Anh hiFOTig cua cu'd'ng do be tong den hieu qua gia cu'd'ng khang cat cua tam FRP trong dam be tong cot thep
Ngay nhan bai; 6/8/2014 Nguyen Minh Long, Ngay su^ bai; 13/8/2014 Phan T r i N h a n , Ngay chap nhan dang: 28/8/2014 Xran Quang OuTc
T O M T A T :
De tai nghien cdu thuc nghiem anh hddng cua yeu to cUdng dp be tdng den hieu qua gia cttdng khang cat ciia tam sdi thuy tmh (GFRP) va sdi carbon (CFRP) dang tam U lien tuc tren dam be tdng cot thep (BTCT) co san vit mit. ChdOng trinh thi nghiem dtl^fc' tien hanh tren 9 dam. co cung kich thu6c hinh hoe, ham Idpng cot doc, cot dai va ham lUdng soi gia cUc(ng. Cac dam dildc chialam' 3 nhom khac nhau ve cddng dp be tong (32, 57 va 75 MPa); moi nhom gom 1 dam ddi chiing va 2 dam dtldc gia cUdng tSm GFRP va CFRP dang U lien tuc, Ket qua thUc nghiem cho thay (1) gia tri bien dang cua tam gia cUdng dang U lien tuc tren cac dim tW nghiem ehiu anh hddng dang ke bdi cddng dp chju nen ciia be tong, theo do tang cUc(ng dp be tong (tii 32 MPa len 75 MPa) lain tang dang ke bien dang keo trong tam (den 36%); (2) tam gia cUdng lam tang manh kha nang khang cdt (den 137%), phuc hoi dang ke dp cdng cua dam va sU gia tang kha nang khang eat cua dam gia cUdng co xu hUdng giam khi ciJdng dp chiu nen cua be tfing tang; (3) sd gia tang cddng dp be tdng lam thay ddi kieu pha hoai cua dam td cat - nen vd be tong sang cat - bong taeh tam va ti&n CFRP phat huy vai trd gia cUc(ng tdt hon tam GFRP trong trtfdng hop dam co cUdng do be tong cao,
Td khoa: cUdng dp be tong; dam be tdng cdt thep; gia cUtmg; k h i nang chiu cat; GFRP, CFRP.
ABSTRACT
This paper deals with the effect of concrete strength on the shear strengthening efficiency of carbon and glass fiber-reinforced polymer (CFRP and GFRP) jackets in steel reinforced concrete (RC) pre-cracked beams rehabilitated by CFRP and GFRP U-shaped jacket. The tests were carried out on total nine beams those have same geometrical dimensions, longitudinal tensile rebar ratio, stirrup ratio, and FRP reinforcement ratio. These beams were divided into three groups with varying concrete strength (32,57and 75 MPa). Each group consists of two steel RC beams rehabilitated by CFRP and GFRP U-shaped jackets and one control RCbem The beams were simply supported and tested under two concentrated loads.
The test results show that the behavior of the FRP strengthening jackets was considerably affected by concrete strength of the tested beams, where the increase of concrete strength results in higher tensile strain in the FRP jackets. The FRP jackets significant increase shear capacity of the beams and effectively improve their stiffness, h is worth noting that, the increase of shear capacityoE' the FRP rehabilitated beams has a tendency to decrease as concrete strength increases. The increase of concrete strength changes failure mode of the beams from shear-concrete crushing mode to shear-debonding mode. Morever, CFRP jacket is more effectl^
than GFRP one in strengthening beams having high concrete strength, ; Keywords: concrete strength, reinforced concrete beam, shear capacity, rehabilitation; carbon and glass fiber-reinforced polyni
(CFRP and GFRP) jacket. "^
TS Nguyen Minh Long. Bo mon Cong trinh, khoa Ky thuat Xay ddng, trUcvng Dai hoc Bach Khoa Tp. Ho Chi Minh Email: nguyenminhlong@hc mut.edu.vn
Th.S Phan Tri Nhan, Cong ty Cd phan Tu van Xay ddng va Dau tH Nam Hai.
