patch quad

[Mohammadf]

Hi Dear all
is it important to name four corners of the quadratic shape in patch quad command (ie. i, j, k, l), counter clockwise or not?

best

[AHARSHIAN]

Well, do exactly as it is written in the command manual! It is written COUNTER CLOCKWISE and it is important!

[Mohammadf]

thanks dear

[civil]

does it depends on local axis?
what does it should be in 1 to 4 cases? counter clockwise or clockwise?

1- local y axis: is facing up, local z axis: is to the right
2- local y axis: is facing up, local z axis: is to the left
3- local z axis: is facing up, local y axis: is to the right
4- local z axis: is facing up, local y axis: is to the left

5- how it is determined?

tanks in advance

[fmk]

it's counter clockwise ABOUT THE X-AXIS ... use the right hand rule to figure out the x axis dirn for the 4 cases mentioned above.

[civil]

so in case of 1 & 4 it should be clockwise and in case 2 &3 it should be counterclockwise.
Is it true?

[fbeckwit]

Your cases are redundant and two cases are not even possible because OpenSees employs the right-hand rule to determine local orientation. Consider an element in the 3D case:
The local x direction corresponds to the line connecting the two endpoints of the element;
The local z direction is defined by a vector in the xz-plane;
The local y direction is formed by the cross product of z onto x;

That said, the local axes are determined exactly the same way, so there really isn't a case 1-4. From how you describe it, case 3 is how it is shown on the wiki and case 2 is a rotation of case 3 by 90 degrees (redundant). Cases 1 & 4 are left-hand versions of the previous two which don't exist in OpenSees.

Regardless, the quad section is determined just as mentioned previously, in the counter-clockwise direction about the local x-direction of the element. That said, care should be taken so that you don't orient the section about the wrong axis if it is not doubly symmetric.

[civil]

Thanks
Dear vesna
could you please tell me why it is clockwise in :
http://opensees.berkeley.edu/wiki/index ... ection.tcl
i think it is case 1. is'nt it?

[vesna]

to me this is a counter-clockwise

[civil]

dear vesna
sorry for inconvenience.
could you please tell me the local axes Direction? is local y axis facing up and local z axis to the right?
why is it counter-clockwise?

[vesna]

Irrespective of the direction of Y, as long as y and z follow the right hand rule, IJKL are gonna be in the counter-clockwise direction.