BANG PHU'QNG PHAP PHAN TIJ HU'U HAN

PHAN II - XAY Dt,]NG vA BAO VE CONG TRINH... 479

TINH

T O A N K £ T C A U B E

TONG

C 6 T

THEP CO SLP DUNG LU'OI THEP KHONG GIAN 3 CHI^U (3D)

B A N G

PHU'QNG

P H A P P H A N

TIJ HU'U HAN

TS. Nguyin Thdnh Cdng"' ThS. Nguyin Chi Thanh"'

Tom tk:

Ket c l u be tdng cot thep cd si> dung ludi thep khdng gian ba chieu (3D) hien dang dugc SU" dung rdng rai trong nganh xay dung. Ket c l u be tdng cdt thep 3D cd nhieu uu dilm la kha nang chiu luc tdt, do cirng cao, chuyen vj va bidn dang rit Idn trudc khi bj pha hoai, va cd trgng lugng nhe han cac kdt cau BTCT truyen thong. Tuy nhien, mdt khd khan trong qua trinh img dung nd la tinh chit chju luc rit phifc tap. O nudc ta hien nay chua cd tieu chuin, quy pham danh cho thiet ke va thi cdng cdng trinh cd su dung vat lieu nay. Ly thuyet tinh toan cung nhu su nghien cifu day dO ve ket c l u ludi thep khdng gian 3D dugc lam rd se mg ra kha nang ipng dung rdng rai trong thuc tiin. Phuang phap giai tich td ra kem hieu qua va chira dung nhieu sai so khi tinh toan ket c l u BTCT 3D. Bai viet nay trinh bay ve ket qua nghien CUPU ket cau t i m BTCT 3D thdng qua md hinh sd va md hinh vat ly;

xac djnh phuang phap tinh toan ket c l u t i m BTCT 3D phan anh dugc thuc te lam viec cua ket c l u .

1. IVId>dau

Kit ciu tim be tdng ludi thep khdng gian (3D) dang ngiy cang dugc su dung rpng rai trong xay dyng. Kit tim ciu be tdng ludi thep 3D cd nhilu uu diem; Vdi uu dilm ndi trpi la k h i nang chju lyc tdt, dp ciing cao, chuyin vj v i biln dang rit ldn trudc khi bj p h i hoai. Viec bo tri cdt thep khdng gian 3D trong kit ciu be tdng nhim muc dinh phin tin cic dilm chiu img suit tip trung tren be tdng, Iam tang khi nang chju lye ciia cau kien.

Loai kit ciu nay nhe han so vdi tim kit ciu be tdng cdt thep die cimg khi ning chju lye. Kit ciu cd thi dugc sin xuit theo hudng cdng nghiep hda hang loat trong xudng dudi sy ho trg cua he thdng thilt bj ty dpng nen chit lugng dugc kiem soit chat che va cd thi giim ding k l thdi gian thi cdng.

Tuy nhien, v l ly thuyit tinh toin thilt kl cho loai kit cau niy chua thyc sy phit triin tuong ximg vdi k h i nang irng dung ciia nd. Viec thilt ke chu yeu dya vao cic ket

' Vien Thiiy cong. Ngirdi phan bien: PGS.TS. Nguyin Quoc Dung

qui thi nghiem miu tryc tiep. Mdt sd phuong phip giai tich nhu qui ddi ket ciu ve dang dim hay tim dac tuang duong cung da dugc phat trien, tuy nhien chiia dyng nhilu sai sd tinh toin, do viec xic djnh cac die trung ve do ciing tuang duang chua dugc chinh xic [3].

