Steel Footbridge Research Articles

Degradation of Steel Footbridges with Neglected Inspection and Maintenance

Upon representative case studies, the paper illustrates importance of management, maintenance and reconstruction of steel footbridges. Particularly inspection importance for timely discovering imperfections, potentially reducing safety and load carrying capacity are illustrated at effected investigations of actually common structural systems. The paper presents a summary of the findings and conclusions from diagnostic of seven steel footbridges. Focus is paid on the corrosion of structural steel and its influence on overall condition of footbridge structures.

Analysis of Harmonic Vibration of Cable-Stayed Footbridge under the Influence of Changes of the Cables Tension

Abstract The paper presents numerical analysis of harmonically excited vibration of a cable-stayed footbridge caused by a load function simulating crouching (squats) while changing the static tension in chosen cables. The intentional synchronized motion (e.g., squats) of a single person or group of persons on the footbridge with a frequency close to the natural frequency of the structure may lead to the resonant vibrations with large amplitudes. The appropriate tension changes in some cables cause detuning of resonance on account of stiffness changes of structures and hence detuning in the natural frequency that is close to the excitation frequency. The research was carried out on a 3D computer model of a real structure - a cable-stayed steel footbridge in Leśnica, a quarter of Wrocław, Poland, with the help of standard computer software based on FEM COSMOS/M System.

NUMERICAL ANALYSIS OF THE EFFECTS OF THE BENDING STIFFNESS OF THE CABLE AND THE MASS OF STRUCTURAL MEMBERS ON FREE VIBRATIONS OF SUSPENSION BRIDGES

The article determines natural frequencies of vibration and the corresponding mode shapes of a suspension bridge with the varying bending stiffness of cables and examines variations that occur in these characteristics with respect to parametric changes in the bridge. A single span suspension steel footbridge with flexible cables has been selected as an initial model used for studying the dynamic characteristics of a suspension system. With the help of the finite elements (FE) method, parameter studies of the bridge model are presented in which vibration characteristics are studied as a function of structural and material parameters such as the flexural stiffness of the cable and the mass density of structural components. It has been generally found that the bending stiffness of the main cable contributes to a considerable effect on natural frequencies for this type of the suspension system. A simplified expression of predicting natural bending frequencies of the suspension bridge taking into account the bending stiffness of the cable has been developed for the application as the first step in the design process.

A New Footbridge in Valletta Grand Harbour to Fill A Geometric and Historic Gap, Malta

The St. Elmo breakwater was constructed in the first decade of the twentieth century to convert the unique Valletta Grand Harbour to an all-weather port. An opening near its land end was retained to prevent water stagnation and shorten the distance to the adjacent harbour for smaller craft. Accessibility to the breakwater was guaranteed by a two-span steel footbridge, which was partly demolished during World War II. The breakwater and the lighthouse remained isolated for more than 70 years, accessible only by boat. The bridge presented in this paper was selected from more than 20 entries to a design-and-build competition for the creation of a new crossing. The footbridge uses an innovative design concept to successfully solve a complex problem: the reconstruction of a part of Valletta’s history in harsh environmental conditions and exceptional construction constraints caused by site inaccessibility. The new design is functional, contemporary, transparent and durable, its maintenance is easy and it is respectful of history.

Fatigue Resistance and Durability of New Mechanical Connections of Currently Developed Temporary steel Footbridges and Railway Bridges

On the workplace of paper authors’, the experimental studies of the fatigue behaviour and fatigue resistance of several new types of steel mechanical connections have been performed recently. The problems of mechanical connections mentioned above have been solved in the past within the projects of the development of new types of advanced temporary steel bridges and footbridges, with the support of the programme of applied research, development and innovations of the Technology Agency of the Czech Republic. These newly developed connections represent the assembly joints based on the bolts and pins together with plates. Within this investigation, fatigue tests of connections have been performed. The experimental studies have been oriented to the verification of the behaviour of those connections and especially, the fatigue strength, and subsequently the fatigue resistance and durability of the structural detail according to the configuration and structural design.

Evaluation of human-induced vibration of continuous footbridges

With the development of construction materials and the introduction of high strength steel and concrete, the human-induced vibration became a dominant criterion for the design of pedestrian bridges. Currently, longer spans and lightweight bridges have been comprised in most of design trends. This leads to lower the natural frequencies of the system which have a great effect on the dynamic performance of bridges subjected to human activities. Although the design of steel footbridges could reach the optimum level of design in terms of strength criterion, it might not reach the acceptance level for vibration condition. This will enforce the designer to choose section profiles with higher inertia to enhance stiffness of the whole system. This paper presents an overall assessment for floor vibration problem due to pedestrian induced vertical forces on continuous composite footbridges. The footfall method presented by concrete centre CCIP-016 is adopted in this study to evaluate the response factor and acceleration of pedestrian bridges using a FEA software package Robot Structural Analysis.

