Dynamic Wind Action Research Articles

Modal parameters and damage evaluation of steel fiber reinforced concrete under flexural cyclic loadings

Structures may be subjected to static and dynamic loads during their service life. When it comes to the dynamic spectrum, wind action, ocean waves and seismic loads are key examples and are responsible for cracking evolution and material degradation along their lifespan. Therefore, the fatigue behavior of cementitious materials has been receiving great attention due to cyclic loading that can be of natural occurrence or induced by human activity lately. The present research aims to investigate the evolution of the modal parameters of steel fiber reinforced concretes under flexural cyclic load and to evaluate how the mechanical degradation can be monitored from a non-destructive impact modal testing over the cycles. The dynamic properties of the material, including natural frequencies, vibration modes and damping ratios, were tracked to assess the level of fatigue damage using modal testing techniques. Hence, it was possible to evaluate the material mechanical degradation as a function of the dynamic parameters. From the dynamic test, it was possible to evaluate the presence of damage, which was corroborated by the observed stiffness degradation. The first flexural mode and the following second, third and sixth vibration modes were more affected along the cycles. Finally, the proposed non-destructive methodology was effective in assessing the mechanical decay of cementitious composites.

Lyapunov stability of suspension bridges in turbulent flow

In the era of sleek, super slender suspension bridges, facing the issue of stability against dynamic wind actions represents an increasingly complex challenge. Despite the significant progress over the last decades, the impact of atmospheric turbulence on bridge stability remains partially not understood, evoking the need for innovative research approaches. This study aims to address a gap in current research by investigating the random flutter stability associated with variations in the angle of attack due to turbulence, which has not formally been addressed yet. The present investigation employs the 2D rational function approximation model to express self-excited forces in a turbulent flow. The application of this type of models to bridge dynamics yields a viscoelastic coupled dynamic system characterized by memory effects and driven by broad-band long-time-scale noise, described here by a linear homogeneous time-variant differential equation, which shows apparent nonlinear features, and which has rarely been matter of research. Utilizing a Monte Carlo methodology, this work innovates in applying the largest Lyapunov exponent (LE) and the moment Lyapunov exponents (MLE) to study bridge random flutter stability. The calculation of LE and MLE under diverse turbulent wind conditions uncovers lower flutter stability than without turbulence effects. In most cases, sample and low-order p-th moment stability thresholds closely align with the bridge dynamic response pattern; therefore, the flutter critical wind speed is unequivocal. However, under certain turbulence scenarios, it is necessary to resort to MLE for a complete description of stability, evoking some additional consideration of which statistical moments should be considered for the engineering assessment of the flutter limit. Finally, this work provides a qualitative insight into the instability mechanisms by approximating the random parametric excitation with a sinusoidal gust and evaluating the time-periodic system stability via Floquet theory.

Optimization of a reinforced concrete structure subjected to dynamic wind action

This work proposes a methodology to optimize a reinforced concrete structure. For this, the Whale Optimization Algorithm (WOA) algorithm was used, an algorithm from the group of metaheuristic algorithms, which presents an easy computational implementation. As a study object, a frame structure adapted from a real reinforced concrete building was used, subjected to the dynamic action of artificially generated synoptic wind. The objective function is to reduce the volume of concrete of the structure. For that, the dimensions of the cross-sections were used as design variables, and the maximum displacement at the top imposed by the ASCE / SEI 7-10 standard as a lateral constraint, as well as the maximum story drift between floors. In addition to this structural optimization, it was also proposed the use and optimization of Tuned Mass Dampers (TMD), in different quantities, positions and parameters, improving the dynamic response of the reinforced concrete building. The results show that for this situation it was possible to reduce the concrete volume of the structure by approximately 24%, respecting the maximum limit of displacement at the top required by the standard.

