Getting a program to suggest solution from bank of known quantities

Question

Finlay Brierton 2020-1-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/499590-getting-a-program-to-suggest-solution-from-bank-of-known-quantities

Hi,

As you can see from my screenshot and code, I have calculated the Mr (max bending moment) for a steel portal frame of dimensions (w,L,h).

Having calculated this moment I would like the programme to suggest a steel section with a suitable max bending moment resistance. A made a small example list at bottom of my coding, but I will be putting in all the sections and their corresponding bending moment resistance so I can get suggested sections for when I change the frame variables.

How can I get the program to suggest suitable section sizes for the calculated Mr?

Thanks

% program code equivalent to the graphical design method %
% as far as rafter selection %
w = 10; % w is the udl on the fram
L =  30; % L is the span of the frame
h = 6.5; % h is the height to eaves of the frame
theta = 12; % theta is the roof pitch of the frame
N = L/2 + h/tand(theta); % N is the distance from stanchion to base of reactant line where it meets the ground level
syms m
eqn = m^2/(2*w) + m*(5*N/3 - L/3) + w*L^2/8; % the derived equation from the graphical method to find gradient
M = solve(eqn,m); % solving the equation
m1 = max(double(M)); % choosing the smaller negative negative gradient (so smaller number)
Y = -(w/2)*(-m1/w).^2 + w*L^2/8; % the equation for the parabola at max bending moment (at x-bar)
R = -(m1.^2/w) - m1.*N; % the equation for the reactant at max bending moment (at x-bar)
Mr = Y - R; % (KNm) the differce in y values at x-bar gives the max bending moment in the rafter
steel sections: 406x178x67, 406x178x74, 406x178x85 % dimensions of specific steel sections (taken from steel design book)
section moment: 370, 413, 459 % Bending moment resistance for the sections labelled above (taken from steel design book)