Nghien CLFU mo hinh c a che lam viec cua ong noi thep cho cot thep thu'ang dung trong ket cau be tong cot thep lap ghep
Ngay nhan bai: 4/12/2013 Ngay sira bai: 11/12/2013 Ngay chap nhan dang: 28/12/2013
Nguyen Dinh Hung, Chu Quoc Thang
T ( 5 M TAT:
Bai bao nay trinh bay nghien cflu ve co che lam viec cfla ong noi bom vfla cho cot thep thfldng trong Icet cau phan doan iap ghep.
Ba loai ong noi dfldc danh gia. Ong noi NMB cd dfldng kinh ngoai nho hen nen thi cong vdi ong noi NMB cd the don gian ban so vdi ong noi LK va D410. Tuy nhien pha buy tai gifla ong NMB, hay pha huy cua cdt thep dflOc noi tai dau noi ren va pha huy do ren d ong noi LK can dfloc xem xet. Ong noi NMB va LK dflpc mo hinh bang mo hinh 3D, cac mo hinh vat lieu dfldc phan tich, dac biet la mo hinh dinh bam gifla vfla vcii thanh thep va dng noi bang phan tfl tiep xflc. Ket qua phan tich kha giong vdi ket qua thi nghiem.
Tfl khda: Ong noi bom vfla, ket cau lap ghep, phan tfl tiep xuc.
ABSTRACT
This paper presents analytical study on mechanical behavior of splice sleeves for normal reinforcement of precast segmental concrete structures. Three splice sleeves were evaluated.
Diameter of NMB splice is smaller than that of LK and D410 splices. So construction with NMB may be simpler than others.
However, splice fracture failure in NMB splice, bar fracture and thread failures of LK splice need to be considered. Splice sleeves were modelled by 3D modei> Constitutive laws of all materials were analysed, especially in bonding model between grout and splice or bars by interface element. Analytical result shows a good agrrement vrith experimental result 1).
Keywords: Splice sleeve, precast segmental concrete structure, interface element.
TS Nguyin Dinh Hung
Trfldng dai hoc Quoc te - Dai hoc Qudc gia Tp. Ho Chi Minh, Di dong: 01688 488 H I
Email: [email protected] PGS. TS Chu Quoc Thing
Trfldng bo mon Ky thuat xay dflng - Trfldng dai hpc Quoc te Dai hoc Quoc gia Tp. Ho Chi Minh
Di dong: 0913 725 364 Email: cqthangrahcmiu.edu.vn
l.GlOlTHieu
Viec x i y dung cic cau can trong t h i n h pho bang cdng nghe lap ghep ket hpp vdi sfl dung dng ndi vfla cho cdt thep thudng cd the mang lai hieu q u i ve mat kinh te nhU tiet kiem thdi gian thi cdng, g i i m un t i c giao thdng, g i i m khdi lupng vat lieu, kiem soat dUpc chat lupng be tdng. Hon nfla, de day nhanh tien dp thi cong va kiem soit chat lupng trong cac cdng trinh n h i cao t i n g , ket c i u l i p ghep cung l i mdt lUa chpn thfch hpp.
Trong ke't cau lap ghep, viec ndi cdt thep thudng cd the i n h hudng den c h i t lupng cfla ket cau. Mat khac, ket hpp vdi sfldung thep d u flng luc, su khdng lien tuc cfla cdt thep thudng tai cac mdi ndi cung i n h hudng den k h i nang chju luc cua ket cau lap ghep. Do dd, viec i p dung dng ndi bom vfla de ndi cdt thep thudng la mdt trong nhUng g i i i phap c i i thien d i n g ke k h i n i n g chju luc cua ket cau lap ghep.
