Ejercicio Resuelto Analisis Estructural Parrillas

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EJERCICIO N° 1

Resuelva completamente la parrilla mostrada, por el método matricial de los desplazamientos:

GJ= 1200 TN-m² EI= 1500 TN-m²

Solución: 1) Se empieza numerando las barras, los nudos y orientando los elementos:

2) Calculamos [k’] las propiedades

BARRA 1 GJ 1200 = =400 L 3 2 EI 2(1500) = =1000 L 3 4 EI 4(1500) = =2000 L 3 6 EI 6(1500) = =1000 L² 3² 12 EI 12(1500) = =666.67 Lᶟ 3ᶟ

BARRA 2 GJ 1200 = =240 L 5 2 EI 2(1500) = =600 L 5 4 EI 4(1500) = =1200 L 5 6 EI 6(1500) = =360 L² 5² 12 EI 12(1500) = =144 Lᶟ 5ᶟ BARRA 3 GJ 1200 = =400 L 3 2 EI 2(1500) = =1000 L 3 4 EI 4(1500) = =2000 L 3 6 EI 6(1500) = =1000 L² 3² 12 EI 12(1500) = =666.67 Lᶟ 3ᶟ

Elaboramos el cuadro de resumen (kN y m) BARRA

L

GJ/L

2EI/L

4EI/L

6EI/L²

12EI/L³

1 2 3

3 5 3

400 240 400

1000 600 1000

2000 1200 2000

1000 360 1000

666.67 144 666.67

3) Hallamos [K] = [B] ⸆. [k’]. [B] BARRA 1

∝ 0

C 1

S 0

[ ]

1 0 0 [R ]= 0 1 0 0 0 1

BARRA 2 ∝ 90

C 0

[

S 1

0 −1 0 [R ]= −1 0 0 0 0 1

BARRA 3

]

∝ 180

C 1

S 0

[

−1 0 0 [R ]= 0 −1 0 0 0 1

]

4) Calculamos [k ' ] de cada barra BARRA 1

[ k ' ]1=¿

[

400 0 0 666 . 67 0 1000 −400 0 0 −666 . 67 0 −1000

0 −400 0 1000 0 −666 .67 2000 0 −1000 0 400 0 −1000 0 666 .67 1000 0 −1000

0 −1000 1000 0 −1000 2000

BARRA 2

[ k ' ]2=¿

BARRA 3

[

240 0 0 −240 0 0

0 144 360 0 −144 −360

0 −240 0 0 360 0 −144 −360 1200 0 −360 600 0 240 0 0 −360 0 144 −360 600 0 −360 1200

]

]

[ k ' ]3=¿

5) Hallamos

[

400 0 0 666 . 67 0 1000 −400 0 0 −666 . 67 0 −1000

[

[B]= [R] [0] [0] [R]

0 −400 0 1000 0 −666 .67 2000 0 −1000 0 400 0 −1000 0 666 .67 1000 0 −1000

]

BARRA 1

[ B ] =¿

BARRA 2

[ B ] =¿

BARRA 3

[ ] 1 0 0 0 0 0

0 1 0 0 0 0

0 0 1 0 0 0

0 0 0 1 0 0

0 0 0 0 1 0

0 0 0 0 0 1

[ ] 0 −1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 −1 0 0 0 0 1 0 0 0 0 0 0 0 1

0 −1000 1000 0 −1000 2000

]

[ B ] =¿

[

−1 0 0 0 0 0 0 −1 0 0 0 0 0 0 1 0 0 0 0 0 0 −1 0 0 0 0 0 0 −1 0 0 0 0 0 0 1

]

6) Hallamos [ k ] BARRA 1

T

[ k ] 1=[ B ] 1∗[ k ' ]1∗[ B ]1=¿

[

400 0 0 −400 0 0 666 . 67 1000 0 −666 .67 0 1000 2000 0 −1000 −400 0 0 400 0 0 −666 .67 −1000 0 666 .67 0 −1000 1000 0 −1000

0 −1000 1000 0 −1000 2000

BARRA 2

[ k ] 2=[ B ] T2∗[ k ' ]2∗[ B ]2=¿

[

144 0 0 240 360 0 −144 0 0 −240 −360 0

360 0 1200 −360 0 600

−144 0 −360 0 −240 0 −360 0 600 144 0 −360 0 240 0 −360 0 1200

]

]