Galloping performance of various shape of bridge hanger

Long span bridge and slender element of the bridge is sensible to dynamic wind action such as flutter buffeting, vortex induced vibration and galloping. For arch bridge, vibration of hanger due to dynamic action of the bridge has been experienced including hanger vibration of Tayan Bridge. The possible phenomena of the vibration are flutter, galloping and vortex induced vibration. This paper presenting the study of galloping phenomenal on the hanger of the Tayan Bridge. Several shape of the bridge hanger has been considered in this study. Computation Fluid Dynamic has been used to determine the static wind coefficient of the hanger. Glauert-Hartog Criteria has been applied to examine the performance of the bridge hanger to galloping. The result showed that that only circle shape that is not experiencing galloping

Sensitivity Study of Dynamics Variability for Mild-carbon Steel Structures Affected by Corrosion

Background:Corrosion propagation mainly occurs due to environmental conditions and to the absence of adequate maintenance. The corrosion propagation affects the structural performances of slender and thin structures, in particular in the case of structure very sensitive to the wind action and its dynamical phenomena, because commonly they are designed with a precise optimization of the stiffness/mass ratio. The static and dynamic wind action represent an immediate safety hazard in the case of structural stiffness and mass reduction due to the corrosion depth.Objective:This paper discusses the dynamics behavior variability due to the corrosion depth propagation for two significant examples of slender and thin structure (i.e.tower and truss roof).Methods:The structures assumed as case of study are made of mild carbon. The corrosion depth variability was estimated based on literature references. The structural natural frequencies and modal shapes are assumed as significant magnitudes to discuss the effect of the corrosion on the structural elements.Results:Results have shown that the corrosion depth gives a significant reduction of frequencies and modification of modal shapes.Conclusion:Results have shown that the corrosion depth affect the structural behavior long before a structural collapse. It suggests that a monitoring must be done to estimate the structure reliability for the Serviceability limit state under Characteristic design loads.

A system for measuring environmental data in full-scale

The paper presents a system created for measuring wind speed and its direction in full-scale conditions. The system consists of devices used to measure environmental parameters in one point at a time and a complex weather station. On the basis of the results obtained from the first part of the system, the static effect of wind action on structures or climatic comfort can be approximated, while the second part of the system is used to determine the dynamic wind action on objects. The use of the designed system is illustrated by in-situ studies.

Stohastičko opterećenje vetrom kod kontejnerske dizalice

This paper describes the research on the mechanical behavior of a container crane subjected to variable wind loading. In the first step the wind action was studied and defined. Stochastic wind loading was simulated by means of power spectrum method. Preliminary analyses were carried out on a chimney (100 m) because its geometry is very simple. Many different schematizations were implemented both to evaluate the results convergence and to define the correct finite element method schematization. At the end, the results were compared with those obtained by classical methodology, i.e. by response to an equivalent force which was evaluated by multiply the wind pressure with the front area and defined coefficients. The next step was to design the crane (pay load =50 t) and to study the mechanical response of the structure to the dynamic wind actions defined in the previous step. The results (displacement) of numerical analyses show that the classical method used to study the wind actions applied on the structures overestimates those determined by power spectrum method.

Some critical issues on the distribution of the maximum value of the wind-excited response of structures

Most verifications at the ultimate and serviceability limit states involve the evaluation of the maximum value of a structural parameter and its comparison with a threshold. This evaluation has thus a dominant impact on engineering, design and codes that reflects on the safety and economy of built environment and society. The distribution of the maximum value of the wind-excited response of structures is usually determined by the Davenport’s model assuming that the structural response is a random stationary Gaussian process and the up-crossings of high response thresholds are rare independent events. The hypothesis that wind actions are stationary limits the analysis to synoptic phenomena. The hypothesis that wind actions are Gaussian implies that turbulence is small and the atmospheric stratification is neutral. The hypothesis that the up-crossings of high response thresholds are rare independent events raises some doubts on its application to flexible and low-damped structures, just those structures most susceptible to dynamic wind actions. This paper aims at inspecting this topic with special regard for some aspects almost ignored in literature, namely the properties of real wind velocity records and their influence on the distribution of the maximum value, the simulation of wind velocity histories with particular concern for the length of the signals, and the classic use of some theoretical models of the maximum value with special attention to the aprioristic acceptance of the representativeness of its mean value. Analyses are here carried out in the classic framework of stationary Gaussian processes. The results achieved point out some shortcomings in the classic engineering practice and provide some remarks for future research.

Static and modalanalysis of Solidarity Bridge in Płock

Cable-stayed bridges are stunning structures, which thanks to their dimensionsand shapes fascinate not a single observer. Designing such an object is awesomechallenge for designers. These structures must transfer forces resulting from dead load,operational loads, temperature changes and coming from wind pressure. Nowadays, eachcable-stayed bridge and suspension bridge must be subjected to special analysis to guaranteesafe usage. Designers cannot allow the situation, which took place on November7th,1940 in north-western part of the United States of America near the town Tacoma,where the collapse of the suspension bridge occured. The structure was destroyed as theresult of coincidence of natural vibrations and the dynamic wind action. Authors of thepaper undertake the task to provide dynamic analysis of Solidarity Bridge in Płock exposedto the wind action. The mentioned structure is the longest cable-stayed bridge in Poland andat the same time, the longest in the world with the arch suspended at one axis to the columnarpylon fixed to a platform. Additionally static analysis is made in order to verify horizontaland vertical displacements as the result of combined variable loads.

