Tinh toan thanh canh thap thep tiet dien thep goe dan CO ke den giam yeu va do lech true tai vj tn nut
Calculation of single equal leg angle members of steel tower that includes the weakening cross section and the eccentricity at the node position
Pham Thanh Hung Tom tat
Thap thep c6 chieu cao nh6 thirdng duac cau tao tir cac thanh thep goe San, chiing co hai mat phang vuong goe vol nhau nen di lien ket vdi nhau.Tuy nhien, vi lien ketdcanh ciia tiet dien nen true thanh va true lien ket bj lech tam. SUlech tam nay gay them mo men uon cue bo tac dung len thanh canh tai vi tri nut Bai bao nay gi6i thieu kiem tra thanh canh co ke den sU giiim yeu do lien ket va mo men uon tai vi tri niit
tkeo tieu chuan Nga [SNIP 11-23-81*).
Tir klida: Thdp thep, thep gdc, tiet dien gidm yiu Abstract Steel towers of small iieight are usually composed of steel angles because steel angles has two perpendicular plane so easily
linked together. However, the alignment on the lateral side ofthe shaft and the linlt axis is eccentric. This eccentricity causes the bending effect on the mam member at
the node position. Tfiis article introduces the main member calculation that includes the weakening cross section and bending moment al the node position according to the Russian Standard (SNiP 11-23-81*) Keywords: Steel tower, steel angle,
weakened cross section
TS. Ph(im Thanh Hung Khoa Xdy dung Trudng Dgi hgc Kiin true Hd NQI EmatI, [email protected]
1. Dat van de
Hien nay, cac cong trinh thip thep ngiy cing pho biin, thuung duoe dting lam eot dudng diy tai dien, egt ang ten v l tuyin, cit giln khoan. Kit cau cua thap thuung la he khlng gian ba m$t tro len, duuc ciu tao lir cac thanh (thanh canh va thanh byng) lien kit vcyi nhau tai eae nut. Tiit diln thanh thuong duo'c sir dung la thep goe, thep ing, thip hinh chO I hay to hup tu cac thip goe. Voi cac logi thap thep be va viea thi tiit di|n thep goe do-n (L) dugc su dyng phi bien nhat.
Tgi eae niit, lien kit thuong duuc sir dung la lien kit bu long, do do, tilt dien ele thanh bi giam ylu (Hinh 1) Mat khic, cac thanh bung lien kit vol thanh canh tai mat ben do vay cac lue khlng di qua true thanh canh tao ra mo men leeh tam. Tai vi tri nil ehong thanh canh hole thay dii tiit dien thanh eanh (Hinh 2), li,i'c doe tac dung len tiln dien 1 va 2 eo su lech true gay ra m6 men uin tai vj tri nay.
Viec tinh toin thanh cInh theo TCVN hi|n nay ehua d l c§p cii thi din din mo men do d6 llch true gly ra, anh huang ciia mo men uon v l cae ylu to bat Igi khae duge dua vio he s i dieu kiln Ilm vile y^ (Bang 3, TCVN 5575 - 2012) [3] Theo tieu ehuan Nga (SNiP 11-23-81*) viec tinh loin thanh cInh da tinh din anh hu6ng ciia si,i' giam y l u cung nhu eae ylu t i gly ra mo men do su lech true trong thanh cInh. Trong gioi han noi dung bai bao. se trinh bay each kilm tra cho thanh cInh t i l l dien thep goe don co k l din su giam ylu tilt dien va do lech true theo tieu ehuan Nga (SNiP 11-23-81*) [2].
2. Tinh toan thanh canh chju ILFC true va md men udn
Khi tinh loan thanh cInh tgi vi tri niit, chOng ta phai k i din irng suit gay bui m l men do do lech true khi cic thanh bung liln kit vio mat bin thanh cInh {lue tac dung nay khong di qua trgng tam tiit dien).
