Evaluation and reduction of the truncation effects on modal flexibility-based damage-sensitive features in frame buildings with mass irregularities

Recent approaches for vibration-based damage detection in building structures are based on the calculation of modal flexibility (MF) based deflections. These deflections are estimated by applying uniform loads (UL) to experimentally derived modal flexibility matrices of the structures, and the interstory drifts are considered as damage-sensitive features (DSFs). However, in practical applications only a limited number of modes is usually identified from vibration data, and thus modal truncation effects are introduced on the deflections. To address this problem a mass proportional load (MPL) has been proposed, in a previous study by the authors, as an alternative to the uniform load with the aim of reducing the truncation effects on the displacement components of MF-based deflections of structures with mass irregularities. The objective of this work is to investigate further the mentioned problem by evaluating the truncation errors that affect the MF-based interstory drifts of frame buildings (i.e. the DSFs that can be conveniently used for damage detection). For structures with mass irregularities the truncation errors related to the application of the proposed MPL are thus compared with those related to the UL. Parametric studies were carried out on numerical models of shear-type frame buildings by considering structures with a different number of stories and various distributions of the story mass ratios, and by considering different subsets of modes included in the calculations.