Optimisation problem not solving for maximum values

I have made the code shown below to find the maximum d/t and kl/r values possible within specific constraints given. I would expect that d would close to 1000 and t close to 35. However in the solution it is giving is d=2 and t=1. Any ideas how I can fix this? When giving these values it is also throwing up the message :

Solving problem using ga.

Optimization terminated: average change in the penalty fitness value less than options.FunctionTolerance

but constraints are not satisfied.

Any help would be greatly apreciated thank you.

%% Clear workspace
clear;
clc;

%% Input Variables
l=14830; % Member length (mm)
k=1;     % Effective length factor

d0.d=1000; %initial guess
d0.t=30;   %initial guess
%% Equations
prob = optimproblem('ObjectiveSense','maximize');

d = optimvar('d', 1,'Type','integer');
t = optimvar('t',1,'Type','integer');
%% Variables
din=d-(2*t);                   % Member inner diameter
a=3.1415/4 * ((d^2)-(din^2));  % Member cross sectional area
i=3.1415/64 * ((d^4)-(din^4)); % Member second moment of inertia
r=(a/i)^0.5;                   % Member radius of gyration

prob.Objective= (d/t) + ((k*l)/r);

%% Constraints
cons1 = d>=1;
cons2 = d<=3000;
cons3 = t>=1;
cons4 = t<=100;
cons5 = d/t<=30;
cons6 = d/t>=1;
cons7 = k*l/r<=40;
cons8 = k*l/r>=1;

prob.Constraints.cons1 = cons1;
prob.Constraints.cons2 = cons2;
prob.Constraints.cons3 = cons3;
prob.Constraints.cons4 = cons4;
prob.Constraints.cons5 = cons5;
prob.Constraints.cons6 = cons6;
prob.Constraints.cons7 = cons7;
prob.Constraints.cons8 = cons8;

show(prob)

sol = solve(prob,d0)

sol.d
sol.t

Answer 1

[Matt J]

We can easily do a discrete sweep over the allowable d and t values to see where the feasible region is, approximately. Based on the sweep below, it does not appear that there are any feasible (d,t) pairs.

l=14830; % Member length (mm)
k=1;     % Effective length factor

[d,t]=meshgrid(1:0.5:3000,1:0.5:100);

din=d-(2*t);                   % Member inner diameter
a=3.1415/4 * ((d.^2)-(din.^2));  % Member cross sectional area
i=3.1415/64 * ((d.^4)-(din.^4)); % Member second moment of inertia
r=(a./i).^0.5;                   % Member radius of gyration

feas=true(size(d)); %feasibility map

 expr=d./t;

feas( expr>30 | expr<1 | ~isfinite(expr) )=false;

 expr=k*l./r;

feas( expr>40 | expr<1 | ~isfinite(expr) )=false;

[d,t]=find(feas)  %search for feasible d,t

d =

  0×1 empty double column vector


t =

  0×1 empty double column vector

[Maximilian]

Right ok thank you for your help. You are completely right. I have just found the mistake and it is in one of my variables. Sorry to have wasted your time. I really appreciate the help.