Viee kilm tra ben Igi tiit dien lai vj tri gilm y i u ciia thanh cInh chiu luc true v l m l men duac xac ^nh theo bieu Ihire sau [1];
N M . „ ( V , - + M,^Jl,,x,-L„ .ny,
KXn-K. (1)
trong d6:
N - li/c doc trong thanh tai tilt dien dang xet;
An - dien tieh tiit di^n thuc eiJa thanh tai hoac mat cit ngang hole mat c i i zich zic (Hinh 1);
Mjin: Myn" ^ ^ Tien uon doi vai cac Iriic x^ v l y,, do su dit lech tim eua luc truyin tir thanh gilng vio ni5t phia doan thanh einh dang xel M,n, M^n xle dinh theo bilu thirc (2);
x^, yn - la ele true trung tam tai mat cit gilm y i u dang xet;
'in. lyn" f"o f"^" '^^^^ ^^^^ '^'^^ ^1®* ^iln thuc doi vai cac tryc x^, va yn;
11 l i 21
11 5i, i i 6i
Hinh 1. Nut thap thep, cac mat cat tai vj tri giam yeu de xac dinh tiet dien thu'c, mat cat ngang (1-1, 2-2, 3-3, 4-4) va mat cat zich zSc (a-b-c-d-e), (f-g-b-c-h-k)
67
KHOA HOC & CONG N G H E
Ixn.Vn - "10 men quan tinh li Ilm ciia tiit di^n thuc dii vai he true (Xr„yn);
Xi.y, - Ipa do diim kiim tra irng suat trong he In^e (Xn.yn),
f - cuang do tinh toin.
Mo men uon Mxn va Myn dii vo'i cic true Xn va y^ do iy'e tac dung lech trgc ciia thanh iaung dugc xae dinli theo biiu thiresau [1]:
M„ = ki;N,,„e,;M^=kXN„,„e„
(2) trong do
k - h | s i phan phii mo men tai niit cho liit dien tren va duo'i nut, k phu thu6c li s i dO cirng dan vi eiJa thanh canh tren nOt va thanh canh dual nut.
Trong truang hap tilt dien khong thay doi, nilt dang xet la nut trung gian (nhu Hinh 4a) he s i k dugc xic dmh nhu sau - He s i phan phii mo men cho tiil dien dual nut:
- He s i phan phii mo men cho tiit dien tren niil:
Hinh 2. Mat cat tai vj t r i thay doi tiet dien
1, 2 - tiet dien thep gdc;
3, 4 - trong tam cua tiet dien 1, 2
L
(3b)vai Im va lrn.i 11 khoIng elch tir nOt dang xet din nut duai va nut tren k l n6;
e,,, Byi - khoang each tir dilm dat luc Nmjj den cic true Xn va yn;
Nn,rt, - lue do cae thanh bung tie dung len l i Ihir j theo phuang dgc true
T i l c l cic dai lugng (N, M,n, M,n, x„
y,) trong cong thirc (1) phai di ciing v6i diu cCia chiing, L,yc doe N duac eoi la duang khi no gay keo, mo men M,^, va
Myn, coi II ciuong khi no gan nin eho phan song, Diu cLJa mo men M^^ v l M^n duge ty dong xic djnh khi eae dai luang (Nny)|. e,„ Oy,) trong eong thirc (2) dugc dua vao tinh toin CLing vai diu ciia chiing, khi do Nma, xem la duang nlu chung huang tir khoang chira thanh dang xet lai tilt dien xem xet.
Momen quin linh li tam ciia t i i l dien gilm yiu I,|„yn doi VO'I he true (x^,y„) duge xac dinh theo eong thirc gan dung sau [1].
!„„„ = -abA,
(4) vai. a,b - khoing each tir trpng tam tiit dien giam ylu din cae trye X2 v l y2;
An - dien tich tilt dien gilm ylu. vu6ng goe vai tryc thanh.
Khi linh loan v6i tiit di^n giam yiu, lai nhCrng nai eo tic dyng Ige eiia thanh xien len thanh eanh, h i s i dilu kien lam viec YJ. duac lay bing 1,0.
3. Vi du tinh toan
Kiim tra u'ng suit keo tren thanh eanh tgi vi tri niit nhu tren Hinh 5. Niit dang xet II niil trung gian so 4, Ihanh eInh sir dung II thip goe diu cgnh L110x7. Thep CT34 c6 f = 21 KN/cm^
Hinh 3. Xac djnh vj tri 16 giam yeu. Vj t r i h& true toa dp
b)
1 p i N m d
/ '
Mt
1 ^
E—
Hinh 4. Phan phoi mo men len tiet dien thanh canh tren niit vk du'di nut
a ~ phan phoi mo men tai nut trung gian b - phan pho*! mo men tai nut gan chan thap
Tai nut 4 thanh canh duac kiim Ira bin keo tai hai m?t cit 1-1 va 2-2 nhu tren Hinh 5.b
Ouang kinh 15 bu long d, =21,6 em; d; =17,6 cm, khoing each tir Ilm 16 bu long 1, 2 den song t i l l dien Ian lugtl^
Coi=6,0 cm; Co2=6,0 em. Chilu dai eic doan thanh canh 3-4 v l 4-5 lin lugt la ln,.i=200,0 cm; ln,=220,0 cm.
