I want to write a VBA or a spreadsheet that calculates bar forces in a statically determinate truss of any configuration. I do a lot of truss calculations and a spreadsheet would be handy
What structural software is in your possesion? Does it allow text file input? Use excel to pre-process input and to post-process the results of commercial program. Writing your own solver even for statically determined structure will take lots of efforts, much more than you wish to spend.
I've done what you're asking for frame analysis using MATLAB. As yakpol says, even with no GUI and a lot of user-unfriendly input requirements, it was an incredible amount of effort.
I don't know of a free solver from the net. You can write one yourself using matrix analysis methods.
I used to use a program called Imaes 3D which would accept ASCII data input created from a VB program I wrote that solicited a configuration for analysis. The output was also ASCII and easily post-processed. Same for an old version of SAP4. Good luck!
If your geometry is fairly similar each time, then I would use Excel or Mathcad or something and make my own using their matrix inversion routines. If the geometry changes radically from one problem to another, I might have STADD or something. This can be upgraded by creating your input file with the help of Excel to compute your geometry and stuff. I once used these methods to analyze OH sign structures. Good Luck.
Matrix Analysis of Structures by Weaver and Gere has a nice fortran routine. I translated the plane frame program into visual basic for a school project. It runs inside excel. I made a lot of changes, additions and (improvements?). I still use it at work. It is very quick to set up frames. I wish I could release it under something like a GNU public license, maybe someone would help improve it, 3-d plates etc., but I am unsure of copyright issues. I might try to rewrite the core with a public domain solver etc.
I also saw a simple plane frame and truss program by an Australian professor. It works fine with a relatively slow gaussian solver. I will look for the author if anyone is interested.
Dr. Andrew Deeks of the University of Western Australia used to have a few Excel spreadsheets for truss and frame analysis using visual basic macros on his class website. I couldn't find them when I looked the other day. He seems to be on sabatical in England at the moment. If someone asks, you never know, he might be willing to send a copy.
I won't post my spreadsheet as I'm uncertain about software copyright issues. Does anyone know how to judge when something is altered enough to no longer be a copyright infringement? Also does any know of an open source matrix analysis code that could be translated to visual basic to run inside Excel? I have seen a few open source programs out there but they are a bit more involved than I have time to deal with.
Numerical Methods for Engineers. Griffiths and Smith
Blackwell Scientific Publications.
Covers Linear Algebra and the matrix operations/solutions you requested, non-linear, eigenvalue, interpolation, integration, ODEs and PDEs - all with Fortran 77 subroutines for you to convert to VBA.
This was a third year eng school text which I found quite usable and useful later on.
Numerical Methods for Engineers. Griffiths and Smith
I think I read some of this book in school. If it is the book I think I used it was very helpful. I don't think I could distribute a program using the code legally though, even though it is in the book. Doesn't redistribution of a published work constitute copyright infringement?
I am leaning towards a federally written bit of software, BLAS or TNT that is in the public domain, but I haven't found more than the solver yet. Otherwise I might look into using/modifying a GNU GPL license program like OOFEM. Has anyone worked on or is anyone interested in developing a GPL finite element package oriented towards civil engineering? Seems a bit daunting but it might be fun.