Ảnh hưởng của ăn mòn đến khả năng chịu uốn của dầm bê tông cốt thép tiết diện chữ t

Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (263.57 KB, 3 trang )

(1)<div class='page_container' data-page=1>

Anh hLPang cua an mon den kha nang chju uon cua

dam be tong cot thep tiet dien c h i j t

Effect of corrosion on degradation offlexural strength inT-section reinforced concrete

beams.

Ngay nhan bai: 11/10/2014

Ngay sita bai: 8/11/2015

Ngay chap nhan dang: 10/12/2015

T O M T A T :

An mon cot th^p dildc xac dinh la mot

nguyen nhan quan trong dan den sd pha

huy ket cau be tong cdt thep (BTCT)

trong mdi trdtfng c6 tinh an m o n cao n h d

trong moi trddng b i l n . Bai bao nay

n g h i l n cdu sii suy giam kha nang chiu

uon cua cau kien dSm b l tdng cdt thep c6

tilt diet dien chC T chiu anh hudng cua

tac nhan an mon. Kit qua cua bai bao co

t h i l i m tdi H?u tham khao cho cac cdng

tac thiet ke, tham tra, kiem dinh cac ket

cSu lam viec trong moi tnfdng ven b i l n .

Tii khoa: Kit c i u b l t6ng, an mon, kha

nang chiu u6n.

ABSTRACT:

Corrosion of steel reinforcement is

identified as a significant cause of damage

in reinforced concrete structures exposed

to corrosive environment. The paper

studies the flexural strength degradation

of T-section reinforced concrete beams

due to corrosion. The results of the paper

can make reference to the design,

verification and inspection of reinforced

concrete structures in coastal

environments.

Keywords: Reinforced concrete,

corrosion, flexural strength.

D i o Ngpc T h i Ltfc

T n t d n g Dai hoc Bach Khoa - Dai hpc

Da N i n g

TrSn Dinh Manh Linh

Tnicfng Dai hpc K i l n Tnic Da Nang

1 . G i t i t h i # u

Su an mon cau kien be t o n g la m6t v^n de
mang tinh cap thiet tren toan cau. Cac tac nhSn
an mon la mot trong nhutig nguyen nhan hang
dau gay nen sU suy giam kha nang chiu lUc cua 
cac cong trinh, dac biet la cac cong trinh ven
bien.Hien nay, co rat nhieu de tai nghien cuU ve
ii(ngxCrcuaketcauBTCTdu'6isU3nhhi/dngcua
cac tac nhan an mon. C^c de tai chii yeu nghien
cuU ve thdi gian an mfin, su hinh thanh phat
trien cCia cac vet nilt cung nhif sif suy giam lUc
dinh giua be t6ng va cot t h e p bj an m o n [2],[

3],[ 5-7]. Rat hiem de tai sU suy giam Wia nang
chiu uon (M^) cua cau kien do tac nhan gay an
mon, nhat la suy giam iWn cCia cau ki#n BTCT tiet
dien chiKTdUdi ^nh hUdng cua an m 6 n . Bai bao
nay xay dUng mo hinh tinh khi nang chiu uon 
cua cau ki&n BTCT tiet dien chCt T difa tren tieu
chuan ACI 318-11 c6 xet den sU suy g i ^ m lUc
dinh giCfa be l o n g va cot thep d o an mon.