Email: [email protected]
KS Tran Quang Diic, Phong thi nghiem Ke't cau Cong trinh, khoa Ky thuat Xay ddng, trt(c(ng Dat hoc Bach Khoa Tp Ho Chi Mind.
Email: tranquangduc91@gmaii,com Di ddng. (+84)1678 830 814
1. Giori thieu
Vat lieu FRP (Fiber Reinforced 'olymer) vdi c^c dac tinh ndi bat nhi/
:h6i liTdng rieng nhe, ci/dng dp chju keo :ao, khong bj an mdn, khong bj nhi^m is. va khS nang t u no! soi nhd vao cac Am bien spi quang dupe long ghep vao )en trong dang n6i len nha mot gidi
>hap gia cu'dng ket cau hieu qua ben :anh cac ky thu^t truyen thong. Mac dCi 'ay, hien nay ky thuat gia cUdng sCf dung am FRP v3n chUa dupc silr dung r6ng rai rong thUc te nhu mong dpi. Mpt trong ihtJTng nguyen nhan chinh la do su hieu net cua cac ky su va ngay c5 nhDng nha ighien ciJu ve tirng xCf cCia dang ket c^u lay van cdn chUa day dCi, daic biet la ilng Lf cat [2,3,4].
r Kha nang chiu c3t cCia dam BTCT fuyen thdng bj cinh hudng bdi nhi^u eu to [5, 6, 7, 81, trong dd, cUdng dp .hiu nen cCia be tdng la mpt yeu to quan j-png. Ddi vdi nhUng dam gia cudng tam RP, tam quan trpng cua yeu td cudng
•.d b^ tdng chju nen cSng trd n§n rd iing hon, bdi vi nd dnh hUdng den khd .ang bam dmh va bien dang hieu qud
!ia tam FRP, tC/ dd quyet djnh den kieu ha hoai vk khd nang khang cat cua am. Cho den nay, mpt vdi nghien ctiTu a dupc thiic hien cd lien quan den dnh ,Udng cQa yeu to cudng dd be tdng chiu 3n den khd nang khang cdt cua dam rCT cd gia cUdng CFRP (Carbon Fiber '5inforced Polymer) dang chuf U [6, 9].
'ly nhien, cac nghien ciJu nay dupc 'uc hien tren dam cd kich thudc nhd va /dng do chju nen ciJa be tong da phan 'id hdn 55 MPa. Ngoai ra, cac nghidn ''(u hien cd chi mdi tap trung cho loai W CFRP nen chua cd bao cao nao trinh ly anh hudng cua cudng dp be tdng
•n hieu qud gia cudng tam GFRP (Glass Der Reinforced Polymer).
" Bai bao nay trinh bdy nghien cuTu uc nghigm ve dnh hUdng cua yeu to 'dng dp be tdng den tirng xir va kha ng khang cdt cua dam BTCT vdi vet t cd san dupc gia cu'dng tam spi thCiy h (GFRP) va tam spi caebon (CFRP) ngbaophCichiJrU.
' 2. Churcmg t r i n h thiTc nghiem 2.1.Vatlliu
Bdng I . C a p p h o i b e t d n g d u n g trong thi nghiem Thanh p h i n
Xi mang Holeim PC40 Da 5-10 m m Da 10-20 m m Cat song 0 ^ m m Da nghien 0-4 m m Nude sinh hoat Phu gia Sil^ament 2000AT Phu gia Glenium 6013
Khoi luang / m^
A 315 kg 1130l<g
_
896 leg
-
156 kg 3 lit
-
B 538 kg
1386 kg 703 kg
-
156 kg 5.3 lit
C 547 kg 374 kg 560 kg 280 kg 654 kg 185 kg
8.67 lit Cap phdi be tdng dung cho 3 nhdm
dam thi nghi&m {A, B va C) dupc trinh bay trong Bdng 1. Cudng dp chju nen trung binh (f^^^J va cudng dp chiu k^o che (^5p,cube^ cila be tong cua t i ^ g nhdm dam dupc xac djnh tren 3 mau lap phUdng tieu chua'n (canh 150 mm). Theo do, cac dam nhdm A cd f^^^^^^ = 32.2 MPa va f, ^^^^
= 2.65 MPa; n h d m V c d f^^^^ = 57.4 MPa va f be ~ 2-^^ ^^^ ^^ nhom C cd f ^^^^ = 75.1 MPa v a f _ , . = 3.62 MPa.
