Thiết Kế Sàn Phẳng Ứng Lực Trước !

Thit k sn phng ng lc trc ! Sn phng ng lc trc l mt cng ngh hin i c du nhp vo nc ta t nhiu nm nay .T thit k v thi cng u kh phc tp khng ging nh sn thng .Ti tham gia thi cng nhiu sn nh ng lc trc TPHCM v H ni nhng khi quay v thit k ti li lng tng .
y ti mun hi cc bn c kinh nghim v thit k sn ng lc trc :
- Khi no th m hnh sn hai phng v khi no th m hnh sn 1 phng ? Vi nhp bao nhiu th cn t cc dm bn rng ?
- Cch trch xut khi tnh ni lc ca cc di nhp .C th dng phn mm SAFE c khng ?( Ci ny quan trng nht v sn vi dm ch khc nhau im ny thi )
- Kim tra vi 3 trng thi ng sut : After transfer prestressed , service, ultima strength tng ng vi cc ti trng no ?
Thn i !Xin gioi thieu voi cac ban mot so van de toi tim hieu duoc . Cac ban cung trao doi kinh nghiem nhe .

Vi sao lai phan biet giua cam bam dinh va khong bam dinh ?

Sn ng lc trc cng sau thng s dng 2 loi bm dinh v khng bm dnh. Cp bm dnh thng oc s dng ch yu c cn M v Anh th ch yu dng cp khng bm dnh

1.c im chung
sn ng lc trc, lc bm dnh gia b tng v cp th cha c pht trin nu nh b tng cha t n cng v thp cha c ko cng. t c iu th ngi ta dng cc v bc hoc ng ghen v b tng c xung quanh chng. ng ghen t n d bm dnh vi b tng nhng n ngn cn s tip xc gia cp v b tng v cp vn t do dch chuyn. Sau cp c ko cng v neo ti u neo.

sn ng lc trc cng sau c bm dnh, ng ghen c bm va sau khi ko cng v s bm dnh gia b tng v cp c thit lp, qua trung gian l ng ghen.Nh ng ca ci tn ca n, sn ult cng sau khng bm dnh, ng ghen thng gi l v bc trong trng hp ny khng c bm va v cp gi c ng sut gn nh khng i so vi ng sut vng u neo.

ng ghen dng trong sn ult bm dnh thng tit din trn. 50-75mm ng knh hoc tit din 20x75mm, v thng c lm t kim loi m in hoc cht do c gp np .S gp np nh hng ti ng ghen khi n chu un dc, n c th d dng un theo prfile mong mun trong khi tit dien vn gi nguyn. Vi ng ghen dng gp np , cp c th cong vi bn dnh nh nht l 2,5mm trong khi vi ng ghen khng c gp np th tht kh dt n v ch lm c profile thng.

Sau khi cp c ko cng v chiu di cp tha c ct b, ng ghen c bm va gm c ph gia , xi mng.. bm dnh cho cp vo ng ghen. Vt liu ct th t dng cho ng ghen c ng knh nh. Khi d lc bm dnh s nh hng n tng ng sut.V u neo c th tr nn khng cn thit hay khng hiu qu na.

Vi sn ng lc trc cng sau khng bm dnh, nh 1 phn ca qu trnh s sn xut, c 1 lp v mng polypropylen v c bi m .Mc ch ca n l ngn cn s bm dnh v s xm thc nh hng tnh cht ca cp.Si cp c trc tip trong b tng m khng cn ng ghen v lun gi nh vy sau khi thi cng xong cng trnh. Cng nh sn ult bm dnh, cp vn s c cng sau khi b tng cng , nhng ng sut trc c truyn qua vng u neo.

