1,720,984 research outputs found
Load-carrying capacity of compressed wall-like RC columns strengthened with FRP
Full text linkThe analytical prediction of the effectiveness of fiber-reinforced polymer (FRP) in the confinement of a rectangular reinforced concrete (RC) column with a high aspect ratio (wall-like) still has an uncertain solution. In this paper, a numerical investigation of the axial response of RC wall-like columns strengthened with FRP systems was developed. Analytical solutions proposed in the literature for the assessment of the axial load capacity were presented and compared with each other and with the available experimental results. Moreover, non-linear finite element analysis was carried out, and the results were discussed, providing a simple model for the assessment of the axial compressive strength of wall-like RC columns strengthened with FRP
Probabilistic assessment of footbridge response to single walkers
Full text linkAmong the load scenarios considered for the serviceability assessment of human-induced footbridge vibration, is that of the transient action of a single pedestrian or a small group of pedestrians. Although such action is stochastic due to the variability of gait parameters, available Codes and Guidelines all assume it is deterministic and equal to that coming from the “worst pedestrian ever” for the given footbridge. This approach is sound from an engineering point of view but does not allow control of the probability of failure. The present work deals with a reliability-based procedure for the serviceability assessment of the footbridge peak characteristic accelerations due to pedestrian induced actions. Based on the results obtained incorporating the effects of the inter-subject variability of gait parameters and of the uncertainties in footbridge dynamic properties, a design response spectrum is proposed for both vertical and lateral vibrations. The proposed procedure lends itself for immediate Code implementation
Axial Load Capacity of Wall-Like RC Columns Strengthened with FRP
No full textThe confinement with fibre-reinforced polymer (FRP) is one of the most used techniques to enhance strength and ductility of existing reinforced concrete (RC) columns. Although the effective of FRP confining systems on columns with circular, square or rectangular cross sections has been extensively studied and standardized, these results are limited to sections with an aspect ratio between the two sides less than two. However, many applications of wall-like columns (member with rectangular cross section with higher aspect ratios) strengthened with FRP are developed in the practice. Moreover, the prediction of their load carrying capacity still remains of uncertain solution. In order to clarify this issue, a review of the existing analytical models is first presented. Then, available experimental results are selected from the literature to compare the performance of these models. Finally, the results are discussed to quantify their accuracy in the prediction of the axial member capacity
Correction of historical records to improve the reliability of design wind speeds
No full textIt is not uncommon that design wind speeds are derived from measured data for which the sampling period is longer than the averaging time, e.g. 10-min averages measured once every hour; we call these downsampled data. Using downsampled data has the effect of shifting the calibrated distribution of the yearly maxima to the left, thus reducing the predicted return wind speed. The origin of this has probably to be found in the fact that a large amount of research on the assessment of design wind speeds was developed in the UK, where hourly wind speed averages were available, measured twenty-four times a day, i.e. contiguously. Procedures were then applied also in the case in which downsampled data were available, apparently disregarding the bias this brings. Indeed, even contiguous measurement of mean wind speeds is insufficient, as for the proper evaluation of the return wind speed continuous measurements would be needed. In this paper, the difference between continuous, contiguous disjunct and downsampled disjunct data measurements is pointed out, and the effects of downsampling on the statistics of the extreme wind speed are quantified. A technique for correction of disjunct measurements is proposed and validated in order to remove the bias deriving from downsampling and to improve the reliability of design wind speeds and velocity pressures. Finally, the procedure is applied to datasets from four Italian meteorological stations showing an increase of the return velocity pressure after correction of about 10% to 30%
Codifiable probability-based model for footbridges response to random walkers
No full textThe response to the transient action of a single pedestrian or a small group of pedestrians is required for the serviceability assessment of human-induced footbridge vibrations. The approach adopted by standards and guidelines is proved to lead to a non-uniform level of reliability. This is in contrast with both the stochastic nature of pedestrian gait parameters and the probabilistic approach adopted by modern structural codes. In this paper, firstly the analysis of peak accelerations is developed according to the Eurocode for a number of simply-supported footbridges, both in vertical and lateral directions. These are shown to correspond to different level of probability of exceedance, that is larger for short-span footbridges and smaller for long-span footbridges. Then, a model for the assessment of the characteristic footbridge acceleration is provided. This is based on the prediction of the basic acceleration, i.e. the response of simply-supported footbridges to single pedestrian crossings, and the application of an acceleration ratio factor for footbridge configurations other than simply-supported
Uncertainty in the dynamic properties of tall buildings and propagation to the wind-induced response
No full textThe response of tall buildings to wind actions is commonly assessed through the quasistatic approach considering mean, background, and resonant components of the action. The latter accounts for the amplification due to resonance and depends on the dynamic properties of the buildings, that is, modal mass, frequency, and damping ratio. Selecting appropriate values of the modal parameters of tall buildings is not immediate and is usually done using predictive models. These contain uncertainty, which eventually
propagates to the dynamic response. The main aim of the paper is the assessment
of uncertainty in the dynamic response of flexible buildings to wind action arising from
a not perfect knowledge of their dynamic properties. The paper explicitly refers to the