^'^'"''g"™™ '' """' '• TT
Hinhl.lJldisfli:(a) GFRP; (b) CFRP Cdt dpc chju keo cCia dam cd du'dng ki'nh 22 mm. Cot thep thanh cd dUdng kinh 12 mm dupc sCr dung lam cdt dpc phia ben tren cau tao. Cdt dai cd dudng kinh 6 mm. Cudng do chiu keo cilia cot thep dupc xac djnh thdng qua thf nghiem keo thep doc true; thi nghiem 3 mau roi lay gia tn trung binh. Doi vdi cdt dpc, gidi han chdy (f^) va gidi han ben (fJ tUPng trng la 430 MPa va 617 MPa. Ddi vdi cdt dai, gidi han chdy (f ) va gidi han ben (f^) tuong Ung la 323 MPa va 489 MPa. Modun dan hdi cua cdt thep la 200 GPa.Tim spi caebon va spi thCiy tinh mot hu'dng (Hinh 1) cd chieu day tUPng iing la 1.1 mm va 1.3 mm dupc sCrdung gia gudng cho dam vdi dang chit U. CUdng dp chiu keo {f^^} va md dun dan hdi (E,) cua tam GFRP va CFRP do nha san xuat cung cap lan lupt la 460 MPa va 20,9 GPa;
986 MPa va 95.8 GPa. 2.2. Mau d^m thi nghigm
Tong cdng 9 dam dupc chia lam ba nhdm (Bdng 2). Moi nhdm gom 1 dam ddi chiJrng, 1 ddm gia cudng tam GFRP va 1 dam gia cudng tam CFRP (dang ddi lign tuc chU U). Dam c d kich thudc 150x450x3100 mm, nhip tinh toan L=2700 mm, nhip cdt a^900 mm. Cac dam cd ham lupng cdt dpc va cdt dai lan lupt la p^ = 2.38% va p^^ = 0.13%. Thdng sd ky thuat cOa d i m dupc trinh bay chl tigttrgnHinh2.
tr- rr%+
u
Dem dup 11 DOlLimi 16 iiui-fh.
-I
Hinh 2. Chi tiet mau dam thi nghiem 2.3. Quy trinh thi nghiem (binhS) Ddm dupc t H nghiem theo so do dam don gian chiu 2 tai tap trung (Hinh 2). Hai cdm bien di&n trd (SG) dUpc sii dung de do bien dang cCia cdt dai, va bdn SG dupc sii dung de do bien dang cua tam FRP. Bien dang keo dpc true ciia cdt dpc dt/pc do bSng mot SG dan tai giQa nhjp dam. Sau SG khac dUpc dan tai nhip chju cat de do bien dang cdt dpc trong vung xuat hien vet mit xien nham muc dich kiem chtj'ng cd hay khdng sU chay d^o cua cdt dpc tai day Bien dang nen be tdng dpc theo chieu cao tiet dien dam dupc xac dinh thdng qua bdn SG.
Nam thiet bi do chuyen vj (LVDT) duoc lap dat de do dp vdng tai giOa nhip, tai vj tri dat tdi va tai goi tua cua dam (Hinh 3).
63
Hinh 4. Hinh thai vet ni)t cOa cai dam tri/dt khi diTcfc gia ci/cmg bang tam FRP
Thi nghiem dUpc tien hanh theo 2 giai doan. Trong giai doan 1, cac dam dupc gia tdi vdi d p Idn c i p tai 10 kN cho den khi xuat hien vet niJrt xien cd be rdng 0.3 m m t h i di/ng lai va d d tai (Hinh 4). Be mat cilia cac d a m can gia cudng duac
lam phang bdng may mai tay va lam sach bdng may hut bui va sau dd dupc tien hanh gia cUdng dan t a m FRP. Giai doan 2, cac dam sau khi dupc gia cudng 7 ngay, dUdc tien hanh t h i nghiem lai cho den khi bj pha huy. Cfng vdi m6i cap tdi trpng, cac gia trj d p vdng, bien dang cua t a m FRP, cdt doc, cdt dai va be tdng deu dupc ghi nhan.
