Complex Bridge Research Articles

Structural full-field responses reconstruction by the SVD and pseudo-inverse operator-estimated force with two-degree multi-scale models

The measured structural response currently is in a deficient state for structural health monitoring (SHM). To obtain complete structural responses, a good solution is first estimating the external input, then applying the estimated input to the finite element model (FEM) of a structure, and calculating the complete structural responses by the FEM. The key content is estimating the unknown structural input from the limited measurements, which indicates that an under-determined differential equation should be solved. In the previous literature, the dynamic equilibrium equation is usually converted into the state space and solved as a discrete-time linear system. In this paper, the external input time history is estimated from the difference of the state space vectors at different moments combining with the singular value decomposition. The complete structural responses are then obtained by applying the estimated load vectors to the FEM. Adopting a single degree of freedom system, the robustness of the approach is theoretically deduced. The modeling error can merely change the estimated external force, while the reconstructed structural responses retain accuracy. To improve computational efficiency, the two-degree multi-scale FEM is proposed. The first model is a simplified model of the original structure, only adopting interior elements such as the beam elements. This model is to quickly estimate the external inputs and to reconstruct the displacement responses. The second model is a FEM adopting both interior and superior elements such as the beam and shell elements, and it can reconstruct both the displacement and detailed strain–stress responses. Finally, numerical simulations of a complex bridge FEM are carried out demonstrating that the proposed approach has high accuracy under different loading conditions, including the vehicle load, impact load, and random load. An in-field experiment has also validated the proposed framework applies to the quasi-static plus dynamic loading condition.

Human-machine system as a control shell in the implementation of mooring operations

Mooring is a complex and responsible process for a boat master, so modern trends determine the need to create automated and automatic systems for mooring vessels to minimize the human factor. The study researched the vessel ergatic control complex and the towing group with the use of mathematical apparatus in the implementation of mooring operations. The human-machine or “ergatic” system is the control shell under the active influences of the bridge complexes and is an auxiliary tool for the watchman on the navigation bridge. This is the essence – a human, as a controlling and observing link, is an integral part of the human-machine complex. Automation, even in systems with artificial intelligence, will not soon replace the flexibility of the human brain, despite possible and sometimes very serious human mistakes. Taking into account the fact that the automated mooring system applies all kinds of monitoring sensors to prevent docking impact, the control and responsibility for the mooring process still lie with the navigator operator.

Coupled CFD–FEM Simulation Methodology for Fire-Exposed Bridges

Evaluating the fire performance of bridges is necessary for damage mitigation as more fire-related accidents occurred on bridge structures. Current solutions adopting temperature curves can result in significant inaccuracy by neglecting the inhomogeneous characteristic of the fire-induced thermal environment. This paper proposed a numerical methodology for analyzing the coupled thermomechanical response of various bridges exposed to fires. The computational fluid dynamics (CFD) approach was implemented to reproduce the fire condition more realistically by modeling the combustion process and fire-driven flow. Then, an interface was adopted to extract the thermal boundary from the fire model. At last, the thermomechanical finite-element method (FEM) was coupled with the CFD model for determining the fire-induced response of the global bridge, thermally and structurally. By incorporating the multiscale FEM, this methodology can be extended to various large-scale bridges subjected to localized fires. The proposed approach was validated through a real fire experimental study on a steel column. To demonstrate the application of this strategy, a complex case study was carried out. A long-span cable-stayed bridge was investigated considering its girder segment was exposed to an under-deck tanker fire. Numerical results showed that the proposed method was able to capture the surrounding temperature field with strong thermal gradients and can predict not only the localized thermomechanical response of exposed segments but also the global structural performance evolution for large-scale complex bridges. The under-deck fire can introduce a significant impact on the entire cable-stayed bridge. Thereby, the multiscale FEM modeling strategy is required for the long-span bridges exposed to localized fires.

