upper columns,
and orientation.
Why it is Essential to Check Column Alignment?
The correct alignment of the column is vital for a building structure since it transfers loads from beams, slabs, and other elements to the ground properly.
A wrongly aligned column can cause serious issues such as beam-column misalignment, uneven wall thickness, and difficulties in masonry works. For example, an inaccurate column position will lead to additional plastering works, incorrect door/window openings, and increased plaster thickness. Moreover, eccentricity of the column might cause structural problems, whereas misalignment of the column on different floors will result in faulty alignment of doors and windows.
That is why it is essential to check column alignment even before reinforcement, shuttering, and concrete pouring.
Tools Required for Column Alignment Checking
Depending on the project’s complexity, the tools required for column alignment checking may differ. However, typically, the following tools are used:
Total Station
This advancedinstrument is highly accurate and allows transferring grid coordinates and column reference points to the column under inspection.
Auto Level
An auto level is primarily used for leveling works. However, to check column alignment, it can be used as an auxiliary tool.
Plumb Bob
A plumb bob is a simple and inexpensive tool used to check the verticality of the column shutter. This tool is suitable for use on small-scale construction sites.
Measuring Tape
A measuring tape is required to measure the distance between column centerlines, offsets, and other points.
Laser Level
A laser level is applicable in column alignment checking when the site conditions allow using this instrument.
Column Alignment Checking Procedure
It is essential to understand the general procedure for checking column alignment. The procedure typically comprises the following steps.
Step 1: Study Structural Drawing
Beforehand, a site engineer should thoroughly study the structural drawing and pay attention to the following details:
Grid,
Column number,
Column size,
Centerline,
Offset,
Orientation,
Floor to floor dimensions.
Never align columns based on the previous floor. Always use the structural drawing as a reference.
Step 2: Establish Grid Lines
A grid is a reference system based on which columns are aligned. For instance, if a column is designed at the intersection of Grid A and Grid 3, then the centerline of this column should be established using Grid A and Grid 3. A surveyor or a site engineer should establish reference lines using a total station.
Step 3: Mark Column Centerline
Using a reference system established in Step 2, mark column centerline on the slab or working surface. For a rectangular column, it is essential to mark two centerlines – lengthwise and widthwise. For example, for a 300×450 column, a reference line will help to ensure that the column’s width and length are correctly set to 300 and 450.
If the column’s centerline is wrongly set, the column itself will be wrongly placed.
Step 4: Check Column Position
Now, it is time to check column position. Measure the distance between the column centerline and grid reference lines. For instance, if the distance between two column centerlines should be 4.0 m, then measure this distance on-site and compare it to the design.
If the distance does not match the design, find out why before proceeding to the next step.
Step 5: Check Column Shutter
After column reinforcement is installed and the column shutter is set, check the following:
Column size,
Centerline,
Verticality,
Position,
Orientation,
Cover,
Shuttering and its support.
The column shutter should be appropriately set so that it does not deform under the pressure of concrete.
Step 6: Check Column Shutter using Plumb Bob
Using a plumb bob, check if the column shutter is set vertically. To do that, hold the plumb bob at the top of the column and ensure that the plumb bob line is aligned with the reference point at the bottom of the column. If the distance between the plumb bob and the reference point is different at the top and bottom of the column, the column is not vertical.
Before concrete pouring, it is essential to fix the column shutter so that it remains at the design position.
Step 7: Check Column Alignment to the Lower Column
For multi-story buildings, it is essential to check column alignment vertically as well. A column on the second floor should be aligned with a column on the first floor. If the structural drawing does not indicate otherwise, a column on different floors should have the same centerline. It can be checked using a total station, laser plummet, plumb bob, and other tools depending on the project’s needs.
How to Check Column Alignment using a Total Station
For large-scale projects, a total station is the preferred tool for checking column alignment.
The general procedure for column alignment checking using a total station is as follows:
Set the total station at the established reference point,
Set the reference point using control points,
Call up the necessary grid or column coordinates,
Establish the designed column center point,
Mark the point on the slab,
Transfer the column centerline,
Check the column shutter in accordance with the established centerline.
After the column shutter is set, the survey team can check if it is aligned with the design.
This procedure is much more accurate than measuring the column alignment with a measuring tape.
How to Check Column Alignment Before Concrete Pouring
Before concrete pouring, a site engineer should make a final check of the column alignment. A check list can be developed as follows:
Check
Status
Column location
Grid alignment
Centerline
Column size
Verticality
Reinforcement position
Concrete cover
Shuttering support
Column orientation
Level
Only when all items on the list are fulfilled, the column can be poured.
Common Errors During Column Alignment Checking
There are several common errors that occur during column alignment checking:
Measuring from the wrong reference,
Not following the latest structural drawing,
Checking column alignment only at the bottom of the column,
Loose column shutter,
Incorrect column verticality,
Not checking column alignment after adjustment,
Using only a measuring tape.
Site Engineer’s Tips
It is essential to follow a few simple rules to ensure column alignment:
Establish permanent grid or control points,
Protect survey benchmarks,
Clearly mark column centers,
Always check columns before concrete pouring,
Always recheck the column shutter after adjustment,
Check both column position and verticality,
Follow the latest structural drawing,
Document important checks of column alignment in the site inspection report,
And do not ignore minor column misalignment without assessing its impact on the project.
Conclusion
Checking column alignment is a routine task for a site engineer. It is essential to ensure that the column is correctly placed in terms of position, size, verticality, and orientation. It will ensure that other building elements such as beams, slabs, walls, and other elements are correctly placed as well.
A proper column alignment checking procedure comprises establishing a reference system, marking the column centerline, checking the column position, checking the column shutter size, checking the column verticality, and a final check before concrete pouring.
For small-scale projects, some of the steps mentioned can be omitted. However, for large-scale projects, it is essential to use advanced survey equipment such as a total station to ensure precision.