Responses Of Bridge Deck Research Articles

A hybrid approach for fatigue assessment of reinforced concrete bridge deck considering realistic bridge-traffic interaction

Reinforced concrete (RC) bridge decks are directly exposed to daily traffic loads and often experience surface cracking caused by excessive stress or fatigue accumulation. The bridge deck fatigue performance over traffic loads needs to be assessed based on accurate dynamic interaction analysis of the bridge and realistic moving vehicles. Most of existing studies on fatigue assessment focus on either the bridge global response without sufficient details about the bridge deck, or refined bridge deck modeling without considering the full dynamic interaction between moving traffic and the bridge structure realistically. A hybrid fatigue assessment approach is developed by combining mode-based global bridge-traffic dynamic interaction analysis, finite-element (FE)-based refined bridge deck model, and fatigue assessment method directly based on the vehicle loads and shear strength of the bridge deck. The proposed approach is demonstrated with a typical 3-span concrete bridge under realistic traffic and road surface conditions. Based on the dynamic interaction and stress analysis results, the fatigue damage factor is further investigated with different road surface roughness levels and heavy truck proportions. It is found that the proposed analytical approach provides a useful tool to predict the bridge deck response and potential fatigue damage under realistic traffic flow.

Frequency domain modeling of long-span sea-crossing bridge under stochastic wind and waves

In this study, a frequency domain modeling framework that assembles aero- and hydro-dynamic approaches to characterize the structural motions of a long-span sea-crossing bridge under stochastic wind and waves is proposed as an efficient alternative for the conventional time-consuming time domain analysis. The improved quasi-steady buffeting model is employed to investigate the fluctuating wind actions on structural components and the aero-elastic effect of bridge decks. Potential flow theory associated with constant boundary element method is applied to calculate the linear as well as quadratic hydrodynamic transfer functions and both first- and second-order wave loads are considered and coupled in the modeling framework. The proposed methodology is well validated using a benchwork experiment of a flexible cylinder subjected to wind and waves. The dynamic performance of a long-span sea-crossing bridge under extreme wind and wave conditions is modeled using the proposed framework. The effects of wind and waves, different mode combinations, directionality and nonlinear wave loads on global responses are discussed. In the proposed approach, a combination of only a few main modes is necessary to yield plausible displacement responses of bridge deck, while more modes are required to obtain converged internal force responses.

Prediction of aeroelastic response of bridge decks using artificial neural networks

The assessment of wind-induced vibrations is considered vital for the design of long-span bridges. The aim of this research is to develop a methodological framework for robust and efficient prediction strategies for complex aerodynamic phenomena using hybrid models that employ numerical analyses as well as meta-models. Here, an approach to predict motion-induced aerodynamic forces is developed using artificial neural network (ANN). The ANN is implemented in the classical formulation and trained with a comprehensive dataset which is obtained from computational fluid dynamics forced vibration simulations. The input to the ANN is the response time histories of a bridge section, whereas the output is the motion-induced forces. The developed ANN has been tested for training and test data of different cross section geometries which provide promising predictions. The prediction is also performed for an ambient response input with multiple frequencies. Moreover, the trained ANN for aerodynamic forcing is coupled with the structural model to perform fully-coupled fluid–structure interaction analysis to determine the aeroelastic instability limit. The sensitivity of the ANN parameters to the model prediction quality and the efficiency has also been highlighted. The proposed methodology has wide application in the analysis and design of long-span bridges.

Influence of Separation Interference Method on Aerodynamic Responses of a Pentagonal Shaped Bridge Deck