Spin‐State‐Switching Rearrangements of Bis(dioxolene)‐Bridged CrCo Complexes: A DFT Study

AbstractDensity functional theory calculations (UTPSSh/6‐311++G(d,p)) of electronic structure, energy characteristics and magnetic properties of a series of heterometallic CrCo complexes comprising redox‐active bis(dioxolene) bridging ligands (3,3,3’,3’‐tetramethyl‐5,6,5’,6’‐tetrahydroxy‐1,1’‐spiro‐bis(indan) and 2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene) and ancillary tetradentate nitrogen‐containing bases (tris(2‐pyridylmethyl)amine and N,N′‐dialkyl‐2,11‐diaza[3.3]‐(2,6)pyridinophane derivatives) were performed. The compounds prone to manifest spin‐state switching rearrangements involving cobalt centre have been revealed. Analysis of the results obtained and their comparison with those found previously open wide prospects for the purposeful search for a broad variety of new magnetically bistable heterometallic dinuclear paramagnetic species with a prospect of useful application in the design of smart dynamic materials.

Effects of pile-cap elevation on scour and turbulence around a complex bridge pier

ABSTRACT In this study, the local scour and the associated flow hydrodynamics around a complex pier with rectangular pile-cap at three different pile-cap elevations are investigated. The pile-cap elevations were selected with respect to the initial sand bed, such that the pile-cap was unexposed (case I), partially exposed (case II), and fully exposed (case III) to the flow. The experiments were performed in a recirculating flume under clear-water scour conditions, and the instantaneous flow velocity was obtained at different vertical planes using the particle image velocimetry (PIV) technique. The partially exposed pile-cap case showed the maximum obtained scour-depth (MSD). The reason behind the MSD occurrence in case II was enunciated through the analysis of turbulent flow field which showed that as the pile-cap got exposed to the flow, it dominantly affected the generation of vortices from the pile-cap corners responsible for the higher scour depth. The effect of the pile-cap on the flow field was prominently seen in case III through the mean velocities, vorticity, Reynolds shear stresses and turbulent kinetic energy contours, but since the pile-cap was away from the bed, the pile-cap corners did not show any direct effect on the scour.

Effects of Different Geometric Parameters of Complex Bridge Piers on Maximum Scour Depth: Experimental Study

This research experimentally investigated local scour depth around complex bridge piers in a clear-water condition. The term “complex pier” is used to define a bridge pier composed of three different sections: a column, cap of pile, and group of pile. Eighty-two experiments were carried out using six types of complex pier models to understand the impacts of the pile cap longitudinal extension from column, arrangement (or configuration) of pile group, extension occurring upstream of pile group, and thickness of pile cap. Through the experiments, a mathematical relationship between the upper limit of the pile cap undercut elevation and pile cap thickness was presented. In fact, the proposed formulation aimed to assess the undercutting elevation of pile cap. It was found that the variation of pier-foundation geometry significantly affected the maximum scour depth. The result showed that increasing pile cap thickness thereby decreased the pile cap undercutting elevation. When the piles number in line with flow increased, the maximum scour depth decreased.

Association between the developing sphenoid and adult morphology: A study using sagittal sections of the skull base from human embryos and fetuses.

The developing sphenoid is regarded as a median cartilage mass (basisphenoid [BS]) with three cartilaginous processes (orbitosphenoid [OS], ala temporalis [AT], and alar process [AP]). The relationships of this initial configuration with the adult morphology are difficult to determine because of extensive membranous ossification along the cartilaginous elements. The purpose of this study was therefore to evaluate the anatomical connections between each element of the fetal sphenoid and adult morphology. Sagittal sections from 25 embryos and fetuses of gestational age 6-34weeks and crown-rump length 12-295mm were therefore examined and compared with horizontal and frontal sections from the other 25late-term fetuses (217-340mm). The OS was identified as a set of three mutually attached cartilage bars in early fetuses. At all stages, the OS-post was continuous with the anterolateral part of the BS. The BS included the notochord and Rathke's pouch remnant in embryos and early fetuses. The dorsum sellae was absent from embryos, but it protruded from the BS in early fetuses before a fossa for the hypophysis became evident. Although not higher than the hypophysis at midterm, the dorsum sellae elongated superiorly after gestational age 25weeks. In early fetuses, the AP was located on the side immediately anterior to the otic capsule. The AT developed on the side immediately posterior to the extraocular rectus muscles. At late term, the greater wing was formed by membranous bones from the AT and AP. The AT and AP formed a complex bridge between the BS and the greater wing. A small cartilage, future medial pterygoid process (PTmed) was located inferior to the AT in early fetuses. At midterm, one endochondral bone and multiple membranous bones formed the PTmed. The lateral pterygoid process (PTlat) was formed by a single membranous bone plate. Therefore, we connected fetal elements and the adult morphology as follows. (1) Derivative of the OS makes not only the lesser wing but also the anterior margin of the body of the sphenoid. (2) Derivatives of the BS are the body of the sphenoid including the sella turcica and the dorsum sellae. (3) Most of the greater wing including the foramen rotundum and the foramen oval originate from the AT and AP and multiple membranous bones. (4) The PTmed originate from endochondral bones and multiple membranous bones, while the PTlat derive from a single membranous bone.

