Bridge Safety Research Articles

Progressive bridge collapse analysis under both scour and floods by coupling simulation in structural and hydraulic fields. Part Ⅰ: Numerical solver

Hydraulic bridge failures have become the greatest threat to the structural safety of bridges. Combined numerical simulations are rare due to the high computational cost of structural nonlinear finite element analysis (NLFEA) and computing fluid dynamics (CFD). Structural analysis and design for extreme hydrological hazards are challenging due to complicated hydrodynamics-soil-structure interactions. This paper proposes a numerical solver to simulate hydraulic bridge failures through coupling simulations. The solver applies hydrodynamic load and updates scour boundary in a structural model by utilizing a scatter linear interpolation method based on the Delaunay triangulation algorithm in each loop solution. Then, a simplified sediment stress model considering external forces in the vertical plane and a complex model with an arbitrary slope in three-dimensional coordinates are introduced into the basic incipient motion model of sediment, resulting in a more realistic stress state of sediment. Finally, the numerical solver is adapted to provide an accessible method to investigate the influence of such a modified model on the scour process and structure response. Meanwhile, the validation of this numerical solver is conducted in a companion paper based on the comparison between the numerical result of the hybrid model and the field data.

Deflection calculation method for UHPC composite beams considering interface slip and shear deformation

The mid-span deflection is an essential index for evaluating the safety of bridge safety and service life. In contrast, the existing deflection calculation methods cannot accurately predict the deflection of ultra-high performance concrete (UHPC) composite beams. The flexural behavior of steel-glass fiber reinforced polymer (GFRP) strips-UHPC composite beam under a positive bending moment was investigated and compared with that of the steel-UHPC composite beam. The flexural behavior of UHPC composite beam was analyzed and discussed in terms of failure mode and mechanism, mid-span load-deflection response, changing laws of cross-section strain and interface slip. The deflection calculation method for the UHPC composite beams considering interface slip and shear deformation was derived. Moreover, a calculation method of ultimate bearing capacity for the UHPC composite beams is developed. The results showed that all the UHPC composite beams failed because of yielding of steel beam, and the influence of GFRP strips on the flexural behavior of steel-UHPC composite beam was very small. The theoretically calculated results of the mid-span deflection and ultimate bearing capacity for the UHPC composite beams were in good agreement with the experimental results and have higher accuracy.

Shear strengthening of precast prestressed I‐girders using carbon fiber reinforced polymers and in‐fill concrete blocks

AbstractDue to the rapid increase in traffic volumes, existing infrastructure demands proper assessment and in some cases rehabilitation is needed. Prestressed concrete (PC) I‐shaped girders are widely used in prefabricated girder bridges. With sequel generations of shear design provisions their shear capacity might need to be increased in the framework of assessing safety of aging bridges. Earlier attempts in shear strengthening this specific type of girder with fiber reinforced polymers (FRP) has shown early debonding along the concrete surface at the web‐flange corner so that the increase in shear strength was very limited. This study presents the results of full scale PC I‐girders strengthened with CFRP through epoxy bonded concrete in‐fill blocks that locally transforms the I‐section to a rectangular section at the position of CFRP strips. This transformation eliminated the early debonding of CFRP shear reinforcement and for the studied configurations a 30%–40% increase in shear capacity was obtained with respect to the unstrengthened control specimen, without and with additional CFRP spike anchors, respectively. In comparison, similar configurations without in‐fill blocks reached 5% and 12% increase in shear capacity, respectively. As such, the use of in‐fill blocks appeared more effective than local anchorage of the CFRP at the web‐flange corner. Analytical verification of the experimental results confirmed that existing formulations lack ability to predict the shear capacity of strengthened I‐girders, and further work is needed in this respect.

