The calculation proceeds in the same way as for a non-fire exposed section, only this one uses a reduced cross-section and reduced reinforcement and concrete parameters, according to Temperature distribution

The calculation can be carried out with fyd = f2.0 or fyd = f0.2 for reinforcement depending on the limits for the deformation in fire. 

The temperature in the shear reinforcement is calculated as the maximum of all temperatures in all corners of the shear reinforcement. 

The temperature in a corner is calculated as an average temperature on a half length on each side of the corner. HD profiles are calculated according to EN1168, Annex G.1.3: 

Vrd,c = [k ⋅ (0.58 ⋅ Sigma.png(FRa,fi / fyk) / bw ⋅ d)1/3 + k1 ⋅ min(kcM) ⋅ σcp, 20°C ,  Sigma.pngFra,fi,p / Ac] ⋅ bw ⋅ d

  • k1 = 0,15. 
  • kc is the fire strength reduction factor for concrete in compression. 
  • k = 1 + (200 / d)0,5 ≤ 2,0, with d in mm 
  • FRa,fi = f2.0d ⋅ As for reinforcement 
  • FRa,fi = min((Xpr ⋅ fbpdpr,fi + X ⋅ fbpd,fi ) / α2 ⋅ φ, f2.0d ) ⋅ As for prestressed reinforcement
    • Protruding tendons are not allowed here, therefore Xpr = 0. 
    • X = ηp2 ⋅ φ ⋅ σspi ⋅ α1 ⋅ α2 / fbpd,fi 
  • Then FRa,fi = min((ηp2 ⋅ σspi ⋅ α1), f2.0d ) ⋅ As for prestressed reinforcement
    • σspi = The initial prestressing stress. 
    • α1 are according to EN 1992-1-1 8.10.2.3 
    • ηp2 are according to EN 1992-1-1 8.10.2.3 
    • ηp2 = 1,4 for indented wires and 1.2 for 7-wire strands. (Recommended values)
    • α1 =1,25 for sudden release and indented, else α1 =1,0. 
  • bw is the smallest width of the cross-section in the tensile area (mm). 

σcp = NEd / Ac

where:

  • NEd is the axial force in the cross-section due to prestressing (in N) (NEd > 0 for compression). The influence of imposed deformations on NE may be ignored. 
  • Ac is the area of concrete cross-section (mm2), 

VRd,c is in (N) 

The shear force VEd should always satisfy the condition

VEd ≤ 0,5 ⋅ bw ⋅ d ⋅ υ ⋅ fcdM)

where:

  • υ = 0,6 (1 - fck / 250) (fck in MPa)
Created by Fredrik Lagerström on 2020/06/11 10:57
Copyright 2020 StruSoft AB
PRE-Stress Documentation