Cable-Stayed Bridge Loads Caused by Traffic Congestion on the Deck Measured with Bridge Monitoring System

Structural safety of a bridge depends, among other things, on the number of vehicles passing on its deck, their weights and distribution of loads to their axes. A large number of vehicles can accumulate on the bridge in a controlled state, i.e., during an acceptance test including load testing, and during traffic congestion on the bridge, which is a fortuitous event addressed in this paper. The paper deals with the analysis of load intensity on one bridge carriageway when it is fully and randomly filled during traffic congestion. The influence functions of the forces in the cables are used to determine the effects of loads exerted by the vehicles moving at very low speed. Effects of such loads are studied considering an exemplary cable-stayed bridge. Since the measurement basis was limited, the iterative algorithm was used. It consists in shortening the girder sections under analysis to the area appropriate for determining the load in each successive step of iteration. Ineffectiveness of the traditional algorithm, where the determined system of equations is resolved, is an important premise for using such algorithm. The results of numerical analysis show that the load intensity caused by traffic congestion is relatively high. It has been demonstrated that the matrix method may be successfully used to determine the real load of bridges on the basis of selected parameters measured in the bridge structure, also for complex scheme bridges, including the cable-stayed bridges.

Dynamic enzymatic synthesis of γ-cyclodextrin using a photoremovable hydrazone template

Dynamic enzymatic synthesis of γ-cyclodextrin using a photoremovable hydrazone template

Cable-Stayed Bridge Loads Caused by Traffic Congestion on the Deck Measured with Bridge Monitoring System

Structural safety of a bridge depends, among other things, on the number of vehicles passing on its deck, their weights and distribution of loads to their axes. A large number of vehicles can accumulate on the bridge in a controlled state, i.e., during an acceptance test including load testing, and during traffic congestion on the bridge, which is a fortuitous event addressed in this paper. The paper deals with the analysis of load intensity on one bridge carriageway when it is fully and randomly filled during traffic congestion. The influence functions of the forces in the cables are used to determine the effects of loads exerted by the vehicles moving at very low speed. Effects of such loads are studied considering an exemplary cable-stayed bridge. Since the measurement basis was limited, the iterative algorithm was used. It consists in shortening the girder sections under analysis to the area appropriate for determining the load in each successive step of iteration. Ineffectiveness of the traditional algorithm, where the determined system of equations is resolved, is an important premise for using such algorithm. The results of numerical analysis show that the load intensity caused by traffic congestion is relatively high. It has been demonstrated that the matrix method may be successfully used to determine the real load of bridges on the basis of selected parameters measured in the bridge structure, also for complex scheme bridges, including the cable-stayed bridges.