Blast response of cantilever retaining wall: Modes of wall movement

For the past few decades, there has been an increase in awareness regarding the safety of highway bridges from blast loads. Since abutments/Retaining walls (RWs) are portions of bridges, investigating abutments/RW or RW behaviour under blast loads is important. As there have not been any studies investigating the dynamic response of retaining walls due to blast loading, an experimental study was conducted to examine the influence of blast loads on the dynamic behaviour of reinforced concrete retaining wall (RCRW) with sand as a backfill material. A shock tube was used to generate blast loads on the soil-RW model. The influence of the relative density, backfill saturation, blast load intensity, and traffic load equivalent surcharge on the blast behaviour of RCRW with sand backfill was studied. The results showed that the modes of wall movement were affected by the backfill relative density, blast load intensities, and degree of saturation. Under the same load conditions, an increase in the wall movement was noticed in loose backfill, and a translation response mode was evident in this condition. A relationship between wall relative movements and mobilized earth pressure coefficients was determined. The mobilized passive resistance of the RW backfill induced by blast load was used to determine the force–displacement relationship. Acceleration time histories for RW/backfill were found for all conditions. The findings of this research will help to properly evaluate and design bridges’ abutment and to develop resilient transportation infrastructure systems.

Checking the Accuracy of Selected Formulae for both Clear Water and Live Bed Bridge Scour

Due to severe scouring, many bridges failed worldwide. Therefore, the safety of the existing bridge (after contrition) mainly depends on the continuous monitoring of local scour at the substructure. However, the bridge's safety before construction mainly depends on the consideration of local scour estimation at the bridge substructure. Estimating the local scour at the bridge piers is usually done using the available formulae. Almost all the formulae used in estimating local scour at the bridge piers were derived from laboratory data. It is essential to test the performance of proposed local scour formulae using field data. In this study, the performance of selected bridge scours estimation formulae was validated and statistically tested using field data for existing bridges in Canada, Iraq (Kufa, Najaf), Pakistan, Bangladesh, and India. The validated formulae were HEC-18, Forehlich, and Johnson. The validation was conducted by comparing the predicted local scour depths obtained from applying the above selected formulae with the local scour depths obtained from the field data. The comparison between them was presented using a scattergram. However, statistical tests were used to present the accuracy of the local scour predictions. The tests were conducted using three statistical indices, namely, Theil’s coefficient (U), Mean Absolute Error (MAE), and Root Mean Square Error (RMSE). Among the tested formulae, the Jonson formula gave satisfactory performance since the values of U, MAE, and RMSE were found to be 0.112, 1.351, and 1.650, respectively.

Early Warning for Abnormal Cable Forces of Cable-Stayed Bridges Considering Structural Temperature Changes

The deterioration or damage of stay cables can threaten the safety of bridges. It is difficult to judge whether a stay cable is deteriorated only by the variation in cable force because cable force also varies with temperature. Therefore, an early warning method for abnormal cable forces of cable-stayed bridges considering structural temperature changes is proposed in this paper. In the proposed method, a baseline model is established to characterize the normal relationship between the healthy cable force and structural temperatures, so the abnormal cable force can be detected by inspecting the residual between the identified cable force to be detected and the cable force predicted by the baseline model. First, the frequency–temperature relationship (FTR) model obeyed by a healthy cable is established by analyzing the mechanism of cable force change caused by structural temperature changes in bridge components from the perspective of deformation coordination. Then, the prediction error is inspected by constructing a mean value control chart of the modeling error generated from the baseline FTR model. An early warning will be triggered when the prediction error exceeds the control limits. Finally, the proposed method is applied to an actual cable-stayed bridge to verify its effectiveness. The results show that the modeling and prediction capabilities of the established FTR model are satisfactory and that the abnormal changes in cable forces can be detected by the proposed early warning method with satisfactory accuracy.

