Pull-Out Strength of a Cast-In-Place Anchor Bolt in Concrete Exposed to High Temperature

Transcription

1 Pull-Out Strength f a Cast-In-Place Anchr Blt n Cncrete Expsed t Hgh Temperature Katsuk Takguch, Jun Hashmt Tky Insttute f Technlgy, Japan. ABSTRACT! Many anchr blts are used n nuclear-related facltes n rder t fast sme equpments and ppes. Abut these anchr blts, the pssbltes shuld exst n beng expsed t hgh temperature due t accdent. Hwever, lttle nfrmatn s avalable regardng the effects f hgh temperatures n the behavr f anchr blts. T btan basc expermental data and t examne the respnse f cast-n-place anchr blts t hgh temperature expsure, pull-ut strength f an anchr blt durng heatng and after heatng was examned. The maxmum temperature n ths test s 5 C. Tests results shw that the pull-ut strength under hgh temperature up t 5 C decrease sgnfcantly. Based n these results, a lnear relatnshp between pull-ut strength and temperature s emprcally frmulated. 1. INTRODUCTION Sme recent research n hgh temperature behavr f cncrete shws that ts strength wll decrease wth further ncrease f temperature and ther mechancal prpertes als get wrse, due t dryng shrnkage, thermal stress and s n. 1) It s als reprted that the spallng happens n the surface f cncrete subjected t elevated temperature. 2) In nuclear facltes, many anchr blts are embedded n cncrete structures n rder t supprt equpments and ppes. There s pssblty that these anchr blts wll be expsed t hgh temperature n a shrt tme by sme accdent, and that the pull-ut strength wll decrease. Hwever, lttle nfrmatn s avalable regardng the effects f hgh temperatures n the behavr f anchr blts. Therefre, they are usually desgned wthut cnsderatn fr hgh temperature effects. In ths research, pull-ut tests f cast-n-place anchr blt were carred ut at dfferent temperatures up t 5 C. The bjectves are t btan basc expermental data and t examne the respnse f cast-n-place anchr blts t hgh temperature expsure. At present, there are frmulas t determne pull-ut strength f a cast-n-place anchr blt. ACI 3) prpses the frmula as fllws; P = 1.1~~ A~ (1) A~ = z~h (h + d) (2) Where, P" pull-ut strength (kg), qb :reductn factr, cmpressve strength f cncrete (kg/cm2), Ac: effectve area f cne faled surface (cm2), h: embedment depth (cm) and D" dameter f a stud (cm). In "Desgn Recmmendatn fr Cmpste Cnstructn ''4) publshed by the Archtectural Insttute f Japan s gven as fllws; P = A~~ (3) Anther frmula prpsed by R. Elgenhausen 5), P = kx/ ~ x h 1"5 (4) where, k s the emprcal ceffcent (=15.7kg/cm).

2 2. EXPERIMENT 2.1 SPECIMEN In all, twenty-three specmens wee prepared. The dmensns and detals f the specmens are llustrated n Fg.1. All f specmens are square cncrete blcks wth a sde length f 24mm cnsderng the cne faled area, and wth a depth f 12mm. An anchr blt used n ths study s JIS standardzed M12-blt wth a nmnal length f 8mm, and wth a thread length f 3 mm as shwn n Fg.2. In rder t prevent tensn falure, a headed stud blt wasembedded at the center f the tp surface f all the specmens, and the embedment depth frm the tp surface f the cncrete t the upper surface f the blt head s 3mm as shwn n Fg.3. Fur square nuts and steal ppes were nstalled t be fxed wth the testng apparatus. Only fve specmens equpped wth therm-cuples t measure the temperatures f the cncrete and the blt nsde the specmen durng heatng. Tw therm-cuples are t measure the temperatures f anchr blt and the thers are t measure the temperature f cncrete. (See Fg.l) Ordnary nrmal cncrete was used wth desgn cmpressve strength f 35kg/cm 2. Sx hurs after castng f cncrete, the specmens were cured by cverng wet sand. Ths curng sand remved n the day f testng. The ages f the cncrete at the test were 48~94days. The results f cmpressve and splt tests f cncrete cylnder durng the testng days are shwn n Fg.4. The average f cmpressve and splttng tensle strength f the cncrete cylnder at the testng was 479kgf/cm 2 and 35kgf/cm 2, respectvely I M b~ b~!,~;;'~,, ~ J 5 [ Fg.2 Detal f Anchr blt II 1.2[ tt3 "e-',-: f 3 -r "-, L,~ _'- -~r~,,,,,,,, ',', I',,,,,.... ~ Steel Ppe I ~ ~ Cncrete Temperature measurement pnts Fg.1 Detal f specmen Fg.3 Detal f embedment

