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Phn II- Phn mm SAP2000 91

Chng 1 Nhng khi nim c bn

1. S kt cu - S tnh

1.1. Cng trnh v s tnh

Khi tnh ton mt cng trnh hay kt cu, vn ch yu l xc nh ni lc,chuyn v, phn lc... trong cng trnh. Tuy nhin nu k n mt cch chnh xc v y cc yu t hnh hc ca cc cu kin th bi ton s qu phc tp, do phi dng phng php tru tng khoa hc thay th cng trnh thc bng s tnh ca n .

S tnh ca cng trnh l hnh nh n gin ho m vn m bo phn nh st vi s lm vic thc t ca cng trnh. Bi vy, trong s tnh ngi ta lc b cc yu t khng c bn v ch xt n cc yu t ch yu quyt nh kh nng lm vic ca cng trnh v ngi tnh phi bit la chn s tnh .

Khi la chn s tnh, nhng yu t cn quan tm lm c s cho qu trnh chuyn i t cng trnh thc sang s tnh l :

1. Cu to ca kt cu v tm quan trng ca n .

2. Kh nng tnh ton ca chng trnh hay phng php tnh s s dng.

3. Ti trng v tnh cht ca ti trng.

4. S phn nh c s lm vic chnh xc ca cng trnh hay cha .

5. C th s dng mt s gi thit chp nhn c n gin s .

Cc bc cn thit khi bin i t mt cng trnh thc v s tnh:

1. Thay cc cu kin ca kt cu thnh cc phn t ni vi nhau qua cc nt. Tu thuc vo loi kt cu m phn t c th biu din qua ng trc ( vi kt cu h thanh ) hoc biu din bng cc mt trung gian ( kt cu tm, v .. )

2. Thay cc tit din bng mt s i lng c trung nh din tch (A), mmen qun tnh ( I ) . . . hoc cc gi tr A, I tng ng .

3. Thay cc thit b ta bng cc lin kt ta l tng ( khng ma st ) gi l cc gi ( gi cng, gi n hi).

ng dng Tin hc trong Thit k cng trnh

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4. a ti trng tc dng trn b mt cu kin v cc nt, trc hoc cc mt trung gian .

5. B qua mt s yu t gi vai tr th yu (khng cn thit ) n gin cho qu trnh a v s tnh .

V d :

Hnh 1.1 S cng trnh Hnh 1.2 S tnh

1.2. Phn loi cng trnh

Cng trnh c phn loi da theo tnh cht lm vic ca kt cu :

Kt cu phng : khi tt c cc cu kin ca cng trnh u nm trong mt phng v ti trng ch tc dng trong mt phng th cng trnh thuc loi h phng. Tuy nhin trong thc t, ngi ta thng a mt s cng trnh khng gian v s tnh l h phng cho n gin, p dng trong nhng trng hp khi b hn ch bi phng php tnh v cng c tnh. Lc ny, c th da theo tnh cht lm vic ca cng trnh coi l h phng .

Kt cu khng gian : nu cc cu kin ca cng trnh khng nm trong cng mt mt phng hoc ti trng tc dng ngoi mt phng th h c gi l h khng gian

Cng trnh phn loi theo hnh dng phn thnh : dm, dn, khung, vm, v, tm, bn, khi hoc kt cu hn hp . . . ( c th l kt cu phng hoc khng gian)

1.3. Tnh ton cng trnh

Tnh ton cng trnh c ngha l xc nh ni lc v chuyn v trong cng trnh ( tnh ng sut, bin dng ), sau s tu theo tnh nng ca vt liu m kim tra xem cng trnh c


kh nng chu cc nguyn nhn tc dng ln n ( ti trng, nhit , ln, lt, mi ...) hay khng .

Ngi ta c th tnh cng trnh theo cc kiu khc nhau :

Tnh cng trnh theo bn: nhm m bo cho cng trnh c kh nng chu tc dng ca ti trng cng nh ca cc nguyn nhn khc m khng b ph hoi (khng gy, , bin dng kt cu . . . ) .

