Three-tower self-anchored suspension bridge (TSSB) is more and more favored because of its beautiful structure and strong adaptability to terrain and geological conditions. However, there are few engineering practices and related researches on super long-span three-tower self-anchored suspension bridges. A three-dimensional finite element model for the Fenghuang Yellow River Bridge, with the world’s longest span of its kind under construction, is established using the ANSYS finite element program, and the structural dynamic characteristics of the super long-span TSSB are studied and compared with those of several bridges of the same type or with similar spans. In addition, the influence of the key design parameters such as the stiffening girder stiffness, tower stiffness, main cable and suspender stiffness, central buckle, and longitudinal constraint system on the dynamic characteristics of the structure is analyzed. The results show that the first mode of the TSSB is longitudinal floating, the lower-order modes are dominated by vertical bending modes, while the higher-order modes are primarily vibration modes of the main cables, and the torsional modes exhibit strong coupling with the lateral sway of the towers and main cables. The frequency of the first antisymmetric vertical bending mode of the TSSB has an inversely proportional relationship with the main span length. Compared with a double-tower ground-anchored suspension bridge and cable-stayed bridge with similar spans, the TSSB has the lowest frequency for the first antisymmetric vertical bending mode and the highest frequency for the first symmetric vertical bending mode, with a more pronounced coupling with the towers and main cables in the torsional modes. Analysis of the structural parameters shows that the frequencies of the longitudinal floating mode, first antisymmetric vertical bending mode, first symmetric vertical bending mode, and first torsional mode are most sensitive to the longitudinal bending stiffness of the side tower, central buckle, vertical bending stiffness of the stiffening girder, and torsional stiffness of the stiffening girder, respectively. The research findings and relevant conclusions can provide basic data for response analysis of long-span TSSBs under dynamic loads and offer an engineering reference for the design of similar bridges around the world.
Bridge construction is one of the cores of traffic infrastructure construction. To better develop relevant bridge science, this paper introduces the main research progress in China and abroad in 2019 from 13 aspects, including concrete bridges and the high-performance materials, the latest research on steel-concrete composite girders, advances in box girder and cable-supported bridge analysis theories, advance in steel bridges, the theory of bridge evaluation and reinforcement, bridge model tests and new testing techniques, steel bridge fatigue, wind resistance of bridges, vehicle-bridge interactions, progress in seismic design of bridges, bridge hydrodynamics, bridge informatization and intelligent bridge and prefabricated concrete bridge structures.
This paper proposes a simplified hand-calculation methodology that permits a fast response assessment (both in vertical and lateral direction) under different pedestrian scenarios. This simplified method has the same accuracy than that of very sophisticated numerical nonlinear finite element models including pedestrian inter-variability, interaction among pedestrians in flows, and pedestrian-structure interaction. The method can capture the effects of pedestrian loads in and out of resonance. This methodology is based on a new, and experimentally contrasted, stochastic pedestrian load model derived by the authors implementing a multi-disciplinary state-of-the-art research, and on a large set of sophisticated finite element analyses.There is a significant gap in the literature available for bridge designers. Some current codes do not indicate how the performance for serviceability limit-states should be assessed, in particular for lateral direction. Others define methods that are not based on the latest research in this field and that require the use of dynamic structural analysis software. A very sophisticated load model, such as that described above, and recently proposed by the authors, may not be accessible for most of the design offices, due to time and software constraints. However, an accurate assessment of the serviceability limit state of vibrations during the design stages is paramount. This paper aims to provide designers with an additional simple tool for both preliminary and detailed design for the most typical structural configurations.First, the paper presents the methodology, followed by an evaluation of the impact of its simplifications on the response appraisal. Second, the paper evaluates the validity of the methodology by comparing responses predicted by the method to those experimentally measured at real footbridges. Finally, the paper includes a parametric analysis defining the maximum accelerations expected from pedestrian streams crossing multiple footbridges. This parametric analysis considers different variables such as section type, structural material, span length and traffic-flow characteristics, and shows the sensitivity of the serviceability response to traffic-flow characteristics and span length in particular.
