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Robustness analyses are very well referenced for concrete or steel frame structures but less for spatial structures; in particular for truss roofs. Here, we present a robustness analysis of an existing airport space structure. A finite element model was implemented based on the original design documents, where the structure is modeled as a spatial truss composed of elastic, perfectly hinged bars. With respect to five main design loading conditions, the most stressed bars among the top layer, the bottom layer and the diagonals, were alternately removed, and the stress variations in the remaining bars monitored. A total of fifteen analyses with removal of either the most stretched or the most compressed bar were run. Also, reductions of the most stressed bars’ axial stiffness were considered to investigate the effects of such local reductions on the global structural flexibility. Linearized global buckling analyses were also conducted to point out again the effect of a global loss of stiffness, due to local losses. The study gives basic information about the general behavior of the structure in case of failure, or damage, of a key element. Results show that this kind of lightweight and efficient structures are very sensitive to local losses, since their redistribution capabilities are not large.

Most snow avalanches occur unobserved, which becomes particularly dramatic when human lives are involved. Seismological observations can be helpful to unravel time and dynamics of unseen events, like the deadly avalanche of January 18, 2017, that hit a Resort-hotel at Rigopiano in the Abruzzi (Italy). Particle motion analysis and spectrograms from data recorded by a close seismic broadband station, calculation of synthetic seismograms, as well as simulation of the flow, allowed us to construct the dynamics of the snow avalanche that buried alive 40 people, killing 29. Due to the bad weather conditions, no visual observation was made, thus making it impossible to determine the exact moment of the avalanche and to report necessary observations of the dramatic event. On-site inspections revealed that the hotel was horizontally cut by shear forces and dislocated by 48 m in 70°N direction, once the increasing avalanche pressure exceeded the structural shear strength of the building. Within an eligible 24 min time range of the avalanche, we found three weak seismic transients, starting at 15:42:38 UTC, recorded by the nearest operating station GIGS located in the Gran Sasso underground laboratory approximately 17 km away. Particle motion analysis of the strongest seismic avalanche signal, as well as of the synthetic seismograms match best when assuming a single force seismic source, attacking in direction of 120°N. Simulation of the avalanche dynamics—calculated by using a 2D rapid mass movement simulator—indicates that the seismic signals were rather generated as the avalanche flowed through a narrow and twisting canyon directly above the hotel. Once the avalanche enters the canyon it is travelling at maximum velocity (37 m/s) and is twice strongly deflected by the rock sidewalls. These impacts created a distinct linearly polarized seismic “avalanche transient”s that can be used to time the destruction of the hotel. Our results demonstrate that seismic recordings combined with simulations of mass movements are indispensable to remotely monitor snow avalanches.

The paper illustrates the development and the application of an active monitoring system, and analyzes the investigated dynamic behaviour of the structure where the system is applied. The system is installed on a 250 m suspended arch steel bridge that has been instrumented with sensors of different type. This work focuses on the employed methodologies and obtained results related to the dynamic monitoring of the bridge. The use of the Operational Modal Analysis techniques with data-driven stochastic subspace identification algorithms allows the extraction of the structural dynamic characteristics: natural frequencies, damping ratios, and mode shapes. These data are in overall accordance with those calculated through the computational model utilized by the active monitoring system. Besides, the definition of a range of scattering of modal parameters, under specific conditions, has been obtained. The bridge has very low vibration frequencies, below 1 Hz for all significant modes. The outcomes indicate that the estimation of dynamic characteristics and the corresponding accuracy is influenced by several factors, including the length of the accelerometric acquisitions and the followed specific procedures. The impact of environmental factors, with particular reference to the temperature, is examined. Compared to the damping ratio, the natural frequency shows higher estimation accuracy and marked sensitivity to the environmental factor. Consequently, in the selection of benchmark for damage detection, it should be taken into account that the two modal parameters have specific criticalities. Once that the modal parameter has been chosen, values outside the estimated uncertainty range can be considered as alarm triggers.

