Elastic period of sub-standard reinforced concrete moment resisting frame buildings     

Gerardo M. Verderame  Iunio Iervolino  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2010,8(4):955-972

The fundamental period has a primary role in seismic design and assessment as it is the main feature of the structure that allows one to determine the elastic demand and, indirectly, the required inelastic performance in static procedures. In fact, the definition of easy to manage relationships for the assessment of the elastic period has been the subject of a significant deal of both experimental and numerical/analytical studies, some of which have been acknowledged by codes and guidelines worldwide. Moreover, this kind of information is useful for territorial-scale seismic loss assessment methodologies. In the majority of cases, the assessment of the period is considered as function of the structural system classification and number of storeys or height. Reinforced concrete structures, comprising most of the building stock in Italy and in seismic prone areas in Europe and in the Mediterranean region, were built after the Second World War and are designed with obsolete seismic codes, if not for gravity loads only. Therefore, a class of buildings featuring the same height and/or number of storeys may show a significant variability of the structural system. This, along with the contribution of the stair module, may affect the elastic periods in the two main directions of a three-dimensional building. In the study presented these issues are investigated with reference to a population of existing RC structures designed acknowledging the practice at the time of supposed construction (e.g., simulated design) and with reference to the relative enforced code. The elastic period is evaluated for both main directions of the buildings of the considered sample, and regression analysis is employed to capture the dependency of the elastic dynamic properties of the structures as a function of mass and stiffness.  相似文献   

Effects of suspended sediments from reservoir flushing on fish and macroinvertebrates in an alpine stream     

Giuseppe Crosa  Elena Castelli  Gaetano Gentili  Paolo Espa 《Aquatic Sciences - Research Across Boundaries》2010,72(1):85-95

The downstream ecological consequences of two controlled “free flow” flushing operations designed to remove sediments accumulated in an alpine reservoir are described. The main objectives of the study were (a) to verify to what extent the suspended solid concentration (SSC) in the receiving water course can be controlled by flushing operations, (b) to determine the biological consequences of flushing operations, and (c) to produce technical guidelines for the future planning and monitoring of these activities. We found that the flushing of large volumes of accumulated sediment had clear effects on the stream ecosystem due to the unpredictability of short duration SSC peaks (70–80 g L⁻¹) and the high average SSC (4–5 g L⁻¹) within flushing periods. The main impacts were decreased fish densities (up to 73%) and biomass (up to 66%). A greater mortality recorded for juveniles will likely result in long-term impairment of the age-structures of future fish populations. The zoobenthic assemblages, despite exhibiting a drastic reduction in abundance following the first floods, showed substantial recovery within 3 months of the beginning of flushing operations. Regular sediment removal by yearly flushing is recommended in order to avoid SSC peaks and to facilitate the control of scouring effects caused by the water used to wash out sediments. We also recommend maximum allowable SSCs of 10 g L⁻¹ (daily average) and 5 g L⁻¹ (overall average) for flushing operations carried out in similar environmental contexts.  相似文献   

High-frequency maximum observable shaking map of Italy from fault sources     

Gaetano Zonno  Roberto Basili  Fabrizio Meroni  Gemma Musacchio  P. Martin Mai  Gianluca Valensise 《Bulletin of Earthquake Engineering》2012,10(4):1075-1107

We present a strategy for obtaining fault-based maximum observable shaking (MOS) maps, which represent an innovative concept for assessing deterministic seismic ground motion at a regional scale. Our approach uses the fault sources supplied for Italy by the Database of Individual Seismogenic Sources, and particularly by its composite seismogenic sources (CSS), a spatially continuous simplified 3-D representation of a fault system. For each CSS, we consider the associated Typical Fault, i.e., the portion of the corresponding CSS that can generate the maximum credible earthquake. We then compute the high-frequency (1–50?Hz) ground shaking for a rupture model derived from its associated maximum credible earthquake. As the Typical Fault floats within its CSS to occupy all possible positions of the rupture, the high-frequency shaking is updated in the area surrounding the fault, and the maximum from that scenario is extracted and displayed on a map. The final high-frequency MOS map of Italy is then obtained by merging 8,859 individual scenario-simulations, from which the ground shaking parameters have been extracted. To explore the internal consistency of our calculations and validate the results of the procedure we compare our results (1) with predictions based on the Next Generation Attenuation ground-motion equations for an earthquake of M_w 7.1, (2) with the predictions of the official Italian seismic hazard map, and (3) with macroseismic intensities included in the DBMI04 Italian database. We then examine the uncertainties and analyse the variability of ground motion for different fault geometries and slip distributions.  相似文献   

