Model calibration in the presence of resonant non-structural elements

Abstract

Accurate finite element models are needed in many applications of Civil Engineering. Non-structural elements (NSEs) often interfere with the main structure, altering its stiffness and modal signature. Neglecting such interaction, although a common practice in design, may lead to unreliable predictions of the structural dynamic response and to biased interpretations of experimental vibrational tests. In the literature, the role of NSEs in vibration-based finite element model calibration is well documented for NSEs working “in parallel” with the main structure (e.g. masonry infills in buildings, pavements or railings in bridges) but remains essentially unexplored for NSEs working “in series” with the main structure (e.g. non-structural appendages like suspended ceilings, piping systems, storage tanks and antennas, but also partitions and facades in their out-of-plane modes). Through the analysis of numerical and experimental case studies, this paper shows that “in series” NSEs accidentally resonating with some structural mode may deeply contaminate the overall modal behaviour and severely invalidate model calibration, unless their role is properly addressed while performing experimental modal analysis and structural modelling. Two alternative calibration strategies are finally discussed which prove effective in the presence of resonant NSEs, based on, respectively, excluding/including the NSEs from/into the model structure.