Evaluation of seismic hazard for the assessment of historical elements at risk : description of input and selection of intensity measures

The assessment of historical elements at risk from earthquake loading presents a number of differences from the seismic evaluation of modern structures, for design or retrofitting purposes, which is covered by existing building codes, and for the development of fragility curves, procedures for which have been extensively developed in the past decade. This article briefly discusses: the hazard framework for historical assets, including a consideration of the appropriate return period to be used for such elements at risk; the intensity measures that could be used to describe earthquake shaking for the analysis of historical assets; and available approaches for their assessment. We then discuss various unique aspects of historical assets that mean the characterisation of earthquake loading must be different from that for modern structures. For example, historical buildings are often composed of heterogeneous materials (e.g., old masonry) and they are sometimes located where strong local site effects occur due to: steep topography (e.g., hilltops), basin effects or foundations built on the remains of previous structures. Standard seismic hazard assessment undertaken for modern structures and the majority of sites is generally not appropriate. Within the PERPETUATE project performance-based assessments, using nonlinear static and dynamic analyses for the evaluation of structural response of historical assets, were undertaken. The steps outlined in this article are important for input to these assessments

Μη-γραμμική σεισμική αλληλεπίδραση εδάφους-θεμελίου-υψίκορμης κατασκευής

The dissertation provides theoretical and experimental support to the concept ofdeliberately seismically under-designing shallow foundations to invoke strong below-groundnonlinearity in the form of rocking, and thereby render RC structures safe under intenseseismic excitation. To this end,(I) A series of small-scale (1-g) and centrifuge tests are conducted investigating theperformance of elastic single bridge pier models supported on shallow foundations ofdifferent sizes. Static and seismic loading scenarios explore the potential benefits andlimitations of under-designed rocking foundations in comparison to conventionalalternatives. (II) A validated nonlinear numerical method is developed to provide further insights onthe different shallow foundation response mechanisms with emphasis on soil failure. Themethodology of Anastasopoulos et al. [2010] is incorporated and extended to account forscale effects in cohesionless soil. (III) For a realistic modelling of the nonlinear response of the superstructure, the novelsmall-scale physical model of Knappett et al [2011] is utilized and further developed tofabricate 1:50 scaled replicas of well-confined modern RC bridge piers. A total of 26 suchpiers were constructed. The validity of their response was verified by a number of 4-pointbending tests. (IV) Four shaking table centrifuge tests investigate and compare the performance of twoRC model bridge piers, having the same structural section in each case, but with twodifferent foundation designs — a conventional design and a rocking isolation design. Eachalternative is tested under two different seismic loading scenarios, where the sequence ofreal ground motions was imposed at the soil model base in such an order as to allow alsoinvestigation of the effect of the exact seismic history. (V) To improve rocking isolation design so as to avoid large foundation settlements, anadditional set of 9 centrifuge tests (4 static and 5 dynamic) are conducted involving severalhybrid foundation schemes. In these schemes the shallow rocking footing is suitably“strengthened” by geometrical modifications or various means of soil improvement: (i) avariable–geometry foundation, whose small rocking stiffness and capacity increase withfoundation rotation after some threshold angle; (ii) a rocking-isolated footing standing ontop of an appropriately designed “cofferdam”, which provokes uplifting by hindering theformation of bearing capacity failure mechanisms under the footing; (iii) combineddensification with a 2 x 2 group of unconnected piles (one under each foundation corner);and (iv) a grid