Cd thi thiy ring sy khdng cd mat d Idp be tdng giiia lam cho kit cau nhe hon, nhung ddng thdi khi ning chju cat ciia ket ciu ciing bj giam di rat nhieu. Chinh vi vay, cic thanh thep cheo cd muc dich chinh la chju cat vi rang budc do ciing giiia 2 Idp be tdng cot thep. Chiing lim cho ca he thdng lim viec ddng thdi, die biet l i khi ket ciu tam chju udn. Khi so sinh vdi mdt tam die chju udn, ta thiy cd the sir dyng ly thuyet tim udn nhu binh thudng, nghTa la cic gii thiet nhu phin td thing cd the sir dung tuong ddi phil hap. Tuy nhien, ddi vdi ket ciu tim ludi thep 3D nhu chiing ta dang xem xet, sy khdng lien tuc d viing giUa tam lam cho viec sir dung gii thiet phan td thing khdng the ip dung dugc, ban nira liic niy, sy chju cit phu thudc chinh vao cic thanh thep cheo. Chinh vi viy hudng nghien cim sir dung ket cau tuong duang nhu [3]

khdng giii quyet dugc bii toin mdt cich thiu dio, nd chi nen dugc sir dung khi da cd nhieu khio sit hay thi nghiem dugc tien hanh.

Nhu vay, ket ciu tim be tdng ludi thep 3D cd iing xir phiic tap vi cic Iy do chinh sau day: vit lieu lam viee phi tuyen, do ciing chung vi sy chju lyc cua ket ciu phu thudc chinh vao ludi thep duge bd tri theo khdng gian, die diem va sy phan bo cua tii trgng.

Phuang phip sd Ii mdt cich tiep can hieu qui hon nhieu so vdi phuang phap giii tich. Sy md phdng cic iing xir phitc tap ciia vit lieu be tdng ciing nhu cic lien ket edt thep-be tdng trong khdng gian hoin toan cd the dugc thyc hien vdi diy du sy chinh xic ve hinh hgc ciing nhu cic gii thiet vat lieu diing din ban din timg diem cua kit ciu.

Phuang phip phin tir hiru ban la mdt trong nhiing phuong phip sd manh vi ngay cang dugc phit trien rpng rai, die biet trong lmh vyc phin tich kit ciu.

Bai viet nay trinh biy viec lya chgn phuang phip phin tir hiiu han li cdng cu chinh de md hinh hda va tinh toin ket cau tim be tdng ludi thep 3D. Ly thuyit vl md hinh hda vi phan tich ket ciu tim be tdng ludi thep 3D cung dugc phit triin tren ca sd phuang phip niy. Ndi dung chinh la: xay dyng ly thuyit md hinh hda vit lieu, hinh hpc, lien ket vi tii trpng ciia kit ciu be tdng cdt thep va ludi thep khdng gian; xiy dyng cac md hinh phin tir hiiu ban cho mdt so dang chju lyc ciia kit ciu tim be tdng cdt thep 3D; phin tich lya chpn phin mim thieh hgp dl dinh gii img xir cua kit ciu nghien ciru theo md hinh da lip. Ngoii ra, mdt sd miu thi nghiem thyc tl ciing se dugc tiin hanh nham kiem tra dinh gii lai ly thuyit tinh toin da xay dyng.

2. c l u tao be tong cdt thep 3D

Cau kien BTCT 3D cd ciu true nhu d hinh 1. Gdm cd: Hai ldp mat ngoii cua

Panel la hai ldp be tdng ludi thep (cd dudng kinh tir 2 -;- 4 mm, ldp each d giira la loai

vit lieu xdp, nhe, bing polystyrene da xir ly chdng chiy).

P H A N II - X A Y DLING VA BAO VE CONG TRINH.. 481 2.1. Vira be tdng

Vira dimg trong ket ciu Panel 3D la vira be tdng hoac vira xi mang; tuy muc dich sir dung m i cd the diing vira be tdng mie 200-300, da 1x2, hoic be tdng cdt lieu nhd,...;

cd the chia thinh 2 loai: Be tdng phun va be tdng thdng thudng.

lti*;p ngafvo

Thep tJoc 1

Ihcpxipn I

' tfnl vL/a I hcac D€:ong j

Hinh 1. Sff dd cdu tgo Panel 3D 2.2. Sffi thep

Sir dung thep CT3 keo ngudi, eudng dp chju keo R > 4000 Kg/cm^, dudng kinh tir (2,0-^4,0)mm, mat dp d ludi l i (52x50)mm hoic (lOOxlOO)mm; sgi thep dugc ma kem de tang k h i nang chdng gi set.