C hai kiu sn, th vng neo, th u neo u t vung bin ca sn v c ko cng bng kch thu lc sau c ct u tha, c bm vo cht chng xm thc nh va bm dnh v m t trc cp ko bm dnh. Say u neo c bt bng va xi mng, ph gia..
Cp bm dnh yu cu ng ghen kim loi hoc do v s thm vo ca qu trnh bm va. N c anhs gi l an ton hn khi chng li nhngg tnh hung nguy him ph hoi bt ng.Cp bm dnh th thng xuyn dng trong sn phng hoc di dm trong khi cp khng bm dnh th thng dng trong sn k ln cc di dm

2 . Thit k v s dng
Cp bm dnh c ng ghen th thng ln hn v bc trong cp khng bm dnh v cho mt lch tm nh hn .Bi th nu nh gi v lch tm ln nht th cp bm dnh li khng hiu qu bng
Mt tit din b tng th vi cp bm dnh s c cng ti hn chu un cc b cao hn so vi cp khng bm dnh.Ti trng ti hn, bin dng, ng sut ko trong cp chu nh hng ca b tng quanh n. Cp khng bm dnh cng c s lin h tng i vi b tng xong s lm vic ng thi km hn do ch yu qua vng u neo v mt phn ma st .Vi lc ma st nh hn th cp khng bm dnh phi chu mt lc ln hn trng thi s dng

Bm va c th gy ra s xm thc nu nh khng kim sot tt v khi n s nh hng xu n b tng. Qu trnh bm va cng khng d dng lm tt.

Cp khng bm dnh hu nh ph thuc hon ton vo vng neo . Nu nh vng neo b ph hoi th s xy ra s ph hu do xm thc v mi s ko cng thnh v ngha. Cn vi cp bm dnh th khi vng neo b ph hoi th vn cn lc ko cng do bm dnh gia cp v b tng trong lng b tng.

Nu nh cp khng bm dnh b ph hu mt sn lin tc v sau mt serie nhp lin kt vi n cng b tn tht. Vi cp bm dnh tn tht ch gii hn cho mt s nhp c bit. Mt cht lng m bo ca si thp s cung cp thm trong sn khng bm dnh trnh ri ro.
Nu nh cp b ph hoi th vi cp khng bm dnh th d thay hn do n c tit din nh hn v trt c vi cp bm dnh th khng th.
Trong trn hp chu la, cp bm dnh s bo v tt hn v ng ghen c ng knh ln hn.
Nu trong trng hp ti trng vt ln th s phn b vt nt trong sn bm dnh s tt hn so vi sn khng bm dnh

3 . Vt liu dng c v thi cng
Cp bm dnh cn c vt liu c bit nh ng ghen v qu trnh vn chuyn , lu tr phc tp hn.

h thng bm dnh, ng ghen c t trc v sau cp s c xuyn qua sau ng ghen cn c bm va. Trong khi vi cp khng bm dnh s c t trc tieeps v khng cn bm va.

Cp bm dnh phi gm nhiu si, dng c ko cng nng n hn di chuyn v thi gian ko cng s ko di.Dng c thi cng cng nng n hn vi dng c bm va.B tng ST tit kim c 15-30% khi lng BT v 60-80% khi lng ct thp so vi cu kin BTCT thng, nhng li phi tng chi ph cho b tng cng cao, thp cng cao, neo v cc thit b khc. i vi cu kin nhp ln th s dng BT ST ni chung kinh t hn.
- Cn nu xt v cng th khung sn BT ST trc cha chc cng hn khung dm sn

Cc bc thit k BT ng lc trc c th tin hnh nh sau:

1. La chn vt liu (cp, BT)

2. Tnh lc ng trc.

3. Tnh lc cng bng.

4. Tnh hao ng sut.

5. Tnh s lng cp.

6. Kim tra.

7. B tr cp.

Sn LT bn phi tch ring ra tnh, nu cng trnh ca bn c nhp u nhau v m bo yu cu tnh khung tng ng th bn ch cn chn di trn ct c chiu di bng chiu di nhp tnh v kim tra theo khung tng ng.
Nu mt bng phc tp th bn c th dng phn mm SAFE tnh ra ni lc sn v chia di tnh theo biu moment, hoc chia di theo mt bng sn. Sau tnh ton v kim tra cho tng di theo ni lc tnh ton.

