DIA KY THUAT - TRAC OIA
PHAN TiCH BI^N DANG CClA BE TRONG MONG BE - COC TREN N^N CAT THANH P H 6 H O C H I MINH BANG CHLTONG TRINH PRAB
K S . C A O V A N H O A
T r u ' d n g dai hpe B a c h K h o a , dai h o c Q u d c gia - Ho C h i Minh
Tdm tat: Noi dung cua bai bdo Id phan tich cac yiu td anh hwdng din chuyin vj vd biin dgng cOa be trong mong cgc noi chung vd mong be - cgc noi rieng, bao gom: dg cung cOa be, sa do bd tri, so Iwgng, chiiu dai cgc. Bai bao sCr dung chwang trinh PRAB de khao sdt biin dgng cua be khi cho cac yiu td anh hwdng neu tren thay doi, nhdm xac djnh moi quan hg giira chung. Tir do, mgt mat la kiem chu'ng vd djnh iwgrtg cac kit ludn ctia cac tac gia trong nwac vd tren thi gidi vi cac mdi quan he giira cac yiu to neu tren vdi biin dgng cua be, mat khde la di higu chuan chwang trinh PRAB phye vy cho cong tdc nghien cwu sau nay.
1 . G i d i thieu
Khi t h i l t k l k i t e l u phan thdn cGa cdng trinh, cae ky su thudng khdng quan tdm d i n s u lam viec cGa k i t cau mdng - nen cpc d ben d u d i . do gia t h i l t k i t e l u mdng la tuydt doi cdng. Nguge Igi, cac ky s u dja ky thugt khi thilt k l mong cung ehi lay npi Igc chdn ept/vaeh l u k i t cau ben tren d l phdn tich mdng, ma
khdng quan tam d i n dng x d cGa k i t cau ben tren.
T h i nhung, mpt trong cdc mgc tieu cGa t h i l t k l mong la kiem soat c h u y i n vj, dgc biet Id ehuyln vj Igch.
Chinh ehuyen vj Igch ( b i l n dgng cOa be) la nguydn nhan d i n den phan phoi Igi npi Igc cua k i t c l u ben tren, sai khac vdil tinh toan ban dau cGa ky s u k i t cau.
S g sai khac ngi Igc nay cua k i t e l u ben tren ke ca ngi Igc tai cdc chdn cpt den lugt no gdy nen hgu qua la c h u y i n vj va ehuyen vj lech eua k i t cau mdng lgi thay doi so vdi tinh todn ban dau eua ky s u dja ky thugt.
T u dd, eho thay can t h i l t phai kiem soat bien dgng eua be, de hgn c h i anh h u d n g qua Igi giua k i t c^u ben tren va k i t c l u mdng ben d u d i . Niandou &
Breysse [1] eho rang, khi thiet k l k i t cau phan than, quan nigm be ed dg eung vo han so vdi k i t e l u phan thdn, trong khi dd trong ehung mgc ndo dd be phai dO mem so vdi d i t n i n , d l dgt d u g c d i l u dd ty so hVk -*
0 {h: chieu day be, /c do cung epe). Ngugc Igi, khi t h i l t ke cpc, tai trpng phdi d u g e phan bo deu cho cac cpc, do dd h^/k -> oo. Rd rang ton tgi nghjch ly khi thiel k l be nhdm thda man cdc gia thiet khi t h i l t k l k i t clu ben tren vd hg niong.
STT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Bang 1 Ten cong trinh iHC
ftn Lac Plaza, Ho Chi Minh Hyde park barrack cavalry - London
Sailing lower. Ho Chi Minh Bao Gia, Ho Chi Minh Sai gon Pearl Treptower, Berlin VielComBank Tower,H6 Chi Minh
DRB - FBC
^esserturn Franfurt Bitexco Tower, Ho Chi Mmh Commerz Bank Franfurt Dubai Tower Mega Tower HongKong Incheon Tower, Korea
Cac d$c tnrng cua mot so Cong trinh thdng /fe 1
(m) 2.0 2.5 1.52
2.5 2.5 2.5 3.0 2.75
4.0 6.0 4.0 2.5 -4.45
2.5 8.0 5.5
H (m) 60 70 90
95 109.5
125 121 125
150 256 262.5
299 400 480 601
B (m) KAD 10.5x10.5 35.9x26.9
22.8 X 20.5
• 67x69.5 40x120 37.1x37.1 51 x49
KAD 58 8 X 58.8 35 6 X 53.0
KAD KAD KAD 88 X 77.5
Lc (m) KAD
5.0 X 7.0
KAD KAD 9 9 . 5 - 1 0
KAD KAD KAD 4.5 - 7 5
KAD KAD KAD
n (m) KAD 16 51
36 KAD 500 54 84
KAD 64 109 111 232 240 71
D x L p (m) KAD 1.0x50.0 0.91 X 24.8
KAD KAD- 1.2x69 0.8S X (12.5-16)
0.8 X 2.4 1.0x2.8(54-34)
KAD 1.3 X (26.9x34.9)
1.5 X (75-85) 1.8 X 45 1.5x(12, 22, 32
1-1.5x2.8-95.