Tnh cng trnh theo cng: nhm m bo cho cng trnh khng chuyn v v rung ng ln dn n cng trnh mt trng thi lm vic bnh thng ngay c khi iu kin bn vn m bo ( khng nt, vng, ln . . .qu ln ).

Tnh cng trnh v mt n nh: l tm hiu kh nng bo ton v tr v hnh dng ban u ca cng trnh trong trng thi bin dng ( khng bin dng cu kin ) .

Tnh cng trnh m bo tin cy, chu mi : i khi s dng cc l thuyt tnh ton thng thng kim tra cng trnh theo ba tiu chun trn m bo nhng theo thi gian, ti trng gy ra nhng tc dng khc ( v d mi ) dn n cng trnh b ph hu. Cng nh vy, nu xt mt cch ton din, cng trnh c th h hng bng mt yu t cha lng trc c v phi k n tin cy khi tnh ton .

Trong hu ht cc phn mm tnh ton kt cu trc y ngi ta ch ch gii quyt vic xc nh ni lc v chuyn v . Thi gian gn y cc chng trnh ln xt n bi ton thit k ( thit k cc cu kin b tng, thp, t chn tit din ) .

Qu trnh tnh ton thc cht l chu k lp, bi v qu trnh tnh bn, cng, n nh ca cng trnh lin quan n tnh cht c hc ca vt liu, hnh dng v kch thc ca cu kin . . . trong khi , kch thc ca cu kin li c quyt nh qua kim tra ni lc trong cu kin m tnh ni lc li phi gi thit trc cc kch thc tit din . . . Do vy trong thc t ta thng gp hai dng bi ton:

Bi ton kim tra : s dng khi bit r hnh dng, kch thc ca cng trnh cng nh nguyn nhn tc ng bn ngoi. Trong trng hp ny cn phi xc nh trng thi ni lc v bin dng ca h di tc ng bn ngoi xt xem cng trnh c m bo bn, cng v n nh hay khng, c kinh t hay khng ?

Bi ton thit k : s dng cho qu trnh thit k cng trnh, l cn xc nh hnh dng, kch thc c th ca cc cu kin trong cng trnh mt cch hp l cho cng trnh bn, cng v n nh di tc ng ca cc nguyn nhn bn ngoi bit. Bi vy, i vi bi ton thit k qu trnh lp vi cc bc sau :

Gi thit cc kch thc, hnh dng ca cu kin theo kinh nghim hoc cc phng php thit k s b .


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Tin hnh gii bi ton : tnh ton theo bn, cng, n nh .

Kim tra kt cu c m bo cc tiu chun trn hay khng trn c s chnh li cc gi thit ban u v lp li hai bc sau cho n khi tho mn th dng .

Tm li c hai dng bi ton trn u lin quan n qu trnh tnh ni lc, chuyn v ca ca kt cu khi bit hnh dng, kch thc ca cc cu kin v cc tc ng bn ngoi.

2. cc thnh phn c bn ca s kt cu

2.1. Nt ( joint )

Nh bit, cc kt cu thng c to bi nhiu vt th ni vi nhau qua cc nt cng chu ti trng. Ni chung, nt phi c t cc v tr giao im ca cc phn t. Ngoi ra, nt cn c th t thm bn trong phn t ti nhng v tr m ngi dng cn bit thm cc thng s ca ni lc, chuyn v . . .

i vi mt h kt cu mun a t cng trnh thc v s tnh th mt trong nhng yu t quan trng l phi bit t nt vo nhng v tr no. Trong mt s phn mm tnh kt cu trc y, bit cch nh s nt v t v tr nt hp l dn n gim nh khi lng ca d liu nhp vo cng nh c th ly ra nhng kt qu mong mun mt cch hp l. Trong SAP2000, i vi nt, mt s im lu s trnh by trong cc mc sau y.

2.1.1. V tr ca nt phi t : Ti im lin kt gia cc phn t.

Ti nhng v tr thay i v c trng vt liu, c trng hnh hc ( khng bt buc ).