2. M d h i n h t i n h kha nang d i [ u u o n (Mn)
cilia cau ki#n BTCT co t i e t d i e n chiilT

Nguyen nhan gay nen sU an m o n ket chu 
be t o n g cot thep la sU xam thUc cCia cac tac
nhan gay an mon nhU Ion Ci". Khi hoi t u du ham

\uang dorua tren be mat cot thep, dong t h d i

nU6c va oxi cung co san 6 xung quanh cot thep
thi se xay ra qua trinh an m o n dien hoa. San
pham an mon smh ra c6 the la FeO, FejOj,
FejO*, Fe(OH)j, Fe{OH),, Fe(OH}3.3H30,...Cac sin 
pham an mon sinh ra co the tfch idn hon t h ^ p
ban dau nen se gSy ra ap lUc an mon 6 mat tiep
xue cot thep v^ b& tong. Ap lUc nay la nguyen 
nhan gay ra sir hinh thanh va ph^t trien vet niJt
trong long ket cau be t o n g . B& tong n u t d i n
den khi nang lam viec chung giua be t d n g va 
cot thep giam, mat khac he so ma sdt giCa be
t d n g va cot thep b; an mon giam d o sein pham

an mon bao quanh cot thep. NhCfng dieu nay
dan den suy giSm lUc dfnh. Cuoi ciing, kha nang
chiu uon cOa cau kien giSm.

2.1. Ap lu'c an mdn (pcoi)

D l tinh ap life an mon gay ra bdi cac sin pham 
an m o n l^n be mat t i l p xue gifla be t o n g cot
thep, ta gia thiet rSng idp b^ tdng bao quanh
cdt t h e p la m d t hinh t r u thanh day. Ban kinh
trong cOa hinh tru la Ro^djl, vdi db la dUdng

Dao Ngoc The Lu'c,

Tran Dinh Manh Linh

kinh ban dau cOa cot thep, ban kinh ngoSi ciia
hinh tru la Ft=Ro+C, vdi C la c h i l u dhy Idp bi 
tdng hSo ve

Kinhl M5hinhhmhtTuthlinhd^y

Ifinh 2. {lieu kien can bing tren mat cat hinh tru

1 ^ — ^ 4

- N L I L /

Hinh 3. Cac tii5nc| so hinh hoc va sif tumig tac CO hoc giQa flianh
cot thep CO gdva be long

Ap luc an mon uTig vdi tnldng hc(px£Xa[11]

p„.R(, = p,R,-i-|"'afl{r)dr (1)

Ap lye an mon iJlng vdi trudng hop x>Xo [11]

p „ J ? ( , - p , R , + p a j , { r ) d r (2)

2.2. Life dinh giula be t d n g va cdt thep bi an
m d n

Cae t h d n g sd hinh hoc eCia thanh cdt th^p
CO g d va su t u o n g tae ca hoc cua no ddi vdi b^ 
t d n g d t r ^ n g thai bi pha huy difOc t h e hien d
Kmh 3 [131.

</div>
(2)<div class='page_container' data-page=2>

M d hinh t r o n g bai bao d u a tren eac gid
thiet sau: (1) Tai t h d i d i l m li/c P gSy pha hoai luc
dinh giCa be t d n g va edt t h e p t h i phan t o be

tdng tai d i e m d a t gidi han pha hOy; t r o n g d d
diem A Ici d i l m cdch mat cdt t h ^ p m o t khodng
3h.. (2) Qng suat la phan b d d e u d d i e m A. Cac 
t h d n g sd d Hinh 7 dUOc tfnh theo cdc cdng thiJc

A . ^
F „ '

+ X{6).

K.

(10)

Luc dinh d o sif ngdm giCf cua g d cdt t h ^ p

trong bi t d n g dUoc t i n h theo edng thiSc Error! 
Reference source not found.. LUe dinh giCia 
be t d n g va cdt t h e p khdng k l den dnh hu'dng

> hf thi true trung hda se di qua canh, cdn c <

hf thi true trung hda se d l qua bung tiet d i l n
chOT.

