DIEN BAN KHOA HOC CONG NGHE
PHAN TiCH KET CAU KHUNG THEP PHANG CO LIEN KET MEM TREN MONG CQC CHjU TAI TRONG DA LAN
TS. Vo T h a n h L i i d n g
Hpc vien Ky thuElt QuSn sii, , Tel: 0913217722 TliMTAT:
Trong bdi bdo tdc gid di/a ra kit qua khdo sdt cttuy^n vj ngang va tii trong ci/c dai cua k6t ciu khung th^p pbing tren m6ng coc be tflng c6t 1ti6p, xfit flin flfl mem ciJa lien kk dim - cflt vd vdt !i6u ISm k^t cau Wiung Id dan - d6o ly ti/flng, dnh hifang dd m^m cfla li§n k^ ddi vdi coc vd dnh hudng cfla vj tri m6i n6i cgc den trang thai chuySn vj cfla khung - dai cgc - cgc trong mdi tn/dng nen vdi mfl hinh phi tuyln. Tren cd sd ma trdn dfl cfltig cua phin tfl' Bianh cd lien ket nCfa cdng trong vd ngoa mdi truflng ddn h6i, tdc gid da xay ddng chddng tiinh phan tich khung th6#p tr6n mdng cgc chju tdi trgng va cham, cdc k6t qud minh hd? dd chi ra ring dnh ht/dng cfla cac frang thdi li§n kit ddi - coc vd vj M mdi n6i cpc cung nhd dnh hddng ciJa dd mem lign kit dim - cflt vd vdt lieu ddn dSo Id ddng ki.
Tir kh6a: Kit ciu khung thep, iien kgt mim, mdng coc, dd Idn
l.fidt van de
Theo truy§n thdng khi phdn tich kSt cJiu khung, cac lien kit d4m - cpt thiremg gid thilt ik cufng hoan toan hoac \k khdp 1;^ tudng. Tuy nhien, trong thac t l v^
b^ng cdc nghiSn cijru thuc nghigm da chi ra rdng, liSn kit cdc thanh dirgic ndi co chuyin vi tiicfng dli vol nhau khi chju luti, ndn cac lien kit nay 1^ liSn kit niia Cling (Semi - Rigid Connections) [7]. Bi xdt thiJC trang chju luti cua kit cdu, khi phdn tfch kit cdu khung thep cdn xdt t6i dd mdm cua cdc lien kit, khdng gia thidt lidn kdt ddm - cot vd c$t - mdng la ci}ng tuydt ddi hoac id cdc khdp ly tudng.
Mdng coc thuOng di^ng hai lo^i coc phd bidn Id cpc chl sdn (coc dong ho^c coc dp) va rac nhdi (coc do tai chd). Vdfi su phdt trien cua mdy tinh ca nhan vd phuang phdp phdn tCr hiJU han, hidn nay 6 cdc nudc Tdy Au - Bdc My, ngudi ta thudng tinh todn cpc lam vipc ddng thdi vdi nen (nhdt la bai todn cpc chju tdi trpng ddng). Bdi vd^ kit cdu cpc ddng hoac dp, cdc cpc thudng duoc ghdp tU cac doan cpc vdl mdi ndi sir dung bdn mat bich vd han ndi, mdi ndi dd cung cd bidn dang khi chm luc vd cung Id lien kit niJa cUng [7].
Cdc cdng trinh xdy di;ng gdm hai phdn: phdn thdn noi trdn mat ddt vd phdn mdng ndm ngdm dudi mat ddt. Trudc ddy, ngudi ta thudng tinh phdn thdn vd phdn mdng ridng biet nhau. Trong thdi gian gdn ddy da cd mdt s6 phdn mdm nhu FB - MultiPier (2004) [10] phan ti'ch cdu bd tdng cdt thep Idm vide ddng thdi vdi mong cpc. Phiitfng phdp ttnh nhu vay cho kit qud gan vdi thi/c t l hon. Do v^y, bdi toan phdn tich kit cdu khung thep cd lidn kit nCia cumg trdn mdng cpc dudi tdc dung cua tdi trpng tTnh vd d^ng la mdt trong nhOfng vdn d i ttiuc tiln, rdt cdn thilt va ddng dupc quan tdm.