Genuine Influence Line and Influence Surface Identification from Measured Bridge Response Considering Vehicular Wheel Loads

A bridge influence line (BIL) and a bridge influence surface (BIS) reflect the relationship between the bridge responses and the loads on the bridge and have been commonly used in techniques such as bridge damage detection, bridge safety evaluation, bridge model correction, bridge weigh-in-motion, and so on. Conventionally, a BIL can be extracted from the bridge response under a moving vehicle with known axle loads, while a BIS can then be obtained by lateral interpolation from BILs obtained for key transverse positions. However, in the traditional BIL-extracting methods, the transverse distance between the coaxial wheels was not considered; that is, the coaxial left and right wheel loads are simply treated as one concentrated load (usually referred to as the axle load). Therefore, the obtained BIL is the bridge response under two loads rather than one. Hence, errors may be introduced to the obtained BILs and propagated to the interpolated BIS. Moreover, the potentially significant effect of the unbalance of coaxial wheel loads on BIL identification is ignored. In this research, a new method for determining a genuine BIL and BIS is proposed. The wheel load rather than the axle load was taken into calculation in this method, where the effect of the transverse distance between the coaxial wheels and the unbalance of the coaxial wheel loads was naturally taken into consideration. Laboratory experiments and numerical simulations were performed to verify the effectiveness of the proposed method. Furthermore, a comprehensive parametric analysis was conducted to investigate the effects of some important parameters such as vehicle velocity, lateral deviation of the center of gravity of vehicles, axle count, and road surface condition on the identification performance. The results show that the BIL and BIS can be identified with satisfactory accuracy.

Dynamic performance of triple-column bridge pier under barge collision

Growing incidents of pier cracks or even failure of the whole structure induced by ship-pier collision have attracted social attention to the safety of water-crossing bridges. In this study, finite element (FE) models are successfully established to gain insight into the collision between a modified barge and a three-column bridge pier in the non-navigable zone. Firstly, numerical models of the bridge pier and barge are satisfactorily verified against experimental results, through which the dynamic performance of the bridge under typical collision scenarios is investigated with respect to the kinetic energy, internal energy, and impact force. A new performance index, i.e., internal energy power slope (IEPS), calculated from the second derivative of the structural internal energy, is then proposed to prescribe the damage states of the impacted column. The usefulness and applicability of the IEPS are further explored through structural reliability analysis and a parametric study. Moreover, the efficacy of two protective jackets made in alloy honeycomb (AH) and aluminum foam (AF) for enhancing the structural anti-impact capacity is investigated by comparing the associated values of IEPS. It is observed that the proposed IEPS has a strong correlation with the structural damage state, and thus can be favourably used as a new performance metric for analyzing barge-pier collisions. The results also evidence that adopting UHPC (ultra-high performance concrete), densifying stirrup spacing, and adding protective jackets are effective measures to reduce the IEPS and hence improve the structural anti-impact capacity.

Multi-point detection method of dynamic deflection of super long-span bridge based on chain laser model

Real-time monitoring of bridge deflection is of great significance for ensuring bridge safety. Aiming at the problems of poor real-time performance and low precision of deflection measurement of continuous multi-span and super long-span bridges, this paper proposes a multi-point chain laser detection model and method for dynamic deflection of super long-span bridges. Firstly, we construct a multi-point deflection parameter detection model based on chain laser reference and image processing, and give the system error adjustment scheme of the model; Then, the hardware framework of the system is designed, and the real-time deflection parameter data acquisition, processing and solution methods are analyzed. In addition, the related factors affecting the measurement accuracy of the system are analyzed, and the system error is analyzed and corrected. Finally, the principle prototype is built, and the intelligent monitoring platform based on cloud data processing is designed. The system parameter calibration experiment is carried out and verified on the displacement platform built outdoors. The results show that the measurement accuracy of the system can reach 1 mm under the condition of considering the pitch angle of the monitoring equipment, which can realize the real-time, dynamic and high-precision monitoring of the deflection of the long-span bridge beam.

