# illogical graph values when plotting shear diagram

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Ali Ramadan il 29 Mar 2020
Commentato: Image Analyst il 29 Mar 2020
I am trying to solve the following problem where i need to plot the shear diagram but in deed when ever i try to plot my graph it comes with illogical values
i am forced to use the function calc with no change to it (thats the only condition ) i can only change my script and in what context do i call my function
am getting the following graph
My script :
clc;
clear all;
w=2;
EI=1e6;
L=10;
x=linspace(0,L,1000)
a1=1;
an=4;
UDL=an-a1;
a=linspace(a1,an,1000);
dis=linspace(1,L,1000);
for i=1:length(a)
res=calc(dis(i),L,[w a(i)],EI);
v(i)=res(1);
m(i)=res(2);
y(i)=res(3);
end
plot(x,v);
the function calc :(should not change anyhting in it)
function [ res ] = calc( x,L,Load,EI )
%it is used to find the shear moment and deflection
%for a simply supported beam in 2 cases
res(1) = P*L/2-P*x;
res(2) = P*L/2*x-P*x ^2/2;
res(3) = -P*x/(24*EI)*(L^3-2*L*x^2+x^3);
b=L-a;R1=F*b/L;R2=F*a/L;
if x <= a
res(1) = R1;
res(2) = R1*x;
res(3) = -F*b*x/(6*L*EI)*(L^2-x^2-b^2);
else
res(1) = -R2;
res(2) = R1*x -F*(x-a);
res(3) = -F*b/(6*L*EI)*(L/b*(x-a)^3+(L^2-b^2)*x-x^3);
end
else
res=[];
end
end
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### Risposte (1)

Image Analyst il 29 Mar 2020
Your x is just a single value, not a list of every x location for each v location. But you can leave it out and just plot x as the index number:
plot(v, 'b-');
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Ali Ramadan il 29 Mar 2020
i updated it the code and inserted the graph that am getting but in deeed its illogical , the shear diagram should be a staright line then a decrease of y=ax+b form then continue as a straight line and it should decrease by 2 overall , which is not happening any ideas?
Image Analyst il 29 Mar 2020
It IS a line, followed by a decrease/drop of about 2, then another line. At around x = 1.2, the y goes from about 1.75 to -0.25, which is a drop of 2. I have no idea about the physics of that program - it just looks like an uncommented, alphabet soup to me. You maybe can take it up with your professor.

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