Ti cc im cn xc nh chuyn v hoc im c chuyn v cng bc.

Ti cc im xc nh iu kin bin.

Ti cc v tr c ti trng tp trung (tr ti tp trung trn Frame).

Ti cc ni c t khi lng tp trung.

2.1.2. Khi khai bo nt trong SAP : Cc nt c to t ng khi v phn t.

S hiu nt c gn t ng.

C th thm cc nt ti cc v tr bt k trong phn t.

H to cho nt c th ly mc nh theo h to tng th hoc h to ring ca nt.


Khi khai bo mt s thnh phn ca kt cu nh cc im lin kt, bc t do, lc tp trung, khi lng tp trung thng s dng h ta ring ca nt.

2.1.3. Bc t do ca nt Kt cu b bin dng v vng ch yu do chuyn v ca cc nt. Mi nt c ti a su thnh phn chuyn v, ba thnh phn chuyn v thng dc theo trc k hiu l U1, U2, U3 v ba thnh phn chuyn v xoay quanh cc trc k hiu R1,R2, R3. Su thnh phn ny l cc bc t do m t nh trn hnh sau:

Hnh 1.3 Nt v cc bc t do

Bn cnh cc nt thng thng ( l mt thnh phn ca kt cu ), chng trnh t to ra cc nt ch, thng khai bo cng vi cc rng buc( constraint) cng c su bc t do .

Mi bc t do c th l mt trong cc loi sau :

Active : khi phn tch bi ton, s tnh chuyn v ca cc bc t do ny.

Restrained : khai bo mt s chuyn v b cn, khi phn tch, cc phn lc s c tnh cho cc thnh phn ca nhng bc t do tng ng ny.

Constrained : chuyn v ca cc bc t do ny c tnh theo (ph thuc) vo chuyn v ca cc bc t do khc .

Null: chuyn v ca cc bc t do ny khng nh hng n kt cu do khi phn tch b qua cc thnh phn ny .

Unvailable : Khi phn tch, cc chuyn v theo cc bc t do ny b loi tr, khng k n n. Nu chia theo nhm th c th coi c hai nhm bc t do l Available v Unavailable .

2.1.4. Mt s i tng khc lin quan n nt Khi phn tch kt cu, mt s thnh phn ch phi khai bo ti nt nh :

Cc lc tp trung ( Joint Load )


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Khai bo khi lng tp trung ( Mass )

Khai bo cc mu ti trng ( Joints Pattern )

Trong cc phn mm tnh kt cu v SAP2000, mt s kt qu ch xut ti cc nt nh:

Cc gi tr chuyn v

Cc gi tr phn lc ca gi cng v gi n hi

Cc lc lin kt ( Forces )

Cc dng dao ng

2.2. Phn t

Mi phn mm tnh ton kt cu, ty theo chc nng v kh nng ca phn mm m c nhng loi phn t (PT) khc nhau. Thng thng phn mm no cng c phn t thanh, tm v. C nhng phn mm do c th tnh ton c phn t nc, PT ng, PTcp ... SAP2000 c cc loi phn t sau:

2.2.1. Phn t thanh ( Frame, Cable, Tendor, Brace ) Phn t thanh dng m hnh ha cho cc kt cu dm, dn, khung phng (2D),

khung khng gian (3D), thanh ging, dy cp...

Trong s tnh phn t thanh biu din qua mt on thng l trc ca cc cu kin, mi phn t c hai nt, nt u k hiu l i v nt cui k hiu l j ( theo trt t v phn t ).

Mi thanh c mt h ta a phng ring, dng khi m t cho cc i lng: tit din, khai bo ti trng trn phn t v biu th cc kt qu ni lc. Cu trc h ta ring PT c 3 trc : Trc 1 ( ) nm dc theo trc thanh, chiu i t i n j, trc 2 (trng),trc 3 (xanh) hp vi trc1 theo qui tc bn tay phi.

