The effects of reinforcement corrosion need to be included in the assessment of existing Reinforced Concrete structures for a reliable evaluation of the structural performances over time and a ...correct choice of the renovation strategy. The DEMSA protocol proposes straightforward tools available to professional engineers, enabling the calibration of equivalent damage parameters able to describe corrosion effects starting from environmental easy‐measurable conditions. Guidance to implement the equivalent damage parameters describing corrosion effects at a sectional level in the structural analyses is provided. Then, a simplified approach to model the corrosion attack distribution along the bar length is proposed. Finally, nonlinear static analyses are carried out on reference RC frames subjected to different corrosion patterns by adopting fiber modeling technique, to show how the equivalent damage parameters allow detecting the impact of corrosion effects on the structural performances, in terms of internal actions distribution, reduction of stiffness, strength, and ductility.
Turbulence is one of the main characteristics of urban flows, but its effect on the performance of small VAWTs (often used in urban wind installations) has not been thoroughly researched. This ...experimental study focuses in testing a H-Darrieus VAWT prototype in different turbulent conditions inside the wind tunnel, in order to study the influence of turbulence intensity, integral length scales and Reynolds number. Passive grids are used to increase the wind tunnel free stream turbulence up to Iu = 15%, with integral length scales of Lux = 0.18 m and Reynolds numbers of ReD ≈ 300,000. The measurements are repeated in two wind tunnels of different size, which strengthens the results and helps quantify the effect of blockage on the turbine ratings. The results show power coefficient increases up to 20% from smooth (Iu = 0.5%) to turbulent (Iu = 15%) flows, an effect that is enhanced at low λ but that fades as ReD > 400,000. The study of the crossed influence of ReD, Iu and Lux offers valuable data in the process of optimizing the operation of small VAWTs inside urban environments.
•H-Darrieus VAWT tested in different turbulent conditions inside two wind tunnels.•Passive grids used to increase wind tunnel free stream turbulence up to Iu = 15%.•Study of the crossed influence of Reynolds number, Iu and Lux on VAWTs.•20% increase of mechanical power from smooth (Iu = 0.5%) to turbulent (Iu = 15%) flows.•Blockage corrections evaluated in two wind tunnels of different size.
The paper presents a synergic and multidisciplinary approach where laser scanner survey, radar interferometric monitoring and finite element (FE) numerical modelling are used for expeditious and ...no-contact dynamic identification of monumental masonry towers. The methodology is applied to a real case of great historical interest: the “Torre del Mangia” (Mangia's tower) in Siena (Italy). The tower geometry was acquired through Terrestrial Laser Scanning (TLS) techniques. The tower oscillations were detected using an interferometric radar in “Piazza del Campo”, the square facing the Mangia's Tower, along three alignments, and movement of the structure at several heights were recorded. A FE model, built on the basis of the geometry acquired through the TLS, was used to interpret and verify the physical meaning of the experimental results. Through the discussion of the case study, the paper shows that the proposed approach can be considered as an effective and expeditious method for assessing the dynamic behavior of monumental buildings (and to plan interventions) on territorial scale.
A careful modeling of vortex-induced vibration of a bridge deck allows to avoid fatigue damages and the reduction of travel safety and/or comfort levels for the users. The existing empirical models ...do not seem to be fully reliable because they are not able to predict the response oscillation amplitude for values of the mass and damping away from those at which their aeroelastic parameters were estimated. A van der Pol-type equation is used in the Ehsan–Scanlan's model, which for practical reasons seems to be the more suitable model for vortex-induced vibration of bridge decks. In this work this model was deeply studied and wind-tunnel tests on a 4:1 rectangular cylinder were performed to apply it to a realistic case study. Numerical integrations of the van der Pol-type equation highlighted its physical coherence to model vortex-induced vibrations of structures prone to the wind action. Moreover, it was verified that the assumptions standing behind the Ehsan–Scanlan's identification procedure of the aeroelastic parameters are justified. Finally, an alternative identification procedure was proposed, consisting in a numerical estimation of the aeroelastic parameters directly from the nonlinear differential equation.
The interaction between galloping and vortex-induced vibration was experimentally investigated for an infinitely long rectangular cylinder with a side ratio of 3:2, free to vibrate in the transverse ...mode in smooth flow. This geometry showed strong proclivity to instability and large oscillations occurred also at high Scruton numbers, in a range of flow speeds where no excitation was expected according to the classical theory. A high value of the ratio of the quasi-steady galloping critical wind speed to Kármán-vortex resonance velocity is necessary to avoid such a combined instability. Measurements of transverse displacements, velocity fluctuations in the wake of the oscillating body and pressures on its surface highlighted nonlinear features of the fluid-structure coupled system, such as superharmonic resonances and hysteresis. In particular, for low values of the Scruton number, non-negligible excitation was observed at low reduced wind speed due to secondary resonance.
