Service Life Design for Sustainable Infrastructures - Durability Design of Concrete Structures in Present Japan and Future -

Transcription

1 Serve Lfe Desgn for Sustanable Infrastrutures - Durablty Desgn of Conrete Strutures n Present Jaan an Future - UEDA Tamon Hoao Unversty ABSTRACT: Ths aer ntroues the urablty esgn n Stanar Sefaton of Conrete Strutures ssue by Jaan Soety of Cvl Engneers (JSCE) whh s onsere the most avane methoology n Jaan. The man feature of the urablty esgn s to rove arorate verfaton methos for reventng any egraaton of strutural erformane ue to eteroraton fators urng serve lfe. The Stanar Sefaton roves the verfaton methos for hlore on enetraton, arbonaton, freeze-thaw, alal-sla reaton an hemal atta. Ths urablty esgn s aote n other esgn oes suh as JSCE s Guelnes for Performane-Base Desgn of Steel-Conrete Hybr Strutures an Desgn Coe for Ralway Conrete Strutures. The latter half of ths aer outlnes the exete reton of the urablty esgn n Jaan an neessary researh to mrove the resent urablty esgn. More avane urablty esgn s to show how to ret hronologal hanges (or egraaton) of strutural erformane. Most of the requre erformane s relate to mehanal roertes of strutures an members, suh as strength, stffness, eformablty, an rang. Thus, the reton of strutural erformane shoul be base on the materal roertes n amage onrete strutures. The mehanal roertes of onrete member amage by ngress of hlore on an yl freeze-thaw are resente as an examle. Keywors: Durablty esgn, Performane-base onet, Chronologal hange n strutural erformane 1

2 INTRODUCTION Durablty s a rmary ssue for any struture n the 21 st entury. Construtng a urable struture woul onserve resoures an energy rovng an envronmentally frenly soluton. Jaan s a leang ountry to ntroue urablty esgn n a ratal strutural esgn. Ths aer ntroues urablty esgn n the latest JSCE s Stanar Sefaton [1], where verfaton formula to mae strutures urable are rove for the frst tme n Jaan. Sne the resent methoology for the urablty esgn s not n a fnal form, ths aer ntroues researh reton to mrove the urablty esgn. JSCE STANDARD SPECIFICATIONS FOR CONCRETE STRUCTURES Jaan Soety of Cvl Engneers has been ublshng Stanar Sefatons for Conrete Strutures for more than 70 years. These sefatons serve as a moel oe for vl engneerng strutures n Jaan. The latest verson of the Stanar Sefatons ublshe n 2001/2002 onssts of the followng 7 arts [1]: Strutural Performane Verfaton Sesm Performane Verfaton Materals an Construton Mantenane Dam Conrete Pavng Test Methos an Sefatons The Stanar Sefatons are reare wth the erformane-base onet. Ths onet sefes erformane requrements; Safety Serveablty Envronmental aatablty (nlung aesthets) Restorablty (or rearablty) Construtablty Mantanablty Eonomy Reommene methos for verfaton, whh are base on lmt state esgn methoology, are rove for verfaton of safety, serveablty, restorablty an onstrutablty. Restorablty s the ablty to assure tehnologally an eonomally feasble restoraton by lmtng amages n a struture, whh s at resent only ale to Sesm Performane Verfaton. Durablty s not lste among the erformane requrements. Ths, however, oes not mean that the Stanar Sefatons gnore urablty. The Stanar Sefatons onser that urablty s the ablty to assure that all the erformane requrements are satsfe urng esgn serve lfe. Durablty Desgn 2

