Kt cu thp s dng trong xy dng dn dng v cng nghip Vit Nam

Thp l mt trong hai loi vt liu quan trng nht trong xy dng Vit Nam hin ti, cng vi vt liu b tng ct thp. c bit trong cc nm gn y, vic s dng thp pht trin nhanh chng, thay th cho b tng ct thp (BTCT) trong phn ln nh xng, nh nhp ln v nhiu cng trnh cng cng khc.

Bi ny nu tng quan v vic s dng kt cu thp trong xy dng dn dng v cng

I. Cc h thng kt cu thp qua cc thi k.

1. Vit Nam l thuc a ca Php t cui th k 19 n u th k 20. Mi cng trnh

2. Trong nhng nm 50 v 60: Sau khi ho bnh lp li ng Dng, min Bc Vit

nghip Vit Nam trong cc thp k va qua.

xy dng, cng ngh ch to v thi cng lin quan n thp u l ca Php. Do b tng ct thp ch c p dng Vit Nam t nhng nm 30 v hu nh khng c kt cu nhp ln, nn hu ht cc nh cng nghip v cng trnh nhp ln nh hi trng, rp ht u dng kt cu thp, t ra l h mi. V d Nh ht ln H Ni, mt cng trnh ni ting hon thnh vo thp k u tin th k 20, c kt cu c xy dng hon ton bng gch v thp, khng c b tng ct thp. Mi vm trn l cupn hnh nn gm cc sn hnh tam gic, ta trn vnh gi. Thp cacbon thp, c cng xp x thp CT3. Mi sn nh ln, ban cng, cu thang u lm bng dm thp ch t hp inh tn, cc dm thp hnh v cun gch to mt sn. Cu to sn kiu dm thp v cun gch ny c p dng trong hu ht cc mt sn v c p dng trong hu ht cc nh tng c tng gc c xy dng thi k . Cc nh xng ln bng thp ng k l: nh my xe la Gia Lm, nh my ru Hi Dng, cc hng ga may bay Gia Lm v Bch MaiCng ngh v hnh thc kt cu l vo trnh ng i: thp cacbon thp, lin kt inh tn, thp cn c nh, s kt cu c in.

Nam bt u xy dng c s cho nn cng nghip ho, trc ht l cc nh my cng nghip nng v cng nghip nh. Lc , thp l vt liu him c v rt qu gi, do hon ton nhp t cc nc x hi ch ngha m ti cc nc ny, thp cng rt qu v him. Phng chm thit k kt cu thp l: tit kim mc cao nht. Do , ch dng thp cho

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nhng nh xng ln, c cu trc nng, ct cao v nhp rng. in hnh l cc nh xng ca Khu Lin hp Gang thp Thi Nguyn. Ti , c nhng khung ton thp vi dn nhp 30 n 40m, ct rng bc thang cu trc 20 n 75tn, dm cu trc nhp 18m cao ti 2m. Lng thp tnh cho mt mt vung sn l kh ln: 70 n 100kg/m2. Mt cng trnh ng k na l nh my Supe Pht pht Lm Thao: phn ln cc phn xng nhiu tng hay mt tng u dng kt cu thp. Do vic s dng thp nhiu m nh my ny c hon thnh nhanh hn 1nm so vi vic dng kt cu b tng, vic ny mang li li ch khng nh cho nn cng nghip lc , (theo kin pht biu ca mt v lnh o ngnh xy dng). S h thng kt cu thng dng l: dn gm cc thp gc, ct v dm t hp tm v thp cn; lin kt hn, khng dng inh tn.

Ngoi ra, cc trng hp khc u ch dng kt cu b tng ct thp: trong tt c cc nh

3. Trong thp k 70 v 80: Cng tc xy dng ch yu l khi phc cc cng trnh b ph

Bt u s dng nhiu kt cu thp tin ch nhp t nc ngoi. in hnh l loi Khu

c ci to lm kt cu cho nh xng c cc ca tri v cu trc, nh th thao, v

min Nam Vit Nam trong cc thi k , k thut xy dng c pht trin nhanh

4. T nhng nm 90 n nay: Cng vi s pht trin nhanh chng ca nn kinh t v ca

S thay i v vic s dng thp c th l do cc nguyn nhn sau:

dn dng, trong phn ln nh xng, k c xng nhp ln. C th nu v d Nh my ng tu Bch ng, xng rng 21mt dng dn btng ct thp ng lc trc, nng hn 10tn, thi cng cc k kh khn trong khi mtb dn thp tng t ch nng 1,5 tn nhng khng c dng. Ti nhiu trng hp khc, my tm fibr xi mng nng 100kg, dng x g b tng nng ti 500kg ch khng dm dng mt x g thp nh nhng. Nhng v d ny cho thy r ch trng khng dng kt cu thp mi khi c th c.

