A Syntactic Model of Mutation and Aliasing

Traditionally, semantic models of imperative languages use an auxiliary structure which mimics memory. In this way, ownership and other encapsulation properties need to be reconstructed from the graph structure of such global memory. We present an alternative "syntactic" model where memory is encoded as part of the program rather than as a separate resource. This means that execution can be modelled by just rewriting source code terms, as in semantic models for functional programs. Formally, this is achieved by the block construct, introducing local variable declarations, which play the role of memory when their initializing expressions have been evaluated. In this way, we obtain a language semantics which directly represents at the syntactic level constraints on aliasing, allowing simpler reasoning about related properties. To illustrate this advantage, we consider the issue, widely studied in the literature, of characterizing an isolated portion of memory, which cannot be reached through external references. In the syntactic model, closed block values, called "capsules", provide a simple representation of isolated portions of memory, and capsules can be safely moved to another location in the memory, without introducing sharing, by means of "affine' variables. We prove that the syntactic model can be encoded in the conventional one, hence efficiently implemented.Comment: In Proceedings DCM 2018 and ITRS 2018 , arXiv:1904.0956

Structural health monitoring of an onshore steel wind turbine

The study presents the development of a structural monitoring system installed in a 45-m-high steel wind tower located in Italy. The installed monitoring system was composed by 16 strain gauges placed in the tower wall, in a pattern of four Wheatstone bridges at 45°, together with thermal couples, at 21 m from the ground (half-height of the tower). Moreover, several accelerometers were placed along the tower height (with one of them located next to the strain gauges). The wind velocity and directions were obtained directly from the turbine own monitoring system. Such a monitoring system was designed because, due to the decrement of the total height from the original design, the tower suffers from resonance problems. In fact, the investigated tower was originally designed with 65 m of height but then, to comply with local regulations, the height was decreased to the actual size. Therefore, to allow safe operation and avoid excessive fatigue due to the increased displacements, the velocity of the rotor has been manually limited causing an important reduction in the energy production. The results of the study show the importance of monitoring the resonance issue. The differences between the damage indexes obtained with two different working conditions are discussed: tower working with limited operational capacity and tower working at its maximum capacity (in resonance)

STRUCTURAL BEHAVIOR OF STEEL STORAGE RACKS UNDER DIFFERENT FIRE SCENARIOS

Steel solutions commonly used in logistic to store goods and products (i.e. racks) are assembled by thin-walled cold-formed components and their competitiveness on the market depends essentially on the total weight of the framed system. Despite great efforts have been done on seismic and static design, very limited attention was given to the problem of the fire design and to the robustness of such structures. Due to the limited thickness of the structural elements, it is well-known that their resistance to the fire load is quite limited. No specific design rules or design procedures have been developed till now. Nowadays, the only way to protect these frames against fire is the use of sprinkler or more complex solutions, like isolated chambers. However, fire hazard cannot be always eliminated and when these strategies were not effective, global structural collapse of the racks, during a fire, have been observed. In this paper a parametric analysis is proposed to deeply understand the behavior of racks against fire. In particular, starting from an existing rack configuration, different fire scenarios were modeled by changing the fire position along the fame and the fire design curve. Moreover, the progressive collapse of the rack is discussed proposing also two reinforcing strategies. Final results discuss about the best way to design these slender structures against fire, trying to prevent the global failure or, at least, to guarantee a safe collapse mode

A TMD APPLICATION IN THE SEISMIC IMPROVEMENTS OF AN HISTORICAL CHIMNEY

open3noThe paper analyzes the seismic improvement of an historical masonry chimney by the tuned mass dumper (TMD) application. The chimney was built at the beginning of XX century in the northern region in Italy and the mechanical characteristics of the masonry, in terms of elastic modulus and compressive strength, used in the finite element models (FEMs) has been determined by a set of experimental tests. A first FEM is implemented by element beam (FEM 1) a second FEM is implemented by solid elements (FEM 2); in both, two configurations are studied: the chimney without TMD and the chimney with TMD. By a time history analysis the main characteristic of the TMD in the terms of mass, stiffness and damper values are valued and optimized for different positioning of the oscillating mass. Finally, a structural solution for the support of the TMD is proposed.Longarini, Nicola; Zucca, Marco; Migliacci, AntonioLongarini, Nicola; Zucca, Marco; Migliacci, Antoni

STRUCTURAL VIBRATION CONTROL BY TMD'S USE

The paper refers the use of Tuned Mass Dumper (TMD) in different constructions recently built in Italy to improve their serviceability structural performances. In two footbridges and a new tall building the dynamic behaviors are analyzed in the two conditions: without and with TMD. The structural analysis show the improvements in the Serviceability Limit State (SLS). In the footbridge cases the use of the TMD allows the control of the deck vibrancy, either in the daily use and in extreme overcrowding case; in the tall building case the improvements are appreciated in relation to a greater comfort for the occupants due a better wind structural response