Ap dung cic s i n pham dng ndi tLr nudc ngoai thudng cd gia t h i n h rat cao, do p h i i n h i p khi'u vat lieu, nen viec ap dung cua dng ndi cho cdt thep thudng chua chiem Uu the trong xay dung. Do dd, nghidn cflu cdng nghe dng ndi sfl dung v i t lieu dja phUOng de lam giam g i i t h i n h l i mdt van de cap thiet, gdp phan v i o g i i i quyet van de cua x i hdi. Trong b i i bao nay, nghien cflu md hinh mdi noi cdt thep cho ket cau lap ghep bang dng ndi bom vfla dupc thuc hien. Tren co sd do d i n h g i i uu nhupc diem cua mdi noi cotthep cho ket cau lap ghep tai Viet Nam. Sudinh bam gifla vfla vdi dng noi thep v i cdt thep thfldng can ndi dupc xem xet v i d i n h gia de hieu co che lam viec cua mdi ndi sfl dung dng ndi bom vfla. Trong md hinh, phan t f l tiep xuc dUpc i p dung de md t i sU dinh b i m gifla vfla vdi dng ndi va cdt thep. Cac md hinh cua vat lieu se dupc d i n h g i i de lam s i n g t d cP che lam viec cua dng ndi.
2. cAc LOAI 6 N G N 6 I
2.1 Cac loai dng ndi bcnn vura cho ket cau BTCT iSp ghep 6 n g ndi bom vQa de ndi cdt thep thudng trong ket cau lap ghep thudng dung la loai Lenton Interlock (LK), dng ndi NMB v i D410 n h u trong Hinh 1.
Cic dng dupc thiet ke sao cho cd flng s u i t tdi han Idn hon 125% flng s u i t c h i y cua cic cdt thep dUpc ndi. 6 n g ndi cd kich thudc khac nhau phu thupc v i o dudng kinh cfla thanh thep dupc ndi. 6 n g ndi LK v i dng D410 cd flng suat chay la 448 MPa. Ong ndi NMB co flng suit c h i y la 413 MPa hoac 590 MPa. 6 n g ndi LK cd mdt dau dng noi vdi thep bang ren.
Budng kinh ren nhd dan t f l trong ra ngoai. Chieu dai doan ndi bang ren t f l 22mm den 70mm. 6 n g ndi NMB v i D410 sfl dung vfla de ndi thanh thep d c i hai dau.
C i ba loai dng ndi deu sfl dyng cic g i n ben trong Idng dng de t i n g cudng dinh b i m gifla vfla va dng. G i n dflpc bd tri tren toan bd chieu d i i Idng dng LK. 6 n g NMB chi cd t f l 4 den 7 g i n dupc bd tri t f l dau mdi dng. Khoang c i c h cac g i n trong dng LK va NMB la 15mm. Trong khi dd, k h o i n g each c i c gan trong dng D410 la 17,8mm. Hau het dng D410 cd
oi.2oi4BiiinH:ifln i s i
C )
I dng noi LK
dudng kfnh ngoai va chieu d i i dng ldn hon cic dng cdn lai. Dudng kinh ngoii cua dng LK hoi nhd hon so vdi dng 0410. DUdng kinh ngoai cua dng NMB la nho nhat. Chieu d i i cfla dng NBM nhd hon dng D410 mpt chut. Chieu dai cua dng LK l i nhd nhat. Cd the ndi, vdi kich thudc nhd gpn hPn hai dng cdn lai, nen thi cdng dng ndi NMB don g i i n ban.
2.2 So sanh cac dieu kien ap dung d Viet Nam
Cdt thep cho ket cau be tdng cdt thep cung cd sU khic nhau gifla cic nudc. d Viet Nam, ket c i u be tdng cdt thep (BTCT) trong cong trinh x i y dung d i n dung, cdng nghiep v i giao thdng thuy lpi v i cic cdng trinh khic, cdt thep van theo tieu chuan TCVN 1651-2-20081) gdm cic loai nhu CB300V, CB400 va CB500 vdi gidi ban c h i y tuong flng l i 300 MPa, 400 MPa v i 500 MPa. Cic thanh thep cd dudng kinh t f l 10mm den 50mm. d My, cdt thep dung cho ket c i u BTCT l i theo tieu chuan ASTM A615 cd gidi han c h i y la 420 MPa v i cd dudng kinh t f l 10mm de'n 57mm. Thep v i n cho ket c i u BTCT d Nhat Bin theo tieu ehui'n JIS G 3112-2004 cd c i c loai SD295A cd gidi han chiy la 295 MPa, loai SD295B cd gidi ban chiy t f l 295 den 390 MPa.
