Have I solved this iterative equation correctly?

  • Context: Graduate 
  • Thread starter Thread starter Tygra
  • Start date Start date
Click For Summary
SUMMARY

The forum discussion centers on solving an iterative equation for calculating rotations at rigid joints in structural engineering, specifically using MATLAB. The iterative formula provided is based on a structural engineering book from 1979, which outlines the calculation of rotations using initial values derived from a specific formula. The user has implemented the iterative procedure in MATLAB, iterating through the calculations for multiple levels, and seeks validation of their approach.

PREREQUISITES
  • Understanding of structural engineering principles, specifically related to rigid joints.
  • Proficiency in MATLAB programming for numerical computations.
  • Familiarity with iterative methods and convergence criteria.
  • Knowledge of flexural stiffness calculations for columns and girders.
NEXT STEPS
  • Review MATLAB's numerical methods for solving iterative equations.
  • Study the principles of structural dynamics and load distribution in rigid frames.
  • Explore advanced topics in finite element analysis for structural engineering.
  • Investigate the impact of varying flexural stiffness on joint rotations in structural models.
USEFUL FOR

Structural engineers, civil engineering students, and MATLAB users focused on iterative calculations in structural analysis will benefit from this discussion.

Tygra
Messages
55
Reaction score
8
TL;DR
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:
Physics news on Phys.org
Sorry, I'm having real trouble with the latex.

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

Similar threads

  • · Replies 1 ·
Replies
1
Views
903
  • · Replies 0 ·
Replies
0
Views
937
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 0 ·
Replies
0
Views
1K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 21 ·
Replies
21
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
643
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K