3 6 5 -~ Cmpressve strength I " 8 rq [ O Splttng tensle strength "--@- % 6 4 "~ 2 Dameter and heght f cylnder: 1cm ~ 2cm (fr cmpressve strength test) 1cm ~ 1cm (fr splttng tensle strength test) I J, I 48days 49days 59days 68days 77days 94days Fg.4 Results f cmpressve and splt test fcncrete cylnder 2.2 PULL-OUT TESTING AND HEATING METHOD The apparatus fr pull-ut test s llustrated n Fg.5. The specmen was fxed t the testng apparatus wth fur blts as shwn n Fg.6, then ts anchr blt was cnnected t the end f the ladng beam. T examne the rat f frces f these fur blts durng the pull-ut test, the stran gauges were fxed n each f blt. (See Fg.7) Ths measurement was carred ut n fur specmens. Fg.8 shws the detal f cnnectn f the ladng beam and anchr blt. At frst, anchr blt was cnnected wth treaded steel bar by usng cupler. Then, ths treaded steel bar was cnnected t ladng beam. The tensle lad s appled t an anchr blt by applyng lads t the ther end f ladng beam. Here, the tensle lad frm the ladng beam was prevusly measured. The detal f heatng the specmen s llustrated n Fg.9. T mprve thermal effcency, the nsulatrs were nstalled arund the specmen and the heaters. One sde f specmen wth anchr blt was heated by ht ar by ncreasng ts temperature usng the electrc heater wth Nchrme wres. Abve the specmen, a therm-cuple was emplyed t measure the ar temperature near the heatng surface f specmen. (See Fg.1) Ths temperature was cntrlled wth the prcesses f heatng as shwn n Fg.11. Unless the specmens fracture at earler stage, each temperature (15 C, 3 C, 5 C) was kept cnstant fr tw hurs. Hwever, the ntal temperature ncrease depends n the perfrmance f the heaters and was nt cntrlled. Insulatr ~ ' I-Inge Ladng Beam / I 14!! t Fg.5 Apparatus fr the pull ut test

4 ' A ~Cncrete '. [ ":~:~,,' P" :~.. ~?);~ ~j~/~f"'k..embedded Square Nut Steel ppe ~ I ~ ". A [ Blt.1_.- f7 I~ III ~~" Insulatr ~\\\\\\\"~ I~\\\\\~ Washer Steel Beam I n' I t _J ~/ ~ ~ A-A' '- Sectl )n... "-~:" Steel Plate _fl~~~fl,..-,, Pn.. ',.. Bearng upler I~.JlTreaded Steel Bar Fg.6 Detal f methd t fx specmen t apparatus Fg.7 Detal f blt wth stran gauge I I Fg.8 Detal f cnnectn f ladng beam and anchr blt Heater, Steel Plate v /AA,////////)/'//I~'; I';~l~H~'~' ";'~nsul r Therm-cuple I /~[2. ~1" Insulatr~. _, ~.-,,, g//z,~ ~, ~';.:,~ ~ c~ r///a.%... %.-.. ~:2.,~, ~ / f.,-.. I'///Am ~.;x;: -'~ z:2 zx :;.,.:;: ~ / Therrr,,pe IV//,I ~! ~\ ~! cj /... x r///j//////////////, / Blt Fg.9 Methd f heatng [ II 'p ~ [~ Cncrete_. Fg.1 Detal f therm-cuple t measure ar temperature 6 [ 5 C (I) 5 C (II) _ ] 5 r-, ,t... "... "a~/ t 4 / (Endm~f / heatng) (End f heatng) I e / 3c 3... / ~:~ I ~ h e a t n g ) OOlt... I 1 ~ (End f heatng) ] Or., I / Tme(hr.).. Fg.ll Prcess f heatng

