Domenico Asprone

Application-Oriented Chemical Optimization of a Metakaolin Based Geopolymer

In this study the development of a metakaolin based geopolymeric mortar to be used as bonding matrix for external strengthening of reinforced concrete beams is reported. Four geopolymer formulations have been obtained by varying the composition of the activating solution in terms of SiO2/Na2O ratio. The obtained samples have been characterized from a structural, microstructural and mechanical point of view. The differences in structure and microstructure have been correlated to the mechanical properties. A major issue of drying shrinkage has been encountered in the high Si/Al ratio samples. In the light of the characterization results, the optimal geopolymer composition was then applied to fasten steel fibers to reinforced concrete beams. The mechanical behavior of the strengthened reinforced beams was evaluated by four-points bending tests, which were performed also on reinforced concrete beams as they are for comparison. The preliminary results of the bending tests point out an excellent behavior of the geopolymeric mixture tested, with the failure load of the reinforced beams roughly twice that of the control beam.

Assessment of Urban Ecosystem Resilience through Hybrid Social–Physical Complex Networks

One of the most important tasks of urban and hazard planning is to mitigate the damages and minimize the costs of the recovery process after catastrophic events. In this context, the capability of urban systems and communities to recover from disasters is referred to as resilience. Despite the problem of resilience quantification having received a lot of attention, a mathematical definition of the resilience of an urban community, which takes into account the social aspects of an urban environment, has not yet been identified. In this article, we provide and test a methodology for the assessment of urban resilience to catastrophic events which aims at bridging the gap between the engineering and the ecosystem approaches to resilience. We propose to model an urban system by means of different hybrid social–physical complex networks, obtained by enriching the urban street network with additional information about the social and physical constituents of a city, namely citizens, residential buildings, and services. Then, we introduce a class of efficiency measures on these hybrid networks, inspired by the definition of global efficiency given in complex network theory, and we show that these measures can be effectively used to quantify the resilience of an urban system, by comparing their respective values before and after a catastrophic event and during the reconstruction process. As a case study, we consider simulated earthquakes in the city of Acerra, Italy, and we use these efficiency measures to compare the ability of different reconstruction strategies in restoring the original performance of the urban system.

Experimental Analysis on Tensile Dynamic Behavior of Existing Concrete under High Strain Rates

The presented research is part of a wider research project involving the study of the dynamic behavior under extreme loads of the Tenza Bridge, a concrete arch bridge located in southern Italy. The dynamic behavior of the concrete of the bridge under tensile loads is herein investigated. Several dynamic tensile tests under different strain rates were performed on concrete specimens at the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland using modified Hopkinson bars. The results were then processed in terms of strength dynamic increase factor-strain rate relationships. These are fundamental to assess constitutive laws of concrete to be implemented in analytical models of the bridge under dynamic loads. The results are compared with existing analytical formulations that attempt to predict the dynamic tensile strength of concrete. The comparisons show that, even though tested concrete was taken from an existing structure, the relationships found in the literature accurately describe its tensile dynamic behavior.

Developing an integrated framework to quantify resilience of urban systems against disasters

AbstractUrban resilience against disasters represents a key issue for contemporary society. The increasing complexity of cities along with more severe threats induced by climate change is pressing modern societies to search for new paths to prevention, preparedness and rapid recovery. As a result, resilience is triggering an increasing interest within many scientific contexts to explore the capabilities of communities to withstand extreme events. The present study proposes a framework aimed at quantifying disaster resilience of urban systems while ensuring an adequate level of sustainability, all according to a social and human-centric perspective. Urban networks are modelled as hybrid social–physical networks (HSPNs) by merging both physical and social components, and engineering measures are performed on HSPNs, as a measure of urban efficiency, within a multi-scale approach. Thence, social indicators are identified in order to characterise quality of life in the aftermath of a catastrophic event. Both efficiency and quality of life indicators are evaluated using a time–discrete approach before and after an extreme event occurs and during the recovery phase in order to measure inhabitant happiness and environmental sustainability. This approach allows handling different kinds of information simultaneously, being potentially implemented both in peacetime and during the recovery process. The former can be effective for urban coping capacity assessment in order to reduce risks as a mitigation instrument. The latter can be used in the post-event to identify the best recovery paths needing to be followed for adaptation.

Tensile High Strain-Rate Behavior of Reinforcing Steel from an Existing Bridge

Events such accidental or deliberate explosions need to be considered in load design, but this can be difficult due to the uncertainty related to load definition for blast actions. This paper highlights a dynamic characterization that was carried out on reinforcing steel belonging to an existing structure. The steel was from the Tenza Bridge, a reinforced concrete arch bridge in southern Italy. The behavior of both concrete and reinforcing steel under dynamic loading rates at high strain-rate levels was investigated. Tensile failure tests were performed on steel specimens at different strain rates using a modified Hopkinson bar device. Data from the tests were processed to obtain stress-strain relationships under different strain-rate conditions, and the results were compared with existing formulations, providing the dynamic increase factor of yield and ultimate stresses for reinforcing steel. Finding show that the reinforcing steel was strain-rate sensitive in terms of yield stress, ultimate stress and ultimate strain. As the strain rate increased, yield stress increased more than ultimate stress.

