Nodes are the connections of the Strut & Tie model at which struts and ties converge and/or the location at which forces are redirected within a Strut & Tie model.
While struts and ties are linear elements, nodes are not and can be made with different combinations of elements: compression or tension concrete elements connected to tension ties, in a variable number, like:
Pic. 3. Different nodal configuration describes compression (C) and tension (T) in the node
The compression resistance of nodes must be assessed, and equilibrium satisfied. Eurocode (NEN-EN#6.5.4) gives different indications concerning the limit values for the node’s compression strength σRd,max.
Factors affecting the size of the nodal zones:
- The size of bearings;
- The size of loaded areas;
- The geometry of the member;
- The location and distribution of reinforcement or/and the size of tendon anchorages.
Nodes optional can be detailed to be either hydrostatic or non-hydrostatic. For a hydrostatic node, the stress acting on each face of the node is equivalent and perpendicular to the surface of the node. In most cases achieving hydrostatic nodes for geometric configurations of the Strut and Tie model is nearly impossible. For this reason, most models utilize non-hydrostatic nodes:
Hydrostatic node Non-hydrostatic node