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Page 2 The joint and member numbers are indicated in Fig. 25.2b. The possible degree of freedom are also shown in Fig. 25.2b. In the given problem 2 1 ,u u and 3 u represent unconstrained degrees of freedom and 0 8 7 6 5 4 = = = = = u u u u u due to boundary condition. First let us generate stiffness matrix for each of the six members in global co-ordinate system. Element 1: . 00 . 5 , 0 m L = ° = ? Nodal points 2-1 [] 2 1 4 3 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 2 1 4 3 1 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (1) Element 2: . 00 . 5 , 90 m L = ° = ? Nodal points 4-1 Page 3 The joint and member numbers are indicated in Fig. 25.2b. The possible degree of freedom are also shown in Fig. 25.2b. In the given problem 2 1 ,u u and 3 u represent unconstrained degrees of freedom and 0 8 7 6 5 4 = = = = = u u u u u due to boundary condition. First let us generate stiffness matrix for each of the six members in global co-ordinate system. Element 1: . 00 . 5 , 0 m L = ° = ? Nodal points 2-1 [] 2 1 4 3 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 2 1 4 3 1 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (1) Element 2: . 00 . 5 , 90 m L = ° = ? Nodal points 4-1 [] 2 1 8 7 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 2 1 8 7 2 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (2) Element 3: . 00 . 5 , 0 m L = ° = ? Nodal points 3-4 [] 8 7 6 5 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 8 7 6 5 3 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (3) Element 4: . 00 . 5 , 90 m L = ° = ? Nodal points 3-2 [] 4 3 6 5 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 4 3 6 5 4 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (4) Element 5: . 07 . 7 , 45 m L = ° = ? Nodal points 3-1 [] 2 1 6 5 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 07 . 7 2 1 6 5 5 ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - = EA k (5) Element 6: . 07 . 7 , 135 m L = ° = ? Nodal points 4-2 Page 4 The joint and member numbers are indicated in Fig. 25.2b. The possible degree of freedom are also shown in Fig. 25.2b. In the given problem 2 1 ,u u and 3 u represent unconstrained degrees of freedom and 0 8 7 6 5 4 = = = = = u u u u u due to boundary condition. First let us generate stiffness matrix for each of the six members in global co-ordinate system. Element 1: . 00 . 5 , 0 m L = ° = ? Nodal points 2-1 [] 2 1 4 3 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 2 1 4 3 1 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (1) Element 2: . 00 . 5 , 90 m L = ° = ? Nodal points 4-1 [] 2 1 8 7 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 2 1 8 7 2 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (2) Element 3: . 00 . 5 , 0 m L = ° = ? Nodal points 3-4 [] 8 7 6 5 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 8 7 6 5 3 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (3) Element 4: . 00 . 5 , 90 m L = ° = ? Nodal points 3-2 [] 4 3 6 5 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 4 3 6 5 4 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (4) Element 5: . 07 . 7 , 45 m L = ° = ? Nodal points 3-1 [] 2 1 6 5 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 07 . 7 2 1 6 5 5 ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - = EA k (5) Element 6: . 07 . 7 , 135 m L = ° = ? Nodal points 4-2 [] 4 3 8 7 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 07 . 7 4 3 8 7 6 ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - = EA k (6) There are eight possible global degrees of freedom for the truss shown in the figure. Hence the global stiffness matrix is of the order ( 8 8 × ). On the member stiffness matrix, the corresponding global degrees of freedom are indicated to facilitate assembly. Thus the global stiffness matrix is, [] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - - - - - - - - - - - - - - - - - = 271 . 0 071 . 0 0 0 071 . 0 071 . 0 20 . 0 0 071 . 0 271 . 0 0 20 . 0 071 . 0 071 . 0 0 0 0 0 271 . 0 071 . 0 20 . 0 0 071 . 0 071 . 0 0 20 . 0 071 . 0 271 . 0 0 0 071 . 0 071 . 0 071 . 0 071 . 0 20 . 0 071 . 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 0 071 . 0 271 . 0 0 20 . 0 20 . 0 0 071 . 0 071 . 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 2 . 0 071 . 0 271 . 0 AE K (7) The force-displacement relation for the truss is, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - - - - - - - - - - - - - - - - - = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 271 . 0 071 . 0 0 0 071 . 0 071 . 0 20 . 0 0 071 . 0 271 . 0 0 20 . 0 071 . 0 071 . 0 0 0 0 0 271 . 0 071 . 0 20 . 0 0 071 . 0 071 . 0 0 20 . 0 071 . 0 271 . 0 0 0 071 . 0 071 . 0 071 . 0 071 . 0 20 . 0 071 . 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 0 071 . 