Flat Steel Box Girder Research Articles

Investigation of the Influence of Spoiler and Maintenance Track on Second-Order Heaving Vortex-Induced Vibration

To improve the guidance for the wind tunnel test, this study initially conducted thorough research on the wind environment at a coastal bridge site to ascertain the characteristics of the wind parameters varying along the bridge span. Subsequently, the measured results were utilized to steer wind tunnel test research, focusing on analyzing the influence of the spoiler and maintenance track on the second-order heaving vortex-induced vibration of the flat steel box girder. This investigation uncovered two distinct distributions in the angle of attack along the span: bimodal distribution and asymmetric unimodal distribution. The angle of attack of the incoming flow was primarily concentrated within ±5°. Both the two-side and the windward spoiler were found to exert similar effects on the second-order heaving vortex-induced vibration, primarily impacting the second lock-in region. Furthermore, the outer maintenance track could effectively suppress the vortex-induced vibration, while the spacing of the inner maintenance track significantly affected the vortex-induced vibration at high wind speeds.

A field study of temperature field distribution characteristics of flat steel box girder and its influential environmental factors

As one of the mainstream girder types of long-span bridges, the flat steel box girder (FSBG) under thermal action has been one primary concern for bridge engineers and researchers. This research presents a field study of the temperature field distribution characteristics of FSBG and its influential environmental factors. To achieve this, an acquisition equipment that comprises of thermometers and environmental sensors is applied to a prototype cable-stayed bridge under construction, in which the structural temperature field of FSBG and the surrounding environmental data are collected and analyzed thoroughly. The results indicate that the vertical temperature distribution (VTD) in certain time instants exhibits significant variations and the maximum vertical temperature gradient can reach up to 27.9 °C. Despite of this, it is found that the VTD of FSBG can be covered by several current standards such as AASHTO standard and New Zealand standard. As for the transverse temperature distribution (TTD), it is found that both the variation and temperature difference of TTD in certain time instants are considerable, especially at the deck surface, which far exceed those of the TTD prescribed in current standards. This indicates that the TTD of FSBG should be seriously considered during the bridge design phase. Furthermore, the field study reveals that the wind speed has negative effect on the structural temperature of FSBG (when the air temperature is less than that of FSBG), while the solar radiation exerts positive effect on the structural temperature of FSBG. The outcome of this study can provide valuable references for thermal design, monitoring and control of long-span bridges employing FSBGs as bridge main girder.

Calculation of Temperature Action of Flat Steel Box Girder of Long-Span Bridges Using a Joint Model of ARMA Mean and GARCH Variance

Using the monitoring temperature field data from the flat steel box girder, the time histories of temperature data and temperature difference data are investigated using the extreme value analysis method. Because the calculation of standard values of temperature action needs massive temperature field data, the simulation of daily extreme values of temperature data and temperature difference data is carried out by virtual of Probability Statistical Method. The seasonal and nonstationary trend terms are described using the weighted sum of a series of basic elementary functions. The random fluctuation term is represented by a joint model of ARMA mean and GARCH variance. Moreover, the yearly extreme values of temperature data and temperature difference data are considered as statistical variables, and their standard values of temperature action with 50-year return period are calculated by means of the general extreme value (GEV) distributive function. The research results can supply references for temperature action of flat steel box girder.

Temperature gradient modeling of a steel box-girder suspension bridge using Copulas probabilistic method and field monitoring

A novel copula-based probabilistic model is proposed to establish the temperature difference analysis model for a long-span suspension bridge’s steel box girder. The key idea is to express a two-dimensional function of the temperature difference in flat steel box girder by using copulas. The maximum and minimum values of daily temperature difference model was developed using long-terms structural health monitoring data. Then, the correlation between adjacent temperature differences is investigated using five types of copulas. Akaike information criterion (AIC) is used to select an optimal model from five types of copulas, and the optimal joint function (two-dimensional function) for steel box girder’s temperature difference is established. Finally, the structure’s temperature gradient model is extrapolated for the service life of the structure by using Monte Carlo method. Moreover, this paper discusses the temperature gradient models using five types of common copulas and four types of time-varying copulas. The result shows that the t-copula is the optimal function to build the two-dimensional functions for steel box girder’s temperature difference, and the temperature model along the transverse direction can offer useful information that is not available in the design codes.

