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KHOA HOC VA CfiNG NGHE MONGHIEN CUU LY THUYET TINH TOAN SUlC KHANG UON CUA DAM BE TONG SUT DUNG THANH POLYMER
THAY THE COT THEP CHIU LU'C
ThS. DANG QUANG HUY, ThS. TRAN MANH HUNG Trwdng Dai hgc Md-Dja chat
V
at lidu polymer cdt sai da du'p'C nghien eifu va irng dung phd biln trdn thd giai. Gdn day, mdt sd tae gia trong nu-ac da cd cac cdng trinh nghidn eifu SLP dung loai vat lidu nay trong sLPa chifa vd gia cu-d-ng eac k i t clu chju udn, chu yeu Id cae dam clu bd tdng elt thep bi xudng elp.Tuy nhidn, irng dung cua vat lieu polymer cot sai cdn cd thd du'p'C sa dung trong k i t clu be tdng vdi vai trd taang ta nha cdt thep chju lye nhang cd au diem la bin vifng han trong mdi traang mudi, axit va nhilu chit an mdn khac Hud'ng nghidn eifu nay hidn cdn rit mai me a Vidt Nam. Do do, vide nghidn cau nguyen ly thilt k l sij dung thanh polymer cit sai (FRP) trong kit clu bd tdng d l thay thd cdt thdp chju Itfc cd y nghTa thae tidn va pham vi ap dung rdng rai trong hlu hit cae edng trinh xay dyng, d?c bidt la cac cdng trinh nglm va cdng trinh ven bidn hoae trong vimg cdt thdp eo nguy ea bi dn mdn cao.
1. So sanh dac tryng vat lieu cdt thep va thanh FRP
Cdt thanh chju lye FRP cd dac tinh ndi bat la cadng dg chiu keo tdt va trong laang nh^ han nhilu lln so vd'i cot thep thdng thyd-ng. Do do thanh FRP ed t h i sa dung dd thay thd cdt thdp chju Iyc trong mpt sd elu kidn be tdng tuy dilu ki0n sa dyng. Cac dac tinh vat lidu khdc anh huang din kha nang irng dung eua thanh FRP gIm ed md dun dan hdi, he sd gian na nhidt, gid'i hgn biln dang kdo dift. Tuy thudc vdo nguon gdc cua soi polymer tdng hap, tinh chit cua cac loai thanh FRP tgo thdnh eung khac nhau Cae loai thanh polymer FRP si> dung trdn the giai hien phd biln 3 logi cd nguon gdc khac nhau la: vat lieu polymer ngudn goc aramid AFRP, v$t lieu polymer nguon gdc cacbon - CFRP va vdt lieu polymer nguon gdc thuy tinh - GFRP {hinh H 1).
C6NGNGHliPMOS05-2Q13
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H.l. Mdt so san pham thanh FRP [1]
Mpt sd dac trang vat lidu co ban eua eae loai thanh FRP dagc trinh bay trong Bang 1.
Bang 1. Dac tinh vat liiu thanh FRP [1]
Vat lieu Cirong do chay. MPa CLrong do chiu keo, MPa
Bien dang chay Bien dang
keo dirt Mo dun dan
hii. GPa Trong iuong neng, G/cm
cat thep 400
0,002
200 7,90
Thanh GFRP
483+
1600
0,014 35-t51 1,25*
2,10 Thanh CFRP
600+
3690
0,014 120+
580 1,50+
1,60,.
Thanh AFRP
1720+
2540
0.014 j 41-12^
1,25* j - 1,40 j 2. Cac mo hinh pha hoai cua c l u kien be tong c6t thanh FRP
Tu'o'ng tu' nhu' k i t c l u be tdng cat thfep. si>c khang uln cua ket c l u b§ tang c6t thanh FRP
KHOA HOC VA CONG NGHE MO
_ ^ ^
dapc tinh toan theo nguydn ly can bdng bien dgng ciia mat cit, trong dd trang thai pha hoai can blng la khi cot thanh chju keo vd bd tdng chju ndn bj pha hoai dong thd'i. Ty 1$ cdt thanh FRP chju Iyc b i tri trdn mdt cit daac xac dinh theo cdng thifc:
0 trang thdi pha hoai can blng (hinh H 2), ham lagng c6t thanh FRP daoc ky hieu Id pn, va dag-c xac dinh theo nguydn ly can blng bidn dgng theo cdng thCfC dadi day [1];
Pfb-0,85^
Pfb=0,85pi Ef^ci Uu EfEa
(2a) {2b) Dya vao ham laang c6t thanh FRP chiu \uc (pf), cd t h i phan biet 2 tru'O'ng hap pha hogi khac cua kdt clu Id: phd hoai vung bd tdng chju ndn (hinh H.3), pf>pib; va pha hoai cdt thanh FRP ehiu kdo (hinh H 4), pf< pn,. Cac hinh ve du'di day thd hidn cac trgng thai pha hogi taong ang
h "
o A5 rj b
^.. " • " ' ' " " i f ; a=|!,c [ True tmng hoa
- ^ ^ - fr
0.85 f; ba
^ ^
H.2. Trwdng hop pha hoai vung be tdng chiu nen - Pha hoai gidn
W
i''
1, ^
0 A . a b
i i . ' ' ' ' ^ " a , f j .1 =p,c
Iruc Irung lioa
- 0,85 IV ba
- A r f , .
