Strongly coupled lattice gauge theory with dynamical fermion mass generation in three dimensions

We investigate the critical behaviour of a three-dimensional lattice \chiU\phi_3 model in the chiral limit. The model consists of a staggered fermion field, a U(1) gauge field (with coupling parameter $\beta$) and a complex scalar field (with hopping parameter $\kappa$). Two different methods are used: 1) fits of the chiral condensate and the mass of the neutral unconfined composite fermion to an equation of state and 2) finite size scaling investigations of the Lee-Yang zeros of the partition function in the complex fermion mass plane. For strong gauge coupling ($\beta < 1$) the critical exponents for the chiral phase transition are determined. We find strong indications that the chiral phase transition is in one universality class in this $\beta$ interval: that of the three-dimensional Gross-Neveu model with two fermions. Thus the continuum limit of the \chiU\phi_3 model defines here a nonperturbatively renormalizable gauge theory with dynamical mass generation. At weak gauge coupling and small $\kappa$, we explore a region in which the mass in the neutral fermion channel is large but the chiral condensate on finite lattices very small. If it does not vanish in the infinite volume limit, then a continuum limit with massive unconfined fermion might be possible in this region, too.Comment: 27 pages, 16 figure

Seismic response assessment and protection of statues and busts

Recent post-earthquake surveys carried out in Europe have shown that earthquake actions pose an immense threat to museums and their contents. For example, during the earthquake on 21 July 2017 in the island of Kos (Greece), severe and widespread damage on the city’s archaeological museum was reported (Figure 1). The earthquake extensively damaged the sculpture exhibition, where many pieces were dislocated, leaned against the walls, or overturned. Fortunately, the earthquake occurred when human visitors were not in the museum, since the damage to the exhibits varied from very light (minor fracturing) to severe (complete overturning and fracture of artefacts). In the case of heavy and slender sculptures, the overturning mechanism, apart from damaging the sculptures themselves, is a serious threat to other standing exhibits in the gallery and the visitors. It is, therefore, of paramount importance to have at our disposal methods and tools for characterising the seismic risk of museum artefacts and, where necessary, proposing cost-efficient protective measures. The study of the seismic vulnerability of museum artefacts, especially of slender, human-formed statues, is related to the research on the dynamic response of rocking rigid blocks. The dynamic characteristics of the hosting structures are also important. This is evident from the fact that, on many occasions, damage to the structure was reported leaving the exhibits intact and vice-versa. Although the problem is coupled, it can be studied looking separately at the structure and its contents, provided that the contents are not attached to the building. The seismic response of building contents is a topic of growing interest, since it is directly related to seismic loss assessment and earthquake community resilience. Building contents can be either attached to the structure, or may consist of objects that are simply standing. Museum exhibits belong to the latter category, while free-standing components are often studied as rocking objects and hence their response is sensitive to acceleration and velocity-based quantities and also to their geometry. Today, there is lack of standards, while the existing approaches are general in concept and do not sufficiently address the variety of rocking objects. The problem becomes more complicated when it comes to priceless objects such as museum artefacts where more refined and targeted studies are required for understanding their seismic response and also for proposing rapid tools for assessing their seismic risk. The paper presents an extensive experimental campaign on the seismic response of artefacts, with emphasis on statues and busts. The tests took place in the framework of SEREME project (Seismic Resilience of Museum Contents) at the AZALEE seismic simulator of CEA in Saclay, Paris under the auspices of the SERA project. The aim is to understand the seismic response of statues and busts and then develop novel and cost-effective risk mitigation schemes for improving the seismic resilience of museum valuable contents. The study is focused on the investigation of the seismic response of two real-scale marble roman statues and three busts of three roman emperors standing on pedestals of different types and size. Both isolated and non-isolated artefacts are considered, while two new and highly efficient base isolation systems, tailored to art objects, will be tested. The first isolator is a pendulum-based system, while the second utilizes Shape Memory Alloy wires. Furthermore, the paper examines the importance of the hosting building, i.e. building type and story. Specifically tailored, numerical models of varying complexity, for single and two-block rocking systems, were developed for the needs of this study and are also assessed against the experimental results

Rocking isolation of a typical bridge pier on spread foundation

It has been observed that after some earthquakes a number of structures resting on spread footings responded to seismic excitation by rocking on their foundation and in some cases this enabled them to avoid failure. Through application to a standard bridge supported by direct foundations, this paper discusses the major differences in response when foundation uplift is taken into consideration. Special focus is given on the modifications of rocking response under biaxial and tri-axial excitation with respect to uniaxial excitation. It is found that inelastic rocking has a significant isolation effect. It is also shown that this effect increases under biaxial excitation while it is less sensitive to the vertical component of the earthquake. Finally, parametric analyses show that the isolation effect of foundation rocking increases as the size of the footing and the yield strength of the underlying soil decreases

Engineering reconnaissance following the August 24, 2016 M6.0 Central Italy earthquake

