The effect of preloading on the strength of jacketed R/C columns

The influence of core preloading on the strength of jacketed reinforced concrete (R/C) columns is analytically investigated. A recently proposed method for arbitrary composite section analysis in biaxial bending and axial load is extended to include preloading actions. A parametric evaluation of the preloading effect using quantitative indices is performed, considering the variability of several parameters such as section geometry, amount of reinforcement, and various axial and moment preloading levels. Results are presented in the form of 3D failure surfaces and moment-curvature curves. Specific cases where the preloading effect is more pronounced are finally highlighted

Bridge-specific fragility analysis: when is it really necessary?

In seismic assessment of bridges the research focus has recently shifted on the derivation of bridge-specific fragility curves that account for the effect of different geometry, structural system, component and soil properties, on the seismic behaviour. In this context, a new, component-based methodology for the derivation of bridge-specific fragility curves has been recently proposed by the authors, with a view to overcoming the inherent difficulties in assessing all bridges of a road network and the drawbacks of existing methodologies, which use the same group of fragility curves for bridges within the same typological class. The main objective of this paper is to critically assess the necessity of bridge-specific fragility analysis, starting from the effect of structure-specific parameters on component capacity (limit state thresholds), seismic demand, and fragility curves. The aforementioned methodology is used to derive fragility curves for all bridges within an actual road network, with a view to investigating the consistency of adopting generic fragility curves for bridges that fall within the same class and quantifying the degree of over- or under-estimation of the probability of damage when generic bridge classes are considered. Moreover, fragility curves for all representative bridges of the analysed concrete bridge classes are presented to illustrate the differentiation in bridge fragility for varying structural systems, bridge geometry, total bridge length and maximum pier height. Based on the above, the relevance of bridge-specific fragility analysis is assessed, and pertinent conclusions are drawn

Soil-structure interaction effects in analysis of seismic fragility of bridges using an intensity-based ground motion selection procedure

The paper focuses on the effects of Soil-Structure Interaction (SSI) in seismic fragility analysis of reinforced concrete (RC) bridges, considering the vulnerability of multiple critical components of the bridge and different modelling approaches for soil-foundation and bridge-embankment interactions. A two-step procedure, based on the introduction of springs and dashpots at the pier foundations and the abutment to account for inertial and kinematic SSI effects, is incorporated into a component-based methodology for the derivation of bridge-specific fragility curves. The proposed methodology is applied for quantifying the fragility of a typical highway overpass at both the component and system level, while the effect of alternative procedures (of varying complexity) for modelling foundation and abutment boundary conditions is critically assessed. The rigorous SSI modelling method is compared with simpler methods and the results show that consideration of SSI may only slightly affect the probability of system failure, depending on the modelling assumptions made. However, soil-structure interaction may have a notable effect on component fragility, especially for the more critical damage states. This is an observation that is commonly overlooked when assessing the structural performance at the system level and can be particularly important when component fragility is an issue, e.g. when designing a retrofit scheme

