•Interdisciplinary approach between architectural and structural surveying.•3D modelling issue as an important intersection between two complementary disciplines.•Filling the gap between FE ...structural analysis and TLS technology.
This paper presents a multi-disciplinary approach for identification of historic buildings structural health with combination of Terrestrial Laser Scanning (TLS) survey, Deviation Analysis (DA) and Finite Element (FE) numerical modelling. The proposed methodology was discussed through the application to an illustrative case study: an early medieval period brick minaret (Eğri Minaret) located in Aksaray (central Turkey). After standing upright for several centuries, the minaret has developed tilt, and today the structure is supported with steel cables. Precise direction of inclination, leaning angle, local deviations from circular building shape, deflections from vertical planes, local curvatures and related maps were obtained with high accuracy by DA, based on detailed point cloud 3D mesh model. Differently from traditional approaches in FE analysis, the paper discusses a method for direct transfer of high accuracy TLS based 3D model to FE structural analysis software, subsequently employed to interpret and verify structural health of the historic building. Through the discussion of the results, it can be considered that the integration of these different techniques (being the whole process non-destructive, effective and expeditious for surface analysis) is a promising methodology for health assessment and analysis of historic constructions.
•Bell swinging registered signals have been compared with these proposed by DIN4178 and some unsafe situations are detected.•By OMA analysis, damping ratio is evaluated under ambient and forced ...vibrations.•The use of genetic algorithms for the model updating presents a high dispersion of the results.•The optimum lateral confinement has been evaluated to update the FEM model.•A general methodology is proposed to analyze the damage generated by the swing of bells.
Recent years have seen a growing interest toward implementation and testing of structural health monitoring techniques for cultural heritage structures, and many scientific papers report on the application of operational modal strategies as an effective knowledge-based tool for vulnerability reduction of masonry buildings. Focusing on historic masonry bell-towers, being such structures particularly prone to earthquake-induced damage, the most part of the studies discuss structural monitoring and vibration-based identification methods with the goal of their seismic protection. As a consequence, while there is great number of researches that investigate masonry towers behaviour under earthquake loads, only a few scientific papers discuss their structural response under service loads such as bell-loads. This issue is also of paramount importance, since in many real cases the bell-ringing has been stopped due to the dynamic interaction phenomena that are activate between the bells and the host structure. With the aim to contribute of improving the knowledge in this field, this paper focuses on a methodology for the study of the dynamic interaction between bells and slender masonry towers. The proposed methodology is divided into four phases: (i) Geometric and structural characterization of the tower and bells; (ii) Evaluation of the dynamic forces generated by the swinging bells; (iii) Experimental campaign to characterize the dynamic properties of the tower by means of operational modal analysis; (iv) Parametric finite element analysis. To illustrate the methodology, a real case of masonry bell-tower in which bell-ringing had to be stopped due to a history of strong vibrations is discussed. The paper includes a method of analysing the dynamic properties of masonry bell-towers, in which the dynamic interaction between the harmonic bell forces and the fundamental tower modes is analysed by means of a calibrated numerical model and the dynamic amplification factor.
Wind characteristics in wind farms situated on a hilly terrain are considerably different than on a flat terrain. This issue is particularly important in strong-wind situations, when the wind ...velocity exceeds 25 m/s. In those situations, wind turbines are designed to remain in the parking position (no rotation of rotor blades) to prevent damage or even collapse of wind turbines. The present wind-tunnel study thus focuses on flow and turbulence characteristics in wind farms situated on a hilly terrain subjected to strong winds. A particular emphasis is on wind conditions for wind turbines placed at various positions in wind farms, as well as on a distance between a hill and a wind farm. The hill model is observed to strongly influence flow and turbulence characteristics at the wind-turbine model position in the wind-farm model. The most prominent aerodynamic features are flow retardation and turbulence enhancement, whereas the velocity power spectra show different trends along the height of the wind-turbine tower model. These experimental results present an important input for engineers attempting to design more robust and reliable wind turbines for hilly terrains.