Numerical study of wind actions applied to a low profile container crane

The target of this numerical study is to investigate the problems involved in the design of a low profile container crane exposed both to static and dynamic wind actions, in order to establish if these loads are dangerous when compared with the load induced by standard container load and unload operations. In the first step the work was performed by means of different schematizations of the wind load action allowed by the standards; the second step regarded the application of a real trend (velocity of wind versus time) obtained experimentally on a similar crane positioned in an Italian harbor. The results obtained in terms of maximum displacement depend on the crane load conditions and on the different schematizations used for the wind action. Using a variable wind pressure, the research shows that the effects of wind loads are greatly influenced by the natural vibration frequencies of both the structure and the elements that compose the structure.

Assessment of Stiffening Type of the Cutout in Tubular Wind Turbine Towers Under Artificial Dynamic Wind Actions

The effectiveness of alternative stiffening types of the cutout provided near the base of tubular steel wind turbine towers is assessed, taking into account the dynamic nature of wind loading. To that effect, artificial wind load time histories are first obtained using the public domain aero-elastic code FAST. Finite element models that have been previously validated by means of comparison with experimental results, are then used to carry out fully nonlinear dynamic analyses and compare strength and overall structural performance.

Badania modelowe i numeryczna analiza aerodynamiczna mostu łukowego dla pieszych

Complex aerodynamic analysis of the "Kazimierz-Podgórze" bridge for pedestrians and bicycles traffic over Vistula River has been presented in the paper. The analysis consists of model tests performed in the wind tunnel and aerodynamic calculations. Aerodynamic coefficients of drag Cx, lift Cy and moment Cm for three sections of the bridge in dependence on the angle of wind attack in the range -15° to +15° have been obtained from the wind tunnel tests. These functions of the aerodynamic coefficients have been used to determine the wind action on the footbridge according to the quasi-steady theory, and to estimate the possibility of self-induced vibrations of the bridge deck. The bridge dynamic characteristics: frequencies and mode shapes, as well as displacements, internal forces and stresses in particular structural elements under the dynamic wind action have been determined numerically. Static analysis of the bridge under a deadweight only has been performed for comparison. Due to circular cross-section of an arch girder, dynamic analysis of the bridge with vortex excitation of the arch girder has also been performed. This excitation has been applied to the structure simultaneously with the dynamic wind action at the mean wind speed equal to the critical wind speed. The criteria for pedestrian comfort in presence of vibrations generated by wind have also been examined.

Analiza aerodynamiczna mostu pieszo-rowerowego o kształcie sinusoidalnym

Computer aerodynamic analysis of the bridge “Kazimierz-Ludwinów” located in Cracow, designed for pedestrians and bicycles traffic is presented in the paper. Authors’ own model of the dynamic wind action based on the quasi-steady theory has been applied. The data, obtained in model studies performed in a wind tunnel, have been assumed as the basis for calculation. The following aerodynamic coefficients have been measured: aerodynamic drag Cx, aerodynamic lift Cy, and aerodynamic moment Cw for three sections of the bridge as the functions of the wind attack angle in the range from -10° to +10°. The aerodynamic analysis presented in the paper includes: wind tunnel tests, determination of dynamic characteristics and calculation of the response of the bridge subjected to the dynamic wind action.

Calculation of Timber Outlook Tower with Influence of Behavior of “Steel-Timber” Connection

The paper describes the dynamics analysis of the timber truss tower structure located near Bohdaneč village. Regular static analysis and response on dynamic wind action detailed calculations of tower was performed. Article contents description of elaborated analysis, results summary and qualifying reliability of the structure considering dynamic wind effect in direction of the flow, vortex excitation and pedestrians’ movement action.

