Una procedura per il dimensionamento di muri in terra rinforzata soggetti ad eventi sismici intensi

In questa nota si presenta una procedura per il dimensionamento di muri in terra rinforzata mediante il metodo pseudo-statico. In essa, il coefficiente sismico k è calibrato su prefissati livelli di prestazione del muro, espressi in termini di valori limite degli spostamenti permanenti accumulati durante l’evento sismico. Un’equivalenza di upper bound tra gli spostamenti indotti da sisma e i valori di k è stata ottenuta applicando il metodo di Newmark al database di accelerogrammi italiani, aggiornato alle registrazioni del 2017, e correggendo le relazioni empiriche ottenute per tenere conto della forma dei meccanismi plastici interni alla zona rinforzata, ai quali corrisponde la massima domanda di resistenza dei rinforzi. Fissata la prestazione sismica, il muro viene quindi dimensionato per ottenere un coefficiente sismico critico associato ai meccanismi interni (kcint) inferiore a quello associato ai meccanismi esterni (kcext), così da promuovere l’attivazione di meccanismi plastici che prevedano la mobilitazione della resistenza del sistema terreno-rinforzo, dotato di rinforzi caratterizzati da adeguati livelli di duttilità

Seismic design of geosynthetic-reinforced earth retaining walls following a pseudo-static approach

Geosynthetic-reinforced earth (GRE) retaining walls show a better performance than conventionally-designed walls during destructive earthquakes, due to their capability of redistributing seismic-induced deformations within the reinforced zone. In this paper, a recently-proposed method to design GRE walls is first recalled, where the wall is designed to trigger an internal plastic mechanism in the presence of strong earthquakes. Following a pseudo-static approach, the seismic coefficient k is therefore assumed equal to the internal seismic resistance of the wall kcint. The seismic coefficient is then calibrated against given seismic wall performance, expressed in terms of limit values of earthquake-induced displacements. Permanent displacements are evaluated through empirical relationships that were previously developed on the basis of a parametric integration of an updated Italian seismic database. Effectiveness of the proposed procedure is then demonstrated by assessing, through Finite Difference nonlinear dynamic analyses, the seismic performance of two walls, namely a GRE and a conventional gravity wall, characterised by the same seismic resistance but triggering an internal and external plastic mechanism, respectively. They are both subjected to a real strong motion, capable of activating a plastic mechanism. Results showed that lower permanent displacements are accumulated in the GRE wall where internal mechanisms are triggered

Cholangiocytes: Cell transplantation

Background:Due to significant limitations to the access to orthotropic liver transplantation, cell therapies forliver diseases have gained large interest worldwide.Scope of review:To revise current literature dealing with cell therapy for liver diseases. We discussed the ad-vantages and pitfalls of the different cell sources tested so far in clinical trials and the rationale underlying thepotential benefits of transplantation of human biliary tree stem cells (hBTSCs).Major conclusions:Transplantation of adult hepatocytes showed transient benefits but requires immune-sup-pression that is a major pitfall in patients with advanced liver diseases. Mesenchymal stem cells and hemato-poietic stem cells transplanted into patients with liver diseases are not able to replace resident hepatocytes butrather they target autoimmune or inflammatory processes into the liver. Stem cells isolated from fetal or adultliver have been recently proposed as alternative cell sources for advanced liver cirrhosis and metabolic liverdisease. We demonstrated the presence of multipotent cells expressing a variety of endodermal stem cell markersin (peri)-biliary glands of bile ducts in fetal or adult human tissues, and in crypts of gallbladder epithelium. Inthefirst cirrhotic patients treated in our center with biliary tree stem cell therapy, we registered no adverse eventbut significant benefits.General significance:The biliary tree stem cell could represent the ideal cell source for the cell therapy of liverdiseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by JesusBanales, Marco Marzioni, Nicholas LaRusso and Peter Jansen

Interazione dinamica terreno - struttura di pozzi di fondazione di pile di ponti e viadotti