In recent years, great attention has focused on the development of automated procedures for infrastructures control. Many efforts have aimed at greater speed and reliability compared to traditional methods of assessing structural conditions. The paper proposes a multi-level strategy, designed and implemented on the basis of periodic structural monitoring oriented to a cost- and time-efficient tunnel control plan. Such strategy leverages the high capacity of convolutional neural networks to identify and classify potential critical situations. In a supervised learning framework, Ground Penetrating Radar (GPR) profiles and the revealed structural phenomena have been used as input and output to train and test such networks. Image-based analysis and integrative investigations involving video-endoscopy, core drilling, jacking and pull-out testing have been exploited to define the structural conditions linked to GPR profiles and to create the database. The degree of detail and accuracy achieved in identifying a structural condition is high. As a result, this strategy appears of value to infrastructure managers who need to reduce the amount and invasiveness of testing, and thus also to reduce the time and costs associated with inspections made by highly specialized technicians.

Resilience is the ability to undergo disruptive events without suffering complete failure and minimizing undesirable consequences thereof. Many attempts have been done in the recent literature in order to define quantitatively synthetic resilience measures of mechanical structures. They have been conceived as to be useful in comparing and classifying the resilience of different structures. In this paper we propose a novel rational and deterministic structural resilience index, based on a worst-case disruptive event, and making use of a minimalistic kinematics-based mechanical description. Particular emphasis is given to the computation of such a new structural resilience index for a generic frame structure, it being possible without the use of automated algorithms and an analytic expression of it has been achieved in terms of the numbers of ports (modules) and floors. First of all, keeping fixed the number of modules, the resilience index decreases as the number of floors increases. Secondly, keeping fixed the number of floors, the resilience index increases as the number modules increases. Finally, we notice that the case with infinite floors has a lower resilience index with respect to case of infinite modules, which is, as expectable, more resilient.

Industry 4.0 is encouraging the introduction of pioneering technologies even in the construction industry. Along with the development of high technology, such as augmented reality, virtual reality, and cloud computing, the development of digital twin has been growing. This contribution aims to present the potential of digital twin in the construction field, suggesting a framework that outlines the many different possible applications in construction, with reference to school buildings. First, it summarizes the current overview of digital twin applications in building construction. Then it shows that significant steps that are being taken beyond the digital model, even if the implementation of the digital twin concept in its full meaning is still a long way off. The research is moving in this direction and the evolution of the current state of the art, combined with the experience gained in the industrial sector, will soon bring a new revolution in the construction industry.

A hemi-variational formulation for a damaged non-homogeneous Timoshenko beam is proposed here for the purpose of fast simulation of the properties of a dam. The dam is therefore modeled as a damaged non-homogeneous Timoshenko beam embedded in 2D space. The damage evolution and the mechanics of the beam are governed both by the hemi-variational principle and by the assumption on the form of the deformation energy functional, that comprehends the dissipative part owing to damage-aging effects. In the formulation, the Karush–Kuhn–Tucker (KKT) condition is derived and the damage, which locally decreases the stiffness (i.e., axial, bending, and shear stiffness) of the beam, becomes relevant once a measure of the elastic energy, called the normalized undamaged elastic energy, reaches a certain threshold that is constitutively prescribed ab initio. The aging effect is assumed by reducing such a threshold in the neighborhood of the bottom of the beam, where the concentration of the chemical and physical attacks is higher. As a result, we show a method for the calculation of the mechanical failure condition. In addition, we observe that, even though this threshold is assumed to decrease in a large region far from the bottom of the dam, the damage is confined at the bottom of it. Thus, we have proved that the trapezoidal shape that is used in the dam design is useful not only to decrease the state of stress in the elastic regime, but also to confine the effects of damage evolution owing to the aging effects.

The study of progressive collapse and structural robustness has advanced significantly after 9/11 event. There is a growing interest in the phenomenon, as well as in the development of numerical and experimental techniques that have led to great progress in understanding the structural robustness and integrity. However, the general ideas, concepts and definitions have been merely changed over the past twenty years. These concepts and definitions are first developed in the framework of a threat-independent methodology, implicitly focused on blast-induced progressive collapse (or other short-term extreme events) in framed structures, and then, generalized to other structural types, mechanisms and triggering events, without scrutinization. In this paper, the current definitions of the terms progressive collapse, initial (local) damage and progressive collapse analysis are challenged, their insufficiency is discussed and possible improvements are provided. The suggested definitions and discussions provide a deeper and more general nomenclature for progressive collapse and related topics.

