beam_nst

(./beam_nst.m)

Function Synopsis

[n,s,t] = beam_nst(Pi,Pj,beta);

Help text

function [n,s,t] = beam_nst(Pi,Pj,beta);
%---Computes vectors n, s, and t for a beam element
%      based on its end points and a specified rotation of
%      the strong axis from the up direction (assumed to
%      be y) or north (for columns; assumed to be x)

Cross-Reference Information

beam_k         ./beam_k.m
plot_truss     ./plot_truss.m

Listing of function ./beam_nst.m

function [n,s,t] = beam_nst(Pi,Pj,beta);
%function [n,s,t] = beam_nst(Pi,Pj,beta);
%%---Computes vectors n, s, and t for a beam element
%%      based on its end points and a specified rotation of
%%      the strong axis from the up direction (assumed to
%%      be y) or north (for columns; assumed to be x)

%%---Could be global
up = [0;0;1];
north = [0;1;0];

%%---Get n from the end points
n = (Pj - Pi)/norm(Pj-Pi);

%%---Get a candidate t:
t = cross(n,up);

%--- Is it a column or a beam?
if  norm(t) == 0
    %---it's a column
    s = [cos(beta);0;sin(beta)];
    t = cross(n,s);
else
    %%--it's a beam
    s_temp = cross(t,n);
    %%--now account for beta
    s = cross(n,s_temp)*sin(beta)-cross(n,t)*cos(beta);
    t = cross(n,s_temp)*cos(beta)+cross(n,t)*sin(beta);
end  %--endif

n = column(n);
s = column(s/norm(s));
t = column(t/norm(t));