A Quick Assessment and Optimization Method for a Flutter Aerodynamic Measure of a Typical Flat Box Girder

Flutter is one of the most serious wind-induced vibration phenomena for long-span bridges and may cause the collapse of a bridge (e.g., the Old Tacoma Bridge, 1940). The selection and optimization of flutter aerodynamic measures are difficult in wind tunnel tests. It usually takes a long time and consumes more experimental materials. This paper presents a quick assessment and design optimization method for the flutter stability of a typical flat box girder of the long-span bridges. Numerical analysis could provide a reference for wind tunnel tests and improve the efficiency of the test process. Based on the modal energy exchange in the flutter microvibration process, the global energy input and local energy input are analyzed to investigate the vibration suppression mechanism of a flat steel box girder with an upper central stabilizer. Based on the comparison between the experimental and numerical data, a quick assessment method for the optimization work is proposed. It is practical to predict the effects of flutter suppression measures by numerical analysis. Thus, a wind tunnel test procedure for flutter aerodynamic measures is proposed which could save time and experimental materials.

Effects of the wide-body suspension bridge auxiliary structure on flutter characteristics by CFD

This paper is focused on the CFD numerical simulation of flutter characteristics of the wide-body flat steel box girder of Chongqing Cuntan Yangtze Bridge. The specific influence on the aerodynamic performance and flutter critical wind velocity have been studied by setting different railing ventilation rates. The results show that: the subsidiary structures of the main beam have an adverse effect on the stability of bridge flutter. The ventilation rate of the railings affects the flutter derivatives and the critical wind speed of the flutter.

Effect of wind barriers on the flow field and aerodynamic forces of a train–bridge system

This paper investigates the effect of a wind barrier on the aerodynamic performance of a train–bridge system under crosswind using a numerical simulation method. The studied bridge is a long-span cable-stayed bridge with a flat steel box girder, located in Chongqing, China. The flow field around the train–bridge system with and without a wind barrier is numerically simulated. Wind barrier porosities varying from 10 to 60% are evaluated. The tricomponent coefficients of the train, bridge, and train–bridge system are obtained and investigated in detail. The effect of the wind barrier on the aerodynamics of the train–bridge system is revealed through the determination of the aerodynamic forces, pressure mapping, and flow visualization. The results show that a wind barrier successfully decreases the mean velocity above the girder and consequently decreases the drag force and moment on the train; however, the wind barrier also significantly increases the drag force on the girder. Therefore, installation of a wind barrier improves the running safety of the train but is detrimental to the wind resistance of the bridge. Additionally, the efficiency of the wind barrier depends on the porosity. A lower porosity improves the train safety but is more detrimental to the bridge safety. An optimal wind barrier porosity of 30% is obtained based on the aerodynamic forces of both the train and the bridge. Compared to a train–bridge system without a wind barrier, the drag force and moment on the train decrease by 66.1 and 62.9%, respectively; the drag force on the bridge girder increases to 0.86, and the drag force on the train–bridge system equals that without the wind barrier.

Investigation of temperature actions on flat steel box girders of long-span bridges with temperature monitoring data

The worldwide application of streamlined flat steel box girder on long-span bridges calls for more knowledge of its temperature distribution. The rapid development of structural health monitoring techniques offers a great opportunity to address this issue. A comprehensive approach of installing monitoring equipment, collecting data, and applying long-term temperature monitoring data to study the temperature distribution of flat steel box girders is developed. As demonstrated through the analysis of 1-year data of a suspension bridge, first, a mapping relation between effective temperature and ambient air temperature is established. Such a relation enables identifying the optimal time to finally join the flat steel box girders at the designed effective temperature based on the easy-to-obtain ambient air temperature. Second, the cycling variation of effective temperature is presented to provide information for design and assessment of expansion joints and bearings, including not only the maximum design displacements but also cumulative displacements related to the long-term durability and remaining life of expansion joints and bearings. Finally, both vertical and transverse temperature gradients are studied to provide some new insights about the temperature characteristics of flat steel box girders. The study suggests that the transverse and vertical temperature gradients should be applied to the bridge cross section individually since the data analysis supports that the two gradients are independent.