5 2.3 SUMMARY OF EXPERIMENT In ths expermental nvestgatn, twenty-three specmens, as shwn n Table 1, were tested. These specmens were dvded nt three man seres. In seres N.l, pull-ut strength under nrmal temperature was examned. T examne the effect f hgh temperature n pull-ut strength, ffteen specmens were tested n seres N.2. The specmens are heated whle applyng cnstant tensle lad n the anchr blt. The tensle lad was decded based n the pull-ut strength under nrmal temperature, that s the results f seres N.l, and the results f specmens tested earler n the same seres. Fve specmens were tested n seres N.3 t study temperature transent nsde the specmens. Abut N.3-a, the effect f successn f heatng n cncrete was examned by heatng fur tmes up t 3 C. Fr the specmens f seres N.2 that dd nt fal durng heatng and the specmens f seres N.3, pull-ut test was carred ut after ther temperatures g dwn t nrmal temperature. Here, the specmen was cled wth r wthut nsulatrs, and the effect f dfference f prcess f clng n pull-ut strength was examned. Table 1 Lst f specmens Name f specmen N.l-a Tesle lad (P) Prcess f heatng Pull ut test under nrmal temperature,n.2-a 1.31 t (.7P) '~1 3c d'~2.935 t (.5P) 3 C 5 c( I ) N.3-a j.56 t (.3P) 5 C( I ) k.29 t 5 C( I ) 1.42 t (.23P) 5 C( I ) m.8 t 5 C( II ) n.7t 5 C ( II ) 1.31 t (.7P) 15 C 3 C (4tmes) 3 C (2tmes) (wth and wthut nsulatrs) c 5 c( I ) d 5 C ( II ) e 15 C ~ 1 P : Average f pull-ut strength f nrmal temperature ~2 Abut nly N.2-d, the prcess f heatng was changed n testng, and the lad was als changed durng heatng.

6 3. EXPERIMANTAL RESULT 3.1 THE RATIO OF STRAIN OF BOLTS Fg.12 ndcates the relatn f the'rat f stran f fur blts used t fx the specmen t the testng apparatus and the lad appled t an anchr bblt. It can be bserved frm ths fgure that, even thugh the lad appled t anchr blt was ncreased, the rat f stran f fur blts was cnstant durng pull-ut testng. The measured rat f stran f blts f fur specmens s als shwn n Fg.12. Frm ths fgure, t can be seen that, as t tw specmens, the lad appled the anchr blt was evenly dstrbuted t the fur blts. On the ther hand, the lad was unevenly dstrbuted as t the thers, and the mnmum stran was 7% f the maxmum stran ~ ll--i------ll- -ll--- ll--u-'-ll'---i--lll-- ~l--ii-- -II --II ~. - n- --I!--. ll- -ll.9 "~.8 ~.7 Q ~ ::...:: ~l, ,- -~ - -~ , 4, --4~ ~ !...!...!... ::. :.4 I Lad appled t anchr blt Fg.12 Rat f strans f fur blts 3.2 RESULTS OF PULL-OUT TESTS Fg.13 shws the hstry f the temperature and the lad f the specmens f seres N.2. In ths fgure, the temperature shws the value by the therm-cuple abve the specmen t be measured the ar temperature near the heatng surface f specmen. The specmens N.2-e,f and the specmen N.2-g were cled wthut and wth the nsulatr, but the effect f dfference clng n the pull-ut strength f them was nt seen. Cmparng the results f the specmenn.2-k and N.2-n, the temperatures nsde these specmens at the end f heatng and the pull-ut strength f them were almst the same. Therefre, the effect f the dfference f prcess f heatng between 5 C( I ) and 5 C( ]I ) n the pull-ut strength was nt als seen. The specmen N.2-d dd nt fracture under.935t f the tensle lad even when the ar temperature reached 5 C. Hwever, the specmen N.2-h and fractured under the same tensle lad when the ar temperature reached abut 4 C. Fg.14~17 shw the results f temperature measurement f the specmens n seres N.3. Frm Fg.14, whch ndcates measured temperature transent f the specmen N.3-c, t can be bserved that there s lttle dfference amng the