Long-span bridges often exhibit vibration under wind action. Various aerodynamic countermeasures have been developed over the years to enhance the aeroelastic responses of the long-span bridge deck and Separation Interference Method (SIM) is one of these. Engineers should have sound knowledge about the flow mechanism of the aerodynamic countermeasures of the bridge deck for further improvement of the aerodynamic responses and better design of the bridge deck. In the present study, a numerical investigation was carried out to disclose the flow mechanism of SIM on a pentagonal bridge deck. Simulation was conducted by using unsteady RANS for a pentagonal bridge deck with and without SIM techniques and their aerodynamic responses were compared. In the first part performance of unsteady RANS was evaluated to predict the dynamic responses for a pentagonal bridge deck. Then, the steady state responses and flow fields were explored for a bridge deck with and without SIM. Later, the dynamic responses such as flutter derivatives and unsteady pressure characteristics were evaluated and compared. It was found that SIM can improve the aerodynamic responses of the bridge deck. The addition of the curb affected the flow field around the bridge deck and the important flow features noticeably. The leading-edge top and bottom surface separations and the trailing-edge bottom surface separation are the most significant flow features to control both the steady state and dynamics responses of the bridge deck.

Moving force identification based on modified preconditioned conjugate gradient method

This paper develops a modified preconditioned conjugate gradient (M-PCG) method for moving force identification (MFI) by improving the conjugate gradient (CG) and preconditioned conjugate gradient (PCG) methods with a modified Gram-Schmidt algorithm. The method aims to obtain more accurate and more efficient identification results from the responses of bridge deck caused by vehicles passing by, which are known to be sensitive to ill-posed problems that exist in the inverse problem. A simply supported beam model with biaxial time-varying forces is used to generate numerical simulations with various analysis scenarios to assess the effectiveness of the method. Evaluation results show that regularization matrix L and number of iterations j are very important influence factors to identification accuracy and noise immunity of M-PCG. Compared with the conventional counterpart SVD embedded in the time domain method (TDM) and the standard form of CG, the M-PCG with proper regularization matrix has many advantages such as better adaptability and more robust to ill-posed problems. More importantly, it is shown that the average optimal numbers of iterations of M-PCG can be reduced by more than 70% compared with PCG and this apparently makes M-PCG a preferred choice for field MFI applications.

A truncated generalized singular value decomposition algorithm for moving force identification with ill-posed problems

This paper proposes a new methodology for moving force identification (MFI) from the responses of bridge deck. Based on the existing time domain method (TDM), the MFI problem eventually becomes solving the linear algebraic equation in the form Ax=b. The vector b is usually contaminated by an unknown error e generating from measurement error, which often called the vector e as ‘‘noise’’. With the ill-posed problems that exist in the inverse problem, the identification force would be sensitive to the noise e. The proposed truncated generalized singular value decomposition method (TGSVD) aims at obtaining an acceptable solution and making the noise to be less sensitive to perturbations with the ill-posed problems. The illustrated results show that the TGSVD has many advantages such as higher precision, better adaptability and noise immunity compared with TDM. In addition, choosing a proper regularization matrix L and a truncation parameter k are very useful to improve the identification accuracy and to solve ill-posed problems when it is used to identify the moving force on bridge.

Measurements and improved model of vortex-induced vibration for an elongated rectangular cylinder

This paper deals with vortex-induced vibrations of a rectangular 4:1 cylinder with a twofold purpose. First, it provides experimental results as a benchmark for checking the predictions of mathematical models and computational techniques. In particular, a wide wind tunnel campaign on a sectional model in smooth flow yielded the oscillation amplitudes in the lock-in range for several Scruton numbers. The dominant frequency of the velocity fluctuations in the wake of the oscillating body was measured. The second purpose of the paper is the improvement of a current approach for assessing vortex-induced vibrations of bridge decks. For this reason, prior to starting the analysis an overview of the existing mathematical models is reported. Afterwards, it is shown through wind tunnel tests that the single-degree-of-freedom model developed by Scanlan at the beginning of the 1980s is unsuitable to predict the VIV response of bridge decks for Scruton numbers different from that at which the model parameters were identified. Finally, an improved version of the model is proposed, allowing to approximate accurately the limit-cycle amplitudes for the entire range of Scruton numbers tested. The identification of the aeroelastic parameters of the improved version of the model requires only three decay-to-resonance tests for three different Scruton numbers. From the engineering point of view, this represents an important advantage, especially when the mass and the damping of the structure are uncertain or dampers have to be designed, as it makes the assessment of the sensitivity to vortex-induced vibration of bridge deck cross sections less time-consuming and expensive. In the future, it will be necessary to verify that the functional form postulated for the aeroelastic parameters of the model is valid not only for elongated rectangular cylinders but also for bridge deck cross sections.

