9. Prestress Materials

8/19/2019 9. Prestress Materials

1/24

REINFORCED CONCRETE ELEMENT II

INTRODUCTION TO PRESTRESSED CONCRETEPre-stressed Materials

M LUTFI MANFALUTHY


2/24

OBJECTIVES2

Upon completion of this topic, student will be able to:

• Distinguish the differences between reinforcing steel and pre-stressing steel.

• Distinguish the shapes of pre-stressing tendons.

• Recognize mostly used stand types.

• Understand the effect of relaxation, temperature, fatigue, an corrosion

to pre-stressing steel.• Understand the composition of concrete used in pre-stressed

concrete.

• Recognize stress-strain diagram of concrete.

• Understand the most useful mechanical properties of concrete f!c,

f!tc, fr, "c, n#• Understand the effect of creep, $hrin%age, fatigue, temperature,

• and steam curing to pre-stressed concrete.


3/24


4/24

PRE-STRESSING MATERIALS4

aterial used in pre-stressed concrete are:

• &re-stressing steel• oncrete• uxiliary

nchorage *endon ducting

ement grout


5/24

PRESTRESSING STEEL5

As prestressed looses in the steel (not inclde !riction" c#n o!ten

#ppro#ch $%%MP#& th#t is #'ot e#l to the t)pic#l )ieldstren*th o! o! co++on rein!orcin* '#rs& it is cle#r th#t +ini++tensile stren*th o! prestressed steel +st 'e hi*er th#n this,#le-

Ide#ll) # tendon +#teri#l shold not onl) h#,e hi*h stren*th 't

#lso.• re+#in el#stic pto rel#ti,el) hi*h stress

• sho/ s0cient dctilit) 'e!ore !#ilre

• h#,e *ood 'ondin* properties& lo/ rel#1#tion& *ood

resist#nce to• !#ti*e #nd corrosion

• 'e econo+ic#l #nd e#s) to h#ndle


6/24

Type of pre-!re"#$ !e#%o#&'

Cortes) o! S+ito+o2s Tensionin* M#teri#ls& 3#p#n


7/24

Type of pre-!re"#$ !e#%o#&(


8/24

Me)*+#")+, +#% S!re-S!r+"# proper!"e

Mini++ Properties o! pre4stressin* tendon-


9/24

S!re-!r+"# %"+$r+. of pre-!ree"#$ !ee,/

Fro+ 5*re& prestressin*steel.• O6er s'st#nti#ll) hi*her

stren*th th#n rein!orcin*steel #cco+p#nied ')

lo/er !#ilre str#in-• Do not sho/ /ell de5ned

)ieldin* 'eh#,ior-• H#,e rel#ti,el) hi*h

proportion#l li+its-


10/24

S!ee, Re,+0+!"o#1

Relaxation is the loss of tension o)er time in a stressed tendon maintained at

constant length and temperature. *he relaxation is negligible for stress smaller

than /0 percent of ultimate strength. *emperature increase also caused significant

effect on loss of stress in prestressing steel.(*$ $urabaya# Reinforced oncrete ((


11/24


12/24

S N Cre +#% S."!* D"+$r+.12


13/24

CORROSION13

*he magnitude and conse'uences of corrosion in prestressing

steel are mush more se)ere than in reinforcing steel. *his is notonly high-grade steel is more susceptible to corrosion but also

because the diameter of prestressing tendon is relati)ely small.

*hus e)en small corroded spot substantially reduce the cross-

sectional area of steel.

&restessing steel are generally susceptible to two ma6or types of corrosion:• "lectro chemical corrosion.

an a'ueous solution must be present, e)en in the form of thin

film, and air oxygen# is needed.

• $tress corrosioncauses brittleness in the steel under certain conditions of stress

and en)ironment.

*o guard against corrosion, prestressing steel must be transported

and stored in closed waterproof container.


14/24

CONCRETE14

oncrete is a )ersatile composite material of a )ery complex nature, yet

it can be approached at any desired le)el of sophistication.

*he technical le)el at which concrete must be approach is higher in

prestressed concrete than in reinforced concrete. (n designing

prestressed concrete, the designer does not only consider the strength

of concrete but also its time-dependent properties such as creep and

shrin%age.


