Global and local axes systems

In SeismoBuild, a fixed x-y-z global axis system is in place, used to define length (x), depth (y) and height (z) of all structural models. In addition, and being a 3D modelling program, SeismoBuild requires also that local 1-2-3 coordinate systems are assigned to all structural elements, so that their orientation in space is known. By convention, local direction (1) refers to the chord axis of the element, whilst axes (2) and (3) define the plane of the cross-section and its orientation. Although there are no constraints imposed on the definition of local axes (2) and (3), it is common for users to associate axis (2) to the "weak direction" of the member and to link axis (3) to the "strong direction" of the element, as illustrated below, where a beam is schematically represented. This is the convention also adopted in the illustrative drawings employed in the Modify/View additional reinforcement window available in the Building Modeller sections' properties.

Whilst the orientation of local vector (1) results unambiguously characterised by the line joining the two end-nodes of the element (positive direction is that going from node n1 to node n2), the so-called right-hand rule is employed in order to fully describe the orientation of the two other remaining local axes, and thus that of the cross-section.

Note: For column members the orientation of the elements is automatically defined by the program. The default orientation for the local vector (1) is from the lower to the upper floor, i.e. the node n1 is the node of the lower floor and the node n2 is the node of the floor above.