An earthquake with a moment magnitude reported as 6.0 from INGV (Istituto Nazionale di Geofisica e Vulcanologia); occurred at 03:36 AM (local time) on 24 August 2016 in the central part of Italy. The epicenter was located at the borders of the Lazio, Abruzzi, Marche and Umbria regions, about 2.5 km north-east of the village of Accumoli and about 100 km from Rome. The hypocentral depth was about 8 km (INGV). We summarize preliminary findings of the Italy-US GEER (Geotechnical Extreme Events Reconnaissance) team, on damage distribution, causative faults, earthquake-induced landslides and rockfalls, building and bridge performance, and ground motion characterization. Our reconnaissance team used multidisciplinary approaches, combining expertise in geology, seismology, geomatics, geotechnical engineering, and structural engineering. Our approach was to combine traditional reconnaissance activities of on-ground recording and mapping of field conditions, with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. We anticipate that results from this study, will be useful for future post-earthquake reconnaissance efforts, and improved emergency respons

Superstructure-Piers-Foundation-Soil Interaction of an Arch Road Steel Bridge with Composite Deck

141 σ.Το αντικείμενο της παρούσας διπλωματικής εργασίας χωρίζεται σε δύο ενότητες: (α) το σχεδιασμό και τη διαστατιολόγηση του μεσοβάθρου και της θεμελίωσης με πασσάλους μιας οδικής, μεταλλικής, τοξωτής γέφυρας δύο αμφιέρειστων ανοιγμάτων με σύμμικτο κατάστρωμα και (β) τη διερεύνηση της καταπόνησης των μελών και της ευαισθησίας που παρουσιάζει όταν αναπτύσσονται μεγάλες παραμορφώσεις στη θεμελίωση του μεσοβάθρου, όπως αυτές που δημιουργούνται από τη ρευστοποίηση του εδάφους. Η υπό μελέτη γέφυρα έχει μήκος 42 m και πλάτος καταστρώματος 15 m. Ο σχεδιασμός του φορέα έχει ήδη υλοποιηθεί σε προηγούμενη διπλωματική, γι’ αυτό η παρούσα διπλωματική εργασία επικεντρώνεται στη διαστασιολόγηση του μεσοβάθρου και της θεμελίωσής του, τόσο σε επίπεδο προμελέτης όσο και σε επίπεδο οριστικής μελέτης. Γίνεται όμως διερεύνηση του ενδεδειγμένου τρόπου προσομοίωσης του σύμμικτου καταστρώματος. Επίσης, γίνεται διαστασιολόγηση των εφεδράνων και των αρμών. Στο δεύτερο μέρος της εργασίας γίνεται διερεύνηση, μέσω μη-γραμμικών αναλύσεων, των επιπτώσεων στην στατική επάρκεια της ανωδομής της εκδήλωσης μεγάλων μετακινήσεων και στροφών στη θεμελίωση του μεσοβάθρου. Σε αυτές τις αναλύσεις, τα ακρόβαθρα προσομοιάζονται με ισοδύναμα μεταφορικά και στροφικά ελατήρια και αμελούνται οι πάσσαλοι του μεσοβάθρου, αφού οι φορτίσεις που εξετάζονται αφορούν σε επιβαλλόμενες μετακινήσεις του κεφαλόδεσμου. Τα αποτελέσματα δείχνουν ότι η συγκεκριμένη γέφυρα μπορεί να αναλάβει χωρίς σημαντικά προβλήματα μεγάλες μεταφορικές μετατοπίσεις στη βάση του μεσοβάθρου, αλλά είναι αρκετά ευάλωτη σε επιβαλλόμενες στροφές του κεφαλόδεσμου, ιδιαίτερα γύρω από το διαμήκη άξονα της γέφυρας.The present diploma thesis consists of two parts: (a) the seismic design of the midpier and its pile foundation of a steel, arch road bridge consisting of two simply supported spans and composite deck; and (b) the investigation of the forces induced to the structural members and their sensitivity to large displacements/rotations developed at the foundation of the pier, like the ones caused due to liquefaction of the sub-soil. The length of the bridge under consideration is 42,00 m and the deck’s width is 15,00 m. The design of the deck has already been completed in a previous diploma thesis. For this reason, the present thesis focuses on the design of the pier and its foundation, first at the level of pre-design and then at the level of final design. However, an investigation on the most appropriate method of modeling the composite deck is also performed. Furthermore, the design of the bearings and the joints is performed. In the second part of the thesis, the effect of large displacements and rotations induced at the level of the foundation of the pier on the structural efficiency of the superstructure is investigated through non-linear analyses. In these analyses, the abutments are simulated with equivalent displacement and rotation springs and the piles of the midpier are neglected, since the displacements are applied directly on the pile cap. The results show that the bridge under consideration can sustain large displacements at the base of the pier without significant damage. However, the superstructure is quite vulnerable to imposed rotations of the pile cap, especially around the longitudinal axis of the bridge.Αντωνία Ι. Ψυχάρ