Experimental study on local scour at complex bridge piers under steady currents with bed-form migration

Local scour at pile-supported bridge foundations in coastal and offshore areas are an essential factor to engineering design and evaluation. This study experimentally investigates live-bed local scour at complex bridge piers under the influence of bed-form migration. The results show that the variation of the mean scour depth as a function of flow intensity ratio U/Uc (Uc= threshold velocity for incipient motion) depends on the pile-cap elevation and is significantly different to single piers. Instantaneous bed level, cross-correlation analysis, and power spectra show that bed-forms approaching an exposed pile group may be damped, leading to mean bed level fluctuation that are slightly smaller than the bed-form heights. In contrast, when the pile-cap is completely buried by the original bed but can be exposed during scour, approaching bed-forms tend to keep their individual features and cause larger scour fluctuation at pile-cap's leading edge. The enlargement is due to the concurrence between the enhanced (or weakened) scouring capacity and the decreased (or increased) upstream sediment supply. The scour predictor proposed by previous studies is extended to live-bed range and performs better than existing predictors.

State -of -the -Art and Development of Seismic Analysis for Complex Bridges

Due to the complexity of dynamic response characteristics of complex bridges, it is difficult to give uniform regulations to give comprehensive and complete guidance for its seismic analysis. In order to promote the development of seismic analysis of complex bridges, the research status and progress of complex bridge seismic analysis were discussed in detail. Firstly, the characteristics of the commonly used seismic analysis methods for bridges and their applicability to complex bridges were summarized. Secondly, the selection and synthesis methods of far-field and near-field seismic used for bridge seismic analysis were concluded. Meanwhile, the seismic input methods and the most unfavorable input direction of curved bridges were discussed. Then, the anti-seismic analysis model of the main components of bridges were summed up, and the medium-structure interaction (including pile-soil-structure interaction, abutment-soil-structure interaction and water-structure interaction, etc.) were investigated. Finally, on this basis, the unsolved problems and the future development directions in this research field were pointed out. It is concluded that the seismic analysis of complex bridges still has some shortcomings, which needs to be improved and developed.

Pixel-level bridge crack detection using a deep fusion about recurrent residual convolution and context encoder network

To cope with the complex bridge crack detection environment, we developed a flexible crack identification system. Firstly, the acquired images are processed by sliding window technology to construct a bridge crack dataset. Then we propose a trainable context encoder network which uses the recurrent residual convolutional neural network (RRCNN) to improve the encoder structure to better extract low-level features. Additionally, it combines dense atrous convolution block (DAC) and residual multi-kernel pooling block (RMP) which can retain more crack information and features from the crack image, as well as improve the performance of crack segmentation. Finally, our research results are validated in the developed software platform. The experiments show that our method is more stable and accurate than other methods, its accuracy and mean intersection over union (mIoU) have reached 98.62% and 80.93%, respectively. Moreover, it performs well in cracks facing complex conditions, which can be applied to the bridge maintenance projects.

Progressive numerical model validation of a bowstring-arch railway bridge based on a structural health monitoring system

This paper presents a progressive numerical model validation of a bowstring-arch railway bridge based on the analysis of experimental data from different structural response measurements, namely, static deformations under environmental actions, modal vibrations, and transient dynamic responses under traffic loads. This work also addresses an integrated approach that uses structural health monitoring (SHM) measurements in combination with FE modelling to understand the structural behaviour of a long-span complex bridge. A progressively phased in situ SHM system has provided a diverse set of data streams ranging from static and dynamic responses to the measurement of environmental and operational traffic loads. The first phase consists of defining a detailed baseline finite-element (FE) model of the bridge, envisaging the initial condition of the structure immediately after construction, and its validation using modal parameters (natural frequencies and mode shapes) derived from an ambient vibration test. Since overall in-service deflections in general do not exercise the non-linear regime of the bridge response, the second phase focuses on the analysis of static response data and temperature measurements to validate the non-linear behaviour of the structural system, particularly at the bearing devices, under slow actions. The third and final phase addresses the dynamic analysis under traffic actions, which provides greater sensitivity in the detection of non-linear behaviour due to the effects of high-amplitude actions induced by regular train loading profiles. To guarantee the accuracy of the baseline numerical model, particularly under temperature and traffic actions, it was necessary to use contact restrictions in some specific bearing devices. This improvement is in line with the structural changes detected in some bearing devices through visual inspections. As a result, an updated numerical model capable of reproducing the modal, static, and dynamic structural responses was achieved, showing a very good agreement between experimental and numerical data. In future applications, this updated numerical model will be useful for assessing the condition of the bridge under traffic loads, namely to identify damages and support the adoption of life cycle maintenance strategies based on the integration of SHM systems with (stochastic) load and failure models.

