KHOA H O C - C 6 N G NGHE
So 5/2016
Mpt so dieu chinh va luu y trong tinh toan
thiet ke ket cau be tong ttneo tieu chuan AASHTO tu phien ban nam 2007
• TS. NGUYEN OJNH H()HG - TrUdng Dgi hgc Quoc ti-Dgi hgc Quoc gia TP.H6 Chl Minh
• TS. VU HONG NGHIEP - TrUcffig DaihgcGiao thong vdn tdi TR Ho Chf Minh
TOM TAT: So VOI Tieu chuan AASHTO tai bin lan ttiii 3 n i m 2004, cac tai b i n tu lan thd 4 n3m 2007 trd dl CO mpt so dieu chinh va thay doi. Bai bao neu len mot so luu y va thay ddi trong tinh toan mat mat ung suit va mpt so dieu kho^n trong kiem tra trang thai sd dyng nhu xac djnh ham \ugr\g cdt thep tdi thieu va khong che v l t ndt. Bai bao lift ke each tinh toan mpt sd logi mat mat dng suit co ke d f n trinh ty thi cong cua ket cau, each tinh toan ham lupng cdt thep tdi thieu va khong che vet nirt theo phien bin tu nam 2007, dong thdi giii thich mpt so sy khac nhau nay T C K H 6 A : Mat mat dng suit, co ngan, co ngot, td bifn, ty chung, ham lupng cdt thep toi thteu, khong che vet nyt.
ABSTRACT: To compare with AASHTO specifications 3'" editon in 2 0 0 4 , some articles in later versions from 2 0 0 7 are changed or added This paper presents some changes and consideration in calculating stress losses and checking in service limit stage such as minimum reinforcement and cracking control. Procedure in calculating stress losses considenng the effect of construction stage and limit for reinforcement as well as cracking control in later versions of AASHTO specifications from 2007 are shown and interpreted.
KEYWORDS: Stress losses, shrinkage, creep, relaxation, minimum reinforcement, crack control.
I . D A T V A N O i
6 Vift Nam, Tieu chuan thiet k l cau edng duoc ap dung thdng nhat trong e i nude dau t i l n t d 1979 la Tiiu chuin nganh 22TCN 18-79"', dUoc bien soan dUa t r i n cac tieu chuin cu nam 1 9 6 2 v i n i m 1967 eCia Nga.Trong giai doan t d nam 2001 d f n 2005, Tiiu ehuan 22TCN 18-79 va 22TCN 272-01'=' cung dUoe i p dung.Trong do,Tieu chuan 22TCN 272-01 dUOe bien soan t d AASKTO LRFD phien b i n 1998'*' cua My. v i dUoe Bd GTVT ban hanh de sddung tam thdi trong thdi gian 2 nam. Nhung d i n n i m 2005, Tiiu chuin 22TCN 272-05''", phiin b i n mdi cua 22TCN 272- 01 mdi duoc ban h i n h de ap dung 6 Viet Nam thay the h o i n toan cho 22TCN 18-79 v i 22TCN 272-01 .Tieu chuan 22TCN 272-05''", dUoe b i i n djch lai nhung van dua vao phiin b i n AASHTO LRFD 1998 .Tai nUde My th) phiin b i n
n i m 2004 da cd mdt sd difu khoin duoc thay ddi hoac/
v i t h f m vao. Nam 2005 v i 2006, mdt sd difu khoin cda phifn ban Tieu chuan AASHTO LRFD 2004'^' eung lien tuc dupe chinh sda va duoe tai b i n chi'nh thdc Ian thd 4 v i o nam 2007'*'. Tieu chuan niy edn tiep tuc t i i b i n Iin 5,6 v i 7 v i o eic n i m 2009,2012 v i 2014. Phiin b i n Iin thd7 da duoc chinh sda va xuat b i n nam 2016"^.
Bai b i o tap trung v i o mdt sd thay ddi trong Tieu ehuan cua AASHTO LRFD b i t dau t d t i i ban Iin thd4 n i m 2007 so vdi phien ban Iin thd3 n i m 2004 trong cich tinh m i t mat dng suat va mdt sd d i l u kifn trong trang t h i i gidi han khai thac nhu gidi han v f cdt thep va khdng c h l vet ndt trong ket c i u be tdng cdt thep (BTCT) thudng.