Static and dynamic behavior of a selected cable‐stayed footbridge with respect to change of the cable tension

AbstractThe paper presents the theoretical analysis of the possibilities of using the authors' own method of actively reducing resonant vibration in cable‐stayed footbridges. The method of actively reducing vibration was earlier tested on a laboratory model of a steel footbridge, [1]. The method relies on changing the static tension in chosen cables. The term “active” refers to the fact that the tension changes would only be introduced when resonant vibration of the structure occurred. A change in the cable tensions should cause a change of the natural frequencies for which resonant vibration amplification appeared earlier. Eigenproblem sensitivity analysis, formulated for the structure according to the second order theory, is the basis for choosing the cables in which the tension should change. Apart from analyzing the effectiveness of the active method for reducing resonant vibration, the influence of cable tension change on other values was also studied. These values included the changes in vibration amplitudes, as well as changes of cross‐section forces, tensions, and static bend of the structure elements that are most sensitive to tension change. It was also established whether the tension changes in chosen cables, which were large enough to cause a practically significant reduction of resonant vibration, cause exceeding the levels of Serviceability Limit State (SLS) and Ultimate Limit State (ULS) for the structure as a whole or for some of its elements. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Forced-Vibration Testing and Experimental Modal Analysis of a Steel Footbridge for Structural Identification

Abstract Dynamic characteristic identification provides an important insight about structural behavior of steel structures. The experimental modal analysis is used to detect dynamic characteristics and consists of several phases. First, forced-vibration tests are carried out, spectral functions are produced, dynamic characteristics are determined by analyzing processed spectral functions, and, finally, analytical models are calibrated or updated depending on experimental analysis results. In this study, forced-vibration testing is conducted on the steel footbridge by using an impact hammer. Low-amplitude broadband excitations are applied using an impact hammer to excite the bridge. The excitation force and measured responses are processed by passing them through a band-pass filter to obtain frequency-response functions, cross-power spectra, auto-power spectra, power spectral densities, and spectrograms. The system-identification procedure is based on input–output measurements. The obtained system-identification results are compared with the analytical results, which were obtained in a different previous study. A very good agreement is observed, thus providing a reliable set of identified modal properties (natural frequencies, damping ratios, and mode shapes) of the structure. The good correlations between analytical and experimental analyses show that no anomalies are detected along the structure. The experimental mode shapes are similar to what is expected from this type of structure. There is not any unexpected mechanism that changes the dynamic characteristics of the system.

Load capacity and serviceability conditions for footbridges made of fibre-reinforced polymer laminates

The contribution is focused on derivation of the Ultimate Limit State (ULS) and Serviceability Limit State (SLS) design criteria for footbridges built of fibre-reinforced polymer matrix (FRP) laminates. The ULS design criterion is based on the design guidelines for above-ground, pressure, FRP composite tanks and the Tsai-Wu failure criterion, which is used to predict the onset of FRP laminates damage. The SLS criterion is based on vertical deflections and natural frequencies limitations of the analysed FRP footbridge. As a part of the research, a special design procedure is established for FRP footbridges design process, covering both the preliminary and detailed engineering calculations. As an illustrative example, the procedure is applied to glass-fibre reinforced vinylester laminate with 90°C heat deflection temperature and 50-year service life. A deflection-based serviceability limit state criterion is established using the same approach as that currently used in the design of steel footbridges. Moreover, the second serviceability limit state criterion is proposed. It limits the range of possible fundamental natural frequency of footbridge without any load and loaded with an additional mass 70 kg/m2 applied to simulate load created by moderate pedestrian traffic.

휴대용 계측기를 이용한 보도교 진동계측분석

The design of foot-bridge is often influenced by natural frequency. Consequently, vibration frequency becomes important. The empirical expressions used to quantify this parameter at the design phase have not been developed enough to give guideline to Korean foot-bridge. This paper is concerned with the vertical natural frequency of steel foot-bridges. It describes the vibration measurement methods employed for testing structures and presents reliable methods of assessing natural frequency from jumping vibration tests. Data from measurements on 16 structures in Seoul are given. Regression formulas of natural frequency for steel-framed foot-bridges are suggested. Finally, obtained formula are compared with empirical expressions of Seoul City's guideline.