2.5 (36-66) Tap chi KHCN Xay d ( m g - so 2/2015
D\A KY THUAT - T R A C DIA
Ghi ehu: t - ehieu day be, H - chieu cao cdng trinh, B - chilu rpng be, Lc - khoang each cpt, n - so lugng cpc, D - dudng kinh cpc (cpc barrete: ehieu day, chieu cao t i l t dign), Lp - ehieu dai epe, KAD - khdng cd so ligu.
GB 50007 - 2002 eho r i n g c h i l u day cGa mdng be dugc thilt k l chu y l u theo cac tieu chi dam bao kha nang chju uon, chdng chgc thung, vd thudng phy thudc vao edc k i t cdu ben tren [2]. Tomlinson (1994) quan nigm be d u g c thiet k l nhu Id mot ban eung chju tai tgp trung t d cac cpc. Poulos [3] dua ra 4 tieu chi thilt ke sa bp be mdng la: md men Idn nhat, luc edt Idn nhit, dp Igc tgi mgt t i l p xGc Idn nhat, va tieu chi chuyen vj eye bp d u d i be. Bang 1 t h i hlgn cdc so lieu thong ke c h i l u ddy be, c h i l u cao tang, c h i l u dai, dudng kinh va sd lugng cpc cGa cde edng trinh cao t i n g da d u g c t h i l t ke va thi cdng trong nude cung nhu tren t h i gidi; cho t h i y chieu day eua be d u g c thilt k l r i t Ign (td 1.5 d i n 8 m). Vdi chieu day be dugc thilt k l nhu vdy, kha nang chong uon eua be Id r i t Idn nhung lugng vgt t u s u dyng cung r i t Idn. Cdu hdi dugc dgt ra la chieu ddy be trong he mdng nen duge thilt k l nhu t h i ndo mdi hgp ly de phdn phoi dong d l u tai trpng xuong n i n vd cpc, eung nhu dam bao d i l u kign .ngdm cua k i t c l u ben tren?
Cd t h i nhgn t h i y chuyen vj, b i l n dgng cGa be chju dnh hudng cGa he cpc (chieu dai, dudng kinh, so lugng, khoang each giua eae cgc) nhu da d u g c
Iai ti^n^
ehung minh trong cac nghien cdu cGa Tan et al (1996), Maybaum et al (2000), Poulos (2001), Chow et al (2001), Oh et al (2006), Rabiei (2009), Vasudev
& Unikrisnan (2009), Ziaie - Moayed et al. (2010);
cung nhu chju anh hudng cGa d i t nen vd k i t e l u ben trdn nhu trong nghien euu cua Thangaraj &
lllampamthi (2009), iviayerhoff (1947) va Summer (1957).
Trong khi dd bien dgng cGa be lgi la ham so eua c h i l u day bd (Westergaad, 1925). Bai bao se phdn tich vigc s d dyng cae sa do bo tri cpc khac nhau, gom eac y l u to anh hudng neu tren, k i t hgp vdi chieu day be d l gidm ehuyen vj Igch. Bai bao eung tam thdi bd qua anh h u d n g cGa dp cdng k i t cau ben tren, cung nhu md dun ddn hoi eua d i t n i n , . . . se Id npi dung cGa nhung bdi bao tiep theo.
2. Phuang phap va mo hinh nghien c d u 2.1 Lya chgn phuxmg phap nghien cijv
Tdc gia bdi bdo s u dgng chuang trinh PRAB, do Gido s u Matsumoto Tatsunon, Trudng- dgi hpe Kanazawa tgng khoa xay dgng trudng dai hoc K i l n tnJe Tp. Ho Chi Minh, d l phdn tich bien dgrig cua be.
Bdy Id chuang trinh d u g c phat t r i l n tren ca sd hoan thign eac quan nigm cGa Poulos (1991), Clancy &
Randolph (1993), Poulos (1994) de thiet k l mdng be - cpc. PF?AB la mpt phan mem da cgp nhat cae h i l u b i l t mdi ve thilt k l mdng be - cpc. C a s d ly t h u y l t cua chuang trinh PF?AB d u g c trinh bay trong [4].
