ALBERT

Description: In this paper, the effectiveness of different design solutions for tuned mass dampers (TMD) applied to high-rise cross-laminated (X-Lam) timber buildings as a means to reduce the seismic accelerations was investigated. A seven-storey full-scale structure previously tested on shaking table was used as a reference. The optimal design parameters of the TMDs, i.e. damping and frequency ratios, were determined by using a genetic algorithm on a simplified model of the reference structure, composed by seven masses each representing one storey. The optimal solutions for the TMDs were then applied to a detailed finite element model of the seven-storey building, where the timber panels were modelled with shell elements and the steel connectors with linear spring. By comparing the numerical results of the building with and without multiple TMDs, the improvement in seismic response was assessed. Dynamic time-history analyses were carried out for a set of seven natural records, selected in accordance with Eurocode 8, on the simplified model, and for Kobe earthquake ground motion on the detailed model. Results in terms of acceleration reduction for different TMD configurations show that the behaviour of the seven-storey timber building can be significantly improved, especially at the upper storeys. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Description: The paper investigates the degree of accuracy achievable when some non-linear static procedures based on a pushover analysis are used to evaluate the seismic performance. In order to assess the significance of different sources of errors, three types of structural systems are analysed: (i) single-degree-of-freedom (SDOF) systems with different hysteretic behaviour; (ii) shear-type multi-degree-of-freedom (MDOF) systems with elastic-perfect plastic (EPP) shear force-interstorey drift relationships; (iii) a steel moment-resisting frame with rigid joints and EPP moment-curvature relationship. In SDOF systems, the source of approximation comes only from the calibration of the demand spectrum, while in MDOF systems some further errors are introduced by the schematization with an equivalent SDOF system. The non-linear static procedures are compared with rigorous time-history analyses carried out by considering ten generated earthquake ground motions compatible with the Eurocode 8 elastic spectra. It was found that SDOF systems with longer periods satisfy the equal displacement approximation regardless of the hysteretic model, while hysteresis loops with smaller energy dissipated indicate lower response for shorter periods. This is the opposite of what predicted by the ATC-40 capacity spectrum method, which underestimates and overestimates, respectively, the actual response of low- and high-ductility systems. Conversely, the inelastic spectrum method proposed by Vidic, Fajfar and Fischinger leads to the most accurate results for all types of structural systems. The analyses carried out on EPP shear-type frames point out a large concentration of the ductility demand on some storeys. However, such a concentration markedly reduces when some hardening is accounted for. Copyright © 2006 John Wiley & Sons, Ltd.

Description: The paper investigates the dynamic behaviour of hybrid systems made of partially restrained (PR) steel-concrete composite frames coupled with viscoelastic dissipative bracings. A numerical model that accounts for both the resisting mechanisms of the joint and the viscoelastic contribution of the dissipative bracing is introduced and briefly discussed. The model is first validated against experimental outcomes obtained on a one-storey two-bay composite frame with partial strength semi-rigid joints subjected to free vibrations. A number of time-history analyses under different earthquake ground motions and peak ground accelerations are then carried out on the same type of frame. The purpose is to investigate the influence of the type of beam-to-column connection and property of the viscoelastic bracing on the performance of the hybrid system. The inherent stiffness of the bare PR frame and the plastic hysteresis of the beam-to-column joints, which always lead to only limited damage in the joint, are found to provide a significant contribution to the overall structural performance even under destructive earthquakes. This remark leads to the conclusion that the viscoelastic bracing can be effectively used within the hybrid system. Copyright © 2008 John Wiley & Sons, Ltd.

Description: In many parts of the world, the repetition of medium-strong intensity earthquake ground motions at brief intervals of time has been observed. The new design philosophies for buildings in seismic areas are based on multi-level design approaches, which take into account more than a single damageability limit state. According to these approaches, a sequence of seismic actions may produce important consequences on the structural safety. In this paper, the effects of repeated earthquake ground motions on the response of single-degree-of-freedom systems (SDOF) with non-linear behaviour are analysed. A comparison is performed with the effect of a single seismic event on the originally non-damaged system for different hysteretic models in terms of pseudo-acceleration response spectra, behaviour factor q and damage parameters. The elastic-perfect plastic system is the most vulnerable one under repeated earthquake ground motions and is characterized by a strong reduction of the q-factor. A moment resisting steel frame is analysed as well, showing a reduction of the q-factor under repeated earthquake ground motions even larger than that of an equivalent SDOF system. © 2002 John Wiley & Sons, Ltd.