- #1

chandran

- 139

- 1

I have understood the stiffness matrix generation for a single rectangular element as below. I consider each node having 2 translational dofs

each in x and y coord system. There are 4 nodes in this rectangular plate element and hence 8 dofs overall.

K11U1+K12U2+K13U3+K14U4+K15U5+K16U6+K17U7+K18U8= F1

K21U1+K22U2+K23U3+K24U4+K25U5+K26U6+K27U7+K28U8= F2

K31U1+K32U2+K33U3+K34U4+K35U5+K36U6+K37U7+K38U8= F3

K41U1+K42U2+K43U3+K44U4+K45U5+K46U6+K47U7+K48U8= F4

K51U1+K52U2+K53U3+K54U4+K55U5+K56U6+K57U7+K58U8= F5

K61U1+K62U2+K63U3+K64U4+K65U5+K66U6+K67U7+K68U8= F6

K71U1+K72U2+K73U3+K74U4+K75U5+K76U6+K77U7+K78U8= F7

K81U1+K82U2+K83U3+K84U4+K85U5+K86U6+K87U7+K88U8= F8

where K(IJ) is the stiffness influence coefficient saying the force at ith dof due to a unit displacement at jth dof.

U1,U2,U3 ETC is the displacement at ith dof.

F1,F2,F3 ETC is the force at the ith dof.

Now i have a question. In nastran or other fea packages how this K(IJ) is calculated for rectangular elements. I know that for rod element it is

AE/L where A is the rod area,E youngs modulus and

L is the length of the rod. But for solid elements and plane elements how this is calculated.

One more question regarding rod or truss elements. There is a line of 10mm length horizontal to x axis. Why shouldn't i divide the

line into 10 rod or truss elements. What will be the error? Can i divide the line with 10 beam elements?