3D Displacement Measurement of Railway Bridge According to Cyclic Loads of Different Types of Railcars with Sequential Photogrammetry

In the early days of railroads in Korea, railway bridges were constructed as steel plate-girder structures, which are vulnerable to vibration and torsion. Many of these bridges have since been replaced with concrete-slab structures, which have high stability. Nevertheless, steel railway bridges still remain all over the country, and a lot of manpower and cost is being invested in the maintenance and repair of such bridges. Moreover, there have not been experimental analyses aiming to measure the cyclic loads that occur when a train enters. To ensure bridge safety, it is necessary to periodically inspect deformations. To this end, the present study proposed a sequential photogrammetric technique for measuring the deformation of a steel railway bridge for three types of railcars. Sequential stereo images of the bridge with multiple feature points are obtained using sequential photographing cameras, to determine the ground coordinates of each point as a function of time based on the space intersection from the relative orientation with coplanarity and the scale adjustment. All of these processes are performed through automated techniques using only the cameras and the targets. With this setup, the 3-dimensional dynamic motions of the bridge due to the cyclic loading of trains could be measured. In addition, the displacements by the proposed method were compared to those obtained with the 3D Laser tracker. The horizontal displacements errors did not exceed 0.5 mm and the vertical error was within 2.3 mm in root mean square error (RMSE) at camera-to-object distances of about 9 m.

Reliability-assisted determination of partial factors for the design of main cables considering secondary stress effect

The main cables of suspension bridges typically serve as the primary load-carrying components. Determination of reasonable main cable sizes is crucial for the bridge safety and functionality. The limit state design method with the combination of partial factors has been widely used in multiple countries as a substitute for the factor of safety design method. Determination of reasonable partial factors that can properly satisfy a target reliability index has received much attention. However, most of the existing research neglects the secondary stress effect, which can be of a significant magnitude, for the main cable. To address the gap, this paper proposes a reliability-assisted framework for the determination of the partial factors considering both first and secondary stresses for the main cable design. Three suspension bridges with main span lengths ranging from 850 m to 2300 m are used as the engineering background. Results show that the recommended design factors can be used in the preliminary design stage to facilitate a reasonable cable design that yields the target reliability index, therefore validating the feasibility of the proposed framework.

Development of a BIM-based bridge maintenance system (BMS) for managing defect data

Bridges might experience many defects during use, such as pavement cracks and reinforcement corrosion, which easily produce an accumulated impact that threatens bridge safety. Thus, there is a need for the regular inspection and maintenance of bridges. This paper presents a bridge maintenance system (BMS) based on building information modelling (BIM), which is utilized in bridge defect information management using a digitalization method. A bridge defect three-dimensional BIM (BIM3D) library is established and combined with a bridge model to visualize bridge defect conditions. Based on bridge inspection data, bridge defect information is digitally classified and encoded according to the international framework for dictionaries (IFD) standard and used to establish a database. An evaluation of bridge technical conditions is performed, and the results are graded and displayed in different colours, reflecting the visualization function of BIM technology. Maintenance suggestions are provided according to the range of bridge technical condition scores, reflecting the informatization function of BIM technology. With the Xinjiang Cocodala Bridge in China as a case study, a bridge BIM3D model and inspection data are imported into the BMS to utilize the functions of ‘visualization of bridge defect conditions’, ‘evaluation of bridge technical conditions’ and ‘recommendations of bridge maintenance methods'.

Improving running safety of railway bridges during earthquakes by equipping vehicle with lateral fuse stopper

Ensuring the safety of the railway vehicles over bridges shaken by earthquakes is a practical issue in the seismic design of railway bridges. To improve the vehicle’s running safety on railway bridges during earthquakes, the stopper (or bump-stop) between the bogie and the car-body of the vehicle was modified as a fuse-type element, i.e., it was designed to break under large impact due to earthquake occurrence. The efficacy of the fuse stopper was illustrated by a full-scale vehicle-track shake table test. The fuse stopper element was introduced to the vehicle-bridge interaction model, whose accuracy was also demonstrated by comparison with the test results. The fuse stopper was designed to remain intact under service level earthquakes (SLE) to avoid frequent replacement or repair, while it should fuse to improve vehicle safety on a group of bridges under design basis earthquakes (DBE). The bridge group includes 24 simply-supported bridges with pier heights ranging from 6m to 60m, covering the most simply-supported bridges in the China railway network. A total of 10 ground motion records were used in the analysis to account for the uncertainty of ground motions. Through vehicle-bridge incremental dynamic analysis (IDA) simulation, the optimal fusion strength of 188 kN and the extended gap of 0.04 m were proposed for the fuse stopper at DBE intensity, in which the bridge group can achieve derailment-free. The design procedure of the fuse stopper may provide a cost-effective way to improve the vehicle’s running safety on a group of bridges during earthquakes.