3 All the rovsons relate to urablty esgn aear n the Materals an Construton Part at resent. Sne egraaton of strutural erformane ue to envronmental atons an mehanal loangs suh as fatgue s a man roblem for nfrastrutures, the urablty ssue has beome mortant. It s, therefore, vtal to ret hronologal hanges, whh s usually egraaton, n strutural erformane urng serve lfe. If the rete strutural erformane satsfes all the erformane requrements even after the hronologal hanges, the urablty s assure (see Fg.1 (a)). In Fg.1 (a) R s strutural erformane showng a hronologal hange suh as member strength whle S s requre erformane suh as maxmum setonal fore. R s always greater than S urng the serve lfe, meanng that the erformane requrement suh as safety s satsfe. In other wor the verfaton of erformane requrements shoul be onute wth onseraton of hronologal hanges n strutural erformane. In the urrent Stanar Sefatons to assure urable strutures s to rove verfaton methos for reventon of the strutures from beng subjete to egraaton of ther strutural erformane exet for egraaton ue to fatgue (see Fg.1 (b)). Fgure (b) shows that R s greater than S at the ntal stage an oes not egrae urng the serve lfe, meanng that the erformane requrement s satsfe. The reason for aotng ths onet s that the urrent tehnologal level s goo enough to rove reventon measures for strutural egraaton but not to ret egraaton of strutural erformane. Beses the erformane verfaton an be smlfe wth ths onet beause the hronologal hanges n strutural erformane s not neessary to be onsere. PERFORMANCE INDEX PI R S t l (serve lfe) t PI R S t l (serve lfe) TIME (a) (b) Fgure 1 Conet of urablty esgn n urrent JSCE Stanar Sefatons The urablty verfaton methos are rove for arbonaton, ngress of hlore ons, yl freezng an thawng, hemal atta an alal aggregate reaton. The verfaton 3

4 methos for arbonaton, ngress of hlore ons an yl freezng an thawng are gven n quanttatve ways wth verfaton formula. Verfaton for arbonaton Lmt state for arbonaton s ntaton of orroson of steel renforement. Carbonaton eth, y s use as the nex for verfaton. The verfaton formula s as follows: y γ 1.0 (1) y lm s a safety fator to reresent the mortane of the struture. The lmt for arbonaton eth, s y lm y lm = y t (2) = γ b α where s over eth an s remanng non-arbonate thness, whh may be taen to be 10 mm for a normal envronment an 10 to 25 mm for hlore rh envronments. On the other han, the esgn value for arbonaton eth s alulate by the followng formula, whh s base on the square-root law: y = γ α t (3) b b s a safety fator to aount for the varaton n the esgn value of arbonaton eth, t s the esgn serve lfe, an α s the esgn value of arbonaton see oeffent, whh an be alulate as follows: α = γ β α (4) e s a safety fator to aount for a fferene n onrete roerty between that at the atual ste an at laboratory, β e s a oeffent to reresent the effets of envronment an may be taen to be 1.6 for a art of a struture fang north. α s the haraterst value of arbonaton-see oeffent, whh s set an assure by the followng formula: α γ 1.0 (5) α s a safety fator to aount for the auray n etermnng α, an α s an estmate value of oeffent reresentng rate of arbonaton (mm/ may be obtane from Eq. (6). year ) an normally α = a + b W B (6) 4

5 where a an b are onstants base on the roertes of the ement an other materals use, whh shoul be etermne usng the real ata obtane from exerments, an W B s effetve water- bner rato. a = 3.57 an b = 9. 0 are shown as test results for 17 fferent onrete mxes. Verfaton for ngress of hlore ons The lmt state for ngress of hlore ons s also an ntaton of orroson n steel renforement. The nex use for esrbng the lmt state s the hlore on onentraton at steel renforement. The verfaton formula s as follows: C γ 1.0 (7) C lm s a safety fator to reresent the mortane of the struture. The lmt value for hlore onentraton C lm may be normally taen as 1.2 g/mm 3. The esgn value of hlore on onentraton C at eth of steel renforement may be alulate by the followng equaton: C 0.1 = γ l C0 1 erf (8) 2 D t l s a safety fator to aount for varaton n the esgn value of hlore on onentraton, C 0 s hlore on onentraton at onrete surfae (g/m 3 ), whh may be taen from Table 1, s onrete over (m), t s the esgn serve lfe (year) an erf ( s) s an error funton gven by the followng equaton: erf 2 s () s = e π η 2 η (9) Table 1 Chlore on onentraton at onrete surfae (g/m 3 ) DISTANCE FROM COASTAL LINE (m) Tal slash zone Near oastal lne The esgn value of ffuson oeffent for hlore on D may be alulate by the followng equaton: D 2 w w = γ D + D0 l w (10) a 5

