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1 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>>Temperature distribution]].
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3 The calculation can be carried out with f,,yd,, = f,,2.0,, or f,,yd,, = f,,0.2,, for reinforcement depending on the limits for the deformation in fire.
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5 The temperature in the shear reinforcement is calculated as the maximum of all temperatures in all corners of the shear reinforcement.
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7 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>>doc:Documents.EN1168.WebHome]], Annex G.1.3:
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9 V,,rd,c,, = [k ⋅ (0.58 ⋅ [[image:Sigma.png]](F,,Ra,fi,, / f,,yk,,) / b,,w,, ⋅ d)^^1/3^^ + k,,1,, ⋅ min(k,,c,,(θ,,M,,) ⋅ σ,,cp, 20°C,, , [[image:Sigma.png]]F,,ra,fi,p,, / A,,c,,] ⋅ b,,w,, ⋅ d
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11 * k,,1,, = 0,15.
12 * k,,c,, is the fire strength reduction factor for concrete in compression.
13 * k = 1 + (200 / d)^^0,5^^ ≤ 2,0, with d in mm
14 * F,,Ra,fi,, = f,,2.0d,, ⋅ A,,s,, for reinforcement
15 * F,,Ra,fi,, = min((X,,pr,, ⋅ f,,bpdpr,fi,, + X ⋅ f,,bpd,fi,, ) / α,,2,, ⋅ φ, f,,2.0d,, ) ⋅ A,,s,, for prestressed reinforcement
16 ** Protruding tendons are not allowed here, therefore X,,pr,, = 0.
17 ** X = η,,p2,, ⋅ φ ⋅ σ,,spi,, ⋅ α,,1,, ⋅ α,,2,, / f,,bpd,fi,,
18 * Then F,,Ra,fi,, = min((η,,p2,, ⋅ σ,,spi,, ⋅ α,,1,,), f,,2.0d,, ) ⋅ A,,s,, for prestressed reinforcement
19 ** σ,,spi,, = The initial prestressing stress.
20 ** α,,1,, are according to EN 1992-1-1 8.10.2.3
21 ** η,,p2,, are according to EN 1992-1-1 8.10.2.3
22 ** η,,p2,, = 1,4 for indented wires and 1.2 for 7-wire strands. (Recommended values)
23 ** α,,1,, =1,25 for sudden release and indented, else α,,1,, =1,0.
24 * b,,w,, is the smallest width of the cross-section in the tensile area (mm).
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26 σ,,cp,, = N,,Ed,, / A,,c,,
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28 where:
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30 * N,,Ed,, is the axial force in the cross-section due to prestressing (in N) (N,,Ed,, > 0 for compression). The influence of imposed deformations on N,,E,, may be ignored.
31 * A,,c,, is the area of concrete cross-section (mm^^2^^),
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33 V,,Rd,c,, is in (N)
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35 The shear force V,,Ed,, should always satisfy the condition
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37 V,,Ed,, ≤ 0,5 ⋅ b,,w,, ⋅ d ⋅ υ ⋅ f,,cd,,(θ,,M,,)
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39 where:
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41 * υ = 0,6 (1 - f,,ck,, / 250) (f,,ck,, in MPa)
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PRE-Stress Documentation