This article presents a numerical assessment of pedestrian-induced vibrations for a wide range of girder footbridges before and after the installation of tuned-mass dampers (TMD). Realistic pedestrian loads are defined using a stochastic model that represents the key characteristics of pedestrians and their intra- and inter-subject variability with the aim of ensuring an accurate estimation of the dynamic response. A comprehensive set of numerical analyses have been performed considering different cross sections, structural materials, span lengths (up to 100 m), and pedestrian flows. The optimal TMD characteristics, number and location, required to reduce the accelerations, down to a level that fulfils serviceability criteria, are identified. Design recommendations for girder footbridges implementing damping devices at the design stage are also included.
One of the most critical components of the US transportation system is railroads, accommodating transportation for 48% of the nation’s total modal tonnage. Despite such vital importance, more than half of the railroad bridges, an essential component of railroad infrastructure in maintaining the flow of the network, were built before 1920; as a result, bridges comprise one of the most fragile components of the railroad system. Current structural inspection practice does not ensure sufficient information for both short- and long-term condition assessment while keeping the operation cost low enough for mandatory annual inspection. In this paper, we document the development process of an autonomous, affordable system for monitoring railroad bridges using the wireless smart sensor (WSS) so that a complete end-to-end monitoring solution can provide relevant information directly from the bridges to the end-users. The system’s main contribution is to capture the train-crossing event efficiently and eliminate the need for a human-in-the-loop for remote data retrieval and post-processing. In the proposed system, an adaptive strategy combining an event-based and schedule-based framework is implemented. The wireless system addresses the challenges of remote data retrieval by integrating 4G-LTE functionality into the sensor network and completes the data pipeline with a cloud-based data management and visualization solution. This system is realized on hardware, software, and framework levels. To demonstrate the efficacy of this system, a full-scale monitoring campaign is reported. By overcoming the challenges of monitoring railroad bridges wirelessly and autonomously, this system is expected to be an essential tool for bridge engineers and decision-makers.
An amendment to this paper has been published and can be accessed via the original article.
Bridge health monitoring (BHM) technology has been widely accepted as a powerful tool to assess structural performance and has moved from research to practice. Driven by the enormous demand of ensuring bridge safety, the application of BHM technology is particularly active in China and has become an emerging industry in the civil engineering community. It is a common belief among civil engineers that the development and implementation of industry standards will be of paramount importance in guiding the healthy development of BHM and increasing the transfer of professional knowledge and techniques to practical applications. This paper presents a comprehensive overview of the standardization construction and development trend for BHM in China. The achievements, characteristics, and challenges of China’s bridge construction are first introduced. Then, the existing problems of BHM and the necessity of constructing the standardization system for the BHM industry are discussed. Following that, these standards published for guiding BHM system design, construction, management, and maintenance, especially sensor selection, sensor placement, sensor installation, data transmission, data storage, data processing, and early warning, are outlined. Finally, work requiring further efforts in the near future is drawn.
Quality of concrete for pile can be checked using Cross-hole Sonic Logging (CSL) Test. A processing method wide-band CSL data is presented herein. First Time Arrival (FTA) is an important consideration. In pile capacity analysis or CSL analysis, it is assumed that pile cross section is uniform with uniform value of elastic modulus of concrete but in real practice both are non-uniform. The procedure identifies the location accuracy and further characterizes the features of the defect. FTA is used to find out the location of the distress in the pile. This method identifies the exact location of any void or defect inside the rebar cage of a drilled shaft. This method provides a significant improvement to current techniques used in quality control during construction of bridges. In this present paper, the analysis has been carried out based on uniform and non-uniform values of pile cross section and E value of concrete. Cross hole sonic and pile load test using O-Cell were carried out on same pile at 7 and 28 days of concreting. Same pipes were used for base grout after cross hole sonic test. These results were used to analyze O-cell test results based on a case study and presented in this paper. The distribution of skin frication and skin friction force has also been presented herein with both uniform and non-uniform cross section and E values of concrete. Based on the field test results and analysis a simplified methodology, has been proposed in this paper, for development of Equivalent Top Down Loading with consideration of elastic shortening of pile and surrounding soil for both cases i.e., uniform and non-uniform E values and pile cross sections.
