function y = BeamElementStiffness(EI,GA,L)
%BeamElementStiffness   This function returns the element 
%                       stiffness matrix for a beam   
%                       element with modulus of elasticity E,  
%                       moment of inertia I, and length L.
%                       The size of the element stiffness 
%                       matrix is 4 x 4.
k=6/5;%¾ØÐνØÃ棬ԲÐÎ10/9
kb=EI/L*[0 0 0 0;0 1 0 -1;0 0 0 0;0 -1 0 1];
ks=GA/(4*k*L)*[4 2*L -4 2*L;2*L L^2 -2*L L^2;-4 -2*L 4 -2*L;2*L L^2 -2*L L^2];
y=kb+ks;
% y = EI/(L*L*L)*[12 6*L -12 6*L ; 6*L 4*L*L -6*L 2*L*L ;
%    -12 -6*L 12 -6*L ; 6*L 2*L*L -6*L 4*L*L];