Nhdng ndi dung nay trong eic Iin t i i b i n sau niy d f u khdng thay ddi so vdi phien b i n n i m 2007. Do dd, khi tinh t o i n thiet ke cin luu y nhdng thay ddi nay.Trinh t u tfnh t o i n cic mat mat dng suit va cie dieu kien trong trang thai gidi han duoe trinh bay cu t h i de t h u i n t i i n cho vifc i p dung t i i u ehuan nay vao thUe t l .
2. MdT SO Ll/U y TRONG T F N H T O A N M A T M A T itNG SUAT
2.1. Tong mat mat dng suit
Td phifn b i n lan thd 4 n i m 2007 eua Tiiu chuin AASHTO LRFD cd mdt sd thay doi trong tfnh toan m i t mat dng suit so vdi phien b i n nam 2004.Tdng mat mat dng suat trong phien b i n nam 2004duac tfnh b i n g edng thde(1)vi(2).
"V^a- =A/;jj +i/"pj, +i/p„+A/-^, trong eau kien cang trUde (1) 'V,r-4''„+iV„*tfw*'V,™+'V,c,+'V„trong cau kifn cang sau (2)
Trong do: Afj. - Tdng m i t m i t dng suit; A / ^ A/"^
A/^, A / j ^ v i A/"^ - Lan luot l i m i t m i t dng do co n g i n d i n hdi cua be tdng do lUc DLfL, do ma sit gida cap v i dng ghen, do bien dang neo, do co ngdt, do t d bien va dotuchungeuaeip.
Trong khi do, trong cic phiin b i n t d Iin xuat b i n lan thd 4 nam 2007 trd dl, cdng thdc tfnh mat m i t du dng suit dUoc xem xet cu t h i theo tdng giai doan eua thi edng nhU: Ngay dd van khudn, ngay eang c i p (cit eip), ngay d6 he tdng ban mat ciu va den khi k i t c i u h i t thdi gian sd dung du kien. Cu the, viic tfnh mat m i t d u dng suit duac chia l i m 2 loai chfnh la mat mat tdc thdi v i mat m i t theo thdi gian. Mat m i t tUc thdi do co ngan d i n hdi, do ma sit gida c i p va dng gen v i do b i l n dang neo. M i t mat dng suit tdc thdi trong cic phiin b i n t d nam 2007 khdng thay ddi so vdi phiin b i n n i m 2004. Mat m i t dng suit theo thdi gian duoc chia Iim hai giai doan, giai doan 4 1
KHOA H p c - C O N G NGHE
thd n h i t duoe tfnh t d Iue b i t d i u cang cap den luc do b i n mat ciu, giai doan thd hai duoc tfnh t d sau khi dd b i n mat cau d i n luc k i t cau h i t thdi gian sd dung dU kiln. M i t m i t dng suat trong cac phien b i n t d n i m 2007 duoc tfnh theo eic edng thdc (3), (4) va (5):
4/',r=4/'„Es+'y,n, trong eau kien cing trUde (3) '<f,T=¥,.+¥M-Ki/,^-!-¥,,, trong cau kif n cing sau (4) 4VT=('V>.*'y",«+'yp,,L+(Af^+A/-,.Q,+v^:-Y,^)., (5) Trong dd: A/^j. - Mat mat dng suit theo thdi gian;
{A/pj„ + A ^ +A/^Hi^« ~ Lin luot l i mat mat dng suit do co ngdt, t d b i l n v i ttf ehung cua cap t d luc eang eip den Iue dd b i n mat cau; W^^„ + A / ; „ -H A/^, - A;;,,),, - Lin luot l i mat mat dng suit do eo ngdt, t d bien va t u ehung eua c i p va g i i m m i t m i t dng suit do co ngdt eua b i n mat eau t d Iue dd ban mat cau den luc k i t c i u h i t thdi gian sddung.