Structure-specific Fragility Curves for As-Built and Retrofitted Bridges

The main objective of the present thesis, titled “Structure-specific Fragility Curves for As- Built and Retrofitted Bridges”, is the development of a new methodology for the derivation of bridge-specific fragility curves, with a view to improving the reliability of loss assessment in road networks and prioritizing retrofit of the bridge stock. The key features of the proposed methodology (different approach according to the desired accuracy level) are the explicit definition of critical limit state thresholds for individual bridge components, with consideration of the effect of varying geometry, material properties, reinforcement and loading patterns on the component capacity; the methodology also includes the quantification of uncertainty in capacity, demand, and damage state definition. Advanced analysis methods and tools (nonlinear static analysis and incremental dynamic response history analysis) are used for bridge component capacity and demand estimation, while reduced sampling techniques are used for uncertainty treatment. Whereas uncertainty in both capacity and demand is estimated from nonlinear analysis of detailed inelastic models, in practical application to bridge stocks the demand is estimated through a standard response spectrum analysis of a simplified elastic model of the bridge. The simplified methodology can be efficiently applied to a large number of bridges (with different characteristics) within a road network, by means of an ad-hoc developed software involving the use of a generic (elastic) bridge model, that derives bridge-specific fragility curves. The backbone of the proposed methodology is the development of a database, including critical bridge components and a variety of geometric, material, reinforcement and loading patterns, in order to explicitly define the case-dependent component capacity and limit state thresholds. The inherent correlation of component properties and limit state thresholds is fully recognised; therefore empirical relationships for as-built and retrofitted components are proposed to quantify component capacity limits for different performance levels in terms of global engineering demand parameters (local to global damage correlation), considering different boundary conditions (pier-to-deck connection) and failure modes. Furthermore, component demand for different levels of earthquake intensity is calculated based on either a detailed inelastic or a simplified elastic model, and multiple stripe (enhanced IDA) or response spectrum analysis, respectively, according to the desired level of accuracy and computational cost (related to whether a single bridge or a bridge stock is addressed). Component fragility is then calculated and is used to estimate system fragility (entire bridge), assuming series connection between components. Finally, in the frame of the proposed methodology, the uncertainty in demand, component capacity, and limit state definition are explicitly defined for every component and limit state, while a total uncertainty value is also proposed for different bridge types. The approximate methodology is applied to a bridge stock, while the detailed methodology is applied to representative as-built and retrofitted bridges in order to compare fragility estimates and reveal the effectiveness of different retrofit measures.Βασικό στόχο της παρούσας διατριβής με τίτλο «Εξατομικευμένες Καμπύλες Σεισμικής Τρωτότητας για Γέφυρες με και χωρίς Επεμβάσεις» αποτελεί η πρόταση μίας νέας μεθοδολογίας υπολογισμού εξατομικευμένων καμπυλών τρωτότητας γεφυρών με σκοπό την πλέον αξιόπιστη αποτίμηση της σεισμικής διακινδύνευσης οδικού δικτύου και εκτίμησης απωλειών, καθώς και την ανάδειξη προτεραιοτήτων ενίσχυσης μεταξύ των γεφυρών του οδικού δικτύου. Βασικό άξονα της προτεινόμενης μεθοδολογίας, η οποία διαφοροποιείται ανάλογα με την κλίμακα του προβλήματος (λεπτομερής και αδρομερής), αποτελεί ο προσδιορισμός τιμών κατωφλίων σταθμών βλάβης των επιμέρους συνιστωσών λαμβάνοντας υπόψη την επιρροή των επιμέρους διαφορετικών δομικών και γεωμετρικών χαρακτηριστικών στον υπολογισμό της διαθέσιμης αντίστασης, καθώς και η ποσοτικοποίηση των αβεβαιοτήτων στη διαθέσιμη αντίσταση, τη σεισμική απαίτηση και τον ορισμό των σταθμών βλάβης. Προηγμένα υπολογιστικά εργαλεία και μέθοδοι ανάλυσης χρησιμοποιούνται κατά την εφαρμογή της λεπτομερούς μεθόδου και την ποσοτικοποίηση των αβεβαιοτήτων, ενώ για τον προσδιορισμό αξιόπιστου στατιστικά δείγματος και τη διενέργεια αναλύσεων, εφαρμόζεται η στρωματοποιημένη μέθοδος δειγματοληψίας LHS. Για την εφαρμογή της μεθοδολογίας σε απόθεμα γεφυρών οδικού δικτύου, χρησιμοποιείται η αδρομερής προσέγγιση, κατά την οποία η σεισμική απαίτηση υπολογίζεται στα σημεία ελέγχου των κρίσιμων συνιστωσών με βάση το τρισδιάστατο απλοποιητικό προσομοίωμα και τα αποτελέσματα δυναμικής φασματικής ανάλυσης. Για το σκοπό αυτόν αναπτύσσεται λογισμικό, στο οποίο ενσωματώνεται όλη η διαδικασία υπολογισμού διαθέσιμης αντίστασης, σεισμικής απαίτησης, καθώς και οι σχετικές αβεβαιότητες για τον υπολογισμό εξατομικευμένων καμπυλών τρωτότητας. Για τον προσδιορισμό εξατομικευμένων τιμών κατωφλίων βλάβης, καταστρώνεται βάση δεδομένων κρίσιμων συνιστωσών θεωρώντας μεταβαλλόμενες παραμέτρους γεωμετρίας, ποιότητας υλικών, όπλισης και φόρτισης. Πραγματοποιούνται ανελαστικές αναλύσεις παραμετρικά ορισμένων συνιστωσών της βάσης δεδομένων και, με στατιστική επεξεργασία των αποτελεσμάτων, προσδιορίζονται οι εμπειρικές σχέσεις υπολογισμού τιμών κατωφλίων για όλες τις στάθμες βλάβης, αναγνωρίζοντας τη συσχέτιση κρίσιμων για την αντισεισμική συμπεριφορά παραμέτρων και αναπτυσσόμενων βλαβών. Οι εμπειρικές σχέσεις υπολογισμού τιμών κατωφλίων προσδιορίζονται για βάθρα με και χωρίς ενισχύσεις, συσχετίζοντας την καθολική παράμετρο βλάβης (μετακίνηση σημείου ελέγχου) με τοπικές παραμέτρους βλάβης (καμπυλότητα κρίσιμης διατομής), ενώ λαμβάνονται υπόψη διαφορετικές πιθανές μορφές αστοχίας (καμπτική, διατμητική) καθώς και η επιρροή των διαφορετικών συνοριακών συνθηκών. Σε ό,τι αφορά στον υπολογισμό της σεισμικής απαίτησης για διάφορες στάθμες σεισμικής έντασης, χρησιμοποιείται η λεπτομερής ή αδρομερής μεθοδολογία ανάλογα με τον επιθυμητό βαθμό ακρίβειας, ήτοι η διενέργεια ανελαστικής (τροποποιημένης) δυναμικής μικροαυξητικής ανάλυσης στο πλήρες τρισδιάστατο αριθμητικό προσομοίωμα ή ελαστικής δυναμικής φασματικής ανάλυσης στο αδρομερές τρισδιάστατο αριθμητικό προσομοίωμα. Ο προσδιορισμός της σεισμικής τρωτότητας του συστήματος της γέφυρας, πραγματοποιείται θεωρώντας σύνδεση των επιμέρους κρίσιμων συνιστωσών σε σειρά. Με βάση τις επιμέρους αβεβαιότητες στη διαθέσιμη αντίσταση, τη σεισμική απαίτηση και ορισμό σταθμών βλάβης, υπολογίζεται ο συνολικός συντελεστής αβεβαιότητας (κοινός για γέφυρες της ίδιας κατηγορίας, σύμφωνα με τα αποτελέσματα ανάλυσης τυπικής γέφυρας της κατηγορίας). Τόσο η αδρομερής όσο και η λεπτομερής προτεινόμενη μέθοδος για τον υπολογισμό της σεισμικής απαίτησης εφαρμόζονται στο πλαίσιο σεισμικής αποτίμησης αποθέματος γεφυρών οδικού δικτύου και μεμονωμένων γεφυρών, αντίστοιχα, ενώ πραγματοποιείται και σύγκριση των αποτελεσμάτων σεισμικής τρωτότητας που προκύπτουν. Στο πλαίσιο της διατριβής, η προτεινόμενη μεθοδολογία εφαρμόζεται σε υφιστάμενες αλλά και σε ενισχυμένες (με διαφορετικές μεθόδους) γέφυρες, με στόχο την ανάδειξη της αποτελεσματικότητας της εκάστοτε μεθόδου ενίσχυσης μέσω της επιρροής της στη σεισμική τρωτότητα για διάφορες στάθμες βλάβης