3. Ket qud va nhan xet (bang 2,3}
3.1. Kieu phd hoai cua dSm Cac dam thi nghiem deu b| pha hoai do cdt. Hinh thai vet nuft va kieu pha hoai dien hinh cua cdcdam dupc the hien tren Hinh 4. Quan sat thay, cac dam cUdng dd be tdng cao cd toe dp phat tnen cOa cac v^t niit nhanh hon va kieu pha hoai cua chiing trd nen gidn hon. Be rdng cua v^t nut do dupe tai thdi diem pha hoai trong cac dam cudng dp be tdng cao cung Idn hon dang ke so vdi cac dam cudng dd be tdng thap (xap xi 1.5 lan).
Trong cac ddm gia cudng, tam FRP bj bong taeh cue bd trude khi ddm bi pha hoai do cdt. Vdi cac dam cd cudng dp chju nen b^ tdng = 32 MPa (nhdm A), tam bj bong taeh keo theo Idp vufa be tdng be mat. Trong khi, vdi cac dam cd cudng do be tdng bang = 57 MPa (nhdm B) va = 75 MPa (nhdm C), tam FRP bi bong taeh ra khdi mat dam ma khdng cd Idp vCra kem theo. Hi^n tUpng nay cd the la do Crng suit keo sinh ra trong tam FRP qud Idn va vUdt qua cudng dp bdm dinh cua Idp keo va be mat b^ tdng.Trong khi, cudng dp be tdng cua cae dam nhdm B va C qua cao, cho nen, Idp keo se bi pha hoai trudc khi be tdng bi pha hoai va lam cho tam FRP bi bong taeh ra khdi be mat belong.
3} MPa I ^ ^ ^ ^ ^ ^ ^ B 32MP3
(a) (b)
Hinh 5. Hinh thji vet niJt va kieu pha hoai dien hinh ciia cac dam: (a) dam doi chtj'ng; (b) dam gia cadng
3.2. Quan h^ tdi trpng - chuydn vi Quan he tdi trpng va chuyen vj cac dam thi nghiem dUdc the hien tren Hinh 6. Trude khi gia cUdng, cac d i m ilng jjiJ giong nhau. Sau khi dupe gia cUcfiig, ehuyen vj cCia eac dam gia cudng gidm dang ke so vdi cac d i m khdng gia cudng xet tai ciing mdt cap tdi. Ket q u i nay cha thay rd rang rdng cac dam da co sU phuc hoi dp cirng kha tdt sau khi dupc gia cudng. ThUc t^, trong giai doan nay, tam FRP b i t dau tac ddng vao ilng XLT cung nhusiiphan bd iing s u i t trong dam, han che sii md rdng cOa cac vet niit xien, cSi thi^n khd nang cai mdc cua cot Ii^u,tan9 dp etirng cho d i m tU do lam cho chuy&i vj cLia cdc dam gia cudng gidm so vdi dam ddi chu'ng xet tai cung mdt d p tdi, Sugidm chuyen vjnaycangrd net khi tSi trong tae dung tiem can tai phd hoai ciHa dam. Dam cd cudng dp be tdng cang eao, sii gidm chuyen vj cang Idn. Cu the, d nhdm A (Hinh 6a), ehuyen vj Idn nhStd vj tri giQa nhjp cua dam ddi chiirng (RC-A) tai cap tdi phd hoai (190 kN) Id 6.15mm.
