Seismic Design of Non‐Structural Components in Industrial Facilities – a Discussion of the EC8 Approach

In industrial facilities, equipment such as production machines, small vessels, conveyors and piping are installed at various elevations of the (building‐) structure. In seismic design, this equipment (referred to as non‐structural components) should be considered integrally with the structure in order to capture the resulting dynamic behaviour of the system adequately.

However, the typical procedure in plant construction is to design the structure in a previous step, where masses of the equipment are introduced only by a rough estimate, and stiffnesses of the equipment are ignored. The seismic design of individual non‐structural components is done in a subsequent step and typically by the respective supplier of the component. He often does know little about the characteristics of the structure – mostly not even the natural frequency. If the equipment is to be installed in an existing structure (e.g. due to changes in the production process or exchange of components) or if existing components have to be re‐verified (e.g. due to new seismic design loads at site), it may be difficult to define the dynamic characteristics of the possibly many years old load‐bearing structure.

In Eurocode 8‐1 as in many other design codes, rules for the design of non‐structural components are given. However, some of these do not seem to be in accordance with mechanics or seem to be based on hidden assumptions. In any case the designer is left with what is felt to be an unsatisfactory design result, which cannot be retraced by the designer.

In the present paper, the structural behavior of typical non‐structural components is investigated: a silo on a structural grid, an elevated tube‐feet tank, and piping. For these, the dynamic behaviour is investigated, when built in a typical plant structure. The findings are compared with the design rules given in EC8‐1. Improvement of the rules towards better understanding of the mechanical background or better ease of use will be proposed.