Lue keo trong 2 doan thanh eInh 3-4 v l 4-5: Nnn=200 KN. Nn,=220 KN
Cae thinh phin lyc tie dung do thanh giang Imyin vio nilt theo phuang doc tme thanh cInh v6i dau tuang (rng:
Tgi mat cit 1-1. N^^, = 30 KN; U^^z = -10 KN, Tai mgt ell 2-2' Nn,di = -30 KN, N^^a = 10 KN, Lue keo lai hai mat ell 1-1 va 2-2.
N,., = 220 -HO = 230 KN; Nj.a = 200 -H 30 ^ 230 KN Thep goe diu eanh L110x7 c6 cic dac trung hinh hgc nhu sau: A = 15,2 cm^; ZQ = 2,96 cm; !>;= 176 cm''
Tai nut 4, t i l l dien bj giam y l u bai hai 16 co di?n tich A,=2,16xO,7=1,51 cm^;A2=1.76x0,7=1.23em^.
Dien lich t i l l dien giam yiu: A^=15,2 -1,51-1,23=12,46
68
TAP CHI KHOA HOC K I E N T R U C - X A Y D U N G0\
.f' Kn
=P==
Al
' 1 1 ^ 5 '•
7. ^
• ^ e y i l
K,
2 - 2
a - scJ do doan thap; b - niit so 4; 1 - diem dat lu'c H^^^-, 2 - diem dat lu'c Nmdz; 3 - trong tam tiet dien giam yeu Hinh 5. Vi du tinh toan
3.1. Kiem tra ting suat ten cac diim A, B, C tai mat cit 1-1 T o a do trpng t a m tiet dien giam y e u trong h e true x , va y i x l e djnh theo bieu t h i r c :
v a i Syi, S , i - m o m e n tTnh eua t i l t di#n giam y l u doi vd'i c i e true y , v i x , . Sy,, S , i d u g c x l e djnh n h u s a u :
S „ , = A z . - A , e . , - A , -
= 1 5 , 2 x 2 , 9 6 - 1 , 5 1 x 6 - 1 , 2 3 x 0 , 3 5 - 3 5 , 5 e m = d , , = AZn - A , A , c . ,
= 1 5 , 2 x 2 , 9 6 - 1 , 5 1 x 0 , 3 5 - 1 , 2 3 x 6 = 37,08 em^
D o d o :
F. R 37 nfi 18 cm;
Theo cong fhire (4) ta co:
I.„,^„ =-2,50x2,63x12,46 = -81,92 cm'' H I so phan phoi mo men k tai niit 4 len dogn thanh canh 4-5 xac dmh lir sa do dam hai nhip liln luc eo lien kit hai d i u d i m la khap (Hinh 4.a). Theo eong thirc (3a) ta co.
1^ +1„_, 200 + 220 Do l|ch true eiJa lye Nm^n.
•^.1 = - [ y o r - ^ j - - ( 2 , 9 8 - 0 , 3 5 ) = -2,63cm,
= (c„, - ( 6 - 2 , 8 5 ) - 3 , 1 5 c m . Do l#ch tryc ciia luc Nnvi2
«.i = {Co2 - VoJ = (6-2,98) = 3.02CI
12,46 12,46 . X o , - - =-{2,85-0,35) = -2,5cm
Thay eae dgi lugng Nma,, N^aj, k, e „ , ey,, e^, 0^2 vao Cac mo men quan linh eiia tiet dien giam yeu Ixn, lyn,
lxn,yn d l i vai eae tme trung lam xn va yn xae dmh bang ap , . . . .
dung eong thirc chuyin tme song song va bo di phin giam ^'^" ^hue (2), ta eo mo men uon doi vai eae true x„ va y,:
M,„ =k2^N„j^e,j
= 0,476x[30x(-2,63) + (-10)x3,02] = -51,93 KNcm, yeu. Ta c6'
I<r=I,+A(yon- ya,- -A,{C(,.
-y.J-
M „ -kZ^r™
= 176 + 15,2(2,98-2,96) -1,51(2,98-0,35) -1,23(6-2,9
= 154,34 cm''
I^=I^+A(Z(,-X(,„) -A,{Co,
-1,23(2,85-0,35)'
= 176 + 15,2(2,96-2,85) -1,51(6-2,1
= 153,51cm'
vo'i i „ ly - m6 men quin tinh ciia t i i l dign nguyen y l u doi vdi eac true trung tam x-x v l y-y;
Toa do trpng lam t i l t dign giam yeu trong h§ true X2 v l yj.