6 s a safety fator to tae aount of the fferene n the qualty of onrete n the atual struture an the ure semen n the laboratory, w s the alulate esgn ra wth, w l s the rato of ra wth to ra sang, w s the allowable ra wth sefe n the Stanar Sefatons, D s a onstant to exress nfluene of ra for 0 hlore on movement n onrete an may be taen to be 200 m 2 /year, an D s the haraterst value of ffuson oeffent for hlore on, whh s set an assure by the followng formula: a D γ 1.0 (11) D s a safety fator to tae aount of nauray of etermnng D, whh s an estmate ffuson oeffent of onrete, by the followng equaton: 2 ( W C) + b ( W C) log D = a + (12) where W C s water ement (bner) rato, an a, b an are onstants base on the roertes of the ement an other materals use, whh shoul be etermne usng the real ata obtane from exerments. As an examle, a = 3.9, b = 7. 2 an = 2.5 are gven for normal Portlan ement. Verfaton for yl freezng an thawng The lmt state of verfaton for yl freezng an thawng s the ntaton of mehanal amage suh as strength an stffness reuton n onrete. Sne there s no ommonly aete nowlege on the mehanal amage n onrete ue to yl freezng an thawng, the relatve ynam moulus of elastty s hosen as an nex for the verfaton. The verfaton formula s as follows: Emn γ 1.0 (13) E s a safety fator to aount for the mortane of the struture, E mn s the mnmum relatve ynam moulus of elastty to revent an mar of the strutural erformane ue to yl freezng an thawng (shown n Table 2). The esgn value of relatve ynam moulus of elastty E s E = γ (14) E s a safety fator to tae nto aount the fferene n the qualty of onrete n the struture (n-stu) an that of laboratory ure semen, an E s the haraterst value of relatve ynam moulus of elastty, whose value s hosen arorately. The followng formula s rove to aheve the hosen value n the onrete. 6

7 E γ 1.0 (15) E s a safety fator to tae nto aount an nauray n etermnng the estmate value of relatve ynam moulus of elastty whh may be obtane from the stanar freeze-thaw test metho (JIS A 1148 A metho the freeze-thaw test metho of onrete ) for usual ases. E Table 2 Mnmum level (erentage of ntal level) of relatve ynam moulus of elastty Exosure of struture Clmate Frequently severe an yl freezng an thawng Moerately severe wth atmosher temerature rarely rong below 0 C Seton Thn General Thn General (1) Submerge n water or often saturate wth water (2) Not overe n (1) above an normal exosure EXPECTED DIRECTIONS FOR DURABILITY DESIGN IN JAPAN As esrbe at the begnnng of the revous hater, the most general aroah for strutural esgn wth erformane-base onet s to verfy that all erformane requrements are satsfe urng the esgn serve lfe tang nto aount hronologal hanges n strutural erformane. It s therefore neessary to evelo methos to ret hronologal hanges n strutural erformane ause by varous eteroraton fators -- both envronmental atons an mehanal loangs. Chronologal hanges ue to orroson of steel renforement, yl freezng an thawng an ther ombne effets are shown as examles. Preton of Chronologal Changes n Strutural Performane Chronologal hange ue to orroson of steel renforement The Stanar Sefatons of JSCE roves the verfaton metho to assure that there woul be no orroson ntaton n steel renforement urng serve lfe. In other wors we an ret when the orroson starts. After orroson starts egraaton of strutural erformane begns. The orroson of renforng bar surfae eterorates ts bon roerty. The orroson also auses an exanson of the renforng bar volume resultng n rang n an sallng-off of the over onrete. Severe orroson reues the remanng strength of the renforng bar. Crang may mar serveablty whle the reue renforng bar strength may mar safety. 7

