Characterisation of an urban bridge portfolio and multi-risk prioritisation accounting for deterioration and seismic vulnerability

This contribution proposes a procedure to prioritise retrofit interventions on stocks of bridges according to their seismic vulnerability. The procedure also combines a previously presented approach to evaluate deterioration effects on bridges at a territorial scale. Thereby, the combi-nation of the two approaches provides a multi-risk classification method for bridge stocks. This method also allows refined prioritisation within each class, based on the proposed quantitative indices and on multicriteria decision-making methods. The method was applied to the bridge stock managed by the municipality of Padova, in North-East Italy. First, an extensive charac-terisation of the analysed stock is provided, according to typological, geometric, and structural parameters. Then, the application of the combined approach is presented, highlighting which bridge types resulted more vulnerable to either seismic actions or deterioration effects

A new combined approach to prioritise seismic retrofit interventions on stocks of r.c. school buildings

This paper presents a prioritisation procedure to rank reinforced concrete (r.c.) buildings that are part of a stock according to their seismic vulnerability, and to plan further verifications and retrofit interventions. The proposed approach is based on visual inspections, qualitative evaluation, and quantitative assessment. The qualitative evaluation is based on a new deficiency form, here presented, whereas the quantitative assessment is carried out through a simplified mechanical model, which provides a ratio of capacity to demand. This work thus proposes a combination of the qualitative and quantitative approaches aimed at prioritisation. In this way, specific limitations of each approach are overcome through the combination. The proposed procedure was applied to the r.c. school building asset managed by the municipality of Padova (Italy). After describing the main characteristics of the inspected stock, the paper discusses the most commonly observed vulnerability factors and the application of the procedure. The qualitative and quantitative approaches integrated each other quite well and showed a general good agreement

Application to an urban bridge stock of a prioritization procedure based on seismic assessment compared with the novel Italian guidelines

The challenge of large-stock maintenance with limited budget is faced by administrations in charge which need tools for management and intervention prioritization. This need is especially perceived for bridges which are strategic structures and represent crucial elements in roadway networks. Since 2016, a combined prioritization procedure has been applied to the bridge stock of the Municipality of Padova (Italy) to assess both the condition state, accounting for degradation, and the seismic vulnerability. The proposed methodology evaluates the level of degradation through visual inspections and type-specific forms for the defect survey, while the seismic vulnerability is assessed by means of fragility curves previously obtained by the authors for typical Italian bridges. This contribution focuses on the application of the seismic-based prioritization. The identification of the bridge typologies which appeared to be more seismically fragile is presented, comparing this aspect with results from the recently issued novel Italian Guidelines for the management of existing bridges

Modeling strategies for non-linear seismic analyses: Comparison among EFM and FEM results on an existing URM case study

Italian building heritage is widely composed of masonry buildings, whose characteristics largely vary depending on geographical location, construction techniques and materials typology. This type of structures has shown a high vulnerability to horizontal loads that must not be ignored, especially due to the high seismic hazard of Italian territory. Hence, appropriate numerical models are required to assess the complex structural behavior of unreinforced masonry (URM) existing structures, implementing the non-linear behavior of both materials and structure. In this framework, two different approaches have been widely acknowledged: the Equivalent Frame Model (EFM) and the continuum Finite Element Model (FEM). This paper presents the application and comparison of these modeling strategies to an URM building dating back to XVII century, located in the Italian Alpine region (Roana, Vicenza). Non-linear static analyses were carried out by means of the software 3Muri (EFM), DIANA FEA and Midas FEA-NX (FEM). Results were compared in terms of ultimate resistance, capacity, ductility, and evolution of the damage state. Finally, assessment of the global behavior was carried out according to the Italian seismic code, pointing out the differences of the two approaches. Results showed that the EFM appears to be more conservative than FEM

RC tied-arch bridges: Typological analysis for the definition of retrofit interventions

The Italian bridge asset is characterized by aged structures, most of which made of reinforced concrete, needing retrofit interventions to improve both their seismic performance and load-bearing capacity towards the increased traffic volume. In order to provide a series of guidelines for retrofit, a research project, carried out by the ReLUIS consortium supported by the Italian Department of Civil Protection, aims to identifying typological deficiencies and vulnerability of the main type of bridges widespread on the Italian territory, defining typological interventions. This paper presents the outcomes of the ongoing research focusing on RC tied-arch bridges, frequently built in the period between the two world wars. A typological study was carried out to define the main design deficiencies and construction details, and how degradation acts on this type of bridge, besides the main structural vulnerability to both gravitational and seismic loads. Numerical and parametrical analyses were carried out on a representative prototype tied-arch bridge with RC hangers, dating back to 1930s. The structural behavior was assessed by means of numerical analysis on FEM models, allowing the evaluation of the static and seismic capacity, the definition of the most vulnerable elements, and thus, the identification of the most suitable type of retrofit interventions

Fragility assessment of the Italian masonry school building asset for risk evaluation at national scale

