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With the increasing of tunnel mileage, one of the most vital problems of broad-scale structures is the intelligent identification and location of structural defects, which require massive data storage capacity and high data processing efficiency. The full-field point cloud data collected by terrestrial laser scanning (TLS) can be extracted to construct three-dimensional measured models more accurately, therefore, the fusion of TLS and the finite element method (FEM) is particularly beneficial to the deformation analysis of tunnel structures. This paper combines numerical simulation and full-field measurement to interactively verify the reliability of deformation analysis based on FEM simulation and point cloud processing. The innovation of this paper is that a three-dimensional FEM is validated through the measured point cloud data of the tunnel structure. The result of this study indicated that FEM simulation and the structural health monitoring analysis are consistent. [ABSTRACT FROM AUTHOR]

In this article, the Carrera Unified Formulation and full Green–Lagrange nonlinear relations are employed to investigate the postbuckling behavior of laminated composite panels subjected to in-plane shear and combined loadings. The layerwise refined plate models are implemented by the efficient Lagrange expansion functions through the laminate thickness. An artificial surrounding area is assumed to model shear conditions. The accuracy of the presented model is validated based on the available literature. Then, the effects of stiffeners on the nonlinear response of panels are evaluated, and comprehensive assessments are provided for the equilibrium curves and stress distributions. [ABSTRACT FROM AUTHOR]

With the rapid development of urban rail transit and the aging of transportation infrastructure, the demand for shield tunnel disaster detection is about to break out. Most of the traditional monitoring methods require considerable manpower and time costs, which cannot satisfy the increasing requirements of tunnel operation and maintenance. Free-form model construction and deviation mechanism analysis are investigated in this paper to monitor the geometric deformation information of shield tunnels quickly and accurately. A method for identifying geometric features of tunnel sections based on the free-form B-spline approximation is proposed. The innovation of this paper lies in the intelligent recognition of common interference targets by the residual classification method. Furthermore, various Root Mean Squared Error (RMSE) distributions are investigated, which successfully realizes and verifies the clustering analysis of certain point cloud features. [ABSTRACT FROM AUTHOR]

Laser-based visual perception technology is an effective way to enhance the intelligent level of tunnel operation and maintenance, which could improve the efficiency of the automatic identification and intelligent positioning of different diseases. Although various sensing and data processing methods for tunnel inspection have been studied, the research on invasion detection based on laser scanning technology is still rare. In this paper, the invasion detection of the tunnel and train is carried out based on terrestrial laser scanning data. A feature-based registration is proposed in order to fuze the tunnel and the train models accurately and automatically in the unified coordinate system, where the local contact points are set as the features and identified by means of the normal vector descriptor. The invasion analysis is achieved with the convex points, which are paired through the convex hull and polar principle. A complete and comprehensive image of the invasion analysis is generated, which offers a reality model base for the design and decision-making. The method proposed can be extended to other similar scale scenarios of invasion analysis and spatial position inspection. It is a reference for the engineering applications of the intelligent operation and maintenance of the tunnel. [ABSTRACT FROM AUTHOR]

The monitoring and prevention of cracks in tunnel structures is an essential problem and the traditional methods are arduous to suffice the rapid increasing of tunnel mileage. Many researches, nowadays, mainly focus on the automatic identification and intelligent detection of cracks. However, crack identification and localization of tunnel structures are merely preliminary for effective prevention. Therefore, how to intelligently analyze and predict the further evolution of cracks will be the top priority of tunnel disaster prevention. In this article, a novel method is proposed which combinates deep learning (DL) techniques and finite element method to detect and analyze the cracks which is significant for the intelligent prevention. The innovation of this article lies that the position of cracks is identified automatically with the DL based on Mask R-CNN method and the evolution of cracks is predicted efficiently with FEM model. [ABSTRACT FROM AUTHOR]

Box tunnels, compared with circular tunnels, can increase the space utilization ratio by approximately 20% and have been increasingly used in urban underground space. Box jacking generates more ground loss due to its special geometric shape, inducing larger ground settlement, compared with circular pipe jacking. Accurate prediction of ground settlement during box jacking is a key aspect for the success of a project. This paper proposes the ground settlement prediction models during box jacking based on stochastic medium theory and cavity expansion theory, and compares the applicability of the models. The comparison shows that the modified Verruijt model based on the cavity expansion theory can provide a relatively accurate prediction for the magnitude and trough width of the ground settlement. The analytical model is validated through numerical simulation and field instrumentation using the project of Shilianjie Station of No. 5 metro line in Suzhou, China as a testbed. The validation shows that the analytical predictions compare reasonably well with the numerical simulation results and field measurements with a maximum error within 13%. The analytical model in this paper can provide a quick estimate on the ground settlement during box jacking. [ABSTRACT FROM AUTHOR]