The box-girder superstructure of coastal bridges is vulnerable to wave-induced damage in the case of small clearances. The analytical method for estimating the wave forces on the box-girder superstructure of coastal bridges is proposed based on the potential flow theory in this paper. The two-dimension problem of the box-girder superstructure under the wave action is defined with some necessary simplifications first. Then, the analytical solutions are solved by the eigenfunction matching method, and the wave force on the submerged box-girder superstructure is calculated using the Bernoulli principle. After validating the accuracy of the proposed method by previous calculations and the experimental test, the influences of the girder type and structural configuration on the wave forces of submerged box-girder are conducted using the proposed analytical method. The results show that the girder type has a significant effect on the wave forces of the submerged superstructure, and the influence of various structural parameters should be considered comprehensively in the structural safety design under wave actions. The results of the present study can provide a useful reference for the estimation of wave forces and the structural design of the box-girder superstructure of coastal bridges.
Structural analysis and construction control of staged construction process is a major subject for modern long-span bridges. This paper introduces the concept of stress-free-state variable of structural elements and deduces the mechanical equilibrium equations and geometric shape governing equations for staged construction structures utilizing the minimum potential energy theorem. As the core of stress-free-state theory, the two aforementioned equations demonstrate following principles, 1) when the stress-free-state variable of a structural element is set, the internal force and deformation of the element are unique at the completion state of the structure regardless of its construction process; 2) the stress-free length of a cable is independent of its external loads, change in stress-free length of the cable corresponds to a unique variation of the cable force when load is constant; and 3) the internal force of a structural element can be independent from its geometric shape within the completion state of a staged construction structure through an active manipulation of stress-free-state variables of the element. Stress-free-state theory establishes the stage-to-stage and stage-to-completion relationships for staged construction bridges, provides a direct and efficient method for theoretical calculations and a flexible and convenient approach for the control of staged construction, and makes parallel construction and auto-filtering of thermal and temporary loading effect possible.
With the increasing demand for land transportation in coastal areas, the number of sea-crossing bridges has increased rapidly. In the construction of sea-crossing bridges, the elevated pile cap foundation is one of the most commonly used foundation types. This paper summarizes four main aspects of the research on the hydrodynamic effects on elevated pile cap foundations through timing analysis and keyword co-occurrence analysis. The relevant studies are reviewed from the aspects of waves, currents, and their interactions; the hydrodynamic load on the elevated pile cap foundation; fluid-structure interactions; and the structural responses of bridges that are supported by elevated pile cap foundations. Finally, the following future prospects for hydrodynamic studies of elevated pile cap foundations for the sea-crossing bridge have been discussed, which include wave-current interaction mechanism, wave-current load, fully coupled fluid-structure interactions, and structural dynamic response under hydrodynamic combined with the other hazards.
Coastal highway bridges are usually supported by pile foundations that are submerged in water and embedded into saturated soils. Such sites have been reported susceptible to scour hazard and probably liquefied under strong earthquakes. Existing studies on seismic response analyses of such bridges often ignore the influence of water-induced hydrodynamic effect. This study assesses quantitative impacts of the hydrodynamic effect on seismic responses of coastal highway bridges under scour and liquefaction potential in a probabilistic manner. A coupled soil-bridge finite element model that represents typical coastal highway bridges is excited by two sets of ground motion records that represent two seismic design levels (i.e., low versus high in terms of 10%-50 years versus 2%-50 years). Modeled by the added mass method, the hydrodynamic effect on responses of bridge key components including the bearing deformation, column curvature, and pile curvature is systematically quantified for scenarios with and without liquefaction across different scour depths. It is found that the influence of hydrodynamic effect becomes more noticeable with the increase of scour depths. Nevertheless, it has minor influence on the bearing deformation and column curvature (i.e., percentage changes of the responses are within 5%), regardless of the liquefiable or nonliquefiable scenario under the low or high seismic design level. As for the pile curvature, the hydrodynamic effect under the low seismic design level may remarkably increase the response by as large as 15%–20%, whereas under the high seismic design level, it has ignorable influence on the pile curvature.
To widen bridges, a usual method is to cast joint connections between new and old bridge decks without traffic interruption. The traffic vibrations have negative influence on the quality of joint connections. Shortening the construction time can alleviate the impact on the traffics, a fast-hardening retarding high-early-strength concrete (FRHC) for the connections is in need. In this study, low-alkalinity sulphoaluminate cement (LASC) concrete was modified to gain these characteristics. Based on FRHC concrete, four slab specimens including a monolithic concrete slab and three joint FRHC slabs were cast to investigate their flexural behaviors. With proper splicing details in joint connections, the joint FRHC specimens behaved approximately similar to the monolithic specimen. Combing the laboratory tests and engineering practice, the newly developed FRHC mixture succeeded in fast-hardening, retarding and high-early strength and the joint connections filled with FRHC have a good flexural performance.