Phng php phn phi trc tip ( DDM ) v phng php Khung tng ng ( EFM ) .
S phn phi Moment un khng phi ng u trn ton Sn m tp trung phn ln di trn ct . D kin khong ( 65-75 ) % Moment theo mi phng c truyn bi cc di trn ct . B rng ca di trn ct c ly sao cho mt na b rng ca di trn ct v mi pha ca ct ly bng nhp ngn ca Sn .

Theo Code ACI 318 quy nh : Chn khong cch gia cc cp ULTr trong di trn ct vo khong ( 3 - 4 ) chiu dy bn ; v khong cch ti a gia cc cp ULTr di gia nhp khng vt qu 6 ln chiu dy bn .

B tng d ng lc B tng d ng lc ti ch trong xy dng chung c cao tng v nh lm vic - t yu cu kin trc, tin dng v gii php kt cu hiu quS nghip cng nghip ho, hin i ho t nc gn lin vi vic pht trin th. H Ni, Thnh ph H Ch Minh v cc thnh ph khc trong nhng nm qua c nhng bc t ph trong vic xy dng cc khu chung c cao tng v nh lm vic. Nhng khu chung c cao tng v nh lm vic v ang xy dng c nhng ci hp l k c v gii php kin trc v gii php kt cu, nhng cng cn nhiu vn phi nghin cu cng trnh xy dng ln va p, bn va tin dng v gi thnh li hp l. Nhng vn cn nghin cu tp trung khu: chiu cao tng, t chc khng gian v lm vic, tnh linh hot ca cng trnh v gi thnh. Trong nhng yu t ny li ph thuc mt cch c bn vo yu cu kin trc s dng, s v h thng kt cuca cng trnh. C th, chiu cao tng ph thuc vo h kt cu c dm hay khng c dm. Nu h kt cu sn khng c dm vi bc ct ln th chiu cao tng c th gim v tnh linh hot ca khng gian trong cc cn h cng nh phng lm vic s cao hn nhiu so vi nh c bc ct b hoc nh c bc ct ln nhng li c dm. c bit l nhng nh c s dng h thng iu ho khng kh trung tm th gii php sn khng dm li rt tin li.
khc phc nhng nhc im trn, ngi vit mun cp n mt gii php kin trc v kt cu cho loi nh chung c cao tng v nh lm vic m hin nay nag c xy dng nhiu. l loi nh chung c cao tng v nh lm vic vi bc ct ln (7x7m, 8x8m, 9x9m) hoc c th c khu ln nhiu hn na- s dng gii php sn khng dm b tng d ng lc
Thng thng, h kt cu chu lc l h sn khng dm kt hp vi ct, vch cng b tr ti cc v tr thang my chu ti trng ng do trng lc ca kt cu, hot ti gm c, ngi s dng v ti trng ngang do gi hoc ng t gy ra. Tnh ton ni lc v chuyn v ca h chu lc khng gian gm sn, ct, vch, li bng cc chng trnh nh: SAP2000, STAAIII... Tu theo nhu cu s dng v quy m u t, nhng theo s tng kt ca cc nh khoa hc, loi nh ny c hiu qu kinh t vi chiu cao t 9 n 30 tng.
i vi nn t H Ni , thnh ph H Ch Minh v cc ni, thng thng mng c dng loi mng cc BTCT tit din 30x30cm ng hoc p cho cc loi nh cao t 9 n 18 tng, cn nhng cng trnh t 19-30 tng vi bc ct ln cn thit phi x l bng cc khoan nhi ng knh 1-1,2m cm vo tng si cui. Sn dng b tng ng lc trc. Thng thng dng loi cp c v bc vi ng knh 15,24mm hoc ln hn vi s lng v ng knh theo tnh ton ca cc nh thit k. Tc thi cng rt nhanh, thng thng vi mt bng sn mt tng t 1.000-2.000m2 th c 10 ngy c th thi cng c
khc phc yu t vng i vi bn sn khng dm vi bc ct ln, bin php hiu qu nht l dng b tng d ng lc. Hin nay, cng ngh ko cng b tng d ng lc trin khai tng i mnh, c bit trong lnh vc cu ng. Mt s cng trnh tr s v nh v ang c thi cng theo cng ngh ny. Nhng pht trin c mt cch mnh m trong lnh vc xy dng nh ca cn c s ch o ca cc nh qun l, lnh o chuyn ngnh cng nh vic thuyt phc cc ch u t v vic p dng loi cng ngh mi ny trn c s chng minh hiu qu ca n nh: bn ca cng trnh, gi tr s dng v yu t gi thnh
1. So snh s lm vic khng gian ca h kt cu dm-sn-ct-vch cng khu vi h kt cu gm sn-ct-vch v ni lc v chuyn v