Column loss is a type of damage that can occur in frame structures subjected to explosions or impacts. The response of such structures largely depends on the capacity of the assembly of elements and on the inertia effects due to the sudden nature of the phenomenon. Frame structures are able to develop various resisting mechanisms that prevent the collapse to progress. The assessment of the robustness often requires complex and detailed numerical modelling. For the preliminary design of a robust frame, simplified methods to assess the effectiveness of the redistribution of the loads after the removal of a member are welcome. In the present paper, an approach based on the idealisation of the damaged structure into a single degree-of-freedom system with an elastic-plastic compliance law is proposed. The output of the method is the dynamic response of a target point, which can serve for assessing the residual safety of the structure. Comparing the obtained results with the outputs of a more sophisticated FE (Finite Elements) analysis, a satisfying accuracy is found.

On 18 January 2017 a catastrophic avalanche destroyed the Rigopiano Gran Sasso Resort & Wellness (Rigopiano Hotel) in the Gran Sasso National Park in Italy, with 40 people trapped and a death toll of 29. This article describes the location of the disaster and the general meteorological scenario, with field investigations to provide insight on the avalanche dynamics and its interaction with the hotel buildings. The data gathered in situ suggest that the avalanche was a fluidized dry snow avalanche, which entrained a sligthtly warmer snow cover along the path and reached extremely long runout distances with braking effect from mountain forests. The avalanche that reached the Rigopiano area was a “wood-snow” avalanche—a mixture of snow and uprooted and crushed trees, rocks, and other debris. There were no direct eyewitnesses at the event, and a quick post-event survey used a numerical model to analyze the dynamics of the event to estimate the pressure, velocity, and direction of the natural flow and the causes for the destruction of the hotel. Considering the magnitude and the damage caused by the event, the avalanche was at a high to very high intensity scale.

In structural engineering beams with non-constant cross-section or beams with variable cross-section represent a class of slender bodies, aim of practitioners’ interest due to the possibility of optimizing their geometry with respect to specific needs. Despite the advantages that engineers can obtain from their applications, non-trivial difficulties occurring in the non-prismatic beam modeling often lead to inaccurate predictions that vanish the gain of the optimization process. As a consequence, an effective non-prismatic beam modeling still represents a branch of the structural engineering of interest for the community, especially for advanced design applications in large spans elements. A straight beam of length l with variable inertia J(z) is provided in figure, subject to a generic live load condition q(z). The vertical displacement y(z) can be obtained from the solution of the differential equation of the elastic line, i.e., taking into consideration the inertia variability and neglecting, as first approximation, any shear contribution. Even if this solution is an approximate one, it is able to deal with the problem in its basic formulation. In this paper a solution for the problem stated is formulated using a series expansion of solutions, in a general load and cross section variability condition. Solution is thus obtained for a generic rectangular cross section beam with a variable height. Analytical solution is presented and evaluated using numerical evaluation of some cases of practical interest.

In structural engineering beams with non-constant cross-section or beams of variable cross-section are represents a class of slender bodies, object of the practitioners interest due to the possibility of optimizing their geometry with respect to specific needs. Despite the advantages that engineers can obtain from their use, non-trivial difficulties occurring in the non-prismatic beam modeling often lead to inaccurate predictions that vanish the gain of the optimization process. As a consequence, an effective non-prismatic beam modeling still represents a branch of the structural engineering of interest for the community, expecially for advanced design applications in large spans elements.

The Alternative Load Path (ALP) method is widely used to assess progressive collapse resistance of steel framed structures. Code-based ALP is a threat-independent methodology, implicitly focuses on a very special triggering event, i.e., a small near-field blast, that can lead to complete and sudden column loss. However, in a real blast-induced progressive collapse scenario, characteristics of the triggering event and subsequent initial damage control the structural response. To study these effects, a wide numerical investigation is carried out. First, the code-based ALP method is applied to assess the threat-independent dynamic column removal responses. The results emphasize the importance of initial damage location and building’s size. Then, the model structures were analyzed in different blast scenarios. A meaningful difference in the obtained results compared with code-based ALP is observed in both quantity and quality. Finally, a novel methodology (modified ALP) is suggested to update the code-based ALP method to capture the threat-dependent parameters, i.e., column removal time (CRT) and damage level. To serve this purpose, a substructure techniques, i.e., equivalent column model, is developed and validated. The results of three methods (threat-independent code-based ALP, threat-dependent blast analysis (BA) and the proposed modified ALP) are compared, and it is observed that the modified ALP method can effectively adjust the dynamic column removal response to reflect the blast effects.

