8/10/2019 Tnh ton thit k dm chuyn btct NCKH.pdf

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TNH TON V THIT K

DM CHUYN B TNG CT THP

Phm Xun Tun

Email : phamxuantuanktct@gmail.comNguyn ThTrngEmail : nguyenthetruong1990ktct@gmail.com

TM TT

Hin nay cshtng v tc thha nc ta ang trn pht trin mnh mv km theo l nhng cng trnh nh nhiu tng, cao c vi cc khng gian kin trc linh hot, a dng nhm phc vtt cho cc lnh vc kinh doanh, thng m i, gii tr Do vic tnh ton v thit kdm chuyn btng ct thp l rt quan trng trong lnh vc xy dng nc ta.

Trong ti ny vic nghin cu kt cu dm chuyn c da trn tiu chun ACI 318-2002 v

phng php gin o(3). Bi vit a ra c sl thuyt v trnh ttnh ton ca hai phng php da trnm hnh thc tv sau i btr thp cho hdm ny.

1. t vn

Theo xu hng ngy nay, nh nhiu tng l nhng cng trnh phc hp p ng nhiu cngnng nh thng mi v dch v cc tng bn di, vn phng lm vic v cc cn h cctng bn trn. c c khng gian kin trc nh trn, yu cu ny i hi cc nhp khung lnbn di v cc nhp khung nhhn bn trn, gii php a ra i hi phi c mt kt cuchuyn i gia cc tng, chnh v l do chng ti chn ti Tnh ton vthit kkt cudm chuyn b tng ct thp.

Mc ch ca vic nghin cu l tnh ton v thit kdm chuyn b tng ct thp da trn

hai phng php: tiu chun ACI 318-2002 v phngphp gin o. V dm chuyn l dng ktcu c kch thc ln hn rt nhiu so vi dm thng thng nn s lm vic ca dm chuyncng skhc so vi dm thng thng, cthl sphn bng sut bn trong dm. Do victnh ton v thit k dm chuyn skhc vi vic tnh ton v thit kdm truyn thng. Hinnay vic tn dng khng gian tn trt v thay i cng nng, kin trc ng thi trong mt cngtrnh nhiu tng l rt phbin. Vy mun thc hin c tt cnhng yu cu trn da trn nntng kt cu truyn thng c khng ?

2. Phng php nghin cu

2.1.Tnh ton v thit kkt cu dm chuyn theo tiu chun ACI 318-2002.[1], [3], [4]

Trong phng php ny c a ra cho ta mt khi nim vdm chuyn v cch phn bitdm chuyn. Thng thng dm chuyn c nhn bit qua tlchiu di trn chiu caonu < 2 l dm chuyn nhp n v nu < 2,5 l dm chuyn nhp lin tc. Vic phn tchn hi cho thy nhng c im quan trng sau y ca sphn bng sut trong dmchuyn nh sau :Cc githit nh tit din phng cho dm khng cn ph hp i vi dm chuyn.C mt vng chu ng sut ln ti vtr gi ta v c bit l mt gi ta.Bin dng dc do lc ct gy ra trong dm chuyn l ln hn nhiu so vi bin dng undo ng vai tr nhiu hn so vi tng bin dng.

8/10/2019 Tnh ton thit k dm chuyn btct NCKH.pdf

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Dm chuyn thng c vt nt xut hin kh sm, thng thng khe nt xut hin theophng ca ng sut nn chnh, tc l vung gc vi phng ca ng sut ko, trong nhiutrng hp, khe nt xut hin thng ng hoc nghing khi dm b ph hoi do lc ct.Thc tdm chuyn c 2 dng ph hoi l: ph hoi do un v ph hoi do ct. V vic tnhton kt cu cho dm chuyn chyu cng da trn hai dng ph hoi chnh.

Theo hnh hc th kt cu chuyn c 4 dng c bn sau :

Hnh 1.Dm 1 ct Hnh 2.Dm 2 ct

Hnh 3.Dm vch lin tc Hnh 4.Dm vch khng lin tc

Quy phm ACI-318 chra rng dm chuyn (dm cao) BTCT lm vic hon ton khc vidm BTCT thng thng.Trong giai on n hi ng sut theo phng ngang trong btng ti cc tit din phn btheo quy lut phi tuyn kh phc tp.

h

l

hx

Trc trungha

x

Trc trung ha

Biu phn bng sut cadm thng

Biu phn bng sut cadm chuyn

Hnh 5.Biu phn bng sut[1],[3]

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2.2.

Tnh ton v thit kkt cu dm chuyn theo phng php gin o.[2], [5]

M hnh gin o c nhiu tc ginghin cu tnhng nm 1920. Mt trong nhng uim ca m hnh ny l thhin c nhng b phn chu lc nn, ko ch yu ca ktcu v ngi thit kc thhnh dung ra mt cch cthc cu chu lc ca s dng

trong tnh ton.

PNt

Thanh dng chai

M hnh thanhchng thng

NtVng nt

Thanh ging

Hnh 6.M hnh gin o nhp n gin trong dm chuyn.[5]

Cc bphn chu nn c thhin bng nhng thanh chng, khu vc chu ko c thaybng cc thanh ging v cc mi ni ca thanh sc xem l vng nt ca gin o.Thanh chng v thanh ging c s dng to nn mt hgin trong cu kin dm btng ct thp c t l chiu cao ln. Ti trng tp trung tc dng trn dm s gy ra cc

bin i trng ng sut ti khu vc t lc v gi ta v cng to ra cc vng D v B.

