Kha nang chiu k^o eiia be tdng kem n l n toan b d lUc keo se do cot thep chiu, trong vUng nen cd ca be tong va edt thep ciing cdng t i e chiu tuc Do vay, neu nang cao dUOc eUdng d[r]
Trang 1Anh hu'O'ng cua cot dai den kha nang chju
Ngay nhan bai: 9/7/2014
Ngay su^ bai: 23/8/2014
Ngay chap nhan dang: 27/8/2014
Nguyen Ngoc Phu'dng
TOM T A T :
Bai bao trinh biy vi?c khao sat bi^n dang
thep xet anh hUdng cua cot dai theo tieu
chuan thi^t EC2, ACt318 va mdt so mo
hinh, qua do lam rd hon sU lam vigc ciia
cot BTCT va ki^n nghi v6i tieu chuan Viet
Nam
ABSTRACT
The article analyzes the deflection and
load capacity survay of reinforced
concrete columns with the effect of
stirrup according to the designed codes
such as EC2, ACI 318 and some models
Consequently responses of reinforced
concrete columns can be seen much more
clearly and suggested to the Viet Nam
codes
TS Nguyen Ngpc Phiitfng
TrUcfng DH Kien triic Ha Ndi
Di dong: 0903405450
Email: Phuong.nguyenngocphuong@
gmail.com
Dat van de Cdt BTCT la cau kien chju lUC chinh trong ket cau cong trinh, la cau ki6n chju nen, nen -udn Kha nang chiu k^o eiia be tdng kem n l n toan b d lUc keo se do cot thep chiu, trong vUng nen cd ca be tong va edt thep ciing cdng t i e cua thep sir dung trong cdt se dan den hieu q u i dang ke khi cdt lam viec Theo tieu chuan t h i l t TCVN 5574 2012, vdi be tdng thUdng, bien dang
eye han s* = 2.10 ^ mddun dan hoi e6a edt t h e p
E = 2.10^ nen de dam b i o sU lam vi^c chung giUa be tdng va cdt thep va han che lang phi, Ung suat trong edt t h i p khdng qua 400 MPa (cudng do tinh loan ve nen ciia cdt t h i p khdng Idn hon 365 MPa) [1,2] Vi vay, k h i nang chiu lUc cda cdt BTCT khdng eao trong khi y l u cau ve
k h i nang chiu nen eiia edt, d i e biet vdi c6t nha cao tang la lat Idn, dan den kich thUdc cdt Idn, anh hudng den edng nang va thi'm my Do dd,
k h i o sat i n h hudng ciia cot dai den sU thay doi bien dang ngang ciia be t d n g , qua d d lam rd hon sy lam viec cua edt BTCT ed x^t den bi^n dang kiem che n d ngang va d i n h g i i k h i nang
va m d hinh la can t h i l t , de t i f dd c6 nhCing luu
y vdi cac ky sU ket eau va k i l n nghi vdi TCVN
1 Tieu chuSn M ^ ACI 318-2005 va chau
Au EC 2-2004
1.1 Tieu chuan ACI 318-2005(3,6}:
- Ong suat eua be tdng khi cd kiem che n d
ngang- t\^ = V^+4,]o^ vdi: f'^ - cUdng d d chiu
nen ciia b l t d n g ; o, - iing suat ciia cot dai:
sb i: A - dien tich t i l t dien cot dai, f - cudng d o cot dai, a - gdc nghieng cua thudc canh eua Idi sb^ - dien tich be mat l d i
- Bien dang eua be tdng khi c6 Ung suat kiem che n d ngang e „ = - ^ vdi E - md d u n d i n hdi ciia be tdng ^
- Kha nang chiu lUc cda cdt:
[N]=0,8(0,85f'^i^^A^ -(- A^f^) - vdi \ - dienlkk
t i l t dien cdt
1.2 Tieu chuan EC2-2004 [5,6]:
- Qng suat ciia be t d n g khi c6 kife cM