8 Beses stues on reton of arbonaton rate an hlore on onentraton, the followng stues are gong on n Jaan n orer to ret the egraaton of strutural erformane: (1) To nvestgate bon stress sl relatonsh of renforng bar after orroson onserng bon egraaton ue to the orroson of renforng bar surfae an slttng ra n over onrete (2) To nvestgate mehanal roerty of member wth egrang bon (3) To nvestgate ra ntaton an roagaton n over onrete ue to orroson (4) To nvestgate mehanal roerty of member wth slttng ra n over onrete (5) To nvestgate stffness/strength reuton n renforng bar ue to orroson (6) To nvestgate mehanal roerty of member wth reue stffness/strength n renforng bar Examles of the stues an be foun n referenes [2][3]. Chronologal hanges ue to yl freezng an thawng It s beleve that frost amage n onrete auses not only rang but also egraaton n mehanal roertes of onrete. However there are only few stues on the mehanal egraaton. JSCE s Stanar Sefatons, therefore, roves the verfaton metho n whh relatve ynam moulus of elastty s use as an nex. Serveablty may be affete by the rang, whle safety by the reue strength. On-gong stues n Jaan to ret the mehanal roertes of member wth frostamage onrete are as follows: (1) To nvestgate mehansm of frost amage (2) To nvestgate stress stran relatonsh of onrete wth frost amage (3) To nvestgate bon stress sl relatonsh of onrete wth frost amage (4) To nvestgate mehanal roerty of member wth frost-amage onrete (5) To nvestgate relatonsh between frost amage n atual struture an semen n laboratory Examles of the stues an be foun n referenes [4][5]. Chronologal hanges ue to ombne effets of renforement orroson an frost amage It s nown that there are ombne effets of ngress of hlore on an yl freezng an thawng. The onsere frost amage mehansms uner the effets of hlore on ngress are () nrease enetraton ressure of water ontanng hlore ue to a fferene n hlore on onentraton between large an small ores n the former of whh e s forme, () resene of unfrozen layer whh reates ressure ue to volume nrease urng freezng, ausng salng effets n surfae layer whh s loate outse of the unfrozen layer (the unfrozen layer s reate by a ombnaton of lowere freezng ont ue to hlore on ontent an temerature graent eenng on the stane from onrete surfae), an () suen erease n temerature of surfae onrete ue to heat absorton whle hlore soum s ssolve nto water [6]. Frost amage ausng small ras n onrete s beleve to nrease ffuson oeffent of hlore on (see Fg. 2 (a)) an erease slt rang strength ue to renforng bar orroson (see Fg.2 (b)). 8

9 Cl - H 2 O Damage (mro ras) Imermeablty an mro ras (amages) (a) Maro rang n amage onrete Crang n frost-amage onrete ue to orroson (b) Fgure 2 Coule effets on onrete egraaton by ngress of hlore on an yl freezng an thawng On-gong stues n Jaan are as follows: (1) To nvestgate frost amage uner effets of ngress of hlore ons rove by sea water an e-er (2) To nvestgate hlore on ffuson through frost-amage onrete (3) To nvestgate over onrete rang ue to renforng bar orroson uner effets of frost amage CONCLUSIONS Stanar Sefatons for Conrete Strutures ssue by Jaan Soety of Cvl Engneers ntroues the latest urablty esgn onet where erformane requrements are verfe urng esgn serve lfe wth onseraton of hronologal hanges (egraaton) n the strutural erformane. The Stanar Sefatons at resent, however, rove only the verfaton metho to assure that there woul be no egraaton urng the serve lfe beause of ffulty to ret egraaton aurately. There are varous stues gong on n Jaan to mrove the resent urablty esgn by larfyng eteroraton mehansm, onsttutve moels of egrae materals an mehanal behavor of members wth materal egraaton. REFERENCES 9

10 1. CONCRETE COMMITTEE. Stanar Sefatons for Conrete Strutures (Englsh Verson): Strutural Performane Verfaton, Sesm Performane Verfaton, Materals an Construton, Mantenane, Jaan Soety of Cvl Engneers, 2004 an KAMEYA, H, SATO, Y, UEDA, T an KAKUTA, Y. Analytal Preton of Cover Crang ue to Corroson of Renforement, Transatons of Jaan Conrete Insttute, Vol.18, 1997, TOONGOENTHONG, K an MAEKAWA, K. Interaton of Pre-Inue Damages along Man Renforement an Dagonal Shear n RC Members, Journal of Avane Conrete Tehnology, Jaan Conrete Insttute, Vol.2, No.3, MIHASHI H., ZHOU, Z Y an TADA, S. Mro Mehans Moel to Desrbe Freezng Inue Stran Behavor of Conrete, Proeengs of the Internatonal Worsho on Mrostruture an Durablty to Pret Serve Lfe of Conrete Strutures, Hoao Unversty, Saoro, 2004, HASAN, M, OKUYAMA, H, SATO, Y an UEDA, T. Stress-Stran Moel of Conrete Damage by Freezng an Thawng Cyles, Journal of Avane Conrete Tehnology, Jaan Conrete Insttute, Vol.2, No.1, 2004, MATERIAL SECTION. Why Does Chlore Soluton Aelerate Frost Damage n Conrete?, Monthly Reort of Cvl Engneerng Researh Insttute of Hoao Develoment Bureau, 2001, (n Jaanese). 10