• 1. Phin tir cgc, ID ^ 3. Phan tu-huu h§n bi, 2D 2. Ld xo phin Iyc nin t^i cgc theo 3 phuung x, y, z 4. L6 xo phan Iyc nin tai be 5. Tuang tic cgc - dit - cgc 6. Twang tac cgc - dit - be 7. Tuang tac bi -dat-be
(Cdc tuang tac 5, 6, 7 theo Idi giai cua Mindlln, 1936) Hinh 1. Mo hlnh mdng bi cgc (Kitiyodom&Matsumoto, 2002-2003)
T9P chi KHCN Xay dung - s6 2/2015
Hinh 2. Cdng trinh nguyin miu TrepTower (Beriin)
DIA KY THUAT - T R A C DIA
Trong PRAB, be d u g c md phdng bang cac phan t u huu hgn ban mdng dan hdi. epe d u g e md phdng bang cdc phan t u huu han dang thanh ddn hoi, vd dat nen duge md phdng nhu eac Id xo tuang tdc. Trong md hlnh md phdng mdng be - cpc (hinh 1), tai mdi nut cgc vd nGt be cd'3 Id xo t u a n g tde lien k i t : mdt Id xo theo phuang ddng (z) vd hai Id xo theo phuang ngang (x va y). Cdc Id xo tuang tac khong Iam viec dpc Igp vdi nhau md chGng tuang tdc vdi nhau. Bdn t u a n g tdc giua cdc Id xo d l cap d tren gdm (epe - n i n - cpc, epe - nen - be, be - n i n - be, be - nen - cpc), d u g c md phdng bdi Idi giai cua IVIindlin (1936).
Bp edng eua eac Id xo n i n d u d i be trong d i t nen dong n h i t nen theo phuang dung K^va theo phuang ngang K^, K^dwac xdc dinh theo Muki (1961). bdi:
4G,a
_ 32(1-vJG^a
K. (1)
K'=K'
(2)7-8v,
Bp cdng cua Id xo cgc - nen tai mui cpc theo phuang ddng K^'' vd theo phuang ngang A"™, K^''cut^Q d u g c xde dinh theo bieu thue (1 va 2). Dg cdng cGa 16 xo n i n theo phuang dung K^va theo phuang ngang ATf, K^ tac dgng dpc than cpc duge xdc djnh theo Randolph & Wroth (1978).
K^ = 27rG^AL/\a(r^/r^) (3) A:; = K^ = qE^AL (4) trong dd:
Gs, V, - md dun chong e l t , va hg so Poisson cGa d i t n i n ;
£s - md dun dan hoi cua d i t n i n ; AL - c h i l u dai cua phan t d cpc;
To - ban kinh cgc;
a = b ! yJK r^ = 2 . 5 1 ( 1 - v / J
b - chilu rpng eua phan l u be;
q=pDlpE^
p - luc ngang phdn bo dpe bien phan t d cpc;
O - dudng kinh cpc;
p - c h u y i n vi ngang t u a n g dng tgi cae nGt xdc djnh theo Poulos & Davis (1980).
Dp cung eua cdc Id xo trong dat n i n nhilu .ldp d u g c xdc dinh theo Lee (1991).
2.2 Nguyen mau
Treptow^er, Beriin [5] d u g c chpn Iam nguyen mau de xdy dgng md hinh nghien cuu (hinh 2). Cdng trinh cd chieu eao 121 m, kieh t h u d c mdng 37.1 x 37.1 m, nam tren nen cdt Beriin ed chieu day 40 m. K i t cau mdng bao gom be dgt tren 54 epe khoan nhoi dudng kinh 0.88 m ddi t d 12.5 - 16 m. Be d u g c thilt k l c6 ehieu day Id 3 m, phan ham Idl thang d u g c khoet sau 3.5 m, be tgl vj tri nay ed c h i l u ddy 2.0 m. K i t cau dan gian cGa mdng Treptower giGp de ddng ddnh gia cdc y l u to anh h u d n g dang nghien edu, logi bd cdc anh hudng'khdng mong muon khac.
2.3 M d hinh nghien ci>u
Md hlnh nghien c u u (bang 2) d u g c thilt ke Igi tren ea s d nguyen mau, trong d i l u kign i^a c h i t qugn 1. Tp. Ho Chi Minh (bang 5 v d hlnh 4).
Mo hinh kit ciu than nha: hg thong chju lgc la h | khung k i t hgp vdeh cdng, mgt bang ept duge b l tri theo ludi d vudng 9 x 9 m, cd tong kich thudc mgt bang Id 36 (4x9) m x 36 (4x9) m. Chieu cao cdng trinh nghidn cdu dwac chpn la 121 m, tuang dng 40 tang.
Cde vach cdng d u g c bo tri giua cac cpt d l chju tdi ngang. Khac vdi edng trinh nguydn m i u , cdng trinh nghien cuu cd so tang Idn han (40 so vdi 32). Ludi cdt va chieu eao edng trinh se d u g c thay doi trong qua trinh nghien euu de xet tdi anh hudng cua . khoang edeh ept, gid tri cGa tai trpng t u k i t c l u ben tren. Ndi lue tgi chdn cdc k i t c l u t h i n g dung nhgn d u g e t u k i t qud phan tieh chuang trinh ETABS, ChGng d u g c s u dgng nhu Id cac ngogi Ige tdc dgng len cdc nGt be ngay tgi vj tri ehdn cpt.
