kill(all);

Channel section dimensions:
h : web heigth, measured at midsurface
b : wing width, mesured at midsurface
t : web and wing wall thickness
(e,f) : xi,eta position of the shear center, with respect to the center of gravity
(m,n) : xi,eta 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
];

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

sec:
[
    A        = 2*epsilon*h^2*upsilon+epsilon*h^2,
    J_xixi   =(epsilon*h^4+6*epsilon*h^4*upsilon)/12,
    J_etaeta =(2*epsilon*h^4*upsilon^3+epsilon*h^4*upsilon^4)/(6*upsilon+3),
    J_xieta  =0,
    Kt       =(epsilon^3*h^3*(h+2*h*upsilon))/3,
    chi_xi   =(15+78*upsilon+138*upsilon^2+96*upsilon^3+24*upsilon^4)/(20*upsilon^4+80*upsilon^3+80*upsilon^2),
    chi_eta  =(6+72*upsilon+300*upsilon^2+480*upsilon^3+240*upsilon^4)/(180*upsilon^2+60*upsilon+5),
    chi_xieta=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
];