The new Italian building code, published in 2018 MIT in NTC 2018: D.M. del Ministero delle Infrastrutture e dei trasporti del 17/01/2018. Aggiornamento delle Norme Tecniche per le Costruzioni (in ...Italian), 2018, explicitly refers to the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage” PCM in DPCM 2011: Direttiva del Presidente del Consiglio dei Ministri per valutazione e riduzione del rischio sismico del patrimonio culturale con riferimento alle norme tecniche per le costruzioni, G.U. n. 47 (in Italian), 2011 as a reliable source of guidance that can be employed for the vulnerability assessment of heritage buildings under seismic loads. According to these guidelines, three evaluation levels are introduced to analyse and assess the seismic capacity of historic masonry structures, namely: (1) simplified global static analyses; (2) kinematic analyses based on local collapse mechanisms, (3) detailed global analyses. Because of the complexity and the large variety of existing masonry typologies, which makes it particularly problematic to adopt a unique procedure for all existing structures, the guidelines provide different simplified analysis approaches for different structural configurations, e.g. churches, palaces, towers. Among the existing typologies of masonry structures there considered, this work aims to deepen validity, effectiveness and scope of application of the Italian guidelines with respect to heritage masonry towers. The three evaluation levels proposed by the guidelines are here compared by discussing the seismic risk assessment of a representative masonry tower: the Cugnanesi tower located in San Gimignano (Italy). The results show that global failure modes due to local stress concentrations cannot be identified if only simplified static and kinematic analyses are performed. Detailed global analyses are in fact generally needed for a reliable prediction of the seismic performance of such structures.
The phenomenon of interference between vortex-induced vibration (VIV) and galloping in the transverse degree of freedom was studied in the wind tunnel in the case of a spring-mounted slender ...rectangular cylinder with a side ratio of 1.5 having the short side perpendicular to the flow. The tests were carried out in a wide Scruton number range, starting from low values and increasing it in small steps by using eddy-current viscous dampers. This study helped understanding the dynamics of the interaction between the two excitation mechanisms and clearly highlighted the transition through four regimes of VIV-galloping interference. It was found that a high value of the mass-damping parameter is required to decouple the ranges of excitation of vortex-induced vibration and galloping completely, and for the quasi-steady theory to predict the galloping critical wind speed correctly. This conclusion is also relevant from the engineering point of view, as it means that structures and structural elements with ordinary mass-damping properties can exhibit sustained vibrations in flow speed ranges where no excitation is predicted by classical theories of vortex-induced vibration and galloping. Although most of the experimental tests were conducted in smooth flow at zero angle of attack, the paper also discusses the sensitivity of the results to a small variation of the mean flow incidence and to the presence of a low-intensity free-stream turbulence.
•The interference of VIV and galloping was studied in the wind tunnel for a rectangular cylinder.•High Scruton number values are necessary for decoupling the two excitation mechanisms.•The transition with the Scruton number through various regimes of interference is described.•The applicability and the limits of the quasi-steady theory is discussed.•Sensitivity study to low free-stream turbulence and small angle of attack.•Low free-stream turbulence is found to boost the interference of VIV and galloping.
Seismic assessment of existing masonry structures requires a numerical model able to both reproduce their nonlinear behaviour and account for the different sources of uncertainties; the latter have ...to be dealt with since the unavoidable lack of knowledge on the input parameters (material properties, geometry, boundary conditions, etc.) has a relevant effect on the reliability of the seismic response provided by the numerical approaches. The steadily increasing necessity of combining different sources of information/knowledge makes the Bayesian approach an appealing technique, not yet fully investigated for historic masonry constructions. In fact, while the Bayesian paradigm is currently employed to solve inverse problems in several sectors of the structural engineering domain, only a few studies pay attention to its effectiveness for parameter identification on historic masonry structures. This study combines a Bayesian framework with probabilistic structural analyses: starting from the Bayesian finite element model updating by using experimental data it provides the definition of robust seismic fragility curves for non-isolated masonry towers. A comparison between this method and the standard deterministic approach illustrates its benefits. This article is part of the theme issue 'Environmental loading of heritage structures'.
