KHOA HOC
CONG NGHE &CUOC SONGQUYTRINHTHIETKETHEO KHA NANG TRONG TIEU CHUAN THIET KE CAC CONG TRINH CHIU
DONG OAT TCXDVN 375:2006
Nguyen Le Ninh Le Trung Phong
ABSTRACT
Where the seismic load is considerable, the building shall be designed accord- ing to TCXDVN 375:2006[1], which the structure shall work at inelastic range.
The problem is to control the seguence of damage - ductile deformation, energy dissipation, damage or collapse
-forthe building with high reliability.
This can be solved by a suitable selec- tion of the areas for energy dissipation
and proper design procedure. This design approach is called capability design procedure.
PGS.TS Nguyen Le Ninh Trirdng dai hoc xay diTng Th.SLe Trung Phong Tong Cty Xay diTng so 1
I.Mddau
Khi chiu tac ddng dpng dat manh, cac edng trinh xay dung dupc thiet ke theo tieu chuan TCXDVN 375:2006[1] lam viee ngoai gidi han dan hdi. Van de ca ban dat ra la lam the nao de cac giai doan lam viec cua cdng trinh nhu bien dang deo, phan tan nang lupng, pha hoai hay sup do phai xay ra theo mdt trinh tu mong mudn djnh trUde vdi dp tin cay cao. Quan niem thiet ke nay dupc the hien trong mdt quy trinh thiet ke cd ten gpi la quy trinh thiet ke theo kha nang hoac ngin gpn hon thiet ke theo kha nang.
II. Noi dung va nguyen ly co ban cua thiet l<e theo l(ha nang
Khi thuc hien thiet ke theo kha nang, mot sd cau kien chinh hoac mot sd vung cua he ket cau ehju luc ngang dupe lUa chpn, thiet ke va eau tao mot each phu hpp de phan tan nang lupng dpng dat, trong khi cae phan cdn lai cua he ket eau dupc thiet ke vdi mdt du trd dp ben phu hpp de dam bao ring, co cau phan tan nang lupnglua chon dupe duy tri trong sudt qua trinh he ket eau ehju tie ddng ddng dat ma dd ben trong cae vung phan tan nang lupng khdng bj suy giam nghiem trpng. Cae vung ed kha nang phan tan nang lupng d cae eau kien ket eau, thudng dupc gpi la eac vung tdi han hoac cac vung khdp deo dupc cau tao de ehju tac ddng udn khdng dan hdi, cdn pha hoai cat duoc ngan chan bing chenh lech dp ben phu
hpp.
Oe l i m rd nguyen ly co ban eua thiet ke theo kha nang, ta xet mot day xich nhu trong hlnh 1 ehju tac ddng cua mot lUc F. Day xich nay dugc tao thanh tU mot m i t xich deo (mau den) va cac m i t xich ddn. Nhu da biet, dp ben cua day xich dUpc quyet djnh bdi dp ben cua mit xich yeu nhat. Ta thay ring bat ke lUc F cd dp Idn bang bao nhieu, kha nang ehju lue eua spi day xich se bj gidi han bdi gia trj them chay F^ cua m i t xich deo. Nhu vay cic mat xich don khdng can phai dupe thiet ke de ehju mdt lUc qua Idn khdng can thiet, ma chi can ehju dupe mot lUc F, = Y „ / ^ la du, trong dd y^^ dupe gpi la he sd vUpt dp ben xet tdi cac yeu td cd the lam tang dp ben (kha nang ehju lUc) trong thUe te, cdn F^ la kha nang ehju lUc (theo thiet ke) cua m i t xich deo. Tich sd y^^^F^ bieu thj kha nang ehju luc thUe te (cdn dupe gpi la dp ben vUpt qua) cua m i t xich deo trong qua trinh lam viec dUdi tac ddng cua tai trong.
Chuyen djeh spi day xich sang he ket eau ehju luc. Luc F bieu thj tac ddng ddng dat len edng trinh, spi day xich bieu thj he ket cau chiu lUc, m i t xich deo bieu thj cic vUng khdp deo, cdn eac mat xich ddn bieu thi eac vUng cau kien duoe gid lai lam viee trong gidi han dan hdi.
Quy trinh thiet ke theo kha nang se eho phep ngudi thiet ke xac djnh dupc eac gia trj ndi lUe Idn nhat tai cac tiet dien lam viec dan hdi cua ket eau tren ca sd kha nang chiu luc thUc 72 5SU»1T1^? . 8.2009
^ 1 n \i—l^
1. MSt xich d o n 2. M5t xich deo
Hinh 1. Nguyen ly thiet ke theo kha nang
I I ,y,M,AiM,,/EMj
"Rb
m
• ( - -"Re
9+'C,Q
'f^M,,
m
"RbIM„
Hinh 2. Cac gia trj dung de xac djnh luc cat d dam khi thiet ke theo kha nang
" R e
^^Rb'-^Rc" -,j_i'.^ "Rb
^ "'iaMl
Y,JIM^ZMJM„,
IMov,<IM, Rb - ' " R e - - /'T
V
1?^
IM, RbZM, Re
Hinh 3. Cac gia trj diing de xac djnh luc cat d cot khi thiet ke theo kha nang
te cua cac vung khdp deo, ddc lap vdi dp Idn cua tac ddng dpng dat F Nhu vay, ve ban chat quy trinh thiet ke theo kha nang cho phep trudc het bao ve cae tiet dien khdng lam viec deo, nghia la chung phai dupe thiet ke de cd dp ben Idn hon dp ben vUpt qua Y„jF^ tai eac khdp deo.