•Wind-tunnel modeling of wind farms in hilly terrain for strong-wind situations.•Focus on wind-turbine position in the wind farm, distance between the hill and the wind farm.•Flow retardation and turbulence enhancement for wind turbines close to the wind-farm windward edge, i.e. close to the hill.•Velocity power spectra change their trends along the height of the wind-turbine tower.
In the framework of energy harvesting from flow-induced vibrations, understanding the behaviour of dynamic systems under high levels of damping is a key issue. In particular, this work refers to ...two-degree-of-freedom elongated rectangular plates prone to the aeroelastic instability of classical flutter. The effect of heaving damping was studied through systematic linear analyses and wind tunnel tests, developing specific aeroelastic setups for both large-amplitude motion and high viscous forces. Some configurations clearly showed a destabilizing effect of damping, both in terms of earlier instability onset and larger post-critical motion amplitudes. For high-inertia systems with low pitching damping, still-air frequency ratios of the uncoupled system away from unity and small mass unbalance downstream of the elastic axis are the key parameters to observe this phenomenon. Both analytical and experimental results suggest that this destabilizing effect relates to the tendency of any configuration to approach the behaviour of the system with unit still-air uncoupled frequency ratio while increasing the heaving damping.
AbstractThe paper reports the results of a research aimed at analyzing and interpreting the cracking pattern on the Cappella dei Principi (Prince’s Chapel, the Medici’s mausoleum) in the Basilica of ...San Lorenzo (Florence, Italy). The research was motivated by the sudden collapse of a keystone of an internal barrel vault sustaining one of the lateral apses. After a brief description of the geometry of the structure, the principal results obtained from in situ surveys (flat-jack tests and cored samples) are described; then the numerical analyses developed both to obtain the static identification of the monument and to assess the possible causes leading to the observed failure are illustrated. The numerical modeling operation has been performed step by step, from linear and quite simple models built with plane elements up to a nonlinear model with three-dimensional elements. The nonlinear FEM, which has been tuned by utilizing the results of the in situ measures, is allowed to both qualitatively and quantitatively reproduce the behavior of the structure and its static problems in the area of the barrel vault over the side apses, allowing for justification of the manifested damage. The comprehension of the structural behavior allows identification of a proper retrofitting strategy.
This study investigates the effect of angle of attack on flow-induced vibrations (FIVs) of sharp-edged rectangular cylinders. In particular, the effect of the afterbody of a rectangular cross-section ...with low mass ratio and the side ratio ranging from 0.67 to 1.5 is analysed by changing the angle of attack with respect to the oncoming free-stream. As already shown for a different side ratio’s rectangle, namely a square section (see Nemes et al., 2012), the angle of attack variation can make the flow-induced amplitude response switch between vortex-induced vibration (VIV) and galloping. Some considerations with respect to the interaction between the two phenomena typical of FIV, VIV and galloping, are also given for the side ratios of 1.5 and 0.67. The amplitude and frequency responses are carefully analysed, comparing the results with those of a square section of comparable mass ratio. The results showed a marked effect of the after-body, even for slight increments of the angle of attack. This can result in different amplitude response curves, as classified by the features of the response. In addition, the influence of interacting higher harmonics components on the amplitude response is also shown and discussed.
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’.
Abstract The application of vibration-based Structural Health Monitoring (SHM) for damage detection is characterised by three fundamental aspects: the features extracted as representative of the ...structural condition that can be directly linked to some form of damage, the metrics selected as novelty or damage index, and the statistical model or classifier built to identify underlying patterns indicative of changes in the structure’s state. Focusing on the first step to improve the performance of vibration-based SHM strategies, the extracted features should be robust to noise, sensitive to the presence of a specific type of damage. Further, damage should induce patterns that are distinguishable from environmental and operational variabilities and other forms of damage such as ageing phenomena. In this paper, the problem is framed as an outlier detection problem and the the use of different modal parameters as Damage Sensitive Features (DSFs) is investigated, evaluating them based on the detection performance of an unsupervised One-Class Support Vector Machine (OCSVM) classifier. In particular, an artificial dataset is generated from the calibrated numerical model of a three-storey steel frame structure in different damage scenarios. The methodology is validated against available experimental data. For the case investigated the natural frequencies were sensitive to damage and robust to noise.
