The load combination in AC! 562-16 Eq. (5.5.3) is recommended in place of those presented in Section 9.2.1 of AC! 440.2R-1 7 related to fire exposure.
Equation (9.2) of ACI 440.2R-17 should not be used to assess strength during exposure to fire. The intent of Eq. (9.2) Is to guard against collapse at normal temperature in the event of damage to the FR? system due to vandalism. inadvertent removal during subsequent renovation, or other non-fire-related causes.
The member strength during the fire event should be based on material properties that reflect reduction due to effects of elevated temperature. A simplified calculation showing basic concepts of evaluating the strength of a reinforced concrete beam, using reduced material properties, Is provided at the end of this TechNote. Consistent with principles described in ASTM E119 and AC! 216.1. the strength reduction factor used in the calculation should be taken as 1.0. Calculations based on principles described in ACI 216.1 and other rational methods represent the type of engineering analysis permitted by the 2018 IBC Section 722. AC! 216.1 does not explicitly address FRP-strengthened members. However, data contained in ACI 216.1 relating to reduced concrete and steel strength can be Incorporated into the calculations. The contribution of the FR!-’ system should be neglected in the calculations unless the continued effectiveness of the FR? materials and bond to substrate can be proven through testing.
For certain types of concrete members, the use of calculations in accordance with IBC 2018 Section 722 may represent a viable method of demonstrating code compliance of nonprotected FR? systems during exposure to fire. In such instances, fire protection is not required to ensure adequate safety against collapse from fire. However, a coating to mitigate flame spread and smoke generation is often required by the building code, even if thermal protection for structural purposes Is not required.
Evaluation by calculations in accordance with !BC 2018 Section 722 Is an accepted and code-compliant approach; it is not an alternate method requiring specific review and approval by the building official. tlnfortunately, many building officials have limited experience with calculations to evaluate fire resistance, and even fewer have experience with calculations Involving FR? systems. Additionally, the building official may be reluctant to accept FR? as a structural material because It is not explicitly listed in the IBC. Therefore, despite specific provisions In the IBC permitting use of calculations, the design professional should consult with the building official at an early stage In the design process to avoid possible delays during plan review and permitting.ACI PRC-440.10 pdf download.