Characterisation of Site Effects by Means of Energy Spectra

The effects of subsoil conditions on surface ground motion are evaluated in terms of energy spectra. Near-field and far-field strong ground motion recorded during recent destructive earthquakes at nearby rock and soil sites characterized by a comprehensive knowledge of the geotecbnical properties are considered. The study suggests that energy spectra at soil sites are amplified with respect to those on rock sites. The maximum spectral amplification is usually well correlated to the natural periods of the sites. The most striking difference between traditional response spectra and energy spectra is the high soil amplification at longer periods, which is not apparent from the consideration of response spectra only

Percorsi e spazi sicuri: dimensione territoriale e centro abitato

Il lavoro analizza le problematiche di un tessuto urbano in condizioni di sisma nell'ambito dei Piani di Ricostruzione del territorio Aquilano. La riduzione del rischio legato ad eventi sismici deve tener conto non solo del rischio del singolo edificio ma anche del rischio dei percorsi, soprattutto nei centri storici italiani caratterizzati da percorsi di dimensioni limitate. Per ognuno dei comuni interessati dal Piano di Ricostruzione, vengono individuati percorsi e spazi sicuri a livello territoriale e di centro urbano sulla base di principi di pericolosità e rischio, proponendo gli interventi necessari sugli edifici prospicient

Definition of a model for the damping modification factor for near-fault records

Damping modification factors (DMF) are scaling factors to be applied to the 5% damped spectral ordinates to take into account damping values higher or lower than the nominal values of 5% of critical. DMF have been already introduced in several seismic codes. Moreover, in different studies the influence of basic parameters on DMF is analysed and empirical expressions are proposed. In this context, the attention is herein focused on the effect of damping ratio on single-degree-of-freedom systems subjected to near-fault records. Specifically, 248 accelerograms recorded in near-fault regions during different earthquakes are considered; the recorded accelerograms have been rotated into fault-normal and fault-parallel components. For the parametric study seven damping ratios (from 2% to 50%) are considered to evaluate the DMF. The effect of magnitude and period of structural vibration on DMF is evaluated and a simple model, obtained from regression analyses, is proposed. The research confirms the period-dependent nature of the DMF and the influence of magnitud

Characterization of the dynamic response of structures to damaging pulse-type near-fault ground motions

The presence of long-period pulses in near-fault records can be considered as an important factor in causing damage due to the transmission of large amounts of energy to the structures in a very short time. Under such circumstances high-energy dissipation demands usually occur, which are likely to concentrate in the weakest parts of the structure. The maximum nonlinear response or collapse often happens at the onset of directivity pulse and fling, and this time is not predicted by the natural structural vibration periods. Nonlinear response leading to collapse may in most cases occur only during one large amplitude pulse of displacement. From the study of the response of both linear and nonlinear SDOF systems, the effects of these distinctive long-period pulses have been assessed by means of : (i) synthetic parameters directly derived from the strong ground motion records, and (ii) elastic and inelastic spectra of both conventional and energy-based seismic demand parameters. SDOF systems have first been subjected to records obtained during recent earthquakes in near-fault areas in forward directivity conditions. The results indicate that long duration pulses strongly affect the inelastic response, with very high energy and displacement demands which may be several times larger than the limit values specified by the majority of codes. In addition, from the recognition of the fundamental importance of velocity and energy-based parameters in the characterization of near-fault signals, idealized pulses equivalent to near-fault signals have been defined on account of such parameters. Equivalent pulses are capable of representing the salient observed features of the response to near-fault recorded ground motions

Recorded Motions of the 6 April 2009 Mw 6.3 L’Aquila, Italy, Earthquake and Implications for Building Structural Damage: Overview

The normal-faulting earthquake of 6 April 2009 in the Abruzzo Region of central Italy caused heavy losses of life and substantial damage to centuries old buildings of significant cultural importance and to modern reinforcedconcrete-framed buildings with hollow masonry infill walls. Although structural deficiencies were significant and widespread, the study of the characteristics of strong motion data from the heavily affected area indicated that the short duration of strong shaking may have spared many more damaged buildings from collapsing. It is recognized that, with this caveat of shortduration shaking, the infill walls may have played a very important role in preventing further deterioration or collapse of many buildings. It is concluded that better new or retrofit construction practices that include reinforced concrete shear walls may prove helpful in reducing risks in such seismic areas of Italy, other Mediterranean countries, and even in United States, where there are large inventories of deficient structures