2 1

3

Hnh 1.4 H ta ring phn t thanh

Trong SAP2000 khi v cc phn t trc giao, nn theo trt t t di ln trn, t tri sang phi, h trc ta ring c dng nh sau :

Theo mc nh : ( trc 2 lun // +Z ) -vi phn t nm ngang ; (trc 2 // +X)-vi phn t thng ng. Trong trng hp ny, hng ca 3 trc s l :


+ Khi trc +1 // +X th trc +2//+Z v trc +3// -Y

+ Khi trc +1 // +Y th trc +2//+Z v trc +3// +X

+ Khi trc +1 // +Z th trc +2//+X v trc +3// +Y

Trong nhng trng hp vi phn t xin v ngi dng mun khai bo h ta ring khng theo mc nh trn, c th dng khai bo Gc to phn t. Khai bo ny c th :

i chiu ca trc 1

Khai bo gi tr gc quay, cho php quay trc 2&3 quanh trc 1 to ra h ta mi so vi h mc nh. Gc l dng khi quay ngc chiu kim ng h nu nhn t chiu dng trc 1.

Cc thanh coi l thng ng nu gc nghing vi trc Z


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Hnh 1.5 Qui c v s tng quan gia cc trc v cc thnh phn ni lc ca phn t thanh

2.2.2. Phn t Area :Shell- Plate- Plane- Asolid Mi phn t tm,v ty theo dng tam gic hay t gic c 3 hoc 4 nt, ly theo mt phng trung bnh ca cc kt cu loi tm, v, bn,sn ... v khai bo qua chiu dy ca PT .Trong h cc chng trnh SAP, ty theo tng phin bn, qui c v k hiu cc loi phn t ny khc nhau i cht.

Hnh 1.6 Hnh dng v h trc ta ring ca phn t Area

Trong SAP2000 t phin bn V8. tr i, phn t Area m t cho nhiu loi phn t bao gm c phn t tm v thng thng v cc loi phn t khi phng. C th phn loi (Type) ca Area nh sau:


Nhm cc phn t Shell gm:

Membrane : phn t mng ch chu ko (nn), chuyn v trong mt phng & xoay quanh trc vung gc vi mt phng PT.

Plate : phn t tm : ch chu un 2 chiu trong mt phng & ngoi mt phng, chuyn v theo phng vung gc vi mt phng .

Shell : PT v 3 chiu c th chu c ko ( nn ) v (hoc) un.

Nhm PT Plane (khi phng Asolid) :

Phn t bin dng phng Plane Strain

Phn t ng sut phng Plane Stress

Phn t i xng trc (Axisymetric Solid).

H to ring ca PT Area qui c : trc 1(), trc 2( trng) ,trc 3(xanh) ; trong trc 1 & 2 nm trong mt phng phn t, trc 3 lun vung gc vi b mt phn t .

Theo mc nh, trc 3 hng ra mn hnh hoc theo phng +Z.

Cng c th khai bo h trc s dng gc phn t (nh trong PT thanh).

Cc loi ti trng tc dng ln PT Area :

TT tp trung ti cc nt.

TT phn b u trn phn t.

Trng lc, TT bn thn.

TT nhit.

TT p lc : c hng vung gc vi mt trong cc mt ca PT (surface Presure ), TT m t qua mt hm theo cc im nt ( Joint Pattern ), thng dng khai bo cho p lc nc hoc tng chn hay cc ti trng phn b 3 chiu trong khng gian .

Ni lc :

Vi loi phn t Area ngoi kt qu ni lc ti cc im nt ca phn t, chng trnh cn cho kt qu ng sut ti cc nt (theo cc phng ca h ta ring phn t hoc & theo phng chnh).

Kt qu ni lc bao gm cc lc dc mng theo cc trc k hiu F11,F12 . . . v m men un k hiu M11,M12 . . . ti cc im nt ca phn t.

Kt qu ng sut cho ti cc nt ca th trn, th di ca phn t.


