Graduate Have I solved this iterative equation correctly?

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The discussion revolves around solving an iterative equation for calculating rotations at rigid joints in structural engineering, based on a formula from a 1979 book. The user has implemented the iterative procedure in MATLAB, using initial values derived from a specified formula. They seek confirmation on the correctness of their implementation and calculations. Key parameters include flexural stiffnesses of columns and girders, as well as the horizontal wind shear at each storey. The user expresses frustration over not receiving assistance and wonders if they should have posted in a different section.
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Equation for computing rotations for a rigid frame
Hi all,

I have a structural engineering book from 1979. I am trying to follow it as best as I can. I have come to a formula that calculates the rotations in radians at the rigid joint that requires an iterative procedure. This equation comes in the form of:

$$ x_i = \frac {Qh_i + Qh_{i+1}}{4K} + \frac {C_{i+1}}{K}x_{i+1} + \frac {C_{i-1}}{K}x_{i-1} $$

The book says to use initial values x by using this formula:

$$x_i = \frac {Qh_i + Qh_{i+1}}{24G_i}$$

So, you can compute the rotations for each level and then using the iterative formula to improve the values of the rotations.

Now, I have used MATALB to do this.

Matlab:
x1(1) = (Q*h/4)/(24*G1)
x2(1) = (2*Q*h/4 + Q*h/4)/(24*G1)
x3(1) = (3*Q*h/4 + 2*Q*h/4)/(24*G1)
x4(1) = (4*Q*h/4 + 3*Q*h/4)/(24*G1)
x5(1) = (5*Q*h/4 + 4*Q*h/4)/(24*G1)
x6(1) = (6*Q*h/4 + 5*Q*h/4)/(24*G1)
x7(1) = (7*Q*h/4 + 6*Q*h/4)/(24*G1 + 2*C)
x8(1) = 0

for i = 1:10
     x1(i+1) = Q*h/(4*K) + C/K*x2(i);
     x2(i+1) = (Q*h + 2*Q*h)/(4*K) + C/K*x1(i) + C/K*x3(i);
     x3(i+1) = (2*Q*h + 3*Q*h)/(4*K) + C/K*x2(i) + C/K*x4(i);
     x4(i+1) = (3*Q*h + 4*Q*h)/(4*K) + C/K*x3(i) + C/K*x5(i);
     x5(i+1) = (4*Q*h + 5*Q*h)/(4*K) + C/K*x4(i) + C/K*x6(i);
     x6(i+1) = (5*Q*h + 6*Q*h)/(4*K) + C/K*x5(i) + C/K*x7(i);
     x7(i+1) = (6*Q*h + 7*Q*h)/(4*K) + C/K*x6(i);
     x8(i+1) = 0;
end

My questions is: have I solved this iterative equation correctly?

Note: C and G are the flexural stiffnesses of the columns and girders respectively; that is

$$ C = \frac {I}{h} $$
$$ G = \frac {I}{L} $$

$$K = (6G_i + C_i + C_{i+1})$$

EDIT: Q is the horizontal wind shear at each storey.

To give you a visual insight, here is a rigid frame illustrating the nodal loads and rotations at the joints:

7 Storey Rigid Frame.webp
 
Last edited:
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Sorry, I'm having real trouble with the latex.

EDIT: Latex Sorted
 
Last edited:
Is there not anyone who can help? Should I have posted this in a different section?
 
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