(15)

Bdng 1. Tdnq h o p cac he thiJc cOa m d hinh h1nh tru t h a n h dav [11]
B i l n dang

vdng
talRo

E ( R O ) < E „

E(R„)>e„

Chieu sau an m d n , x

x < x „

(n-1K2RoX-x=) f. ^ {f^JR,f+^

R,-R„ E„ ° ' ( R , / R , ) ' + 1

( n ^ l ) ( 2 R „ x - x ^ ) ^ ^ ( R , / R „ ) ^ + 1

R^-R„ '^'^' " 2

u ( r ) = ' . . , . < " • ' " ' , + '
Eo ( R , / R , ) ' + l

X > X ^

( n - l ) ( 2 R o X - x ^

( n - 1 ) ( 2 R , x - x '

u ( r )

-) f._nn ( R . / R R J ^ + i

E / ' " " ' ( R , / R , ) ' + 1

* " 2

{ R , / r ) ' + 1

" 2

B d n q 2 . C d c t h d n q s

9

45°

d duoe gid

do
0,96db

t h i l t t r o n q m d hinh life dfnh

0,6db
h.

0,07d,
o
25°

0 , 3 9 8 - 0 , 6 1 8

sau [13].

T "

Hinti 4. Trang thii (Ing suat phan t6 tai A

ti(x) = 0,37-0,26(x-x„) 0 )

P ( x ) ^ - l a r c t a n ^ ^ ' ^ ' " ' ^ ^ ^ ' ' " - " ^ ' P ' 1 (2)
2 L cosp-n(x).5in<p J

y(x) = 9 0 ° - a - p ( x ) (3)

Trong d o p[x} la he so ma sdt giCia be t d n g
vd edt t h ^ p bj an m d n , P(x) la gde phdt trien cua

v i t niJt, Y(x) ta gdc gifla p h u a n g phdt t n l n vet
nist va phuong vudng gdc vdi mat ep v d e i i a bi 
tdng. Tif tr^ng thdi iJng s u i t phdn t o tai A, cae
b i t b i l n Ong suat Ouac tt'nh theo cac cdng Ihufc

".'jf'-,*'',.*';.) m

li=o„4-aj,+o„ (5)

J, =-[(a,. -o„)'+[a,, -o„Y Ha„ -o„)'](8)

J, =(Oh - < T „ ) ( o , . -oJ{cs„ -aJ (6)

Oieu k i | n phd hOy Ottosen duoc iJng d u n g
a l tinh toan sit phd hdy cua phSn t d b l tdng
dudl tde d u n g cua iJing s u i t da truc. PhSn t d A
bSt ddu bi pha huy neu b i l u thilc {10) d i l n g . Cac

he sd A, B, X duoc I i y theo [9].

= ( s i n a ^ f c o 5 a ) . p , .

-cOa cdt thep dai duoc t i n h bdng edng thifc
Errorl Reference source n o t found.. Luc dinh 
giCia be t d n g vd cot t h i p k l den dnh hudng cua
cdt t h ^ p dai duoc tinh bdng cdng thij'c Errorl

Reference source n o t found.. Trong d d K,v 
duac t i n h t h e o [ 1 2 ] .

' • " • " " • ' • ' • • (11)

it.l,.d,.sina

^b.=-i™ + ^ M - P . « t12)
t ^ i = T ^ . K „ (13)
2.3. Khd n a n g chiu u6n ciia c£u kien

BTCT cd t i e t d i e n chOT b j a n m o n
Md hinh tinh Mn theo hai trudng hdp phd
hoai cOa cau kiin. N l u tdng luc dinh tren chieu

dai doan neo ciia cot Ihep hi an m d n Idn h o n
lUc gdy chay d6o cot t h i p t h i eau kien bi phd
hoai do cdt t h i p dat tdi cudng do chiu keo.
NgUOc lai cau kien se b[ phd hoai do si; t u t neo

cdt thep.

Ddm bl phd hoai d o sUchdy deo cot t h ^ p

Tong life keo tac d u n g len cdt thep dUdc
tfnh theo cdng thiie Error! Reference source
n o t f o u n d . . Vdi dx Id dudng kinh thanh edt t h ^ p
bj an mdn. [10]

- . f (14)

0 t r u d n g hap nay gia thiet rSng bien dang
keo ciJa cdt t h e p Idn hon hoac b i n g b i l n dang

tai t h d i diem chdy d i o (Es>Ey), bien dang nen
Idn nhat eua be t d n g bdng b i l n dang tai thdi
diem b l t d n g d a t cudng d o chju nen (ei=&:o).

