Continuous Box Girder Research Articles

Accumulative Bayesian detection of displacement constants of a hybrid indeterminate box girder with variable scale gradient theory

With general Bayesian theory, the accumulative Bayesian objective function of displacement constants of a hybrid indeterminate box girder was found. The gradient matrix of accumulative Bayesian objective function to displacement constants and the calculative covariance matrix were both derived. The finite curvilinear strip controlling equation of a pinned box girder was derived and the hybrid indeterminate problem of a continuous curvilinear box girder with diaphragm was solved based on agglomeration theory. Combined with one-dimensional (1D) Fibonacci automatic search scheme of optimal step length, the variable scale gradient theory was utilized to research the stochastic detection of displacement constants of the hybrid indeterminate curvilinear box girder. Then the detection steps of displacement constants of the hybrid indeterminate curvilinear box girder were presented in detail and the detection procedure was developed. Through some classic examples, it is achieved that the accumulative Bayesian detection of displacement constants of the hybrid indeterminate curvilinear box girder has perfect numerical stability and convergence, which demonstrates that the derived detection model is correct and reliable. The stochastic performances of displacement constants and structural responses are simultaneously deliberated in an accumulative Bayesian objective function, which proves to have high computational efficiency. The variable scale gradient method incessantly changes the spatial matrix scale to engender new search directions during the iterative processes, which makes the derived accumulative Bayesian detection of the displacement constants more efficient.

Shear Test of Variable Depth RC Beams with Inflection Point

Variable depth continuous box girder bridges are widely used recently. However, the influence mechanism of the inflection point and variable depth on the shear behaviour of this type bridge has not been fully understood. In this paper, reinforced concrete (RC) beams with constant depth and variable depth were designed as constrained beams to create the inflection point. Firstly, a theoretical uncoupling theory for shear and flexural deformation of variable depth beam was derived. Then, the after cracking shear deformations and the ultimate failure loads were measured. Further, preliminary reveal of the influence mechanism of inflection point on the shear capacity was attempted. Finally, the development of after-cracking shear strain and the degradation of shear stiffness were studied. The formation of first critical diagonal cracks and yielding of stirrup are the turning points of shear stiffness. Increasing stirrup ratio provides more apparent enhancement for residual shear stiffness, which means more effective inhibition on shear deformation.

Tensioning-Phase Box Girder Deformation Prediction Model Based on Ant Colony Algorithm and Residual Correction

The girder of prestressed concrete continuous box girder bridge strengthened by a stay cable system has a very complex deformation mechanism, and it is difficult to establish accurate numerical model for prediction. For these problems, a prediction method based on the combination of ant colony algorithm and residual combination correction model is proposed. In this method, the measuring points are considered as the cities in TSP ant colony algorithm, the information function model and heuristic function model are constructed, the pheromone update mechanism and ant search mechanism are established, and the deformation prediction of the main girder based on ant colony algorithm prediction model is achieved. On this basis, in order to fit the random change process of main girder deflection better, the periodic function generated by harmonic transform and sine function are introduced to modify the predicted results, which makes up for the low precision defect of single model. The results show that compared with finite element method, unequal interval gray model (1,1) (UIGM (1,1)), one-time residual correction UIGM (1,1), Markov chain residual correction UIGM (1,1), and ant colony algorithm model, this model can reflect the space-time effect and casual fluctuation feature of the development of girder deformation better and also has higher prediction accuracy and efficiency. The mean relative error of the predictive value is 3.39%, the posterior error ratio is 0.060, and the accuracy level reaches level 1. This model provides a new way for the girder deformation prediction of bridge strengthened by the stay cable system.

Accelerated optimization method for low-embodied energy concrete box-girder bridge design

Structural optimization is normally carried out by means of conventional heuristic optimization due to the complexity of the structural problems. However, the conventional heuristic optimization still consumes a large amount of time. The use of metamodels helps to reduce the computational cost of the optimization and, along these lines, kriging-based heuristic optimization is presented as an alternative to carry out an accelerated optimization of complex problems. In this work, conventional heuristic optimization and kriging-based heuristic optimization will be applied to reach the optimal solution of a continuous box-girder pedestrian bridge of three spans with a low embodied energy. For this purpose, different penalizations and different initial sample sizes will be studied and compared. This work shows that kriging-based heuristic optimization provides results close to those of conventional heuristic optimization using less time. For the sample size of 50, the best solution differs about 2.54% compared to the conventional heuristic optimization, and reduces the computational cost by 99.06%. Therefore, the use of a kriging model in structural design problems offers a new means of solving certain structural problems that require a very high computational cost and reduces the difficulty of other problems.

