Cover Calculator

Name: Cover for FRP - Columns and Walls
Brand: PROMAXA
SKU: 5199d639-c895-4365-a69c-7f128e145814

Provided by Promaxa, this calculator assists engineers and specifiers in determining appropriate reinforcement cover for concrete elements, accounting for durability exposure conditions and fire resistance requirements in accordance with AS3600:2018

Required axis distance

a_s = 0 mm

Required cover for fire

c_f_i_r_e = 0 mm

Reinforcement cover for fire (AS 3600:2018) - Columns and Walls

This calculator determines the minimum reinforcement cover and axis distance required to achieve a specified Fire Resistance Period (FRP) for braced concrete columns (AS 3600:2018 Cl. 5.6) and walls (Cl. 5.7).

Workflow - Columns:

Set Element to Columns.
Pick the column method - Restricted (Cl. 5.6.3) or General (Cl. 5.6.4).
Select the load level (μ_f_i for Restricted; η and ω for General) and the column exposure. For the Restricted method, AS 3600 Table 5.6.3 tabulates the ‘one side only’ case only for μ_f_i = 0.7, so that exposure option is offered only when μ_f_i = 0.7 is selected.
Select the required FRP - only the fire periods with a tabulated value for the chosen method and load level are listed.
Select the column dimension b - only the sizes with a tabulated axis distance for the chosen FRP are listed.
Enter the bar diameter d_b and tie/fitment diameter d_s.

Workflow - Walls:

Set Element to Walls and select the required FRP.
Choose whether the wall requires structural adequacy (Cl. 5.7.2) in addition to insulation (Cl. 5.7.1).
If structural adequacy is required, pick the wall load level μ_f_i and exposure (one or two sides), then enter d_b and d_s.

The FRP, column dimension and exposure lists are filtered to valid combinations, so only values with a tabulated result can be selected. The required axis distance a_s is taken from the AS 3600 tables and the cover for fire is computed as c = a_s - d_b/2 - d_s. For walls, the minimum wall thickness is the larger of the insulation and structural adequacy requirements.

Eligibility limits (Cl. 5.6.2): Tables 5.6.3 and 5.6.4 cover only braced columns. For unbraced/sway columns or those outside the tabulated limits, refer to Cl. 5.3.1 (performance solution).

Restricted method (Cl. 5.6.3) additional limits: effective length under fire conditions l₀_,_f_i<= 3 m; first-order eccentricity e <= 0.15 b and <= 100 mm; A_s<= 0.04 A_g (or use the General method); when A_s >= 0.02 A_g and FRP > 90 min the longitudinal bars must be distributed on all faces (8 or more bars).

General method (Cl. 5.6.4) additional limits: e/b < 0.25 and e <= 100 mm; slenderness λ_f_i<= 30; A_s<= 0.04 A_g; when A_s >= 0.02 A_g and FRP >= 90 min the longitudinal bars must be distributed evenly along the sides (8 or more bars).

Required axis distance

a_s is the axis distance to the centre of the longitudinal reinforcement, read from the applicable AS 3600 table for the selected element, method and load level: Table 5.6.3 (Restricted) or Table 5.6.4 (General) for columns, and Table 5.7.2 for walls. The required cover for fire is then c_f_i_r_e = a_s - d_b/2 - d_s.

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Required cover for fire

c_f_i_r_e = a_s - d_b/2 - d_s. Compare against the cover required for durability (Section 4); the greater governs.

Not Available

Notes and limitations:

The cover from this calculator is for fire resistance only (AS 3600 Section 5). The governing cover is the larger of cover for fire and cover for durability (Section 4) per Cl. 4.10.1.
For prestressing tendons, the axis distance shall be increased by 15 mm for strand or wire and 10 mm for prestressing bars per Cl. 5.3.3.
Linear interpolation between tabulated FRP values is permitted per Cl. 5.3.2 and is applied to the column tables in this calculator. b values are floor-snapped per Cl. 5.6.3(a) / 5.6.4(a) - the actual b shall not be less than the tabulated value.
Restricted column method (Cl. 5.6.3): only braced columns; effective fire length l₀_,_f_i <= 3 m; first-order eccentricity e <= 0.15 b and <= 100 mm; A_s <= 0.04 A_g; when A_s >= 0.02 A_g and FRP > 90 min, longitudinal bars must be distributed on all faces (>= 8 bars).
General column method (Cl. 5.6.4): only braced columns; e/b < 0.25 and e <= 100 mm; slenderness λ_f_i <= 30; A_s <= 0.04 A_g; when A_s >= 0.02 A_g and FRP >= 90 min, longitudinal bars must be distributed evenly along the sides (>= 8 bars). Some cells in Table 5.6.4 are marked Note 1 (require b > 600 mm and assessment for buckling) and are returned as zero in this calculator - the user must verify against the published table.
Walls (Cl. 5.7.2): insulation (Cl. 5.7.1) always applies. Structural adequacy is satisfied by Cl. 5.7.1 alone where the lateral support at the top of the wall is provided on one side only by a member not required to have an FRL.
Out of scope: Cl. 5.6.3 Eq. 5.6.3(2) (effective fire length) and other Cl. 5.6 eligibility checks (must be checked separately); Cl. 5.7.3 wall slenderness limit H_w_e / t_w <= 40 (must be checked separately); Cl. 5.7.4 chases / recesses; Cl. 5.8 FRP enhancement by added insulating materials.