how to correctly get values for stress for Y >82 values should be close to zero at Y = 88.25

p = -100;
y = 0:0.25:88.25;
l = 1:1:199;
ybar = 63.17;
i = 790200.11;
t = 88.25;

[L,Y,P] = meshgrid(l,y,p);

 V = p.*L;
 Q1 = -3.125.*(Y.^2) + 394.81.*Y;
 Q2 = -82.8.*(((Y.^2)/2)-63.17.*Y)-139163.72;
 
if Y >= 82
    stress = abs(V.*Q2)/(i*t);
else
    stress = abs(V.*Q1)/(i*t);
end

contourf(L,Y,stress);

[VBBV]

Where do you use ybar variable in equations of the program ?

Declare p as vector having same size of l and y as

p = -100:1:100;% the size of p must match with size of vectors l and y... shown e.g

[Joel Rebello]

yeah sorry ybar is not used. it can be excluded

[Joel Rebello]

[L,Y,P] = meshgrid(l,y,p) creates a matrix the same size to l and y for p?

[Joel Rebello]

the 1st if condition is not being recongnised for Y >82

[VBBV]

Bcoz you were not using a loop for matrix Y. Use a for loop instead instead to step thru each value of Y as

 % if true
    % code
  %end
for i = 1: length(Y)
  for j = 1: length(Y)
   if Y(i,j) >= 82
     ...
   else 
     ...
   end
end 
end 
contourf(...)

Answer 1

[Asad (Mehrzad) Khoddam]

You can use vectorized if statement:

Q = Q2 .* (Y >= 82) + Q1 .* (Y < 82);
stress = abs(V.*Q)/(i*t);

[Joel Rebello]

Perfect!!! this worked. Thanks Asad

[Asad (Mehrzad) Khoddam]

Great

[VBBV]

The results produced however may not be correct.

Asad logic produces results by adding the stress vector. which may not be correct

See the difference in two results attached. if you use for loop instead

clc; clear all ;
p = -100;
y = 0:0.25:88.25;
l = 1:1:199;
ybar = 63.17;
i = 790200.11;
t = 88.25;

[L,Y,P] = meshgrid(l,y,p);

 V = p.*L;
 Q1 = -3.125.*(Y.^2) + 394.81.*Y;
 Q2 = -82.8.*(((Y.^2)/2)-63.17.*Y)-139163.72;
[R C] = size(Y) 
for i = 1: R
  for j = 1: C
   if Y(i,j) >= 82
     stress(i,j) = abs(V(i,j)*Q2(i,j))/(i*t);
   else 
     stress(i,j) = abs(V(i,j)*Q1(i,j))/(i*t);
   end
end 
end 
contourf(L,Y,stress);

[Joel Rebello]

thanks vasishta, the analysis is with regards to the shear stress on a T-beam, i checked the results from the code you presented and not sure why but the contour does not represent the behaviour of the stress caused by shear (V) acting on the beam. For shear stress the stress is maximum stress should be around the neutral axix (ybar) where Y =63.17, but your results indicate the maximum value is around Y = 5.

Appreciate your help

Answer 2

[KSSV]

You have to use logical indexing to achieve this.

clc; clear all ;
p = -100;
y = 0:0.25:88.25;
l = 1:1:199;
ybar = 63.17;
i = 790200.11;
t = 88.25;

[L,Y,P] = meshgrid(l,y,p);

 V = p.*L;
 Q1 = -3.125.*(Y.^2) + 394.81.*Y;
 Q2 = -82.8.*(((Y.^2)/2)-63.17.*Y)-139163.72;
 stress = zeros(size(L)) ; 
 
 stress(Y>=82) = abs(V(Y>=82).*Q2(Y>=82))/(i*t);
 stress(Y<82) = abs(V(Y<82).*Q2(Y<82))/(i*t);
 

contourf(L,Y,stress);