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2.2.3. Phn t khi 3D (Solid ) Phn t khi 3D m t qua 9 nt, dng cho cc kt cu khi chu ti trng 3 chiu nh kt cu , p, mng . . . Trong gio trnh ny, khng gii thiu chi tit loi phn t ny.

i vi cng trnh tnh theo phng php phn t hu hn, ti cc vng cn quan tm trong kt cu cn ch li chia phn t phi nh t chnh xc v s phn b ng sut v s bin thin ca chuyn v .

2.3. Lin kt

Lin kt gm c cc loi :

Lin kt(LK) ti giao im ca cc phn t ( Node )- k hiu LK1 ng vi ton b cc nt trong kt cu.

Lin kt ni t k hiu LK2: lin kt cng hoc mm (n hi).

Rng buc chuyn v (Constraint) : m t chnh xc s lm vic ca kt cu, trong mt s trng hp ti nhng v tr lin kt c nhng thnh phn chuyn v lin quan n nhau. Hnh 1.7 Lin kt

2.3.1. Lin kt cng (Restraints) - tuyt i cng Lin kt cng trong SAP2000 c cc loi :

Fixed (ngm) : 6 thnh phn chuyn v UX,UY,UZ ,RX, RY, RZ c gi tr bng 0;

Hinge (Gi c nh ) : 2-3 thnh phn chuyn v UX,UY,UZ c gi tr bng 0;

Rolles (Gi di ng): 1 thnh phn chuyn v ca UX,UY,UZ c gi tr bng 0.

Cc gi tr chuyn v theo cc bc t do ca nt c gn bng 0 tng ng vi cc phng ny s c cc thnh phn phn lc.

Cc thnh phn gn Restraint c th khai bo chuyn v cng bc theo loi TT Displacement Load (chuyn v ca cc bc t do c gi tr = chuyn v cng bc, chuyn v ny cng gy ra ni lc trong m hnh ).

Lin kt Restraint m bo cho m hnh khng b bin hnh. Nu kt cu b bin hnh, chng trnh s thng bo " Structure to be unstable "


2.3.2. Lin kt n hi (Spring) Cng c cc thnh phn chuyn v(CV) :

Translation U1, U2, U3= UX,UY,UZ

Rotation R1, R2, R3= RX, RY, RZ

cng ca gi c gi tr hu hn.

c im ca lin kt mm:

Phn lc ca gi l phn lc n hi. Hnh 1.8

Gi tr chuyn v ca LK l hu hn v ph thuc vo cng ca gi n hi (H).

Lin kt cng phi m bo cho kt cu khng bin hnh.

Gi H cng c th chu cc chuyn v cng bc & phn lc H,gi tr tnh bng tng phn lc ca 2 chuyn v .

Khng c khai bo lin kt Spring trng vi khai bo Restraint trong mt nt.

Hnh 1.9 Lin kt cng v LK mm

2.3.3. Lin kt v phn lc Nu chuyn v ca mt nt theo hng ca mt bc t do no c gi tr bng 0 (ti cc im ta gi cng) hoc c mt gi tr bit ( ti cc gi n hi hoc nt c chuyn v cng bc ) th ti bc t do phi t mt lin kt. Gi tr bit ca chuyn v c th khc nhau gia cc trng hp ti trng, nhng nhng bc t do c lin kt th p t cho tt c cc trng hp ti trng. Mt khc, c th trong mt trng hp no c mt s chuyn v bit v trong trng hp khc cha bit (khng t lin kt ti ).


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Lin kt cng nn t nhng bc t do available trong kt cu ni m cng bit bng 0, v d nh ti cc phng chuyn v thng ngoi mt phng v xoay trong mt phng ca mt khung phng, nu khng kt cu s mt n nh v nghim ca phng trnh cn bng tnh hc s sai.

Lc hoc mmen sinh ra trong cc bc t do b cn ( lin kt ) gi l phn lc v n c xc nh qua qu trnh phn tch. Phn lc c th khc nhau mi trng hp ti trng. Lin kt coi l ni cng gia cc bc t do ca nt v nn .