Effects of friction pendulum bearing wear on seismic performance of long-span continuous girder bridge

To clear the wear effect of friction pendulum bearings (FPBs) on the seismic performance of multiple long-span continuous girder bridges, the rapid sliding performance test of the FPBs was carried out to get the wear degree of the modified poly tetra fluoroethylene (PTFE) wear plates. Taking a 6×110 m long-span continuous girder bridge as the engineering background, the seismic response of the bridge with different wear degrees of the FPBs was analyzed. The results show that the modified PTFE wear plate of the FPBs was severely worn in the rapid sliding performance test, and the friction coefficient was first increased to 0.09 and then decreased to 0.016. When the maximum displacement was reached, the bearing collided with the limitation block. Moreover, the internal forces of the critical pier were increased, and the bottom of the piers entered plasticity due to the wear of the FPBs. Due to the change in the seismic performance of the bridge, it is suggested that the rapid sliding performance of FPBs should be tested to ensure the structure safety of the long-span continuous girder bridge in rare earthquakes.

Automatic Inspection of Bridge Bolts Using Unmanned Aerial Vision and Adaptive Scale Unification-Based Deep Learning

Bolted connections are essential components that require regular inspection to ensure bridge safety. Existing methods mainly rely on traditional artificial vision-based inspection, which is inefficient due to the many bolts of bridges. A vision-based method using deep learning and unmanned aerial vision is proposed to automatically analyze the bridge bolts’ condition. The contributions are as follows: (1) Addressing the problems that motion blur often exists in videos captured by unmanned ariel systems (UASs) with high moving speed, and that bolt damage is hard to accurately detect due to the few pixels a single bolt occupies, a bolt image preprocessing method, including image deblurring based on inverse filtering with camera motion model and adaptive scaling based on super-resolution, is proposed to eliminate the motion blur of bolt images and segment them into subimages with uniform bolt size. (2) Addressing the problem that directly applying an object detection network for both bolt detection and classification may lead to the wrong identification of bolt damage, a two-stage detection method is proposed to divide bolt inspection into bolt object segmentation and damage classification. The proposed method was verified on an in-service bridge to detect bolts and classify them into normal bolts, corrosion bolts, and loose bolts. The results show that the proposed method can effectively eliminate the inherent defects of data acquired by UAS and accurately classify the bolt defects, verifying the practicability and high precision of the proposed method.

A regional model for classifying, managing, evaluating, and monitoring the seismic safety of bridge structures: the MLAZIO project

The MLAZIO Project, developed at the Department of Engineering of Roma Tre University, intends to create a methodology for the construction of an efficient Bridge Management System (BMS) for Lazio Region. Inspired by the recently developed Italian guidelines, the project aims at classifying, managing, evaluating and monitoring the safety of bridges in the regional territory, by following a multi-level approach. Satellite monitoring, BIM, GIS and methods for risk assessment, both static and seismic, are some of the innovative techniques included in the methodology, validated through the application to several case studies. This paper describes the structure of MLAZIO project and its state of progress, from the creation of a relational database (used for cataloging structures and developing optimized GIS and BIM environments) to the development of an expeditious procedure for the quantitative evaluation of the seismic risk. The attention is focused on the seismic risk assessment procedure that, based on probabilistic approaches, provides a first overview of the state of the bridge network, starting from a restricted number of input data. It allows to identify the bridges in most critical conditions that will need more in-depth vulnerability analyses. Preliminary results coming from the application of this procedure to a case study are shown and critically discussed.