Khodng cdch c giCfa true trung hda va mat
t r ^ n cOa t i l t dien dupe t i n h bSng edng thUe

Error! Reference source n o t f o u n d . [8]. N l u c

0,85.f^.b^.p,

TrUdng hop trung trung hda d i qua ednh,

anh hudng cua c6t thep chju n^n d e n M„ Id 
khdng ddng ke nen c d t h i b d qua Khd nang
chiu udn cOa cdu kiftn be tdng cdt thep chCrT
duoc tinh theo cdng thdc Errorl Reference

source n o t found. [8] vdi d la e h i l u cao lam

vi^c cila dam BTCT,

M „ = T , . { d - p , c / 2 ) ( 1 6 )

Trudng hdp true trung hda di qua b u n g ,

tong luc n i n tac dung i^n phdn n h d ra ciia ednh 
(Crf) duac xac dinh theo cdng thUc Error! 
Reference source n o t f o u n d . , d d sdu true
trung hda c duoc tfnh bdng cdng thUc Error!

Reference source n o t f o u n d . (8].

B i l n dang va t 6 n g lUc n^n tac dung l^n cdt

t h ^ p (G) vd be t d n g (Cw) trong v i i n g n i n dUpc
tfnh theo cdng thUc Error! Reference source
n o t f o u n d , vd Error! Reference source n o t
f o u n d . [8]

Crt=0,85.f,j,.(b.-b).h, (17)

c . i S ^ 08) 
0.85f,fcb|3,

C , - A ' , . { E , . E ' , - 0 , 8 5 . f ^ ) (20)

C c „ = 0 8 5 f ^ P i C b (21)

Vay khd nang chju u o n cua c i u kien trong
t r u d n g htJp nay dUpe tfnh theo cdng thUe

Error! Reference source n o t f o u n d , vdi C»,

theo [81

M „ = C ^ ( d — ! - ) + C „ ( d -!^)+C(d-d') (22)

D i m bj phd hoai d o su t g t neo c o t thep
T6ng li^c keo tde dung l i n cdt thep dupc

tfnh theo edng thiic (23) [10]

T , = - c ^ . 7 t d . l , (23)

Bien dang cOa cdt t h ^ p chiu keo Cs, b i l n
dang n^n Idn nhat eOa v u n g be t d n g ehiu nen 
EtdUpc tfnh theo cdng thUc (24) vi (25).

4T,

" l t d ' E ,

c - d

(24)

(25)

Tfnh todn tUcmg t u n h u t r u d n g hpp d i m
phd hoai do sU chdy d i o cdt t h e p . Oiem khdc

bi^t la gia t r i 0,85 trong cdc cdng thUe dUoc
thay t h i b i n g gid tri Oi, Oi va Pi dUOc Uy theo
[4]. Diem ddng luu y d ddy d d la gid trj e trong

cdng thUc Error! Reference source n o t f o u n d .
la mdt gid trj chua biet. De tfnh e, ban dau ta
eho true trung hda d i qua mat dUdi cua ednh.
K i l m tra n l u t o n g life nen t i c d u n g len b l t d n g

</div>
(3)<div class='page_container' data-page=3>

vd edt Xhip Idn han tSng luc keo thi t m e trung 
hda d i qua ednh vd nguoc lai. SiJrdung vdng lap
chpn c sao cho phuong trinh can bdng luc tren
tiet dien thda mdn. Khd nang chju uon eua eau
kien iing vdi t i ^ g trudng hop eua true trung
hda duac tinh theo edng thUc Error! Reference

source not found, va Error! Reference source 
not found..