•Vehicles and trains are particularly sensitive to wind effects on viaducts and bridges.•Experiments are carried out to determine an optimal wind barrier design for viaducts and bridges.•Increasing ...the barrier porosity enhances wind velocities and decreases vorticity.•Increasing the barrier height moves flow and turbulence upwards from the road.•An optimal wind barrier proved to be the one with 30% porosity and 5m height.
Vehicles and trains are particularly sensitive to wind effects when passing on bridges and viaducts. As a possible countermeasure, wind barriers are considered to be a valuable engineering feature in alleviating an undesirable wind-induced instability of those vehicles. Hence, wind-tunnel experiments are carried out to determine an optimal aerodynamic design of wind barriers for viaducts and bridges. In this study, effects of porosity and height of the wind barrier, as well as orientation of barrier elements on flow and turbulence are studied. Mean velocity fields and vorticity fields are determined using the Particle Image Velocimetry (PIV) technique, while freestream velocities are measured using hot-wires and Pitot tubes. In general, physical phenomena which have been observed as influencing wind conditions behind the wind barrier are freestream wind buffeting, flow separation from a bridge leading edge and wind barrier top, flow bleeding through the barrier. With increasing the barrier porosity, wind velocities behind the barrier increase, particularly in the area immediately downstream from the barrier, while simultaneously there is a decrease in vorticity. Large freestream velocity, as well as vorticity due to flow separation from the wind barrier top, approaches the road surface close to the bridge trailing edge. Increasing the barrier height vertically moves a strong velocity and vorticity away from the road surface. In the paper, two different wind barrier configurations have been tested and analyzed; both orientations of tested wind barrier elements create similar flow field conditions behind the barrier for the same freestream flow and turbulence characteristics. In general, in order to achieve optimal wind conditions for vehicles behind wind barriers on bridges it is necessary to search for a compromise between barrier porosity and height, as these two parameters proved to be the key factors in creating safe transportation environment. In this study, an optimal wind barrier design is considered to be the one with 30% porosity and 5m high barrier.
This paper reports on a pilot project for long-term structural health monitoring of historical city gates. This structural typology is what today remains of the defensive structures that ...characterised the medieval centres of many European cities. Even though in the last years the scientific community has paid great attention to the structural analysis and on the structural health monitoring of masonry towers, which are apparently similar to the typology of city gates, only a few studies explicitly approach such heritage buildings. In most cases, the surviving gates are immersed in the daily vehicular-traffic flows and hence continuously subjected to traffic-induced vibration. Consequently, a key point both for their conservation is the assessment of the optimal sensors position to be used for reliable structural health monitoring procedures. These issues are here discussed with reference to a specific case: the San Niccolò gate in Florence (Italy). First, an expeditious experimental campaign performed with a reduced number of accelerometers is reported. This test is aimed to identify a numerical model that is subsequently employed to design the optimal sensor position of long-term structural monitoring. This optimal sensor grid must be assessed to ensure a low-cost and sustainable dynamic monitoring system but, at the same time, to maximize the information contents.
The recent developments of micro-electro-mechanical systems and wireless sensor networks allow today the use of low-cost and small-size sensors for continuous monitoring of civil structures. Both ...these features are very important for the low impact of the sensor grid in heritage structures, ensuring a low-cost and sustainable dynamic monitoring system. Over the last 20 years the use of sensor networks for continuous monitoring has received a growing interest. Anyway, still numerous questions remain opened about the sensitivity of measurement devices, the optimization of number and positioning of sensors, the energy efficiency of the network, and the development of algorithms for real-time data analysis. This paper, based on the aforementioned motivations, discusses about a monitoring system made of micro-electro-mechanical sensors connected through a wireless network. The architecture of the wireless sensor network and the automatized procedure proposed for the continuous processing of the recorded signals are discussed and described with reference to an explicative masonry tower case study. It is believed that the proposed technologies can provide an economical and relatively non-invasive tool for real-time structural monitoring and that, moreover, the availability of large amounts of data from actual measurements can give effective information on the structural behaviour of historic constructions.