hoi, xy dng nhng xng my mi loi nh.p dng rng ri s kt cu hn hp: ct b tng v dn thp.

kho Tip. l khung nhp 12 n 15m, dn bng thp ng, ct thp cn t hp v x g l cu kin thnh mng cn ngui. Khung ny l nguyn l lm kho c, sang n Vit Nam

thm ch c ga hng khng. Ngoi ra, nhiu cng trnh dn dng nh trng hc, bnh vin do cc t chc nhn o tr gip nhp t nc ngoi, c lm bng kt cu thp tin ch 1 tng v 2 tng. Phng chm tit kim thp khng cn sc mnh na; cc yu t thun tin cho vn chuyn, cho thi cng, cho vic hon thnh nhanh tr nn quyt nh.

vi s h tr ca cng ngh phng Ty. Cc xu hng thit k l ging nh ca phng Ty: thp c p dng rng ri trong cc cng trnh cng nghip, xng ng tu, nh cao tng (ti 16 tng), hng ga my bay v c nh chung c nhiu tng.

ngnh xy dng, vic s dng thp tng nhanh cha tng thy. Hu nh 100% nh xng l lm hon ton hay i b phn bng thp. Nhng mi nh nng n bng b tng ct thp bin mt, thay th bng mi tn nh t trn x g thnh mng. Khng thy u dn BTCT, dm mi BTCT c sn mt thi pht trin.

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- Gi tin thp khng cn l vn quan trng hng u na; n ch chim khong 50% gi tr kt cu. Khng nht thit phi c gim trng lng vt liu i, nh hng n ph tn ch to v dng lp v lm chm thi gian hon thnh xy dng.

- Cng ngh ch to tin b, c bit trong vic ct v hn, vic to hnh ngui. S chn nhng loi kt cu tin cho vn chuyn dng lp nh dm t hp hn thay th cho dn thp rng, trc y hay dng v d ch to nhng kh vn chuyn v lm tn chiu cao nh.

Mt loi h thng kt cu c p dng nhiu nht l h thng nh tin ch, xut pht t trng phi Metal building system ca M. C s l lun ca h thng ny, nh ta bit, yu cu vic hp l ho ton din trong thit k, ch to v dng lp ca mi loi cng trnh nht nh. Do phi tiu chun ho trong vic thit k tng th, thit k chi tit v ch to, phi ng dng rng ri tin hc trong thit k v sn xut. hng trm cng trnh nh xng, nh lm vic, nh thi u c xy dng Vit Nam bng h thng nh ny. u tin l cc cng ty nc ngoi nh Zamil Steel Buidings, Kirby, BHP mang vo v ch to ti Vit Nam, n nay nhiu nh my, doanh nghip, thm ch c hp tc x cng ch to thnh cng loi h thng ny, vi trnh khc nhau. S kt cu thng dng nht l: khung cng bn c, gm ct vt chn khp ni cng vi dm cng thay i chiu cao; cc kt cu th yu gm dm cu trc, x g, dm tng, ct tng, tt c u c tiu chun ho. nh my m Ph M vi chiu di nh 700m l nh s dng khung tin ch ln nht nc ta.

u tin c s dng trong nh tin ch nh nhng cu kin th yu l x g, dm tng, n nay kt cu thnh mng to hnh ngui bt u c s dng ring bit di dng khung nh nh nh trng hc, nh sn xut nng nghip, nh vng su, vng xa. Mi hi trng A1 nhp 20m l kt cu ln nht c thc hin bng thnh mng.

Trong vi nm gn y, vi s xy dng nhiu nh nhp ln nh hi trng, nh trin lm, nh thi u, bt u pht trin nhanh loi kt cu c trc tinh th, thng c gi n gin l dn khng gian. C th k: nh ga hng khng Ni Bi, nh thi u Nam nh, nh biu din c heo Tun Chu, H Long, Nh trin lm Hi ch Hi Phngv hng chc nh thi u th thao c xy dng phc v cho SEA GAMES 2003. Nhp ln nht thc hin ti 62m. Cc thanh l thp ng do Vit Nam ch to, nt ch yu l nt cu, hoc mt vi kiu khc, dop Vit Nam sn xut.