V d a ra trnh by l mt nh lm vic cao 9 tng, li ct ti a l 7mx8,4m. Phng n chn c xem nh ti u l h kt cu chu lc gm ct + vch cng t khu vc thang my + sn khng dm. Ct vung c chn vi tit din 65x65cm, sn dy 20cm, b tng d ng lc mc 350, vch cng dy 20cm.
Phng n so snh l phng php thng thng lu nay cc nh thit k v cc nh thu xy lp thng thch dng l h kt cu khung ct + vch chu lc + dm + sn vi b tng ct thp (BTCT) mc 200, thp thng. H kt cu thng ng chu lc ngang vn dng h ct vung 65x65cm v vch cng dy 20cm v tr cu thang nh phng n thp d ng lc. im khc phng n ny l sn dng h dm chnh v dm ph chu lc. Bn sn dy 12cm da trn yu t m bo vng cho php v t l thp, h dm chnh tit din 25x65cm, h dm ph tit din 22x35cm. Qua kt qu tnh ton khng gian theo chng trnh STAADIII cho 2 phng n trn ta nhn thy:
Ni lc ti cng mt tit din ca cng mt chn ct
Phng n BTCT thng c dm
- Lc dc: N=393,994 tn
- Mmax = 0,612tm
- Lc ct Qmax = 0,198 tn
Phng n b tng d ng lc
- Lc dc: N=447,686 tn
- Mmax = 3,792 tm
- Lc ct Qmax = 0,916 tn
Chuyn v ti cng mt tit din ct trn nh cng trnh
x = 0,00064 cm
y = 0,43591 cm
z = 1,92053 cm
x = 0,21846 cm
y = 0,27509 cm
z = 2.11529 cm
- Mt nhn xt gn nh l quy lut l i vi cc nh cao tng c vch chu lc th vch cng thng ng chu ti trng ngang ch yu. Ct ch chu mt phn rt t.
-So snh hai phng n ta thy ni lc ca chn ct cng khng khc nhau nhiu lm nn phng n mng cng tng ng nhau.
- Chuyn v ngang trn nh cng trnh cng trong phm vi cho php v c gi tr tng ng nhau
- T ni lc ca dm chnh, dm ph v sn ca 2 phng n ta tnh c thp dm
sn, ct ca 2 phng n
- T kch thc ca cc cu kin ca 2 phng n so snh khi lng b tng ca 2 phng n (xem bng)
2. So snh phng n u nhc im ca 2 phng n
u im
- Thi cngn gin hn
- Mc b tng thp hn
- Tnh ton n gin hn
- To c trn p
- Chiu cao tng c nng cao bi khng b hn ch dm
- bn cng trnh cao, v mc b tng cao, thp cng cao ko cng v khng cho php c vt nt
- Khng phi lm trn
- Thi cng nhanh
- Khng gian s dng linh hot
Nhc im
- Chiu cao tng s b hn ch
- c bit vi nhng phng rng 100- 150m2 th chiu cao tng 3,6m, dm cao 70cm th thng thu ch cn 2,9m, thp qa
- bn cng trnh khng cao do c s xut hin vt nt dn ti s n mn thp nhanh
- Trn c dm nn phi lm trn
- Thi gian thi cng lu hn
- Thi cng cn n v c kinh nghim
- Mc b tng cao hn
- Tnh ton phc tp hn
3. So snh khi lng b tng, thp v kinh t ca 2 phng n
Phn sn: (so snh 1 sn)
B tng
- B tng mc 200
- 167,29m3 x 402.612/m3= 67.352.961
- B tng mc 350
155,m3 x 6392.450/m3= 99.114.750
Thp
Thp thng
35,9 tn x 5.000.000/t=179.500.000
12,55tn x 5.000.000/t=62.750.000
Thp ng lc
(cp+u neo+ nhn cng)
5,0tn x 20.000.000 /t=100.000.000
Cp pha thnh dm
347,4m2 x 22.000/m2 = 7.642.800
Xy tng
[( 30,8 = 26= 9,6) 0,11+ (7+ 14) 0,22]
0,5= 6m3 x 348.234 /m3
2.089.404
Tng cng cho 1 sn
254.495.761
263.954.154
4. Kt lun v kin ngh
Qua kt qu tnh ton v s so snh v nhng mt u nhc im nh trnh by trn, y l mt vn quan trng m cc nh u t, qun l cng nh cc nh t vn thit k cn xem xt c ting ni chung. Mc ch cui cng l to c nhng cng trnh tt, p, c tnh s dng cao v nhp xy dng hin i.
(Ngun: Hi tho kt cu v cng ngh xy dng mi Vit Nam)B tng ST tit kim c 15-30% khi lng BT v 60-80% khi lng ct thp so vi cu kin BTCT thng, nhng li phi tng chi ph cho b tng cng cao, thp cng cao, neo v cc thit b khc. i vi cu kin nhp ln th s dng BT ST ni chung kinh t hn.
- Cn nu xt v cng th khung sn BT ST trc cha chc cng hn khung dm sn

