Miguel A. Astiz

Fundamental Mode Estimation for Modern Cable-Stayed Bridges Considering the Tower Flexibility

The design of cable-stayed bridges is typically governed by the dynamic response. This work provides designers with essential information about the fundamental vibration modes, proposing analytical expressions based on the mechanical and geometrical properties of the structure. Different bridge geometries are usually considered in the early design stages until the optimum solution is defined. In these design stages, the analytical formulation is advantageous, because finite-element models are not required and modifying the bridge characteristics is straightforward. The influence of the tower flexibility is included in this study, unlike in previous attempts on mode estimation. The dimensions and proportions of the canonical models proposed in the analytical study stem from the previous compilation of the dimensions of a large number of constructed cable-stayed bridges. Five tower shapes, central or lateral cable-system layouts and box- or U-shaped deck sections, have been considered. The vibration properties of more than 1,000 cable-stayed bridges with main spans ranging from 200 to 800 m long were extracted within an extensive parametric analysis. The Vaschy-Buckingham theorem of dimensional analysis was applied to the numerical results to propose the formulation for period estimation. Finally, the formulas were validated with the vibration properties of 17 real cable-stayed bridges constructed in different countries. The importance of the tower flexibility is verified, and the errors observed are typically below 15%, significantly improving the estimations obtained by previous research works.

Nonlinear Train-Bridge Lateral Interaction Using a Simplified Wheel-Rail Contact Method Within a Finite Element Framework

The evaluation of running safety of railway vehicles on viaducts requires the study of lateral dynamics for the coupled vehicle-bridge system. This includes the structural deformation of the bridge, the vehicle multibody dynamics, and the consideration of wheel to rail contact. In this work, a fully nonlinear coupled method for such study is presented. The model is developed in a modular way using finite element models for the structure and multibody dynamics models for the vehicles in an absolute reference, and implemented within an existing finite element commercial code. A key feature is the consideration of the kinematics and dynamics of nonlinear wheel to rail interface, considering elastic-frictional contact. This contact is based on a global geometric constraint between wheelset and track and tangential forces at local level of each contact point. Some elementary applications are presented for the behavior of the model for stable and unstable hunting motion when subjected to transient lateral loads such as a wind gust. These results show the relevance of considering nonlinear effects and in particular wheel to flange contact.

Analysis and Control of Cable-Stayed Bridges Subject to Seismic Action

Abstract Cable-stayed bridges are key points in transport networks and at present one of the most challenging structures for the civil engineering community. The integrity of these bridges should be guaranteed even under extremely large earthquakes. This paper begins with a discussion of the advantages of a new non-linear static “Pushover” procedure that includes the three-dimensional contribution of the governing vibration modes. The efficacy and the accuracy of the proposed Pushover in the non-linear seismic analysis of bridges with significant coupling between the towers, deck and cable system is verified. In the second part of this paper, the seismic responses of several cable-stayed bridges have been studied, verifying the influence of the tower shape, cable arrangement and the main span length on the structural behaviour under strong ground motions. Severe damage is identified at critical tower sections by means of extensive non-linear dynamic analyses. Finally, retrofit solutions with viscous dampers (VDs) and yielding metallic dampers (MDs) connecting the deck and the tower in the transverse direction are explored. The proposed connection with dampers effectively prevents yielding of the reinforcement and cracking in the tower legs.

A methodology for analysing lateral coupled behavior of high speed railway vehicles and structures

Continuous increment of the speed of high speed trains entails the increment of kinetic energy of the trains. The main goal of this article is to study the coupled lateral behavior of vehicle-structure systems for high speed trains. Non linear finite element methods are used for structures whereas multibody dynamics methods are employed for vehicles. Special attention must be paid when dealing with contact rolling constraints for coupling bridge decks and train wheels. The dynamic models must include mixed variables (displacements and creepages). Additionally special attention must be paid to the contact algorithms adequate to wheel-rail contact. The coupled vehicle-structure system is studied in a implicit dynamic framework. Due to the presence of very different systems (trains and bridges), different frequencies are involved in the problem leading to stiff systems. Regarding to contact methods, a main branch is studied in normal contact between train wheels and bridge decks: penalty method. According to tangential contact FastSim algorithm solves the tangential contact at each time step solving a differential equation involving relative displacements and creepage variables. Integration for computing the total forces in the contact ellipse domain is performed for each train wheel and each solver iteration. Coupling between trains and bridges requires a special treatment according to the kinetic constraints imposed in the wheel-rail pair and the load transmission. A numerical example is performed.

Wind-Induced Vibrations of the Alconétar Bridge, Spain

A vibration event which happened in the Alconétar arch bridge during construction is described and studied in this paper. Vibrations are interpreted as being caused by vortex shedding under wind and they were the result of a very light structure and a tandem cross section. Wind tunnel tests have confirmed this interpretation and they allow a satisfactory prediction of vibration amplitude by applying the correlation length model. The arch was equipped with wind deflectors which proved to be very effective to reduce vibrations. Some modifications of the correlation length model have been studied to better explain the actual behaviour of the bridge when the wind deflectors are in place.

AQUEDUCT, IMPERIAL CANAL OF ARAGON, ZARAGOZA, SPAIN

The third ring road around Zaragoza, Spain has to cross the Imperial Canal of Aragon at a point where the canal and a road cross a small valley on an 18th century masonry wall. A new aqueduct was designed as a single structure with the ring road bridge. The total length of the aqueduct is 88 m with a 40 m long central span over two ring road carriageways and two 24 m long lateral spans. The aqueduct carries the canal and two carriageways and two pathways. The design and structural concept are outlined. Structural analysis was conducted using finite element models. The deck is prestressed both longitudinally and transversally. The most difficult operation during construction was the deck concrete casting due to the high degree of reinforcement and because of the curved shape of the deck. Details are given of the owner, designer, contractor, costs and service date.

Wind Vibration Reduction at Alicante Airport Control Tower, Spain

The control tower of the Alicante airport is 47 m high and is composed of a concrete core, which has elevators, stairs, and a steel structure containing the technical, resting and the air-traffic control rooms. This steel structure is supported by a concrete pole with a tubular section, which is connected at different levels to the concrete core by means of steel trusses. This paper presents results of an investigation on the causes and remedies for vibrations in an air-traffic control tower. It has been shown that wind induced vibrations may disturb air traffic control for acceleration values which are lower than the thresholds as defined in ISO Standards. Besides small differences between theoretical and experimental results, buffeting analysis through numerical methods has proved to be useful to investigate the behaviour of tuned mass dampers and to adjust their design when applied to structures with well defined vibration frequencies.