2.2. M^t mat Ung suat do co ngan dan hoi Trong cie phifn b i n eua Tieu chuin AASHTO, mat mat do CO ngin dan hdi trong c i p DLTL cing trudc ducjc xac dinh bdi cdng thdc (6) sau:
¥,,s, --^f^ (6) Trong do: E va E^^ - Lan luot la md-dun d i n hdi cua
cap D J L va b i tdng tai thdi diem truyln lUe DL/UX Cfng suit trong b i tdng d trpng t i m dam edt thep do fuc DLfL va tai trpng b i n than cua k i t eau gay nen.Tuy nhien, khi tinh /^ p h i i k l den ehfnh mat m i t dng suit cCia cap DL/L do eo n g i n dan hdi cCia be tdng. Trong thuc t l tinh t o i n , nhieu khi i n h hudng nay khdng dupc k l d i n . Cdng thdc de tinh / dupc the hifn d cdng thdc (7):
Trong d6:f - Lfng suit trong eip DL/L ngay sau khi truyln lUe; A. /, - Difn tfch v i md-men q u i n tinh eua mat c i t d i m ; e - Dp Ifch tam eua d i m edt thep den true trung h6a;M - Md-men do t i i trpng b i n t h i n . The edng thdc (7) vao eong thdc (6), ed the rut ra edng thdc tfnh mat m i t dng suit trong cap DL/L eang sau do eo ngan d i n hdi thuc chat dupc tfnh bdi cdng thdc (8):
..„('. " i ^ . K ^ '''
M i t m i t do co n g i n d i n hdi trong cdng thdc (8) mdi ehi tinh d i n giai doan cang cip. Khi d6 be tdng b i n mat c i u v i t i l trpng chit t h i m (DW), m i t m i t dng suit do co ngan d i n hdi 6 giai doan sd dung phai tfnh them thanh phan cd Ipi de lam g i i m dng suat eo ngan dan hdi trong cic bd cap do i n h hudng cCia tTnh tai giai doan 2 ngoai tai trpng ban t h i n d i m trong cdng thdc (9):
4 ^ ^ . = ^
A/^IJ: (9)
Trong dd: M^ l i md-men do t i i trpng eua ban mat cau;
e. /,^ va JWgi^ - Lan lUcrt I i dp Ifch tam cua bd c i p so vdi true tmng hda, md-men t i i trpng chit them v i md-men q u i n tinh eOa dam d giai doan sd dung.Tdng m i t m i t dng suat do CO ngin dan hdi dglai doan sddung ddpc tfnh theo edngthdc(lO):
¥^=^^,*^^2 (10) Trong cdng thdc (10), mat mat do co ngin dan hdi chi
mdi tfnh cho trudng hop d i m ehi c6 dam cdt t h i p d thd chju keo. Trong trudng hpp d i m ed cdt thep d thd chju nen, thi viic xac dinh mat m i t dng suit do eo n g i n dan hdi ^ d i m edt thep chju k i o va chiu n i n trd len phdc tap hun.
Ddi vdi trudng hpp eo n g i n dan hdi sd dung c i p DL/L eang sau, edng thdc tfnh m i t mat dng suat eho trddng hpp nay la cdng thdc (11) v i (12):
- y w - ^ - ^ / . . (11)
" " ^ ^ . „ ( / , - u ) * ^ f^^*
Gii tn mat mat dng suit trong cdng thdc (12) l i mit m i t dng suat trung binh cua eie bd eip DL/L.Tuy nhiin, khi sd dung c i p DL/L eang sau, cac bd cap thUdng duoc cang trinh tU tdng bd mdt. Rit ft khi t i t c i cac bd cap dupc cang ddng thdi. Vifc k l d i n trinh t d cing c i p dupc t h i h i i n qua sd bd cap N. Viee tinh toan nay k h i dOn gian va eho g i i tn g i n dung. Hon nda, trong qua trinh tfnh toan mat m i t dng suit n i y cdn chua ke den mat m i t dng suit do ma sit v i mat m i t do b i l n dang cua neo cap.