Aerodynamic Admittance Research on Wide-body Flat Steel Box Girder

Aerodynamic admittance is a key parameter affecting the analysis accuracy of the bridge buffeting response. However, few articles have covered the issue of the wide-body flat box girder with much smaller depth-width ratio (such as 1/12 studied in this paper). Therefore, to explore the real buffeting force of the wide-body flat box girder, experiments of the static force coefficients and aerodynamic admittance are carried out in wind tunnel. Wooden segmental model has a scale ratio of 1/60 to an actual 42 m wide suspension bridge girder. Using the high-frequency-force-balance (HFFB) equipment fixed with the segmental model under the conditions of different wind speeds and different wind attack angles, wind power spectrums of the buffeting force are measured and the variation of aerodynamic admittance parameters is analyzed. The results show that the aerodynamic admittance of the box girder measured in the experiment with this so much smaller depth-width ratio differs from the corresponding classical Sears expression. Some inspiration can be presented for the future study of the buffeting response for this kind of much wider bridge with the similar ratio in this paper.

Vehicle Effect on Vortex-induced Vibration of Flat Steel Box Girder

Vortex-induced vibration (VIV) occurs at low wind speed under normal condition, affected greatly by section type of bridge and its ancillary facilities. Few researches on VIV of vehicle-bridge system are conducted, and many researchers pointed that vehicle-bridge system should be paid attention to in wind tunnel test. In this paper, type of vehicle, number of vehicle and distance of traffic flow’s influence on VIV were studied with a flat steel box girder model. Results obtained from wind tunnel tests were displayed in order to prove the following rules: First of all, compared with conditions without vehicles, response of VIV is reduced severely when a vehicle is placed on the bridge. Secondly, response of VIV and range of VIV with three vehicles are greater than one vehicle on the bridge. At last, VIV is reduced when distance of traffic flow increases. Mechanism from fluid dynamic point view is given by simulating the working conditions with ANSYS 14.5.

Long-Term Temperature Monitoring and Statistical Analysis on the Flat Steel-Box Girder of Sutong Bridge

AbstractUsing the flat steel-box girder of China’s Sutong Cable-stayed Bridge as a research object, its temperature field is long-term monitored and analyzed based on bridge’s structural health mon...

Estimating extreme temperature differences in steel box girder using long-term measurement data

The extreme temperature differences in flat steel box girder of a cable-stayed bridge were studied. Firstly, by using the long-term measurement data collected by the structural health monitoring system installed on the Runyang Cable-stayed Bridge, the daily variations as well as seasonal ones of measured temperature differences in the box girder cross-section area were summarized. The probability distribution models of temperature differences were further established and the extreme temperature differences were estimated with a return period of 100 years. Finally, the temperature difference models in cross-section area were proposed for bridge thermal design. The results show that horizontal temperature differences in top plate and vertical temperature differences between top plate and bottom plate are considerable. All the positive and negative temperature differences can be described by the weighted sum of two Weibull distributions. The maximum positive and negative horizontal temperature differences in top plate are 10.30 °C and −13.80 °C, respectively. And the maximum positive and negative vertical temperature differences between top plate and bottom plate are 17.30 °C and −3.70 °C, respectively. For bridge thermal design, there are two vertical temperature difference models between top plate and bottom plate, and six horizontal temperature difference models in top plate.