The study presents the dynamic structural response of steel member subjected to a localized impact from falling rock blocks in rockfall areas. A novel compliance contact model is derived for the interaction between the elastic-plastic member (the target) and an impacting rock block. Unlike other existing models, the proposed compliance contact model accurately evaluates the material properties of the rock block (considered as a deformable indenter) and of the steel target (considered as an elastic-plastic target of finite thickness). A simplified two degrees of freedom (2-DOF) lumped masses model accounting for nonlinear contact interaction and material nonlinearities is used to describe the dynamics of the phenomenon. The proposed contact law and the 2-DOF model are validated with detailed static and dynamic analyses conducted with finite element software ANSYS. The results are compared and commented in order to be implemented in future civil engineering applications.

Detailed finite element modelling of key elements is necessary to improve the robustness assessment of structures subjected to a coupled effect of fire and blast loads. This paper presents a method for a realistic multi-hazard approach by studying the residual load bearing capacity of steel columns under fire conditions and followed by an explosion. The approach adopts the use of a material constitutive law able to take into account both the strain rate sensitivity and the thermal softening. Explicit nonlinear dynamic analyses are performed using the explicit commercial code LS-DYNA. Results show that the residual load bearing capacity is influenced by the stand-off distance. The time of fire loading at which an explosion is triggered is a critical parameter as well. High strain rates in the typical blast range (10 2 ÷ 10 3 s −1 ) are numerically obtained as a consequence of explosions in the close proximity. A comparison with the Eurocode approach is also reported. The results can be of great interest to establish the initial conditions that could potentially lead to the onset of progressive collapse in steel framed structures subjected to a combined effect of fire and blast loadings.

An innovative approach, defined by the term “Active Monitoring”, has been designed and implemented by the Company ARCOS Engineering for a steel suspended arch bridge, starting from its design phases, for the sake of structural control and maintenance operations. The structure has a span of 250 m with a central arch that supports the runway through steel tendons. The bridge deck consists of a central beam and cantilevered lanes. The bridge has been instrumented with load cells at suspension cables, high precision servo inclinometers, steel surface temperature, differential pressure and humidity sensors, triaxial accelerometers. Data from sensors are the input of a finite element computational engine that evaluates derived quantities. Then, the coherence between the acquired and computed quantities is verified. Warning signals are provided if this check is not met. In this manner, a real-time structural assessment is carried out in a fully automated way, highlighting potential anomalies without human interaction. Therefore, this strategy becomes a valuable support for management and maintenance planning of infrastructure assets. The paper illustrates the layout and implementation of the system as well as some of the results that have been attained.

To reduce the mass of CO2 released into atmosphere by the construction industry, the performance strategy can be adopted. It is based on the use of High-Strength Concrete (HSC) in alternative to Normal-Strength Concrete (NSC). Such concretes are herein considered to design the reinforced concrete structures of three buildings, having 14, 30 and 60 floors, respectively. For each building, the structural analyses, carried out for four classes of concrete (i.e., C25, C40, C60 and C80) in accordance with Eurocode 2, provides different dimensions of the structural elements. In other words, the amount of CO2, released in the atmosphere due to the production of the structural materials, is a function of both concrete strength and height of the building. As a result, the minimum impact of low-rise buildings occurs when the structural elements are made with NSC. Conversely, only when HSC is used to cast the structural elements of tall buildings, can the carbon footprint be effectively reduced. Keywords: Performance strategy, Carbon footprint, FEM analyses, Reinforced concrete structures

Seismic hazard represents one of the possible triggering causes for NaTech accidents in refineries and production plants. The vulnerability of steel storage tanks was evaluated within the framework of a rapid risk assessment. Tanks dataset is composed of 70 refinery items in located in various parts of Italy and the seismic calculations are performed in accordance to API 650 Annex E Standard. The paper summarizes the results of the investigation through two normalized parameters related to the masses and to the seismic load. Some trends in the solution are highlighted. The empirical fragility curve obtained from the analysis is compared with similar curves found in the literature and the resulting similarities (and dissimilarities) are critically discussed.