Theo cc quy trnh thit kkt cu b tng ct thp gn y, cc vng D sc tnh tonring bit. Khi nim cbn vng D v B.

Vng B (Beam) l cc vng c trng thi ng sut tun theo cc gi thit ca dm vtit din chu un, chyu phn gia nhp chu tc dng ca moment un, lc ct nhhoc

bng khng. Ti cc vng ny vn c thtnh ton thit knh vi cu kin chu un theocc tiu chun tnh ton kt cu b tng ct thp hin hnh.

Vng D (Discontinuity zone) l vng c trng thi ng sut phc tp, thng xut hinti cc vng mi ni, thay i tit din t ngt, c lkhot, gp khc hoc ti cc lin ktgi ta v im t lc tp trung tn cu kin. Cc vai ct, cc mv cng xn ngncng thuc cc dng kt cu c vng D.

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3. Kt qu

Cng trnh thc tc sdng tnh ton trong ti l: Cao c cn h - Bit thcao cpBMCHng Long. Vtr : s60/7Hunh Tn Pht - phng Ph NhunQun 7 ThnhPhHCH MINH., cao c BMC HngLong ta lc trn din tch gn 20.000m2. Gm 865 cn(860 cnhv 5 cnbit th) c phn thnh 5 cao c ( 2 cao c cao 22 tng v 3 cao c cao 25tng). Kt cu cng trnh c thit ktheo tiu chun xy dng ACI ca M. Kt cu cng trnh

c sdng sn khng dm v dm chuyn. Dm chuyn nm vtr tng 4 vi cao +13.900m,vi tit din 1.2m x 2.8m hvch cng khng lin tc.

Dm chuyn tit din 1.2m x 2.8m c gii thng qua hai phng php v c kt qu:

Tnh ton dm chuyn theo tiu chun ACI-318-02.

Ct thp chu moment dng : As = 189.992 cm2, chn 28 thanh thp No= 10. Chn v b tr

theo TCVN l: 28 32.

Ct thp chu moment m : As = 226.476 cm2, chn 30 thanh thp No= 10. Chn v btr theo

TCVN l: 30 32.

Thp chu lc ct: thp No= 6 khong cch btr sv= sh= s =180mm. Chn v btr theo TCVN

l: thp 20 v khong cch btr sv= sh= s = 200mm.

Tnh ton dm chuyn theo phng php gin o (Strut and tie Model).

Ct thp chu moment dng: As = 452.108 cm2, chn 56 thanh thp No= 10. Chn v btr theo

TCVN l: 58 32.

Ct thp chu moment m: As = 341.981 cm2, chn 42 thanh thp No= 10. Chn v b tr theo

TCVN l: 45 32.

Ct thp chu lc ct: Thp No= 6 khong cch btr sv= sh= s = 180mm.Chn v btr theoTCVN l: thp 20 v khong cch btr sv= sh= s = 200mm.

4.

Kt lunKt cu dm chuyn vi nhng c im cu to hnh hc v kh nng chu lc c s

dng trong cc kt cu nh cao tng BTCT, p ng c yu cu vmt cng nng, c th lgii php tng i tt trong mt strng hp i hi cn hkt cu chuyn vt nhp ln giacc tng trn v tng di ca ta nh.

Cc phn mm tnh ton kt cu hin nay cha c ng dng ring tnh ton dm chuyn,nn phng php tnh ton vn chyu da vo cc cng thc thc nghim l chyu.

c im lm vic ca kt cu dm chuyn cng nh nguyn l cu to ca loi dm nykhc so vi kt cu chu un thng thng.

Do dm chuyn phi nhn ti trng rt ln t ct hay vch cng pha trn truyn xung

dm nn dng ph hoi do lc ct thng hay xy ra vi dm chuyn, nn cn phi c bit quantm n tnh ton chu ct khi thit kloi dm ny. Sphn bng sut bn trong vng nnkhng cn nh gi thit c sdng, gi thit tit din phng khng cn ph hp vi dmchuyn. V vy khi tnh ton dm chuyn cn lu ti c im ny.

ti a ra hai phng php tnh ton kt hp vi m hnh phn thu hn tnh tonct thp chu un, ct thp chu ko v ct thp chu ct cho loi dm c bit ny.

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V tiu chun ACI-318-02 c sdng nhiu hsan ton, cn phng php gin o th angtrong thi gian hon thin. Nn vic la chn phng php no tnh ton v thit kkhngc ra trong ti ny.

5. Phn cm n

Chng em xin gi li cm n n Ban Gim Hiu nh trng cng ton th cc thy, c

Khoa KThut Cng Trnh quan tm to u kin thun li nht cho em hon thnh tt bibo co NCKH ny, c bit em mun gi li tri n n thy Th.s Nguyn Quc Thng tn

tnh gip , chbo cho em trong qu trnh nghin cu ti ca mnh.

6. Ti liu tham kho

Ti Liu Ting Vit

[1] .Nguyn Trung Ha (2003),Kt cu b tng ct thp theo quy phm Hoa K, Nh xut bnXY DNG, H Ni.

[2] .Nguyn Vit Trung (2005), Tnh ton kt cu b tng ct thp theo m hnh gin o, Nhxut bn XY DNG, H Ni.

[3] .Trn Mnh Tun (2011), Tnh ton kt cu b tng ct thp theo tiu chun ACI 318-2002, Nh xut bn XY DNG, H Ni.

Ti Liu Ting Anh

[4] .ACI 318-02,Building Code Requirements for Structural Concrete

[5].James K.Wight, James G.Macgregor (2012), Reinforced concrete Mechanics andDesign, University of Michigan, American.