Determining the dynamic amplification factor of multi-span continuous box girder bridges in highways using vehicle-bridge interaction analyses

The impact factors of multi-span continuous box girder bridges in highways are influenced by many factors, including road roughness, vehicle-bridge interactions (VBIs), and travelling velocity. Currently, the empirical formulas specified by bridge design codes are based on single factors (bridge length or fundamental frequency). These formulas yield inconsistent results that can differ widely. In this paper, the regularity of the dynamic amplification factors (DAFs) of continuous beam bridges is investigated by selecting 15 continuous beam bridges and conducting VBI analyses. The results indicate that the DAFs of the continuous beam bridges increase dramatically when resonance phenomena occur. The vehicle-bridge resonance is closely related to vehicle frequency, bridge frequency and the disturbance frequency caused by vehicle movement. The travelling velocity exerts an important influence on the resonance. In most cases, the DAF of a continuous beam bridge peaks at the velocity range of 40–60 km/h. Vehicle-bridge resonance may be caused by the first-order or second-order mode of a bridge. Second-order curvature modes exert an especially crucial influence on the DAF of the negative moment at the interior supports. The empirical formulas used in current bridge design codes fail to account for the influence of resonance and travelling velocity on the DAFs of bridges. The maximum DAF at the interior supports of the continuous beam bridges may exceed 1.7.

Stability against Overturning of Curved Continuous Box-Girder Bridges with Single Column Piers

This paper introduces the factor of stability against overturning (FSO) for curved bridges, and examines the influence of curvature radius and bearing eccentricity on FSO under self-weight and vehicle loads as well as other important parameters. The results show that FSO variation rules are indeed affected by curvature radius and bearing eccentricity. Lane loads are identified as crucial parameters in the overturning resistance of curved bridges. Bearing eccentricity influences the inner side and outer side reactions of abutment bearings, but the optimal bearing eccentricity can ensure uniform torque distribution; said optimal eccentricity is expressed as a function of curvature radius. FSO increases as bearing eccentricity increases, but decreases first followed by a later increase as curvature radius increases. The FSO curve with curvature radius is concave. There exist specific curvature radii near the lowest point in the FSO curve which must be avoided in the design stage to meet necessary safety demands. When curvature radius exceeds 500 m, the FSO converges on an identical curve which can be expressed as a function of curvature radius.

Research on Comprehensive Evaluation Method for Antioverturning Safety of Bridges with Bent-straight Beam

Based on study of the critical state of overturning and the selection of overturning axis, a comprehensive evaluation method for anti-overturning safety is given for the continuous beam of bridge axis located on the bent-straight beam line. Based on the failure mechanism of the continuous box girder, the model of support separation is given for the overturning failure of bridge, and the specific calculation method for the safety factor of overturning is given. Taking a reinforced continuous box beam of the single-column pier on bent-straight-combined line as an example, a case study of a real bridge is carried out, and a full calculation of the support separation, the support angle and the overturning safety factor of the bridge is carried out. The application of a real bridge shows that the safety evaluation method for anti-overturning safety of bridges with bent-straight beam proposed in this paper is practical and reasonable.

Theoretical and Numerical Study on the Natural Frequencies of Bridges With Corrugated Steel Webs

The dynamic characteristics including natural frequencies, mode shapes, and damping ratios are essential to investigate the vibration response of a structural system, in which the natural frequency is deemed the most important parameter. Research on the vertical natural frequencies of prestressed concrete (PC) box girders with corrugated steel webs (CSWs) is limited. In this research, the energy variation method proposed by E. Reissner and Galerkin method was adopted to study the single-span and multi-span continuous prismatic PC box girders with CSWs and simply-supported condition. To the accurately derive the formula for the vertical natural frequencies, the shear lag effect and shear effect from the box girder and CSWs, respectively, are considered. Numerical simulations were carried out to validate the theoretical solution. Sensitivity studies using the analytical equation were also conducted to investigate the effects of the waveform of CSWs, the outer top flange, and the thickness of corrugated steel webs.