The Eddystone Lighthouse is an imposing granite structure that has guided mariners through the treacherous waters off the Plymouth coast for nearly 150 years. The General Lighthouse Authorities (GLAs) of the UK and Ireland, recognising the continuing importance of rock-mounted lighthouses as physical aids for navigation, funded a pilot project, commissioning Plymouth University to monitor the tower. The present study aims to provide more information on the structural behaviour of the Eddystone Lighthouse under the impacts from wave loading, through the utilisation of a 3D finite element model. Data from geophones, an offshore wave buoy and video cameras installed on the tower have been used to calibrate and validate the model; in particular, the wave that caused the maximum displacement during the winter 2013/2014 storms has been considered. The point of application of the wave load is important in the tower’s structural response; the lighthouse being especially vulnerable to larger displacements when the wave acts above its cylindrical base. Finite element analysis suggests that the lighthouse is stable with regard to material failure, and for failure mechanisms of overturning and sliding there are factors of safety of 6.3 and 8.0 respectively. A hypothetical unbroken wave of 17.5 m height would be required to overturn the lighthouse, and one of height 17 m would cause cracking at the base, but in such a location these waves would not be possible.

Damage tolerance is a fundamental prerequisite for the safety and robustness of large complex systems. Here we analyze the response of a system of parallel rods under a damage event. The approach is based on the presence of multiple load paths in a complex structure, that is, various ways to perform a task. We found that, as much as the complexity increases, the presence of effective ways of carrying the load becomes crucial for the robustness of the structural system under a damage process acting at random on the structure. In addition, the size of the system plays an important role: although tendentially more fragile, large systems are able to redistribute and absorb the effects of damage even with low complexity. The results, here discussed with reference to mechanical systems, can be exported to other disciplines.

In this paper the high strain rate behaviour in tension and in a wide range of elevated temperatures of the S355 structural steel is presented. A Split Hopkinson Tensile Bar for the mechanical characterisation at high strain rates, equipped with a water-cooled induction heating system is used. These data are collected with the purpose of evaluating the extreme combined effect of dynamic loadings and elevated temperatures (200 °C, 400 °C, 550 °C, 700 °C and 900 °C), e.g., a fire load followed by an explosion. The reduction factors for the main mechanical properties are reported. The novelty of our data is the addition of the strain rate dependency to the temperature. High strain rate tests at 550 °C highlighted the phenomenon known as blue brittleness where an increase of strength and a decrease of ductility were ascribed to the dynamic strain ageing. Focusing the attention on the thermal softening parameter, m, the widely used constitutive law proposed by Johnson and Cook during the eighties is critically reviewed highlighting some weaknesses. The results can be of great interest for the assessment of robustness in structures where a fire induced progressive collapse should be evaluated focusing the attention to the extreme combined effects. Keywords: Fire induced progressive collapse, Robustness, High strain rates at high temperatures, Extreme combined effect, SHTB, S355 structural steel, Material constitutive law, Dynamic strain ageing

Structural monitoring is a research topic that is receiving more and more attention, especially in light of the fact that a large part our infrastructural heritage was built in the Sixties and is aging and approaching the end of its design working life. The detection of damage is usually performed through artificial intelligence techniques. In contrast, tools for the localization and the estimation of the extent of the damage are limited, mainly due to the complete datasets of damages needed for training the system. The proposed approach consists in numerically generating datasets of damaged structures on the basis of random variables representing the actions and the possible damages. Neural networks were trained to perform the main structural monitoring tasks: damage detection, localization, and estimation. The artificial intelligence tool interpreted the measurements on a real structure. To simulate real measurements more accurately, noise was added to the synthetic dataset. The results indicate that the accuracy of the measurement devices plays a relevant role in the quality of the monitoring.

This paper reviews the state-of-art in progressive collapse studies on framed building structures. Such types of failure start with a local damage which extension increases, up to the whole structure. First, emphasis is placed on the current techniques to study collapse propagation, i.e., numerical, experimental and analytical. In particular, the various numerical methods found in the literature are reported and discussed and the experimental studies and technologies involved in the laboratory tests are listed and compared. As reviewed, the method of analysis depends on the collapse mechanism and the triggering event. Thus, an in-depth review of the collapse typologies is proposed. Pure and mixed progressive collapse mechanisms are discussed and debated. The various triggering events, their modeling and their effects on the framed structures are examined. Details on the available literature on multi-hazard scenarios are provided. Finally, robustness techniques against progressive collapse are summarized, compared and contrasted. The paper concludes with an ambitious comprehensive list of open questions and issues covering different aspects of future needs.