D = + X , „ - - -2,85 0,7 2,50 c
= 0,476x[30x3,15 + (-10)x(-2,5)] = 56,88 KNcm Tpa do cac diim A, B, C Irong h0 tryc x^ va y^- XA= 11 - 2,85 = 8,15 cm; yA =-2,98 em;
Xa = -2,85 cm, ye = 11 - 2,98 = 8,02 cm;
Xc = - 2,85 em, yc = -2,98 em.
Kiem Ira irng suit tgi cac diim A, B, C trIn m|t e l l 1-1 duac thuc hien theo efing Ihire (1).
230 (-51,93)[l53,51(-2,98)-(-81,92)8,15]
' ' " 12,46 154,34 153,51-(-81,92)' 56,88[154,34 8,15-(-81,92)(-2,98)]
154,34-153,51-(-81,92)'
= 21,21 KN/cm^>21KN/cm^
69
M^\ KHOA HOC & CONG NGHE
2 3 0 ( - 5 1 , 9 3 ) [ l 5 3 , 5 1 - 8 , 0 2 - ( - 8 1 , 9 2 ) ( - 2 , 8 5 ) ] ' ^ ^ ~ 1 2 , 4 6 1 5 4 , 3 4 - 1 5 3 . 5 1 - ( - 8 1 , 9 2 ) '
5 6 , 8 8 [ l 5 4 , 3 4 ( - 2 , 8 5 ) - ( - 8 1 , 9 2 ) 8 , 0 2 ] 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) '
= 16,14 K N / e m ' < 2 1 K N / c m ' ,
2 3 0 ( - 5 1 , 9 3 ) [ l 5 3 , 5 1 ( - 2 , 9 8 ) - ( - ^ 1 , 9 2 ) ( - 2 , 8 5 ) ] '^'^ ~ 1 2 , 4 6 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 . 9 2 ) ^
5 3 , 0 6 [ l 5 4 , 3 4 ( - 2 , 8 5 ) - ( - 8 1 , 9 2 ) ( - 2 , 9 8 ) ] 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) '
= 18,28 K N / e m = < 2 1 K N / e m ' .
V a y t i l l dien 1-1 khong thoa m a n d i l u kien b i n tai d i l m A.
3.2. KiSm tra Crng suit t^i cac diem A, B, C tai mat cat 2-2 He s i p h i n phoi m o m e n k tai n i i l 4 len d o g n thanh eanh 4 - 3 X l e djnh ILJ' s a d i d a m hai nhjp lien l y e co lien k i t hai d a u d i m I I k h 6 p (Hinh 4 a) T h e o cflng t h i r c (3b) l a eo:
2 2 0 - = 0,524
( - 6 2 , 5 7 ) [ l 5 4 , 3 4 ( - 2 , 8 5 ) - ( - 8 1 , 9 2 ) ( - 2 . 9 8 ) ] 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) '
= 18,65 K N / e m ^ < 2 1 K N / e m ^ .
V a y l i i l dien 2-2 k h o n g thoa m i n dieu k i l n b i n lai dilm B.
3.3 Kiim tra irng suit tai niit 4 theo TCVN 5575 - 2012 V i l e k i i m tra b i n tai t i i t dign g i a m y i u cua thanh canh ehiu l u c true d u g c x i c dinh t h e o b i l u t h i r c s a u [3], [4]:
N
^ f / c
(5)
= 17,66 K N / c m = < f y ( . = 2 1 x 0 , 9
„ + ! , , _ , 2 0 0 + 2 2 0
Tren mat e i t 2-2 c a c d a i l u g n g Xgn, yon, Ixn. 'yn. 'xn.yn. e , , ,
^x2< 6 / 1 . fiyz. XA. VA. >tB. VB- ^C- VC iLfong t u n h u tren mat cat 1-1.
C i e l y c Nmd, t i e d y n g len t h a n h 4 - 3 v a i d i u q u y u a c Nn^i = - 3 0 K N , N „ r t 2 " 1 0 K N ;
Thay c i c dai l u g n g Nmoi, Nn,d2. k, e , i , e^i, e ^ , e^ v i o b i l u thLFC (2), ta CO m 6 m e n u i n d i i v a i eae t m e x^ v l y^:
M . „ = k ^ N ^ ^ , e ^
= 0,524x[(-30)x(-2,63) + 10x3,02] = 57,13 K N e m ;
= 0,524x[(-30)x3,15 + 10x(-2,5)] = - 6 2 , 5 7 K N e m .