Tai d p tai nay, chuydn vi cCia dim gia cudng GFRP-A va CFRP-A lan lUpt la 4.9 mm va 4.8 mm. NhU vay, chuyen vi ciia 2 d i m gia cudng gidm tii 26% 6^n 28%
so vdi dam khdng gia cudng. TUdng tU cho cac dam nhdm B (Hinh 6b), x^t d cap tdi pha hoai (310 kN) ehuyen vi giita nhjp cua d i m khdng gia cUdng (RC-B) \i 12.4 mm, nhUng chuydn vj cCia dam gia cudng tam FRP (GFRP-B, CFRP-B) chl xap xi la 7.6 mm va 7,2 mm, giam den 65%
va 72% so vdi d i m khdng gia cudng. 06i vdi cac d i m nhdm C (Hinh 6e), chuy^nvj ciJa 2 dam gia cudng giam 67% vd 75%
so vdi dam khdng gia cudng.
Hinh 6. Bieu do tai trong - chuyen vi dam; (a) nhom S - f ^ = 3 2 MPa; (b) nhom B - f^_„=57 Mil (c) nhom C-f^=75 MPa ' " '''
Ngoai ra, cac dam gia ci/dng tam
Bang 2. Tong hdp ket qud thi nghiem giai doan 1 Nhom
1
2
3
Mhu dam K - A GFRP-A CFRP-A K - B 3FRP-B CFRP-B RC-C GFRP-C CFRP-C
Kich thudc (mm)
150x450x3100
fccube (MPa)
32.2
57.4
75.1 f.p.ube (MPa)
2.65
2.78
3.62 V„.ft..
(kN) 30 30 40 40 40 40 50 50 SO
V.,sh (kN) 100 100 120 120 140 140 140 160 160
Vcr,,t,.D.3 (kN) 140 160 165 190 190 190 210 215 210
E, {%»)
e « o j ( % o ) 1 33 1 39 1.41 1.33 1.37 1 3 4 1.30 1.36 1.33
Ss.oj.mld (%o}
0.70 0 80 0.87 0.94 0.95 0.97 1.06 1.06 0.95
E.,03,e™l (%D) 0.48 0.57 0.65 0.65 0.70 0.67 0.77 0.80 0.76
Ki^U plia hoai
S
S
s
Bang 3. Tdng hpp ket qua t h i nghif rr Nhom
1
2
3
MSu d^m IC-A GFRP-A CFRP-A K - B GFRP-B CFRP-B
^C-C GFRP-C CFRP-C
Kich thudc (mm)
150x450x3100
giai doan 2
fccub.
(IVlPa)
32.2
57.4
75.1 fiwut-e (IWPa)
2.65
2.78
3.62 Vc,,n„
(kN) 30
40
50 V c s h (kN) 100
120
140 Vu,,o,,e.c,
(kN) 190 390 450 300 430 490 390 500 660
Efu ( % o )
3.35 2,28
3 75 2.55
4.05 3.58
t . . (%o) 4.62 1.91 1.94 4.53 3.43 2.21 4.47 3.66 2.78
E,„,„id {%o) 0.95 1.97 2 6 ! 1.44 2.48 3.19 1.95 2.95 3.79
E.u.^d (%o) 1.83 1.54 1.69 1.86 1.73 1.85 2.05 2,06 2.23
Kieu phd hoai
S S-D S"C
s
S-C S-C
s
S-D S-D Ghi chu:
f ^^^^: Cudng dp chiu n^n be tdng mau lap phUPng, MPa;
f^ njbe- Cudng dd chiu keo che be tdng mau lap phuong, E, : Bien dang cua t i m gia cudng;
Efy : Bien dang Idn nhat eCia tam gia cudng;
%f>3 '• ^ ' ^ " ^^^^ '-^^ ^^' ^^' ^ ^ ''^'^9 ^^* niitxi^n dat 0.3mm;
£ ^ : Bi^n dang Idn nhat cot dai;
E^^^j^: Bi^n dang Idn n h l t cdt dpc tai giUa nhjp khi be rdng vet niJt xi^n dat 0.3mm;
E^^^jj: Bien dang Idn n h l t cdt doc tai giUa nhjp;
E^jjj^^^ : Bien dang Idn nhat cdt dpc trong nhjp cat khi be rdng vet nut xien dat 0.3mm;
^suend' ^ ' ^ " ^ang Idn n h l t cot doc trong nhip cat;
S : Kieu pha hoai eat eCia dam be tong cot thep;
S-C : Kieu phd hoai cat cua dam gia cudng ket hpp vdi nen vd be tdng;
S-D : Kieu pha hoai cat cCia dam gia cUdng ket hpp vdi bdc taeh t i m .
