Fachwerk is aimed at structural engineers who analyse and design reinforced concrete structures. It intends to simplify the application of discontinuous stress fields and strut-and-tie models.
The program calculates strut-and-tie models. It only uses equilibrium conditions. Thus, unlike common programs, it does not assume elastic material behaviour.
If the modelled system is statically indeterminate, Fachwerk will nevertheless calculate the forces of the members that are determinate. One can assign forces to the remaining members. If more forces than needed to accomplish a statically determinate system are assigned to members, and the equilibrium condition is not fulfilled, Fachwerk will indicate that the system is inconsistent.
The current version is 0.4.5 (February 22, 2017).
The documentation «Calculating strut-and-tie models with Fachwerk and Fachwerk3D» introduces the program on 30 pages and shows illustrated examples. Supporters will get this documentation (pdf). The first chapters are freely available for download.
The example shows a simple strut-and-tie model for a prestressed girder with indirect bearing. The system is statically indeterminate. A force (700 kN) has been assigned to the blue member and then the calculation was started. The members represented by thick lines are determinate: black indicates ones with tensile force, green ones under compression. Seven members remain indeterminate (indicated by thin black lines). One of these members can be set (see the number in the status field on the bottom ath the right side). If then the calculation is run again, all members will be determinate.
Every program for frame analysis can calculate trusses and, therefore, is able to find a possible solution that respects the equilibrium conditions. However, there is a problem if the system is statically indeterminate. The common linear-elastic programs calculate the forces according to the rigidity of the members. For the calculation of strut-and-tie models (for reinforced concrete structures) however, the rigidity of the members has no meaning and should, consequently, not be used. Instead, one may want to assign the yielding force of a number of reinforcement bars to a tie of the model. This is what Fachwerk is designed for.
For designing girders with constant depth, one may want to have a look at the program Balken. It calculates simple discontinuous stress fields.
A. Vontobel. Contact.