2.3. L&p mdp (mushy polysteren)

Cd die tinh cich dien, cich nhiet tdt, nhe, nhung dii cirng de ddng vai trd vin khudn khi thyc hien do Icip be tdng.

Cic tim niy dugc mang den cdng trudng, lap ghep va lien ket lai vdi nhau theo hinh ding kien true cdng trinh thiet ke; sau dd tien hanh phun hoac trit be tdng de trd thanh mdt he toan khdi.

3. Phipo-ng phap mo hinh hinh hoa va phan tich k§t clu tim BTCT 3D

Phucmg phip md hinh hda va phan tich ket cau dugc chgn dua tren phuang phip phin tir hiru ban. Khi nghien ciru img xir ciia cac miu ket ciu tim 3D, cac md hinh sau dugc phit triin ddng thdi: Mdt l i md hinh phin tir khdi cho phin vit lieu be tdng va phin tir thanh cho cic thanh thep lam viec ddng thdi. Hai la md hinh phin tir vd cho phin bin be tdng, phin tir thanh cho cic thanh thep v i sudn be tdng lam viec ddng thcri vdi nhau. Hai md hinh tinh toin nay cho kit qui kha sit vdi sy lam viec thyc t l ciia kit ciu, sai sd tuong ddi giira chiing la khdng nhilu. Md hinh tinh thii hai, diing phin tir vd md hinh hda ban be tdng sii dung hgp ly hon diing md hinh phin tu khdi vi khdi lugng tinh toan cua phin tir vd nhd han khdi lupng tinh toin cua phin tir khdi nhieu, v i quan trpng han l i kit qui cua md hinh nay cho ta la ndi lyc dan vj (md men udn, lyc mang, lyc cit), edn md hinh phin tir khdi thi chi cho kit qui la irng suit. Khi kilm toin vl mat dp bin eua bin be tdng, ngudi ta cin ndi lyc ehir khdng cin irng suit. Vi viy, chpn md hinh nghien cim ling xu cua cic miu kit ciu tim 3D la md hinh phin tir vd cho

phin bin be tdng, phin tir thanh cho cic thanh thep va sudn be tdng lim viec ddng thdi vdi nhau [1]. Cie phin tir thanh lam viec tiep xiic vdi phin tir vd; dl tuong thich ve chuyin vi giOa hai loai phan tir niy ta diing phan tir thanh 2 dilm mit hoac phan tir bac cao 3 diem nut tuong irng vdi viec khi sir dung phin tir vd 4 hoic 8 diem mit.

4. Xay dirng chu'O'ng trinh phat sinh mo hinh phin tip hOu han tinh kit c l u tim 3D Nhu da neu d tren, phuang phip PTHH dugc [ 1 ] lya chgn de md hinh hda vi tinh toin ket ciu tam 3D; va md hinh phin tir dugc lya chgn li md hinh phan tir vd cho phin bin be tdng, phan tir thanh cho cic thanh thep vi sudn be tdng lim viec ddng thdi vdi nhau.