Bt k bc t do no trong su bc t do ca mt nt trong kt cu c th c lin kt n hi theo phng thng v xoay. Nhng gi n hi ny ni cc nt vi nn. Cc gi ta n hi theo cc bc t do b gi khng tham gia vo cng ca kt cu. Cc lc n hi t ti mt nt quan h vi cc chuyn v ca nt bng ma trn i xng 6x6 ca cc h s cng n hi. Cc lc ny hng ngc vi hng chuyn v. Cc h s cng n hi khai bo theo h to ring ca nt. Cc lc v mmen n hi k hiu F1, F2, F3, M1, M2,M3 tnh theo cng thc :

6

5

4

3

2

1

6

5

4

3

2

1

3

2

1

3

2

1

000000000000000000000000000000

uuuuuu

uu

uu

uu

MMMFFF

Trong u1, u2, u3, r1, r 2 ,r3 l chuyn v v gc xoay ti nt v u1,u2,u3,r1,r2,r3 l cc h s cng n hi . Chuyn v ca im lin kt vi nn ca gc n hi c th khai bo bng 0 hoc khc 0 ( khi c chuyn v cng bc ). Chuyn v nn c th khc nhau gia cc trng hp ti trng. Gi n hi c th coi l ni mm gia nt v nn.

2.3.4. Rng buc chuyn v (Constraint) Khai bo cc rng buc chuyn v m hnh lm vic ng tnh cht thc ca n

vkhng bin hnh ng thi gim s phng trnh v khi lng tnh ton.Trong SAP2000 c cc kiu Constraints : Body, Plan, Diaphragm, Rigid body . . .

Mt rng buc ( constraint ) bao gm mt tp ca hai hoc nhiu hn cc nt c chuyn v rng buc vi nhau. Chuyn v ca mt cp nt trong rng buc quan h vi phng trnh rng buc. Cc kiu lm vic ca kt cu c th khai bo iu kin rng buc l :


S lm vic ca vt th cng ( Rigid body ) trong cc nt rng buc c chuyn v thng v chuyn v xoay cng vi nhau nh c ni bng cc lin kt cng. Cc kiu lm vic tuyt i cng c th xut hin trong m hnh :

Vt th cng ( Rigid body ): cng hon ton cho mi chuyn v .

Mng cng (Rigid Diaphrgam) : cng i vi cc phn t lm vic trong mt phng.

Tm cng (Rigid Plate ) : cng i vi tm chu un trong mt phng .

Thanh cng ( Rod) : cng i vi s dn di dc trc .

Dm cng (Rigid Beam): cng i vi dm chu un trn mt trc .

Khai bo Constraint m t s lm vic ti cc nt rng buc c mt s hoc tt c cc thnh phn chuyn v (c th l chuyn v thng v chuyn v xoay) bng nhau.

iu kin i xng v phn xng cng khai bo bng Constraint.

2.3.5. Rng buc mng ( diaphragm constraint ) Rng buc mng l loi thng dng nht to ra tt c cc nt rng buc vi n di chuyn cng vi nhau nh mt mng phng cng chng li cc bin dng mng. Tht s l, tt c cc nt rng buc c ni vi cc nt khc bng cc lin kt l cng trong mt phng, nhng khng nh hng n bin dng ngoi mt phng. Rng buc ny c th dng vi:

M hnh sn b tng hoc sn ti ch trong kt cu nh cao tng, trong in hnh l c cng trong mt phng rt cao.

M hnh mng trong sn cu ( brigde superstructures ). Dng rng buc mng vi kt cu nh cao tng kh c vn chnh xc s xut hin khi cng trong mt phng ln ca mt bn sn c m hnh ho vi cc phn t mng (membrane) . iu ny rt c ch trong tnh ton ng ca nh nhiu tng chu ti trng ngang, n lm gim ng k kch thc ca bi ton gi tr ring khi tnh .