The study discusses some recent results regarding the identification of the static and dynamic behavior of the Brunelleschi's Dome of Santa Maria del Fiore in Florence, which was declared part of the ...UNESCO World Heritage sites in 1982 together with the city center. First, a brief sketch of the main geometric characteristics and the relevant constructive aspects conceived by Brunelleschi are outlined with a description of the present crack pattern. Then a finite element model was built to assess the static and dynamic behavior of the monument and identified taking into account the results of an in situ investigation developed in the 1980s. The numerical model was used with an ad hoc nonlinear procedure to replicate the mechanical behavior of masonry. Obtained results allowed to assess and to discuss both the Dome's internal stress and cracking pattern. The identified numerical model was subsequently employed to provide a first evaluation of the seismic behavior of the Dome. While showing how advanced numerical analyses can provide useful hints to evaluate the existing damage on monumental heritage, this study aims at contributing to the assessment of the safety and vulnerability of one of the most emblematic masonry domes all over the world.
This paper discusses the cracking pattern in a historical Italian palace proposing a diagnosis for the origin of the actual damage state. The analyzed building, which dates back to the seventeenth ...century, is a masonry building with a rectangular plan section located in Piancastagnaio (South Tuscany, Italy). The building exhibits a severe and variegated vertical and horizontal cracking pattern mainly affecting the southern and eastern façades. Due to the damage, the palace was evacuated by the Public Authorities during the 1980s and a series of provisional remedies (mainly steel chains) was added. Through the use of the finite element technique, the paper provides an interpretation of the manifested damage. The aim of the diagnosis, supported by the numerical results, is to design an extensive
in-situ investigation on the palace. Moreover, the paper aims at evaluating the effectiveness of the actual temporary retrofitting (mainly steel chains) used to freeze the present damage. At the end of the paper the
in-situ investigation is presented and discussed.
Equivalent static loads on buildings are usually evaluated following the quasi-steady approach, assuming that instantaneous approaching wind velocities are directly translated into surface pressures ...at all points on the building faces. Such an approach is in contrast with the actual nature of pressures, acting on the faces, exposed to a separated flow. For these, mean and fluctuating pressures are not directly related to the characteristics of the oncoming flow and, to an even lesser extent are fully correlated to those acting at corresponding points on the windward surfaces. To investigate the characteristics of the pressure fluctuations on the leeward and side faces of medium-rise, rectangular plan buildings and to quantify the error associated with the quasi-steady assumption, in this paper the results of wind tunnel pressure measurements are discussed. The characteristics of fluctuating pressures and the equivalent static load are compared with those arising from the application of the quasi-steady approach and from the use of codes of practice.
This paper presents an application of a methodology for the seismic vulnerability reduction of masonry towers by reversible prestressing. The approach is applied on a medieval tower located in San ...Gimignano, Italy, which is considered as a world heritage site. The 3D FE models are calibrated with experimental data and assessed by nonlinear static analyses including the seismic demand of the site and an accurate validated masonry model. The vertical prestressing is applied at key points identified in the seismic vulnerability assessment. This technique is in compliance with the demand for architectural conservation because it may be fully reversible. The seismic performance is enhanced by increasing force, displacement and internal confinement. It is observed at ultimate limit conditions an upgrading of 14.3% of displacement with the medium prestressing level and 9.5% with the high level. The results are analyzed and discussed in terms of earthquake energy dissipation and failure mechanisms.
•Application of two seismic assessment approaches on a medieval Italian tower.•Main failure modes are representative of bell towers with large openings.•Experimental, historical and structural data for calibration of 3D FE models.•Seismic retrofitting by two prestressing levels and one removable FRP device.•Medium prestressing is the optimum level for attaining EQ energy dissipation.
One issue that dominates the serviceability design of many modern tall buildings is wind-induced discomfort. The assessment of discomfort risk for the buildings occupants due to the wind action is, ...therefore, of primary importance. It can be properly carried out only through a reliable estimation of the acceleration responses which, particularly in the across-wind direction, may be influenced by aeroelastic effects. Within this context, a wide experimental campaign was carried out in this study in order to evaluate the wind-induced loads and responses of a continuous equivalent aeroelastic model of a regular square-section tall building. Measurements of surface pressures on 126 taps, overall forces, across-wind displacements and across-wind and along-wind accelerations were simultaneously carried out. Aeroelastic effects involving the across-wind response, which largely exceeds the along-wind one, are evaluated in terms of aerodynamic damping using an experimental-numerical procedure. Across-wind aerodynamic damping is found to take positive values for the model tested having high Scruton number. A general procedure for wind risk assessment of tall buildings related to comfort, in line with the Performance-Based Design (PBD) approach and the PEER (Pacific Earthquake Engineering Research Center) equation, is proposed and applied to a case-study building whose aeroelastic response is known from the wind tunnel tests performed.
•We test a continuous aeroelastic model of a tall building even in lock-in condition.•We measure simultaneously pressures, overall forces, displacements and accelerations.•Across-wind aerodynamic damping is identified through an inverse response approach.•We propose a PBD procedure for wind-induced discomfort risk of tall buildings.•The procedure is applied to an ideal building to estimate its discomfort risk.
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