T?p chi KHCN Xay dyng - so 2/2015
DjA KY THUAT - TRAC DIA
So do 4 40 cgc dai 34m)
So do 2 (40 coc dai 34m)
So do 5 (45 cpc dai 30m + 4 cpc dai
40m)
Sado 3 (49 cpc dai 31m)
So-do 6 (mong be)
Hinh S.Sa do bo tri cgc
Bang 2. Cac die trung cOa md hinh Cac dac tru'ng
H (tang) t (m) U (m) D, (m) Lp (m) n (coc) E, (MPa) S., (%)
Gia tri 40 2 - 8 9 2.0 Xem bang 2 Xem bang 2 Xem hinh 4 0.05% va 0.2%
Ghi chii: H - so tang, t - chieu day be, Lc - budc cgt. Dp - dudng kinh <xic, Lp - chieu dai cgc, n - so lugng cpc. Es - mo dun dan hoi cua dat nen. Sep - chuyen vj Igch cho phep
Sa do bo tri cgc: Cpc d u g e bo tri d u d i be theo - Randolph ,PDR [3], the hign tren hinh 3. Rieng nhieu sa d l khae nhau. So l u g n g , c h i l u dai cgc d u g c dudng kinh cpc trong nghidn cuu nay dw(?c chpn Id 2 xac djnh sa bp theo phuang phap cGa Poulos - Davis m.
Bdng 3. Sue chju tai cue hen a)a coc c6 duvng idnh 2 m Chieu dai coc (m)
Si>c ch!U tai ci,rc han (MPa) 30 10,374
31 11.420
34 13,572
45 22,902
Bang 3 the htgn sue chju tdi cgc hgn cGa cpc. Id gid tri trung binh t u b i n p h u a n g phap: theo ehi tieu ca ly, theo chi tieu c u d n g dp, theo Meyerhoff vd theo phuang phdp Nhgt Ban (TCVN 205 - 1998). Gid trj
sue chju tdi cgc hgn tinh d u g c dem so sanh vdi phuang phdp beta trong Fellenius (2011), cho k i t qua tuang d u a n g . Do dd chGng d u g c c h i p nhgn d l t h i l t k l sa bp cdc sa do mdng the hlgn tren bang 4.
Bang 4. Tinh toin cac thong so cOa hi mong
30 0 ~0 so Sado
1 2 3 4 5"
6 "
Dp (m) 2 2 2 2 2 0
(m) 45 34 34 31 30 0
n 25 40 40 49 49 0
P/P.1I
(%)
1.09 1.01 1.01 0.93 0.93 0
P 42.2 28.7 28.7 25.2 25.2 0
I P (MN) 1150 1158 1158 1149 1149 0 Ghi chu: * co 45 cpc dai 30 m va 4 cpc dai 40 m,
" trudng hgp mong be
So chiy SPT dem doVJC rXi Hinh 4. Kit qua thi nghigm SPT
M6 hlnh nin. Dat n i n tgi qugn 1, thanh pho Ho Chi Minh nai dang ed mgt dp cong trinh cao tang Idn, d u g c s u dyng d l Idm ea s d nghien cuu. D u d i day be Id Idp cdt chgt v d a d i n chat bao hda n u d c (hinh 4 vd.
bang 5), d u g c gia dinh dong n h i t ed chieu day 72 m (khde v d i thgc t l , Idp cat chi cd c h i l u ddy 35 m). Md dun dan h i i cGa eat d u g e xdc djnh theo bleu thuc E =
766 N (kPa). vdi b i l u thdc nay gid tri md dun dan hoi xac djnh dwac thien v l an toan so vdi b i l u thdc cua Stroud & Butler ( £ = 3500A/ eho d i t eat vd = 500W cho set ngng). T d dd md dun dan hoi tgl ddy be cd gia trj la 15,6 MPa, tang dan theo c h i l u sau theo gid trj NSPT, tgi dp sdu 72 m cd gia trj la 31,2 MPa. He so Poisson cho cat chgt d u g e chpn Id 0,3.
Tap chi KHCN Xay dung - s6 2/2015 55
B|A KY THUAT - TRAC DIA
Cac gia tri trung Bang 5. Bang thing ke cac dgc tnmg ca ly cua dit
binh tieu bieu - Khu vyc quan 1, Tp. Ho Chi Minh (Chi (Chau Nggc An, 2002}
L a p d a t 1 2 3 4 5 6
z (m) 3,20 1,60 2,80 3 3 , 4 15,5 4,40
" " 3 g / c m 1,81 1,96 1,92 1,91 2 , 0 0 2,01
W
%
2 2 , 8 2 0 , 0 2 3 , 7 2 4 , 7 2 0 , 2 19,0
Thf n g h i e m n e n d a t E l
1KG/C m ' 0.701 0 , 6 1 3 0 , 6 4 7 0 , 6 7 2 0 , 5 2 6 0 , 5 1 7
E 2 2KG/C
m^
0 , 6 4 5 0,593 0 , 6 0 8 0 , 6 4 9 0 , 4 9 8 0 , 5 0 3
£3 3KG/C
m ' 0 , 6 1 6 0 , 5 8 1 0 , 5 8 6 0 , 6 3 8 0 , 4 8 4 0 , 4 9 6
£4 4 K G / C .
m=
0 , 6 0 8 0 , 5 7 8 0 , 5 7 8 0 , 6 3 0 0 , 4 7 9 0,490
0 0 8 1 4 13 2 7 16 3 1
qin BO 1 0 1 6 15 2 9 1 8 3 3
C l KG/C
m=
0 , 1 2 0 , 3 0 0 , 2 1 0 , 4 5
Cll KG/C
m ' 0 1 5 0 , 3 2 0,24 0,50
-
Mo 0,35 0,40 0,40 0,25 0,42 0,25 Ghi chG: z - chieu day Idp dat.