On the collapse of a post-tensioned reinforced concrete truss bridge during the construction phases

On March 2018 a post-tensioned reinforced concrete (RC) truss bridge, built inside a North American university campus using the Accelerated Bridge Construction (ABC) method, collapsed during the construction phases, while the bars of a diagonal member were being re-tensioned. This process was not part of the scheduled construction phases, but it was decided by the designers after having observed several cracks in the structural nodes. This paper aims to analyse the final design of the bridge useful to determine the hypothetical causes of the collapse. Several numerical analyses have been performed to reproduce the behaviour of the different structural elements during the construction phases. In particular, construction stage analyses have been carried out to obtain the internal actions acting on the structural elements and on the nodes during the different construction steps and in order to analyse in detail the critical phases where the occurrence of the collapse has been hypothesized. The collapse mechanism is identified in the shear failure of a node of the concrete truss during the re-tensioning of a diagonal element. In fact, the reapplication of the post-tension had increased the axial force of the diagonal and consequently the shear action on the node. Moreover, the results obtained have shown that the bridge has never been in safe conditions, mainly because the interface surface of the cold joints had not undergone any type of work and remained smooth

Seismic vulnerability assessment of an Italian historical masonry dry dock

Abstract The paper presents the seismic vulnerability analysis of the military dry dock built in 1861 inside the Messina's harbor. The study appears very important not only for the relevance of the dry dock itself, but also for its social, military and symbolic role. As a first step, the historical documentation about the dry dock delivered by the Military Technical Office, in charge of its maintenance, was thoroughly examined. This activity was fundamental to understand the construction methods, the rehabilitation works executed after the severe earthquake of 1908 and, finally, the works carried out to increase the size of the dry dock in 1950. After this first step, numerical seismic analyses were done with some implemented finite element models (FEM) of the structure. In each FEM, the vertical loads were applied according to the "construction stages" analysis technique, in order to achieve an appropriate representation of the soil stresses around the structure. The analysis results were evaluated according to the Italian design code (NTC 2008) in order to determine the seismic vulnerability of the dry dock

Tuned mass dampers for improving the sustainability and resilience of seven reinforced concrete chimneys under environmental loads

In the late 1950s, driven by economic development and environmental considerations, industrial plants began utilizing reinforced concrete (RC) for chimney construction, lacking specific earthquake-resistance provisions. However, RC chimneys exhibit an inelastic response and a potential for brittle collapse under seismic loads. The reconstruction of these chimneys presents a challenge, considering their significant symbolic value within the community and the increasing focus on sustainability, material recycling, and environmental resilience. In response to this need, we explore the performance of seven historic RC chimneys retrofitted with Tuned Mass Dampers (TMDs). This study considers the nonlinear material properties of concrete and steel rebars subjected to five European earthquakes. The TMDs’ effectiveness is evaluated by their impact on top displacement, base shear, and base moment. Additional aspects, such as equivalent damping and mode changes, are scrutinized. Through a parametric investigation, we analyze the influence of slenderness ratio, taper ratio, height, and vertically distributed mass on chimney response to earthquakes. Notably, the slenderness ratio emerges as a crucial factor affecting mass ratio, optimizing TMD parameters, base shear, and base moment. Notably, geometric characteristics seem to exert minimal influence on equivalent damping. Additionally, examining energy dissipated by TMDs reveals their contribution to increased elastic damping energy in chimneys, concurrently reducing kinetic and hysteretic (inelastic) energies. Elastic damping energy involves dissipation through inherent system elasticity, while hysteretic damping encompasses energy dissipation due to material damping effects. This research sheds light on the potential of TMDs in enhancing the seismic resilience of historic RC chimneys and provides insights into the key parameters influencing their performance

Seismic Vulnerability of R.C. Bridges Exposed to Corrosion

Recently, the engineering interest about the durability of existing reinforced concrete structures has significantly in- creased as confirmed by the conspicuous scientific literature. The results of these studies are influencing the development of new structural codes. Among the wide range of existing reinforced concrete structures, motorway viaducts stand out for their strategic relevance. Most of these structures were built between ’60 and ’70 years and, nowadays, the materials degradation phenomena are leading to strength capacity reduction, either in serviceability condition or in presence of exceptional loads such as the seismic ac- tion. In order to evaluate the degradation phenomena effects on the seismic vulnerability of motorway viaducts, this paper shows a new procedure to evaluate the seismic performance of reinforced concrete bridges starting from the modelling of the materials deg- radation - according to several scenarios - and by carrying out multimodal pushover analyses. The degradation is considered in terms of reduction of the concrete cross-section and steel rebar area. The results give an accurate estimation of seismic performance in terms of seismic vulnerability index variation and consequent management activities (e.g. planning and execution of rehab works)