Classifying concrete defects during a bridge inspection remains a subjective and laborious task. The risk of getting a false result is approximately 50% if different inspectors assess the same ...concrete defect. This is significant in the light of an over-aging bridge stock, decreasing infrastructure maintenance budgets and catastrophic bridge collapses as happened in 2018 in Genoa, Italy. To support an automated inspection and an objective bridge defect classification, we propose a three-staged concrete defect classifier that can multi-classify potentially unhealthy bridge areas into their specific defect type in conformity with existing bridge inspection guidelines. Three separate deep neural pre-trained networks are fine-tuned based on a multi-source dataset consisting of self-collected image samples plus several Departments of Transportation inspection databases. We show that this approach can reliably classify multiple defect types with an average mean score of 85%. Our presented multi-classifier is a contribution towards developing a mostly or fully inspection schema for a more cost-effective and more objective bridge inspection.
•The presented method can automatically multi-classify concrete bridge defects on image patches in accordance with existing inspection guidelines.•The cross-learning strategy of using a pre-trained network and refine this to domain-specific knowledge can be successfully applied for concrete bridge surface defects.•The multi-classifier can adapt to local variations and consider possible (and impossible) defect combinations.
•Load tests on bridges can be diagnostic load tests or proof load tests.•Diagnostic load testing is used to update an analytical model with field data.•Proof load testing is used to directly ...demonstrate that a bridge fulfils the requirements.•Proof load testing is currently mostly described in codes for buildings.•Stop criteria for brittle failure modes need to be defined.
Load testing of bridges is a practice that is as old as their construction. In the past, load testing gave the traveling public a feeling that a newly opened bridge is safe. Nowadays, the bridge stock in many countries is aging, and load testing is used for the assessment of existing bridges. This paper aims at giving an overview of the current state-of-the-art with regard to load testing of concrete bridges. The work is based on an extensive literature review, dealing with diagnostic and proof load testing, and looking at the current areas of research. Additional available information about load testing of steel, timber, and masonry bridges, buildings, and collapse testing is briefly cited. For the implementation of load testing to the aging bridge stock on a large scale, efficiency in procedures is required. The areas requiring future research are identified, based on the available body of knowledge.
Many very large bridges with high piers and long spans are under rapid construction in mountainous regions especially in Western China. However, the current seismic design methods in China are based ...on a code which only applies to bridges with span up to 150 m. To evaluate the risk of the inapplicable design method and the influence of spatially variable ground motions (SVGM) on the seismic response of very large bridges, a high-pier, long-span, continuous RC frame bridge is numerically studied. This study considers whether multiple support excitation can be simplified into specific uniform excitation cases while guaranteeing the conservative seismic demands for this bridge. Non-stationary SVGM on both bedrock and the surface of multiple soil layers are simulated including wave passage effects, coherency effects and site amplification effects. The nonlinear dynamic finite element model of the bridge is analysed for two groups of earthquake motions, namely group 1 - bedrock and group 2 - ground surface excitations. Each group contains three different excitations, i.e. i) multiple support excitation ii) the largest and iii) the smallest accelerations from the SVGM. The relative displacements, internal force responses and ultimate damage modes are obtained and compared. For this bridge the uniform ground motion input with the largest accelerations provides conservative seismic demands for most structural components when the site amplification effect is not considered (group 1). However, for the ground surface motions, where site amplification needs to be taken into account (group 2), in several cases the uniform ground motion with the largest accelerations results in lower response than that predicted when considering SVGM. The present results indicate that only when the bridges are located on ideal simple topography where site effects have little influence, the uniform excitation with the largest accelerations taken from the SVGM may be an alternative input for seismic analysis. However, for bridges on complex terrain, where site effects can significantly amplify the ground motions at the bedrock, SVGM need to be applied as input for the seismic analysis. As spatial variability of input motion is not a mandatory requirement in the Chinese bridges design code, these results suggest that the existing design code for very large bridges should be modified accordingly.
•A simulation method for SVGM with consideration of local site effects is developed.•Both geometric and material nonlinear are considered in seismic analysis of the bridge.•Uniform excitation is an alternative for seismic design of bridges on simple terrain.•Multi-support excitation is necessary for large bridges on irregular terrain.•The seismic design methods and codes for large bridges should be modified by applied SVGM.