15/24

CONCRETE STRESS STRAIN CURVE15

• 7eft figure shows stress strain diagram

of concrete, first part is ascending

portion up to the pea% point maximum

stress# and descending portion, the

strength, f8c , corresponds to the

maximum stress.

• (t can be obser)ed that the higher the

concrete strength, the steeper the

descending portion of the stress-strain

cur)e. steep descending portion is

often associated with brittleness or lac%of ductility of material.


16/24

De!er."#+!"o# of Mo%, fro. S!re-S!r+"# D"+$r+.1'

Fro+ stress4str#in di#*r#+ SNI7ACI se el#sticit) (Ec" ,#le t#8en thet#n*ent o! line !ro+ ori*in to point %-$9!2c(ITS Sr#'#)#" Rein!orced Concrete II


17/24

ELASTICIT6 FROM SEVERAL CODES1(


18/24

CONCRETE S7RIN8AGE1

• Concrete cont#ined +ore/#ter th#n is strictl)reired ') che+ic#lre#ction o! ce+ent- Thee1cess /#ter c#lled !ree/#ter& its loss thro*h

e,#por#tion le#ds to*r#d#l shortenin* o!+e+'er /ith ti+e&descri'ed #s shrinkage-

• As the +e+'er shortens&

the prestressin* steel losesp#rt o! its prestress& this isc#lled shrinkage loss-


19/24

CONCRETE CREEP1/

• Creep is ti+e dependent str#in ine1cess o! el#stic str#in indced in+#teri#l s':ected to # sst#inedstress-

• Unli8e shrin8#*e& creep is c#sed

') lo#din*- I! the lo#d is re+o,ed&the initi#l el#stic str#in is reco,eredi++edi#tel)- A p#rt o! the creepstr#in is *r#d#ll) reco,ered o,erti+e #nd re+#inin* p#rt is non4reco,er#'le-

• E6ect o! #*e #t lo#din* isrepresented on le!t 5*re- One tonoted th#t e#rlier the prestressin*lo#d& hi*her the loss o!prestressin*-


20/24

DISPLACEMENT CAUSED B6 CREEP2

• As pointed ot e#rlier& thecreep o! concrete le#ds notonl) losses o! stress in theprestressin* steel& 't #lsoto lon* ter+ de!or+#tion orde;ection o! the strctre-

This illstr#ted in le!t 5*re-• Note th#t the de;ection

cr,e !or const#nt lo#d is,er) si+il#r in sh#pe to thecr,e o! creep str#in nderconst#nt lo#d-

• For #ct#l condition in the5eld /here continos,#ri#tion in te+per#tre #ndh+idit)& /ill le#d to;ct#tin* cr,es /ith +ch

less de5ned li+itin* ,#les-


21/24

CONCRETE FATIGUE21

It is *ener#ll) o'ser,ed th#t concrete in direct co+pression c#n

sst#in # ;ct#tin* stress 'et/een o to 9% percent o! its st#ticco+pressi,e stren*th !or #t le#st


22/24

EFFECT OF TEMPERATURE ON CONCRETE22

Concrete he#ted p to =%%C does not nder*o si*ni5c#ntph)sic#l or che+ic#l ch#n*es- It *ener#ll) loses its !ree /#ter#t


23/24

REMAR8S23

• The +#teri#l properties s++#ri@ed here #re essenti#lele+ents to the !ll nderst#ndin* o! restressed concrete'eh#,ior- The) help to cl#ri!) the '#sic !or +#n) desi*nprocedres tre#ted l#ter-

• Not #ll the properties #re o! i++edi#te se in desi*n-Ho/e,er& the +ore 5n#l the desi*n& #nd the +ore co+ple1

the strctre& the *re#ter is the need to #ccont in desi*n !orthe #ct#l 'eh#,ior o! the +#teri#ls #nd their inter#ction-

• Prestress losses depend not onl) on +#teri#l properties 't#lso on strctr#l 'eh#,ior #nd en,iron+ent#l condition- Atthis point& their i++edi#te #nd thoro*h tre#t+ent +#)

con!se /ho ne/l) #c#inted /ith prestressed concrete-


24/24

Re"#for)e% Co#)re!e E,e.e#! II

THAN YOU

Documents

9. Prestress Materials