Strain-Rate Sensitivity of a Pultruded E-Glass/Polyester Composite

Structural analysis of composite structures subjected to dynamic loads requires detailed knowledge of the mechanical behavior of component materials under high strain-rates. This paper presents the results of tests to investigate the tensile dynamic behavior of a pultruded E-glass/polyester composite used in a steel-less blast protection barrier. The described activity is part of the Security of Airport Structures research project, focusing on structural protection of airport infrastructures against disruptive action. Modified Hopkinson bars and hydropneumatic machine devices were used to conduct strain-rate controlled tensile failure tests on glass fiber-reinforced polymer specimens. The results are discussed and then implemented within a viscoplasticity constitutive model and a strain-rate-dependent failure criterion in order to simulate the exhibited mechanical behavior.

LCA-based study on structural retrofit options for masonry buildings

PurposeOver the last decade, the rehabilitation/renovation of existing buildings has increasingly attracted the attention of scientific community. Many studies focus intensely on the mechanical and energy performance of retrofitted/renovated existing structures, while few works address the environmental impact of such operations. In the present study, the environmental impact of typical retrofit operations, referred to masonry structures, is assessed. In particular, four different structural options are investigated: local replacement of damaged masonry, mortar injection, steel chain installation, and grid-reinforced mortar application. Each different option is analyzed with reference to proper normalized quantities. Thus, the results of this analysis can be used to compute the environmental impact of real large-scale retrofit operations, once the amount/extension of them is defined in the design stage. The final purpose is to give to designers the opportunity to monitor the environmental impact of different retrofit strategies and, once structural requirements are satisfied, identify for each real case the most suitable retrofit option.MethodsThe environmental impact of the structural retrofit options is assessed by means of a life-cycle assessment (LCA) approach. A cradle to grave system boundary is considered for each retrofit process. The results of the environmental analysis are presented according to the data format of the Environmental Product Declaration (EPD) standard. Indeed, the environmental outcomes are expressed through six impact categories: global warming, ozone depletion, eutrophication, acidification, photochemical oxidation, and nonrenewable energy.Results and discussionFor each retrofit option, the interpretation analysis is conducted in order to define which element, material, or process mainly influenced the LCA results. In addition, the results revealed that the recycling of waste materials provides environmental benefits in all the categories of the LCA outcomes. It is also pointed out that a comparison between the four investigated options would be meaningful only once the exact amount of each operation is defined for a specific retrofit case.ConclusionsThis paper provides a systematic approach and environmental data to drive the selection and identification of structural retrofit options for existing buildings, in terms of sustainability performance. The final aim of this work is also to provide researchers and practitioners, with a better understanding of the sustainability aspects of retrofit operations. In fact, the environmental impacts of the retrofit options here investigated can be used for future research/practical activities, to monitor and control the environmental impact of structural retrofit operations of existing masonry buildings.

Linking Disaster Resilience and Urban Sustainability: A Glocal Approach for Future Cities

Resilience and sustainability will be two primary objectives of future cities. The violent consequences of extreme natural events and the environmental, social and economic burden of contemporary cities make the concepts of resilience and sustainability extremely relevant. In this paper we analyse the various definitions of resilience and sustainability applied to urban systems and propose a synthesis, based on similarities between the two concepts. According to the proposed approach, catastrophic events and the subsequent transformations occurring in urban systems represent a moment in the city life cycle to be seen in terms of the complex sustainability framework. Hence, resilience is seen as a requirement for urban system sustainability. In addition, resilience should be evaluated not only for single cities, with their physical and social systems, but also on a global scale, taking into account the complex and dynamic relationships connecting contemporary cities.

Applications of Shape Memory Alloys in Structural Engineering

Shape memory alloys (SMAs) have physical and mechanical features that make them successful candidates for use in structural engineering applications. Primarily, SMAs play a key role toward the development and implementation of smart materials/devices, which can be integrated into structures to provide functions such as sensing, energy dissipation, actuation, monitoring, self-adapting, and healing of structures. Other excellent properties of SMAs can be exploited in civil engineering applications, such as good fatigue and corrosion resistance, large damping capacity, and good versatility in terms of their many possible shapes and configurations. This chapter discusses the variety of SMA applications in structural engineering based on the application domain.

Adaptive daily forecasting of seismic aftershock hazard

Abstract Seismic aftershock‐hazard analysis is one of the first steps toward establishing an integrated risk‐based decision‐making support framework for emergency management in the event of an ongoing aftershock sequence. This work focuses on providing adaptive daily forecasts of the mean daily rate of exceeding various spectral acceleration values (the aftershock hazard). Two well‐established earthquake‐occurrence models suitable for daily seismicity forecasts associated with the evolution of an aftershock sequence, namely, the modified Omori’s aftershock model (MO) and the epidemic‐type aftershock sequence (ETAS) are adopted. An adaptive and evolutionary MO‐based aftershock occurrence model with distinct spatial and temporal components is proposed. In this model, the parameters deciding the temporal decay are updated based on the data provided by the ongoing aftershock sequence. This model adopts an evolutionary spatial seismicity pattern loosely based on spatial clustering of aftershock events in the sequence. Bayesian updating is also employed to provide sequence‐based parameter estimates for a given ground‐motion prediction model. Daily forecasts of the mean rate of exceedance of various spectral acceleration levels are calculated based on alternative occurrence models and the updated ground‐motion prediction relation. As a numerical example, daily forecasts of the aftershock‐hazard curve are obtained for the L’Aquila aftershock sequence based on the MO‐based and ETAS occurrence models, and an updated version of the Sabetta and Pugliese (1996) ground‐motion prediction model. These daily hazard forecasts are then compared with the observed daily rates of exceeding various spectral acceleration thresholds.