Developments in Seismic Vulnerability Assessment of Tunnels and Underground Structures

Underground structures are being constructed at an increasing rate in seismic prone areas, to facilitate the expanding needs of societies. Considering the vital role of this infrastructure in densely populated urban areas and interurban transportation networks, as well as the significant losses associated with potential seismically induced damage, its assessment against seismic hazard is of great importance for stakeholders, operators, and governmental bodies. This paper presents a state-of-the-art review of current developments in the assessment of seismic vulnerability of tunnels and underground structures. Methods for the development of fragility functions for the assessment of bored tunnels in rock or alluvial, and cut and cover tunnels and subways in alluvial, against ground seismic shaking and earthquake-induced ground failures are presented. Emphasis is placed on the estimation of the capacity of the examined structures, the selection of appropriate intensity measures to express seismic intensity, the development of rational probabilistic seismic demand models and the estimation of epistemic and aleatoric uncertainties, related to the seismic fragility of underground structures. Through the discussion, acknowledged gaps in the relevant literature are highlighted

Seismic Fragility Curves of RC Buildings Subjected to Aging

A large number of existing reinforced concrete (RC) buildings have surpassed their anticipated service life and show signs of degradation due to aging; this degradation is a function of the construction practices adopted in the past as well as environmental conditions. This paper discusses seismic fragility and the risk assessment of RC structures, emphasizing the impact of corrosion due to concrete aging and the associated deterioration mechanisms. The literature on this topic is critically reviewed, and a methodology for studying the seismic fragility of deteriorated RC buildings is proposed. As a case study, a four-story RC building designed according to contemporary code provisions is examined. The investigation encompasses the derivation of fragility curves, considering critical parameters such as the corrosion rate, the initiation time, and the cover depth. The proposed approach enables the evaluation and quantification of the impact of corrosion mechanisms on the seismic performance of buildings

Seismic resilience of interdependent built environment for integrating structural health monitoring and emerging technologies in decision-making

The functionality of interdependent infrastructure and resilience to seismic hazards have become a topic of importance across the world. The ability to optimize an engineered solution and support informed decisionmaking is highly dependent on the availability of comprehensive datasets and requires substantial effort to ingest into community-scale models. In this paper, a comprehensive seismic resilience modeling methodology is developed, with detailed multi-disciplinary datasets, and is explored using the state-of-the-science algorithms within the Interdependent Networked Community Resilience Modeling Environment (IN-CORE). The methodology includes a six-step chained/linked process consists of 1) community data and information, 2) spatial seismic hazard analysis using next-generation attenuation, 3) interdependent community model development, 4) physical damage and functionality analysis, 5) socio-economic impact analysis and 6) structural health monitoring (SHM) and emerging technologies (ET). An illustrative case study is presented to demonstrate the seismic functionality and resilience assessment of Shelby County in Memphis, Tennessee, in the United States. From the results discussion, it is then concluded that data from structural health monitoring and emerging technologies is a viable approach to enhance characterising the seismic hazard resilience of infrastructure, enabling rapid and in-depth understanding of structural behaviour in emergency situations. Moreover, considering the momentum of the digitalization era, setting a holistic framework on resilience, which includes SHM and ET, will allow reducing uncertainties that still a challenge to quantify and propagate, supported by sequential updating techniques from Bayesian statistics