2. Xfiy di/ng vd giai bai todn khung thep lam vide ddng thdi vdi m6ng coc
2.1. Phuang trinh dao dpng cua kit cau khung thip trin mdng cpc chju tii tong va dap
Sit dunci phuwig phap phdn ti!r hOu han kit hpp vdi md hinh ndn phi tuyln, phuong trlnh chuyin ddng hd kit cdu khung thep trdn mdng cpc cd lidn kit dan hbi dKcA tac dung cua tdi trong va ddp dudc vilt dudi d?ng ma trdn [6]:
[M]{u}+[C]{u}+[K]{u} = {p(t) (1) trong do:
{u}, {li}, {ii} tuong Ung Id vdctd chuyen vi, vdn t6c va gia tic nut ciia kit cdu trong hd toa 66 chung;
[M], [C] vd [K] tuong Ung Id ma tran khdi luong, cdn va dp Cling cua todn kit cdu tron^ hd tpa dp chung, phu thudc vdo chuyin vj ciia kit cau va gid trj dd mem cua lien kit 6 ddu phdn tir thanh tuong Ung;
{p(t)} Id vecto tdi trpng nut cua kit cdu trong he toa dp chung.
Cdc ma tran khli tuong vd ma trdn dd cdfng cila todn kit cdu duoc xdy dung tU cdc ma trdn khdi iucing [M]^ vd ma tran dp ciifng [K]' cua cac phdn tir. Viec xdy dung cdc ma trdn [M]", [K]' da dupc cdc tdc gid xdy dung vd trinh bay trong [1, 2, 3, 4]. Trong bdi bao [4]
nhom tdc gia da trinh bay phUdng trinh dao d$ng cOa khung thdp phang cd lidn kit mdm phi tuyln chju tdi trpng tap trung gia djnh theo hinh sin nhung coi mi^g la tdm cUng cd 6inh. SO dung ma tran dO cUng phltfi tir thanh co lien kit nira ciJrtig trong mdi trudng ddn h6l da xdy dung trong bdi bao [2] nhdm tdc gid dd phdn tich nhdm cpc chju tai trgng va ddp theo phucmg ngang trong bdi bdo [1]. Tuy nhidn, trong bdi bdo ndy da sir dung tai trpng xung va ch^m nhung kit cdu trdn he mdng cpc mdi chi Id mdt trg be tdng cit thdp. Kit hpp nhijmg bai bao trdn, trong bdi bao ndy se trinh bdy chucAig trinh phdn tich Idiung thep cd lidn kit nilia Cling phi tuyln cDng ldm vide v& hd mdng cpc bd tdng cdt thdp nhu mot thi thdng nhit khi chju tdi trpng va Cham. D l Idm dut?c didu dd trong chuong trinh da vilt mdt chuong trinh con nhdm nh$n dang cdc phin tCf theo vi tri vd vdt ii$u. Cu t h i d^ nhdn dgng vj trf cua NGUdl X A Y D U N G S O T H A N G 11 & 12 - 2015
PHAN TiCH KET CAU KHUNG THEP PHANG..
phdn ttr da sir dung he sd ndn ban ddu: khi phdn tir nam trong khdng khf thi he sd ndn bdng khdng cdn khi ndm trong ddt thi he sd ndn khdc khdng. Chung loai vat lieu ciia mdi phlin tir dupc cho thdng qua cdc dac tnmg v^t lidu nhu md dun dan hdi, cutftig dp tfnh todn v.v...
Tai trgng xung dgng cd t h i do xe cd hoac da lan va dap vao cdng trinti. Hdm thdi gian ciia tdi trpng va chgm cd t h i dupc md td bdi 3 y l u td: Tai trpng cao nhdt, thdi gian tang tai (tUc la thdi gian de dat tai trpng Idn nhdt), vd thdi gian va cham. Mpt bieu dd dang hinh sin thudng duoc thda nhdn phfi hpp vdi tdi trpng va cham [8] vd duoc sOr dung trong bai bdo nay. Odi vdi va cham cua xe cd vcd mdng cdu or Ei-Tawi et al, thdi gian tdng tai duoc bdo cao vdi khoang tCr 0,03-0,05 s, khoang thdi gian va cham 0,15-0,2 s; va dinh ciia tai trpng lidn quan ddn van t i c va loai xe cd. Vi vdy, s u tdng theo thdl gian cua tdi trpng va cham do dd ldn trong bdi bdo ndy dope Idy khodng 0,05 s.