Deformation Forecast of Main Girder Enhanced by Stay Cable System with Unequal Interval Grey Model and Residual Composite Correction

This paper aims to achieve the accurate prediction of box girder deformation in SCS-enhanced PSC continuous box girder bridges. To this end, the authors proposed a box girder deformation prediction model based on unequal interval grey model (UIGM) and residual composite correction (RCC). Firstly, the tension forces of cables and the deformation data of box girder were regarded as the time sequence and the original unequal interval sequence, respectively, and the UIGM was constructed to predict the box girder deformation. Secondly, the sine function was constructed on the average features of the residual sequence waveform, and the periodic sequence function was generated by harmonic transform. The two functions were employed to extract the implicit periodic information and overcome the limitation of the UIGM (i.e., the UIGM only generates the change rate of a single index). Finally, the Markov chain method was adopted to treat the random fluctuations and further enhance the prediction accuracy and adaptability of the model. Then, the proposed UIGM-RCC was applied to predict the box girder deformation of Dongming Huanghe River Highway Bridge and forecast the settlement of a building mentioned in previous research. The results show that the proposed model can reflect the exact periodicity and random fluctuations of box girder deformation in SCS-enhanced PSC continuous box girder bridges. The research findings provide a meaningful reference for improving deformation prediction accuracy in SCS-enhanced structures.

Vertical Dynamic Responses of the Cantilever Deck of a Long-Span Continuous Bridge and the Coupled Moving Trains

It may be necessary to arrange railway traffic on the outer edge of the cantilever deck of a box girder bridge for the sake of transportation planning. A continuous box girder bridge was designed in China to carry a single-track urban rail transit traffic on the cantilever deck of the bridge and three-lane highway traffic on the other part of the deck. In order to investigate the possible resonant responses of the coupled train–bridge system, the resonance condition of the cantilever deck under moving train loads is discussed analytically, and then numerical analyses of the vertical train–bridge dynamic interaction considering local vibration of the cantilever decks are carried out. The degrees of freedom of the bridge modeled by shell elements are so large that mode superposition method is used to reduce the computation efforts. It is found that the resonance speed of the cantilever deck predicted by the analytical method is 305 km/h, which agrees well with the numerical result. The numerically computed results also indicate that the serviceability of the bridge deck and the ride quality of the railway vehicles in the vertical direction are in good condition below the critical speed of 200 km/h.

NC-UHPC Composite Structure for Long-Term Creep-Induced Deflection Control in Continuous Box-Girder Bridges

NC-UHPC Composite Structure for Long-Term Creep-Induced Deflection Control in Continuous Box-Girder Bridges

Concrete Curved Box Girders Interacted with Vehicles in Braking or Acceleration

In this study, an experimentally validated spatial analysis method for the vehicle–bridge interaction system was modified to include the features of vehicle braking and accelerating. The effect of braking or accelerating was considered as external force acting on the vehicular center of gravity and was quasi-statically distributed to every tandem, for which the formulae of load redistribution were derived. The effect of centrifugal force was also incorporated in the model. Based on the modified spatial analysis method, the dynamic responses of a three-span continuous concrete box girder bridge due to vehicle braking and accelerating were studied. Impact factors, including deflection, bending moment, torsional moment and shear force, were examined. The results show that vehicle braking has considerable effect on dynamic responses and the impact factors are related to braking rise time and braking position, but cases of vehicle braking do not always cause larger effects. While the increase in initial speed can produce higher maximum dynamic responses and corresponding impact factors, the dynamic responses in the first span of a multi-span bridge are smaller than those in other spans due to vehicle accelerating.

Study on PC Continuous Girder mechanical properties Based on Tendon Tensioning Pattern

prestressed concrete continuous box girder in China. With the change of condition in the construction site, the construction sequence of the bridge will be changed inevitable, so to adjust the tendon tension mode accordingly, which will cause the alteration of structural mechanics performance. The finite element analysis model of a continuous girder will be built to compare the difference with two tendon tension cases according to relevant pouring sequence. The related conclusions are obtained, so can help to provide beneficial reference for the similar engineering.

Seismic vulnerability assessment of a continuous steel box girder bridge considering influence of LRB properties

Bridges are one of the most crucial facilities of transportation networks. Therefore, evaluation of the seismic vulnerability of bridge structures is perpetually regarded topic for researchers. In this study, we developed seismic fragility curves for a continuous steel box girder bridge considering the effect of different levels of mechanical properties of lead rubber bearing (LRB) devices including initial stiffness and yield strength on the seismic performance of such structure. A powerful framework for an earthquake engineering simulation, OpenSees, is used to perform nonlinear analyses of the bridge model. In order to construct fragility curves for this structure, a set of 20 ground acceleration records is adopted and various scales of the peak ground acceleration (PGA) from 0.1 to 1.6 g are considered. Besides, a series of damage state of the bridgeis defined based on a damage index, which is expressed in terms of the column displacement ductility ratio. Fragility analyses result reveals that reducing the initial stiffness of LRBs reduces the seismic vulnerability of bridge piers and vice versa. Meanwhile, the changes of the yield strength of LRBs have trivially effected on the seismic behaviour of the bridge piers. On the other hand, the short pier has performed more susceptibly than those of the high pier in both seismically-isolated and non-isolated bridge cases. Lastly, the results in this research also indicate that the bridge structures equipped with seismic isolation devices (e.g. LRBs) significantly mitigated the damages due to earthquakes.

