Long-span Girder Bridges Research Articles

A simplified ANN-based evaluation method for creep sensitive girder bridge identification at preliminary design stage

Excessive deflection which exceeded expectations has been identified as one of the main problems contributing to long-term performance degradation of long-span girder bridges. Although the 3D refined finite element model of the full bridge can improve the prediction accuracy of long-term creep deformation, there is still a lack of efficient creep-sensitive structural judgment methods in the preliminary design stage. This study was thus intended to develop a new evaluation method and model to identify the possibility of excessive deflection will occur by utilizing simple structural design parameters, which contributed to new understandings of the creep deformation of bridge structural level. A finite element model database established by 20 long-span prestressed concrete girder bridges with actual project backgrounds was used for providing training, testing, and validation sample datasets for the artificial neural networks (ANN). The Back Propagation (BP) model was chosen for creating mappings among variables and results and solving complex problems with a fairly accurate prediction even without sufficient information. The indicator of deflection-span ratio difference between creep models was proposed as the key analysis factor. A case study was conducted to validate the effectiveness of the ANN model. The mean absolute error (MAE) between the results of the ANN model and FE analysis was 6.25%, which indicated a high consistency. The analysis of bridge design parameters using the ANN model revealed that it had a high risk of excessive deformation, which was consistent with the conclusion of the actual situation. Multiparameter sensitivity analysis results from the model also suggest that the side-span ratio, the main span, and the deflection caused by the pavement are the most three significant impacts compared to different input variables in this model. Based on the results, it can be concluded that the performance of the ANN-based technique can predict possible excessive creep problems in advance.

Pounding performance between a seismic-isolated long-span girder bridge and its approaches

For girder bridges located in regions with a high seismic hazard level, seismic isolation bearings are usually implemented to suppress the seismic inertial force transmitted from the superstructure to substructures, protecting the pier columns and foundations. However, whether potential pounding might happen for these seismic-isolated girder bridges between adjacent units are scarcely considered, especially for those with long spans where the wave passage effect is of great significance. This paper develops a finite element model for a typical hybrid truss-girder bridge, based on which the influence of seismic isolation bearings and wave passage effect on pounding is carefully investigated considering both near-fault and far-field motions. The results show that for this type of long-span girder bridges, pounding may happen even the adjacent bridge units are designed with similar vibration periods, especially when near-fault motions and wave passage effect are considered. Under non-uniform excitations with different apparent wave velocities, the employment of isolation bearings can reduce the relative displacement at expansion joints and thus improve the performance against pounding; however, the occurrence of pounding and damage of expansion joints cannot be fully avoided. Further, motions with lower apparent velocities generally correspond to more devastating responses, which should be particularly considered during engineering practice.

Deflection-based multilevel structural condition assessment of long-span prestressed concrete girder bridges using a connected pipe system

Several long-span prestressed concrete (PSC) girder bridges have exhibited excessive deflection over time that can affect their normal use and safety. Thus, monitoring the time-dependent deflections of PSC girder bridges is required to ensure a timely warning of deficient bridge conditions. This study measured the deflections of a PSC box-girder bridge using a connected pipe system to provide health monitoring and condition assessment. A deflection-based, multilevel assessment approach was proposed wherein the individual deflection components (traffic-induced, temperature-induced, and long term) were used to evaluate the bridge state. The assessments of each component were fused using the Dempster–Shafer evidence theory to achieve an integrated outcome. Results show that a connected pipe system can accurately monitor the real-time deflection of long-span girder bridges. The proposed multilevel assessment approach makes full use of the structural condition information from the acquired deflection data, demonstrating the effectiveness and practicality of the fusion algorithm.

Analysis of long-span bridge fluctuations for finding its optimal safe operation

The paper studies the intense oscillations sustained by the Volgogradsky Bridge on May 20, 2010. The studies were carried out based on physical and mathematical experiments. The introduction indicates the causes of emergence of the intense aeroelastic oscillations. Description is given of the physical nature of one of the types of these oscillations, i.e. stall flutter. Catastrophes are considered that had been caused by the flutter. Methodological fundamentals of the experiment are named and modern software capabilities of computer-aided fluid and gas dynamics are listed. The results of the experiment are supplied, including visualization of the Karman vortex street and determination of the Strouhal number. The recalculation of the experimental data to natural conditions is substantiated. A description is given of calculation of the bridge’s aeroelastic oscillations. The main results of the aerodynamic calculation are supplied: the Strouhal numbers and critical velocities. The results of mathematical and physical experiments tallied well. A tally of the calculation and estimated full-scale results is pointed out. Results of this calculation (bridge oscillation amplitudes) are supplied. The conclusions point to the prospective viability of the mathematical experiment method. The proposed methods can minimize risks for the construction of long-span girder bridges, ensuring the precise estimation of their subsequent safe operation.

Friction characteristics of post-tensioning tendons in full-scale structures

Friction characteristics between the strands and the duct have a significant effect on the distribution of prestressing force and can be incorporated by the curvature and wobble friction coefficients in the design of prestressed concrete structures. However, the recommended friction coefficients show a wide range of variation, which can cause the inaccurate estimation of prestressing force. In this study, the friction coefficients were evaluated based on the strains of tendons measured by Smart Strands using optical fiber sensors in a full-scale test specimen and two actual long-span girder bridges. The test specimen was investigated to determine how the duct shapes and other factors affect the friction coefficients. Simultaneous equations method and least squares method for obtaining friction coefficients were employed and the results were compared in the actual bridges. This study shows one of the applications of the developed Smart Strand system that can overcome several drawbacks of the existing measurement system.

