kill(all);

Channel section dimensions:
_h : web heigth, measured at the thin wall midsurface
_b : wing width, measured at the thin midsurface
_t : web and wing wall thickness
(e,f) : Gx,Gy position of the shear center, with respect to the center of gravity
(m,n) : Ox,Oy position of the center of gravity, with respect to the web midpoint
upsilon: _b/_h
epsilon: _t/_h
Chassis dimensions:
a   : half wheelbase
b   : half the distance between the profiles
c   : half the axle track

dim : 
[
    a=1200,
    b=400-m,
    c=600,
    _h=80         * _h_mult,
    upsilon=40/80,
    epsilon=6/80  * _t_mult / _h_mult
],_t_mult=1,_h_mult=1;

mat : 
[
    G  = 210000 / 2 / (1 +3/10),
    E  = 210000,
    nu = 3/10    
];

sec:
[
    A       = 2*epsilon*_h^2*upsilon+epsilon*_h^2,
    Jxx     =(epsilon*_h^4+6*epsilon*_h^4*upsilon)/12,
    Jyy     =(2*epsilon*_h^4*upsilon^3+epsilon*_h^4*upsilon^4)/(6*upsilon+3),
    Jxy     =0,
    Kt      =(epsilon^3*_h^3*(_h+2*_h*upsilon))/3,
    chix    =(15+78*upsilon+138*upsilon^2+96*upsilon^3+24*upsilon^4)/(20*upsilon^4+80*upsilon^3+80*upsilon^2),
    chiy    =(6+72*upsilon+300*upsilon^2+480*upsilon^3+240*upsilon^4)/(180*upsilon^2+60*upsilon+5),
    chixy   =0,
    e       = (4*_h*upsilon^2+12*_h*upsilon^3)/(12*upsilon^2+8*upsilon+1),
    f       = 0  ,
    m       = (_h*upsilon^2)/(2*upsilon+1),
    n       = 0
],dim;