Vdi nhirng ket cau don giin, qui md hinh hda cd the dugc thyc hien bang tay do khdi lugng xir ly nhd. Vdi nhirng ket cau cd cau tao vi sy lim viec phure tap hon, viec tao ludi phin tir hiru han phii dugc thyc hien tren miy tinh ciing vdi cic phin mem md hinh hda phan tir hiru han. Hien nay, vdi sy phit trien cua cdng nghe thdng tin da cd rit nhieu phin mem hd trg qui trinh niy. Tuy nhien vdi nhirng ket cau chuyen biet thi viec md hinh hda tren cic phin mem ciing gap nhieu khd khan do chiing chi ip dung vdi nhirng ket ciu phd thdng la chinh, gii thinh cao (dac biet vdi nhiing phin mem eua nudc ngoai cdn cd giao dien khdng phai tieng Viet, khdng thin thien vdi cic ky su trong nudc). Ket ciu tam 3D ciing la mdt trong nhung trudng hgp do. Hien nay, khi thiet ke tam 3D, de tinh toin nd cie ky su khdng the ip dyng nhiing md hinh phiic tap vi mit rat nhieu thdi gian va cdng sire. Hg chi cd thi thyc hien tinh toin dya tren cac md hinh da dugc gian hda rit nhieu, do do khdng thi phin inh sit thyc sy lam viec, img xu ciia ket cau tim 3D khi chju tii trgng. [1] da xay dyng thinh cdng phin mim chuyen biet de hd trg phit sinh md hinh phin tir hiiu ban, kit hgp vdi phin mim Midas phuc vu tinh toin tim 3D.

De kilm chiing phin mem xiy dyng md hinh, [I] da tiin hinh nghien ciru thf nghiem tren md hinh sd vi md hinh vat ly vdi ddi tugng nghien ciiu li tim bin BTCT 3D.

5. Thi nghiem mo hinh vat ly va mo hinh s6 cho k i t c l u be tong c6t thep 3D Tien hinh thi nghiem md hinh vit ly vi md hinh sd cho kit ciu ban nhu sau:

5.7. Thi nghiim md hinh vdt ly

T4i trpng

Tam 3D Gdike

Hinh 2. Sff dd chdt tdi eda md hinh thi nghiim

PHAN II - XAY DtJNG vA BAO VE CONG TRINH.. 483 Thi nghiem dugc tiin hanh cho tim cd kich thudc:

- Tim dugc chi tao thi nghiem cd chiiu dai 2200 mm, chiiu rdng 500 mm.

- Tim che t^o gdm 2 tim don cd chiiu day 60 mm, khoang cich giiia tim 2 tim don l i 120 mm (tim 3D diy 180 mm).

Qui trinh chit tii dugc chia thanh 05 cip tii trgng.

5.2. Md hinh phdn tw hdu hgn

- Md hinh vat lieu: cic vit lieu trong md hinh so dugc tao ra vdi cic thdng so tuong duong vdi cic vat lieu sir dung trong thi nghiem.

- Md hinh phin tir: sir dung cac phin tir vd (Shell) dl md ta cic tim don, su dung cac phan tir din de md t i cic cdt thep, sir dung cic phin tii' dim dk md t i cic sucm d hai dau.

i^4^-:

Hinh 3. Md hinh 3D ddm thi nghiim sd

Dinh sd cic nut: cic nut d tim tren va dudi duac danh sd nhu hinh ve

'--i~

:;-

i ^ m

%^

S ^

•.-:

; : S 'i'-

= 5 ;

••ii 5I-I

W 19:

\lk

iBS 54 f 5 ; s

;r L i i -

;«

s^

5 ' 2 }':-i

' - • - • -

-'i'

-A-

5;.:

u

f-

:-,$

r"

»?- i i :

\'f

\6~

ir.

5 i : 0 - )^?

i i ; ;

145 , n - 53-^

>3"

:_:

••^-

: > a

.-^

C-'l ii:

"';;

J S -

M-=

r,i

i 7 ^ 5 6 ' 5 J : - s -

',-.

I;- 4 - . ' i'-^

y

iid

!*'

r ? i^2

'••'i '.-i

:•-'

:-

L - - -

;:-

: • ;

^ 4 i

.-.,

rs

L ' - -

:•_

;;:

}'.i

--"

? : : i - ; :

--

;„

•J

? . ' "

1.5- i - ^ i-i

U

5 3 : 5 : - S-"

\<^ U "

ITS S5:

W m

•ii iV

•' i

J;E

^i-"

SS«:

,T

ii-

^;

ss?

i S ?

ss:

;

5$

i:

7l'~

i^'

jlSS

l i i

5 : : 3 5 -

;•:

=^^

; ; - •

:^- .^.