To reduce the environmental impact of cement-based composites used by the construction industry, stone aggregates can be substituted by unconventional aggregates, such as the rubber from end-of-life tyres. This substitution strategy can be applied to both mortars and structural concretes. Nevertheless, each application requires a specific particle size distribution, to the point that the maximum aggregate size of concrete can be 10 times larger than that of mortar. Consequently, the mechanical response under bending actions, ruled by the fracture energy, can drastically change with the structural dimension. This size-effect is particularly evident in the experimental analyses performed herein, which include three point bending tests on mortar prisms and concrete slabs. As a result, the fracture toughness always increases in presence of rubber, and in the case of large particle size the increment of ductility can lead to the increment of the flexural strength.

To design the retrofit and/or conservation of existing reinforced concrete structures, an assessment of concrete strength is generally required. The current methodologies consist of destructive tests, based on uniaxial compression performed on concrete cores extracted from a structure, and/or non-destructive tests, in which the strength of the concrete is indirectly estimated by measuring other physical properties (like ultrasonic pulse velocity). Nevertheless, in several situations (e.g. the seismic vulnerability assessment of long-term service structures), the traditional tests cannot be performed. Hence, a new simplified approach is introduced and described in this paper. This can be applied to structures located in a precise geographical area, where the average strength of concrete (and the relative variance) is a function of the year of construction. Such a relationship is summarised by the so-called strength curves statistically computed from a huge database stored in the Department of Structural and Geotechnical Engineering of Politecnico di Torino (Italy). Relating to a concrete dam and a stadium built during the 1950s and in 1967, respectively, the strength predicted by these curves is in good agreement with the measurements of destructive tests.

Metamaterials can be engineered to interact with waves in entirely new ways, finding application on the nanoscale in various fields such as optics and acoustics. In addition, acoustic metamaterials can be used in large-scale experiments for filtering and manipulating seismic waves (seismic metamaterials). Here, we propose seismic isolation based on a device that combines some properties of seismic metamaterials (e.g., periodic mass-in-mass systems) with that of a standard foundation positioned right below the building for isolation purposes. The concepts on which this solution is based are the local resonance and a dual-stiffness structure that preserves large (small) rigidity for compression (shear) effects. In other words, this paper introduces a different approach to seismic isolation by using certain principles of seismic metamaterials. The experimental demonstrator tested on the laboratory scale exhibits a spectral bandgap that begins at 4.5 Hz. Within the bandgap, it filters more than 50% of the sei...

This paper presents the experimental and theoretical results of an investigation carried on reinforced concrete plates placed on yielding supports along their perimeter under short-term dynamic loading. The yielding supports are made of elements with annular cross-section. Their functionality allows operations in elastic and elasto-plastic stages with a further turning to hardening stage. This particular support scheme has been adopted in order to simulate the different boundary conditions that r.c. slabs subjected to impacts may encounter in practical applications of civil engineering (e.g. roofs, vertical panels, retaining walls, guardrails, etc.). The experimental results showed that influence of support deformability on the structural response under impact depends on their rigidity and on the deformation stage. The results of numerical simulations based on a simple mechanical model qualitatively agree with the experimental results. Therefore the model can be adopted for simulation and design of reinforced concrete panels under impact or high-strain loading situations.

One-dimensional diffusion problems in bounded porous media characterized by the presence of nonlocal interactions are investigated by assuming a Darcy’s constitutive equation of convolution integral type. A power law attenuation function is implemented: Analogies and differences of the flow-rate-pressure law with respect to other nonlocal and fractal models are outlined. By means of the continuity relationship, the fractional diffusion equation is then derived. It involves spatial Riemann-Liouville derivatives with a noninteger order consisting of between 1 and 2. The solution is obtained numerically using fractional finite differences, and results are presented in both the transient and the steady-state regimes. Eventually, the physical meaning of fractional operators is discussed and potential applications of the analysis are suggested.