H.3. Trud'ng hop pha hoai can bing
h i
0 A, 0 ll - -
•;. ' ^ ' ' ' " i f ; . ' a=|3|<:
/
True trung hoa f
- 0.85 f ; ba
3. Sijc khang udn cua cau ki#n 3.1. Trw&ng hap pha ho^i gidn
gion Khi da viing be tong chju nen flat biln dang nen cue dai 0.003 can cot thanh FRP co biln dang keo nho hon bien dang keo cue dai {Ei<e(u) Truong hpp didn tich cat thanh FRP be tri Du'a vao cac phuong trinh can blng lire va biln tr§n mat c i t (pi) vuct qua di#n tich yeu cau d l dang cda mJt cit, sCrc khang uln danh dmh pha hoai can blng (pfb). k i t c l u se bj pha hoai duoc tinh nhu sau [1]:
CONG NGHIEP mo SO 5 - 2013
^ ^ KHOA HOC VA CdNG NGHE Md
Mn=Afff[d-|j
3_ Afff 0,85fcb ff-Ef^c
M l
(3) (4) (5)
f f -
0,85 khifc<28MPa
0.85-0.005'^^"^^'>0,65khif' >28MPa Tif 2 phaang trinh (4) va (5) ta tim daac ff
Ef£cu -0,5Ef£, (6)
|(EfEci
Pf ffu (7)
Mn=Afffu d (8)
Thay gia tn fftim dap'c vao phaang trinh (3) tinh daac sLfc khang udn IVln
3.2. Trwdng hgp phi hoai deo
a. Tinh toan theo nguyen ly can bing biin dang Tradng hgp dien tich edt thanh FRP bd tri trdn mdt elt (pf) it hon didn tieh ydu clu d l pha hoai can bang (pfb), cdt thanh FRP dat irng suit eye dai ffj va bl pha hogi do keo dift khi biln dang vung be tdng chju ndn chaa dat ddn trgng thai gidi han (ec<ecu=0,003) SifC khang uon danh dinh dago tinh nha sau [1].
Viec xac dinh tham sd c trong phaang trinh (3) dagc thyc hien blng phaong phap Igp va thir d i n cac gia tn cua e cho d i n khi Iyc keo va Iyc nen trong mat elt la blng nhau theo nguyen ly can blng Iyc va tuang thich bidn dang theo sa dd H 5 dadi day
b. Tinh toan gin dOng theo tieu chuin ACl Mdt phaong phap don gian han tinh sue khang udn cua trang thdi phd hoai deo dugc ACl daa ra dya trdn eac cdng thire cua trang thai pha hoai can blng. Tuy nhien phuong phap nay thidn ve an toan khi l l y sCrc khdng udn blng 80% sifc khang udn o trang thai can blng, bidu dien blng cdng thuc sau [1]:
Trong do:
l„=0,8A,f,u[^d
SM—Id + ':fuj
<:b = (10)
Thdng so' ddu vao _ T _ Tfnh toan cac he so Pr.Pfb,Pi
He sd Pi duge quy dmh trong Tieu chuIn nganh giao thdng van tai cua Viet Nam 22TCN 272-05 [2]
va tinh theo cdng thifc
.. f
Ti'nh lire keo (T), Gia thiet c = c | lire nen (C) theo c •
J . '^:,.^ c = T JI::>—-
" Diing M , - A f f , , ( d - - ^ )
H. 5. Sa di xic djnh Uiam so c trong phuong tnnh (3) 4. He sd sine khang udn
Didu kien dd clu kien dam bao an toan khi thiet k l theo trang thai gidi hgn Id:
M,><pU^ _ (11) Trong dd: q> - He sd su'c khdng udn, dugc lay blng
0,9 ddi vdi k i t c l u be tdng cdt thep ch|u uln.
Biln dang cua vgt lieu FRP khdng cd giai dogn chay deo ndn cac trudng hgp pha hogi didn ra dpt ngdt va khd dy bdo trud'c so vdi cdt thdp thdng thudng. Do chua cd tieu ehuin thidt kd cua Vi$t Nam cho clu kien sCr dung FRP nen vi^c lua clipn he sd sifc khang uon ddi vd'i cac k i t elu nay phai tham khao mgt sd cdc tai Ii0u nud'c ngoai va khong cd sy thing nhit. cu thd Id:
Bang 2. He so sdc khing uon cua vit lieu FRP Vat lieu
AFRP CFRP GFRP
JSCE [3]
1/1,3 1/1,3 1/1.3
CAS [4]
0.75 0.75 0,75
CHBDC t ^ f l 0,6 1 0.75 1
0,5 1
CONG NGHIEP MO SO 5 - 2 0 1 3
Hiep hOi cac ky sut Nhat Ban JSCE kiln nghi 1 ^ q)=1/1.3 (0,77) cho cau ki#n bS tong c6t sci Pt.