Ground motion observations and simulation for local earthquakes in the Campi Flegrei volcanic area     

Danilo Galluzzo  Francesca Bianco  Mario La Rocca  Gaetano Zonno 《Bulletin of Earthquake Engineering》2016,14(7):1903-1916

Ground motion produced by low magnitude earthquakes can be used to predict peak values in high seismic risk areas where large earthquakes data are not available. In the present work 20 local earthquakes (M_D∈[?0.3, 2.2]) occurred in the Campi Flegrei caldera during the last decade were analyzed. We followed this strategy: empirical relations were used to calibrate synthetic modeling, accounting for the source features and wave propagation effects. Once the source and path parameters of ground motion simulation were obtained from the reference data set, we extrapolated scenarios for stronger earthquakes for which real data are not available. The procedure is structured in two steps: (1) evaluation of ground motion prediction equation for Campi Flegrei area and assessment of input parameters for the source, path and site effects in order to use the finite fault stochastic approach (EXSIM code); (2) simulation of two moderate-to-large earthquake scenarios for which only historical data or partial information are available (M_w4.2 and M_w5.4). The results show that the investigated area is characterized by high attenuation of peak amplitude and not negligible site effects. The stochastic approach has revealed a good tool to calibrate source, path and site parameters on small earthquakes and to generate large earthquake scenario. The investigated magnitude range represents a lower limit to apply the stochastic method as a calibration tool, due to the small size of involved faults (fault length around 200/300 m).  相似文献   

Seismic demand on light acceleration‐sensitive nonstructural components in European reinforced concrete buildings          下载免费PDF全文

Crescenzo Petrone  Gennaro Magliulo  Gaetano Manfredi 《地震工程与结构动力学》2015,44(8):1203-1217

In this paper, a parametric study is conducted in order to evaluate the seismic demand on light acceleration‐sensitive nonstructural components caused by frequent earthquakes. The study is motivated by the inconsistent approach of current building codes to the design of nonstructural components; the extensive nonstructural damage recorded after recent low‐intensity earthquakes also encouraged such a study. A set of reinforced concrete frame structures with different number of stories, that is, 1 to 10 stories, are selected and designed according to Eurocode 8. The structures are subjected to a set of frequent earthquakes, that is, 63% probability of exceedance in 50 years. Dynamic nonlinear analyses are performed on the reference structures in order to assess the accuracy of the equations to predict seismic forces acting on nonstructural components and systems in Eurocode. It is concluded that the Eurocode equations underestimate the acceleration demand on nonstructural components for a wide range of periods, especially in the vicinity of the higher mode periods of vibration of the reference structures; for periods sufficiently larger than the fundamental period of the structure, instead, the Eurocode formulation gives a good approximation of the floor spectra. Finally, a novel formulation is proposed for an easy implementation in future building codes based on the actual Eurocode provisions. The proposed formulation gives a good estimation of the floor spectral accelerations and is able to envelope the floor spectral peaks owing to the higher modes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Assessing reparability: simple tools for estimation of costs and performance loss of earthquake damaged reinforced concrete buildings          下载免费PDF全文

Maria Polese  Marco Di Ludovico  Marco Marcolini  Andrea Prota  Gaetano Manfredi 《地震工程与结构动力学》2015,44(10):1539-1557

Tools for assessing building reparability via the estimation of expected performance loss (PL) and associated costs for repair of existing RC building classes damaged by an earthquake are presented. The assessment approach relies on the availability of a number of suitably developed: (i) capacity curves for representative building classes; (ii) curves relating global ductility demand μ to the expected PL for the same classes; and (iii) PL–cost for repair relationship calibrated on database collecting cost data of more than 2300 buildings damaged after 2009 L'Aquila earthquake. The tools are developed applying a simplified procedure involving the simulated design of existing building classes, the assumption of predefined collapse mechanism types and the analyses of the seismic behavior of equivalent SDOF systems representative of ‘intact’ and ‘damaged’ structures after an earthquake. The use of these tools may give useful preliminary indications to decision makers for establishing reparability priorities in the aftermath of damaging earthquakes or to insurance companies to value sound insurance premium for existing building classes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A performance‐based framework for adaptive seismic aftershock risk assessment          下载免费PDF全文

