Department of Civil and Environmental Engineering
Duke University
Henri P. Gavin, Ph.D., P.E.
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Department of Civil and Environmental Engineering Duke University Henri P. Gavin, Ph.D., P.E. |
Frame3DD is free open-source software for static and dynamic structural analysis of 2D and 3D frames and trusses with elastic and geometric stiffness. It computes the static deflections, reactions, internal element forces, natural frequencies, mode shapes and modal participation factors of two- and three- dimensional elastic structures using direct stiffness and mass assembly. Frame3DD has its own text-file input format (.3dd), but additionally supports matlab (.m) and spreadsheet (.csv) file formats, and offers graphical output including mode shape animation via Gnuplot.
The program is written in plain ANSI C. The source code includes: frame analysis, LDL' decomposition, LU decomposition, Newton-Raphson iteration, sub-space iteration, Stodola iteration, Sturm eigenvalue check, static condensation, Guyan reduction, and dynamic condensation.
Frame3DD is licensed under the GNU General Public License 3.0 and is maintained at GitHub.
A new (2026) graphical user interface to Frame3DD is availabile at the GitHub repository vf
The following input data files are included in the Frame3DD repository. Click below to see formatted and commented input data, the associated output data, as well as plot and movie outputs generated using the program.
| Example | Input Data (.txt) | Output Data (.txt) | Input Data (.csv) | Output Data (.csv) | Plot | Movie |
| (A) 2-D Pratt Truss | exA.3dd | exA.out | exA.csv | exA_out.CSV | Plot | |
| (B) Pyramid Frame | exB.3dd | exB.out | exB.csv | exB_out.CSV | Plot | Movie |
| (C) Tetrahedral Frame | exC.3dd | exC.out | exC.csv | exC_out.csv | Plot | Movie |
| (D) Un-Restrained Frame | exD.3dd | exD.out | exD.csv | exD_out.CSV | Plot | Movie |
| (E) Lateral-Torsional Coupling | exE.3dd | exE.out | exE.csv | exE_out.CSV | Plot | Movie |
| (F) Building with Seismic Isolation | exF.3dd | exF.out | exF.csv | exF_out.CSV | Plot | Movie |
| (G) Building with Set-Back | exG.3dd | exG.out | exG.csv | exG_out.CSV | Plot | Movie |
| (H) Pedestrian Ramp Lateral Sway | exH.3dd | exH.out | exH.csv | exH_out.CSV | Plot | Movie |
| (I) Triangular Tower | exI.3dd | exI.out | exI.csv | exI_out.CSV | Plot | |
| (J) Tesseract | exJ.3dd | exJ.out | exJ.csv | exJ_out.CSV | Plot |
Frame3DD is free software: you may redistribute it and/or modify it under the terms of the GNU General Public License (GPL) as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
Simply put, the GPL says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. By distributing the complete source code for Frame3DD under the terms of the GPL, we guarantee that you and all other users will have the freedom to redistribute and change Frame3DD.
Frame3DD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License (GPL) and the GNU General Public License FAQ for more details.
© 1992-2026 Henri P. Gavin.
Verbatim copying and distribution is permitted in any medium, provided this notice is preserved.
Department of Civil and Environmental Engineering
Duke University, Box 90287
Durham, NC 27708-0287