Nhung thf nghiem va cham da dupc trinh bay bdi Chu vd Zhang bao gdm nhDng khdi aluminum roi xudng dpc theo mdt dudng ranh vd va cham vdi mdng c l u . Thf nghiem tUdng t u nhu s u va cham cua da, vi vdy, theo cdng thdc cua kinh nghiem cho tfnh todn dinh cua nhOmg tai trpng va cham thu dUdc dua trdn nhung k i t qud cua thf nghiem dupc chdp nhdn trong bdi bdo ndy. Nd dudc the hien dudi cdng thirc [8]:
Prr^x = agC(DWTy-V'"m"™ (2) trong dd:
Pmax la ^ n h cua tdi trpng va cham (MN);
ttg Id hd sd kich thudc nhdm cpc;
C Id he so cdng cua mui tdu thuydn;
u Id vdn tdc va cham (m/s);
DWT Id trong luong tTnh ciJa ddi tuong va cham (Tdn);
m Id trong luong tTnh cua ddi tupng bi va cham (Tin).
2.2. Bir&ng cong p-y
Hinh 1. Dddng cong p-y cho cgc ddn Ddt khdng phdi Id vdt lidu ddn hdi t u y l n tfnh, vi v$y dO cting cua gdi ddn hdi ngang (k^ = p/y) khdng phdi Id hdng sd nhu quan hd t u y l n tfnh ma gidm ddn nhu trong quan hd phi t u y l n trdn Hinh 1.
Hinh dang vd dp ddc cua dudng cong khdng nhOmg phu thupc vdo tfnh chdt ciia ddt, ma cdn phu thupc vao dd sdu doan coc dang xet, kfch thu'dc cpc, muc nudc ngdm vd dang tai trong (tTnh hay ddng). Chi t i l t cac dudng cong p-y cho cac loai ddt khac nhau, cdc dudng cong nay duoc FHWA (Hiep hdi dudng lidn bang My), API (Vien nghidn cUu d i u My) vd nhidu to chufC khdc khuydn nghj sir dung cd the tham khdo trong cdc tdi lieu [5, 9]. Ta thdy phuong trinh md ta dudng cong p-y trinh bdy trong cdc tai lieu khd phde tap. Tuy nhidn, de khao sdt dnh hudng cua vj tri mdi ndi d i n trang thai ndi luc - chuyen vj cua cpc ta sir dung dufeftig cong p-y cho cat ciia O'Neill (1984) da cd sdn trong thu vien cua phdn m i m FB-Pier (ddt toai S0iL=1) bdi vl chi cdn nhdp mpt sd thdng sd ddn gidn nhu diidng kfnh cpc, trpng lupng ridng cua Idp ddt, gdc ma sat trong, md dun b i l n dang ngang [9].
nam so dgng life hgc cua dat. Phuong phdp diJng he Id xo - gidm chdn dupc siJr dpng trong phdn mdm FB-MultiPier [10] de tfnh toan ddng l i ^ cua tuong tdc cpc - ddt. NhCmg tham sd ddng luc hpc ydu cdu bao gdm sd tdi trpng tudn hodn, tdc dd tdi trpng, he sd suy b i l n cua ddt, vd he so cdn ciia dat. He sd suy bidn cua ddt duoc siJr dung de xdc dinh s u suy gidm duftfng cong p-y dpng tir dudng cong p-y tTnh ban ddu. Tuy nhien, chi cd xung ddu tidn cua tai trpng Id quan trpng trong s u phdn tich cua tru cdu dudi nhung va cham cua ddt dd. Vi vdy, hd sd suy b i l n cua ddt khdng duoc sif dung trong tnidng hpp chju tai trpng va cham [8]. He sd cdn cua ddt dupc cho bdi cdc hd s6 can Rayleigh hoac ty sd cdn .
2.3. Giii phtrang trinh can bSng cua ket ciu Bi nhdn dUdc n$i luc vd chuyen vj ciJa cdc phdn tir nhdm ddnh gid thuc trang ky thudt ciia k i t cdu khung thep tren mdng cpc trong trudnp hpp phdn tif cpc cd lien k i t mdm vdi tjmg xit phi tuydn ciia ddt ndn ta cdn gidi phuong trinh phi t u y l n (1). Oldu do cd the Idm duoc nhd phuong phap tich phdn tnic t i l p Newmark k i t hpp vdl phuong phdp lap Newton-Raphson [6].