Hossein Ebrahimian  Fatemeh Jalayer  Domenico Asprone  Anna M. Lombardi  Warner Marzocchi  Andrea Prota  Gaetano Manfredi 《地震工程与结构动力学》2014,43(14):2179-2197

Operative seismic aftershock risk forecasting can be particularly useful for rapid decision‐making in the presence of an ongoing sequence. In such a context, limit state first‐excursion probabilities (risk) for the forecasting interval (a day) can represent the potential for progressive state of damage in a structure. This work lays out a performance‐based framework for adaptive aftershock risk assessment in the immediate post‐mainshock environment. A time‐dependent structural performance variable is adopted in order to measure the cumulative damage in a structure. A set of event‐dependent fragility curves as a function of the first‐mode spectral acceleration for a prescribed limit state is calculated by employing back‐to‐back nonlinear dynamic analyses. An epidemic‐type aftershock sequence model is employed for estimating the spatio‐temporal evolution of aftershocks. The event‐dependent fragility curves for a given limit state are then integrated together with the probability distribution of aftershock spectral acceleration based on the epidemic‐type aftershock sequence aftershock hazard. The daily probability of limit state first‐excursion is finally calculated as a weighted combination of the sequence of limit state probabilities conditioned on the number of aftershocks. As a numerical example, daily aftershock risk is calculated for the L'Aquila 2009 aftershock sequence (central Italy). A representative three‐story reinforced concrete frame with infill panels, which has cyclic strength and stiffness degradation, is used in order to evaluate the progressive damage. It is observed that the proposed framework leads to a sound forecasting of limit state first‐excursion in the structure for two limit states of significant damage and near collapse. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Bayesian Cloud Analysis: efficient structural fragility assessment using linear regression   总被引：1，自引：1，他引：0  

Fatemeh Jalayer  Raffaele De Risi  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2015,13(4):1183-1203

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Momentum and energy transport in the Sun's convection zone under the observational constraint of flux and temperature homogeneity at the surface     

Gaetano Belvedere  Lucio Paternò 《Solar physics》1978,60(1):203-206

A previous authors' non-Boussinesq model of solar differential rotation (BPCM) is used to determine the angular velocity distribution within the convection zone, when the momentum and energy equations are solved with boundary conditions expressing the homogeneity of flux and temperature at the Sun's surface.  相似文献   

Some SH-wave seismic reflections from depths of less than three metres     

Gian Piero Deidda  Gaetano Ranieri 《Geophysical Prospecting》2001,49(5):499-508

Shallow SH-wave reflections are far from routine, although their study can provide insights into important properties of near-surface materials that cannot be inferred from P-wave data alone. Difficulties in separating SH-wave reflections from Love waves are generally considered the major obstacle to progress in shallow SH-wave seismic reflection. This may be the case in surveys undertaken at great depths, but it is not necessarily true for reflection data gathered at shallow and ultra-shallow depths. This paper shows that when SH-wave data possess wavelengths greater than the thickness of the superficial layer, Love waves are not greatly dispersed. In this case, misinterpretation between parts of reflection hyperbolae and waveguide arrivals is sufficiently limited. In a one-layer model earth, which well approximates typical situations of the near-surface underground, the most energetic modes (the lowermost modes) of the dispersed surface waves have a dominant frequency band that falls below the wavelet spectrum of the shallow reflections; therefore, they can be filtered out in the frequency domain. Higher modes, although their spectral content overlaps that of the reflections, exhibit small amplitudes on seismograms and leave strong reflections unaffected.We present field examples from three different sites where we were able to obtain ultra-shallow reflections (< 3 m) in unconsolidated sediments. The high level of resolution (vertical resolution up to 15 cm) suggests that SH-wave reflection imaging has the potential to complement other high-resolution techniques, such as P-wave reflection and ground-penetrating radar (GPR) imaging, allowing a better and more complete characterization of the near-surface environments.  相似文献