Gii sd trinh tucang cap DL/L t d 1 d f n N. Khi ke den trinh t d cing cac bd cip, cd t h i tinh t o i n m i t m i t dng suit eua tdng bd eip. M i t m i t dng suit cua bd eip cing cud!
cung N theo edng thdc (13) v i (14):
'*P•m{'g*^^e^s^'*g)+•
(13)
fp^m-fp>m -4^.(,v, -A/"^,^, (14) M i t m i t dng suit do eo n g i n dan hdi cCia cac bd k l
t i l p duac tfnh theo cdng thdc (15) va (16):
=/^,«-„-'y:.,.v-„-'V^,^
-Sv^
(15)
(16) Trong cdng thdc (15) va (16)/= 1 d i n N-l. Mat mat dng suat do co n g i n trung binh tai trpng t i m cic bd cap tinh theo cdng thdc (17):
^.m.=j^t^^.„ (17)
Tuong t u nhu trudng hpp eang trUde, trudng hpp cang sau eung phai ke d i n i n h hudng cCia t i i trpng phin 2 lam giam mat mat dng suit co n g i n dan hdi t i c dung ddng thdi I i n eic bd c i p nhU trong edng thdc (9) trong giai doan sddung.
2.3. Mat mat tTng suat do co ngot
Td phien b i n 2007 trd di, vifc tinh t o i n m i t mat do CO ngdt phdc tap hon v i xem x i t theo hai giai doan la trUde va sau khi dd b f tong mat cau. M i t mat dng suit do CO ngdt t d luc cang c i p den Iue dd be tdng b i n mat ciu duoe tinh bang cac edng thdc td{18) den (27):
¥^-^,^E^.K., (18) s.^-^^=k,k^k,k^^^,0.4SxlO-' (19) k,=l4S-'Q.]3{V/S)^i-0 (20) k^ =(2-0.014//) (21)
' - ^ < ^ ^ '
(23) 61-0.58/,H
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So 5/2016
ftA„-1.56-0.O08//
(24) (25) (26)
^ - - - a i - o . s ^ ; . , ^ - '27) Trong eae edng thdc t d (18) d i n (27): s^,^ - Biln dang
do eo ngdt cua c i u k i i n tU luc cang c i p d i n ICie do ban mat eau; K_^ - H f sd mat c i t bj b i l n ddi t d luc cang e i p d i n luc dd ban mat c i u ; A^ - H i sd i n h hudng cua ty sd gida the tich, V- Difn tich be mat, 5 eua ket c i u ; k^- He sd k l d i n i n h hudng eua cudng dp chju n i n eua be tdng tai thdi d i l m cang c i p , / ^ , it^ v i h^ - Lan lupt la he sd cho tinh t o i n co ngdt v i t d bien k l d i n dd i m cCia mdi trudng, H; k^^ - H f sd k l den sU p h i t t r i l n eua co ngdt theo thdi gian; ^,^^^^^j va -t^^^ - Lan lUOt tinh den iue do mat c i u va d i n h i t thdi han sd dung cda ket cau; '^/t ,t) - Hf sd t u b i l n cda eau kien d i n thdi d i f m k i t c i u dat tudi tho thiet ke; t^ t/t^J. t^(tj^J - Lan lucrt l i tudi cua be tdng tdng luc cing cap (cit cap), khi do be tdng b i n mat cau v i khi h i t han sddung.
Mat mat dng suit do eo ngdt sau khi do be tdng b i n mat c i u d i n h i t thdi han sd dung eua k i t c i u , A/"jp dupe tinh theo cie edng thdc t d (28) d i n (31):
^ho = ^t^E^,K,j (28) (29)
(30) (31)
. ^ > .
0 7T.{<,.0]Trong do: z^ - Biln dang do co ngdt cua c i u kifn tdsau iue do b f tdng b i n mat ciu; e^^,-Bien dang doco ngdt eua cau kien t d Iue eing eip d i n sau Iue het thdi han sir dung ci!ia k i t cau; k^- He sd k l d i n i n h hudng cCia cudng do chju nen cCia be tdng den luc dat cudng do thift k l ; K^- Hf sd mat c i t bj bien ddi t d sau khi do be tdng b i n mat cau; e - Dd Ifch tam cua cie bo eip DJL so vdl true trung hda d giai doan sddung.