Temperature gradient and its effect on flat steel box girder of long-span suspension bridge

The temperature field variation law and distribution characteristics of an orthotropic flat steel box girder under sunny conditions were analyzed through a field temperature test on the steel box girder of the operational Runyang Yangtze River Bridge (the suspension bridge part). Function optimization fitting and error analysis of the test data were conducted. A temperature gradient distribution curve applicable to a hexagonal flat steel box girder was proposed. Based on the measurement results, the temperature effect of an orthotropic flat steel box girder was analyzed using finite element method and the effects of different temperature gradient modes on the mechanical characteristics and stress distribution of the steel box girder were compared. Under sunny conditions, heat conduction in the flat steel box girder structure shows distinct “box-room effect” characteristics, and the actual temperature gradient distribution is inconsistent with the one suggested by the existing standards. The thermal stress of a steel box girder calculated from the measured temperature gradient mode exceeds that calculated from the standard, and the intensity approximates that under the action of designed vehicle loads. The temperature-induced stress is distributed centrally near the manufacturing welds of the orthotropic steel box girder, which should be considered in design, construction and research. Results from this study could supplement the existing bridge and culvert design standards.

Thermal field characteristic analysis of steel box girder based on long-term measurement data

Thermal loads are important factors that affect the serviceability of long-span bridges. In this paper, the distribution characteristics and statistical features of thermal field in flat steel box girder are presented based on long-term field measurement data collected by the structural health monitoring system (SHMS) permanently installed on the Runyang Suspension Bridge (RSB). Firstly, the daily variations as well as seasonal ones of measurement temperature and temperature differences in the box girder cross-section are summarized. Secondly, employing a combined probability distribution model defined by the weighted sum of one Weibull distribution and one normal distribution, the probability density function (PDF) of each temperature difference is formulated. Thirdly, making use of the extreme value analysis, the extreme temperature differences are predicted with a return period of bridge design working life and compared with the expected values in British standard (BS EN 1991-1-5, 2003). Finally, the critical temperature difference models in cross-section are proposed for thermal stresses calculation according to correlation analysis. The results provide a clear understanding of thermal field in flat steel box girder bridges and have reference values for structural design and evaluation.

Fatigue Evaluation of Flat Steel Box Girders with Closed Stiffeners of Large-Span Suspension Bridges under Different Heavy Trucks

Due to its outstanding aerodynamic shape and light weight, the trapezoidal cross-section flat steel box girder with orthotropic decks and thin-walled longitudinal stiffeners of trapezoidal cross section are widely used in long-span suspension bridges in the world. However, because of the geometrical characteristics and the relative flexibility of their components, these structures may be quite susceptible to traffic loadings that fatigue cracks tend to appear in these structures. In this paper, Jiangyin Bridge is used as a case study to investigate the fatigue performance of the steel girders of suspension bridge Jiangyin Bridge is the second longest bridge in China, which has the main span of 1385m. The stress analysis of steel box girders is firstly carried out based on the analysis of fatigue life. Fatigue assessment method is proposed on the basis of in-situ measurement data combined with finite element analysis. A complete fatigue assessment is made in this paper. Key words: flat steel box girder; orthotropic decks; finite element analysis; fatigue assessment

Accurate Stress Analysis on Steel Box Girder of Long Span Suspension Bridges Based on Multi-Scale Submodeling Method

The streamline flat steel box girder is broadly used in long span cable-supported bridges all over the world. As one of the most important part of the bridges, its stress level and distribution under various dynamic loads are especially concerned. However, it is difficult to obtain the accurate stress of the steel box girder by common finite element (FE) calculation. The Runyang Suspension Bridge (RSB) is taken as an example. To increase the accuracy of results, a 3-dimensional FE full model for the RSB is created by ANSYS and a spatial submodel of the steel box girder is particularly built with greater detail. Submodeling method is then employed as a connection technique to link different scale models. After the global analysis and connecting process, the local stress of the steel box girder under various vehicle loads is obtained by submodel analysis. The composite action between the full model and the submodel is analyzed, and the reasonable mesh size for the submodel is specially investigated. The numerical results are proved to be accurate by the field test results. This study demonstrates the reliability and efficiency of the submodeling method; and can provide references for accurately analyzing and designing the steel box girders of other long span bridges.