Identification, Model Updating, and Validation of a Steel Twin Deck Curved Cable‐Stayed Footbridge

AbstractTo perform a realistic reliability analysis of a complex cable‐stayed steel footbridge subject to natural hazard and corrosion, this article addresses a rational process of modeling and simulation based on identification, model updating, and validation. In particular, the object of this study is the Ponte del Mare footbridge located in Pescara, Italy; this bridge was selected as being a complex twin deck curved footbridge because it is prone to corrosion by the aggressive marine environment. With the modeling and simulation objectives in mind, a preliminary finite element (FE) model was realized using the ANSYS software. However, uncertainties in FE modeling and changes during its construction suggested the use of experimental system identification. As a result, the sensor location was supported by a preliminary FE model of the footbridge, although to discriminate close modes of the footbridge and locate identification sensor layouts, Auto Modal Assurance Criterion (AutoMAC) values and stabilization diagram techniques were adopted. Modal characteristics of the footbridge were extracted from signals produced by ambient vibration via the stochastic subspace identification (SSI) algorithm, although similar quantities were identified with free‐decay signals produced by impulse excitation using the ERA algorithm. All these procedures were implemented in the Structural Dynamic Identification Toolbox (SDIT) code developed in a MATLAB environment. The discrepancies between analytical and experimental frequencies led to a first update of the FE model based on Powell's dog‐leg method that relied on a trust‐region approach. As a result, the identified FE model was capable of reproducing the response of the footbridge subject to realistic gravity and wind load conditions. Finally, the FE was further updated in the modal domain, by changing both the stationary aerodynamic coefficients and the flutter derivatives of deck sections to take into account the effects of the curved deck layout.

Vibration Measurements of Steel Foot-Bridges Using Mobile-Phone

The design of foot-bridge is often influenced by natural frequency. Consequently, vibration frequency becomes important. The empirical expressions used to quantify this parameter at the design phase have not been developed enough to give guideline to Korea foot-bridge. This paper is concerned with the frequency of steel foot-bridges. It describes the vibration measurement methods employed for testing structures and presents reliable methods of assessing natural frequency from jumping vibration tests. Data from measurements on 30 structures in Seoul are given. Regression formulas of natural frequency for steel-framed foot-bridges are suggested. Finally, obtained formula is compared with empirical expressions of Seoul Citys guideline and Bachmanns curve.

Structural Design of Newly Developed Temporary Footbridge

The paper deals with the design of steel structure of the temporary footbridge, intended especially for the usage in the construction site for pedestrian and bicycle traffic. In the period of last two years, on the authors workplace, in the co-operation with the mounting company, the new type of steel footbridge is being developed. Within this development the attention is, among others, paid to the structural design, in particular to the harmonization of static solution and structural detailing, to achieve the efficient design. In the course of solving this problem, two types of the footbridge are being developed in parallel. Both footbridges are composed as the structures with a lower deck, truss main girders and bracings; the first structure (short footbridge) with a small self-weight may have the span up to 18 m; the second structure (long footbridge) with a normal self-weight may have the span up to 36 m. The paper is focused on the brief description of structural composition and parameters of the short footbridge, as well as structural detailing of the joints of main load-carrying parts. The configuration of the whole structure and individual structural details have been designed with respect to the static, dynamic and fatigue affects, which have been experimentally verified using loading tests of the footbridge prototype with the span of 18 m and fatigue tests of significant structural details.

Application of EN 1990/A1 Vibration Serviceability Limit State Requirements for Steel Footbridges

In the paper a brief characteristic of vibration comfort criteria requirements for footbridges according to EN 1990/A1 and their comparison with recommendations of different authors and guidelines have been presented. Moreover, the requirements of ISO 10137 standard and Flaga & Pańtak propositions of vibration comfort criteria have been shown and characterized. Furthermore, examples of dynamic analysis of several steel footbridges and assessment of the vibration comfort criteria for the footbridges have been presented.