dynamic models given by Eurocode 1, but the approach is general, and the analyses
can be repeated selecting any other model. It is found that the bias in the dynamic factor is always less than one, with values on average between 0.86 and 0.98. This indicates that the approach of Eurocode 1 is conservative. The only exception is that of
the acrosswind response of steel buildings with an high aspect ratio, in which case the
bias can be as large as 1.16. As to randomness, the coefficient of variation of the
alongwind dynamic factor is very seldom found to exceed 10%, with average values
around 5%. Such values are much lower than those of the coefficient of variation of
damping, which is in the order of 50% or more. This indicates that uncertainty attenuates when it propagates to the response. On the other hand, the coefficient of variation of the acrosswind and torsional dynamic factors reaches values of 20% or more, indicating that such attenuation is much lower in that case
The Relationship between Wind Pressure and Pressure Coefficients for the Definition of Wind Loads on Buildings
Full text linkWind induced pressures on buildings are the product of a velocity pressure and a pressure coefficient. The way in which these two quantities are calculated has changed over the years, and Design Codes have been modified accordingly. This paper tracks the evolution of the approach to wind loading of buildings from the practice in the 1950s, mainly referring to the Swiss Code SIA, to the most recent advances including probabilistic methods, internet databases, and advanced modelling of meteorological phenomena
Experimental Tests on the Wave-Induced Response of a Tension Leg Platform Supporting a 5 MW Wind Turbine
No full textFloating offshore wind turbines are complex dynamic structures, and the analysis of their environmental loads requires experimental test investigations. This paper aims to provide the experience gained from wave basin experiments performed at the Danish Hydraulic Institute on a floating wind turbine Tension Leg Platform within the framework of the EU-Hydralab IV Integrated Infrastructure Initiative. Froude-scaled model was subjected to regular waves and steady wind loads. Measurements were taken of hydrodynamics, displacements and wave induced forces at the mooring lines. First, free vibration and hammer tests were performed to obtain the natural frequencies of the floating motions and tower elastic behaviour, respectively. Then, displacements, rotations, and forces were measured under regular waves and parked and rated wind conditions. Spectral analyses were carried out to investigate the dynamic response of TLP wind turbine. The results show that most of the dynamic response occurs at the wave frequency and natural frequencies
Feasibility analysis for floating offshore wind energy
Full text linkPurpose
The assessment of the economic feasibility of foating ofshore wind farms (FOWFs) plays an important role in the future possible spreading of this challenging technology in the wind power industry. The use of specifc economic analyses is fundamental to point out the potential of FOWFs and to sustain their technical value. Within this topic, the implementation of the FOWF life cycle cost model and producibility analysis in a geographic information system is developed, with the aim of carrying out a feasibility analysis at the territorial scale, for diferent types of foater. Moreover, a simplifed model for a quick life cycle cost assessment is proposed and calibrated.
Methods
The available cost model is frst validated comparing the costs of FOWFs based on diferent foaters (Semi-Submersible Platform—SSP, Spar Buoy—SB and Tension Leg Platform—TLP) with corresponding results available in the literature. Then, it is implemented in QGIS to be used for territorial-scale analyses and sensitivity analyses of the cost parameters. A feasibility analysis is developed through the main fnancial parameters. Finally, the results are then used to calibrate a simplifed version of the cost model that depends on three main parameters, namely distance to shore, distance
from the port of operation and bathymetry.
Results and discussion
The FOWF cost values are found to be in good agreement with those coming from analytical methods similar to the one from the authors. However, some discrepancies with those based on average costs are observed. Then, the results of the sensitivity analysis are presented as life cycle cost maps, giving an overall picture of the variation of the total cost of FOWF installations on a reference domain. The results show that among the three types of foaters considered here, the SSP proved to be the most promising one, giving lower costs than the SB and the TLP. Moreover, a good agreement between the results in terms of total cost of FOWFs calculated with the analytical and simplifed models for SSPs, SBs and TLPs is observed. Finally, the feasibility analysis showed that the fnancial parameters are more infuenced by the wind speed than by the cost of the farm.
Conclusions
The paper aims to provide guidance on how to carry out feasibility analyses of a specifc site for FOWF installation, thus supporting decision-making procedures. The approach and the results presented here are meant for use in the early stage of the decision-making process, as a tool for the assessment of the economic feasibility of FOWFs installation
Seismic retrofit of a multispan prestressed concrete girder bridge with friction pendulum devices
Full text linkThe paper deals with the proposal and application of a procedure for the seismic retrofit of an existing multispan prestressed concrete girder bridge defined explicitly for the use of friction pendulum devices as an isolation system placed between piers top and deck. First, the outcomes of the seismic risk assessment of the existing bridge, performed using an incremental noniterative Nonlinear Static Procedure, based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra, are described and discussed. Then, a specific multilevel design process, based on a proper application of the hierarchy of strength considerations and the Direct Displacement-Based Design approach, is adopted to dimension the FPD devices. Furthermore, to assess the impact of the FPD nonlinear behaviour on the bridge seismic response, a device model that reproduces the variation of the normal force and friction coefficient, the bidirectional coupling, and the large deformation effects during nonlinear dynamic analyses was used. Finally, the paper examines the effects of the FPD modelling parameters on the behaviour of the retrofitted bridge and assesses its seismic response with the results pointing out the efficiency of the adopted seismic retrofit solution
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