2. Definition of theoretical tolerances

2.1 Positioning tolerances

They are closely linked to the design and existing margins, which in turn are linked to safety factors.

There are two essential cases to consider.

• The design has been carried out without analysis: in this case, the positioning of the support is based on experience, which is generally expressed in the form of tables or charts appearing in normative documents that provide recommended spans between supports. These tables and charts are always conservative with regard to permissible deformation (deflection) or stress criteria.

• In this case, the computer uses code or standard criteria to judge the admissibility of deformations and stresses....