Aeroelastic instability of long-span bridges: contributions to the analysis in frequency and time domains

Sepe, Vincenzo,Caracoglia, Luca,D'Asdia, Piero Techno-Press 2000 Wind and Structures, An International Journal (WAS Vol.3 No.1

According to research currently developed by several authors (including the present ones) a multimode approach to the aeroelastic instability can be appropriate for suspension bridges with very long span and so with close natural frequencies. Extending that research, this paper deals in particular with: i) the role of along-wind modes, underlined also by means of the flutter mode representation; ii) the effects of a variation of the mean wind speed along the span. A characterisation of the response in the time domain by means of an energetic approach is also discussed.

Examination of experimental errors in Scanlan derivatives of a closed-box bridge deck

Rizzo, Fabio,Caracoglia, Luca Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.26 No.4

The objective of the investigation is the analysis of wind-tunnel experimental errors, associated with the measurement of aeroelastic coefficients of bridge decks (Scanlan flutter derivatives). A two-degree-of-freedom experimental apparatus is used for the measurement of flutter derivatives. A section model of a closed-box bridge deck is considered in this investigation. Identification is based on free-vibration aeroelastic tests and the Iterative Least Squares method. Experimental error investigation is carried out by repeating the measurements and acquisitions thirty times for each wind tunnel speed and configuration of the model. This operational procedure is proposed for analyzing the experimental variability of flutter derivatives. Several statistical quantities are examined; these quantities include the standard deviation and the empirical probability density function of the flutter derivatives at each wind speed. Moreover, the critical flutter speed of the setup is evaluated according to standard flutter theory by accounting for experimental variability. Since the probability distribution of flutter derivatives and critical flutter speed does not seem to obey a standard theoretical model, polynomial chaos expansion is proposed and used to represent the experimental variability.

New GPU computing algorithm for wind load uncertainty analysis on high-rise systems

Wei, Cui,Luca, Caracoglia Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5

In recent years, the Graphics Processing Unit (GPU) has become a competitive computing technology in comparison with the standard Central Processing Unit (CPU) technology due to reduced unit cost, energy and computing time. This paper describes the derivation and implementation of GPU-based algorithms for the analysis of wind loading uncertainty on high-rise systems, in line with the research field of probability-based wind engineering. The study begins by presenting an application of the GPU technology to basic linear algebra problems to demonstrate advantages and limitations. Subsequently, Monte-Carlo integration and synthetic generation of wind turbulence are examined. Finally, the GPU architecture is used for the dynamic analysis of three high-rise structural systems under uncertain wind loads. In the first example the fragility analysis of a single degree-of-freedom structure is illustrated. Since fragility analysis employs sampling-based Monte Carlo simulation, it is feasible to distribute the evaluation of different random parameters among different GPU threads and to compute the results in parallel. In the second case the fragility analysis is carried out on a continuum structure, i.e., a tall building, in which double integration is required to evaluate the generalized turbulent wind load and the dynamic response in the frequency domain. The third example examines the computation of the generalized coupled wind load and response on a tall building in both along-wind and cross-wind directions. It is concluded that the GPU can perform computational tasks on average 10 times faster than the CPU.

Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

Thai-Hoa Le,Luca Caracoglia 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent “structures” of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent “events” and the “coherent structure” of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a “modified” complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

Le, Thai-Hoa,Caracoglia, Luca Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

Estimating life-cycle monetary losses due to wind hazards: Fragility analysis of long-span bridges

Seo, D.W.,Caracoglia, L. IPC Science and Technology Press ; Elsevier Scienc 2013 Engineering structures Vol.56 No.-

A numerical framework was developed for estimating the life-cycle monetary losses (maintenance and repair costs) due to wind-induced damage on a long-span bridge. The wind loading on the bridge deck was evaluated by means of flutter derivatives (FDs), which are measured in a wind tunnel test on a section-model of the deck. These aeroelastic coefficients are random due to experimental errors. A statistical approach was employed to evaluate the effects of this uncertainty source on the wind-induced response and the damage produced on the structure. In the first part of the study ''fragility curves and surfaces'' were used to estimate the exceedance probability of representative structural performance threshold indicators by accounting for experimental errors in the estimation of FDs. These thresholds were based on deck acceleration (for user comfort) and peak deck displacements (for structural damage). In the second part the results of the initial fragility analysis were used to analyze monetary losses, produced by wind loading. The proposed model for cost analysis was adapted from an existing life-cycle simulation algorithm for earthquake hazards. The pilot study employs a 1200-m suspension bridge model and data from wind tunnel experiments conducted at Northeastern University in the United States.

High-order, closely-spaced modal parameter estimation using wavelet analysis

Thai-Hoa Le,Luca Caracoglia 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.3

This study examines the wavelet transform for output-only system identification of ambient excited engineering structures with emphasis on its utilization for modal parameter estimation of high-order and closely-spaced modes. Sophisticated time-frequency resolution analysis has been carried out by employing the modified complex Morlet wavelet function for better adaption and flexibility of the timefrequency resolution to extract two closely-spaced frequencies. Furthermore, bandwidth refinement techniques such as a bandwidth resolution adaptation, a broadband filtering technique and a narrowband filtering one have been proposed in the study for the special treatments of high-order and closely-spaced modal parameter estimation. Ambient responses of a 5-story steel frame building have been used in the numerical example, using the proposed bandwidth refinement techniques, for estimating the modal parameters of the high-order and closely-spaced modes. The first five natural frequencies and damping ratios of the structure have been estimated; furthermore, the comparison among the various proposed bandwidth refinement techniques has also been examined.

Life-cycle-cost optimization for the wind load design of tall buildings equipped with TMDs

Ilaria Venanzi,Laura Ierimonti,Luca Caracoglia 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.30 No.4

The paper presents a Life-Cycle Cost–based optimization framework for wind-excited tall buildings equipped with Tuned Mass Dampers (TMDs). The objective is to minimize the Life-Cycle Cost that comprises initial costs of the structure, the control system and costs related to repair, maintenance and downtime over the building’s lifetime. The integrated optimization of structural sections and mass ratio of the TMDs is carried out, leading to a set of Pareto optimal solutions. The main advantage of the proposed methodology is that, differently from the traditional optimal design approach, it allows to perform the unified design of both the structure and the control system in a Life Cycle Cost Analysis framework. The procedure quantifies wind-induced losses, related to structural and nonstructural damage, considering the stochastic nature of the loads (wind velocity and direction), the specificity of the structural modeling (e.g., non-shear-type vibration modes and torsional effects) and the presence of the TMDs. Both serviceability and ultimate limit states related to the structure and the TMDs’ damage are adopted for the computation of repair costs. The application to a case study tall building allows to demonstrate the efficiency of the procedure for the integrated design of the structure and the control system.