0 271 . 0 0 20 . 0 20 . 0 0 071 . 0 071 . 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 2 . 0 071 . 0 271 . 0 u u u u u u u u EA p p p p p p p p (8) The displacements 2 1 ,u u and 3 u are unknowns. Here, 12 3 5kN ; 10 ; 0 pp p ==- = and 0 8 7 6 5 4 = = = = = u u u u u . Page 5 The joint and member numbers are indicated in Fig. 25.2b. The possible degree of freedom are also shown in Fig. 25.2b. In the given problem 2 1 ,u u and 3 u represent unconstrained degrees of freedom and 0 8 7 6 5 4 = = = = = u u u u u due to boundary condition. First let us generate stiffness matrix for each of the six members in global co-ordinate system. Element 1: . 00 . 5 , 0 m L = ° = ? Nodal points 2-1 [] 2 1 4 3 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 2 1 4 3 1 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (1) Element 2: . 00 . 5 , 90 m L = ° = ? Nodal points 4-1 [] 2 1 8 7 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 2 1 8 7 2 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (2) Element 3: . 00 . 5 , 0 m L = ° = ? Nodal points 3-4 [] 8 7 6 5 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 0 . 5 8 7 6 5 3 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (3) Element 4: . 00 . 5 , 90 m L = ° = ? Nodal points 3-2 [] 4 3 6 5 1 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 . 5 4 3 6 5 4 ? ? ? ? ? ? ? ? ? ? ? ? - - = EA k (4) Element 5: . 07 . 7 , 45 m L = ° = ? Nodal points 3-1 [] 2 1 6 5 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 07 . 7 2 1 6 5 5 ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - = EA k (5) Element 6: . 07 . 7 , 135 m L = ° = ? Nodal points 4-2 [] 4 3 8 7 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 07 . 7 4 3 8 7 6 ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - = EA k (6) There are eight possible global degrees of freedom for the truss shown in the figure. Hence the global stiffness matrix is of the order ( 8 8 × ). On the member stiffness matrix, the corresponding global degrees of freedom are indicated to facilitate assembly. Thus the global stiffness matrix is, [] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - - - - - - - - - - - - - - - - - = 271 . 0 071 . 0 0 0 071 . 0 071 . 0 20 . 0 0 071 . 0 271 . 0 0 20 . 0 071 . 0 071 . 0 0 0 0 0 271 . 0 071 . 0 20 . 0 0 071 . 0 071 . 0 0 20 . 0 071 . 0 271 . 0 0 0 071 . 0 071 . 0 071 . 0 071 . 0 20 . 0 071 . 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 0 071 . 0 271 . 0 0 20 . 0 20 . 0 0 071 . 0 071 . 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 2 . 0 071 . 0 271 . 0 AE K (7) The force-displacement relation for the truss is, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - - - - - - - - - - - - - - - - - = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 271 . 0 071 . 0 0 0 071 . 0 071 . 0 20 . 0 0 071 . 0 271 . 0 0 20 . 0 071 . 0 071 . 0 0 0 0 0 271 . 0 071 . 0 20 . 0 0 071 . 0 071 . 0 0 20 . 0 071 . 0 271 . 0 0 0 071 . 0 071 . 0 071 . 0 071 . 0 20 . 0 071 . 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 0 071 . 0 271 . 0 0 20 . 0 20 . 0 0 071 . 0 071 . 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 2 . 0 071 . 0 271 . 0 u u u u u u u u EA p p p p p p p p (8) The displacements 2 1 ,u u and 3 u are unknowns. Here, 12 3 5kN ; 10 ; 0 pp p ==- = and 0 8 7 6 5 4 = = = = = u u u u u . ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - - - - - - - - - - - - - - - - - - = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - 0 0 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 20 . 0 0 071 . 0 271 . 0 0 20 . 0 071 . 0 071 . 0 0 0 0 0 271 . 0 071 . 0 20 . 0 0 071 . 0 071 . 0 0 20 . 0 071 . 0 271 . 0 0 0 071 . 0 071 . 0 071 . 0 071 . 0 20 . 0 071 . 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 0 071 . 0 271 . 0 0 20 . 0 20 . 0 0 071 . 0 071 . 0 0 0 271 . 0 071 . 0 0 0 071 . 0 071 . 0 0 2 . 0 071 . 0 271 . 0 0 10 5 3 2 1 8 7 6 5 4 u u u EA p p p p p (9) Thus, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - = ? ? ? ? ? ? ? ? ? ? - 3 2 1 271 . 0 0 20 . 0 0 271 . 0 071 . 0 20 . 0 071 . 0 271 . 0 0 10 5 u u u (10) Solving which, yields AE u AE u AE u 825 . 53 ; 97 . 55 ; 855 . 72 3 2 1 = - = = Now reactions are evaluated from the equation, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? - - - - - - - = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 3 2 1 8 7 6 5 4 071 . 0 20 . 0 0 071 . 0 0 0 0 071 . 0 071 . 0 0 071 . 0 071 . 0 071 . 0 0 0 u u u p p p p p (11) 45 6 7 8 3.80 kN ; 1.19 kN ; 1.19 kN ; 3.8 0 ; 15.00 kN pp p p kNp =- =- =- = = In the next step evaluate forces in members. Element 1: . 00 . 5 , 0 m L = ° = ? Nodal points 2-1Read More
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1. What is the direct stiffness method in truss analysis? |
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