Tieu chuIn thilt k l cua Canada CSA S806-02.ii
KHOAHOCVACONGNGHIMO Canadian Highway Bridge Design Code (CHBDC) [4] kidn nghi lly hd sd sue khang uon tp tif 0.5^0.75 tuy theo logi vdt lidu theo Bang 2.
Nghidn cCfu day du han theo [1] cho phdp xac djnh he so tp nhu sau:
[0,5 khi pf < pfb
jj,-0.85-0,05 • = 0,76
khipfb<pf <1,4pfb (12) Pf
2Pfb
[o.7 khipf>1.4pfb
Nhu vdy ed thd thiy he so sire khang khi diing thanh FRP Id kha thdp so vai su dung cdt thep, phan dnh mire do tin cdy thip hon khi su dung thanh FRP so vd'i cot thdp.
5. Vi du ap dung thidt kd d i m be tdng c6t thanh FRP chju luc
Cae thdng so thiet ke: Tinh toan sCre khang udn eua dim bd tdng cudng dd chju nen 40 MPa c6t thanh FRP chju lye vdi eac thdng sd thidt k l nhu sau
•:• Dudng kinh thanh FRP, dtj=12 mm;
• Di^n tich 1 thanh FRP, Ab=120 mm^;
• Cudng dd chiu keo gid'i han thanh FRP.
ffu=630 MPa;
•> Biln dang cue hgn cua thanh FRP, Eru=0.01575;
• Md dun dan hdi eua thanh FRP, Ep40000 MPa;
•:* Chieu ddy ldp bd tdng bao vd, 30 mm,
•> Dudng kinh cdt thdp dai 10 mm,
•:• Mdt cit ngang dim nhu hinh ve H.6.
600 D-lOnim
4 thanh CFRP
1 350 nun ] H.6. Mit cit ngang dam Cdc bud'c tinh todn nhu sau:
Bu6c 1 • Xde dinh trgng thdi phd hoai cua kit clu- Chilu cao tif trong tam cdt thanh FRP din thd ngodi cung chju ndn.
d=600 - 30 -10 -12/2=554 mm Ty s6 cit thanh FRP tinh todn:
A , ^ 4x120 ^
" bd 554x350
Ty s6 c6t thanh FRP d trgng thdi phd hogi cdn blng theo cdng thue 2a hogc 2b vd'i:
Pfb=0.85|5i ffu^cu+tfu
Pfb = 0 , 8 5 x 0 . 7 6 ^ - ^^^ -0,0086
^° 630 0,003 + 0,01575 Nhu vgy pf < pfb clu kien bi pha hoai deo.
Budc 2. Xac djnh he sd sue khang uln Tif dilu kien v l trgng thai pha hoai deo, theo cdng thifC (12) xac djnh dugc (p=0,5.
Budc 3 SCfc khang udn eua tilt dien:
a. Tinh theo nguyen ly cin bing bien dang -Tinh tham sd e.
Thu vdi c=Cb Ap dung cdng thuc (10).
^ ( 0^003 ^ ^^^ ^ gg g^
^ l,0.003 + 0,01575j
Lye nen C = 0,85fc|3iCbb=868,18 kN Lye keo T = Afffu =302,40 kN Kidm tra didu kidn C=T khdng thoa man.
Chon lai c=33 mmrn
Luc ndn C = 0,85fc^cb=304,10 kN Lue keo T - A f ffu =302,40 kN Kilm tra dilu kidn C=T, dgt yeu clu - Tinh sue khdng udn theo edng thifc (8):
Mn-163.72(kNm) Mr-0.5x163.72 = 81.86(kNm) b. Tinh theo tieu chuan ACl Apdung edng thi>e (9). (11).
M „ = 0 , 8 x 4 x 1 2 0 x 6 3 0 [ 5 5 4 - 5 ^ I ^ ^ ] x 1 0 - « Mn =125,83 (kNm)
Mr = 0,5 X 125,88 = 62.91 (kNm)
Nhu vgy ed thi thiy tinh toan sue khang udn Mr theo nguydn ly cdn blng bien dang cho gia trj cao han so vdi tinh toan gin dung thidn vd an toan theo tidu chuIn ACl. Cach tinh nay cd thi tilt kiem vat lidu han ndn dugc khuydn khich su dyng trong thyc te.
6. Kdt luan va kidn nghj
Thanh FRP cd cde uu dilm la trpng lugng nhe, cudng dp chju keo cao va chdng an mdn tdt han so vdi edt thdp. Tuy nhidn vat lieu FRP khdng co giai doan chay deo ndn khi thilt k l can ed hd so an toan cao. Hd so sue khang uon eho clu kidn be tdng cdt thdp tp blng 0,90 nhung ddi vdi kit clu be tdng cdt thanh FRP (p chi nlm trong pham vi tCf 0,5^0,77. Khi thilt k l can can cCf vao ham lugng FRP bd tri trdn mat cit de cd sy lya chon hd so tp cho phu hgp.
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