stresses & forces output for Quad Elements

[farzadreza]

Hi,

I am using Quad Element with PDMY material for utilizing in a SSI problem.

I want to extract the stresses and forces in this element under simple gravity loading.

1- what is the difference between stress recorder for PDMY material vs. stress recorder for Quad Element.(Plane Strain)

2- Asking for Stresses to be recorded for Element of interest, results in 13 columns of data.(the first one is Step(Time) column). so why would this recorder report 12 columns of stresses?

3- the 12 column data seems to be related to 4 gauss points of quad element. but these 4 points are not at the same depth of the element then how come that the values in all 4 points are equal to stresses in mid-depth of element???? the output is like this:

1 -19.5643 -45.65 -1.34096e-015 -19.5643 -45.65 1.91566e-016 -19.5643 -45.65 -7.66266e-015 -19.5643 -45.65 -8.42892e-015

-45.65 is the exact Vertical Stress figure in the "middle" of element of interest by hand calculations.(which is repeated 4 times)
-19.5643 is the exact Horizontal Stress figure corresponding to Vertical stress in the middle of the element of interest by hand calculations.(which is repeated 4 times)

Bearing in mind that the PDMY material with Quad elements has 2 dimensions with "2" translational degrees of freedom, why do we have the third column for each point?(Even though it is virtually zero.)

Also I can not understand the concept of reporting "Stresses" on "Points" !! how is it possible?.(In side sway conditions(like active state of soils), the 12 columns of stress output are totally different from each other)


Next extracting forces from that element it gives 9 columns this time (first column is Step(time) column). so it seems it reports 2 perpendicular forces for each node. it is like this:

1 4.89107 24.9 -4.89107 24.9 -4.89107 -20.75 4.89107 -20.75

Again these figures are the exact amount of forces related to the stresses in the quad which are divided between nodes.

Are these 8 values, again, related to 4 gauss point or 4 nodes of the quad? I mean it exactly reports the calculated "forces" out of stresses in exact depth of each node.

for depth equal to 2 bottom nodes of quad stress is 49.8 KN/m^2 then it multiplies it with area of 1 m^2 of element(Plan view) and reaches 49.8 KN. then divides it between two bottom nodes and reaches 24.9 KN.
for depth equal to 2 top nodes of quad stress is 41.5 KN/m^2 then it multiplies it with area of 1 m^2 of element(Plan view) and reaches 41.5 KN. then divides it between two top nodes and reaches 20.75 KN.

so it seems that these values in force recorder are reported for exact coordinates of quad element's NODES and NOT the Gaussian Points. is that true?

but again for the horizontal forces(4.89107), it calculates the stress at mid-depth of the element(19.6295 KN/m^2) and multiplies it by side area of the element(0.5 m^2) and then divides it between the two node of the element on each side with different(!!) depths and reaches 4.89107 KN.

so why is the concept different when it calculates the horizontal or vertical force in the same recorder?(for vertical forces it uses exact depth of each point but for horizontal forces it uses the mid-depth value of the quad nodes for all 4 nodes.)

Also force recorder does not report third column for each node unlike stress recorder


*********just for the records! this element is a quad element with 1.0*0.5 (length*height)meters dimensions and nominal thickness of 1.0 meter. and the mid-depth of the element is at 2.75 meters from the top.
*********density of soil= 1.66 and Gravity Accel. = 10.0 =====>>> Gamma = 16.6 KN/m^3
*********Poisson ratio is 0.3 as a result ======>>>> K0 (at rest) = 0.428571429

[fmk]

sorry missed this .. did you sort it out .. if not i need to see element and recorder commands