Probabilistic analysis of a twin deck curved cable-stayed footbridge subjected to multiple inputs and corrosion

In order to investigate the benefits of Circular Hollow Section (CHS) structural members to a complex cable-stayed footbridge, this paper presents a simulation-based probabilistic assessment of this type of structures when erected in an aggressive environment. The footbridge studied is located in Pescara, Italy, next to the Adriatic sea. We validated a Finite Element (FE) model of this bridge, and then, we performed a probabilistic study. Owing to corrosion during the bridge design life, both general and localized corrosion models capable of evaluating the reduced load bearing section were adopted; and appropriate probability distributions were assigned to input model parameters. Afterwards, the probabilistic evaluation of the bridge deck response was conducted using non-linear simulations based on Monte Carlo Sampling, where the convergence was accelerated by using Latin Hypercube Sampling (LHS). Serviceability limit state for stresses was satisfied for the footbridge service life for both wind and pedestrian loads. However, for the limit states referred to maximum deck deflection and rotation, the probabilities of failure crossed limiting values suggested in Eurocodes. As a result, for the twin deck curved cable-stayed footbridge with CHS members, the probabilistic analysis was able to predict the exceeding time of limit states’ thresholds. Thus, both repair and a retrofit plan within its design lifetime could be set.

Blast Resistance of Steel Orthotropic Bridge Decks

The main objectives of this study were to: (1) study the response of bridge decks to blast effects resulting from an explosion on the deck; and (2) develop efficient technologies and systems that can be used in design and construction of bridges to enable them to survive blast attacks without collapse. To understand the actual behavior of orthotropic decks subjected to blast loads, typical steel orthotropic decks used in long-span, cable-supported bridges were modeled using MSC/Dytran nonlinear finite-element analysis software, and the models were subjected to simulated explosions occurring on the deck. The parameters that varied in the analyses were the size of the explosive device in terms of equivalent TNT, the axial compressive force present in the deck, and the high-strain-rate mechanical properties of the material of the steel used in the orthotropic decks. Through dynamic analyses, the behavior of the orthotropic decks under blast loads was established and their failure modes were identified. Also, implementation of a new and effective blast-resistant technology, the “fuse system,” was simulated. In this system, to limit the effect of a blast to a localized area of the bridge and to prevent catastrophic progressive collapse of the span, special “fuses” (comparatively weaker structural elements) are placed between two deck segments.

Forward Time Domain Ground Penetrating Radar Modeling of Scattering from Anomalies in the Presence of Steel Reinforcements

Ground penetrating radar (GPR) for nondestructive testing is applied to civil infrastructure such as bridges and roadways. Conventional methods of processing and analyzing GPR data for civil infrastructure are often qualitative, using relative reflection amplitude from subsurface boundaries or reinforcing steel (rebars) as an indicator of health. A Finite Difference Time Domain (FDTD) simulation of GPR is used to generate a bridge deck response of a heterogeneous model of a healthy bridge deck. The result is a healthy deck background that can be removed from measured data to bring anomalies to attention. For the purpose of this article, the measured data is also simulated. In lieu of modeling the identified rebars as perfect electrical conductors (PECs), they are modeled as hard point source excitations to allow for examination of the effect that the scattered waves from the rebar can have on an anomaly. This is an important consideration for application of many inversion methods.

A MOM-based algorithm for moving force identification: Part I - Theory and numerical simulation

The moving vehicle loads on a bridge deck is one of the most important live loads of bridges. They should be understood, monitored and controlled before the bridge design as well as when the bridge is open for traffic. A MOM-based algorithm (MOMA) is proposed for identifying the timevarying moving vehicle loads from the responses of bridge deck in this paper. It aims at an acceptable solution to the ill-conditioning problem that often exists in the inverse problem of moving force identification. The moving vehicle loads are described as a combination of whole basis functions, such as orthogonal Legendre polynomials or Fourier series, and further estimated by solving the new system equations developed with the basis functions. A number of responses have been combined, some numerical simulations on single axle, two axle and multiple-axle loads, being either constant or timevarying, have been carried out and compared with the existing time domain method (TDM) in this paper. The illustrated results show that the MOMA has higher identification accuracy and robust noise immunity as well as producing an acceptable solution to ill-conditioning cases to some extent when it is used to identify the moving force from bridge responses.

