En

Expression

A.Jx<p = (14)(6 for circular rentiers

= {7/3 6) ? for 7-wire strands /pi = fytJdesign value of «eel tensi le sir /bod is design value of bond strength

Not used as a separate parameter in S, 10.2

Bond strength at release

= 1.4 for indented or crimped wires = 1.2 for 7-wire strands rjpi = 1.0 for good bond conditions

= 0.7 for other cases frjf(r) is design value of tensile strength at release

where r}f ] = 2.1 for indented wires = 3.2 for 7-wire strands rfi =1.0 for good bond conditions acc. to 8.4.1 = 0.7 otherwise {unless good bond conditions can be verified)

Transmission length

OS =1.0 for gradual release = 1.25 for sudden release CC3 =1.0 for anchorage length ULS

= 0.5 for stre sses at re le ase «in = 0.7 for indented or crimped wires

= 0.5 for strands ObL is steel stress just after release

where is the same as orj in MC 90 a-_ = 0.2 5 for circular tendons = 0.1? for 7-wire strands

Note. MC'90's oj is taken into account by 0,8 and 1,2 111 expressions (8.16) and (8.17), ffjo by ij,].

Design values of/pt

See factor ag above

Jpd = 0.8/pt (8.16) lp2 = 1,2/pt <5 J 7)

Bond at anchorage

./bpd = rjpi 7p/ctd (6.9-12) where fui is design value of tensile strength

Jb?d= rfp2 IJlfcxA (8-19) where rjB: is the sajne as rfa in MC90

Ofi is tendon stress to be anchored is tendon stress due to pre stress after losses

^bpd = ^pt2 ~~ a2 4> (o"pd " Opac) ;'„/bpd (S-2G)

where is upper design value of transmission length Of,, is tendon stress due to pre stress after losses

Table 8.2. Summary of rules in MC90, 6.9.11, and EN 1992, 8.10.2

Table 8.2. Summary of rules in MC90, 6.9.11, and EN 1992, 8.10.2

8.10.2.2.2 Rules in MC90

8.10.2.2.2.1 Basic anchorage length

Asp/^9 - 9/4 for circular tendons, (7/36)9 for 7-wire strands fpd - fptk/ys design value of tensile strength of tendons fbpd design value of bond strength, see below

8.10.2.2.2.2 Design value of bond strength fbpd - %1%2fctd(t)

where

%1 takes into account the type of prestressing tendon: ^p1 - 1,4 for indented and crimped wires and

- 1,2 for 7-wire strands

%2 takes into account the position of the tendon: ^p2 - 1,0 for good bond condition,

fctd(t) is the lower design value of concrete tensile strength at time of release, or at 28 days for verifications in ULS.

lbpt a8a9a10lbp f Tpd where a,8 considers the way of release:

a,8 - 1,0 for gradual and 1,25 for sudden release a9 considers the action effect to be verified:

ag = 1,0 for calculation of anchorage length when moment and shear capacity in ULS

is considered, and ag = 0,5 for verification of transverse stresses in the anchorage zone aio considers the influence of bond situation: aio = 0,5 for strands and aio = 0,7 for indented or crimped wires api is the steel stress just after release

8.10.2.2.2.4 Anchorage length in ULS

l _ l + l apd ' apcs bpd bpt 'bp f Tpd where apd tendon stress under design load (apd ^ fpd) apcs tendon stress due to prestress including all losses

The rules in 8.10.2 are summarized below and compared to those in MC90. The "basic anchorage length" used as a separate parameter in 8.10.2 is instead incorporated directly in the expressions for transmission length and anchorage length.

8.10.2.2.3.1 Transfer of prestress

8.10.2.2.3.1.1 Bond strength

The bond strength governing the transmission at release of prestress is fbpt _ %1 fctd(t)

where

^p1 takes into account the type of tendon and the bond situation at release ("push-in") _ 2,7 for indented wires ("crimped" wires are hardly used anymore, therefore not incl.) _ 3,2 for 7-wire strands

_ 1,0 for good bond conditions (see 8.4.1) or _ 0,7 otherwise, unless good bond conditions can be verified fctd(t) _ fctk,0,05(t) /yc, design value of tensile strength at the time of release, related to the compressive strength at the same time according to table 3.1 The factor is the same as in 8.4.1 (and the same as r|p2 in MC90). However, a possibility to assume "good bond conditions", even if the criteria in 8.4.1 are not met, has been added for cases where good conditions can be achieved by other means, and verified.

The factor |p1 here includes two factors, which in MC90 are applied to the transmission length instead, namely the factor a10 and the mean value of ag, (0,5 + 1,0)/2 _ 0,75:

^p1,EN_ ^p1,MC90 which gives ^,EN _ 1,4 _2,7 for wires a10ag,mean 0,7x0,75

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