7 ' 6. '. '., 1 "" ~N~*~~, 3524 f ~ rature I "... ' '~ ::., "lrme(hr.~ : ~ I--..,.,,.,~.l ~ 2 " <N.2-a> 6 ~.... : :. 5 ~Hstry f temperature /......:~~~ ".". 'Tm~hr'.'' ' 3.5 3!. ':!,~, "~ ~ "'' ~.. X ~ : ', <N.2-d> ~6 ~:~'5!~Hstryftemperature[... '," "'... ~ 4... ;--. '....,~ 3 ~!~ 1 '}... "": "}... m e(hr, : ! Hstry f ladng I ', I :: ; :: 6, ; :',! 5,-, "'l--hstry f temperature I', "...!.. 4 : :: 3O ~ 1.. ~ ; :.1.2' ' , :,! '~ Hstry f ladng......:: ~".51'52!!:!!~l! ':,!~~. l..l. ' <N.2-b>,--, 6 / : ~ ~ : I 5 [1 ~Hstry f temperature I / 4 U-' : : : '...!...',... 3 ~!! ! ;... [ ~ :: Tmb(hr.] 5 I 15 2,~,- ~, ~! 2'5 ~"~ ~/ --,..,.,,-,.q :... ": ~"~".51'52I l!ll l 'l ~. I <N.2-e> 6 : : ', 4... ~ ~" ~!! ~~..("r: ' I ~:!~: I 2 l :;... '~..:;... 6,.~ 5 4 E perature I OO I ~ " ; Thae(hr.)l ', , <N.2-c> 6, :.!, 11 ~ " " " '" ~m;hr.) } 25 3,. :, 2,5 I --Hstryfladng]" }... }... I.5 <N.2-f> ~,,, 4 fl... 1 ~ " ' ~ ~: t:me(hr ~.6.7 ; ; r ', Hstry f ladng_ [...!... : ',!....5 <N.2-g> : :, : ] ~" ~ ~ -- ~me(hr.] ~.; ~" ', I -- Hstry f ladng......!"~...,~,"'2~ 1.51 l' ~" 'll l.., 2. '" ~, !..!.!!!! <N.2-h>,--,6. : ~ I 4 5 ' ~ ~ ftemperature -... ~ 3 ~-2 ~1 [ ~! Tme(hL ~" ' 4 5 t--"~--y "='n'l <N.2-> 6 :!! : 5 ' ~Hstry f temperature " " :: " ' ', " I...! , m(h; : :. ~. ~ :...., :.... / <N.2-j> <N.2-k> <N.2-1> 6... I 6 ' ': '' "-, " " ~Hstry f temperature ' ""... 4 ~ ~ 3 :.,. '... "... loo../...!... +mw; ~..... : ' ' stry f lad g 3f, 2 " stry f,adr, "" ~' 1.53f! ] 6 ~5,,y,,m,,a,u,... I... '...,... t 4 ~ 3 ~2 ~1 V...!... "! T~e(hr H...s. t. r.y...!...a.d!n '-.- -." -." -.5 t <N.2-m> <N.2-n> <N.2-> Fg.13 The hstry f temperature and ladng.:: "

8 :: 6 5 [...::... - f - S - 7 ~......,~.. ~ ~ /' /' Tme(hr.) Fg.14 Temperature transent n hrzntal lne f specmen 6 : ~ ~' 4 I.l/s T = u ~. ~ - ~ -. I 3,~; ':~"~~~"'~.~~... I..4 ;/t,:,,.~"": ~" ~'" ~'"... ~'~... n l a a Tme(hr.) Fg.15 Temperature transent n vertcal lne f specmen Once Twce 35 - ~ Three tmes Fur tmes 3... f "'" ~ ~_,,,IL-., m.-,nm~ dna-,l- ~ ~ ,... ~-... "~':--'~--'--'- m, e,~ ~ ~.,,, 2 I,,:... "-- ~ ~... :: ~... ;... ~... ;.--;... -r.~-,, :,, ~,.. 6.~, ~, !... :-" "~-,~"~"..., ~. ~ ~ m ~ m n,,, I,,, I,,, I,,, I,,, Tme(hr.) Fg.16 Temperature transent n specmen heated repeatedly