of micro-pile inclusions. The results demonstrate the virtues of rocking-isolation shallow foundations, which stemfrom: (i) reducing accelerations transmitted onto the deck; (ii) increasing system ductility; (iii) limiting permanent deck drifts; and (iv) increasing resistance against damageaccumulation in successive earthquakes. Yet, these tests also highlight the main drawback ofrocking isolation. That is, the so called “sinking response”, or in other words the gradualaccumulation of settlement caused by strongly inelastic soil behaviour. The four newconcepts for improving the performance of rocking foundations that were introduced andtested in this dissertation prove capable of ameliorating this drawback while retaining thebenefits of rocking isolation.Αντικείμενο της διδακτορικής διατριβής είναι η θεωρητική και πειραματική τεκμηρίωση της ιδέας της σεισμικής μόνωσης κατασκευών εξ ωπλισμένου σκυροδέματος μέσω της εκούσιας υπο-διαστασεολόγησης της θεμελίωσης η οποία θα επιφέρει μή γραμμική συμπεριφορά του συστήματος εδάφους-θεμελιώσεως με αποτέλεσμα τη λικνιστική απόκριση της κατασκευής. Στην κατεύθυνση αυτήν εκτελέστηκαν οι παρακάτω εργασίες: (I) Πειράματα μικρής κλίμακας σε 1-g και φυγοκεντριστή στα οποία διερευνήθηκε η συμπεριφορά ελαστικού βάθρου θεμελιωμένου επί επιφανειακών πεδίλων διαφόρων μεγεθών. Επιβλήθηκαν τόσο δυναμικές όσο και στατικές φορτίσεις ώστε να εξεταστούν τα πιθανά οφέλη των υπο-διαστασεολογημένων θεμελιών σε σχέση με τα συμβατικώς σχεδιασμένα. (II) Αναπτύχθηκε και τεκμηριώθηκε μή-γραμμική αριθμητική μεθοδολογία που χρησιμοποιήθηκε για την εμβάθυνση στους μηχανισμούς απόκρισης επιφανειακών θεμελίων με έμφαση σε περιπτώσεις εδαφικής αστοχίας. Στα ανωτέρω ενσωματώθηκε η μεθοδολογία των Anastasopoulos et al. [2010] η οποία επεκτάθηκε ώστε να λαμβάνει υπόψιν φαινόμενα μικρής κλίμακας σε μη συνεκτικό έδαφος. (III) Για την ρεαλιστική προσομοίωση της μή γραμμικής απόκρισης της ανωδομής υιοθετήθηκε η πρωτοποριακή διαδικασία των Knappett et al [2011] η οποία επεκτάθηκε ώστε, με βάση αυτή, να κατασκευαστούν πειραματικά ομοιώματα σύγχρονων βάθρων γεφυρών σε κλίμακα 1:50. Κατασκευάστηκαν 26 ομοιώματα, ενώ η τεκμηρίωση της ορθότητας της προσομοίωσης πραγματοποιήθηκε μέσω δοκιμών καμπτικής φόρτισης 4 σημείων. (IV) Εκτελέστηκαν 4 πειράματα φυγοκεντριστή στα οποία συγκρίθηκε η σεισμική συμπεριφορά δύο ζευγών βάθρων γεφυρών θεμελιωμένων επί συμβατικού ή υπο-διαστασεολογημένου επιφανειακού πεδίλου. Σε κάθε περίπτωση εξετάστηκαν δύο σενάρια φόρτισης επιβάλλοντας τη διέγερση στη βάση της εδαφικής στήλης ώστε να διερευνηθεί η επιρροή της αλληλουχίας των σεισμικών γεγονότων. (V) Προκειμένου να διερευνηθούν τρόποι περαιτέρω βελτίωσης της συμπεριφοράς των σεισμικώς μονωμένων –μέσω λικνιστικής απόκρισης του θεμελίου- συστημάτων, εκτελέστηκαν επιπλέον 9 δοκιμές φυγοκνετριστή (4 υπό στατική και 5 υπό δυναμική φόρτιση). Στόχος των εν λόγω πειραμάτων ήταν η πρόταση υβριδικών θεμελίων τα οποία θα εξασφαλίζουν μεν τη λικνιστική απόκριση χωρίς όμως να συσσωρεύουν καθιζήσεις. Για τον σκοπό αυτόν προτάθηκαν οι εξής μέθοδοι “αναβάθμισης”: (i) πέδιλο μεταβλητής γεωμετρίας του οποίου η λικνιστική δυσκαμψία και αντοχή αυξάνει έπειτα από μία δεδομένη τιμή της στροφής (ii) σεισμικώς μονωμένο πέδιλο επί καταλλήλως εγκιβωτισμένου εδάφους το οποίο περιορίζει τη δυνατότητα εδαφικής αστοχίας τύπου φέρουσας ικανότητας εξαναγκάζοντας το θεμέλιο σε λικνιστική απόκριση (iii) συνδυασμός συμπύκνωσης με ομάδα 2 x 2 ασύνδετων πασσάλων (ένας σε κάθε γωνία του θεμελίου); και (iv) κάνναβος μικροπασσάλων. Τα αποτελέσματα της έρευνας επιβεβαιώνουν τα οφέλη της λικνιστικής απόκρισης ως μέσου σεισμικής μόνωσης κατασκευών τα οποία συνοψίζονται ως: (i) μείωση της σειμικής επιτάχυνσης που μεταδίδεται στην ανωδομή; (ii) ενίσχυση της πλαστιμότητας του συστήματος; (iii) περιορισμός της μόνιμης (μή-αναστρέψιμης) μετακίνησης στο κατάστρωμα ; και (iv) περιορισμός της συσσώρευσης βλαβών λόγω διαδοχικών σεισμικών γεγονότων. Ταυτοχρόνως, αναδείχθηκαν τα κύρια μειονεκτήματα του εν λόγω σχεδιασμού, το κυρίαρχο εκ των οποίων είναι η σταδιακή συσσώρευση καθιζήσεων κατά τον λικνισμό λόγω της μή-γραμμικής εδαφικής συμπεριφοράς. Εντούτοις, τα αποτελέσματα των δοκιμών ανέδειξαν τα προαναφερθέντα υβριδικά συστήματα ως ικανά να διατηρήσουν τα οφέλη της λικνιστικής απόκρισης περιορίζοντας δραστικά τη συσσώρευση των καθιζήσεων

