J. Á. Jurado

Cable optimization of a long span cable stayed bridge in La Coruña (Spain)

This document describes an optimization problem of cable cross section of a cable stayed bridge considering constraints of cable stress and deck displacement. Since the bridge is still in the design phase, the geometry and the mechanical characteristics are subjected to changes. In order to avoid creating different structural models, a computer code was written to produce a model from geometrical and mechanical data and solve the optimization problem. At the end of the document, two examples are included to show the capabilities of the methodology presented.

Analytical approach to sensitivity analysis of flutter speed in bridges considering variable deck mass

Design techniques based upon sensitivity analysis are not usual in the current design of suspension bridges. However, sensitivity analysis has been proved to be a useful tool in the car and aircraft industries. Evaluation of sensitivity analysis is a mandatory step in the way towards an efficient automated optimum design process which would represent a huge jump in the conception of long span bridges. Some of the authors of this paper were pioneers in establishing a methodology for obtaining the sensitivity analysis of flutter speed in suspension bridges a few years ago. That approach was completely analytical and required the evaluation of many matrices related to the phenomenon. In those works the total mass of the deck was considered as constant and such a circumstance supposed a limitation of the method. In the present paper the complete analytical formulation of the sensitivity analysis problem in bridges considering variable deck mass is presented, as well as its application to the design problem of the Great Belt Bridge. Analytical evaluation of sensitivities is a time demanding task, and in order to avoid excessive computation times, distributed computing strategies have been implemented which can be considered as an additional benefit of this approach. For the application example, it has been found that deck cross-section area and torsional inertia are the structural properties with the greatest influence on the flutter performance.

Efficient cable arrangement in cable stayed bridges based on sensitivity analysis of aeroelastic behaviour

Construction of cable supported bridges has experienced a great impulse in the past decade. Bridges having more than 800m of span length were built in France and Japan and some bridges with span length of more than 1km are going to be built, such as the Stonecuters bridge in Hong-Kong, and the Chongming in China (Fig. 1). Because of the increasing length of this class of bridges, they are becoming prone to phenomena like flutter in a similar way than long span suspension bridges. Cable stayed bridges may present a few different alternatives for the cable system. At least harp, fan or modified fan arrangements can be discussed at the beginning of the design. Also variations in the number of cable planes can be studied. Usually, during the design process changes are made by carrying out a number of analyses and using trial and error techniques relying in heuristic rules that are based upon the particular skills of the engineer. This approach can be inefficient in new problems and commonly it needs to be supported with results coming from experimental testing which makes more expensive the whole design process. Instead of that, an approach based in sensitivity analysis can be very helpful for the designer.

Distributed Computing For The Evaluation Of TheAeroelastic Response And Sensitivity Analysis OfFlutter Speed Of The Messina Bridge

This paper explains the formulation that allows the calculation of a bridge flutter speed and the evaluation of the sensitivity of the aeroelastic response with regards to the mechanical parameters of the deck. This methodology requires the previous evaluation of the natural frequencies and mode shapes of the bridge in second order theory, and the sensitivity analysis of those frequencies and mode shapes. Then, the advantages of introducing distributed computing in order to save time and share the computational effort between a set of connected computers are presented. Finally, the results obtained using the previously introduced methodology and distributed computing are shown for the Messina strait bridge.

The role of surrogate models in combined aeroelastic and structural optimization of cable-stayed bridges with single box deck

The aeroelastic phenomena represent a crucial issue in the design of long span bridges and their relevance grows as the length of the spans is increased, which is the current trend in these mega-structures. The search for the best performing deck cross-section, as well as the search of the most economic bridge design, are two of the most relevant goals for bridge designers. Hence, the pursuit of good aerodynamic performance of the bridge deck cross-section and the structural optimization of the bridge are destined to converge in a unified process to achieve more efficient bridge designs, given their interdependence. This paper presents an integrated methodology based on a surrogate-based optimization process to obtain an optimum bridge design considering structural and aeroelastic constraints. The deck cross-section used in this work is the well-known G1 section, in which two deck shape variables are considered. The aerodynamic behavior of the cross sections analyzed by the optimization algorithm is given by a surrogate model trained with a set of designs calculated with CFD techniques. The structural performance is analyzed by means of finite element analysis. The areas and prestressing forces of the stays and the deck shape and plate thickness are considered as design variables, and the optimization of the bridge is carried out by a gradient-based optimization algorithm.