Thiet ke sa bg: Tong npi Igc tac dyng len chdn cpt l l y t u ETABS Id 1,283 MN (trudng hgp cdng trinh eao 121m (40 tang). Phuang phap PDR [3] d u g c s u dyng d l thiet k l sa bd he epe. Dp cdng eua mdng be xdc dinh theo Muki (1981) Id Kr= 1.566 MPa. Dp edng cGa he cpc xac djnh theo Fleming et al (1992), tren ca s d dp cdng cGa epe dan (Randolph & Wroth, 1978) la Kp =6.207 MPa. Dp cdng cGa mdng be - epe do dd duge xac dinh Id Kp, = 5.619 MPa. T u dd ed t h i tinh todn duge ty Ig tai trpng do be chju la 1 1 % , k i t qua Iga chpn sa bp cae sa do bo tri, chieu dai, dudng kinh epe d u g c d l xuat d bang 4.
3. Ket qua va binh luan
3.1 Phan tich cac so" do bo tn cgc de giam chuyen vi va chuyen vj lech cho mong be
Hlnh 5a eho t h i y neu t h i l t k l mdng be, ehuyen vj tinh toan r i t Idn vd gid tn ldn n h i t d tdm be len toi 1.237 mm. N l u tdng c h i l u day be, ea chuyin vj d tdm be va ehuyln vi Igeh deu giam (hinh 5b,e). Trong khi ehuyln vj Igch cd t h i giam v l gia tri "0" khi chilu day be dG Idn, thi e h u y l n vj Idn cGa mdng be chi cd the giam d u g c bang each tang c u d n g cpc d u d i be. Vi^c s u dyng cpc d l giam c h u y i n vj va ehuyln vj Igch d u g c lan lugt phdn tich trong 5 sa do bo tn' (hinh 3), k i t qua the hign tren hinh 6, 7, 8, 9 nhu sau:
1 1 B f l m Be 2HI B& Jim B d 4 m BSSm B d 6 n i - Be 8m
0 0
"
>, Klidng d(^u " ' ' '
- \ \ ^ _
1 . 1 1 1 . 1 .
Chiiw ddv be (m) Hinh 5. Chuyen vi cua mdng bi. Sa do 6
S a do 1, be ddy 4 m va cd 25 cpc dudng kinh 2 m, dai 45 m, bo tri tgp trung d tdm be, chuyen vi Idn n h i t cua mdng be giam edn 167 mm, chuyen vj tgl tdm be la nhd n h i t (hinh 6). C h u y i n vj lech Id 80,3 mm. Ngugc Igi d sa do 2, be day 4 m, co 40 cpc dudng kinh 2 m ddi 34 m, bo tri xung quanh ehu vi be, chuyin vj eOa mdng be gidm edn 190,5 mm, gia tri ehuyln vj ldn nhat tgi tdm be. Chuyen vj lech la 50,7 mm (hinh 7).
Nhu vgy, n l u bo tri cgc d tam be thi chuyen vi d mep be la Idn nhit, cdn neu bo tri epe d mep be thi
ehuyln vj d tam be Idn n h i t . Vi vay, thu nghiem bo tri 16 cpc d chu vi be vd 24 cpc d tam be, dudngkirih 2 m, ddi 34 m (sa do 3 - hinh 8). Gia tri chuyin vj khi be day 4 m Id 246,1 mm Idn han 2 trudng hgp tren, ehuyln vj Idn n h i t d tam be, nhung e h u y l n vj Ifch nhd han ehi edn 21,5 mm. T h u nghidm t i l p theo Id b6 tri 49 cgc d u d n g kinh 2m, dai 31 m (sa do 4 - hlnh 9}
phan bo deu tren todn dign tieh be. Gia trj chuyin 'A khi be ddy 4 m la 246 m m . chuyen vj nhd nhdt tgi tdm be, ngugc lgi vdi s a do 3. C h u y i n vj Igch Id 9.4 mm, nhd han so vdi sa do 3.