III. Thiet ke theo l<ha nang cac l<et cau theo TCXDVN 375:2006[1 ]
1. Lua chpn mdt co eau pha hoai deo cd the xay ra d ket cau. Co cau pha hoai deo dupe lua chpn la co cau cd dp deo chuyen vi tong the can thiet dupc xac djnh tU cac chuyen vj xoay khdng dan hdi nhd nhat tai cae khdp deo.
2. Sau khi chpn dupe co cau pha hoai deo phu hpp, xac djnh vdi dp chinh xac tuong ddi cao vj tri eac vung phan tan nang lUpng (eac vung khdpd^o).
3. Cac vung khdp deo phai dupc thiet ke de cd kha nang chiu lUc (R^) Idn hon cac he qua t i c dpng (E^) xuat hien tai cae vung nay dUdi tac ddng eua lue ddng dat thiet ke. Odng thdi eac vung khdp deo phai dupc cau tao dac biet de thda man cac yeu cau ve dp deo du kien.
4. cac phan ket cau duoc gid lai
l i m viec trong gidi han dan hdi phai dupe thiet ke sao cho dudi cac tac ddng Idn nhat tUOng dng vdi dp ben vUpt qua (Y„JRJ) tai cae khdp deo, khdng cd bien dang khdng dan hdi nao cd the xuat hien trong cac phan ket cau do.
Nhu vay, theo tieu chuan TCXD- VN 375:2006[1], cac phan ket cau dupe giu lai lam viee trong gidi han dan hdi phai dupc thiet ke vdi cae gia trj ndi luc tinh toan (he qua t i c ddng thiet ke) E^ bing dp ben vupt qua tai eac khdp deo, nghia la:
Ea = Y„,R. (1) Trong do:
R, - kha nanq chiu lUc (dd ben thiet ke) cua tiet dien tai khdp deo;
V„ R, - he sd vUot do ben xet tdi
' Rd d
eudng dp cot thep Idn hon eudng dp chay dac trUng, sU gia tang cUdng dp cot thep do bj bien cdng khi ehju cac bien dang Idn, sugia tang eudng do eua be tdng, khdi xay,... theo thdi gian, sUgia tang cUdng dp ehju nen cua be tdng do cot dai,...
Khae vdi cac vung khdp deo, cac phan ket cau dupe gid lai lam viec trong gidi han dan hdi dupc cau tao theo cac quy djnh cua tieu chuan thiet ke khdng khang chan.
5. Cac kieu pha hoai ddn hoac
khdng mong mudn khae:
- Pha hoai c i t cac cau kien ehju luc;
- Pha hoai cac nut khung;
- Tap trung cac khdp deo vao cac cot thupe eung mot tang cua nha nhieu tang;
- Mdng bj bien dang deo;
- cae cau kien dupc thiet ke de lam viec trong gidi han dan hdi bj bien dang deo;
- Cot thep bj mat lUc dinh ket hoac bj tupt neo... khdng dupe phep xuat hien.
cac kieu pha hoai tren se khdng xuat hien neu cac ndi lUc tinh toan (he qua tac dpng thiet ke) trong cac vung lua chpn chu djnh dUpc xac djnh t d cae dieu kien can bing (1) khi cac khdp deo vdi cac dp ben vUpt qua cd the cua chung xuat hien trong cac vung lien ke.
IV. Vain de xac dinh cac he qu^
tac dpng thiet ke khi thiet ke theo kha nang
Theo nguyen ly va ndi dung cua thiet ke theo kha nang trinh bay trong cae phan tren, ngoai trUeae he qua tac ddng dung de thiet ke cac vung tdi han chiu cae bien dang udn khdng dan hdi Idn la lay tU phan tich
JSllllI.l^T . 8.2009 73
he ket eau trong tinh hudng ehju dpng dat, cdn cac he qua t i e dpng dung de thiet ke eac phan cau kien hoac ket cau dupc gid lai lam viee dan hdi hoac nhim loai trUcic kieu bien dang khdng mong mudn nhu pha hoai cit... can phai dupe xac djnh lai tren eo sd dp ben udn thiet ke (kha nang ehju udn) cua cae tiet dien ed khdp deo. Oe minh hoa ta xet trudng hpp khung BTCT.
