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© 2017 Elsevier Ltd This paper aims at assessing the influence of environmental parameters on the modal characteristics of age–old masonry constructions. The results of a long–term ambient vibration monitoring of the San Frediano bell tower in Lucca (Italy) are reported. The tower, dating back to the 11th century, has been fitted along its height with four triaxial seismometric stations, which were left active for about one year. Data from the monitoring system have been processed via the Stochastic Subspace Identification Method in order to identify the tower's modal characteristics and their variations over the year. The dependence of the tower's frequencies on the ambient temperature was first studied and simulated via simple auto–regressive models. Then, some output–only models based on the principal component analysis (PCA) were applied, under the hypotheses of both linear and nonlinear (Kernel PCA) dependence of the natural frequencies on the unknown environmental parameters. The results indicate PCA to be an effective tool for detecting changes in the dynamic characteristics of masonry constructions. ispartof: Engineering Structures vol:156 pages:175-187 status: published

Footbridges are often designed as slender structures, sensitive to human-induced excitation. In the case where the prevailing vibration serviceability requirements are not met, vibration reduction measures such as tuned mass dampers (TMDs) are needed. Both the prediction of the structural response and the design of the TMD rely on the modal parameters of the footbridge. Measurements after construction of footbridges have shown that it is difficult to accurately predict these modal parameters even with detailed finite element models based on structural drawings. Moreover, these parameters evolve in time due to changing environmental conditions and degradation. It is important to take into account these uncertainties in the vibration serviceability assessment as well as in the design of vibration reduction measures. The present paper proposes a robust optimisation approach for the design of a TMD which accounts for uncertainties in the modal parameters. The aim is to minimise the mass of the TMD, assumed as a measure for the cost, by tuning the mass, stiffness and damping values, while guaranteeing that vibration serviceability is satisfied for a range of possible values of the natural frequency and modal damping. In order to investigate the trade-off between the mass of the TMD (cost) and the level of uncertainty, a multi-interval approach is adopted. The optimal parameters are found to change significantly with the level of uncertainty. The TMD mass and damping increase for a higher level of uncertainty to satisfy the vibration serviceability requirements in all possible cases. publisher: Elsevier articletitle: Robust design of a TMD for the vibration serviceability of a footbridge journaltitle: Engineering Structures articlelink: http://dx.doi.org/10.1016/j.engstruct.2016.05.028 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved. ispartof: Engineering Structures vol:123 pages:408-418 status: published

In this paper, the M w 7.2 Duzce earthquake is examined thoroughly with special emphasis on fault normal (FN) and fault parallel (FP) components and response spectra. For the spectra obtained from Istanbul, the seismic demands are highest in the Fatih and Zeytinburnu districts and lowest in the Maslak district. The consequences of the signal processing with Butterworth filters are investigated for various records of the Duzce earthquake. For this purpose, a complete strong-motion signal processing toolbox is developed that can process the data with alternative techniques. The current Turkish Earthquake Resistant Design Code (TERDC) does not take the near fault effects into account. New design response spectra for Turkey are proposed based on a previous attenuation relationship of the authors on 301 horizontal accelerograms from different earthquakes and according to the FEMA 356 specifications. The proposed design response spectra may be considered for implementation in important engineering structures since it accounts for distance and site effects.