Seismic risk and scenario assessments at large-scale provide important science-based tools to support governments and civil protection departments in investment policies and emergency planning. In this framework, school buildings are particularly significant due to the consequences of their damage or collapse and their relevance, as public buildings, in emergency planning. The evaluation of risk requires the definition of its components, i.e., hazard, exposure and vulnerability. To assess the seismic vulnerability of masonry school building assets, this paper presents the fragility curves derived for 265 building types, based on the Italian school building census. Parametric analyses were carried out on 14 representative prototype schools, using a mechanics-based model which considers both in-plane and out-of-plane mechanisms. More than 7500 sample fragilities were calculated and linearly combined to obtain fragility curves representing the Italian taxonomy of masonry school buildings. A macro-seismic heuristic model from the literature was then calibrated to derive a fragility set for each school type, for five damage states, from slight damage to complete collapse. Finally, the paper compares the outcome fragility curves and fragility sets from the literature for residential buildings, highlighting the specificities of school seismic vulnerability. Indeed, masonry school buildings are frequently characterized by intrinsic geometric deficiencies due to significant inter-story height and great distance between transverse walls, both affecting the out-of-plane response and, therefore, the overall seismic fragility

Seismic strengthening of existing URM structures through CLT elements: Numerical analysis of the application of a novel intervention technique

The retrofit of existing masonry buildings plays a relevant role in the Italian building context, both for preservation and requalification of the cultural and architectural heritage. Historically, timber has been widely used in unreinforced masonry (URM) buildings, mainly for horizontal structures. In recent years, the use of timber in the retrofit of existing buildings has gained an increasing interest for the improvements of both structural and energetic performances. Indeed, wooden elements present good hygrothermal properties and, thanks to their lightweight and stiffness, they are suitable for the seismic improvement of masonry buildings. The aim of this paper is to numerically investigate the seismic strengthening of existing URM structures by means of cross laminated timber (CLT) panels, evaluating the coupling degree of the timber-masonry integrated system. The investigation was carried out through a finite element modelling. First a parametric local model of a CLT-masonry coupled wall was calibrated with literature experimental data. Then, the study was extended to a XVII-century URM building located in the Italian Alpine region (Roana, Vicenza province). Non-linear static analyses were carried out in order to assess the local and global behavior of the URM-CLT system and its potential benefits. Results suggested a seismic capacity improvement due to shear strength increase and global weight reduction

Comparative study on two analytical mechanical-based methods for deriving fragility curves targeted to masonry school buildings

Seismic events across several countries in the world have highlighted that strategic buildings, such as schools, may exhibit vulnerability levels that are in some cases higher than those of ordinary buildings. It follows the urgent need of reliable risk analyses to support the decision-making for large-scale mitigation policies. To this aim, the derivation of fragility curves, able to capture typological and constructive characteristics, constitutes an essential requisite. Within this context, the paper presents a comparative study on the use of two analytical-mechanical based methods for assessing fragility curves of Italian masonry school buildings. These are very often characterized by a number of stories rarely higher than three, presence of rigid floors, significant inter-story height, and great distance between transverse walls. Among the others, analytical approaches, either based on numerical or mechanical models, are more suitable to capture the effects of such features on the seismic vulnerability. The two methods discussed in the paper are “Vulnus Vb 4.0-2009”, developed at the University of Padova and based on the integrated use of mechanical and macroseismic approaches, and “DBV-Masonry (Displacement Based Vulnerability)”, a pure mechanical-based model developed at the University of Genoa. Both methods are applied to a stock of 14 masonry schools, selected as prototypes of Italian school masonry buildings. The critical review and comparative application of the two methods allow highlighting their similarities and differences in assessing the fragility associated to in-plane and out-of-plane failure mechanisms. Moreover, as some of the selected schools had been hit by the 2016-17 Central Italy earthquake sequence, the evidence of the real response allows assessing the actual reliability of the methods

Dynamic Identification and Calibration of an Arch Steel Bridge Model for the Evaluation of Corrosion Effects

Bridges play a crucial role as they are critical elements in several road networks. Recent trends in condition state assessment require to evaluate not only the seismic vulnerability and the load carrying capacity for increased traffic loads, but also the damage state due to decay and environmental effects. in order to evaluate the structural reliability of the bridge and define priority lists for interventions on the network. In the framework of a series of inspections carried out at a municipality level for the above mentioned aims, a numerical and experimental analysis was carried out on a historical steel deck arch bridge, called Paleocapa bridge, located in the historic city centre of Padova (Italy). Paleocapa bridge is composed by six arches and is highly vulnerable to traffic load, due to a widespread and advanced corrosion state. In order to study the effects of both internal and external boundaries and the loss of mass and stiffness due to steel corrosion a parametric modal analysis was implemented. The steel material was characterized through uniaxial tensile test and metallographic and chemical analysis, while a dynamic identification test of the bridge was performed in order to extract modal parameters, i.e. natural frequencies, damping ratios and mode shapes. Modal analysis pointed out a decoupled behaviour of arches and deck, and among the same arches, with a consequent significant decrease in load-bearing capacity. The calibrated FE model of the bridge was used to assess the seismic and static capacity of the structure. In particular, the latter was very critical; therefore, it was necessary to limit the transitable load on the deck, in agreement with the public authority