Research on structural dynamic characteristics of continuous steel box girder-bridge with lager ratio of wide-span

Structure natural frequency and mode of vibration can not only reflect the structure modal parameters of dynamic properties, but also incarnate the dynamic evaluation characteristics of bridge structure. This paper applies ANSYS to establish the finite element model based on a continuous steel box girder bridge in order to obtain the corresponding modal analysis parameters. Through the environmental stimulation test, The results show that height of the steel box girder and the setting of diaphragm plate is reasonable, transverse space of piers not merely provide enough support but also ensure lateral stability of the bridge, as well as offering aside the maximum lateral clearance of the existing road. Meanwhile, the calculation results have important engineering practical values. which can provide basic data for the design, construction and maintenance of similar Bridges.

Vibration characteristics change of a three span continuous steel box girder bridge on behalf of environmental changes of temperature and traffic vibration

Vibration characteristics change of a three span continuous steel box girder bridge on behalf of environmental changes of temperature and traffic vibration

大跨径斜弯连续箱梁桥施工监控研究

大跨径斜弯连续箱梁桥施工监控研究

Seismic fragility analysis of deteriorating RC bridge substructures subject to marine chloride-induced corrosion

This paper presents an improved reinforced concrete steel bar deterioration model that incorporates pitting corrosion and considers the change in after-cracking corrosion rate to assess the time-dependent seismic fragility of RC bridge substructures in marine environments. The proposed deterioration model is applicable for both existing and new RC bridge substructures and could be employed for life-cycle analysis of RC bridge substructures in marine environments. In this paper, the model is implemented to conduct a probabilistic seismic fragility analysis of a three-span continuous box girder bridge accounting for uncertainties in establishing bridge geometry, material properties, ground motion and corrosion parameters. Differences in the results obtained when reinforcing steel is subjected to general and pitting corrosion are investigated. The results show that the effect of chloride-induced corrosion cannot be neglected when performing the seismic fragility analysis of RC bridge substructures in marine environments. Additionally, the calculated time-dependent fragility curves indicate that there is a nonlinear accelerated growth of RC column vulnerability along the service life of highway bridges, especially after twenty-five years of exposure to chlorides.

Ambient vibration test-based deflection prediction of a posttensioned concrete continuous box girder bridge

Ambient vibration test generally only outputs basic modal parameters including frequencies, damping ratios, and unscaled mode shapes, which cannot directly support decision making of structural maintenance and management. In this article, structural deep-level parameters including unscaled and scaled flexibility identification of a posttensioned concrete continuous box girder bridge are studied by performing ambient vibration test, which is able to predict structural deflections by multiplying the static load with the identified flexibility. Ambient vibration test of the bridge and basic modal identification are firstly performed. Then, the method of unscaled flexibility identification is proposed by investigating the relationship between the frequency response function estimated from ambient test data and the analytical one. Finally, a mass-changing strategy is utilized to identify the scaled flexibility from output-only data, in which the key issue is to identify mass-normalized scaling factors by performing ambient vibration tests of tested structure before and after changing its mass. Numerical simulation of a simply supported beam and field test of a three-span bridge has been conducted to verify the capability and reliability of the proposed method. The good agreement between the predicted deflections from the identified flexibility and those measured from the static test successfully illustrates the effectiveness of the proposed method.

REHABILITATION OF BOX GIRDER BRIDGE

A large pre-stress continuous box girder bridge consists of two separate parts, ten spans deck and eight spans deck. The bridge was subjected to multiple airstrikes, which caused several damages. The most serious are the complete destruction of four conductive spans in the ten spans deck, the movement of the remaining six spans longitudinally by about 1.25 m and transversely by about 0.1 m. Local damages occurred in other parts of the deck structure and minor damages in the piers and abutments. The deck structures were constructed by incremental launching method (ILM). Rehabilitation of the bridge included repair of the local damages, lifting and re-instatement the six spans, which weighs about 9,000 tons, to its original position, the constructing and launching of new box girder to substitute for missing spans, and finally connecting old and new spans effectively. This paper introduces briefly the re-instatement of the six spans, connection details between the old new structures, then assessing the efficiency of connection by analysis and load testing the connecting span.