3. K i t qui phan tich

D l xdc thuc tinh tin cay, md hinh se p h i n
tich mdt trudng hap cu the la dam BTCT cd t i l t

d\in chCr nhdt (mdt trudng hpp d i e biet cCia t i l t

di^n chU T khi b , = b). K i t qud p i i l n tfch tU md
hinh se dupe so sdnh vdi thi nghiem eiia
Al-Sulaimani [1]. Thi nghiem dupe thue hien tren
mdu Id ddm b^ tdng cot t h e p cd kich thudc t i l t
di^n 150x150 (mm), c h i l u dai d i m L=1000 m m .
B£ t d n g ciia d i m thf n g h i f m cd cudng dp chju 
n^n Id 40 MPa. VOng chiu keo eua t i l t dien ddm
dat mpt thanh t h ^ p cd dUdng kinh db= 12 m m ,
viing chju n i n dat 2 thanh thep ed dUdng kinh
moi thanh db=10 m m . Chieu ddy Idp be tdng
bdo vS c6t t h ^ p chiu keo la C = 2 9 m m . Cdt t h ^ p
dai cua dam cd dudng kfnh dn, = 6 m m , cdch
khodng a» = 50 m m . Cdc dam be tdng trong t h i
nghiem trin bj cho dn m d n d cap dp khac nhau 
vd dUa vdo t h i nghiem udn ngang p h l n g . Tdi
trpng tdc dung tai t h d i diem dam be t d n g bi
phd hoai duae ghi nhan de tU do tinh dupc khd
ndng chju udn cOa mau thf nghiem (Mn). K i t
qud xdc thue duoc the hien d Hinh 5 cho t h i y
sU tuong ddng giUa k i t qud phan tich vdi thf
nghiem.

N h i m t h i y rd su dnh hudng cua an m d n
d i n cdu ki§n BTCT cd tiet dien ehUT, ta xet mdt
trudng h p p cu t h i mdt dam cd ede thdng sd
nhUsau: Cudng d d be t d n g fd. = 30 MPa, cudng
dd cdt t h i p f, = 450 MPa, be rpng bung b = 300
m m , be rdng ednh b^ = 900 m m , e h i l u cao ddm 
h = 500 m m , chieu cao ednh h f - 100 m m , cdt
t h ^ p trong viing chiu keo 2(p18, trong viing

chju nin 2ipl4, cdt dai (p6 cdch khodng 200 
m m , c h i l u ddi doan neo cdt thep Li = 300 m m .
D i m dupe k h i o sdt vdi khodng d p dd an mdn
tif 0% d i n 1%, k i t qud phan tich ddi vdi trudng
hpp cd vd khdng ke den sU lam viee eua ednh
dupe t h i hi#n d Hinh 6. TU bieu d d d Hinh 6, ta
thay r i n g Ung vdi cap d p dn mdn tif 0% den
0.4%, tdc nhdn dn m d n dnh hudng tcJi Mo thdng
qua v i f c Idm suy gidm tiet dien edt thep ehiu
k t o . Su dnh hudng nay Id khdng dang ke. CTng
vdi cap d d an mdn tir 0.4% d i n 1%, tdc nhan dn

mdn dnh hUdng den Mn thdng qua v i l c lam suy
gidm luc dfnh giOta be tdng va cdt thep. Sif anh
hudng nay ed tae ddng Idn den Mn, lam cho Mn
suy gidm nhanh chdng va gay nguy h i l m cho
k i t c l u .