Hinh 7. Bieu do t^i trgng - bien dang tam gia cudng FRP.
(a) nhom A - f ^ = 3 2 MPa; (b) nhom B -f^^=57 MPa; (c) nhom C-f^^=75 MPa
CFRP cd miic gidm chuydn vj nhieu hdn dam gia cUdng tam GFRP nhUng khdng
dangke(ta2%den8%).
3.3. Quan he tai trgng va bien dang tam gia cUifng - anh ht/cfng cua yeu to cififng dp be tong
Quan he tdi trpng va bien dang tam GFRP va CFRP cua eac d i m gia eUdng dupc the hi&n tren Hinh 7. Ket qua cho thay ling xir cua tam gia cudng 6MC ehia thanh 2 giai doan rd ret. Giai doan trudc khi vet nut xien phat trien (0 den 40~60%V^,^^^_), tam FRP bien dang be va khdng bj dnh hUdng bdi cudng dp be tdng dam.Tuy nhien, sau khi vet ntrt xien bat dau phat trien, bien dang cCia t i m
tang nhanh va phu thudc vao cudng dp be tdng dam. Cdc d i m cd cudng dp chju nen cua be tdng eao (dam nhdm C), cd tde dp bien dang eCia tam nhanh hPn so vdi t i m cua dam cd cudng dp chiu nen cOa be tdng thap hon (dam nhdm B va A). Dieu nay cd the la do cudng dp bdm dinh cua tam FRP ti le thuan vdi cudng dp be tdng nhu mdt sd nghien eiiu trUde day da chi ra [6, 9, 10]. D i m ed cUdng dp be tong cao, cudng do bam dinh eua tam cang tang, t i m tham gia chiu keo nhieu hdn va dan den t i m bi bien dang nhanh hon, Trong giai doan nay, tde dp
65
bien dang cua tam GFRP va CFRP trong dam nhdm C Idn hdn so vdi trong d i m nhdm B va A l l n lUdt la 1.66 va 1.73 l l n ; 1.24 va 1.52 lan. Cang ti$m can cap tdi pha hoai, toe dp bien dang cua tam cdng nhanh.
Bi^n dang cCia t i m GFRP dam nhdm A (f„^be= 32 MPa) tai cap tdi pha hoai (390 kN) la 3.35%o. Trong khi dd bien dang cCia tam GFRP d 2 dam gia cudng cua nhdm B (f.^^= 57 MPa) va nhdm C {f„„i^=75 MPa) d d p tdi pha hoai cCia chiing l l n lUdt la 3.75%o va 4.05%o, tang 11 % vd 17% so vdi bien dang ciia t i m gia cudng dam nhdm A.TUong tU, bien dang Idn nhat cOa tam CFRP trong dam nhdm A do duoc la 2.28 %o. Cac tam CFRP d cac dam nhdm B va C cd gia trj bien dang do dupe tai thdi di^m chung bj phd hoai lan lUdt la 2.55%t) va 3.58 %o, tang 11% va 36% so vdi bi^n dang Idn n h l t cCia t i m gia cudng d i m nhdm A. NhUvay hau het cdc gid trj bien dang cua tam gia cudng trong cdc dam thi nghiem deu nhd hdn 4%o. Ngoai trii cd mdt trUdng hpp cda ddm GFRP-A, gia trj bien dang tam Idn hdn 4%o nhUng khdng ddng ke. Ket qua nay phu hdp vdi de xult cOa ACI 440.2R (2008) va TR55 (2000), theo dd gia tri bi^n dang cCia t i m gia cudng dang U khi tinh toan khdng lay vUdt qua gid tn 4 %o.