^c-

; - • ;

=irr

-)-

1 , 1 -

iii.

n^

§~2 i r 5^S

.r.

<-.-

-z:

A-^

'••Z

Ddnh sd cdc nut phdn Id' cua tdm tren: 331 - 660

i-

•^^

,-.,

1 « -

:->

;>

-S

.^•

i ^ A

r

j -

t»f*

iS^

' 4 '

'*;:

;o*

•s

>;<

-•^z : c

-•>

;;.

,-

'•

;•

•_

s::

i-^

1^;

5;

if

•.^i

\^

li-

';. 56"

._

w B i r

?;;

1 1 ; - 1 -

J-1- 3 ; ;

-<;

;•

i -

>-f t "

;•

; ;^

;;^$

rs:

;.;

'.s'

^'•i.

u S :

•^

:^

1 ; ^

'iH-

.?:- 5 : "

S'

:•

' l i iy.

n : nt i i -

• ci

• 2 : j :

r

ih

^ 6 ; , 5 . 3S.' J''^

: ::

m

:-:

;_;:

' M ' • - c

;:^:

• 2 : i i *

U S -

;^ r

Ii-.

Hi

...

3i."

^ T ;

:<;

• i".

.*•'

Ddnh sd cdc nut phdn tir ciia tdm dw&i: 1 - 330

Danh sd cic phin tir: cic phin tir thudc tim tren va t i m dudi dugc d i n h sd nhu hinh ve

1

; ^.-T—ry;— -rr^ zz zznr: z z z = i =z:z z ^zTz zz, iz: ^i;.:^ ^:;;= =^:;; =:^=; ==5:^ :zi;z3; •;:z=z -:. z:z:^ ^4::^ = ^ : — , ^ = s .

Ddnh sd cdc phdn tucua tdm tren: 289 - 576

1

;: ;;: .;-f;:

-- ;:- ;.::;:

y.'.'.'.. 2:2

--- -•

;;; :. ;-:

; ; ^ : . - r

- r - - -!

u : ; - ; ~ ::;::" :;s

. = - • :

; - : . - f ^

i^i^

; - • ; 5

; . E : . : . ; ;

; . . : : . V6

..-: -. .-

2'.: . : ;2i

: : - : • • ; ; ; ; ;

:;::;= :;: :;

•- i-.

: - . • ;

:::;;;

;f

::-

Ddnh sd cdc phdn tir eda tdm dw&i: 1 - 288 5.3. Kit qud tinh todn

So sinh ket q u i do duge d md hinh thi nghiem v i ket q u i tinh toin ung suit va chuyen vj theo md hinh sd.

Bdng 1. Sai so giica ket qud cita iing sudt do dugc lir thi nghiem vd tinh todn theo mo hinh so

Diem do (Phan tir) 1,3(145) 2,4(17) 9,11 (433) 10,12(305)

5,7(159) 6,8(31) 13,15(447) 14,16(319)

T a i l Aax (%)

-9,3%

-17,5%

-0,1%

-

-4,5%

10,6%

Aa, (%) - - - - '—- -

Tai 2 Ao, (%)

-4,5%

-17,2%

-8,45%

-

-0,9%

9,8%

Ao, (%) - - - - - -

Tai 3 Ao, (%)

-9,5%

-12,2%

-24,8%

-

4,46%

17,05%

Ao, (%) - - - - - -

Tai 4 Ao, (%)

28,3%

-12,1%

-38,4%

-

14,4%

19,8%

Ao, (%) - - - - - -

PHAN II - X A Y Dt,JNG vA B A O VE CONG TRINH... 485

Nhdn xet:

- Khi tii cdn be, iing suit keo trong be tdng cdn nhd (dudi 8 daN/cm^) thi sai sd giira tinh toin theo md hinh sd va thi nghiem cd sai sd tir 5%-I0% (trir phin tir sd 17, cam bien do tai dd cd vin de). Day l i sai sd chip nhin dugc khi lim thi nghiem vdi ket cau BTCT. Tir nhan xet niy cho thiy viec tinh toin md hinh sd nhu tren li phan anh dugc thuc te lam viee cua ket ciu 3D nay.