9 - temperatures f the hrzntal pnts n the specmen. Fg.15 shws the temperature transent f the specmen N.3-d durng and after heatng. It can be seen that the temperatures n the specmen went up fr a shrt whle after the end f heatng. Fg.16 shws the temperature transent by repettnal heatng n the specmen N.3-a. The frst heatng was lasted fr 4 mnutes. The temperature transent T the cncrete part whse temperature was under 1 C at the end f the frst heatng fllwed the same path as the frst heatng. Hwever, the temperature f the part f cncrete whse temperature was ver 1 C elevated faster than the prevus heatng. Ths result revealed that the thermal characterstc f cncrete such as thermal cnductvty changed by evapratn f water n cncrete. Hwever, there s lttle dfference between the pull-ut strength f N.3-a and f N.2-e-g, and the effect f repettn f heatng n pull-ut strength was nt seen. Fg.17 shws the temperature dstrbutn n the specmen durng heatng wth each prcess f heatng. Nte that S shaped f temperature dstrbutn was due t the dfference f thermal cnductvty between the blt and cncrete. It was bserved that there were tw types f falure mde n all the specmens. Except N.2-d and, the surface nstalled an anchr blt f all the specmens whch fractured durng heatng brke nt peces wth a sund f explsn. (See Fg.18) Meanwhle, fr the ther specmens, an anchr blt was pulled ut due t radal cracks arund the anchr blt. (See Fg.19) ~, t~ :' '-'' -'' '-'!-' '-'-' '-" ' L_! '_' '_ ' :: ~ 75m';" 3ran' ' --~ + l/- -- <7..._ e Temperature (~) O!... _~ _~ [1/l l/ib/ + '"" ' 12 kll L,,.,~////://,2re,..: r " Temperature ( C) <N.3-b> <N.3-c> /... I ' ' '91jml, n: ' ' '!... D-? mp._ -~ -,,... - I. ~ / ~ Z_,L/_ ]~S//]( ~/~/~ /7/4; 77;;.,, 77/7-- /4m'- + 4Om ran. g -~ ~, a , , ~- -e ~ ~ 8O I ,~a,,n~. ~>~ ~<~~ Temperature (9) Temperature ( C) <N.3-d> <N.3-e> Fg.17 Measured temperature dstrbutn n specmens

10 ~}~..,.~.. :~ ~-:~" :.'- ~:~ ~...~... ~ -' ~ ~-~:~.... ~'k'~:~'~ "..~-.,.::.-., -,--,,,v ~.~;.,-~.:, ~.,~... ~!.,:~ N ~... ~.~...~.~..~: -. ~. ~,....!:::~.+...*~,.*,... "... ~:~'~"~... ~: :~:~ :~... '~. <N.2-c> <N.2-> ~.'.~- "..~ ~:..! ~..., ~.~~ ~~,'-~I~#~.~..~, '.~ ~ ~:~.. ~... ~ ~., ~ ~:~,g~,~=u-:;~:~-~--..~ :. ~.:~,~ ~,.. ' ~ ~ ~::~~ ==========================================.,r~ ~: :..:... ~:~ ~:.... ~::~ ~:: :..,~:,,.,-. ~... ~... ~,:~ "~..~-~ <N.l-b> <N.2-m> Fg.19 Falure mde f the specmen wth crack Surface f~...,...,... f~/~-- 2 '-,-, 4 r~ 6 ~ 8 r~,,,, 1 ' --O-- N.2-a "NSN- N.2-b,c ~N.2-h - "~'-- N.2- :~/::':, ~. N.2-j V ~ '! :, -<z-- N.2.1 -'O-" N.2-12 " : Temperature (~G) O Fg.2 Temperature dstrbutn n the specmens at the breakng pnt 1

