What is the minimum percentage of design strength recommended for removal of forms under girders?

The minimum percentage of design strength recommended for the removal of forms under girders is generally considered to be 80%. This guideline ensures that the concrete has gained enough strength to support its own weight and any additional loads without risk of deformation or failure.

This recommendation is based on the need for safety and structural integrity. At 80% of the design strength, the concrete is sufficiently cured and has achieved enough early strength to bear loads and prevent issues such as cracking or collapse. This level of strength indicates that the concrete has reached a point where it can handle the stresses associated with the construction process, including any subsequent activities or loads applied to the structure.

When forms are removed too early, it can lead to sagging, deflection, or even catastrophic failure of the structural elements. Therefore, waiting until the concrete reaches at least 80% of its design strength helps in ensuring that it can perform as intended in the long term.