Nh thi u Ph Th TP. HCM c kt cu vm nhp 100m l ngi nh thi u ln nht ca Vit Nam v cng l nh dn dng c nhp ln nht.

c mt nh cao tng (30 tng) u tin dng khung thp c xy dng TP. HCM, m u cho giai on pht trin nh cao tng bng thp.

Mi sn vn ng Quc gia M nh (H Ni) c dn chnh nhp 157m, cao 9m lm bng cc thp ng ng knh trn1m, l kt cu ln nht trong xydng nh c thc hinVitNam.

II. Cc cng trnh khc bng thp.

1.Cu: Vit Nam xy dng c rt nhiu cu bng thp.

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2. Thp thng tin v tuyn v ct ti in: Ngy t nhng nm 60, cc nh xy dng Vit Nam c kh nng thit k, ch to v dng lp hng lot cng trnh thp cao cho mc ch vin thng v ti in. ng k nht l ct in vt sng Hng Chm (H Ni), cao 150m, nng 300tn, xy dng trong nhng nm 60,cho n nay vn l cng trnh thp cao nht v cao nht VN (gn y mi c mt vi ct vt sng cao trn cao ny nhng nh hn); Thp TV cao 115m Hi Phng, hon thnh trong nhng nn 70; tr ng ten c day no cao khong 200m s dng trong thi k chin tranh. c bit trn 3000 ct ca ng dy ti in 500kV Bc Nam c thit k v thi cng trong thi gian k lc 2 nm, trong c ct cao nht l 82m vt sng Gianh (Qung Bnh).

3. Cc cng trnh khc: C th k ra:

- B cha du v cha kh, hnh tr v hnh cu, dung tch t 100 n 5000m3, thm ch n 10.000m3, t ti cc kho du trn khp min t nc. Phn ln do Vit Nam t thit k v lp t.

- Cc cng trnh trn bin nh gin khoan, cng trnh bo v thm lc a, cc cng trnh du khi. Chiu cao ti trn 40m, bng thp ng. T nhng cng trnh u tin hon ton nhp ngoi, nay do Vit Nam thit k, ch to v lp t.

- Mt s cng trnh khc nh: ng ng dn ln, ng knh trn 1m, di hng chc km B Ra; cc cng trnh ng cp treo nh ni B en, Yn T, Cha Hng thng c ct bng thp ng cao trn 30m, ng knh trn 1m n 1,4m.

III. Cc tiu chun v Quy phm,.

Tiu chun thit k kt cu u tin ca Vit Nam c ban hnh nm 1963, l da vo tiu chun thit k ca Lin X nm 1955, trong ln u tin trn th gii p dng phng php tnh ton kt cu thp theo trng thi gii hn. Tiu chun thit k c thay i t nm 1972 v bn hin hnh TCVN 5575-91 c bann hnh nm 1991. Phng php tnh ton theo trng thi gii hn l phng php tin tin, tn dng c s lm vic ca vt liu, v do trong nhiu trng hp, mt cu kin tnh ton theo TCVN a n kt qu kch thc nh hn so vi cc phng php ca tiu chun Php hay M. V d: xt mt ct chu lc nn, lm bng thp CT38 ca Vit Nam (tng ng vi thp A36 theo ASTM ca M hay thp E24 theo NF A35-501 ca Php). So snh 3 tit din do tnh ton theo TCVN 5575-1991 (k hiu A1) v theo CM 66 ca Php (k hiu A2) v theo AISC/ASD ca M (k hiu A3), ta c bng sau:

mnh ca ct 30 80 100 150 A2/A1 1.04 1.15 1.20 1.25 A3/A1 1.19 1.27 1.17 1.25

C th c kt qu tng t khi tnh ton dm hay dn.

(Tuy nhin, khi xt tng th c mt cng trnh, c thit k vi c cc Tiu chun khc nh v ti trng, v t hp ti trng th khng hn kt cu thp theo TCVN l lun lun nh hn s vi theo tiu chun nc khc).

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Ngoi tiu chun thit k kt cu thp chung, ta cha c tiu chun thit k cho cc dng c th nh: kt cu thnh mng, kt cu dn khng gianKhi , s phi s dng tiu chun ca nc ngoi.

