A strut-and-tie model is selected according to the load path, and there are two main ways to do it. The first follows the stress flow: struts are laid along the principal compression directions and ties along the principal tension directions. The second is topology optimization — for example ESO (Evolutionary Structural Optimization), which removes the least-stressed material step by step until a truss-like skeleton remains, and that skeleton is idealized as struts, ties and nodes. Either way, the result is an initial geometry, not a finished design: the engineer still refines it into an optimal truss model with nodes at the loads and supports, and checks the strength of every strut, tie and nodal zone.
Selecting the optimal strut-and-tie model from the principal compressive stress flow or the ESO result is where full automation struggles. A 2D plane finite-element analysis can give different results depending on the load positions, the mesh size and, for ESO, the removal rate, and when there are several load combinations, each combination can have a different optimal model. A model selected from these results can also be unstable, meet at angles the design code does not allow, or call for inclined ties that are hard to build. In design practice, therefore, the engineer selects the strut-and-tie model to use in the design, guided by these results.
AStrutTie runs a plane-stress FE analysis in the browser for 2D models and shows the result in two ways: Stress Flow draws the principal compressive stress direction vectors over the member, and ESO steps through the removal stages until the load path is visible. Either can be shown as a background on the STM canvas, so the strut-and-tie model is drawn and edited directly over the load path. AStrutTie does not extract a strut-and-tie model from the ESO result automatically — a general-purpose rule does not give a reliable model across the variety of member shapes, so the engineer selects the model.
- Two routes — follow the principal stress flow (struts along compression, ties along tension), or remove low-stressed material (ESO) until a truss-like skeleton remains
- The result is an initial geometry: the engineer refines it into a truss with nodes at the loads and supports, then checks every strut, tie and nodal zone
- Results vary with the load positions, mesh size and removal rate, and each load combination can have its own optimal model
- In AStrutTie: Stress Flow and ESO for 2D models, shown as a background on the STM canvas — no automatic model extraction