BARRA 3

[

T

[ k ] 3=[ B ] 3∗[ k ' ] 3∗[ B ]3 =¿

400 0 0 666 . 67 0 −1000 −400 0 0 −666 . 67 0 1000

0 −400 0 −1000 0 −666 .67 2000 00 1000 0 400 0 1000 0 666 .67 1000 0 1000

0 1000 1000 0 1000 2000

7) Hallamos [ K ]

{ Q }=[ K ] { D }

{ } [ ]{ } {Q1 } {Q2 } = {Q3 } {Q4 }

¿ ¿ ¿ ¿

¿ ¿ ¿ ¿

{ D1 } { D2 } { D3 } {D 4 }

[ K ¿ ] =[ K 11 ]1+ [ K 11 ] 2+ [ K 11 ] 3

[ K ¿ ] =¿

[

][

][

400 0 0 144 0 360 400 0 0 + + 0 666 .67 1000 0 240 0 0 666 .67 −1000 0 1000 2000 360 0 1200 0 −1000 2000

[ K ¿ ] =¿

[

944 0 360 0 1573 .34 0 360 0 5200

]

]

]

8) Ensamblaje del vector de cargas de fijación

{Q} = {ℝ} + {F} BARRA 1: Mº Y 12=

−120∗1.72∗1.3 =−50.09 9

120∗1.32∗1.7 Mº Y 21= =38.31 9 Z º 12=

120∗1.7+50.09−38.31 =71.93 3

Zº 21=

120∗1.3−50.09+38.31 =48.07 3

Mº X 12=Mº X 21=0

BARRA 2: Mº X 13=−Mº X 31= Zº 13=Zº 31=

−32∗25 =−66.67 12

32∗5 =80 2

Mº Y 13=Mº Y 31=0

BARRA 3: Mº Y 41=Mº Y 14=0 Zº 41=Zº 14=0 Mº X 41=Mº X 14 =0

9) Cálculo de [ r ' ] BARRA 1:

de cada barra:

{ }

0 −50.09 {r ' 1 } 71.93 [ r ' ] 1= = {r ' 2 } 0 38.31 48.07

{ }

BARRA 2:

{ }

−66.67 0 {r ' 1 } 80 [ r ' ] 2= = {r ' 3 } 66.67 0 80

{ }

En la Barra 2 no coinciden los sistemas de coordenadas, por lo tanto: {r }2=[B]{r ' }2

{ }[

]{ }

{r ' 1 } {r 1 } = [R] [0] {r ' 3 } [0] [ R] {r 3 }

∝=90 º Falta ¿

[ ]{ }

1 0 [ r ] 1= 0 0 1 0

0 0 0 0 −50.09 1 0 ¯ 50.09 0 1 71.93 = 71.93 = {r 1 } 0 {r 2 } ¯1 0 0 38.31 0 0 38.31 48.07 0 1 48.07

{ }

[ ]{ }{ }

1 0 [ r ] 2= 0 ¯1 0 0

0 0 −66.67 −66.67 0 0 −50.09 1 0 0 80 71.93 0 1 80 = = −66.67 −38.31 0 0 66.67 0 0 ¯1 0 0 80 48.07 0 1 80

10) Ensamblamos [R ]

{ }{

R1 {r 1 }1+{r 1 }2 +{r 1 }3 R {r }1 { R }= 2 = R3 {r }2 R4 {r }3

{ R }=

}

{ }{ } { }{ { { {

}{} { } { } { } {

0 −66.67 0 + + 0 −50.09 0 71.93 80 0

−66.67 −50.09 151.93

0 −50.09 71.93

0 −50.09 71.93

−66.67 0 80 −66.67 0 80

=

−66.67 0 80 −66.67 0 80

} } } }

Como {F}, entonces: { ℝ } = {R} - {F}

{} { { { {

−66.67 −50.09 151.93

{ R }={ R }−{F }=

0 −50.09 71.93 −66.67 0 80 −66.67 0 80

11) Hallamos

} } } }

{ }

{Q1 } {Q2 } {Q }= {Q3 } {Q4 }

{} { { { {

} } } }

66.67 50.09 −151.93

{ Q }=−{R }=

0 50.09 −71.93 66.67 0 −80 66.67 0 −80

12) De los valores anteriores tomo : {Q L } {Q L }=[ K ¿ ] +{D L }

Para el problema: {Q1 }=[ K 11 ] +{D1 }

{ } { } {} { } D1 x 66.67 50.09 =[ K 11 ] D1 y −151.93 θ

D1 x 66.67 −1 D 1 y =[ K 11 ] 50.09 −151.93 θ

{ } { } } { }{ D1 x 66.67 −1 D 1 y =❑ 50.09 −151.93 θ

D1 x 0.08398 m. = D1 y 0.03184 m. −0.03503 rad . θ

13) Cálculo de fuerzas de extremo de barras: BARRA 1: {d }=

{ }{ } d1 d2

{ D1 } { D2 }

Hallamos {d } :