Sau khi dd be tdng b i n mat cau, do sU eo ngdt cOa b i n mat c i u l i m g i i m m i t mat dng suit theo thdi gian.
Gii tri g i i n i dng suit trong c i p do co ngdt eCia b i n mat c i u ddpc tinh b i n g cdng thdc t d (32) d i n (35).
(33) (34) (35) Trong do: E ^ - Bien dang do t d b i l n cCia be tdng b i n mat c i u ; ft, - Hf sd i n h hudng cCia ty sd giOa the tfch v i d i i n tieh b l mat eCia b i n mat cau; A,^^^ - He sd ke d f n su p h i t trien do co ngdt cua b i n mat c i u d f n h i t thdi han sd dung cCia k i t eau;/'^, - CUdng dp chju nen cua b i tdng b i n mat cau tai thdi d i l m b i t dau gia t i i , thudng liy bang 0,8/V "^/'/j " ^^ ^^ ^^ '^'^" '^^^ ^^^ "lat c i u tai thdi diem dat tuoi tho t h i l t ke.
2.4. Mat mat dng suat do tir b i l n
Trong cie phien b i n t d n i m 2007 trd di, m i t m i t dng suit do t d bifn t d Iue cang c i p den Iue do be tdng b i n mat c i u dUpe tinh theo eie edng thdc t d (36) va (37):
'^^,=^U^.['..t,)K, (36)
*.('..',)=i.9*,*..*/W../,"*"" (37) Trong do: '^/tj.t^ - He sd t d bien cua eau kiin t d thdi
d i l m eing cap d i n khi dd b i tdng b i n mat c i u . Cdng thdc tinh t o i n mat mat dng suit do t d bien t d sau khi dd b i tdng b i n mat ciu, Af^^ dugc tinh theo eie cdng thdc t d (38) d i n (42):
Af,c==4f.™+A/;aii (38) o^^i = ^ K (',,',}-*.('..', )k* (39) '^^o^=^^M'f'X; (40) T,(/,,/^}=1.9i,M/*«ow,',Z', (41) Y . = - w , . * A r ^ * 4 r , . , ) ^ [ i ^ ^ ) - ^ - ^ (42)
Trong do: A/^^, - Mat mat do t d bien do lUe DL/L va tinh t i i b i n than dam; A/^^^ - Phan giim mat m i t dng suit t d biln do tai trpng ban mat cau va t i i trpng chit them; A/^^ - SU thay ddi dng suit d trpng t i m eac bd eip do mat mat dng suit theo thdi gian t d luc eang c i p d i n luc do be tdng ban mat cau, cd ke den tai trpng cua b i n mat c i u va t i i trpng chat them (DW); M^ va W^.^ - Md- men do t i i trpng cCia ban mat eau va t i i trpng ehit t h i m ; e v i / - Lin lupt la dp lech tam cua cap DL/L vdi true trung hda v i md-men quan tinh trong giai doan eang eap;e v i / - L i n lupt la dp lech tam eua e i p DL/L vdi true trung hoa v i md-men quan tinh trong giai doan sddung.
2.5. Mat mat i2ng suat do t u c h i i n g
Trong eac phien ban cua Tiiu chuin AASHTO t d n i m 2007 trd di, m i t mat dng suit do t u ehung trude va sau khi do bf tdng ban mat cau duoc tinh t o i n don g i i n hon v i b i n g eac cdng thdc (43) va (44):
Trong do: K^ lay bang 30 cho trUdng hpp tao c i p va lay b i n g 7 cho cac loai thep Dl/L khac. Khi mudn tinh t o i n chinh xac hon, mat mat do t u chijng trudc va sau khi do be tdng b i n mat cau dugc tinh b i n g cdng thdc (45):
(45) Trongd6:K\ lay bing 45 cho tnJdng hpp eip tUchiJng thap va bing 10 cho thep DL/L dupc khd dng suit; / - Tudi cGa be tdng Iue do b f tdng ban mat cau (ngiy); (-Tudi eiia b i t d n g ILIC truyln Iuc;iir^^-Tinh theo edng thdc (24).