- Khi tii trgng ldn, irng suit trong be tdng vugt qui iing suit keo, be tdng bat diu bj nirt va do dd sai sd cung Idn len, cd diem tdi gin 40%. Dieu niy chimg td rang ta khdng the tinh toin ket ciu be tdng khi da niit theo md hinh tuyen tinh thdng thudng dugc, ly thuyet va thye nghiem da chirng minh dieu nay.

6. Ly thuyit tinh toan k i t clu be tong c6t thep 3D

Trong cic tieu chuan thiet ke xiy dyng trong nudc, nhirng quy tic chung cho qui trinh tinh toin thiet ke van chua dugc thiet lap. Do dd, viec xay dyng ly thuyet tinh toan phil hgp cho loai ket ciu cd sir dung be tdng cdt thep 3D la cin thiet.

Tinh chit ciia be tdng cdt thep 3D cin phii dugc tinh den trong qui trinh tinh toan nhung van trong khudn khd tinh toin ket ciu be tdng thdng thudng. Va dieu nay se md ra khi nang img dung rdng rai trong thyc tien.

Phuang phip dugc lya ehgn dl thilt kl kit cau be tdng cdt thep 3D li phuang phip trang thii gidi han. Diiu kien an toan cho ket cau dugc bieu dien theo bieu thirc sau:

U<(t)Rn (1) Trong dd: U - tii trgng tic dung dugc tinh toan tir cic td hgp lyc;

Rn - do b l ciia ciu kien be tdng cdt thep;

(j) - he sd giim do bin, phu thudc trang thii bien dang cua ket ciu.

6.1. Tinh todn tiit diin cho kit cau bi tdng cdt thep 3D

Viec thilt k l tim 3D dugc bit diu tir lya chgn so bd kich thudc, vit lieu va bd tri ciu tao. Sau dd tiin hanh md hinh hda va tinh toan kit ciu tim 3D da chgn.

N M

f

0,85fc'.b.x

f.As

a - ung suit trong cdt thep

fs - cudng dp cdt thep

Hinh 4. Khd ndng chiu lire ciia mat cdt bi tdng vd thanh cdt thep

Viec phin tich kit qui phii dya tren thdng ke va tdng hgp tit ca c i c ket q u i trong md hinh tinh. D I giim thieu cdng siic tinh toin, [I] da xay dyng mdt chuang trinh cd khi nang ty ddng phin tieh cic ket q u i cua q u i trinh phan tich ket cau.

Viec phan tich eic ket q u i tinh toin tim 3D thyc chit la qua trinh kiem toin tam 3D dudi tic dung ciia eic tii trgng. Sd lieu cua q u i trinh nay chinh l i c i c ket qui, tinh toan npi lyc, img suit trong cic bd phin cua tam. Cic sd lieu n i y se dugc so sanh vdi khi ning chju lyc cua timg bg phan (kha nang chju lyc dugc tinh toan dua tren kich thudc, bd tri ciu tao ciia cic bd phin).

6.2. Kiim todn khd ndng chju Iwc eda tdm be tdng

Cic tim be tdng dugc rdi rac hda thinh nhirng phan tu vd dang ehir nhat. Ket qua npi lyc tinh toin trong cic phin tir la cic thanh phin ndi lye don vj. Vi viy, de kiem tra kha nang chju lyc ciia mdt vj tri, tich ra mdt phan td cd kich thudc dan vj nhu hinh 5.

'M.rr

Hinh 5. Sff dd npi Iwc trong phdn tw vd dgng ehir nhdt

Viec tinh toin khi nang chiu lye dugc xic djnh theo tirng phuang img vdi he tpa dp dia phuang ciia phin tir, tiie l i irng vdi cic mat cit theo cac phuang dd. Tren mpt mat cit, viec tinh toin dya tren khi nang chju lyc kit hgp: lyc dgc -i- md men v i lyc cit.