{ q ' } =[ k ' ] +{d ' } {d ' }1=[ B ] ⸆ 1 +{d }1

]{ }

[

{d 1 }1 {d ' }1= [R ]⸆ [0 ] [0 ] [R] ⸆ {d 2 }1

[ ]{

1 0 0 0.08398 ' {d 1 }= 0 1 0 0.03184 0 0 1 −0.03503

{

0.08398 ' {d 1 }= 0.03184 −0.03503

}

}

BARRA 2: {d ' }2=[ B ] ⸆ 2 +{d }2

[

]{ }

{d 1 }2 {d ' }2= [R ]⸆ [0 ] [0 ] [R] ⸆ {d 3 }2

[

]{

{

}

0 1 0 0.08398 ' {d 2 }= −1 0 0 0.03184 0 0 1 −0.03503 0.03184 {d ' 1 }= −0.08398 −0.03503

}

BARRA 3: {d ' }3=[ B ] ⸆3 +{d }3

[

]{ }

[

]{

{d 1 }3 {d ' }3= [R ]⸆ [0 ] [0] [R ]⸆ {d 4 }3

−1 0 0 0.08398 {d ' 2 }= 0 −1 0 0.03184 0 0 −1 −0.03503

{

−0.08398 {d ' 1 }= −0.03184 −0.03503

}

}

14) Empleamos: {q ' }n =[ k ' ] n+ {d ' }n

n = 1, 2, 3

BARRA 1:

{ }[

q '1 [ k ' 11 ] [k ' 12] = q ' 2 1 [ k ' 21 ] [k ' 22]

{q ' 1 }1=[ k ' 11 ]1 {d' 1 }1

]{ } 1

d '1 d '2

1

[

400 0 0 {q ' 1 }1= 0 666.67 1000 0 1000 2000

]{ 1

}{ }

0.08398 33.592 = 0.03184 −13.803 −0.03503 1 −38.22

1

{q ' 2 }1=[ k ' 21 ]1 {d ' 1 }1

[

{q ' 2 }1=

−400 0 0 0 −666.67 −1000 0 −1000 1000

]{ 1

}{ }

0.08398 −33.592 = 0.03184 13.803 −0.03503 1 −38.22

BARRA 2:

{ }[

]{ }

q '1 [ k ' 11 ] [k ' 12 ] d ' 1 = q ' 3 2 [ k ' 21 ] [k ' 22 ] 2 d ' 3

2

{q ' 1 }2=[ k ' 11 ]2 {d' 1 }2

[

240 0 0 ' {q 1 }2= 0 144 360 0 360 1200

]{ 2

}{

0.03184 7.6416 = −0.08398 −24.70392 −0.03503 2 −72.2688

}

2

{q ' 3 }2=[ k '21 ]2 {d ' 1 }2

{q ' 3 }2=

[

−240 0 0 0 −144 −360 0 −360 600

]{ 2

0.03184 −7.6416 = −0.08398 24.70392 −0.03503 2 9.2148

}{

}

}{

}

3

2

BARRA 3:

{ }[

q '1 [k ' 11 ] [k ' 12 ] = q ' 4 3 [k ' 21] [k ' 22 ]

]{ } 3

d'1 d'4

3

{q ' 1 }3=[ k '11 ]3 {d '1 }3

[

400 0 0 {q ' 1 }3= 0 666.67 1000 0 1000 2000

]{ 3

−0.08398 −33.592 = −0.03184 −56.2568 −0.03503 3 −101.9

1

{q ' 2 }1=[ k ' 21 ]1 {d ' 1 }1

[

−400 0 0 {q 4 }3 = 0 −666.67 −1000 0 −1000 1000 '

]{ 3

}{ }

0.08398 33.592 0.03184 = 56.2568 −0.03503 3 3.19

GRAFICAS 

DIAGRAMA DE CORTANTE



DIAGRAMA DE MOMENTO FLECTOR

3



DIAGRAMA DE TORSION

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