Restoration models for quantifying flood resilience of bridges

[Display omitted]•Novel traffic reinstatement and capacity restoration models for scour-damaged bridges.•Standardisation of damage per bridge component and functionality of scoured bridges.•High uncertainty in restoration task duration, dependencies and overlaps.•Duration of restoration tasks is twice the duration of functionality reinstatement.•Recovery models validated based on documented cases of scoured bridges.Bridges are the most vulnerable assets of our transport networks. They are disproportionately exposed to and hit by multiple natural hazards, with flooding being the leading cause of bridge failures in the world. Their performance is constantly challenged by the combined effects of natural hazard stressors, e.g. flash floods, exacerbated by climate change, ageing, increasing traffic volumes and loads. Bridges are vulnerable to scour and other flood-related impacts, such as hydraulic forces and debris accumulation. In order to assess and quantify the resilience of flood-critical bridges and subsequently deploy bridge resilience models aiming at building resilience into transport networks, it is essential to use reliable fragility, capacity restoration and traffic reinstatement metrics and models. It is surprising that, despite the importance of bridges and their high vulnerability to hydraulic actions, there are no available recovery models. The latter can help quantify the pace of post-flood capacity and functionality gain for facilitating well-informed decision making for reliable prioritisation and efficient allocation of resources in transport networks. The main barrier is the nature and complexity of recovery actions, which encompass engineering, operational, owner resources and organisational challenges, among others. This paper, for the first time in the international literature, aims at filling this gap by generating a set of reliable recovery models that include both bridge reinstatement (traffic capacity) and restoration (structural capacity) models based on a detailed questionnaire that elicits knowledge from experts. Recovery models are then presented and validated for spread and deep foundations for a typical reinforced concrete bridge, including restoration task prioritisation and scheduling, inter-task dependencies, idle times, durations and cost ratios for different damage levels, as well as the evolution of traffic capacity after floods

Caisson Foundations Subjected to Reverse Fault Rupture: Centrifuge Testing and Numerical Analysis

Numerous failures induced by surface faulting have been witnessed in recent large magnitude (M > 7) earthquakes, demonstrating the need to account for tectonic deformation in seismic design. Thanks to their usually-high rigidity, embedded (e.g. caisson) foundations may divert the fault rupture, thus leading to favourable performance, where surface or piled foundations may fail. This paper presents a series of centrifuge model tests undertaken to investigate the response of caisson foundations embedded in a cohesionless soil stratum, the base of which is subjected to reverse faulting. The interplay between the propagating fault rupture and the caisson is elucidated, focusing on the role of the location of the outcropping rupture relative to the caisson. The rigid-body of the caisson is shown to cause diversion and/or bifurcation of the shear localisation, which is forced to develop preferentially around the edges of the caisson. The observed failure pattern and the consequent caisson response depend strongly on the exact caisson position relative to the fault. Three dimensional FE modelling was employed and validated through comparison with centrifuge test results. The numerical method is shown to capture the general interaction mechanisms, showing satisfactory (if not always perfect) agreement with experiments. The validated numerical method is then employed in a parametric investigation, providing further insight into the different possible modes of foundation respons

Flood damage inspection and risk indexing data for an inventory of bridges in Central Greece

This dataset is related to the research paper entitled “Bridge-specific flood risk assessment of transport networks using GIS and remotely sensed data” published in the Science of the Total Environment. It provides the information necessary for the reproduction of the case study that was used for the demonstration and validation of the proposed risk assessment framework. The latter integrates indicators for the assessment of hydraulic hazards and bridge vulnerability with a simple and operationally flexible protocol for the interpretation of bridge damage consequences on the serviceability of the transport network and on the affected socio-economic environment. The dataset encompasses (i) inventory data for the 117 bridges of the Karditsa Prefecture, in Central Greece, which were affected by a historic flood that followed the Mediterranean Hurricane (Medicane) Ianos, in September 2020; (ii) results of the risk assessment analysis, including the geospatial distribution of hazard, vulnerability, bridge damage, and associated consequences for the area's transport network; (iii) an extensive damage inspection record, compiled shortly after the Medicane, involving a sample of 16 (out of the 117) bridges of varying characteristics and damage levels, ranging from minimal damage to complete failure, which was used as a reference for validation of the proposed framework. The dataset is complemented by photos of the inspected bridges which facilitate the understanding of the observed bridge damage patterns. This information is intended to provide insights into the response of riverine bridges to severe floods and a thorough base for comparison and validation of flood hazard and risk mapping tools, potentially useful for engineers, asset managers, network operators and stakeholders involved in decision-making for climate adaptation of the road sector