Helix-mediated over 1 nm-range chirality recognition by ligand-to-ligand interactions of dinuclear helicates.

Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances (dLn–Ln = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes (2Th and 3Th, respectively) used as mediators. Both 2Th and 3Th form one-dimensional (1D) helical structures upon terminal binding of two chiral guest co-ligands (LR or LS). Long-range chiral self-recognition is achieved in self-assembly of 2Th with LR and LS to preferentially form homochiral assemblies, 2Th-LR·LR and 2Th-LS·LS, whereas there is no direct molecular interaction between the two guest ligands at the terminal edges. X-ray crystal structure analysis and density functional theory studies reveal that long-range chiral recognition is achieved by terminal ligand-to-ligand interactions between the bis-diketonate ligands and chiral guest co-ligands. Conversely, in self-assembly of 3Th with a longer helix length, statistical binding of LR and LS occurs, forming heterochiral (3Th-LR·LS) and homochiral (3Th-LR·LR and 3Th-LS·LS) assemblies in an almost 1 : 1 ratio. When phenyl side arms of the chiral guest co-ligands are replaced by isopropyl groups (L′R and L′S), chiral self-recognition is also achieved in the self-assembly process of 3Th with the longer helix length to generate homochiral (3Th-L′R·L′R and 3Th-L′S·L′S) assemblies as the favored products. Thus, subtle modification of the chiral guests is capable of achieving over 1.4 nm-range chirality recognition.

Solving Cold‐Standby Reliability‐Redundancy Allocation Problems with Particle‐Based Simplified Swarm Optimization

Particle swarm optimization (PSO) and simplified swarm optimization (SSO) are two of the state‐of‐the‐art swarm intelligence technique that is widely utilized for optimization purposes. This paper describes a particle‐based simplified swarm optimization (PSSO) procedure which combines the update mechanisms (UMs) of PSO and SSO to determine optimal system reliability for reliability‐redundancy allocation problems (RRAPs) with cold‐standby strategy while aimed at maximizing the system reliability. With comprehensive experimental test on the typical and famous four benchmarks of RRAP, PSSO is compared with other recently introduced algorithms in four different widely used systems, i.e., a series system, a series‐parallel system, a complex (bridge) system, and an overspeed protection system for a gas turbine. Finally, the results of the experiments demonstrate that the PSSO can effectively solve the system of RRAP with cold‐standby strategy and has good performance in the system reliability obtained although the best system reliability is not obtained in all four benchmarks.

Dynamics of coordination of H3O+ and NH4+ in crown ether cavities.

Crown ethers stand out for their ability to form inclusion complexes with metal cations and positively charged molecular moieties. Hydronium and ammonium interact strongly with crown ethers and potentially modulate their ionophoric activity in protic solvents and physiological environments commonly involved in (bio)technological applications. In this work, Born-Oppenheimer molecular dynamics (BOMD) computations are employed to gain insights into the coordination arrangements of H3O+ and NH4+ in the complexes with the native crown ethers 15-crown-5 (15c5) and 18-crown-6 (18c6). Both cations display dynamic changes in coordination inside the cavities of the crown ethers. On the one hand, hydronium explores different coordination arrangements, through rotation around its C3 axis in the 15c5 complex, and through breathing motions, involving rapid inversions of the O atom along the C3 axis in the 18c6 complex. On the other hand, ammonium undergoes a facile rotation in three dimensional space, leading to frequent changes in the NH bonds involved in the coordination with the crown ether. The reduced host-guest symmetry matching of the 15c5 macrocycle enhances the reorientation dynamics and, in the case of H3O+, it promotes short H-bonding distances yielding events of proton transfer to the crown ether. The infrared vibrational spectra predicted by the BOMD computations within this dynamic framework reproduce with remarkable accuracy the action spectra of the isolated complexes obtained in previous infrared laser spectroscopy experiments. The experimentally observed band positions and broadening can then be rationalized in terms of orientational diffusion of the cations, changes in the coordinating H-bonding pairs sustaining the complex and eventual proton bridge formation.