Cdt thep v i n cua N h i t Bin cd dfldng kinh t f l 6,36mm den 50,8mm.
Nhu viy, dudng kinh cdt thep theo tieu ehui'n cua My, N h i t Bin v i Viet Nam l i tuong dUflng. Gidi ban c h i y cua My yeu c i u trong ket cau BTCT l i cao hon so vdi Viet Nam va N h i t B i n . C i ba loai dng ndi LK, D410 va NMB cd the ndi cdt thep loai CB300V va CB400V cd dUdng kinh t f l 16mm trd len cho ket cau BTCT cua Viet Nam. Ddi vdi cdt thep CB500V, dng ndi NMB cd flng suit c h i y Idn hon 590 MPa cd the sfl dung.
S.MOHlNHVATLieu 3.1 Ket qu^ thiTcnghiem
Bai b i o nay tien h i n h md hinh dng noi LK va NMB. Ket q u i cua md hinh dupc so sanh vdi ket q u i thf nghiem bdi Janson2) de k h i n g djnh tinh dung dan cua ket q u i p h i n tich. Thi nghiem dupc thUc hien vdi bdn td hpp. Hai td hop sfla dung dng ndi NMB va hai td hpp sfl dung dng ndi LK. Thep v i n dupc ndi cd dudng kinh la 19mm v i 36mm. Vfla l i vfla cfldng dp cao, dupc s i n xuat bdi mdi cdng t y Cudng dp chju nen cua vfla tai thdi diem 28 n g i y cho dng LK v i NMB lan Iflpt l i 101,3 MPa v i 103,4 MPa.
Lfng suat c h i y va flng suat keo cua dng NMB cho cdt thep cd dudng kinh 19mm va 36mm lan Iflpt la 356.5 MPa v i 605.4 MPa, 524.0 MPa
bj ong no! NMB
Hinh 1: Cac loai ong noi bom viia v i 900.5 MPa.
I l l I
a) dng ndi NMB b)dngndiLK Hinh 2: Mo hinh phan tich d a ong ndi, vda, thanh thep, dinh bam cda vda vdi dng noi va thanh thep, dng ndi vdi thanh thep cua LK
3.2 Md hinh vat lieu cho dng ndi, thanh thep va vCra
Viec md hinh cic mdi ndi dflpc tien hanh bang phan mem chuyen dung va dupc the hien d Hinh 2. Cdt thep ndi cd dfldng kinh 19mm v i 36mm, nen ten mau la 16-NMB, 36-NMB, 16- LK v i 36-LK. Thanh thep, vfla va dng ndi dupc md hinh bang cic phan t f l solid cd kich thudc 5x5x5mm. Quan he flng suit bien dang cfla dng ndi v i thanh thep dupc md hinh b i n g md blnh din dio.
Cing xfl cua vfla khi chju nen dupc md phdng theo md hinh cfla Thorenfeldt et al.". Md hinh cua vura khi chju keo dupc dua theo md hinh Hordijk"'. Or\g suit keo cua vfla dupc x i c djnh dua vao cdng thflc Eq. (1) theo tieu ehui'n thiet ke cua Hpi x i y dung N h i t Bin (JSCEj^
f, = 0 . 2 3 ( f , 0 i , 1 , Trong dd, f, l i flng suit chju keo, f^^ la flng
suit chju neo cfla be tdng.
3.3 Mo hinh vat lieu mo ta dinh bam cua vfla dng noi va thanh thep ndi
Vdi dng ndi bom vfla, lUc truyen qua sU tiep xuc gifla vfla vdi dng ndi va thanh thep. Do dd md hinh dinh b i m cua vfla vdi dng ndi va thanh thep cung p h i i xem xet ky ludng. Sutiep xuc gifla vfla vdi dng ndi va thanh thep dupc md t i bang p h i n t f l tiep xuc. Cfng xfl cua p h i n t f l tiep xuc dupc d i e trung bdi g i i trj dp cflng theo phuong p h i p tuyen, k^ va theo phuong tiep tuyen l i k,. Trong gia doan d i n hdi, dieu quan trpng l i ket c i u khdng bi p h i n t i c h . Vdi ly do do, g i i trj k„ v i k, p h i i du l d n " de md t i sutiep xuc gifla vfla vdi dng ndi v i thanh th^p.