•Wind-tunnel experiments on wind-turbine wake in complex terrain.•Velocity reduction and turbulence enhancement due to mountains.•Wind-turbine nacelle causes flow retardation as well.•Velocity ...fluctuations due to free shear layer separating from mountain ridge.•Flow disturbance diminishes downwind of mountain and wind turbine.
In order to extend lifetime and enhance energy production of wind turbines in complex terrain it is important to learn about their wake characteristics. Hence, wind-tunnel experiments are carried out to analyze the wind-turbine wake downwind of a mountain. The wind-tunnel simulation of the neutrally stratified atmospheric boundary layer (ABL) developing above a flat terrain is first generated using the well established Counihan approach. Once a well developed ABL simulation is achieved for a flat terrain, three various mountain models are separately exposed to that ABL simulation, as well as the flat terrain as a reference case. Wake characteristics of a single wind-turbine model in the wake of those four various terrain models are then studied. The ratios between the height of different mountains to the wind-turbine hub height are 0, 0.417, 0.833, 0.833 (0.417) for the flat terrain, small mountain, large mountain, mountain with a bay, respectively. For the mountain with a bay, there are two different ratios between the mountain height and the wind-turbine hub height; 0.833 at the lateral edges of the mountain, 0.417 in the lateral center of the mountain. All three mountain models are 600mm long in the main wind direction and 1000mm wide laterally to the main wind direction. Small mountain model is 100mm uniformly high, large mountain model is 200mm uniformly high. The mountain with a bay model is 200mm high with a normal slope to 100mm height in the lateral center of the mountain model, whereas this cavity is 200mm wide in the lateral direction. The calculated ABL simulation length scale factor is 1:300, and it is applied on mountain models and the wind-turbine model as well. The wind-turbine model is designed to correspond to commonly used prototype wind turbines. The experiments are carried out for the wind-turbine model in parking position to analyze trends expected in a strong wind situation, when there is no rotation of the rotor blades. Wake characteristics analyzed with respect to the mean wind velocity, turbulence intensity and velocity power spectra indicate several important findings. In particular, the observed flow retardation is more exhibited near the ground surface and the mountains. The mountain-induced flow disturbance enhances with increasing the size and complexity of the mountains. Turbulence intensity in the wake of the mountain and wind turbine is considerably larger than in the atmospheric boundary layer. Velocity power spectra are strongly influenced by the terrain complexity, whereas the effects of the mountain and surface roughness are mostly constrained up to the double mountain height. There is a strong energy content at frequencies corresponding to a free shear layer separating from the mountain ridge. Dominant turbulence structures are displaced vertically, as the wake is transported with the flow in the main wind direction.
•A design procedure for mdof aeroelastic modelling is presented and assessed.•Second order mode shapes response has been added to CAARC standard tall building.•A novel wind tunnel test campaign is ...presented and critically analyzed.•The comparison between the loads of the aerodynamic and aeoroelastic model is presented.
A novel approach to full-aeroelastic model design is presented, considering continuous structures and coupled modes. Its validity is proven by building a full-aeroelastic CAARC standard tall building model featuring 12-degrees-of-freedom at 1:360 scale. A complete description of its design, manufacturing, tuning, and dynamic identification is reported. The model is tested in a novel wind-tunnel experimental campaign performed at the CRIACIV facility (Prato, Italy). A comparative study of aerodynamic and full-aeroelastic response in terms of base moment and accelerations shows that the aerodynamic model tends to overpredict the response along the broader side of the model. The contribution of second modes is found to be relevant for induced acceleration at the rooftop.
PDF