Structural stability of concrete wind turbines and solar chimney towers exposed to dynamic wind action

Apart from burning classical fossil resources or generating nuclear power, alternatives have been developed, like the classical ways to capture energy from wind, water and sun, or the innovative solar chimney concept. The paper presents some structural aspects of classical wind energy turbines, like their high-cycle dynamic loading and reaction as well as their fatigue behaviour. Actual research results concerning pre-stressed concrete tower constructions for wind turbines will be focused on. For the solar chimney concept the structural challenges concerning wind action, eigenfrequencies, stiffening and shape optimization with special focus on the inlet guide vanes will be discussed. Both classical wind turbines and the innovative solar chimney concept may successfully contribute to the future energy supply in Southern Africa.

Performance of Model-based Predictive Control of the Ventilation Rate with Axial Fans

A new algorithm for ventilation rate control in mechanically ventilated buildings was developed and evaluated on a laboratory test installation. It was demonstrated that the current problems with traditional control of axial fans, such as instability due to dynamic wind actions, could be overcome by using a model-based predictive control (MBPC) algorithm. In the laboratory test installation, the performance of the MBPC algorithm was compared to the performance of a traditional proportional, integral, derivative (PID) controller in an airflow range from 1000 to 5000 m3/h (20–100% of fan capacity) and in a normal pressure range from 0 to 60 Pa. The accuracy and the stability of the ventilation rate control and the energy consumption were studied for both control algorithms. It was concluded that the main advantage of a MBPC algorithm over a PID controller lies in its stability in a wider range of the ventilation rates and pressure differences due to an automatic adaptation of the control parameters. The PID algorithm with fixed settings did not generate a stable control of the ventilation rate when the target value deviated more than 500 m3/h (16% of centre capacity) from the ventilation rate that it was optimised for, whereas the MBPC controller remained stable throughout the complete working range of the fan.

Structural response of large stadium roofs due to dynamic wind actions

The paper presents the experimental tests carried out in the Boundary-Layer Wind Tunnel (BLWT) for the design of large roofs of the new Olympic stadium (Karaiskaki) in Pyraeus (Greece), Manfredonia (Italy) and “Delle Alpi” of Turin (Italy). In addition, a report about some results of the time domain (T. D.) dynamic response analyses performed on the Karaiskaki structure and on the Olympic stadium in Rome will be given. The peculiar shape of these large structures and their particular location (two of them are in the immediate sea vicinity) let arise the question about the actual distribution of the wind loads, i.e. on the pattern of pressure coefficients (cp) over the entire roof. For every wind direction investigated, the following quantities have been evaluated: mean values of the aerodynamic coefficients cp, standard deviation of cp, maximum and minimum values of cp. Finally, the recorded data have been used for the numerical simulation of the dynamic response of the structure in Time Domain, whose aim is the definition of the design loads of the steel lattice structures. A numerical model of the “Delle Alpi” stadium is also in preparation, allowing results of dynamic response analyses, which are still in progress. Dynamische Windeinwirkungen an grosen Stadiondachern. Dieser Beitrag stellt die im Grenzschichtwindkanal des CRIACIV-Instituts durchgefuhrten Versuche im Zusammenhang mit dem Entwurf der Dacher fur das Olympiastadion (Karaiskaki) in Piraus (Griechenland), das Manfredonia-Stadion (Italien) und das Delle-Alpi-Stadion in Turin (Italien) vor. Auserdem werden Ergebnisse dynamischer Analysen, die am Karaiskaki-Stadion und am Olympiastadion in Rom durchgefuhrt wurden, vorgestellt. Aufgrund der besonderen Form dieser Groskonstruktionen und ihrer besondere Lage (zwei der Stadien liegen in unmittelbarer Meeresnahe) erhebt sich die Frage nach der Windlastverteilung, d. h. der Verteilung der Druckkoeffizienten (cp) uber das gesamte Dach. Fur alle untersuchten Windrichtungen wurden die Mittelwerte, Standardabweichungen, Maximum- und Minimum-Werte der cp-Koeffizienten analysiert. Die Messwerte wurden als Grundlage fur die numerische Simulation des dynamischen Verhaltens der Konstruktion verwendet, deren Ziel die Definition der Lastannahmen fur die Gittertragwerke aus Stahl war. Ein numerisches Modell des Delle-Alpi-Stadions zur Analyse des dynamischen Verhaltens ist in Vorbereitung.