Cc bc thit k BT ng lc trc c th tin hnh nh sau:

1. La chn vt liu (cp, BT)

2. Tnh lc ng trc.

3. Tnh lc cng bng.

4. Tnh hao ng sut.

5. Tnh s lng cp.

6. Kim tra.

7. B tr cp.

Sn LT bn phi tch ring ra tnh, nu cng trnh ca bn c nhp u nhau v m bo yu cu tnh khung tng ng th bn ch cn chn di trn ct c chiu di bng chiu di nhp tnh v kim tra theo khung tng ng.
Nu mt bng phc tp th bn c th dng phn mm SAFE tnh ra ni lc sn v chia di tnh theo biu moment, hoc chia di theo mt bng sn. Sau tnh ton v kim tra cho tng di theo ni lc tnh ton.

Phng php phn phi trc tip ( DDM ) v phng php Khung tng ng ( EFM ) .
S phn phi Moment un khng phi ng u trn ton Sn m tp trung phn ln di trn ct . D kin khong ( 65-75 ) % Moment theo mi phng c truyn bi cc di trn ct . B rng ca di trn ct c ly sao cho mt na b rng ca di trn ct v mi pha ca ct ly bng nhp ngn ca Sn .

Theo Code ACI 318 quy nh : Chn khong cch gia cc cp ULTr trong di trn ct vo khong ( 3 - 4 ) chiu dy bn ; v khong cch ti a gia cc cp ULTr di gia nhp khng vt qu 6 ln chiu dy bn .

( Tng hp : theo CETEC )

Documents

Thiết Kế Sàn Phẳng Ứng Lực Trước !