Tuy nhien, g i i trj dp cflng ban dau p h i i du nhd de t r i n h c i c v i n de trong p h i n tich sd". Do do, viec xac djnh g i i trj dp cflng ban dau cho phan t f l tiep xuc la dua tren kinh nghiem. Trong md hinh nay g i i trj dp cflng ban d i u theo phuong
c) dng no! D410
p h i p tuyen, kn v i tiep tuyen kt dflpc l i y l i n lupt l i 1000 MPa va 125 MPa.
Cd rat nhieu md blnh vat lieu mieu t i sir dfnh b i m gifla vfla v i thanh thep. Nam 1990, CEB-1997) de xuat md hinh quan he gifla flng suit dinh b i m T v i bien dang trupt s dupc the hien bdi cdng thflc t f l Eq.2 den Eq.5 v i trong Hinh 3.
^=tmax(s;f s ) " v d i O < s s s , (2) 1=^ max vdi S, < s < S; (3)
T = T, vdi Sj < s (5) Trong dd, T^^^ va x^ l i flng s u i t dinh b i m
Idn nhat va flng suat khi p h i buy, s,va s^ la bien dang trupt khi flng suattrupt Idn nhat, s, la bien dang trUpt khi dfnh b i m bj p h i buy.
Dieu kien dfnh b i m cung i n h hudng den dp Idn cua flng s u i t dfnh b i m . Einea" de suit g i i trj flng suat dinh bam Idn nhat la:
k^/^ (7)
Trong do k l i he sd phu thudc vao dieu kien dfnh b i m . 6 n g ndi cd vdng thep ben trong d ngay dau dng, Einea" de s u i t k = 2.24 vdi cUdng dp chju nen cfla vfla la 68.95 MPa. Dfla tren ket q u i thuc nghiem, Bamonte va Gambarova"
de s u i t gia trj cho flng s u i t dinh b i m Idn nhat l i 0.45f'c. Nhu v i y , g i i trj k cfla Bamonte va Gambarova l i 3.74. Cic gan trong dng NMB v i LK tuong t u nhu cac vdng thep trong thi nghiem cua Einea de tang cUdng sU dfnh b i m gifla vfla v i dng ndi. G i i trj k trong ket q u i thf nghiemi) l i 2.7 v i dupc i p dung trong md hinh p h i n tfch nay. Qng s u i t dfnh b i m pha hoai, T,
= ^•^'^m.J'- "^'^ *'•! ^1 v^ ^2 1^" iLTpt la 0,5mm va 1,5mm. Gia trj Sj l i nila k h o i n g c i c h tai c h i n hai g d cdt thep". Lien ket bang ren d dng LK cung dupc md t i bang phan t f l tiep xuc ndi cflng vdi gia tri dp cflng ban dau theo c i hai phuong phap tuyen va tiep tuyen la 200 GPa
4. SO S A N H KgT QUA PHAN T(CH VOl K^T QUATHINGHIEM
Ket q u i thf nghiem" cfla dng LK vdi thanh thep 016 l i p h i huy do dflt thanh thep tai c i c
132|BIIini:[iBIX 01.2014
a ) D 1 6 - L K v a D 3 6 LK b ) D 1 6 - N M B v a D 3 6 N M B Hinh 4: Bien dang trUcrt giiia thanh thep va viia
a ) D 1 6 - L K v a D 3 6 LK b ) D 1 6 - N M B v a D 3 6 N M B Ghi chu: mau do the hien bien dgng ldn han
Hinh 5: Bien dang ciia vUa tai t h d l diem lite gay ra bien dang chay cua mau
800.
0 2 0 4 0 6 0 8 0 Hinh 6: Quan he lite keo va bien dang dpc true
ndi va do tudt ren dupc loai trfl, flng suit c h i y trong cic md hinh tuong flng vdi flng suit c h i y cua cic thanh thep. G i i tri luc tdi ban cung Idn hon 125% g i i trj Iflc gay ra flng suit c h i y cua cac thanh thep. Dieu do chflng td sfltin c i y cua md hinh p h i n tfch.