5 6 T9P chi KHCN Xay dyng - so 2/2015
DIA KY THUAT - T R A C D!A
K i t qua tinh toan cho thay s a dd 1 vd 2 cho va 4 d u g c xem la h g p ly doi v d i cdng trinh nghien chuyen vj trung binh nhd nhat nhung chuyen vj c u u . N l u muon giam e h u y l n vj trung binh cdn 80 Igch rdt Idn. S a do 3 va 4 cho c h u y i n vj lech nhd, mm (TCVN), ed the tang e h i l u ddi cpc d sa do 3 nhdt nhung c h u y i n vj trung binh l d n , neu c h i p hoae 4, tuy nhien v i n d l nay khdng bdn d bdi bao nhan ehuyen vj trung binh Idn (250 mm), s a dd 3 nay.
• S d d d 1
/ / / / ~ / / ~
1.,.,
•
B&2m \ -^
- -B& 3m - • B& 4 m
— B e 5in - - B & 6 m
B & g i n
\ \
, . , 1
100
200
, -
3»a
B6 2m Be3in - - - - B6 4ni Bd5m - - - B&fim BJ: 8m .
^ • ^ Sd do 2
NiU Hinh 6. Sado 1
Niit Hinh 7. Sctfa 2
-Be 2ni Be 3m
• Be 4m Be 5m
Ni'it Hinh 8. Sado 3
1
c
s
Ml)
280 Srfdo4
/A
// .. \\
•c«>i»f«-/" *^^'^''^^V^'»
^sTy V-'-
Be 2m Be 3m - - - - Be 4m Be 5m
Be 6m Be 8m 85 Ntft Hinh 9. Sado 4 T d eae hinh 6, 7, 8, 9 va bang 6 cho thay, d t i t ca
cdc sa do bo tri cgc, khi tang chieu day be chuyin vj lech deu giam. Cd t h i nhan thay khi sa do bo tri cpc khdng hgp ly, v i dy khi be day 4 m, c h u y i n vj Igeh d sa do 1 Id 80,3 mm va d sa do 2 Id 50,7 mm, c h u y i n
v| nay ed t h i giam ve gia trj tuang duang d sa do 4 Id 9,4 mm, n i y tang chieu day be len 8 m. Ngay ca khi sa do bo tri cpc khd hgp ly nhu sa do 3, chuyen vj Igeh la 21,5 mm, d l dat ehuyln vj lech tuang duang sa do 4, can phai tang chieu day be len khoang 7 m.
.Bang 6. Chuyen vj cua cac sa dd ba tri cgc khi chiiu day be thay doi t u
2 3 4 5 6 8
Sty do 1 S 242,5 191,3 167,3 156,4 151,0 146,5
SiM 334,4 160,4 80,3 44,1 26,4 11,4
Sff d 6 2 S 214,8 199,0 190,4 185,7 183,1 180,7
Si^h 141,5 84,9 50,7 30,7 19,4 8,3
Sff d 6 3 S 249,5 247,2 246,1 245,5 245,1 244,8
S » 54,9 35,4 21,5 13,1 8,2 3.8
S a d o 4 S 246,1 245,9 246,1 246,2 246,2 246,2
Sisch 46,5 19,1 9,4 5,2 3,1 1,4
Tap chi KHCN Xay disng - so 2/2015
DIA KV THUAT - TRAC DIA
Ghi chG: tbs - Id chieu day be, S - la c h u y i n vj trung binh cGa hg mdng, S^ch - Id c h u y i n vj lech.
Nhdn xet 1: De giam c h u y i n vj cho mdng be khdng nhdt t h i l t phai bd tri n h i l u cpc, ma ehi edn tang c h i l u ddi cpc, v i dy sa dd 1 chi cd 25 cpc ddi 45 m, nhung chuyin vi trung binh nhd han so vdi so do 4 (cd 49 cpc ddi 31 m). Tuy vdy, d l gidm chuyen vj Igch can t h i l t phdi chpn sa do bo tri cgc hgp ly. Chpn d u g c sa do bo tri cpc hgp ly d l toi u u hda chuyin vj Igeh la rat khd, do dd c h i l u day be cd t h i xem la phuang an d g phdng eho s g b i t thudng khi he cpc khdng Idm vigc nhu ky vpng hogc sa do bo tri epe ehua tdi u u .
3.2 Anh hwdng giam chuyen vf cua cac so' do bo tri coc
Hinh 10a t h i hign c h u y i n vj tgi cac nGt tren mgt cat di qua tam be cua cdc s a do bd tri cpc khac nhau, khi chieu ddy be khdng d i i (3 m). Hinh 10b,e t h i hign mot quan he chuyen vj tmng binh vd ehuyln vj Igdi voi ehilu day be cua cdc sa do bo tri cpc khde nhau.
Chuyen vj trung binh cGa ea 5 sa do cd gia tn tuang duang khi ehieu day be nhd, nhung khi c h i l u ddy be Idn ChGng giam khd manh d s a do 1 vd 2. D i l u nay d u g c ly giai Id: cpc d s a do 1 va sa do 2 dai hon, do dd c h u y i n vj eye bg a i a hg cpc van nhd cho du tai trpng d u g c phdn tra bo sung khi tang chieu ddy be.