Deflection analysis of long-span girder bridges under vehicle bridge interaction using cellular automaton based traffic microsimulation.

Deflection is a crucial indicator to reflect the operating condition of girder bridges, which can be used to evaluate structure condition and identify abnormal loading. The paper analyzed the deflection characteristics of long-span girder bridges based on the coupling vibration between stochastic traffic stream and bridge. First, the latest research advances were integrated to form an analytical model of the coupling vibration between stochastic traffic stream and bridge. Then, a generalized Pareto distribution model based on peaks-over-threshold theory was established to predict the extreme girder deflection. Next, a cellular automaton based microsimulation method was proposed to model the traffic loads on bridges, which utilized the intelligent driver car-following model and acceptance distance based lane-changing model. Finally, these theories were applied in the case study of a long-span prestressed concrete continuous girder bridge. It is discovered from the study that, under the coupling vibration between stochastic traffic stream and bridge, the predicted extreme deflection of the case bridge is far lower than the specified design value. Hence, a grading warning model was established and employed to the analysis of deflection monitoring data of the bridge, showing a wide potential prospect of application.

Effect of holes and segmentation on the structural behavior of a prestressed concrete girder

The developed Holed, Incrementally Prestressed Concrete (H-IPC) girder represents various advanced design concepts. First, the entire self-weight can be considerably reduced by introducing holes in the web, with minimal effect on the moment of inertia. Also, prestress can be efficiently introduced in an incremental way by distributing the anchorages at the holes. The girder can maintain the same sections throughout the span by preventing concentration of the anchorages. This can further reduce self-weight, fabricating time, and cost. Furthermore, the spliced girder system makes it possible to extend the span to more than the conventional length since the segments can be transported and prefabricated on site. The objective of this study is to verify the various advantages of the original design concepts by examining the structural behavior obtained from the loading tests of the 50 m-long full-scale girder specimens. The effect of the holes in the web on overall behavior is one of the main concerns in the test. The test results of a segmented specimen are also compared with those of a non-segmented specimen to investigate the effect of segmentation. It is demonstrated that the segmental H-IPC girder can be effectively used for the design and construction of long-span girder bridges.

Methods of Calculating Wind Loads on Long-Span Girder Bridges with Tall Piers and Comparison of Values

Calculating wind resistance is an important process in the design of highway bridges. The current codes of many countries include different rules and formulas regarding the calculation of wind resistance. In this paper, the transverse-direction wind loads on long-span girder bridges with tall piers were calculated using six codes from different countries under various terrain, pier height, and girder length conditions. The pier-bottom shear force and moment results of transverse wind loads calculated using these six codes were compared with those obtained using the buffeting frequency domain method. Results showed that, in Class B terrain, wind load results predicated on China’s 2004 general codes for the design of highway bridges and culverts, China’s 2004 wind-resistant design specifications for highway bridges, Japan’s 2007 wind-resistant design manual for highway bridges, and Part 2 of Britain’s 2006 steel, concrete, and composite bridge specifications for loads resembled each other closely. Some difference was found to exist among Classes A, C, and D terrain. The 2007 AASHTO LRFD bridge design specifications and China’s 2001 load codes for the design of building structures showed significant differences from the other four codes on all kinds of terrain. The applicability of the wind load rules in the AASHTO LRFD bridge design specifications to long-span girder bridges with tall piers merits further discussion. China’s wind load calculations of load code for the design of building structures mainly depended on the empirical parameters of architectural structures with large dimensions, and had limited applicability to bridge structures. For long-span girder bridges with tall piers, such as bridges with span length-to-width or -depth ratios exceeding 30, or pier height-to-transverse-width ratio exceeding 10.7, the wind load calculated using these codes was generally underestimated due to the neglect of the effects of aeroelastic forces, which must be taken into account in the design of these kinds of bridges.

HPS 100W

Abstract HPS 100W is specified in ASTM A 709 (Standard Specification for Carbon and High-Strength Low-Alloy Structural Steel Shapes, Plates, and Bars and Quenched-and-Tempered Alloy Structural Steel Plates for Bridges) and is being added to AASHTO M270. Initial applications were planned to be those in which an owner bridge engineer would approve the use of HPS 100W. This steel would be most useful for depth control over piers in long-span girder bridges or controlling the size of high-stressed elements in long-span steel truss bridges. This datasheet provides information on composition and tensile properties. It also includes information on forming and joining. Filing Code: SA-555. Producer or source: International Steel Group Inc.

Aerodynamic Stability of Long-Span Suspension Bridges under Erection

The aerodynamic instability of a long-span suspension bridge with a shallow streamlined box girder is a serious engineering concern, particularly during the early deck erection stage. Its characteristics are significantly influenced by the sequence of deck erection. Using the Hoga Kusten Bridge in Sweden as an example, this paper presents an analytical and experimental discussion regarding the evolution of flutter characteristics for a long-span suspension bridge, and a comparison of different erection sequences and analytical prediction of more stable configurations. The general feature of the flutter limit evolution with the erection program of midspan to pylons, which was previously evidenced by wind tunnel tests, has been successfully reproduced analytically, and the advantages of keeping nonsymmetric deck configurations were confirmed. The pylon to midspan program has never been employed for long-span girder bridges, but it was found to be, at least, aerodynamically favorable.