Trdn co s d cdc ma trdn ddc trung cua phdn tir thanh CO lien k i t mdm trong va ngodi mdi trudng dan hdi, k i t hpp vdi thudt toan gidi bdi toan ddng da xdy dung [ 1 , 2, 3, 4], tac gid dd lap chUOng trinh tinh DLFPG (Dynamic Lateral Loading of Frame on Pile Groups) de tinh todn k i t cdu khung thdp tren he mdng coc chju tai trpng ddng theo phucmg ngang vdi md hinh ndn phi t u y l n vd dp mdm lien k i t ddi - cpc, cpc - cpc, chudng trinh dupc vidt bang ngdn ngu' MATLAB phien bdn 6.0.
3. Khao sat khung thep - m o n g cpc c h j u tai t r p n g va c h a m
Bi minh inpa cho thudt giai, xdt mdt k i t cdu khung kieu gidn cd t i l t didn cdt Id thep dng, t i l t didn ddm chGr I djnh hinh, dung dudng hdn gdc lien k i t tnjc tiep cdc thanh.
Kich thudc tidt didn thanh Id tdi uu thdng qua chi tidu chat lupng v l trpng ludng k i t cdu nho nhdt vd chuyen vj ngang dinh khung cue dai trong gidi han cho phdp bang 11,2 cm (1 % chidu cao khung) khi chju tdi trpng ddng ddt Ung vdi dp mem lien k i t d ddm-cpt N G U d l XAY D U N G SO T H A N G 11 & 1 2 - 2 0 1 5
PHAN TiCH K h cAu KHUNG THEP PHANG- cho cSc truimg hop [3]: (1) lien kit cung tu);et dfli (dO
mim IBn kit k = 0); (2) lien kit mim (gia thiit dO mem lien kit k = 0,5.10* rad/kNm).
Biit kit ciu khung thep lam viec theo so d i phang, kit ciu cot tiit dien ing va dim tiit diSn chGl I ^nh hinh. H§ bao gdm 12 niJt vk 13 thanh, tai trong phan b i diu ISn thanh va luc tap trung tai nijt, nhu 6 Hinh 2a.
VSt lieu th^p CO m6dun dan hii E = 2,1.10'kN/cm^
he s i Poisson = 0,3, cu&ng dd tinh toan cua v$t li$u th'#f = 21kN/cm'.
Su phan b i cac d|c tnjng tiit didn cua ciu kien dupc ph§n thSnh bin nhom: nhdm 1 g6m cot c^c ting 1 vk 2 (cot 1 - ing D450 mm); nhom 2 gdm c6t ting 3 (cot 2 - ing D402 mm); nhdm 3 gdm dSm cSc ting 2 va 3 (dim 1 - 150); nhdm 4: dim ting mai (dim 2 - 140).
H$ mdng gdm hai d^i, mdi dSi cd 2 coc b i tn each nhau 0,9m (tU tim din tim); dai cd chiiu dky 1,0m;
chiiu rdng 0,6m. Ckc coc cd mat cit diu, chiiu dai L
= 12m, gia thiit coc gdm 2 doan; tiit didn cpc hinh vudng c6 canh a = 0,30m, v&t lieu be tdng cip bin B22,5 cd mddun d&n hdi E = 2,9.10' kN/m^ cudng dp tinh to4n B„ = I.S.IO" kN/m'. B i t loai SOIL = 1 (FB- Pier) cd trpng lupng riSng Ye = 19 kN/m', gdc ma s^t trong (p = 35°, md dun biin dang ngang k = 27155 kN/m'; hd sd nhdm (giSm gtk tri cua d u ^ g cong p-y) ddi vdi cac cpc Id 0,55. Ngocii tai thing dCmg phan b i diu q = 25 kN/m cho dim tang 2, 3; q = 15 kN/m cho dim m&\ vk cdc tai \kp trung tai cac nut giao glDa dim vk cpt nhu d hinh 2a, khung cdn chiu tdi ngang bing mdt xung va dSp P, = 50sin(30t) KN dat vao cdt bdn trdi tai dd cao 2m ke tir mat mdng vdi thpi gian duy tri tdi Id 0,1 gidy, khi ty sd can ; = 3%.
eokl(l ISkN/m
P(x)
|l I U 1,1 I I u
25kN/m
|l I I t 1,1 I I U I
25kN/m
|l 111 i,U IfTJ
m.
