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How to calculate the length of a reinforcement stirrup?

Compiling cutting lengths for stirrups involves determining the total length of reinforcing bars needed to create the stirrups in a reinforced concrete structure. The process includes considering factors such as the number of stirrups required, the spacing between stirrups, the shape of the stirrups, and any additional lengths needed for overlaps or hooks.

Here's a step-by-step guide on how to compile cutting lengths for stirrups:

Understand Design Requirements:

Review the structural design drawings and specifications to understand the specific requirements for the stirrups. Identify factors such as stirrup spacing, stirrup diameter, and any detailing requirements.

Calculate Total Stirrup Length:

Determine the total length of stirrups needed by multiplying the number of stirrups required by the circumference or perimeter of each stirrup. The formula is: Total Stirrup Length=(Number of Stirrups)×�×(Stirrup Diameter+Additional Length for Hooks or Overlaps)Total Stirrup Length=(Number of Stirrups)×π×(Stirrup Diameter+Additional Length for Hooks or Overlaps)

Consider Bend Lengths:

If the stirrups have bends or hooks, include the lengths of these bends in the calculation. This may involve considering the extensions of the hooks or bends beyond the straight sections of the stirrups.

Account for Lap Lengths:

If stirrups are overlapped or lapped at certain points, include any required lap lengths in the total length calculation. Lap lengths are typically specified to ensure proper overlap and anchorage.

Include Extra Lengths:

Consider any additional lengths needed for tying and securing the stirrups within the concrete structure. This may include extra lengths for overlap, tying, or development.

Use Standard Units:

Ensure that the units used for the stirrup lengths are consistent with the project specifications (e.g., millimeters or inches).

Document the Cutting Lengths:

Document the calculated cutting lengths for each stirrup. This documentation is crucial for the fabrication process and ensures that the correct lengths are used during construction.

Verify Compliance:

Verify that the compiled cutting lengths comply with the project's design specifications, including any tolerances or allowances specified in the design codes.

Fabrication Process:

Provide the compiled cutting lengths to the fabrication team or workers responsible for cutting and shaping the stirrups. Ensure that the stirrups are fabricated according to the documented cutting lengths.

Calculating the length of a stirrup is crucial to ensure the strength of the structure.

The formula to calculate the cutting rectangular stirrup length is =

(2 × long side of stirrup) + (2 × short side of stirrup) + (2×hook length) - (3 × 90° bend) - (2 × 135° bend).

For example, assume column of size 540 x 540 with cover of 60 mm.

For a 10 mm diameter bars stirrup

  • Long side of a stirrup is 470 mm

  • Short size = 470 mm

  • Hook length of standard 75 mm.

  • 90-degree bends = Add 2 x bar dia for elongation.

  • 135-degree bend = Add a 3 x diameter of the bar.

Length = (2x470) + (2x370) + (2x75) - (3x20) - (2x30) = 1,710 mm


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