Nella tesi si studia il comportamento dei pozzi di fondazione di pile da ponte soggetti a eventi sismici di elevata intensità. Dopo un’analisi critica degli studi disponibili nella letteratura scientifica viene studiata l’influenza del comportamento elasto - plastico dei terreni di fondazione sulla prestazione dell’opera, valutata in termini di valori massimi e permanenti degli spostamenti e delle rotazioni ottenuti durante e al termine dell’evento sismico. Nello specifico, viene svolto uno studio parametrico conducendo analisi accoppiate svolte, nel dominio del tempo e in condizioni tridimensionali, con il metodo degli elementi finiti. Nelle analisi, l’input sismico è costituito da storie temporali delle accelerazioni di eventi sismici reali. Il comportamento meccanico dei terreni di fondazione è descritto da un modello costitutivo elasto - plastico incrudente, al fine di ottenere una stima affidabile della risposta in campo non lineare e dello smorzamento isteretico. Le analisi dinamiche non drenate sono svolte in termini di tensioni efficaci. Viene valutata l’influenza di alcuni parametri chiave sulla prestazione del sistema, quali le dimensioni del pozzo e della pila, il contenuto in frequenza e la durata significativa dell’input sismico, l’effetto delle fasi costruttive del pozzo e la modellazione adottata per la sovrastruttura. Tutti i pozzi di fondazione sono caratterizzati dal medesimo valore del coefficiente di sicurezza al carico limite nelle condizioni statiche. Dalle analisi 3D sono stimati i valori del coefficiente sismico equivalente da utilizzare nelle verifiche condotte con il metodo pseudo – statico per valutare la sicurezza nei riguardi degli stati limite ultimi di tipo geotecnico della fondazione. Infine, viene valutata l’influenza dell’inerzia dei pozzi sulle proprietà dinamiche del sistema, mediante analisi modali svolte considerando la cedevolezza del sistema fondazione - terreno.In this thesis, the behaviour of bridge-pier caisson foundations subjected to high-intensity seismic events is studied. After a critical review of papers available in the scientific literature, the role of elasto-plastic soil behaviour on bridge performance is investigated, by evaluating maximum and permanent values of displacements and rotations attained during and at the end of the seismic event. Specifically, a parametric study is performed by carrying out finite element coupled dynamic analyses in the time domain and in three-dimensional conditions. Seismic input motions are applied at the bedrock depth in terms of real acceleration time histories. Soil behaviour is described by an elasto-plastic constitutive model with isotropic hardening, to get a fair estimate of nonlinear soil behaviour and hysteretic damping under cyclic loading conditions. The coupled dynamic analyses are carried out under undrained conditions in terms of effective stresses. The influence of several key factors on the performance of the system is addressed: piers and caisson foundations with varying dimensions are considered, as well as different seismic input motions characterised by different frequency content and significant duration but similar values of the Arias intensity; furthermore, the effect of caisson construction stages and of the model adopted for bridge piers on the performance of the system is evaluated. All caisson foundations are characterised by the same value of the static safety factor against bearing capacity, to evaluate the performance of the systems starting from the same initial conditions. From the results obtained by performing the 3D coupled dynamic analyses, the equivalent seismic coefficient to be used in a pseudo-static analysis to check the safety of bridge-pier caisson foundations against geotechnical ultimate limit states is evaluated; moreover, the effect of foundation mass on dynamic properties of the system is addressed through modal analyses carried out considering soil foundation compliance

Recent advances on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte pathophysiology

Cholangiocytes are epithelial cells lining the biliary epithelium. Cholangiocytes play several key roles in the modification of ductal bile and are also the target cells in chronic cholestatic liver diseases (i.e., cholangiopathies) such as PSC, PBC, polycystic liver disease (PCLD) and cholangiocarcinoma (CCA). During these pathologies, cholangiocytes (which in normal condition are in a quiescent state) begin to proliferate acquiring phenotypes of neuroendocrine cells, and start secreting different cytokines, growth factors, neuropeptides, and hormones to modulate cholangiocytes proliferation and interaction with the surrounding environment, trying to reestablish the balance between proliferation/loss of cholangiocytes for the maintenance of biliary homeostasis. The purpose of this review is to summarize the recent findings on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte pathophysiology. To clarify the mechanisms of action of these factors we will provide new potential strategies for the management of chronic liver diseases

The role of seismic intensity on the performance of caisson foundations supporting bridge piers: preliminary results from dynamic centrifuge

