professor ben schafer's thin-walled structures research group - johns hopkins university

Global Buckling Analysis of Thin-walled Members

The global buckling analysis (flexural-torsional, lateral-torsional, etc) of thin-walled members can be an involved task. CUTWP provides the thin-walled cross-section properties necessary in such analysis and provides classic stability solutions as well. After all Pcr2 = ((Pe1+Pe3)-sqrt((Pe1+Pe3)^2-4*B*Pe1*Pe3))/(2*B); is not a calculation you want to do by hand every day. The December 2006 release of CUTWP has provided corrections to b1 and b2 which are used in lateral-torsional buckling calculations and CUTWP has been modified to read CUFSM input files

Introduction

Global buckling, such as flexural-torsional buckling in columns or lateral-torsional buckling in beams can sometimes be an involved calculation for the engineer. First, the section properties can be onerous to calculate, and second, the elastic stability itself requires the solution of a cubic equation. For thin-walled members the preceding is all the more true, as the unsymmetric nature of many sections requires that the more complicated global buckling modes such as flexural-torsional buckling always be considered. Andrew Sarawit wrote a small piece of code along with an interface for making these section property calculations and global buckling calculations, and this code is made available in open source form for your use here. The program CUTWP was written in Matlab, and includes a full graphical interface.

What does the CUTWP interface look like?

CUTWP uses a single page interface, and reports the section properties as well as the buckling mode shapes for the three global modes of the cross-section. A screen shot of CUTWP in action is given below. CUTWP has been modified to read CUFSM input files.

What is the difference between CUTWP and CUFSM?

CUTWP only calculates global buckling properties. The classical formulas that you find in Timoshenko's Theory of Elastic Stability (or more correctly the work of Pekoz from the late 1960's) are used for generating the solution. CUFSM can calculate local, and distortional buckling modes in addition to global buckling. CUFSM is closer to a general purpose finite element type of software, as opposed to CUTWP which is closer to analytical solutions, i.e., calculate section properties and then solve the standard beam theory differential equations. As of version 3.0 of CUFSM, the reported section properties in CUFSM use the same base code as CUTWP.

Can CUTWP and CUFSM work together?

CUTWP was modified in November of 2005 to be able to read CUFSM files as input. This allows a CUFSM user to perform traditional global buckling solutions without recourse to hand formulas. In particular, approximate solutions when Kx, Ky, and Kt are not equal can be handled readily in CUTWP -- and the formula involved are the same as those typically used in civil engineering design specifications. Further integration of the two programs is being considered.

What's underneath the hood / how does CUTWP work?

Some incomplete snippets of code are provided to give you a sense of the nature of the CUTWP calculation:

% compute the flexural buckling and torsional buckling

...

Pe1 = pi^2*E*I1/KL1^2;

Pe2 = pi^2*E*I2/KL2^2;

...

Pe3 = (G*J+pi^2*E*Cw/KL3^2)/rob^2;

...

Pcr1 = Pe2;

B = 1-(a1/rob)^2;

Pcr2 = ((Pe1+Pe3)-sqrt((Pe1+Pe3)^2-4*B*Pe1*Pe3))/(2*B);

Pcr3 = ((Pe1+Pe3)+sqrt((Pe1+Pe3)^2-4*B*Pe1*Pe3))/(2*B);

...

"..." indicates intermediate code left out - the code for a traditional flexural-torsional buckling calculation is provided above, just to indicate to the user what manner of calculations are performed in CUTWP. The mode shapes are also generated and provided.

Matlab open source version of CUTWP (requires the user have Matlab)

The matlab files necessary for running CUTWP are provided here.

Installation instructions are as follows. Click on download above. Unzip the files to a directory of your choosing. In Matlab change your working directory to the same directory as where you unzipped the files. At the command line, type "cutwp". The program will initiate. (download November 2005 version)

Standalone version of CUTWP (runs on Windows machines)

The libraries and executable files necessary for running CUTWP are provided here.

Installation instructions are as follows. Click on download above. Save the exe file, double-click on cutwp_pkg.exe - this will expand all the files and install a Matlab runtime engine after that run (double-click) cutwp.exe and the program will initiate.

How do I reference CUTWP? CUTWP is open source?

 CUTWP is open source, Academic Free License v 1.2. Please provide a reference to the author (Andrew Sarawit) and note the version you are using.  For example: Sarawit, A. (2006). "CUTWP Thin-walled section properties" December 2006 update and add the date you referenced this web page

*Andrew Sarawit, Ph.D. is the developer of CUTWP. He is currently employed at Simpson, Gumpertz & Heger Inc. and may be reached at atsarawit@sgh.com. Ben Schafer performed the modification to CUTWP to allow it to read CUFSM input files and made corrections to b1 and b2 in December 2006. Also, Ben Schafer maintains this web site, page, and all the commentary above. Send comments, questions, etc. to schafer@jhu.edu.

12/07/06 - schafer@jhu.edu

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