Chuyen vj lech d hai sa do nay von rat Idn, nay giam ve gid trj g i n bang "0", do dd chuyen vj Irung binh giam tuang ung vdi mdc dp giam c h u y i n vj l#ch. Trong khi c h u y i n vj Igeh cua cde sa do 3, 4, 5 kha nhd, do do khi tang c h i l u day be, m d c dp gidm ehuyln vj igch la khdng dang ke, k i t eye Id c h u y i n vj trung binh cua ba sa do ndy a i n g giam khdng dang ke.
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/ D=2m \ / 11-25-49%.
V L=31- 45m \ / X Be 4 m y \
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Sddo 1 Sd do 2 Sddo 3 Sddo 4 Sddo 5 KlioAng each den mep bS (m)
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Chilu day be (ml Hinh 10. Chuyin vj d cic sa di khic nhau
Nhgn xet 2: Rabiei [6] cho rang, n l u cpc bo trf d khu vgc tgp tnjng nhilu tai trpng (dp luc tilp xuc tdn) thi ed t h i giam d u g c c h u y i n vi igch eua mdng, ngugc Igi n l u cpc dugc bo tri d nhung nai it tai trpng (dp Igc tiep xGc be) thi lam tang ehuyen vi Igeh. K i t qua eOa nghien cdu d day cung eho t h i y neu eae epe d u g c dua vdo hg mdng d l giam ehuyln vj Igeh qua ddi (dp cung Idn), thi thay vi lam giam eo t h i idm tang ehuyln vi Igeh d hudng ngugc Igi.
3.3 Anh hwdng giam chuyen vi cda chieu dai cgc
Hlnh 11a t h i hlgn edc b i l u d l chuyen vj cGa hg mdng (sa do 1) tgi mgt edt di qua tdm be, khi cho ehieu ddi cpc thay doi (40, 45, 50, 60 m). Cho t h i y , c h u y i n vj cua hg' mdng khi e h i l u ddi cgc > 45 m, nhd han 3 lan so vdi khi chieu dai cpc 40 m. Hinh 11b,c
58
eho thay, khi tang c h i l u dai cpc, c h u y i n vj trung binh gidm, nhung c h u y i n vj Idch tang. Neu chieu ddi cpc >
45 m, c h u y i n vj trung binh gidm them khdng dang ke, ehuyen vj Igch tdng cung khdng ddng k l . Vigc tang c h i l u dai epe lam cho c h u y i n vj Igch tang (hlnh 11c).
Nhung khi ehieu dai epe Idn (>1,25 B) thi ehuyln vj Igch thay doi khdng cdn ddng k l . Do dd, chilu ddi cpc khoang 45 m (khoang 1.25 lan b l rpng be), Id hOu higu d l giam c h u y i n vj. Dieu ndy phu hgp vdi ket lugn cua Vasudev va Unnlkrishnan [8] khi cho rang e h i l u dai epe higu qua de giam c h u y i n vj Id 6.833 - 1.25 lan be rpng cua bd; hay nhgn xet cGa Gandhi &
Maharaj (1995) khi cho r i n g c h i l u ddi cpc higu qua phdi Idn han c h i l u rpng cGa be.
T u a n g t g v d i s a do 4 , d s a d l 5 ede cpc cung d u g c phdn bo deu tren toan bp dign tich be, nhur%j
T^p chi KHCN Xay dyng - so 2/2015
^ DIA K9 THUAT - TRAC DIA
d s a do ndy ed 4 epe d tdm be d u g c t h i l t k l ddi han (4 cpc dai 40 m va 45 cpc ddi 30 m - hlnh 3).
Cho thay, ehuyen vj nhd nhdt tgi vj tri tdm be d sa do 5 Id 207 mm (hinh 12) nhd han d sa do 4 Id 218 mm (hlnh 9), trong khi dd e h u y l n vj Idn n h i t tgl
mep be bang nhau, do do c h u y i n vj Igch d s a do 5 Idn h a n . Gia s u thay vi tang ehieu dai cpc d tdm be d sa do 5 (lam cho c h u y i n vj Igch tang len), bang viec tdng chieu dai cgc d mep be, thi cd t h i Idm giam d u g c ehuyen vj Igeh.
1 200
>
"- >
\ j
600
-
Coc dai 40 ni Coc d&i 45 m Coc dM 50 in C o c d a i e O i n
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400 9 200
> 1
6 80 75
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Chuyen vi I§ch 40 50 60
Chieu dai coc (m) Hinh 11. Chuyin vj khi chieu dai cgc thay doi
280
Sn do 5 y-
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V y Be 3m Be 5m Be 8m
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,
Nii I Hinh 12. S a d o 5 Nh$n xet 3: De giam c h u y i n vj eye bd cd higu qua nhit, nen s u dyng ege cd c h i l u ddi nhd han 1.25 ehilu rpng be, dGng nhu nhgn xet eua Vasudev va Unnikrisnan [8]. Vigc tang e h i l u dai epe d vi tri chuyin vj Idn nhat, hay giam c h i l u ddi cpc d vj tri chuyin vj nho n h i t , cung ed t h i lam giam ehuyln vj l^ch. K i t lugn. nay phG hgp vdi quan d i l m cua Poulos [3], Randolph [7] la b l tri cpc d nhung vj tri dp Igc t i l p xOe Idn.
