Performance of caisson foundations subjected to flood-induced scour

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Recent developments in seismic site response evaluation and microzonation

Seismic hazard and seismic actions for the design of buildings are strongly influenced by site response because of significant amplification expected for the specific stratigraphic and topographic conditions. Different approaches can be applied at the scale of the single building, but in complex morphological and geological contexts studies at the urban scale can provide relevant informations to be incorportated in the evaluation. The paper builds on the recent experience of seismic microzonation studies in central Italy in the aftermaths of the 2016 seismic sequence to provide an insight on the role of studies at different scales. Within this context, an example is also provided to illustrate recent methodologies that have been conceived to account for uncertainties in the characterization that affects both geophysical tests in situ and geotechnical tests in the laboratory for the assessment of the response of soils to cyclic loadings

Valutazione dei metodi semplificati proposti nelle NTC18 per la stima degli effetti di sito: un approccio stocastico

La valutazione degli effetti di sito è di rilevante importanza nella definizione dell’azione sismica di progetto. A tal proposito, negli ultimi anni, sono stati proposti diversi approcci volti alla stima semplificata della risposta sismica locale. Il presente studio si pone come obiettivo la valutazione dei metodi semplificati proposti nelle nuove NTC18. Il metodo adottato si basa su simulazioni lineari viscoelastiche equivalenti effettuate su un database di modelli 1D di sottosuolo, generati secondo una procedura stocastica. L’input sismico di riferimento consiste in diversi set di accelerogrammi mediamente spettro-compatibili, riferiti a siti caratterizzati da livelli di sismicità crescenti. L’analisi dei risultati ottenuti ha permesso di valutare le previsioni proposte dalla normativa mediante parametri sintetici dell’amplificazione sismica, in termini di attendibilità e dispersione

The PoliTO–UniRoma1 database of cyclic and dynamic laboratory tests: assessment of empirical predictive models

The soil nonlinear hysteretic behaviour is usually described, in the moderate strain range, through the shear modulus reduction and material damping ratio (MRD) curves. In common practice, in absence of specific laboratory tests, the curves are estimated by employing empirical regression models. Such predictive models, typically calibrated on large experimental datasets, correlate the soil response to its physical properties. This research fits within this context, presenting a comprehensive database of cyclic and dynamic laboratory tests conducted on natural Italian soils. The database, publicly available as supplementary data of the paper, contains the results of the tests conducted by the geotechnical laboratories of the Politecnico di Torino (Turin, Italy) and the Sapienza Università di Roma (Rome, Italy) over the past 30 years. The experimental data are employed to assess the performance of some widely used empirical models in predicting the MRD curves of natural uncemented fine-grained soils, emphasizing the importance of using an independent dataset for conducting a reliable statistical analysis. The results show that the use of many soil parameters as proxies for predicting the soil response does not necessarily lead to an improvement in the performance of the model. Therefore, according to Occam’s razor principle, simple models are to be preferred

Microzonazione sismica e risposta sismica locale: specificità e aspetti critici

La pericolosità sismica, ossia lo scuotimento atteso, è fortemente influenzata dalle specifiche condizioni di sito che possono comportare fenomeni di amplificazione dovuti ad effetti stratigrafici e topografici. Gli studi condotti alla scala territoriale e alla scala locale della singola opera rappresentano due elementi complementari, che spesso vengono erroneamente messi in contrapposizione. Nella presente nota vengono considerati gli elementi distintivi delle due tipologie di studi, presentando alcuni esempi tratti dalle recenti esperienze riguardanti gli studi condotti in Centro Italia a seguito degli eventi sismici del 2016. Successivamente vengono considerati due aspetti critici per la valutazione delle azioni sismiche: l’influenza delle incertezze associate alla caratterizzazione del sito e l’affidabilità degli approcci semplificati proposti dalle normative sismiche, con specifica attenzione alle NTC2018

Site response analyses for complex geological and morphological conditions: relevant case-histories from 3rd level seismic microzonation in Central Italy

The paper presents the results of 5 case studies on complex site e ects selected within the project for the level 3 seismic microzonation of several municipalities of Central Italy dam- aged by the 2016 seismic sequence. The case studies are characterized by di erent geo- logical and morphological con gurations: Monte San Martino is located along a hill slope, Montedinove and Arquata del Tronto villages are located at ridge top whereas Capitignano and Norcia lie in correspondence of sediment- lled valleys. Peculiarities of the sites are constituted by the presence of weathered/jointed rock mass, fault zone, shear wave veloc- ity inversion, complex surface and buried morphologies. These factors make the de ni- tion of the subsoil model and the evaluation of the local response particularly complex and di cult to ascertain. For each site, after the discussion of the subsoil model, the results of site response numerical analyses are presented in terms of ampli cation factors and acceleration response spectra in selected points. The physical phenomena governing the site response have also been investigated at each site by comparing 1D and 2D numerical analyses. Implications are deduced for seismic microzonation studies in similar geological and morphological conditions.Published5741–57775T. Sismologia, geofisica e geologia per l'ingegneria sismicaJCR Journa