3. MOT S6 Ll/U t K H A C T R O N G TRANG T H A I SO^DUNG
3.1. Gidi han v l cdt thep
Quy dinh v l lUpng cdt thep tdi thieu p h i i du de p h i t t r i l n sdc khing udn tinh toin. A/, bing gia trj nao nhd hon trong hai g i i trj sau: 1,2 lan md-men khang nult, M^
43
KHOA H O C - C O N G N G H E
va 1,33 Ian md-men tinh t o i n , M^.Trong phifn ban 2004, md-men khing ndt chi ke d i n i n h hudng cda k h i nang khang ndt eua vat lieu, cu the la b i tdng v i d i e trung hinh hpc cCia mat eit v i dupe tinh theo cdng thdc (46), gia tri nay la gia trj gidi han nhd n h i t cd the cua mat cat.
M„=/,-^ (46) Td phifn b i n nam 2007, quy djnh v f luong cot thep
tdi da dupe loai bd. Md-men khang ndt cua mat cat xem xet i n h hudng cda tTnh t i i b i n t h i n k i t eau, b i n mat eau v i khdng dupe vupt qua anh hudng do luc DUL va k h i nang sdc khang ndt cda v i t l i i u gay ra. Md-men khing ndt dupe tinh theo edng thdc (47):
^ . = - S , U - / , ^ ) - w ^ [ | ^ - i l ^ 5 , / . (47) Trong d&.f^ - Cudng dp chju keo udn; y^ - Khoing
cieh t d tryc trung hda d f n thd chiu keo ngoii c i j n g ; ^ - Cudng dd chju nen trong b f tdng d thd chiu keo ngoai cijng do lUc DL/L gay ra; S^ - Md-men quan tinh tmh ddi vdi thd ngoai cung chju k i o cua mat c i t tai giai doan sd dung; .S^- Md-men q u i n tinh tTnh ddi vdi thd ngoii cung chju keo ci!ia mat c i t tai giai doan eang c i p ; M ^ - Md- men do tinh t i i t i c dung trong giai doan cang cap va chua k l d i n h f sd t i i trpng.
3.2. Khdng die vetnutbSng phan bdcdtthep thudng Trong phien b i n tieu chuan xuat b i n nam 2004, d l khdng che vet ndt trong k i t c i u BTCT thudng, dng suit trong cdt thep thudng dupc tao ra sao cho khdng q u i gia tri trong edng thdc (48);
/ . . - ( ^ ^ W . (48) Trong dd: d^ - Chifu cao p h i n b i tdng tinh t d thp
chju kfo ngoii cCing d f n t i m cCia thanh thep gan nhat (khdng dupc Idn hon 50mm); ^_. - Difn tich cCia phan be tdng cd cCing trpng t i m vdi d i m cdt thep chju keo dupc tao bdi cie m i t c i t ngang va duPng t h i n g song song vdi true trung hda, chia cho sd lupng thanh thep; Z - Thdng sd be rdng vet ndt phu thudc vao dieu kien mdi trudng.
Viec tinh toan theo phuong phap nay ed mdt sd han che. Khi mudn g i i m dng suit trong thep, chi can tang chilu d i i t/,. Rd ring d i l u niy la khdng hpp Iy trong ket c i u khi tang chilu d i y b i o vf, die bift l i k i t cau cd chieu cao dam khdng IPn. Vtfc tinh t o i n difn tieh A cOng r i t phdc tap, dac biet l i khi edt thep khdng dupc bd tri theo hinh chd nhat trong nhdng mat c i t d i m cd hinh dang phdc tap. Con mdt d i l m nda I i k i t cau be tong do tai cho hay due sin se cP cie y f u cau chieu d i y bao ve khac nhau.