Mi rng buc mng ni mt tp ca hai hoc nhiu hn cc nt vi nhau . Cc nt c th c v tr tu trong khng gian, nhng c kt qu tt nht, cc nt nn nm trong mt phng rng buc. Ngc li, m men un c th sinh ra ti nhng ni c lin kt rng buc, iu ny khng ng vi tnh cht cng ca kt cu.

Cc phng trnh rng buc cho mi rng buc mng vit theo mt mt phng vung gc. V tr ca mt phng l khng quan trng, ch c hng ca n. Theo mc nh, mt phng c xc nh t ng bi chng tnh t s phn phi khng gian ca cc nt rng buc. Nu khi xt khng ch c mt hng duy nht, s ly mt phng


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ngang X-Y . iu ny c th xut hin nu cc nt l trng nhau hoc cng trn ng tuyn tnh ( colinear ), hoc s phn phi khng gian thin v 3 chiu hn l phng. Bn c th b vic la chn mt phng t ng bng cch khai bo trc ca h to chung ( X,Y,Z ) hoc l vung gc vi mt phng rng buc .

Mi rng buc mng c h to ring ca n, cc trc qui c l 1,2,3. Trc 3 lun vung gc vi mt phng rng buc. Chng trnh chn t ng cc trc 1,2 tu trong mt phng. Hng thc s ca cc trc trong mt phng khng quan trng, ch c hng vung gc nh hng trc tip ti phng trnh rng buc .

Cc phng trnh rng buc : lin quan n chuyn v ti hai nt rng buc bt k (I v J) trong rng buc mng. Cc phng trnh ny vit theo cc chuyn v thng trong mt phng (u1, u2 ) v chuyn v xoay quanh php tuyn v cc to trong mt phng ( x1, x2 ) tt c ly theo h to ring rng buc .

Lin kt iu kin bin ca cc nt : trong bi ton nh cao tng, khi tnh theo m hnh: Li vch chu ti trng ngang.

Khi gn Constraint, Sap2000 cho php khai bo v gn trong nhiu nhm constrait (lu mi mc sn ch c gn mt ln).

Mt nt c th ng thi nm nhiu nhm Constraints.

2.3.6. Cch gn cc nt vo mt nhm constraints: Chn cc nt nm trong nhm

Vo menu Assign Joints Constraints.

Nhn Add (Add Local l n gin nht)

t tn cho nhm Constraints

La chn cc iu kin bin ca nhm. Khi cc nt trong nhm s c cng iu kin bin la chn.

Nhn OK.

Lu :

Mt nt c 6 bc t do: U1, U2, U3 (thng); R1, R2, R3 (Xoay) .

Chiu dng qui c ca cc bc t do tng ng vi 6 thnh phn trong h to tng th.

Bc t do tnh ton: (DOF=Degree of Freedom): S bc tnh ton ca mi nt c th hn ch theo tng loi s ( Analyze - Option Def ).


Bc t do no khng c ti trng, lin kt hay iu kin bin th SAP t ng b qua BTD .

2.4. Ti trng :

Ti trng tnh l ti trng khng thay i theo thi gian : TT bn thn, TT tp trung, phn b, p lc, gi . . .

Ti trng ng : l ti trng c gi tr TT thay i theo thi gian : TT ng t, gi ng, sng bin, TT xe di ng trn cu .

Tr

c gi

a t

c n

n

Trc thi gian t

Hnh 1.10 Mt dng ca TT ph

3. H to

Trong cc s kt cu, khi thit lp m hnh, ngi s dng c th dng mt hoc nhiu h ta khc nhau m t cc tham s sao cho thun tin nht. C th phn h ta trong SAP thnh cc loi nh sau:

3.1. H to chung

C hai loi h ta chung :

H tng th - Global : l duy nht cho mi s kt cu, c chn khi bt u khi xy dng m hnh, c th l h to Decac (vi 3 trc trc giao k hiu X, Y, Z ) hoc h to cu, tr- Cylindrical ( vi 3 trc Z, R, ) .