Kinh 8. Bien dang cua tam FRP tfo dUflc tai cap tai pha hoai theo yeu to ci/cfng do be tong thiu nen
Hinh 8 eho thay sU khdc biet cua bien dang t i m GFRP va CFRP theo tiing nhdm d i m ed cudng dp chiu nen be tdng thay ddi, Ket qua cho thay sU khac biet giiia chiing xuat hien rd net d giai doan sau khi vet nut xien bdt dau phat trien lai {giai doan 2). Trong giai doan nay, tam gia cudng bat dau phdt huy hi^u qud gia cudng cua chiing.Tim CFRP vdi dd ciing doc true Idn hon nhieu so vdi t i m GFRP nen bien dang nhd hon xet tai ciing mdt
d p dp tai. Su khde biet nay cang Idn dan khi tdi tac dung tiem can gid trj tai gidi han (pha hiiy) ciia chung. Trong dam nhdm A va B, bien dang cua t i m CFRP nhd hon 32% so vdi bien dang ciia t i m GFRP tai d p tai phd hoai. Odi vdi cdc dam nhdm C, bien dang ciia tam CFRP nhd hon x i p xi 12% so vdi tam GFRP
3.4. Anh hudng cua ti/ffng tac giCta cUcfng dp be tong va sU lam viec cia tam gia ctidng FRP den lihd ndng fihdng c&tcdadam
Hinh 9. Sir gia tang kh^ nang khang c3t ci)a dam gia cL'cmg tam FRP so vdi dam doi diuTig theo yej to cifcingdochjunenbetong
Hinh 9 cho thay miic dp gia tang khd nang khang cdt ciia d i m gia cudng so vdi dam doi chu'ng xet theo yeu td cudng dd chju nen ciia be tdng. Ddi vdi dam nhdm A, kha nang khang cat ciia dam gia cUdng (GFRP-A va CFRP-A) so vdi dam doi chUng (RC-A) tang tUdng Ling la 105% va 137%. Ddi dam nhdm B, kha nang khang d t ciia dam gia cudng (GFRP-B va CFRP-B) so vdi dam ddi chUng (RC-B) tang tuong ufng la 43% va 63%
va tUdng t u nhdm C la 28% va 69%. Ket qud nay eho thay su gia tang kha ndng khang cat eiia dam gia cudng so vdi d i m ddi chiing phu thude dang ke vao cudng dp be tdng d i m . D i m cd cudng dp be tdng thap, hieu qud gia cudng cang cao va ngUde lai, dam ed cUdng dd be tdng cao, hieu qud gia cudng cd xu hudng
Hinh 10. Tifcmg quan m nang khang cat cua dam theo cucmg do chju nen cua be tong
gidm. Ngoai ra cd the thay, tam CFRP phat huy vai trd gia cUdng tdt hon t^m GFRP trong trudng hpp dam cd cudng dd be tdng cao.