Trong phien ban nam 2007, vifc khdng c h l vet nilt phu thudc v i o chilu day Idp b i tdng bao ve v i khoing cich cCia cac thanh thep d Idp gan be mat thd chju keo nhat. Khi khoing each gida cac thanh cdt thep d thd gan thd ngoai eung chiu k i o thda m i n cdng thdc (49) va {50}
th) vet ndt trong k i t cau BTCT thudng duoc khdng ehe:
^123000?', „ ,
Trong dd: rf. - Chieu cao p h i n be tdng tinh t d thd
44
chiu keo ngoai cung d i n t i m eua thanh thep g i n n h i t ; h - Chilu cao mat eit cCia k f t cau; Y_. - He sd k l d f n mdi trudng nOi kft cau t i l p xue, lay b i n g 1 trong dieu kien mdi trudng it x i m thue nghiem trpng v i l i y b i n g 0,75 trong d i l u kien mdi trudng x i m thuc nghiim trpng;.^ - C/ng suit keo trong cdt thep thudng dtrang t h i i gidi han sCf dung. SCf dung phuong phap niy thuc c h i t t i k l d i n b i n kinh i n h hUdng eua edt t h i p I i n be tdng. Do dd, vile SLf dung khoang each eac thanh thep v i chieu day b i o v f cdt thep cd the gidi han dugc v l t ndt ma khdng i n h hudng den eie loai ket c i u khie nhau.
4. KET LUAN
Cac p h i i n b i n mdi cua Tieu ehuin AASHTO LRFD thudng dupe dieu ehinh h i n g n i m . Mdt sd dieu khoin cd t h i dupc thay the hoan toan dUa t r i n thuc nghifm d l Iim cho k f t q u i t h i l t k l an toan va s i t vdi g i i tri thuc te hon. Mdt sd dieu k h o i n dupe thay ddi cd the lam cho vifc tinh toan trd nen don g i i n hOn hoac phdc tap hon.
D i e b i f t l i tinh t o i n m i t m i t Ung suat, tinh t o i n khdng che vet ndt.
Bai bao nay da neu len sU thay ddi gida cic phifn ban t u sau nam 2007 so vdi nam 2004. Td k i t q u i phan tich t r i n cd t h i thiy, vifc tinh t o i n mat mat dng suit do CO n g i n d i n hdi v i theo thdi gian l i r i t phdc tap v i r i t de bj nham lan do k l d i n q u i trinh thi cdng cCia k i t c i u . Vdi viec l i l t ke cu t h i trinh tU tinh t o i n trong b i i b i o cd the lam eho viec tinh toan trd len dOn g i i n hOn.
Trong phien ban 2007 cung x f t den d i y dCi cac ylu td cd the i n h hudng d i n md-men khang ndt cCia mat cit nhu tinh tai b i n than k i t c i u , b i n m i t c i u , lyc DL/L v i kha nang khang ndt cCia v i t lifu. Vdi vifc thay dot tfnh toan niy, cd t h i t i l t k i i m t h i p hon trong thiet k l . Vif e sCf dung khoing eich cie thanh thep d Idp ngo&i gan thd chju k i o ngoai ciing nhat va be day eCia Idp b i tdng bio vf p h i n anh thue chat hon sU khdng c h l v l t ndt trong kft c i u BTCT thUdng va han chf nhdng nhuoc d i l m cCia phuong p h i p da nfu trong phien b i n n i m 2004.
Tai lieu tham k h i o
[1], 22TCN-18-79, Quy trinh thiet ke cdu cdng theo trgng thdi gidi hgn, 1979.
[2122TCN272-01, Tiiuchudn ThiitkiCdu. 2005.
[3]. AA5HTQ LRFD Bridge Design Specifications, 2"' edition, 1998.
[4]. 22TCN272-05, Tiiu chudn Thietkecdu, 2005.
[5]. AASHTO LRFD Bridge Design Specifications, 3"*
edition, 2004.
[6]. AASHTO LRFD Bridge Design Specifications, 4"' edition, 2007.
[7]. AASHTO LRFD Bridge Design Specifications, Customary U.S. Units, 7th Edition, with 2015 and 2016 Interim Revisions.
Ngay nhan bai: 12/4/2016 Ngay ch^p nhan dang: 5/5/2016 Ngudi phin bien: PGS. TS. Le Van Nam