Kinh 5 )Uc thuc mo hinh vcii Ihi nghiem cua Al-Sulaimani

4. K i t luan

Bdi bdo da xdy dung dupe md hinh tfnh kha
ndng ehiu udn eua cau kien be tdng c5t t h i p cd
l i l t tien chU T bj an mdn cd xet d i n su anh
hudng cua t i e nhdn an mdn d i n su hinh thanh
phdt trien vet nut cung nhU sU suy g i l m luc
dinh eua eau kien bi tdng cdt thep. Md hinh 
dupe x i c thifc vdi cac thf nghiem h\in cd. Ket 
qud cho t h i y md hinh cd dp tin cay cao, cd the

Ung dung d l ddnh gia cdc cau ki^n vdi dieu
ki^n Idm viec thuc te. Tuy vdy, trong bdi bdo, do
chua cd eac thf nghiem trdn dam chO t i l t dien
c h U T b j an mdn nen md hinh chi mdi dUOc xac
thuc vdi mpt trudng hpp ddc bi&t Id ddm ed tiet
dien chu nhat. De tang them tinh tin cay cua
m d hinh, tac gid k i l n nghi can cd them cdc thi
nghiem k h i nang chiu udn tren cdc d i m tiet
dien chor T bi an mdn de xdc t h i f c

Qua sd lieu phdn tich, bai bdo da cho thay
SI/ dnh hudng d i n g k l cua dn m d n den M„

thong qua viec lam suy giam luc dinh giUa be
tong va cdt thep. Do dd can cd cac bien phap
phong ngUa cac anh hudng nay nhutang chieu
day Idp be tdng bao ve, tang chieu ciai doan
neo cdt thep ddi vdc cac dam be tdng cdt thep
lam viec trong mdi trudng bien.

Tai lieu tliam khao

[It Al-Sulaimani G I , Kaieemuiiah M., Basunbui I. A,
,Rasheeduzzafar, "Influence of corrosion and craclung on bund
hehautor and strength ot reinforced concrete members", ACI
Structural loumal 87 (1990], pp 220-231

[2] Amleh L,Mira L, "Corrosion influerce on bond
between steel aid concrete", ACI Struct J. (1999) 96(3), pp.
415-23.

[3] Bong Seok Jatig,Byung Hwan Oh, "Effects of
nc^-unitonn corrosion on the cracking and service iife of remforced
concrete structures", Cement and Concrete Research. (2010] 40,
pp. 1441-1450

[4] Collins MP,Mitchell D, Prestressed concietestructuie,
Prentice Hill, (1991)

[5] Coronelli D, "Corrosion cracking and bond strength
modeling for corroded bars in reinforced concrete.", ACI StmctI
(2002) 99(31, pp, 267-76,

15] E. Chen.Christophei KY Leung, "finite element
modeling of concrete cover cracking due to non-unifoim steel
coiFosion", Engineering Fracture Mechanics. (2015) 134, pp
61-78.

(7] Fang C, iLindgren K, Chen L ,Zhu C, "Corrosion
influence on bond in reinforced concrete", Cem Concr Res.
(2004) 34(ll),pp 2159-2157

|8] lame K Wighl,lame5 G. MacGregor, Reiforced
concrete - Mechanics and design, 6E, ed, Pearson Education,
UpperSaddleRiuer, New leisey, (2012).

(9] Ottosen N S A, "A failure criterion for concrete",
loumal of Engineering Mechanics Division, Proceedings of the
American Society ofCivil Engineering. (1977) 103, pp. 527-535,

110) Sun-jin Han, DeuckHang Lee, Kang Su Kim, Soo-Yectfi
Seo, luhyuk Moon,Paulo J,M Monteiro "Degradation offlenural
strength In reinforced concrete members caused by steel
corrosion". Construction and Building Materials 54. (2014), pp
572-583

[ H i Wang XH,Liu XL, "Modeling effects ot corrosion on
cover cracking and bond in reinforced concrete", Mag Concr Res
(2004) 56(4), pp

191-9-[12] Xiaohui Wang,Xila Liu, "Modeling bond strength of
corroded reinforcement without stirrups". Cement andConcrelf
Research34 (2004),pp,1331-1339

[13] V L . Xu (1990), Expenmental study of anchorage
properties for deformed bars m concrete. Department oiM 
Engineering, Tsmghua University, Bei]ing,

</div>