106

Hnh 1.11 H toa tng th v h ta ring ca nt

Hnh 1.12 Tng quan gia h cc v h ta tr

H ta con - Coordinate System : c th khai bo nhiu h ny trong mt s kt cu. Mi h to con c nhng thuc tnh ring khc nhau v khc vi h global nh li, th vin mu, n v

Khi thit lp cc h to con, s tng quan trong cc tham s khai bo lun so vi h ta tng th. H to Global (chung) thng dng nhp d liu v hin kt qu cho nt, lc nt, lin kt, ti trng tp trung, phn b, phn lc, chuyn v gi ta v chuyn v nt .

3.2. H to ring ( Local Axis)

H ta ring k hiu cc trc l 1, 2, 3 cho cc loi i tng nh nt, phn t, lin kt... (tr phn t Solid khng c h ta ring cho phn t, ch theo h to tng th).

H to ring thng dng nhp d liu cho cc c trng hnh hc phn t, ti trng trn phn t v hin ni lc ca phn t ...

3.3. c im

Trong qu trnh xy dng m hnh, ngi s dng c php chuyn i gia cc h ta (HT), mi thi im ch mt h ta c hin trn cc ca s (cng cc tham s v cc i tng tng ng). . .T SAP2000 V_8 ca s ca cc h ta (hnh 1.13 ) hin gc di bn phi mn hnh, nhn vo chuyn cc HT.

C th sao chp cc h ta v bin i chng trong qu trnh to mi.


4. n v :

Trong mt s phin bn trc ca SAP ( t SAP90 v trc) ngi s dng ch c dng mt h n v duy nht trong sut qu trnh xy dng s kt cu, v mi s liu nh cc gi tru vo, kt qu a ra u ly theo h n v ny. T SAP2000, cho php ngi dng s dng nhiu h n v khc nhau, chn sn t trc khi nhp d liu hoc ngay trong qu trnh nhp (hnh 1.12).

SAP2000 c cc loi n v : Hnh 1.13 Ca s HT & n v

Chiu di : m,cm ,mm, inch, feet . . .

Lc : kgF, KN, T, kip . . .

Nhit : C, F

Trong SAP cho php chuyn i lin tc cc loi n v khc nhau nhp d liu sao cho thun tin v chnh xc nht i vi ngi s dng. V d, c th nhp cc gi tr m un n hi theo kg-cm, trng lng ring v khi lng ring bng T-m trong mt hp thoi, SAP s t chuyn i tng ng gia chng. trnh cc sai st Nn chn n v trc khi bt u thao tc cc qu trnh thit lp s kt cu.

c im ca n v trong SAP :

Cc h n v s c chng trnh t ng qui v mt loi.

Kt qu a ra ch theo mt h n v chung (h khai bo u tin).

chuyn i n v, dng list box trong ca s hin gc di bn phi mn hnh hoc n v nm ngay trong hp thoi.

C th thay i cc h n v lin tc trong qu trnh xy dng s kt cu.

5. Nhng bc chnh khi thc hin phn tch kt cu

5.1. Thit lp s kt cu

xy dng s kt cu cn thc hin cc bc sau:

Xy dng h li hoc chn kt cu t th vin mu

Khai bo vt liu

Khai bo cc c trng hnh hc ( tit din, chiu dy . . . )

V phn t


108

Gn tit din cho phn t

Khai bo lin kt ni t

Khai bo cc trng hp ti trng

Gn ti trng cho phn t cho tng trng hp ti trng :

Ti trng bn thn, TT nt, TT tp trung, phn b, TT phn b khng u . . .

T hp ti trng

Khai bo cc tham s cho thit k

5.2. Phn tch kt cu :

Chn loi kt cu ( dn, khung, v . . . )

Khai bo mt s tham s cn thit ( tham s tnh, in hoc tham s ng )

Thc hin phn tch ( chy chng trnh )

5.3. Xem kt qu

Trn ho

Trn tp vn bn

Xut k qu ra AutoCAD v cc c s d liu khc

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