^

O.SSf'.b.x

A f N • f

O.SSf'.b.x

A f

Mat cat chju nen uon Mat cat chju keo uon Hinh 6. Sff dd npi Iwc tren mat cdt tinh todn Mat cat chju nen uon

Cac phuang trinh co bin irng vdi trang thii gidi ban:

Phuong trinh lyc dgc:

Nn = 0,85fc'.b.x-f3A,

(2)

PHAN II - XAY DUNG vA BAO VE CONG TRINH... 487 Phuong trinh md men:

Mn = 0,85fc'.b.x.(h-x)/2 (3) Mat cdt chiu keo uon

Cic phuong trinh co ban iing vdi trang thii gidi ban:

Phuong trinh lyc dgc:

N„ = fsAs-0,85fc'.b.x (4) Phuang trinh md men:

M„ = 0,85fc'.b.x.(h-x)/2 (5) Trong do:

fc' - cudng do chju nen ciia be tdng;

fs - cudng do thep;

b - be rdng mat eat (liy bing don vj);

h - chieu eao mat cit;

x - chieu cao viing be tdng chiu nen.

6.3. Kiim todn khd ndng chiu Iwc ciia cdc thanh thep

Vdi cic cdt thep va cic thanh thep xien, ket qui kilm toin se dya tren so sinh giira irng suit trong thanh vdi cudng do cua thep ehe tao.

a > fs - thep khdng du khi nang chju lyc;

a < fs - thep du kha nang chju lyc.

* Cong thwc tinh todn vd bo tri thep xien:

Thep xien cd tic dung chdng trugt giira hai bin ciia cira van de hai bin nay lam viec ddng thdi. Do viy, vai trd ciia thep xien la de chju lyc cit va do dd mat do ciia nd se phu thudc v i o do Idn eiia lyc cat.

Xet mdt doan dam cd chieu dii theo phuang dgc true li a. Do cd sy chenh nhau md men udn giiia hai mat cat nen irng suit phip giira hai mat cat cung chenh nhau.

Hgp lyc ciia img suit phip ciia hai mat cat li Ni va N2. De phan to nay can bang thi tren mat eit song song vdi true dim phii xuat hien iing suit tiep Xyz. Hgp lyc ciia Xy,^

tren phin dien tieh F=ab l i T. Ta cd phuang trinh can bang Ni + T - N2 =0. Tir phuang trinh can bing nay, ta d l dang xic djnh dugc Xyz theo cdng thirc:

J..b (6)

Tai vi tri giao giiia ban va thep xien, ta dit x = Xyz, hgp lyc T = tab se dugc tmyIn toin bg sang thep xien. Ndi cich khic, cac thanh thep xien tai dd se chju toan bd luc T. Vi giira hai bin cd khoing cich khi ldn so vdi duong kinh thanh thep nen cic

thanh nay chii yeu chju lyc keo hoae nen. Vay de cho hieu qui, ta nen bd tri cic thanh thep nay xien gdc 45° so vdi mat bin.

Neu tren dien tich F = ab chi cd hai thanh thep xien vudng gdc vdi nhau, ta cd thi xac djnh dugc kich thudc a, b theo edng thiic:

T = xab = 2F,[a] cos45° (7) Trong dd: Ft - dien tich mat cit cua mdt thanh thep xien; [u] - img suit cho phep

ciia thep xien.

j..b (8)

trong dd: S^ = bt—— (tam bd qua phin thep chju lyc cua bin).

, bt^ . f r + t , , J, = — -I- bt = bt

" 1 2 I 2

t^ fr + X^'

n'^i 2

:^ ' - . " • ^ ^

...Zl [7

• y ^ - T - - .^y

&

^- /^

^{V N:}

\~-

Hlnh 7. Biiu dd npi Iwc cua mat cdt tinh todn

\

G

Hinh 8. Sff do bo tri thep xien trong ddm

PHAN II - XAY DLJNG VA BAO VE CONG TRINH..