Study of Aerodynamical Behavior of Suspension Footbridges against Wind Load

An aerodynamical analysis of four existing light footbridges of different measures of making span of footbridges stiff enough (i.e. inclined cable system, horizontal truss, horizontal arches) is presented. A model of wind load adopted in agreement with a quasi-steady concept takes into consideration not only unsteady air onflow but also motion of the structure itself. Wind load caused by vortices is neglected. In addition, it is assumed, that considered structures behave in a linear elastic way. Flaga A. Bosak G. Michalowski T. 2 2 / ) ' ( 2 s u u q + = ρ e e e α e α α η α ξ − + − + − − + − + = * * * )] ' /( )] sin( ) cos( [ ) ' /( ) cos sin ' ( s G G s s u u Y X u u v W Theoretical approach to a problem An analysis of four existing light footbridges is made at assumptions as follows : • Wind action on pylons and cable systems of footbridges is of static-type; • Wind action on spans of footbridges is considered in accordance with a quasi-steady theory [1, 5]. • Linearised small vibrations of footbridges around their mean (static) position are considered. Quasi-steady theory enables to consider several aerodynamic phenomena, such as galloping, special type of flutter, buffeting, and divergence. Three components of wind load include static and dynamic wind actions on span footbridges. These three components of wind load, i.e. drag force, lift force and aerodynamic moment, can be given by : (1) (2) wx = q H [Cx + Cxy W] (3) wy = q H [Cy + Cyx W] (4) wm = q H [Cm + Cmm W] (5) where: ρ density of air; u, u’, v’, α, η, ξ, e – as in fig. 1; H – characteristic diameter of cross-section; XG and YG – coordinate of geometric centre of the outline curve of cros-ssection; Cx , Cxy , Cy , Cyx , Cm, Cmm – aerodynamic coe-fficients; – time averaged value; ∗ = d /dt; ’ – fluctuations; s – spatially averaged value. Fig. 1 Systems of coordinates and relations between different geometrical quantities in the case of a moving structure and an unsteady air onflow 3 EECWE, May, 2002,Kiev, Ukraine 3 Mathematical model of the htree degrees of freedom system as a substitutional system of existing structure Spans of the considered footbridges should be treated as a slender structures, which can be divided into m elements. Each of them is represented by the inner point k of the cross-section (see fig. 2). Fig. 2 A sector of span of bridge under wind load Formulas (1-5), which are related to all points of span next are transformed to the global system of coordinates. It is assumed, that the structures behave in a linear elastic way. Their motion can be described by a matrix equation : [M]{r} + [C]{r} + [K]{r}={w} (6) The Bubnow-Galerkin’s method is adopted. As a result, a system of many degrees of freedom is substituted by a representative system of three degrees of freedom. Motion of the substitutional system under wind load described by the formulas (1-6) can be expressed by : (7) {A(t)}j = [CxWK(t), CxyWK(t)ak(t), CxyWK(t)bk(t), -CxyWK(t)ck(t), CxyWK(t)dk(t), CxyWK(t)ek(t), -CxyWK(t)] (8) {A(t)}j = [CyWK(t), CyxWk(t)ak(t), CyxWk(t)bk(t), CyxWk(t)ck(t), CyxWk(t)dk(t), CyxWk(t)ek(t), CyxWk(t),] (9) {A(t)}j = [HCmWK(t), HCmmWK(t)ak(t), HCmmWK(t)bk(t), -HCmmWK(t)ck(t), HCmmWK(t)dk(t), HCmmWK(t)ek(t), -HCmmWK(t)] (10) ∑ 〉 Φ + + 〈 = = Ψ + Ψ + Ψ m k k T k j T k j T k j j j j j j j t t A t A Y t A X t K t C t M )] ( [ )} ( { )} ( { )} ( { ) ( ) ( ) ( * * *

A Comparative Aerodynamic Analysis of Two Cable-Stayed Bridges Built in Poland

The two longest cable-stayed bridges in Poland (230m and 250m main span lengths) have been subjected to the aerodynamic analyses. This paper presents the main topics in these calculation processes: modal analysis, estimation of internal forces generated by the static load action, analysis of vibrations excited by the atmospheric turbulence and feedbacks, determination of bridge vibrations generated by the vortex excitation, calculation of stresses produced with the dynamic wind action. The dynamic structure response has been calculated using the quasi-steady method, which allowed analysis of just a few representative mode shapes, with the results precision acceptable in the engineering practice. Finally, both bridges have been found safe and resistant to the dynamic wind action, however the Warsaw bridge is more susceptible to the aerodynamic influence, especially its deck.