The effects of gap-width on the aerodynamic characteristics of a twin-deck bridge in a nominally smooth flow were investigated in this paper, with a specific goal of studying the vortex shedding ...mechanisms of the bridge deck. Simultaneous pressure measurements were carried out on five deck configurations, using a rigid sectional model of a twin-deck cable-stayed bridge with different gap-widths. Stream-wise mean and fluctuating pressure distributions around the bridge deck were studied to investigate the potential excitation mechanisms caused by the gap-widths at various angles of wind incidence. The effects of gap-width on the static force and moment coefficients were also analyzed. The results demonstrated that the gap-width has the potential to significantly affect the pressure distribution and hence the corresponding aerodynamic performance of the bridge deck. In addition, the analyzed results showed that the twin-deck bridge in this study is susceptible to vortex shedding and its Strouhal number gradually increases with increasing gap-width due to the change of flow regime around the bridge deck. This knowledge is essential for the complete aerodynamic evaluation of a twin-deck bridge.
► Pressure models were used to study the wind load effects on a twin-deck bridge. ► Parameters studied include gap width and wind angle. ► Vortex shedding and turbulence buffeting remain as dominant excitation mechanisms. ► Twin-deck is an aerodynamically efficient configuration for long-span bridges.
•Temperature-driven structural identification methodology is proposed.•Model optimization is performed using measured vs. model thermal signatures.•Numerical simulations characterize unknown boundary ...and continuity parameters.•Thermal-induced damage of a steel girder integral abutment bridge is identified.
The Tennessee Department of Transportation (TDOT) visually detected recurring structural damage with one of their steel girder bridges in eastern Tennessee, USA. These issues prompted an investigation into the source of the damage. TDOT approached the structural research team in Tennessee Tech University’s Civil and Environmental Engineering Department with what presented as damage related to thermal effects acting on the Anderson County Route 61 Bridge. In the presented study, temperature-driven structural identification is employed on the Route 61 Bridge to assess the structural damage and determine potential causes of such deterioration. An element-level, finite element model is created to provide insight regarding the bridge behavior. The bridge is field instrumented with monitoring equipment to quantify the bridge responses to daily thermal loads. The quantitative results are then used to calibrate the model and represent the bridge in its current condition. The root cause of the damage is identified through multiple numerical simulations and recommendations are provided for the long-term rehabilitation and preservation of the structure. Overall, the study contributes knowledge regarding the thermal behavior of steel girder integral abutment bridges including expansion/contraction movement, built-up strains/stresses, and potential damage produced by thermal loads. This study also provides illustration of an effective temperature-driven structural identification approach for evaluation of these types of structures.
•Lateral static and impact behavior of propped cantilever columns was investigated.•The effectiveness of CFRP seismic-retrofit under impact has been experimentally investigated.•A comparison of the ...lateral impact and static behavior of RC columns is reported.•A semi-empirical equation is proposed to estimate the dynamic response given the static behavior.•CFRP seismic-retrofit is effective in reducing damage under vehicular lateral impact loads.
The effectiveness of Carbon Fiber Reinforced Polymer (CFRP) seismic-retrofit of circular Reinforced Concrete (RC) bridge piers under vehicular lateral impact loading is addressed in the present work performing experimental tests. Sixteen 1/3 scale RC bridge piers with circular cross-sections characterized by three different configurations of longitudinal and transverse reinforcements were tested with and without CFRP seismic-retrofit. In the first case, tested columns represent common shear-deficient RC bridge piers designed with obsolete design practice or for non-seismic areas. In the second case, CFRP wrapping is applied according to common seismic-retrofit practices to increase the shear capacity and ductility of columns.
Experimental tests were carried out under static and lateral impact loading with propped cantilever conditions reproducing a typical short-span viaduct bridge pier configuration. In the static tests, the lateral load was applied monotonically through a hydraulic jacket under equivalent impact conditions. In impact tests, the lateral impact load was applied through a colliding truck equipped with a rigid hammer at the typical vehicular impact location adopting two different impact velocities (3 and 4.5m/s). A critical investigation of the transient dynamic characteristics, damage evolution, and post-impact damage is conducted by comparing the results obtained with and without CFRP seismic-retrofit, and under static and dynamic loading conditions. It is shown that CFRP seismic-retrofitting of circular RC bridge pier can also be effective in reducing the vulnerability under lateral impact loading. The CFRP-retrofit approach adopted in this study meets the requirement of multi-hazard prevention improving the robustness of the bridge. Finally, a semi-empirical equation for predicting the maximum displacement under impact loading is derived based on experimental results. The proposed equation adopts the results of a static test as a proxy for assessing the dynamic behavior allowing for the design of the required shear and flexural load-carrying capacity.