489 Tai tga do z, ta cd

Q(Z)

= ^ ( \ - ^ ] = M ^ f 1 - ^

Thay tat ci cic dai lugng tren vio (8) ta dugc:

^„(r + t)(l-|]HL

Ajl-fJHL, (9)

(10)

(11) Trong thyc te, neu bd tri thep xien gdc 45° so vdi mat ciia tim thi khoing cich a bing khoing each giira tim hai tim don. Khoing cich b se dugc xic djnh hi cdng thiic (11).

V2F,[a]

b =

I-^Wa (12)

7. Ket luan

- Ket ciu tam be tdng ludi thep 3D cd irng xu phirc tap vi cic ly do chinh sau day: vat lieu lim viee phi tuyen, do cirng chung vi sy chju lyc ciia ket ciu phu thupc chinh vio ludi thep dugc bd tri theo khdng gian, die diem va sy phin bd cua tii trpng;

viec sir dung phuang phip giii tich de tinh toin nhu qui ddi ket ciu ve dang dim hay tam die tuong duang chira dyng nhieu sai sd tinh toin, do viec xic djnh cic die trung ve dp cirng tuong duong chua dugc chinh xic. Ket qui nghien ciiu eho thiy, viec lya chpn phuong phip PTHH de tinh toan ket ciu 3D la each tiep can hieu qui hon nhieu so vdi phuong phip giii tich; sy md phdng cic iing xir phirc tap cua vit lieu be tdng cung nhu cic lien ket cdt thep-be tdng trong khdng gian hoan toan cd the dugc thyc hien vdi diy dii sy chinh xic vl hinh hgc ciing nhu cic gii thiet vit lieu dung din hon den timg diem cua ket ciu.

- Vdi nhiing kit ciu dan giin, qui md hinh hda cd the dugc thyc hien bing tay

do khdi lugng xir ly nhd. Vdi nhirng kit ciu cd ciu tao vi sy lam viec phirc tap ban

(nhu kit ciu tim 3D), viec tao ludi phan tir hiru han phii dugc thyc hien tren may tinh

ciing vdi cic phin mem md hinh hda phin tir hiru han. Ket qui nghien cim cho thay da

xay dyng thinh cdng phin mem md hinh hda phin tir ket ciu tam 3D vdi viec lya chgn md hinh phin tir vd eho phin bin be tdng, phin til thanh cho c i c thanh thep va sudn be tdng lim viec ddng thdi vdi nhau. Ket q u i tinh toan tren md hinh sd da dugc kiem nghiem tren md hinh vit ly.

TAI LIEU THAM KHAO

[1]. Nguyin Thanh Cdng (Chu tri) v i nnk (2005-2008), Nghien ciiu irng dung ludi thep khdng gian ba chieu (3D) trong kit ciu be tdng cdt thep cdng trinh Thuy lgi, Vien Khoa hgc Thuy lgi, Ha Ndi.

[2]. "Tieu chudn ACI 318 ", Vien Be tdng Hoa Ky.

[3]. Do Kiln Qudc (Chii tri) v i nnk (2002), "Ly thuyit tinh kit cdu bdng Panel 3D luai thep Iheo mo hinh vo true huang". Dai hgc Bich khoa, TP Hd Chi Minh.

[4]. The Consulting Engineers Group (1991), "Structural Analysis of ICS 3-D Wall Panels", Publication I.C.

[5]. R. Park & T. Pauley (1975), "Reinforced Concrete Structures".

[6]. Robert D. Cook, "Finite element Modeling for Stress Analysis", John Wiley &

Sons INC, 1994.

[7]. O.C Zienkiewicz & R.L Taylor, " The Finite Element Method", Fifth Edition, Volume 1: The Basis, Volume 2: Solid mechanics. Published by Butterworth- heinemann, 2000.

[8]. C.S Krishnamoorth, "Finite Element Analysis-Theory and Programming", Tata McWraw-Hill Publishing Limited, 1996.