n d ngang: f.k.c ^ ^ k ^ + S ^ ) khi o^ s 0,OS|vi f.k, - f ^ ( 1 , 1 2 5 + 2 , 5 y i ) khi O; > 0,05f^^ \ffflfj\ cUdng d o chiu n l n ciia b l t d n g ; o^ - tiKingU
n h u Oj cda ACI
- Bien dang ciia be t d n g khi c6 iing sui
kiem che n d ngang:
^ciZf-^-= 0.002
- K h i nang chiu lUc cua c6t:
[Nl=0,8(0,85f ; ^ / ^ + fiif)
2 M o t so m o h i n h
2.1 Mo hinh cua Legeron vd Paultre (199SI
cua cdt: 7 ^
Hinh 1 Quan li& fing suat-bien dang cia be tong thfi
liinh cua Legeron va Paultre
Md hinh i p dung cho cdt BT duoc kiSmc
n d ngang bdi c i c cot dai hinh chU nhStlK hinh vudng Vdi cot BTCT, Cfng suat k i l m die ngang khong phai la m o t h i n g so ma phu thi
cd lien quan t d i sU n d n g a n g ciia b l tong chiu nen - hieu Ung Poisson (he sd Poisson 0,5 tai giai doan khi cdt dai c h i y d I o ) KhicA dai se e i n t r d n d ngang eiia be t d n g , larnt dang cUc han cua be t o n g khi chju n l n tang len, ket q u i cd t h e nang cao dUOC Cfng suSt trong cdt t h e p chju n l n Bieu d o Ung sucit-' dang ciia be t d n g theo m o hinh n i y dUOi
Trang 21
2
3
4
Tieu chuan va m d hinh
ACI 318-2005
EC2-2004
Legeron va Paultre
Salim Razvi v i Murat
Saatcioglu
" Sai so idn nhat glQa c i c t i l u
chuan v a m d hinh
B i l n dang eye han cda b l tdng £ „
M l 0,002 0,002 0,002 0,002
M2 0,0022 0,0024 0,0023 0,0030 36,4%
Sai sd so vdi M l
1 0 %
2 0 %
1 5 %
5 0 %
M3 0,0023 0,0027 0,0028 0,0037 50,9%
Sai sd so vdi M l
1 5 %
3 5 %
4 0 %
8 5 %
M4 0,0025 0,0030 0,0033 0,0045
8 0 %
Sai sd so vdi M l
2 5 %
5 0 %
6 5 %
1 2 5 %
B i n g 2 K h i nang chiu lye cOa cdt
VH*,''"''
- W K ( 1
lon9l}i[2
^fm;3
' '4
khi(i,)M
T i l u chuan va m d hinh
ACI 318-2005
EC2-2004
Legeron va Paultre
Salim Razvi va Murat
Saatcioglu
betOKiiSai sd Idn n h i t giCfa c i c t i l u
' c h u a n v i m d h i n h
K h i nang chiu lye cua cdt (KN)
M l
2665
2438
2565
2665
M2
2846
2589
2884
2871 11.4%
Sai sd so vdi M l
6 , 8 %
6 , 2 % 8,2%
7 , 7 %
M3
3027
2740
3054
3032 11,5%
Sai so so vdi M l 13,6%
12,4%
14,6%
13,8%
M4
3231
2910
3167
3196
1 1 %
Sai so so vdi M l
2 1 , 2 % 19,4% 18.8% 19,9%
=( ( i l n 6 h i n h 1 [ 3 , 4 ]
- iJng suc!t cda be t d n g khi cd kiem che
^ ^ b ngang: r^ = [ 1 + 2 , 4 ( r / ' ] f ; vdi i ; - chl so
leraiiriW -^'~^^*^ l3 3p iye han c h l n d ngang hieu
ung, trong d d : A^^ - t o n g dien tich mat cat
ong k h o i n g c i c h giUa cac cot dai s, c - dUdng
^, nh Idi b l t o n g han che n d ngang, f ^ - irng s u i t
\ Sng t r o n g cdt t h e p dai, K^ - he sd kiem c h l n d
- ' \ ^ ^ (1-sy4c)' ^ _t^
»^iB\gang hieu q u i : K=—~ voi M « ^
- -: ty' sd d i l n tfch cot t h i p doc tren dien tich b l
j n g han che n d n g a n g
BitifS' Bi^n dang cda be t d n g khi cd <ing s u i t
i l m che n d ngang: i\^ = [1 +3,5(\\y-^].E\
icotSTW 2.2 Mo hinh cua Salim Razvi vd Murat
iih'^^aatcioglu(1999):
Signs' / • !