Bridge resilience is a newly proposed bridge design criterion that involves robustness, redundancy and reparability targeting on the rapidity of functionality restoration after suffering extreme ...actions and long-term durability deterioration. It stipulates a lower probability of reaching the ultimate limit state or strength limit state, which have been only partly involved in bridge design codes around the world. In AASHTO LRFD Bridge Design Specifications and Eurocodes, there are some design principles related to bridge resilience. Yet, it is also necessary to give more requirements for structural ductility and collapse resistance when the actual load exceeds the load combination in the code. This paper focuses on the resilience-based principles for bridge design, and exposes some problematic bridge structural systems and details, such as bridges most likely to overturning, steel bridges with fracture critical members, arch bridges with suspended desk, Morandi cable-stayed bridges, poor details for seismic vulnerability, etc. Whereas overturning is one of the worst anti-resilience scenarios, the resilience design against bridge overturning is highlighted through a detailed discussion including the calculation methods of anti-overturning factor, overturning stability of curved bridges, reasonable disposition of supports, and anti-overturning countermeasures.
•First shake table test of steel girder bridge system constructed with ABC techniques.•Six different ABC connections were included in the bridge model.•Seismic performance assessment of ABC system ...under bidirectional shaking.•Results and discussion focused on both global and local behavior.
This paper presents the discussion and results from the first shake table test of a steel girder bridge system constructed using accelerated bridge construction (ABC) techniques. The bridge model was tested at the multi-shake table testing facility at the University of Nevada, Reno. The objective of this study was to evaluate the seismic performance of a bridge system incorporating six types of ABC connections under strong bidirectional earthquake shaking. The test model was a 0.35-scale, two-span steel plate-girder bridge with seat type abutments. The model was subjected to eight earthquake motions adopted from the 1994 Northridge-Sylmar ground motion applied with increasing amplitudes. The paper presents the global and local response of the bridge model with focus on ABC connections. Moreover, the paper provides a first hand demonstration of a full ABC bridge system seismic performance, which was found to be satisfactory and adequate to adopt the utilized ABC connections for future projects.
► The present study proposed a new strategy to use the substructure method. ► All the substructures are condensed into super-elements except the concerned part. ► The method is applied to model the ...long span hybrid cable-stayed bridge. ► The model is used for the vehicle-induced dynamic analysis of the joint. ► Results show that transition between steel girders and concrete beams is smooth.
Hybrid cable-stayed bridges consist of steel and concrete bridge segments, of which steel–concrete joints are of great importance and raise strong research interest. Due to the limitation of the traditional methods, i.e., the member finite element (FE) method and Mixed Dimensional Coupling (MDC) method, the present study proposes a substructure method to model long span bridges. The current application of the substructure method is to extract some specific parts of the whole structure to refine and analyze them. Different from the routine substructure approach, here the entire structure is modeled in detail and divided into many substructures. All the substructures are then condensed into super-elements except the concerned part. The application of the method is then illustrated through numerical studies of the vehicle–bridge coupling vibration of the Jingyue Yangtze River Bridge with a main span of 816
m. The entire bridge is first divided into many substructures with a reasonable length. Among them, the concerned substructure with 23.8
m in length including the steel–concrete joint is modeled in detail but not formed into super-element, while all the other components are modeled in detail and formed into super-elements using the component mode synthesis (CMS) method. All the components including both the super-elements and non-super-elements are then assembled into a complete and fine full bridge model. Finally, the model is used for the vehicle-induced dynamic analysis under deterministic traffic flows. The results show that the joint works well, and the transition between the steel girders and concrete beams is very smooth.
The fatigue problem of orthotropic steel bridge decks of urban rail transit steel bridges has gradually become one of the hot research topics. And it is also a key problem that restricts the further ...development of rail transit steel bridges. In this paper, the orthotropic steel bridge deck structure of a long-span urban rail transit cable-stayed bridge is studied. Based on the segmental finite element model and full-scale model, the fatigue details of the joint weld between an orthotropic steel bridge deck and U-rib were studied theoretically and experimentally. The theoretical model of the segment is analyzed to obtain the hot spot stress characteristics. On this basis, the full-scale model fatigue test and the fatigue performance evaluation are completed based on the S-N curve. The results show that the fatigue performance of the bridge deck and U-rib joints of the orthotropic steel bridge deck structure model meets the design requirements and has a certain safety reserve. The joint fatigue details of the bridge deck, the U-rib joint weld, and the diaphragm plate are the sensitive areas that are most likely to occur fatigue failure first and need to be paid attention to in the later bridge maintenance and inspection.
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