Miic dp gia tang khd nang khdng cit ciia cac dam ddi chiing va cac dim gia cudng khi cudng dp chju n^n be tong thay doi the hien trong Hinh 10. Sdi vcfi d i m ddi chiing, vi^c tdng cUdng dd chju nen be tdng ttr 32.2 MPa l§n 57.4 MPa va 75.1 MPa Idm tang k h i nang khdng cSt ciia dam len xap xi 58% va 105% (tif 190 kN tang len 300 va 390 kN). Bdi vdi dam gia cudng tam GFRP, khd nang khang cat ciia chung khi tang cudng dp bg tdngtCr 32.2 MPa Ign 57.4 MPa va 75.1 MPa, tang tuong Ung 10% va 28% (tCr 390 kN tang len 430 va 500 kN), vd tUdng tU doi vdi dam gia cudng t i m CFRP, miic dp tang Id 9% va 47% (tif 450 kN tang len 490 va 660 kN). Nhu vly, viec tang cUdng do b4 tdng lam tang manh kha nang khang cat ciia cdc dam khdng gia cudng [dam doi chOrng) nhUng chi lam tang v ^ phcii kha ndng khang cat ciia edc dam gia cudng. Hien tUdng nay rat thd vj vd co the dUdc gidi thich nhu sau. Ddi vdi cac dam khdng gia cUdng, khd nlng khang cSt ciia chung bj chi phdi rat manh bffi cudng dp be tdng, chi^u cao lam viec ciia tiet dign, ham lUdng cdt dpc vS c6t dai. Cac yeu td nhu ehieu cao lam viec cua tiet dien, ham lupng cdt dpc vd cot dai trong trUdng hpp nay la khdng cl6i, cho nen viec tang gidm cudng do dSn den su tang vpt ve khd n l n g khang cat ciia chung. Trong khi, vdi cdc dim gia cudng, ben canh yeu td cudng do be tdng va cac yeu td nhu vUa d^ cap, tam gia cudng ddng vai trd r I t quan trong den khd nang khdng edt ciia dam.Vi|c tang cudng dp be tdng nhung van giiJ nguyen cac dac tinh va thdng sd ky thuSt ciia tam da lam cho khd ndng khdng di ciia dam bj chi phdi bdi yeu to tam gia cudng va vi vay khdng tang manh nha trong trudng hdp dam khdng gia cudng.
Ngoai ra, cac dam trUde khi dUpc gia cudng da cd s i n vet mit xign; dieu nSy lam cho miic dp dnh hudng ciia thanh phan be tdng bj suy gidm do sti suy gidm cua hieu Ung cdi mdc cdt lieu.
4 . K^t luan
Tir ket qud nghien ciJu dd dUdc trinh bay d tren, mpt sd ket luan ed the dupc rUt ranhusau:
1) gia trj bi^n dang Idn n h l t ciia t i m gia cUdng dang U ciia cac dam thi nghiem x i p xI 3.35 %o den 4.05 %o (tam GFRP) va 2.28 %o den 3.58 %o ( t i m CFRP). Gid trj bien dang nay chju dnh hudng dang k l bdi cUdng dp chju nen ciia bg tdng, theo dd tdng cUdng dp be tdng tir 32 MPa Ign 75 MPa lam:
- tang bien dang trong tam GFRP va CFRP l l n lupt 17% va 36%;
- tang toe dd bien dang ciia tam GFRP va CFRP lan lUpt 1.7 va 1.5 Idn;
- thay dot kieu phd hoai cua dam tir d t - nen v d be tdng sang c i t - bong tdch tam
(2) gia cudng 1 Idp tam FRP dang chO U trong nhjp cat lam:
' tang khd nang khd nang khdng d t d i m ttr 28% den 105% ( d i m GFRP) va ttr 69% den 137% ( d i m CFRP);
- phuc hoi ddng ke do cu'ng ciia dam, tif dd lam gidm c h u y i n vj d i m tU 26%
den 67% (dam GFRP) va ttr 28% den 75%
( d i m CFRP).
(3) Su gia tang khd nang khang cat cOa dam gia cudng cdxu hudng gidm khi t i n g cudng do chju nen be tdng dam.
Cu t h i , mti'c gia tang kha nang khdng d t cua cdc d i m gia cudng ed cudng dp bg tdng = 32 MPa la 105% va 137%; vdi cdc dam gia cudng cd cudng dp bg tdng
= 57 MPa, la 43% vd 63%; vd cdc ddm gia cUdng cd cudng dp be tdng = 75 MPa la 28% va 69%. Ngoai ra, t i m CFRP phat huy vai trd gia cudng tdt hdn t i m GFRP trong trUdng hdp d i m cd cudng dp be tdng cao.
L^i dm tfn
Nghign ciiu ndy dupc tai trp bdi Dai hpc Quoc gia Thanh phd Hd Chf Minh (VNU-HCM) trong d l tai ma sd B2012- 20-36. Cac tac gid cdm on edng ty FYFE ASIA PTE LTD., Singapore da ho trp vat lieu FRP, keo dan vd cdc chi dan ky thuat.
TAILICUTHAMKHAO
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