Flood Protection Partial Analysis of the Olt Bridge in Sântimbru

In many places in Transylvania, we can observe the ruins and remains of buildings, from which many interesting conclusions can be drawn. As part of a more comprehensive research, in which the flood protection safety of old Transylvanian bridges is examined, in this case the rebuilt road bridge in Santimbru was investigated. Modelling and hydraulic calculations performed on the basis of in situ measurements can reveal the old hydraulic construction requirements used in the design of the bridge, and then the data were also considered in the light of today's standards.

Study on Compatibility and Safety of Super-slope Bridge and Rack System of Rack Railway

Study on Compatibility and Safety of Super-slope Bridge and Rack System of Rack Railway

Superior survival outcome of blinatumomab compared with conventional chemotherapy for adult patients with relapsed or refractory B-cell precursor acute lymphoblastic leukemia: a propensity score-matched cohort analysis.

Blinatumomab showed a higher complete remission (CR) rate and a safe bridging to allogeneic hematopoietic cell transplantation (allo-HCT) in adults with relapsed or refractory B-cell precursor acute lymphoblastic leukemia (R/R BCP-ALL). We tried to analyze the outcome of blinatumomab compared with the real-world historical data. We expected superior outcome of blinatumomab compared with historical conventional chemotherapy. We conducted a retrospective study using real-world data in the Catholic Hematology Hospital. Total 197 consecutive cases of R/R BCP-ALL were treated with conventional chemotherapy (n = 113) or blinatumomab, which was available since late 2016 (n = 84). Patients who achieved CR underwent allo-HCT if donor was available. We conducted a propensity score-matched cohort analysis using 5 criteria of age, CR duration, cytogenetics, previous allo-HCT, and salvage lines between historical group and blinatumomab. Each cohort consisted of 52 patients. In blinatumomab group, CR rate was higher (80.8% versus 53.8%, p = 0.006) and more patients proceeded to allo-HCT (80.8% versus 46.2%, p < 0.001). Among the CR patients with available minimal residual disease (MRD) results, 68.6% in blinatumomab group and 40.0% in conventional chemotherapy group were MRD-negative. Regimen-related mortality during the chemotherapy cycles was significantly higher in the conventional chemotherapy group (40.4% versus 1.9%, p < 0.001). Estimated 3-year overall survival (OS) was 33.2% (median, 26.3 months) after blinatumomab, and 15.4% (median, 8.2 months) after conventional chemotherapy (p < 0.001). Estimated 3-year non-relapse mortality were 30.3% and 51.9% (p = 0.004), respectively. In multivariate analysis, CR duration < 12 months showed more relapses and poor OS, and conventional chemotherapy showed higher non-relapse mortality and poor OS. Matched cohort analysis showed superior outcomes of blinatumomab compared with conventional chemotherapy. However, large numbers of relapses and non-relapse mortalities continue to occur even after blinatumomab followed by allo-HCT. Novel therapeutic strategies are still needed for R/R BCP-ALL.

Analysis of Influence Factors on Wind Resistance Stability of Long-span Bridges

Long-span bridges (LSB) are common in the developed coastal areas, which is an important node of economic operation. However, LSB often has the problem, such as bridge stability with the condition of wind resistance, which is important for the bridge safety, service life and other important indicators. Therefore, it is meaningful to study and analyze the stability of bridges under wind resistance. This article will from the bridge structure deformation under calm wind load and wind resistance of bridge vibration under these two factors, the research status about the stability of LSB is expounded, and analysis of the specific image factor is applied to bridge structure, how in the end put forward using tuned mass damper (TMD) is used to reduce the influence of bridge vibration on the stability. The conclusion of this paper can be a reference for the design of the wind resistance and implementation of wind resistance measures of LSB.