C4. Modeling the non-structural elements or equipment

Non-structural elements and equipment are elements that do not play any structural role in the behavior of the structure. Three cases can be distinguished:

The element has a low mass and a low stiffness compared to the overall structure. In this case, it can be neglected in the model,

The element has a low mass but its stiffness cannot be considered negligible (e.g. some facade cladding restraining the movements of the supporting structure). In this case, its presence can modify the behavior of the structure, so it is necessary to consider it in the model (at least by considering a fictitious rigidity),

The element has a non-negligible mass but its stiffness can be considered negligible. In this case, an equivalent mass must be included in the model.

Equipment/Non-structural element	Negligible mass	Significant mass
Reliable stiffness	Not considered	Mass to include
Significant stiffness	Stiffness to model	Mass and stiffness to model

For seismic analyses, it is important to ensure that the element will not resonate with the supporting structure. The following publications are useful references to identify when the element/structure interaction should be considered in the model.

J. Betbeder-Matibet - Génie parasismique - volume 3 - Hermes Science Publications (2003).

FD P06-029 - Règles de construction parasismiques - Dimensionnement des ancrages en zone sismique (décembre 2017)

AFPS proposal to know when to consider the dynamic interaction between non-structural elements/equipment and the structure (Recommendations AFPS90, 1993).

Legend :

Me=mass of the equipment or non-structural elements

Mb= mass of the supporting structure

Te= period of the non-structural element

Tb= period of the supporting structure

Note: depending on the direction studied, the mass of the supporting structure may be limited to the support floor only (for more details, refer to the documents mentioned above).

For seismic calculations of buildings, non-structural elements (such as partition walls) must be considered when modeling the structure as they are likely to modify its transverse stiffness. These elements may be subjected to justifications such as in EC8-1, Article 4.3.6 for framing with masonry infill.

It may also be necessary to remove small elements in a model intended for modal analysis.