Control of Wind-induced Nonlinear Oscillations in Suspension Bridges using a Semi-Active Tuned Mass Damper

In this article, the along-wind and across-wind response of the suspended cables and the bridge deck response of a suspension bridge subjected to wind loading are studied. The mean wind direction is assumed to be perpendicular to the planes of the suspended cables. It is shown that the suspended cable, if constructed alone, will gallop in the across-wind direction when the mean wind speed exceeds a certain critical wind speed. Similarly the bridge deck, if constructed alone, will gallop when a critical wind speed is exceeded. The construction of a suspension bridge, through coupling the bridge deck with the suspended cables via vertical hangers, increases the critical wind speed at which galloping occurs. However, the increase in the critical wind speed of a suspension bridge over a normal bridge is not sufficient to prevent galloping at moderate wind speeds. This article investigates the use of a passive or semi-active tuned mass damper control mechanism to increase critical wind speed for a flexible suspension bridge without changing the shape or size of the bridge deck cross section.

Control of Wind-induced Nonlinear Oscillations in Suspension Bridges using Multiple Semi-active Tuned Mass Dampers

The effectiveness of using Multiple Tuned Mass Dampers (MTMD) to increase the critical wind speed of a flexible long span suspension bridge subjected to wind loading is studied. The mean wind direction is assumed to be perpendicular to the plane of the suspended cable. The along-wind response and across-wind response of the suspended cables and the bridge deck response due to wind are studied, and it is shown that using a single passive or semi-active tuned mass damper (STMD) with a large mass at the mid-span of the bridge raises the critical wind speed of the suspension bridge. As the installation of a single large passive or semi-active tuned mass damper is problematic, we investigate the effectiveness of using multiple tuned mass dampers (MTMD) with small masses located at various positions along the bridge deck. In order to further increase the critical wind speed, the passive MTMD are supplemented by velocity feedback active control forces. The effects of the dampers’ locations, the mass ratio and the damping ratio on the critical wind speed are also investigated.

Analysis of Aeroelastic Bridge Deck Response to Natural Wind

The paper discusses a practical method for numerically analysing bridge response to wind effects. A numerical scheme is used which incorporates the natural wind characteristics and the aeroelastic properties of the bridge deck in order to perform a coupled time-history analysis of the dynamic response. The application of the scheme to the footbridge Kehl-Strasbourg, a very slender cable-stayed bridge, is shown and the design of a sophisticated rocker-type Tuned Mass Damper system is outlined.

On the response of a bridge deck to turbulent wind: a new approach

In spite of getting the aerodynamic parameters to be used in numerical simulations of a bridge deck response to turbulent wind, wind tunnel tests play a crucial role. The aerodynamic admittance function is one of the most difficult to be measured since controlling the incoming flow turbulence spectrum is a primary need and because admittance is a function of the mean wind-to-deck relative angle changing in time and space. In the present paper, an active turbulence generator is proposed, capable to generate a controlled and easy-to-change 2D oscillating flow, making it possible to measure a complex admittance function instead of the commonly adopted real function. The main features of the flow given by the generator are analysed and evaluated and the preliminary results are discussed.

