How to Plumb a Column or Vertical Structure with a Total Station

Applies to: Topcon GT-1000/GT-500, Trimble S-Series, Leica TS16/TS07, Sokkia SX series

Plumbing columns is one of the most precision-critical tasks in structural construction. A steel column or precast concrete column that is out of plumb by even a small amount transfers eccentric loading into the connections and base plate, reduces the structure's capacity, and may require costly correction after the ironwork is complete. Using a total station for plumb checks gives you a quantified deviation reading — not just a visual estimate — and allows you to guide corrections in real time before connections are bolted up.

Step 1: Position the Instrument Correctly

Set up the total station in front of the column face you want to check. The instrument must be positioned so you can sight both the base of the column and the top without obstructions. The recommended distance from the column is at least one-third the column height — for a 9-meter (30-foot) column, set up at least 3 meters (10 feet) away. At closer distances, the parallax from small instrument movements introduces significant error in the plumb calculation.

Level the total station carefully. For plumb work, instrument leveling accuracy matters more than for most survey tasks — a poorly leveled instrument introduces tilt error into the vertical angle measurements that becomes a systematic error in the plumb reading. Use the electronic level display and level the instrument to within 10 arc-seconds of level.

Step 2: Sight the Base Reference Point

Aim the total station at a defined reference point near the base of the column. For steel columns, this is typically the column face at the base plate level or a reference mark scribed on the column. For concrete columns, sight the column face at the lift joint or a control mark at the base. Read and record the horizontal angle to this base point.

Lock or record the horizontal angle. On most data collectors, the Lock direction function holds the horizontal angle reading. Alternatively, record the angle manually. The key is that the base horizontal angle becomes the reference for comparison with the top measurement.

Step 3: Elevate to the Top Reference Point

Without changing the horizontal rotation of the instrument, elevate the telescope to sight the corresponding reference point at the top of the column. For a steel column being plumbed during erection, this is typically the column flange face or web face at the top of the shaft. Read the horizontal angle to the top reference point.

The difference between the top and base horizontal angle readings is the angular plumb deviation in one plane. Convert to a linear deviation using the formula: linear deviation = column height x tangent(angular deviation). For small angles (under 10 arc-minutes), the approximation: linear deviation = column height x angular deviation in radians, is accurate. At a column height of 9 meters and an angular deviation of 1 arc-minute, the linear deviation is 9 x (1/3438) = approximately 2.6mm.

Step 4: Check from a Perpendicular Direction

The check from one direction only tells you plumb deviation in the plane of the instrument sight. A column can be plumb in one direction and significantly out-of-plumb in the perpendicular direction. Move the instrument to a position approximately 90 degrees around the column from the first setup and repeat the base-to-top horizontal angle comparison. This second check gives the plumb deviation in the perpendicular plane.

Combine the two deviation vectors to find the total 3D plumb error and its direction. If the column deviates 3mm north and 5mm east, the total plumb deviation is approximately 5.8mm in the northeast direction. Report the plumb deviation to the ironworkers as a compass direction and distance at the top of the column — this is the information they need to apply correction with come-alongs or column jacks.

Step 5: Guide the Correction

While the ironworkers apply correction force to the column, keep the total station on the top reference point and call out the direction and magnitude of remaining deviation. Most columns are plumbed with come-alongs connected to adjacent structure or deadman anchors. The process is iterative — apply correction, re-read, adjust, re-read — until the plumb deviation is within tolerance.

Typical structural steel plumb tolerance is L/500 where L is the column height — for a 9-meter column, this is 9000/500 = 18mm. For more demanding work such as precast concrete parking structures or industrial equipment bases, tolerance tightens to L/1000 or better. Confirm the project specification tolerance before beginning plumb work; different specifications exist for different structure types and loading conditions.

Frequently Asked Questions

What is the acceptable plumb tolerance for steel columns?

AISC specification for structural steel erection allows a plumb tolerance of L/500, where L is the column height, but not more than 1 inch (25mm) for columns not at building perimeter and L/1000 not to exceed 1/2 inch (12mm) for building perimeter columns. Specific project specifications may be tighter — always confirm with the structural engineer and the project spec before accepting a column.

Can I use a plumb bob instead of a total station to check column plumb?

A plumb bob works on calm days without wind interference and for shorter columns where the bob can hang clear of the column face. For columns over 6 meters tall, wind drift on the plumb line becomes significant. A total station gives a quantified, repeatable measurement and works in windy conditions. For critical structural plumb, the total station method is preferred.

How do I check plumb on a round column with a total station?

For round columns, sight the column centerline at the base by measuring two edge points and computing the center. Do the same at the top. The vector from the base center to the top center is the plumb error. Alternatively, place reflective targets on opposite faces of the column at base and top and measure to the targets — the midpoint of each pair gives the center at each elevation.

What is the difference between plumb and level in construction?

Plumb means vertical — a plumb surface or element is exactly perpendicular to horizontal. Level means horizontal — a level surface is exactly perpendicular to vertical. Columns are plumbed (made vertical). Beams, slabs, and grade are leveled (made horizontal). A total station checks plumb of vertical elements and level of horizontal elements with equal accuracy.