Hin ti, Nh nc Vit Nam cho php s dng cc Tiu chun Quy phm ca cc nc sau thit k: Nga, Anh, Php, c, Nht, c. y l vic lm mang tnh cht tnh th trong giai on qu ca vic hi nhp.

V gia cng v nghim thu kt cu thp, ngnh xy dng mi c mt tiu chun TCXD 180-87, chung cho kt cu thp ph thng. Tiu chun ny thc ra l rt s si khng p ng c yu cu hin nay, rt cn sot xt thay i. C mt s tiu chun ngnh nh ca in lc, Bu in, Du kh p dng cho kt cu thp chuyn dng. Khi cha c tiu chun ch to

nghim thu cho cc cng trnh c th, cc n v cng s dng tiu chun tng ng ca cc nc nu tn trn.

IV. Vt liu thp v cng ngh ch to

Vit Nam c mt s c s luyn kim min Bc v min Nam, luyn ra thp cacbon thp, vi sn lng ch khong 20% nhu cu v thp. Ln nht l Nh my Gang thp Thi Nguyn tng sn xut thp bng cc l bng Martin, l quay thi xy, nay lun thp bng l in cng nh mi c s sn xut thp min Trung v min Nam.

Loi thp c p dng nhiu nht cho n nay vn l thp cacbon thp, tng ng CT38 cua Vit Nam, c gii hn chy 23kN/cm2. Phn ln thp s dng l nhp t nc ngoi vi cc mac tng ng: CT3 ca Nga, Q235 ca Trung Quc, SS40 ca Hn Quc v c thp BS 4360gr ca Anh.

Hin ti, c khuynh hng s dng nhiu hn cc li thp hp kim thp cng cao, c bit trong cc nh tin ch, nh: 14G2 ca Nga, A572 (gr.50) theo ASTM, S355 ca chu u, SS49 ca Nht, c gii hn chy khng di 34kN/cm2. Hu ht thp hp kim u phi nhp ngoi.

V thp hnh, Vit Nam mi sn xut c thp hnh cn nng loi nh: thp gc cnh di 125mm, thp C v I di 140mm. Thp ng c mi ni v thp hnh thnh mng cn ngui c sn xut ti nhiu c s ln nh trong c nc, dng phi cun thp mng nhp khu. Mt s nh my ch to cun thp mng i vo hot ng (Bnh Dng), mt s khc ang c xy dng nh Qung Ninh, Ph M n nm 2005 cung cp phi cho cc nh my cn ngui.

Trong cng ngh ch to kt cu thp, Vit Nam c mt s nh my chuyn sn xut nh tin ch, ct in, kt cu dn khng gian (vi dy chuyn my t ng CNC). Phng php hn ph bin nht l hn h quang th cng (SMAW-shielded metal arc welding), vi qua hn t sn xut tng ng nh que hn E42, E50 ca nga hya E60XX, E 70XX ca M (v d que hn Vit c N42 v M50, que hn E6028 v E7018 ca TCty Vinashin). Cc nh my ln u c trang b dy chuyn hn t ng h quang chm (SAW submerged arc welding), hn trong khi bo v (GMAW gas metal arc welding)

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v hn bng dy li thuc (FCAW flux cored arc welding). Ni chung, cng ngh ch to kt cu thp Vit Nam cn cha pht trin.

V . D on nh hng pht trin.

Trong s ln mnh ca nn kinh t v ngnh xy dng, kt cu thp Vit Nam s c vin cnh pht trin mnh m. Hng trm cng trnh ln s c xy dng bng thp. Lng thp s dng trong xy dng s tng t bin.

Cc hng pht trin sp ti ca kt cu thp c th l:

- Nh tin ch tip tc c s dng ngy cng nhiu;

- Kt cu thp nh, bao gm kt cu thnh mng to hnh ngui, kt cu hp kim nhm;

- Kt cu s dng thp ng, bao gm c kt cu dn khng gian;

- Kt cu nh cao tng.

Cc k s Vit Nam c kh nng nghin cu v thit k cc loi cng trnh ny. Nhim v cp bch l y mnh sn xut thp, chuyn giao cng ngh ch to mi, bng cch xy dng mt s nh my luyn thp, cn thp hnh, thp tm, v ch to kt cu. Cc vic ny c d kin trong cc k hoch kinh t ca Nh nc cho giai on 10 nm ti. Trong iu kin , chng ta c th tin tng rng ngnh xy dng cng trnh thp nc ta s c pht trin vt bc.

(Ngun: Ti liu Hi tho kt cu thp trong xy dng)

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