Passive seismic control of cable‐stayed bridges with damped resonant appendages

AbstractA study is conducted to investigate the effectiveness of attaching to cable‐stayed bridges resonant appendages with a relatively small mass and a high damping ratio as a means to reduce their response to earthquake excitations. The study is based on a previously developed formulation that shows that the use of these appendages may increase the inherent damping of building structures and, as a result, may reduce their response to seismic disturbances. It includes numerical and experimental tests that are conducted to assess the validity of such a formulation for the case of cable‐stayed bridges and the extent to which such appendages can reduce their seismic response. In the numerical study, an actual cable‐stayed bridge is modelled with finite elements and analysed with and without the proposed appendages under different earthquake ground motions. Appendages with damping ratios of 10, 15, 20 and 30 per cent and masses that, respectively, represent 0.67, 1.5, 2.7 and 6.0 per cent of the total mass of the bridge are considered. In the experimental test, a 3.7 m long cable‐stayed bridge and an appendage consisting of a small mass, a small spring and a small viscous damper are built and the bridge tested, without and with the appendage, on a pair of shaking tables which are set to reproduce ground acceleration records from past earthquakes. The damping ratio of the appendage in this test is 32 per cent and its mass represents about 8 per cent of the total mass of the bridge model. In the numerical test, it is found that the appendages reduce the longitudinal response of the bridge deck up to 88 per cent. Similarly, in the experimental test it is found that the appendage reduces the longitudinal bridge deck response by about 41 per cent. From these studies, it is concluded that the suggested appendages may indeed be effective in reducing the seismic response of cable‐stayed bridges as they are for building structures.

Effects of Partial Streamlining on Aerodynamic Response of Bridge Decks

The aerodynamic response of long‐span suspended and cable‐stayed bridges can be significantly improved by streamlining the deck geometry. In some cases, a full streamlining may not be practical and, as a compromise, partial streamlining is considered. The present technical note is concerned with the aerodynamic response of the deck of a cable‐stayed bridge. The results of a wind‐tunnel study employing a section model of the deck are presented. The experimental data include the deck response in heave and flow patterns about the stationary and oscillating decks. The effects of modification of the deck geometry (addition of streamlining fairings and removal of traffic barriers) on the vortex‐induced response of the deck are discussed. It is shown that partial streamlining of the deck geometry may result in an increase in the deck aerodynamic response.

On flutter and buffeting mechanisms in long-span bridges

Using linear formulations throughout, the present paper reexamines the problem of the three-dimensional dynamic response of long, flexible bridge decks to wind, particularly with the modern cable-stayed bridge in view. There are some particular motivations for the approach presently used. First, it has been observed that the bridge deck, the principal attractor of aerodynamic forces, undergoes three-dimensional motion having not only vertical and twist components, but lateral sway as well. This is a pronounced feature of many cable-stayed bridge vibration modes; and, since lateral sway can play a strong, contributory role in total aeroelastic action, it is important that its effects be included. Second, under buffeting by turbulent wind, total bridge response is random in the time domain, precluding the direct expression of aeroelastic forces via the well-known flutter derivatives which are applicable only to harmonic motion. In principle their role must be supplanted for general motions by the integrated effects of those motions as weighted by the corresponding aerodynamic indicial functions. However, to date such indicial functions have themselves been derived only through inverse Fourier transformation of experimentally obtained flutter derivatives; hence there exists an impetus to carry out the entire analysis in the frequency domain, where the original flutter derivatives can be used directly. The details of this procedure and its consequences regarding both the stability and level of bridge deck response are pursued in the body of the paper.

The influence of bridge geometry on the seismic behaviour of bridges on isolating bearings

The response of bridge decks supported on elastomeric or a combination of elastomeric and lead-rubber bearings is computed and compared with the response of a bridge deck monolithically connected to piers designed to have a ductile behaviour. A study of the sensitivity of bridge response to changes in geometry was made using the El Centro 1940 N-S earthquake component. The geometrical changes covered a range of uniform pier heights, a range of number of spans.

The influence of non-geometric factors on the seismic behaviour of bridges on isolating bearings

A study of the sensitivity of bridge response to changes in non-geometric parameters was carried out using mainly the El Centro 1940 N-S earthquake component. The response of bridge decks supported on elastomeric or a combination of elastomeric and lead-rubber bearings is computed. The effects of variations in the following parameters on response were studied; a) a range of bearing properties, b) a range of abutment stiffnesses and abutment weights, c) different earthquake records and d) the effect of seismic waves propagating at various velocities and angles of attack with respect to the bridge centreline.