Model updating of a bridge structure using vibration test data based on GMPSO and BPNN: case study

Model updating issues with high-dimensional and strong-nonlinear optimization processes are still unsolved by most optimization methods. In this study, a hybrid methodology that combines the Gaussian-white-noise-mutation particle swarm optimization (GMPSO), back-propagation neural network (BPNN) and Latin hypercube sampling (LHS) technique is proposed. In this approach, as a meta-heuristic algorithm with the least modification to the standard PSO, GMPSO simultaneously offers convenient programming and good performance in optimization. The BPNN with LHS establishes the meta-models for FEM to accelerate efficiency during the updating process. A case study of the model updating of an actual bridge with no distribution but bounded parameters was carried out using this methodology with two different objective functions. One considers only the frequencies of the main girder and the other considers both the frequencies and vertical displacements of typical points. The updating results show that the methodology is a sound approach to solve an actual complex bridge structure and offers good agreement in the frequencies and mode shapes of the updated model and test data. Based on the shape comparison of the main girder at the finished state with different objective functions, it is emphasized that both the dynamic and static responses should be taken into consideration during the model updating process.

Complexing characteristics between Cu(Ⅱ) ions and dissolved organic matter in combined sewer overflows: Implications for the removal of heavy metals by enhanced coagulation

Enhanced coagulation has been widely used in storm tanks to remove heavy metal ions (HMs) from combined sewer overflows (CSOs), but faces challenges on removing the HMs bound to dissolved organic matter (DOM) with small molecular weight (MW). DOM ubiquitously existing in CSOs generally contains a large distribution range of MW, which can significantly impact the MW distribution of HMs by complexing reaction, thereby adding uncertainties for the removal efficiency of coagulation. Therefore, realizing the potential MW distribution of the HMs bound to CSO-DOM is greatly important for cost-effectively removing HMs from CSOs in the coagulation process. This paper presents a comprehensive approach of ultrafiltration, fluorescence quenching titration, excitation−emission matrix parallel factor analysis, complexation model, and two-dimensional correlation fluorescence spectroscopy for exploring the MW-based complexing characteristics between Cu(II) ions and CSO-DOM components. Results show that: (1) Cu(II) ions that bound to the CSO-DOM were mainly distributed in the MW range of <5 kDa, which makes them very difficult to be removed from CSOs by coagulation technique. (2) Concentration effect and molecular composition exerted great impacts on the MW distribution of the Cu(II) ions bound to CSO-DOM. (3) The humic-like component of terrestrial origin with the MW range of 100 kDa∼0.45 μm possessed high binding stability, capacity, and priority with Cu(II) ions, and they could be used at a high concentration to promote the removal efficiency of coagulation for Cu(Ⅱ) ions of CSOs by competitive complexation and inter-molecular bridging.

An elicitation process to quantify Bayesian networks for dam failure analysis

Bayesian networks support the probabilistic failure analysis of complex systems, e.g., dams and bridges, needed for a better understanding of the system reliability and for taking mitigation actions. In particular, they are useful in representing graphically the interactions among system components, while the quantitative strength of the interrelationships between the variables is measured using conditional probabilities. However, due to a lack of objective data it often becomes necessary to rely on expert judgment to provide subjective probabilities to quantify the model. This paper proposes an elicitation process that can be used to support the collection of valid and reliable data with the specific aim of quantifying a Bayesian network, while minimizing the adverse impact of biases to which judgment is commonly subjected. To illustrate how this framework works, it is applied to a real-life case study regarding the safety of the Mountain Chute Dam and Generating Station, which is located on the Madawaska River in Ontario, Canada. This contribution provides a demonstration of the usefulness of eliciting engineering expertise with regard to system reliability analysis.