A growing number of bridge structures spanning over waterways are most susceptible to ship-pier collisions that may result in serious consequences such as ship sinking, failure and collapse of the bridge, even personal casualty, etc. To quantify the impact force and load, ship-pier impact tests and reliable numerical predictions should be carried out. This paper shows experimental tests and numerical simulation results of ship impact on bridge piers. To assess the performance of circular reinforced concrete piers against ship collisions and guide the design of bridge piers against impact, reduced-scale circular reinforced concrete (RC) piers were built and tested, and finite element (FE) simulations based on edge pier of junction pier of Wu-Song River Bridge were also conducted. To evaluate the reasonability of the damage process and failure mode of the pier due to ship impact more accurately, the bridge piers are modeled with nonlinear materials to simulate the bridge pier characteristics instead of rigid and elastic materials. Based on numerical results, the design impact loads prescribed by code current specifications such as Eurocode and AASHTO Bridge Design Specifications were evaluated and compared. To predict impact force, the fiber section model was employed to attain ultimate bearing capacity of the pier.
The serviceability and safety level of bridges often deteriorates due to the environmental or operational conditions. A stochastic deterioration model is of essential importance for describing the time-variation of bridge performance (e.g., stiffness and strength), and for use in the estimate of bridge reliability under a probabilistic framework. In this context, the Gamma process has been widely used to model the resistance deterioration of aging bridges, yet suffers from the deficiency that the statistical characteristics of the process (namely mean value, variance and autocorrelation) are not mutually independent. This paper presents a new stochastic model for bridge resistance deterioration. As a modified version of the Gamma process-based one, the proposed model includes a new parameter that can release the dependence of the process autocorrelation and variance on the mean value. The impact of the new deterioration model on the time-dependent reliability of aging bridges is studied.
Traffic accidents involving vehicles transporting hazardous materials (HazMat) can cause serious fire hazards, threatening the safety of bridge infrastructure as well as nearby traffic. For critical bridges such as long-span cable-stayed and suspension bridges, fire hazards can not only cause severe structural damage, but also serious traffic disruption, congestion, and accidents. Unlike short-span bridges, long-span cable-supported bridges often experience considerable wind effects at the height of the bridge deck which can significantly influence fire hazards. As the critical components of cable-supported bridges, the failure of cables or hangers due to fire may trigger progressive failure of the bridge structure. Existing studies on fire simulation of long-span bridges, however, are very limited. Typical fire hazard scenarios from vehicles transporting hazardous material (HazMat) are simulated with fire dynamics simulation (FDS) software on a suspension bridge with a focus on the threats to hangers. To more realistically consider the potential fire hazards to bridge hangers of long-span bridges, appropriate fuel size, transverse offset distance, and wind effects are considered. The study of a baseline scenario is carried out first and followed by parametric studies to investigate the effects of wind speeds, longitudinal offsets, hazardous material types and spill sizes on the fire simulation results.
Base grout improves the load bearing capacity of a pile and reduces the base settlement. There is no established method presently for the determination of quantity of the base grout. This paper presents a model for the determination of quantity of the base grout and verification of actual quantity executed during the base grouting operation in the field. The depth of the sediment deposit at the bottom of the pile has been observed to vary in the range of 0.3 m to 0.8 m or more for the case study presented. This depth of sediment deposit also depends on the pile drilling method adopted. In this model, it is assumed that maximum depth of deposition of 0.3 m may be allowed for concrete work. Based on the available literature and a Guideline on Pile Construction of Hong Kong, bottom cleaning is required if the depth of deposition is more than 0.3 m. Grout quantity also depends on the diameter and, length of a pile, and number of piles, as well as length and diameter of Tube A Manchette (TAM) Tubes and depth of deposition of sediment which takes place before concrete work execution. A case study has been adopted. Theoretical model has been developed based on the quantity executed during base grouting in field. Actual quantity of base grout shall be more than theoretical quantity due to the possible caving in of the side walls of the piles, increased diameter in the bottom of pile tip with the formation of a bulb at times. Therefore, a variable coefficient ‘K’ has been presumed equating theoretical quantity to actual quantity including loss of base grout quantity. ‘K’ value has been determined at 95% reliability and found to be 1.22. The proposed model for quantity estimation of base grout has also been validated with other field data and the results have been found to be satisfactory.
