Tips to check the verticality for column formwork

Formwork stands for a temporary structural system that provides the casing and supporting to the wet concrete to attain the desired shape. It should be secured with the weight of the concrete, reinforcement, and other live loads all through the construction and compacting of concreting.

Once the formwork for column is erected, it is required to verify the exact verticality prior to concreting.

For small scale formworks, the verticality is examined with a plain center plumb.

Two center plumbs and a steel tape are essential for this method. Center plumbs were suspended at two positions in the similar plane with a recognized distance of 150 mm that is calculated from the inner surface of the plywood sheet(or steel formwork). The distance from the plywood sheet to the thread of the center plumb is computed with the use of the steel tape at both top and the bottom of the form work.

Computation for a plywood formwork is done in the following ways :-

Offset distance from the column edge = 150 mm
Plywood thickness = 12 mm
Distance among the plywood and the plumb = 150-12 = 138 mm

When the verticality of the column is perfect, the distance among the plywood and the center plumb thread should remain 138 mm everywhere. Jack supports or locking systems of the formwork are modified to get the exact verticality for any discrepancy.

To maintain greater perfectness, a thedolite and a steel tape can also be applied. This method is specifically effective while examining a huge number of formworks along a one grid line.

The process is mentioned below: The digital theodolite should be arranged centering a peg which was set up with a 500 mm offset to the column grid. Get the direction by focusing the telescope to a remote peg that was set up with a 90 degree angle to column grid line.

As soon as theodolite was set up properly, turn on the laser beam and focused it to the steel tape that is retained to the formwork. Get the reading of the steel tape through the telescope.

Get the readings of two positions at the same level on both top and bottom levels of the formwork. By getting two readings at the same level any curvature on the surface is detected.

Sample calculation:

Offset distance from the column grid = 500mm
Plywood thickness = 12mm
Size of the column = 300mm
Perfect reading through the telescope = 500-150-12 = 338mm

To maintain proper verticality, 338mm reading should be read through the telescope. Acro jacks and locks are modified to get the exact verticality.