Seismic performance of caisson foundations supporting bridge piers may take advantage of soil inelastic response when subjected to strong seismic events, thanks to the soil nonlinear and hysteretic behaviour. This can bring to a substantial optimisation in caisson design and major cost savings. In the framework of Capacity Design extended to geotechnical systems, temporary attainment of plastic mechanisms may be permitted provided that the resulting permanent displacements are lower than given threshold values, which in turn depend on the considered limit state and performance level required to the structure. Clearly, this new design approach needs to be validated against physically-sound numerical and experimental simulations. A campaign of dynamic centrifuge tests was therefore recently carried out at the Schofield Centre, University of Cambridge, where the seismic performance of caisson foundations was assessed. In this paper, a preliminary interpretation of the experimental results is given, shedding some light on the interplay between seismic intensity and mechanical soil properties. Specifically, the results obtained in two tests are discussed, where a caisson-pierdeck system was subjected to earthquakes of increasing intensity. In the two tests, a soft and very soft clay layer was reproduced, to either avoid or promote the plastic soil behaviour. It is shown that the highly nonlinear and hysteretic response of the very soft clay limits the inertial forces transmitted to the superstructure, thus validating the above-mentioned design approach. The beneficial effect of inelastic soil behaviour entailed permanent displacements increasing with earthquake intensity, which should be checked against limit state prescriptions

Contribution of resident stem cells to liver and biliary tree regeneration in human diseases

Two distinct stem/progenitor cell populations of biliary origin have been identified in the adult liver and biliary tree. Hepatic Stem/progenitor Cells (HpSCs) are bipotent progenitor cells located within the canals of Hering and can be differentiated into mature hepatocytes and cholangiocytes; Biliary Tree Stem/progenitor Cells (BTSCs) are multipotent stem cells located within the peribiliary glands of large intrahepatic and extrahepatic bile ducts and able to differentiate into hepatic and pancreatic lineages. HpSCs and BTSCs are endowed in a specialized niche constituted by supporting cells and extracellular matrix compounds. The actual contribution of these stem cell niches to liver and biliary tree homeostatic regeneration is marginal; this is due to the high replicative capabilities and plasticity of mature parenchymal cells (i.e., hepatocytes and cholangiocytes). However, the study of human liver and biliary diseases disclosed how these stem cell niches are involved in the regenerative response after extensive and/or chronic injuries, with the activation of specific signaling pathways. The present review summarizes the contribution of stem/progenitor cell niches in human liver diseases, underlining mechanisms of activation and clinical implications, including fibrogenesis and disease progression

Intrahepatic cholangiocarcinoma: review and update

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies that could develop at any level from the biliary tree. CCA is currently classified into intrahepatic (iCCA), perihilar and distal on the basis of its anatomical location. Of note, these three CCA subtypes have common features but also important inter-tumor and intra-tumor differences that can affect the pathogenesis and outcome. A unique feature of iCCA is that it recognizes as origin tissues, the hepatic parenchyma or large intrahepatic and extrahepatic bile ducts, which are furnished by two distinct stem cell niches, the canals of Hering and the peribiliary glands, respectively. The complexity of iCCA pathogenesis highlights the need of a multidisciplinary, translational and systemic approach to this malignancy. This review will focus on the advances of iCCA epidemiology, histo-morphology, risk factors, molecular pathogenesis, revealing the existence of multiple subsets of iCCA

3D nonlinear dynamic Finite Element analysis of onshore wind turbines on pile foundation resting on liquefiable soils

The latest development of wind turbines in seismic areas, such as East Asia and Californian coast, has increased the importance of their seismic design. High-intensity ground motions can strongly affect serviceability of wind turbines due to earthquake-induced settlements and rotations. In the presence of loose, saturated sandy soils, liquefaction may also become a concern. In such circumstances cyclic soil behaviour needs to be carefully simulated by considering coupled u-p formulations. In this paper, the main results of fully-coupled Finite Element nonlinear dynamic 3D analyses are discussed, where a typical onshore wind turbine on a piled raft foundation resting on liquefiable soils, with piles penetrating into dense sand, is subjected to high-intensity motions triggering liquefaction. Soil behaviour was described through the constitutive model SANISAND. The numerical results were compared to those obtained through a reduced-scale model tested in the centrifuge available at University of Cambridge, thus providing useful insight on the efficacy and reliability of 3D numerical modelling of such systems, which is anticipated to become more and more common in the near future