hinga"* ,
;p|[ie(iic''~v
dij?**'
jjiJ^* tiinli 2 Quan hS ling suSt-bien dang cua be tong theo mo
0^'
hinh cua Salim va Murat Saatcioglu
Md hinh nay xet tdi t i t ca c i c yeu t d i n h hudng n h u hinh dang cdt dai, ty- sd t h e tich cot gidi han ehay cua cot dai cung n h u cudng do
b l t d n g va kieh thUde hinh hoc cua cdt Bieu dd nay duoc the hien d h i n h 2 [3,4]
- Cfng s u i t cua be t d n g khi cd k i l m
che n d ngang: f'^ - f'^^ + k^f,^ vdi f ^^ = f'^
k,=5,7(fie)"''"; Ung s u i t kiem c h l nd ngang tUdng dUOng f,^ = k^f, vdi f, - iing suat kiem che
n d ngang bi d d n g , \hc djnh nhU o^ trong ACI;
- 0 , 1 5 , <1,0
- Bien dang ciia be t o n g khi eo Ung s u i t kiem
, 40 , „
e h e n d n g a n g : £ = E (l-i-5k K) v d i k j = - : - < 1 0
v a K = -3—
3 K h i o sat tinh t o a n :
Khao sat b i l n dang eiia be t d n g cot va kha nang chiu lUc cua cot cd hinh dang, kich thudc,
c i u tao va bo tri cot thep doc dai n h u hinh 3
4 mau cot:
-I- Mau 1 ( M l ) chi cd edt doc, khong e d e d t dai;
•1- M a u 2 ( M 2 ) : b 6 t r i c d t d a i , 4 ) 8 a l 0 0
+ Mau 3 (M3): b o tri cdt d a i ; 4.8a50
•I- M a u 4 ( M 4 ) : b 6 t r i c d t d a i ( t > 1 0 a 5 0
-Thep doe chiu lUe ciia cdt sU d y n g 8iji20 va edt dai sU dung t h i p cd cUdng d p c h i y deo f
= 295MPa (theo TCVN t u o n g d u o n g nhdm t h e p CII)
- B l tdng:-)-Theo TCVN 5574-2012, si( d u n g 625: R^, = 25 MPa; R,, = 18,5 MPa
•H Theo ACI 318-2005: ^c ^ T ^ = T : ; ^ = ^0
MPa ^'^^ ' ' ^ ^
•1- Theo EC2-2004: C20/25 cd f^^ = 20 MPa, ''icb* = 25 MPa, E,^ = 30x10^ MPa Tinh toan theo ACI 318, EC2va eie m o hinh neu tren Cic k i t q u i tinh t o i n t h e hien trong
c i c bang 1 va bang 2
Cd t h e thay rang khi CO su kiem ehe n d ngang, bten dang cUc han eua be t d n g tang len, tang it nhat la theo ACI va tang len Idn nhat
la 125% GiCta c i c tieu chuan va m d hinh cd sy nay, Idn nhat la vdi m i u 4 (80%)
Cd the thay rang k h i nang chiu lUc ciia cdt theo EC2 la n h d nhat Khi cd sy kiem c h l n d ngang k h i nang ehju luc ciia cot tang len, Idn nhat la 21,2% GiUa c i c t i l u chuan v i m d hinh
cd sy chenh lech nhau ve k h i nang chju lUc Idn
n h a t l a 1 l , 5 % Ket luan;
Khi cd sU kiem che nd ngang bien dang va cudng d o ciia be tdng duoc tang len k h i nang chiu lye cua cdt BTCT cung tang len, ed t h e tang len k h o i n g 18 den 21 (%) va cd t h e sit d u n g
t h e p cd cudng d o cao han
Gidi han c h i y ciia edt t h i p dai cd i n h h u d n g
Trang 3B«20
BfflgQ ? ^ \ *
f V |
Beoioo
f ="+
aesa
fl8Q50 8ggo
020 aim
J 400 1
8050
i
Hinh 3 Cac man cot khao sat
dang ke den su k i l m che nd ngang ciia be tdng
Viec cau tao cdt dai n h u dUdng kinh, khoang
ngang, t J so giCfa ham lUOng edt dai va di&n tieh
ngang cUa b§ tdng
Cic k i t qua tren gdp phan cho cac ky sU
t h i l t k l ket cau trong nghien eUu ve sU lam viee
va tfnh toan, d i n h gia kha nang chiu lUc eiia cot
BTCT, ddng thdi kien nghi trong t i l u chuan thiet
ke ket cau BTCT eua Viet Nam can cd nhUng
nay de bd sung va lam rd han nham hoan thien
TCVN
T A I L I E U THAM KHAO
LPhan Ouang Minh, Ngo The Phong, Nguyen Dinh Cong
(2011), Ket ca'u be long cot thep, M Khoa hot va ky thuat Ha
NOI
2 Tieu chuan Viel Nam (2012), TCVN 5574 2012, Ke't cau
be tong va be tong t o i thep -Tieu chuan thiet ke, Nxb Xay dung,
Ha Noi
3 ACI committee (2005), Building code reguirements
for structural concrete (ACI 318-05), Structrural Engineering
Handbook
4 Ed Chen Wai-Fah (1999), Structural cono¥te Des[gn,
Structrural Engtneering Handbook
5 Eumtode 2 Design of contrete structures
6 MC Graw-Hill (1999), Ciifil Engineering Formulas,
Structrural Engineering Handbook
f ft
eoiBBnnenai 09.2014