4. K i t lugn
Trdn c a s d edc phdn tfch tren, cd t h i dua ra mpt so k i t lugn nhu sau:
- Chi cd t h i giam d u g c chuyen vj trung binh eua mdng be nhd s u dyng hg cpc d u d i be, dGng nhu nhdn djnhcGa Poulos [3]; Oh et al., (2006) vd Reul, (2004). Khdng phai so lugng md ehieu ddi cgc cd higu qud giam chuyen vj tot n h i t ;
- Chuyin vj lech cGa mdng tgi be ed t h i giam'nhd:
hogc Id s d dyng s a d l b l tri cpc hgp \^, hogc la nhd s d dyng be ed e h i l u day ldn. K i t lugn nay phG hgp vdi cae danh gia cGa n h i l u tac gia nhu Poulos [3], Rabiei [6], Randolph [7]. K i t qua nghien euu cGng chi ro, s g nhgy cdm khi bo tri epe de giam ehuyen vj eye bp tgi nhung vj tri cd chuyen vj Idn, vi vigc b l trf ndy ed t h i lam tang c h u y i n vj Igch khi cpc qua ddi. S a do
7>p chi KHCN X§y dyng - so 2/2015
DIA KY THUAT - TRAC DjA
bo tri cpc hgp ly va c h i l u day be la hai yeu to quan trpng anh hudng d i n t h i l t ke chieu ddy be;
- K i t qud t u phan tich edc anh hudng eua sa do bd tri, sd lugng, chilu ddi cpc d i n chuyen vj lech (bien dgng cGa be), phu hgp vdi nghien c d u cGa n h i l u tac gia khae nhu d l cap d myc 1. Cho thdy, chuang trinh PRAB d u g c v i l t tren ea s d phuang phdp phan t u huu hgn k i t hgp vdi md hlnh dan hdi cGa ddt n i n . Id mpt trong cde cdng ey ddng tin cay cd the s d dyng d l tim h i l u hogt dpng eua mdng be - epe. No cd the Id mpt cdng ey d l k i l m chdng, t h i l t ke mdng edc cdng trinh cung nhu d l danh gid s g lam vigc cGa cdc edng trinh hign huu.
L d i cam t g : Trong bdi bdo ndy, tdc gia da s d dyng chuang trinh PRAB, do GS. TS. Matsumoto T.
tang Khoa xdy dgng, Trudng dgi hpe K i l n true Tp. Ho Chi Ivlinh. Bdi bdo nay d u g c hodn thdnh d u d i s u hudng d i n cGa PGS. TS. Chdu Ngoc An. Tac gid bdi bao chdn thdnh cam a n nhung gdp y quy bau cGa cac thay trong bp mdn Dja ca - nen mdng, Khoa xdy dgng, Trudng dgi hpe Bach khoa Tp. Ho Chi Minh.
Tac gia dgc bigt cam a n PGS. TS. Nguyen Bd K l da gdp nhilu ^ phan bign sdu sac de bdi bao duge hoan thanh.
T A I L I E U THAM K H A O
1. NGUYEN BA K t et al [2008], "Mong nha cao tang, kinh nghi§m nudc rigoai", Nhi Xuit bin Xiy dyng. Ha Npi.
2. NIANDOU H. and BREYSSE D.[2005], "Consequences of soil variability and soil-slnjcture interaction on the reliability of a piled raff, ICOSAR 2005, Millpress.
Roterdam, IBSN 90 5966 040 4, pp. 917-924.
3. POULOS H. G. [2001], "Methods of analysis of piled rati foundations", A Report Prepared on Behalf of Technical Committee TC18 on Piled Foundattons.
4. KITIYODOM P. and MATSUMOTO T[2002], 'A simplified analysis method for piled raft and pile group foundations with batter piles", International Journal for Numerical and Analytical Methods in Geomechanics.
vol. 1369, pp 1349-1369.
5. KATZENBACH et al.[199a], "Piled Raft Foundation - Interaction between Piles and Raft", Int. Conf.SSI'm Urban Civil Eng.
6. RABIEI M.[2009], "Parametric Study for Piled Raft Foundations", EDGE vol. 1, Bund. A, no. 1980, pp. 1- 11, (2009).
7. RANDOLPH M. F.[1994], "Design Methods for Pile Groups and Piled Rafts", XIIIICSMMFE. New Dehi. India.
8 VASUDEVS. and UNNIKRISNAN N.[2009], - Behaviour of Piled Raft Foundation in Homogeneous and Layered Sand, Civil Engineering, pp. 6-7.
Ngdy nh$n bdi: 6/3/2015.
Ngdy nh$n bai stra lan cuoi: 29/5/2015.
T9P ch! KHCN Xay dyng - s6 2/2015