I.Doi vdi dam
a. Mdmen udn va lue dpe. Dam la noi cae khdp deo thudng dugc phep xuat hien nen mdmen udn va lue dpe thiet ke dupe lay theo ket qua phan tich ket eau trong tinh hudng ehju tac ddng dpng dat. Cac mdmen udn trong dam cd the dugc phan phoi lai tdi 30% vdi dieu kien tdng cua chung giu nguyen khdng thay doi.
b. Luc cit. Oe cho dam khdng bj pha hoai c i t q u i sdm, luc cat dung de tinh toan phai dugc xac dinh lai tU dieu kien can bang dam dudi t i c dpng cua (i) tai trpng t i c dpng vudng gdc len true dpe dam trong tinh hudng tinh toan khang chan va (ii) cac mdmen udn d dau mut dam M^^ (i = 1, 2 ehi eac tiet dien dau mut dam) bieu thj kha nang ehju mdmen udn cua dam tai eac khdp deo cd xet tdi he sd vUot dp ben ddi vdi mdi hudng (duong hoac am) cua tac dpng ddng dat (hinh 2).
M /RdMRb, mm
T M R Trong do:
Y^j - he sd vUpt dp ben; y^^ = 1,0 cho cap deo trung binh,Yjj^= 1,2 cho cap deo cao
Mj^^ - kha nang ehju mdmen udn cua dam d dau mut i theo chieu cua mdmen udn ddng dat ddi vdi phuang dang xet eua tie ddng dpng dat.
IMp^ va IM^j^ tuong dng la tdng kha nang chiu mdmen udn cua cac cot va tdng eac kha nang ehju mdmen udn cua cae dam quy tu vao nut.
2. Cot
a. Mdmen udn. Cot la bd phan duoc giu lai de lam viec dan hdi do
do mdmen udn dung de tinh toan cot phai dupe xac djnh lai theo dieu kien (1), nghia la tai tat ca cae nut lien ket gida cac dam vdi cae cot khang chan chinh phai thoa man dieu kien:
^M,>Y„,IIV1„, (3) Trong do:
Y^j - he sd vUpt dp ben, y^^ = 1,3 khdng phu thupe vao cap deo cua ket cau.
I M „ va I M „ „ duac dinh nghia
Re R b • • -^
theo (2)
b. Luc cit. Oe cho cot khdng bj p h i hoai c i t trudc khi bj pha hoai udn, luc c i t tinh toan trong cot can dupe xac djnh lai tren co sdcan bang cot dudi tac ddng eua eac mdmen tai cac dau mut M^^(i = 1,2, i chi cac tiet dien dau mut cot) tuang Ung vdi sU tao thanh cac khdp deo ddi vdi moi phuang tac ddng dpng dat (duong hoac am) (Hinh 3).
M : • / „ , M „ j , m i n
' Z M R C ; (4)
= 1,1
= 1,3
Rd
Trong dd:
YR^ - he sd VUpt dp ben; y cho cap deo trung binh va y cho cap deo cao;
M^^ - gia trj thiet ke cua kha nang ehju mdmen udn cua cot d dau mut i theo chieu tac ddng mdmen udn do ddng dat ddi vdi phuang dang xet eua tac ddng ddng dat;
IMp^ va ZMpi, dupe dinh nghia theo (2)
Tren co sd nay, luc c i t trong cot duac xac dinh nhu sau
V,. , Mid + Mid
L, (5)
V. Ket luan
Viec thuc hien thiet ke theo kha nang se dam bao cho cae khdp deo se xuat hien tai cae vj tri du kien, theo thU tu djnh trudc va theo each thde mong mudn tren he ket cau, do dd nd cdn cd ten gpi thiet ke kiem soat dang pha hoai.
Thiet ke theo kha nang se tao ra mdt su ket hop gida eac eau kien cd kha nang ehju luc cao vdi cae eau kien cd kha nang bien dang deo Idn n h i m tdi Uu hoa phan Ung eua he ket cau. Cach thUe thiet ke nay hoan toan ddi nghich vdi each thUe
thiet ke truyen thdng, cdn dupe gpi la thiet ke true tiep, theo dd eac bp phan rieng le cua he ket cau dupc thiet ke de cd kha nang ehju luc cao.
Thiet ke theo kha nang khong phai la mdt ky thuat tinh toan ma la mdt cdng cu thiet ke manh. No cho phep ngUdi thiet keed the "dieu khien" dupe he ket eau va lam eho nd khdng cdn nhay cam trUde cac tac dpng ehua ludng het cua dpng dat. each thde thiet ke nay rat phu hpp vdi quan niem thiet ke mdi trong bdi canh con ngUdi ehUa kiem soat dupe tac ddng ddng dat. •
TAI LIEU THAM KHAO
1. TCXDVN 375:2006. Thie't ke' cong trinh ehju dpng dat.
2. Association Francaise du Genie parasismique.
Guide des dispositions constructives parasis- miques. Presses de I'ecole nationale des Fonts et Chaussees, 2005
3. Filiatrault Andre. Elements de genie parasismique et de calcul dynamique des struaures. Editions de I'ecole Polytechnique de Montreal, 19%.
4. George G. Penelis, Andreas J. Kappos. Earth- quake - Resistant Concrete Structures. E&FN 5P0N, 1997.
5. Nguyen Le Ninh. Oong dat va thiet ke cong trinh ehju dong dat. Nha xuat ban Xay Dung - Ha Noi - 2007
6. Paulay T; Priestley M. J. N. Seismic design of reinforced concrete and masonry. A Wiley inter- science publication, 1992.
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