Stay cables are typically exposed to the environment and traffic loading leading to degradations due to corrosion and cyclic loading after years’ in service. A non-destructive method to detect the defects of cables as early as possible is needed and important for adequate large-span bridge maintenance. Use of a status-driven acoustic emission (AE) monitoring Convolutional neural network (CNN) method is investigated by combing wavelet analysis and transfer deep learning. CNN is used to construct the relationship between AE signals’ scalograms and cable status. The trained CNN is suitable to identify the in-situ monitored signals and evaluate the current status of cables during the operation of a bridge. As a pilot study, the binary AE signals classification CNN is implemented to identify noise & fracture AE signals in static tests of a stay-cable. Accuracy of the method is investigated. In addition, the trained model is examined using AE signals which are not used in the machine learning to check possible improvements of the accuracy. Expectations in recognition of results and status-driven monitoring potentials are addressed in the paper.
Aerodynamic flutter instability has been a major concern for long-span flexible bridges, such as suspension and cable-stayed bridges, subjected to wind actions that result in the so-called self-excited forces. Though turbulence effects on bridge flutter have been studied in the last few decades, its true effects remain a debate due to the limitation of previous wind tunnel facilities, such as using turbulence scales that are too small in these experiments. In this paper, the characterizations of self-excited forces are presented in both the frequency-domain and in the time-domain. Then, the flutter analysis is conducted under both smooth flow and turbulent flow in order to investigate the effect of wind turbulence on the flutter instability. The effect of wind turbulence is directly modeled in the time-domain in order to avoid the complicated random parametric excitation analysis of the equation of motion used in previous studies. By comparing the results of different turbulence intensities with that of the smooth flow, it is found that the turbulence has a stabilizing effect on bridge flutter. The turbulence can change the vibration patterns and weaken the spatial vibration correlation to some extent. As a result, the critical flutter velocity can be increased by 5% to 10% over that under smooth flow.
Deformation monitoring of the girders and towers during strong winds or typhoons is vitally important for serviceability and safety assessment of in-service long-span bridges. Although some field measurements were carried out, our understanding on the features of the bridge deformation during high-speed winds is still limited; therefore, more monitoring-based studies are still required. In this study, the displacements of a long-span cable-stayed bridge during three typhoons are recorded by the Global Positioning System (GPS) in its Structural Health Monitoring (SHM) system. The monitored displacements are decomposed into static and dynamic components using the autoregressive moving average model. The outliers and the low-frequency colored noise in the dynamic components are then analyzed and eliminated. On that basis, the relationship between the static displacements and environmental factors, in terms of wind and temperature, is investigated. Afterwards, the variation of dynamic displacements of the bridge is analyzed with respect to the surrounding environments. Results show that the structural temperature is the major reason that changes the static deformation of the bridge. The dynamic deformation of the girder is mainly controlled by the in-situ wind speed. Nevertheless, the influence of structural temperature on dynamic deformation is mildly. Conclusions are aimed to provide a reference for wind resistant design and assessment of similar long-span bridges.
Prestressed concrete (PC) box bridge girders on the pier top is prone to generate thermal cracks due to large inner-outer temperature difference at hydration age. This paper presents an approach for investigating behaviour of PC box bridge girders at early age of curing. First, based on measured data from a typical PC box bridge girder, an inverse analysis method for adiabatic temperature rise function of concrete hydration heat is proposed using genetic algorithm and thermal analysis. Then, a thermo-hydro-mechanical coupling model is established, using the computer program ANSYS incorporating time-dependent wind speed and ambient temperature, to analyse thermal mechanical behaviour of PC box bridge girders considering pipe-cooling system. Subsequently, parametric studies are carried out to evaluate influence of cooling time, cooling water flow rate, cooling water temperature and cooling period on temperature and stress of PC box bridge girders during curing. Results from analysis show that the principal tensile stress generated in the vicinity of pipe increases more rapidly during cooling, while the temperature and principal tensile stress can be significantly reduced when cooling is terminated. Increasing cooling time, cooling water flow rate or decreasing cooling water temperature can reduce the highest temperature. However, unreasonable value of these cooling parameters will cause PC box bridge girders cracking due to excessive principal tensile stress around pipe. Both one-stage and two-stage cooling are effective measures to minimize the adverse effects of hydration heat in PC box bridge girders.