Vibration Analysis of Light Flexible Steel Footbridge Based on Dynamic Testing

Abstract: A vibration analysis of light flexible steel footbridge is investigates in this paper, which is based on dynamic testing. The finite element model of the footbridge was established. In this paper the reason is also analyzes which causes the vibration characteristic from the ambient excitation and its own structural features. Key words: Footbridge; Vibration Analysis; Dynamic Testing; Modal Analysis; Ambient Excitation;

Evaluating vibrations on a small-scale model of a timber footbridge

In Brazil, the study of pedestrian-induced vibration on footbridges has been undertaken since theearly 1990s, for concrete and steel footbridges. However, there are no recorded studies of this kind fortimber footbridges. Brazilian code ABNT NBR 7190 (1997) gives design requirements only for staticloads in the case of timber footbridges, without considering the serviceability limit state from pedestrianinducedvibrations. The aim of this work is to perform a theoretical dynamic, numerical and experimentalanalysis on simply-supported timber footbridges, by using a small-scale model developed from a 24 mspan and 2 m width timber footbridge, with two main timber beams. Span and width were scaled down(1:4) to 6 m e 0.5 m, respectively. Among the conclusions reached herein, it is emphasized that theEuler-Bernoulli beam theory is suitable for calculating the vertical and lateral first natural frequenciesin simply-supported timber footbridges; however, special attention should be given to the evaluation oflateral bending stiffness, as it leads to conservative values.

Structural Design and Analysis of a Steel Vine Bridge

A steel footbridge with a 27m net span, a worm-shaped curve and a vine bridge style was proposed to be constructed in Diexi city of Sichuan, China. Considering the appearance and the functional requirement, the bridge is designed as follows: the section outline is composed of 21 different ellipse-shaped transverse ribs with 1.5m spacing, and the transverse ribs are connected by 12 longitudinal ribs. Comparison between two optional structure schemes is carried out. Considering the mechanical performance and economy, the structure scheme, a truss structured system at lower part of the bridge, is adopted. Internal force analysis, member design and deformation calculation of the structure are accomplished. Finite elements analysis with ANSYS shows that the welded joints can meet the bearing capacity requirement. Connection between the bridge and the foundation platform is also presented in this paper.

Measurement of the dynamic displacements and of the modal frequencies of a short-span pedestrian bridge using GPS and an accelerometer

Signal analysis techniques (supervised-type learning filter in combination with a Chebyshev filter) constrained and tested by independent accelerometer data were used to process noisy GPS measurements of oscillations of 40 m long steel footbridge excited by coordinated jumps of a group of people. This approach permitted to de-noise the geodetic displacement record and reconstruct a minimum bias waveform for the dynamic displacement of this stiff bridge (4.3 Hz modal frequency, ∼6 mm oscillation amplitude). This result indicates that properly processed high-frequency satellite geodetic data may be used to measure dynamic displacements not only of high-rise buildings, cable-stayed bridges and other flexible structures, but of stiff civil engineering structures as well and may be useful for the Structural Health Monitoring, analysis and design of a large range of engineering structures. It was also found that although currently used 10 Hz sampling rate GPS receivers may underestimate certain high-frequency peak displacements, this will not be a problem for the recently introduced 50–100 Hz receivers.

STUDY OF PEDESTRIAN-INDUCED VIBRATIONS ON TIMBER FOOTBRIDGESC

In Brazil, studies about pedestrian-induced vibrations on footbridges have been carried out since the early 1990s, for concrete and steel footbridges. However, there is no record of such studies and the Brazilian Standard NBR 7190 (1997) for the design of timber structures only presents design requirements for static loads, in the case of timber footbridges. Therefore, this paper aims to general theoretical analysis, numerical and experimental simply-supported beams timber footbridges, with a view to proposing recommendations for projects related to human comfort in these structures. This study was developed from the study of standard guidelines and criteria suggested by several authors, the theoretical analysis of footbridges design according to the criteria of the NBR 7190 (1997), numerical models using finite element and experimental tests on reduced models. Among the conclusions reached, it is emphasized that the formulation of Euler-Bernoulli is suitable for calculating the first natural frequency in vertical and lateral directions simply-supported beams timber footbridges; however, special attention should be given to the evaluation of lateral bending stiffness. Finally, we have suggested a proposal serviceability limit state verification due to pedestrian-induced vibrations on simply-supported beams timber footbridges, concerning the calculation of frequencies and accelerations to be included in a future review of the Brazilian Standard for the design of timber structures.

Ambient Vibration Tests of a Steel Footbridge

The paper presents analytical and experimental modal analysis of a steel footbridge for modal parameter identification. 3D finite element model is established for the steel footbridge based on the design drawing and modal parameters are obtained from deformed configurations. The field test is carried out by ambient vibration test under human walking excitation. Both Peak Picking method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used for the output-only modal identification. From the study, good agreement is found between mode shapes, but some differences in the natural frequencies and analytical frequencies are bigger.