-J
•AJ 2
30x30
(a) V \J (b)_i 2. Sd dd khung ttidp trSn mdng coc Bdng 1, thi hidn chuyin vj ngang cua cdt va ddi mdng trong cdc trudng hpp lidn kdt gitjra ddm vd cdt Id lidn kit cumg ho^c mdm, cdc cpc lien tgc dai 12m lidn kit vdi ddi mdng Id ngdm hoac khdp.
Kit qua tfnh todn gid tri cue dai cua chuyen vj ngang theo ting khi thay tai xung, dang hinh sin bdng
Bang 1. Gid trj chuyin vj ngang c\tc dai [mm] theo tang kiii tdi xung P. = 50sin(30t) kN
TSnj
M^i T^ng3 Tang 2 Mong
{iaingini,LX cdng 6,08 3,e3 3,46 2,40
mhi 6,75 4,28 3,77 2,83
B i i kMp, U ( cdng 7.53 4,78 4,60 4,21
m ^ 7,87 4,30 4,67 5,11
Bdng 2. Gia trj chuyen v| ngang cpc dai [mm] theo tdng khi tdi tTnh P, = 50 kN
TSng
Mai TSng 3 TSng 2 MOng
BSI ngSm, LK ci^g 6,14 5.98 5,54 400
mSm 13,75 10,81 7,64 432
e S I I M p , L K ci}ng 8,30 8,18 787 728
m^m '^
13«v ii,eCs
9,29 J 7,36
1' 1
^ li
tdi trpng tTnh Px = 50 kN clio d Bdng 2.
Qua khdo sdt, cd mpt s l nhdn xdt v l kit qud nhdn dupc nhu sau:
(1) TU cdc gid trj trong Bdng 1 vd Bdiig 2, ta thiy dd mem lidn ket ddm - cdt dnh hudng nhilu din trgng thdi chju luc ciia kit cdu khung thdp trdn mdng cpc bd tong cdt thdp, chuyin vi cue dai khi lien kit mdm ldn hon gia trj tuong Ung khi lien kit cdng trdn 10%.
(2) Khi khung thdp Idm vide d6ng thdi vdi mdng cpc, thi tdi xung dpng dang hinh sin cho hidu qua tdc ddng nhd hon tdi ttnh cd gid trj bdng gia trj ci/c dai cua tdi trpng xung ddng.
Bang 3, the hidn kit qua khao sdt kha nang chju tdi cua hp khung thdp trdn mdng cpc theo d$ mim tidn kit ddm - cdt vd tdi trpng (xung ddng ho^c tTnh) cho trudng hpp cpc dupc t6 hpp tCr hai doan cd chilu ddi tuong dng 1,5m vd 10,5m (mdi ndi giOa cdc doan cpc coi nhu lidn ket khdp) vd cpc lien ddi 12 mdt vdi lien kit ddi - cpc Id cUng hoac khdp, vd han chl hu hdn^
dupe xem Id thda man khi chuyen vj ngang tuong ddi gida cdc tdng dupc gidi han dudi 1% vd chuyin vj ngang cue dai cua ddi mdng (dinh cpc) khdng qud 3 cm (0,1 chilu rdng cpc). Hidu Ung dOng cua tai trpng va Cham cd dnh hudng ddng ke din phan Ung cOa h$
khung - cpc. Kha ndng chju l i ^ ciJa hd khung thep tren dai mdng cpc khi chju tat trpng tTnh vdi gid tri dinh tdi Bang 3.131 trpng cue dai [kN] theo chuyin vj cho phdp kht khung thdp Idm vi$c ddng thdi vdi mdng cpc
V i t l nfii coc (tSi trpng) Ljgn luc (tinli) Lien tuc (dSno) 1,5-10,5 (Snh) 1.5-10,5 (HOng)
OSi ngdm, I K cong 385 510 395 510
m^m 349 360 366 371
D i i kMp. LK cOtig 207 334 50 73
mSm 205 273 50 63 O^m tiin trang lim NGUdl XAY DI/NG S6 THANG 11 & 12 - 20151