Triangular Plate bending element

[Eigen]

Hi All,

I'm attempting to write my own code of triangular plate element in bending. I'm very familiar with theory of bending both thin and thick.
My first attempt was to formulate triangular element which has area coordinates as shape function for the starting point. Having those in hand
my triangular element is always stiffer than any other FEM element.

I started the implementation from FEM book which gave instruction for THT element – Henschel, Tocher, 1969.
The following images are respectively, strain-matrix for bending, stiffness matrix Ke for bending, strain matrix for transverse shear , stiffness matrix for transverse shear
http://i47.tinypic.com/1enkad.jpg // Strain matrix for bending part.
http://i48.tinypic.com/2s1x7wi.jpg // Stiffness matrix for bending part
http://i46.tinypic.com/30a9zyp.jpg // strain matrix for transverse shear
http://i50.tinypic.com/1tuett.jpg // stiffness matrix for transverse shear

Having the overstiff element has made think that I'm facing the shear-lock pehenomenon, but even increasing the thickness doesn't remedy the situation this time I'm suffering that element is over elastic. It's for sure that element shows the soem erratical behaviour, but I couldn't spot whether it's due to my mistyping in the code or instabillity of the THT element – Henschel, Tocher element.

Your help will be appreciated,

[Eigen]

I know it's not directly related with OpenSees, but at least is related with FEM in theory and I know that it's always boresome thing to spot what the someone has done errenously.

At least does anyone can shed the light on whether the THT element ( Henschel, Tocher, 1969) is reliable and widely accepted in the scientific world. Or the uploaded images reflects the correct stiffness matrix? Googling doesn't retrieve so much info about it.

My main puprose is to derive the triangular plate in bending and later on addopt the plate on elastic foundation implementation.

Your help will be appreciated.

[Eigen]

Any comment on that,