5. K^T L U A N
Viec hieu ro ve co che lam viec cua mdi ndi bom vfla cho ket c i u lap ghep giup cho viec i p dung ket c i u an toan v i hieu q u i hon. Trong b i i b i o niy, mdt sd loai dng ndi d i dUpc so sanh v i d i n h g i i . Budng kfnh dng ndi NMB nhd gpn hon so vdi cac dng ndi LK v i D410 nen thi cdng don g i i n hpn. Phi huy d ren ciia LK va d gifla dng ndi NMB can p h i i chu y trong q u i trinh i p dung. Do dd dudng kfnh sau khi bj tien ren cd the sfl dung de tinh t o i n . Cic md hinh vat lieu cua dng thep, thanh thep, vfla v i d i e biet la md hinh dinh b i m gifla vfla v i thanh thep dflpc d i n h g i i va de xuat. Ket q u i chi ra r i n g sU bien dang do trupt gifla thanh thep va vfla d i x i y ra. Cing suit Idn n h i t trong vfla xuat hien d p h i n vfla tai dau dng ndi. Quan he t i i trpng bien dang cua cic md hinh tuong ddng vdi ket q u i thuc nghiem.Tfldd cic md hinh v i t lieu cd the sfl dung de lam cic nghien cflu tiep theo vdi cac ket c i u lap ghep i p dung dng ndi bom vfla cho cic thanh cdt thep thUdng.
d i u ndi ren. Ddi vdi thanh thep D36, mdt mau p h i buy n h u mau D16, hai mau cdn lai p h i buy do tudt ren. Do p h i buy d d i u ndi ren nen lUc g i y ra flng s u i t c h i y cfla mau nhd hon so vdi luc g i y ra flng suat c h i y cua thanh thep. Oieu n g i y la do dien tfch cfla thanh thep bi thu hep tai dau mdi ndi ren. Bdi vdi dng NMB, hai mau D16 va mdt mau D36 bj p h i hfly do dflt thanh thep dflpc ndi 6 ngoai mdi ndi. Mot mau dng ndi D16 p h i hfly do bien dang trUpt cua vfla v i thanh thep, hai mau dng no! D36 cdn lai p h i hfly do dflt dng ndi. Bdi vdi mau p h i buy tai thanh thep v i p h i hfly do bien dang trflpt, flng suat chay cfla mau la flng s u i t c h i y cua thanh thep. Ddi vdi mau g i y ra p h i hfly tai dng ndi, flng suit c h i y cfla mau l i flng s u i t c h i y cua dng ndi. Tuy nhien, bien dang trUpt do sU dfnh b i m gifla vfla va thanh thep xay ra trflde khi mau p h i buy d tat c i c i c mau thf nghiem. LUc tdi ban trong tat
c i c i c mau Idn hon 125% lUc g i y ra flng suit c h i y cua thanh thep. Do dd, thda man yeu cau ve dng ndi bom vfla theo tieu chuan AASHTO LRFD'°i.
Ket q u i p h i n tfch cua c i c mau thf nghiem ehi ra rang bien dang trUpt gifla vfla v i thanh thep x i y ra d t i t c i cac mau n h u Hinh 4. SU p h i hfly d gifla dng ndi khdng xay ra do chieu d i y cua dng ndi bao gdm ca g i n . Phi hfly do tudt ren cung khdng xay ra do phan ndi ren dupe md t i bdi len ket cflng. Bien dang cua vfla trong eic dng nhu trong Hinh 5. Bien dang Idn nhat cfla vfla t i p trung d dau dng ndi v i d phia g i i p vdi thanh thep. Oieu nay l i do vfla khdng bj chju ep ngang. Do dd g i y ra bong vfla tai dau dng ndi nhu ket q u i thf nghiem". Quan he t i i trpng va bien dang cfla md hinh duoc the hien tren Hinh 6. Sfl p h i t trien cua tai trpng v i bien dang kha gidng vdi ket q u i t h i nghiem. Do p h i buy 6 dng
TAI Litu THAM KHAO
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