Mariano Angelo Zanini

Seismic vulnerability of bridges in transport networks subjected to environmental deterioration

This paper investigates the problem of management, maintenance and planning of interventions in transport networks located in seismic zones, in relation to the actual state of degradation of their most vulnerable elements, as bridges. The study consists in two phases: the first phase is concerned with definition of the seismic vulnerability of a typical bridge in the network, through the construction of fragility curves calculated taking into account the corrosion of the reinforcing steel as the main cause of environmental deterioration. Once the fragility curves of the deteriorated bridges are computed, the second phase consists in the analysis of the vulnerability of the transport network in which the bridges are included taking into account the modification of the traffic flows when bridge infrastructures are damaged. The results of this pilot study can be used as a first step for a proper allocation of economic resources in the planning of seismic retrofit interventions to minimize the overall risk and manage the immediate post-earthquake emergency phase and guide rescuers in reaching the affected and critical areas.

Electric Arc Furnace Slag as Coarse Recycled Aggregate for Concrete Production

Electric arc furnace (EAF) slag is a by-product of steel production in electric arc furnaces. Several studies have tried to demonstrate its suitability in civil engineering application, such as in bituminous mixtures and cement-based materials, due to its good physical, chemical and mineralogical properties. Particularly the re-use as coarse aggregate for concrete production has been shown to be a promising valorisation, when physical and chemical stability is guaranteed. Additionally, EAF slags high mechanical strength makes it suitable for high-performance concrete production. In this work three EAF concretes, with various cement content and also with silica fume addition, were compared with a reference concrete, to identify a convenient mix design to reach a concrete strength class between C50/60 and C60/75. Mechanical strength was evaluated analysing compressive and tensile strength, and elastic modulus. A complementary microstructural analysis was performed after the failure of the specimens, with the aim of analysing the morphology of the interfacial transition zone. Results indicate that the use of EAF slag in concrete allows reaching higher compressive strength than with coarse natural aggregates. EAF slag application in structural concrete promotes also the reduction of cement content in the mix to reach the same strength class.

Reinforced concrete and masonry arch bridges in seismic areas: typical deficiencies and retrofitting strategies

In recent years, appraisal of the condition and rehabilitation of existing bridges has become an ongoing problem for bridge owners and administrators in all developed countries. Reliable methodologies are therefore needed in the assessment and retrofit design phases, to identify the vulnerability of each bridge class. The specific problems of common arch bridge types are discussed herein, for both reinforced concrete and masonry structures, proper interventions for their static and seismic retrofitting are illustrated and several examples of applications are provided. Retrofitting is usually coupled with functional refurbishment, according to a methodological approach that takes into account bridge characteristics, state of maintenance and functional requirements, and environmental aspects connected with repair and strengthening systems.

A probabilistic strategy for seismic assessment and FRP retrofitting of existing bridges

This study proposes a holistic probabilistic framework to evaluate existing road and railway bridges after an earthquake by means of analytical fragility curves and visual inspections. Although visual inspections are affected by uncertainties, they are usually considered in a deterministic way, while in this work they are taken into account in a probabilistic point manner. Moreover, extra focus is given on retrofitting interventions by means of Fiber Reinforced Polymer materials and their costs. A probabilistic methodology is formed to evaluate possible standardized interventions on existing bridges after a seismic event. The proposed framework, consists of six basic steps and it is applied on a reinforced concrete bridge case study, which is a common structural typology in Italian roadway infrastructural networks. The main aim is to provide useful information to public authorities in order to decide whether or not they should allow traffic over the bridge and whether to repair immediately earthquake-damaged bridges. The outcomes of this framework can be used to improve procedures used for the seismic assessment of the whole road and railway networks to better plan emergency, post-emergency actions and define a general priority for an optimal budget allocation.

Cost analysis for maintenance and seismic retrofit of existing bridges

Abstract The work describes an extensive cost analysis for maintenance and seismic retrofit of typical existing road bridges, based on integrated procedures for assessment of state and seismic vulnerability. In particular, visual inspections to evaluate total sufficiency ratings and a simplified seismic assessment were carried out for each structure, according to procedures proposed in earlier works. The results were then used as input data for statistical analysis, to calibrate new unit maintenance, seismic retrofit and total cost equations. The procedure was applied to a stock of bridges in the province of Vicenza, north-east Italy. The results will allow public authorities and private managing companies to estimate economic indicators regarding the extent of resources required for bridge maintenance and retrofit in areas subject to seismic events.