Code Provisions for Wind Loads on Short Road Bridges: Spanish IAP code, UNE-EN 1991-1-4 & 2007 AASHTO LRFD Bridge Design Specifications

In September 2007 the Spanish version of eurocode, UNE-EN 1991-1-4 has been published; also in road bridges the Spanish IAP code is considered by designers as a feasible tool for the evaluation of wind actions on conventional road bridges. Additionally the AASHTO LRFD Bridge Design Specifications is a feasible comprehensive code. The aim of this work is to analyze the approaches followed for the aforementioned codes for the design of short road bridges in terms of wind loads values and “user-friendliness”. Thus the general procedures are described in order to get a grasp of their stipulations. Finally, two examples of simple bridges have been considered to evaluate the wind loads to be considered in their design according to the two codes. It has been obtained that eurocode and AASHTO LRFD give higher wind loads than the IAP code. Moreover IAP and AASHTO LRFD are easier to use for practitioners as they are specific bridge norms.

Wind Engineering Studies for a Cable-Stayed Bridge in Talavera de la Reina, Spain

The recently designed highway for by-passing the city of Talavera de la Reina in Spain is currently under construction. The main structural element in the project is a cable-stayed bridge which for sure will become a landmark in the region. The bridge has a main span of 318 m, comprising a concrete box deck 36 m width and a single inclined pylon 164 m high. The singularity of the bridge has recommended a comprehensive analysis regarding wind effects on the structure. The aerodynamic coefficients of the deck have been obtained from wind tunnel tests and they have also been computed using CFD software considering two different turbulence models. Also the flutter functions have been evaluated by means of sectional model tests and the flutter velocity has been obtained. It has been found that the bridge enjoys a safe design for wind actions.

Virtual wind tunnel: An alternative approach for the analysis of bridge behaviour under wind effects

The study of bridge responses under wind-induced loads is based upon full aeroelastic model testing or hybrid methods which use section model tests and subsequent computer analysis. Both methodologies present several strong points and some shortcomings, specially related with the visualization of the bridge dynamic behaviour. Nowadays, advances and improvements in computational power and computer aided design technologies make possible a new way towards the feasible design of long span bridges considering its aerodynamic and aeroelastic behaviour. The virtual wind tunnel (VWT) technique developed by the authors joins together accurate section model testing with computer aided design in order to obtain a detailed computer visualization of the complete bridge behaviour under wind flow. The results obtained for the Tacoma Narrows Bridge and the Messina Strait Bridge are presented.

A Comparison Of Flutter Speed Of The MessinaBridge Considering Several Cable Configurations

The bridge over the Messina strait is an ambitious initiative started a few decades ago, which is likely to become reality in the near future. Several modifications have been made to the continuously changed preliminary design, so that the bridge is safe under a wide range of wind speeds. In this paper, a study of the significance of the cable configuration in terms of the number of cable planes and their location is presented discussing the relative efficiency of each of them.

Numerical simulations of the aerodynamic response of circular segments with different corner angles by means of 2D URANS. Impact of turbulence modeling approaches

ABSTRACT This paper presents the results of numerical and experimental investigations on the force coefficients and Strouhal numbers of circular segments considering different corner angles or chord to sagitta ratios. The research is motivated because these geometries are becoming increasingly popular in several engineering disciplines. The so-called D-section (semi-circular cylinder with a corner angle of ) has been experimentally studied in the past, since it is a galloping prone geometry. However, there is a lack of research for cases with different corner angles, and the numerical investigations related to this topic are particularly scarce. In this work, a 2D Unsteady Reynolds Averaged Navier–Stokes approach has been adopted aiming to study the circular segments at the sub-critical regime, considering corner angles from to , and the flow parallel to the rectilinear side. These sections were found to be particularly challenging since they present massive flow separation on the rectilinear side, alongside the inherent difficulties related to modeling the flow along curved surfaces at high Reynolds numbers. The impact of introducing low-Reynolds-number and curvature corrections in the SST turbulence model and the performance of the Transition SST model have been extensively studied.