K i i m tra i r n g s u i t lai eac d i i m A , B, C tren m a t c l i 2-2 d u g e t h u c h i | n t h e o c o n g t h i r c (1):
2 3 0 5 7 , 1 3 r i 5 3 , 5 1 ( - 2 , 9 8 ) - ( - 8 1 , 9 2 ) 8 , 1 5 l CJ. = + != ^^ —:; i =!- +
1 2 , 4 6 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) ( - 6 2 , 5 7 ) [ l 5 4 , 3 4 . 8 , 1 5 - ( - 8 1 , 9 2 ) ( - 2 , 9 8 ) ]
1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) '
= 15,43 K N / c m ' < 21 K N / c m ' ;
2 3 0 5 7 . 1 3 [ l 5 3 , 5 1 - 8 . 0 2 - ( - 8 1 , 9 2 ) ( - 2 , 8 5 ) ] 1 2 . 4 6 1 5 4 , 3 4 - 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) ^
( - 6 2 , 5 7 ) [ l 5 4 , 3 4 ( - 2 , 8 5 ) - ( - 8 1 , 9 2 ) 8 , 0 2 ] 154,34 1 5 3 , 5 1 - ( - 8 1 , 9 2 ) '
= 21,02 KN / e m ' > 21 K N / e m ' ;
230 57,13[l53,51(^2,98)-(-81,92)(-2,85)]
'^ 12,46 154,34 153,51-(-81,92)'
v a i YJ - h e s o dieu kien l a m v i l e , 7^=0,9 khi thanh Ilm viee chju k e o .
K i l m tra irng s u i t tai eae d i i m A , B, C tren mgt c i i 1-1 d u a c t h u e hien theo eong t h i r c (5):
2 2 0 ' ^ f l - f ' B - ' ^ c - . , 2 , 4 6
= 18,9 K N / c m ' K i e m tra i r n g suat tai eac d i l m A, B, C tren mat e i t 2-2 duoc t h y c hien theo eong t h i r c ( 5 ) :
2 0 0
= iD,uo i \ i v / c m - s r y
= 18,9 K N / c m ' V l y t i i t dien 1-1 v a 2-2 thoa m a n d i i u kien b i n , 3.4. So sanh ket qua tinh theo ti§u chuin Nga (SNiP 11-23- 81') V l theo TCVN 5575 - 2012
Sc] s a n h k i t q u a t i n h l o a n k i i m tra ra i r n g s u i t keo Iran t h a n h c a n h tgi vj t r i n u t t h e o h a i tieu c h u a n , thay r i n g
Lfng suat p h a n b i k h f l n g d i u tren l i l t dien giam y i u ciia t h a n h khi tinh t h e o tieu c h u i n N g a SNiP 11-23-81* va phin bo d i u khi tinh theo T C V N 5 5 7 5 - 2 0 1 2 .
K i t q u a k i l m tra i r n g s u i t k h o n g d a m bao khi tinh Iheo ti§u chuan N g a va d a t t h e o y e u cau khi l i n h theo TCVN.
4 . K i t l u a n
Bai bao d a trinh b a y c l e h t i n h l o a n i r n g s u i t tren thanh eanh t i i t dign t h e p g o e d a n tgi vj t r i nut (bj giam y i u do khoel lo b u Iflng) c o x e t d i n m o m e n d o s y lech t m e eiia luc tac d u n g thanh xien len t h a n h c a n h .
V a i viec k i d i n a n h h u a n g ciia m f l m e n d o s y lech true eiia l u e l i e d u n g t h a n h xien l l n t h a n h c I n h thi tinh loan co s y lam viec a n l o a n va s i t v a i t h y c t i h a n .
D o vay, trong l i n h t o i n thap nen k e d i n mo men do sv lech t r y c e u a l u c t i e d u n g t h a n h xien l e n t h a n h eanh khi tinh t o i n hoac d i n h gia xae dinh lai h i s i dieu kien lam vigcyc trong t r u a n g h g p t h a n h e I n h t h e p g 6 c d o n chju keo de kel qua t i n h s i t v a i t h u c t i h a n . / .
0 * 3 ! l i e u t h a m k h a o
/ nOCOBHE, no npoeKinupoeaHuio cmaibHNX KOiicmpyKiiuii onop soidyuiiibix JiUHUU (BJ!) aicKmponepedamt u ornKpamf' pacnpedejiimeibNbix ycmpoucma (OPV) nodcmamiiiii iianpnaiceuueu cubime I KB (K CHUU 11-23-81V , CHuTl 11-21-81 *, CmajibHbie KOHcmpyKijiiu.
TCVN 5575 2012. Kit edu thep - Tieu chuan llnip ki Kel edu thep 2 Cdng Irinh ddn dyng vd cong nghiep Nhd xuat bdn Khoa hgc va ky thudt
/ ( J TAP CHi KHOA HOC KIEN TRUC • XAY DUNG