Contribution of in situ and laboratory investigations for assessing seismic vulnerability of existing bridges

This work describes the main results of an in situ experimental campaign carried out in the context of the seismic assessment of 71 existing road bridges as representative of the main structural typologies located in the Veneto region and pertaining to the regional roadway managing authority Veneto Strade SpA. An initial in situ and laboratory experimental campaign on basic materials and an overall geometrical survey were carried out for each bridge, using different tests according to the construction typologies, with the aim of characterising the main mechanical parameters of the significant structural elements. Structural assessment has been subsequently carried out according to the parameters derived from the above campaign and the design ground motion action. The results have been compared with those deriving from a preliminary analysis conducted on the basis of some assumptions on materials’ mechanical characteristics related to the original design documents and the construction practice at the time of the structures’ edification. This comparative analysis could give some insights on appropriate and rational planning of inspections on existing bridges and reliability of basic assumptions for their seismic assessment.

Simplified seismic assessment of multi-span masonry arch bridges

The paper describes a simplified methodology for the evaluation of the seismic retrofit intervention types to be performed on clusters of multi-span masonry arch bridges, on the basis of the main bridges geometrical characteristics. The structural behaviour of the analysed sample bridges has been evaluated in their principal directions highlighting the potential local and global vulnerabilities and the related retrofit intervention typologies that need to be selected. The main aim of this study is to take the form of an useful tool for identify the best retrofit strategies for each masonry bridge structure in function of its geometrical characteristics and thus planning rationally the management of bridges belonging to rail and road networks.

Post-quake urban road network functionality assessment for seismic emergency management in historical centres

Abstract In this paper, a procedure for the evaluation of the interaction between existing buildings and urban roadway networks after a seismic event is proposed. This question is relevant in historical urban centres, where urbanisation typology has evidenced, in the past, lack of road networks’ residual connectivity in post-earthquake conditions. The present study proposes a method for the evaluation of the residual functionality in urban context, moving from the execution of building surveys, the application of probabilistic concepts and fuzzy logic with the aim to define probable urban road network damage scenarios. The methodology is applied to the Municipality of Conegliano (northeastern Italy) evaluating the potential seismic damage scenario to the historical urban centre and highlighting criticisms in the post-earthquake rescue operations.

A unified framework for earthquake risk assessment of transportation networks and gross regional product

Natural threats like earthquakes, hurricanes or tsunamis have had serious impacts on communities. In the past, major earthquakes in the United States like Loma Prieta 1989, Northridge 1994, or recent events in Italy like L’Aquila 2009 or Emilia 2012 emphasized the importance of preparedness and awareness to reduce social impacts. In addition to that, earthquake damaged businesses dramatically reduced the gross regional product. Generating scenario earthquakes in a proper way is important to suitably assess the risk in bridge networks and social losses in terms of gross regional product reduction. Seismic hazard is traditionally assessed by means of probabilistic seismic hazard analysis (PSHA). Although PSHA well represents the hazard at a specific location it is not suitable for spatially distributed systems. Scenario earthquakes can overcome this problem; they represent the actual distribution of ground shaking for a spatially distributed system while being hazard consistent. In this work a methodology to generate scenario earthquakes has been proposed using a novel approach with the aim of being the basic step for investigating possible earthquake consequences in seismic areas and contributing to reduce losses.

Reliability-Based Analysis of Recycled Aggregate Concrete under Carbonation

Durability represents a crucial issue for evaluating safety and serviceability of reinforced concrete structures. Many studies have already focused on carbonation-induced corrosion of natural aggregate concrete (NAC) structures, leading to several prediction models to estimate carbonation depth. Less research is devoted instead on recycled aggregate concrete (RAC), about which limited experimental works exist aimed at assessing the carbonation coefficient in accelerated tests. Additionally, deteriorating processes are subject to uncertainty, when defining materials, geometry, and environmental actions during the service life of structures. This work presents a reliability-based analysis of carbonation resistance of RACs, using experimental carbonation coefficients derived from the literature, and applied in the full-probabilistic method prosed in fib Bulletin 34. Results demonstrate how aggregates replacement ratio and w/c ratio influence the reliability of RAC carbonation resistance.