11 . Abut the specmens whch fractured durng heatng, the temperature dstrbutn n the specmens when they fractured are ndcated n Fg.2. Frm ths fgure, t can be bserved that the dfference f temperatures nsde N.2- s much smaller than the thers, and the effect f thermal stress wuld be lttle. Ths prbably caused the dfference f falure mde. Wth the specmens except N.2-, the explsn prbably happened because bth the thermal stress and steam pressure ccurred nsde cncrete and they are added t the stress cnveyed by cncrete by the tensle lad appled t an anchr blt. The relatn f pull-ut strength and temperature durng heatng are pltted n Fg.21 and after heatng n Fg.22. In these fgures, the test results f specmens seres N.1 are als ndcated and the vertcal axs stands fr the pull-ut strength nrmalzed by the average f the test results f specmens seres N.1. The average f tested pull-ut strength under nrmal temperature was hgher than the ne calculated by Eq.(2), and almst the same as the ne calculated by Eq.(3). Frm these fgures, the pull-ut strength durng heatng up t 5 C decreases t abut 2% f t under nrmal temperature, whle the pull-ut strength after heatng decreases t abut 5% f t under nrmal temperature. Based n these results, a lnear relatnshp between pull-ut strength and temperature s emprcally frmulated as shwn n Fg.21 and Fg.22. The lnear relatnshp between pull-ut strength and temperature durng heatng s presented by the frmula as fllws; P / P = x 1-3T (5) The fllwng frmula s the relatnshp between pull-ut strength and temperature after heatng; where, P: pull-ut strength under nrmal temperature(kg), and T: temperature ( C). P / P = x 1-4T (6) 1.2 '1 ' ' ' '! !... k 4 ; hl Temperature ( C) Fg.21 Relatn between pull-ut strength and temperature durng heatng 1.2 'f,' ' '! k O~Bx~hl.5! ' ' '" P.2,,,,!,,, Temperature Fg.22 Relatn between pull-ut strength and temperature after heatng 11 ( C)

12 4. CONCLUSIONS In ths research, the pull-ut testng f a cast-n place anchr blt n cncrete under hgh temperature was carred ut. The results shws that pull ut strengthf a cast-n-place anchr blt decrease greatly bth durng heatng and after heatng. Frm ths expermental nvestgatn wth maxmum temperature 5 C, t s cncluded 1) Putl-ut strength f a cast-n-place anchr blt decrease t 2% whle a cast-n-place anchr blt n cncrete was heated. 2) In the case f a cast-n-place anchr blt whch s tested after beng cled t nrmal temperature, pull-ut strength f a cast-n-place anchr blt decrease t 5%. Based n the results f the test, a lnear relatnshp between pull-ut strength and temperature s emprcally frmulated durng heatng and after heatng. Wth ths expermental research, the basc date f the pull-ut strength f a cast-n-place anchr blt n cncrete under hgh temperature culd be btaned and the utlne f the relatnshp between temperature and pull-ut strength culd be bserved. Based n the results f the experment that were btaned ths tme, s shuld be pnted ut that future studes are needed wth the same specmens reprted n ths paper t btan mre date n pull-ut strength f a cast-n-place anchr blt under hgh temperatures. Frm the results f falure mde n ths test, the specmens were t small wth cne falure. Research s als underway t use bgger sze specmens t btan cne falure type f fracture. Furthermre, the pull-ut tests f a cast-n-place under hgh temperature wll be carred ut by usng the specmens wth the dfferent embedment depth f an anchr blt. T examne the effect f the rate f temperature ncrease n the pull-ut strength f an anchr blt, a cmprehensve test prgram s planed t be carred ut n near future. REFERENCES 1. Abe, T., Furumura, F., Tmatsur, K., Kurha, K. and Kkub, I., "Mechancal prpertes f hgh strength cncrete at hgh temperatures," Jurnal f Structural and Cnstructn Engneerng (Transactns f AIJ), N.515, 1999, pp Inue, A., Suzuk, S. and Yanag, K., "Effect f curng methd and msture cntent f cncrete fr fre resstance f nrmal-weght cncrete and lght-weght cncrete," Summares f Techncal Papers f Annual Meetng, AIJ, 1997, pp Prpsed Addtn t Cde Requrements fr Nuclear Safety Related Cncrete Structures (ACI ); ACI Cmmttee 349, ACI Jurnal, August Archtectural Insttute f Japan, Desgn Recmmendatn fr Cmpste Cnstructn, Rehm, G., Elgenhausen, R. and Mallee, R., Be festngungsrechnk: Betnkalender, Vl. ]I, Takguch, K., Harada, R., "Pull-ut strength f an anchr blt embedded n cracked cncrete," Structural Mechancs n Reactr Technlgy (SMRT-15), Vl.VI, 1999, pp