![]() ![]() k t is a factor dependent on the duration of the load: Φ p = 1,20⋅ Φ wire for single 3 wire strands, where Φ wire is the wire diameter. Φ p = 1,75⋅ Φ wire for single 7 wire strands, Φ p = 1,6⋅√ A P for bundles, where A P is the area of a prestressing steel, With ξ the ratio of bond strength of prestressing and reinforcing steel, according to Table 6.2 Φ S the largest bar diameter of the reinforcing steel Φ P the diameter or equivalent diameter of prestressing steel: With A s the cross sectional area of reinforcement A' p the area of pre or post-tensioned tendons within A c,eff A c,eff the effective area of concrete in tension surrounding the reinforcement or prestressing tendons of depth, h c,ef, where h c,ef is the lesser of 2,5( h - d), ( h - x)/3 or h/2 (see Figure 7.1) ξ 1 the adjusted ratio of bond strength taking into account the different diameters of prestressing and reinforcing steel: ξ 1 = With E cm the secant modulus of elasticity of concrete f ct,eff is the mean value of the tensile strength of the concrete effective at the time when the cracks may first be expected to occur:į ct,eff = f ctm or lower, ( f ctm( t)), if cracking is expected earlier than 28 days ρ p,eff = ( A s + ξ 1⋅ A' p)/ A c,eff ![]() ![]() See application for a rectangular section or application for a T-section E s is the design value of the modulus of elasticity of the reinforcing steel, see § 3.2.7 (4) α e is the ratio E s/ E cm Where: σ s is the stress in the tension reinforcement assuming a cracked section, ![]()
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