04/24/2022 Prepared by: Eng. Chamil Duminda Mahagamage B.Sc.Eng (Hons), C Eng, MIE(SL) 1 International College of Business and Technology 6102BEUG- Lecture Note: 09 Pre-stress losses (Cl. 5.10, EC2) Loss of pre-stresses is the difference between the jacking force in the tendon at the pre-stressing stage and the force after losses have occurred. Some of the losses occur immediately when the force is transferred to the concrete, e.g elastic shortening of the member. Other losses occur with time, e.g. creep of the concrete. The jacking force does not exceed 90% of the characteristic strength of the tendon and is generally not less than 75% (cl 5.10.3(2),EC2). In practice total losses of the jacking force are within the range of 15%-40%. If large losses of pre-stress occur then the advantages of pre-stressed concrete, e.g. no cracks at service load, are lost. It is therefore advantageous to minimize the loss of pre-stress. per cent loss of pre-stress = 100*(jacking stress-final stress)/(jacking stress)
8/13/15Prepared by: Eng. Chamil Duminda MahagamageB.Sc.Eng
(Hons), C Eng, ME(S!)1n"erna"ional College o# Business and
$echnology6102BEUG- Lecture Note: 09Pre-stresslosses(Cl.5.10,
EC2)Lossofpre-stressesisthediere!ce"et#ee!the$%c&i!'forcei!the
te!do!%tthepre-stressi!'st%'e%!dtheforce%fter(ossesh%)e
occurred*+o,eofthe(ossesoccuri,,edi%te(-#he!theforceis
tr%!sferredtotheco!crete.e*'e(%sticshorte!i!'ofthe,e,"er*
/ther(ossesoccur#ithti,e.e*'*creepoftheco!crete*0he$%c&i!'
force does !ot e1ceed 902 of the ch%r%cteristic stre!'th of the
te!do! %!d is 'e!er%((- !ot (ess th%! 352 4c( 5*10*342).E52)* 6!
pr%ctice tot%(
(ossesofthe$%c&i!'force%re#ithi!ther%!'eof152-702*6f(%r'e
(ossesofpre-stressoccurthe!the%d)%!t%'esofpre-stressed
co!crete.e*'*!ocr%c&s%tser)ice(o%d.%re(ost*6tistherefore
%d)%!t%'eous to ,i!i,i8e the (oss of
pre-stress*perce!t(ossofpre-stress9100:4$%c&i!'stress-;!%(stress)/4$%c&i!'
stress)8/13/15Prepared by: Eng. Chamil Duminda MahagamageB.Sc.Eng
(Hons), C Eng, ME(S!)2n"erna"ional College o# Business and
$echnology6102BEUG- Lecture Note: 09 Factors afect to loss of
pre-stress%ela&a"ion o# "he s"eel ('(') *)Shrin+age o# "he
concre"e('(, *)Creep o# "he concre"e(-('- *)Dra. in during
anchorage(/(- *)0ric"ion in "he duc"s and a" anchorage(1(2
*)Elas"ic de#orma"ion o# "he concre"e('('/
*)Note-:6!iti%((-.i!desi'!c%(cu(%tio!s.the(ossofpre-stressis
esti,%ted fro, p%st e1perie!ce %!d (%ter. #he! the sectio! sh%pe
%!d si8eh%s"ee!deter,i!ed.%,ore%ccur%tec%(cu(%tio!is,%de*<
re%so!%"(-%ccur%teesti,%tio!ofthe(ossofpre-stressisre=uired "ec%use
it %ects ser)ice (o%d co!ditio!s* %)* >e(%1%tio! of stee( 4c(*
5*10*7. c(* 3*3*2 %!d
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