Wind‐tunnel experiments were performed to study the wind characteristics on a parked wind turbine downwind of three types of hill and over a flat terrain. The focus of the study is on comparing wind ...characteristics on (a) a wind turbine standing alone and (b) this same type of wind turbine embedded in a wind farm. Particular emphasis is placed on the hill size and shape and the distance between the hill and the wind farm. The hill and wind‐farm models were subjected to an atmospheric boundary layer simulation to create realistic atmospheric conditions. Flow and turbulence were analyzed based on the measured mean flow velocity, Reynolds shear stress, turbulence intensity, and the power spectral density of velocity fluctuations. The experimental results reveal similar trends concerning (a) the wind characteristics obtained on a parked wind turbine embedded in a wind farm downwind of hills of various sizes and shapes and (b) the wind characteristics on this same type of parked wind turbine standing alone in the same position downwind of the same hills. In particular, the discrepancies in the mean flow velocity and turbulence intensity between these test cases are mostly below 5%, thus indicating that a complex terrain clearly has a dominant effect on the wind characteristics, while the effects of parked wind turbines on the wind characteristics are negligible. This important finding indicates that the structural loading of parked wind turbines situated on a complex terrain may be well calculated using the same procedures both for wind turbines standing alone and wind turbines embedded in wind farms if they are both placed at the same distance downwind of the same hills.
Sheltering efficiency of wind barriers on bridges Kozmar, Hrvoje; Procino, Lorenzo; Borsani, Alessandra ...
Journal of wind engineering and industrial aerodynamics,
08/2012, Volume:
107-108
Journal Article
Peer reviewed
Open access
Sheltering efficiency of wind barriers on viaducts was experimentally studied in a boundary layer wind tunnel. Effects of wind incidence angle on flow field characteristics in the wake of a wind ...barrier were reported. Mean velocity fields and vorticity fields were determined using the Particle Image Velocimetry (PIV) technique. Freestream velocities were measured using hot-wire and Pitot tube. Results indicate a possibility of wind-induced instability of high-sided vehicles at larger vertical incidence angles, especially in the traffic lane close to trailing edge of the bridge, as velocity fluctuations and mean freestream velocities approach the road surface when increasing the vertical incidence angle. Removing elements from the wind barrier causes very large local velocities immediately downstream from a barrier and strong vorticity in the entire area in the wake of a wind barrier. Variations in horizontal incidence angle do not seem to affect flow field characteristics significantly. Without a wind barrier, wind velocities on bridges reach 80% of the freestream velocity at height as low as 1m full-scale along with very strong vorticity in the immediate vicinity of the road surface.
► Sheltering efficiency of wind barriers on bridges was studied in the wind tunnel. ► Effects of wind incidence angle on flow field characteristics were reported. ► Wind-induced instability of high-sided vehicles at larger vertical incidence angles. ► Removing elements from wind barriers causes large local velocities and strong vorticity. ► Variations in horizontal incidence angle do not affect flow field significantly.
The manuscript provides a wide database for historic masonry towers collecting their modal, mechanical and geometrical features. This large amount of data was collected according to a literature ...review, then summing up as many as 56 different case studies. The collected data was then used to identify the main physical parameters influencing the modal behaviour of slender masonry towers, including the openings on the façades. After a critical discussion of the data reported in the database, the existing empirical or semi-empirical formulations available for the estimation of the first natural frequency of such structural typology are first evaluated. Subsequently the effects of the openings, as revealed through the analysis of the experimental results reported in the database, are discussed by comparison with a simple but effective numerical model. Despite the difficulties to quantify the effect of the openings along the height of the tower on the main frequency due to a cross-contribution of mass and stiffness, a simple but effective formulation is proposed which is able to account for this parameter.
A comprehensive understanding of the dynamic behavior of a tree can play a key role in the tree stability analysis. Indeed, through an engineering approach, the living tree can be modeled as a ...mechanical system and monitored observing its dynamic properties. In the current work, procedures of dynamic identification used in civil engineering are applied to the case study of a black locust (Robinia pseudoacacia L.). The tree was instrumented with 13 seismic, high-sensitivity accelerometers. Time histories of the tree response under ambient vibration were recorded. Three representative sections of the trunk (the collar, the diameter at breast height, and the tree fork) were equipped with three accelerometers, in order to obtain lateral and torsional vibrations. Moreover, two pairs of accelerometers were fixed on the two main branches. The results show that it is possible to identify the natural frequencies of a tree under ambient vibrations, thanks also to the support of a preliminary finite element model. Even though the optimal position is under the tree fork, the sensors fixed at the diameter at breast height allow a clear identification of the main peaks in the frequency domain.
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