With the rapid development of engineering constructions, especially transportation facilities, the structural models for the simulation of large-scale structures shall be eventually enhanced for predicting the complete three-dimensional stress and strain fields in reinforced concrete-made components. This paper proposes a component-wise approach for the modeling of reinforced concrete structures in which steel rebars and the concrete part are considered as two independent one-dimensional entities. Lagrange polynomials are used to express the cross-section deformations and different component-wise subdomains are joined by simply imposing displacement continuity at the chosen Lagrange points along the component boundary. The Finite Element (FE) method is applied to provide numerical solutions whereas Carrera Unified Formulation (CUF) is used to generate the related stiffness matrices in a compact and straightforward way. The classical case of homogenized beam solutions, as well as the one in which a virtual layer is associated with the steel zones, are implemented too. The three solutions are compared for a number of reinforced concrete beam problems, from single to double reinforced beam, including a T-shape cross-section. A final study considering transverse stiffeners (steel stirrups) is investigated. These stiffeners are modeled component-wise as well. Results clearly show the advantages and superiority of the component-wise FE-CUF based model to completely capture the three-dimensional strain and stress states, including shear ones, of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

For subway safety, it is important to monitor the convergence deformation of shield tunnels in the long term. However, traditional monitoring methods are constrained by high cost and technical difficulties. Herein, improvements achieved through use of a new type of optical fiber (OF) sensor are reported. The new type of optical fiber sensor, namely, the flexible long-gauge Fiber Bragg Grating (FBG) sensor, is proposed with descriptions of design, preparation and strain sensing performance. Then, a method of assessing convergence deformation is proposed based on distributed long-gauge strain measurements. Finally, the proposed method is validated with measurements made on two full size specimens of shield segments. It is also concluded that the seam change shows a strong influence on convergence deformation. From static experiments, convergence deformation can be accurately evaluated to satisfy the demands of tunnel management. Considering the additional advantages of distributed sensing, such as sensing distance, stability and durability, the proposed method exhibits broad application prospects. [ABSTRACT FROM AUTHOR]

Automation and intelligent health monitoring technologies will be one of the most important development directions for rail transit operation and maintenance considering the continuous expansion of the scale of urban rail transit and the increase of labor costs. The highly accurate, full-field data acquisition based on vision measurement technology, which is combined with photogrammetry and three-dimensional scanning technology, is an effective way to improve the intelligence of monitoring. In this paper, accuracy tests of vision measurement and total station technology in multipoint measurement is carried out under the same conditions where the accuracy and reliability are compared according to the various datasets which are collected from experiment and testing. A novel visual measurement technology is proposed for the deformation monitoring of tunnel structures, such as settlement and convergence. The results show that the measurement system has a resolution of 0.01 mm which is better than the total station resolution, and the deviation ratios of the vertical and horizontal displacement are 1.6% and 2.5%, which demonstrate the proposed system has a good potential for practical applications in terms of resolution and accuracy. [ABSTRACT FROM AUTHOR]

Thin-walled structures have been widely adopted in engineering projects because of the advantages of good load-bearing capacity, light weight and low cost. In this paper, a refined finite element method (FEM) based on the Carrera Unified Formula (CUF) is performed to analyze the free vibration of thin-walled beams with the variables cross-section, length and boundary. The low-dimensional FEM method could improve the efficiency of numerical analysis and reduce the time consumption. The one-dimensional (1D) CUF is employed in which the models are assumed to be a beam-like axis-oriented structures. In this case, the geometry of the thin-walled beam can be discretized as a limited number of 1D beam elements along the axis, while the Lagrange polynomial expansion may be used to approximate the displacement field on the cross-beam surface. Thus, FEM matrices and vectors can be written in terms of fundamental nuclei whose forms are independent of beam theories. The validity and capabilities of the method presented are examined in some numerical examples, and a comparative study is carried out between the method proposed and the three-dimensional element method with and without warping solutions. The results obtained by CUF 1D models are in close agreement with the reference solutions. In addition, it has been argued that the innovative approach presented in this paper can be used as a precise tool for structural analysis for complex cross-section thin-walled beams to reduce computational costs. [ABSTRACT FROM AUTHOR]

The study deals with the stress evaluations of the functionally graded beams (FGBs) using refined beam models. The refined beam models are obtained within the framework of the Carrera unified formulation (CUF), where expansions are used across the cross-section to enrich the kinematics of the finite elements and obtain 3 D-like accuracy of the solution. Analyses of FGBs are performed by using different structural theories based on Taylor-like and Lagrange expansions. The results are compared with the literature and 3 D finite element solutions. It is observed that calculation costs are significantly decreased in finite element analyses performed with CUF. [ABSTRACT FROM AUTHOR]

Architectural structures today are increasingly complex and structural health monitoring plays an important role in guaranteeing their safety. How to improve the reliability of deformation analysis is, thus, one of the key problems. This article combines laser-based measurement technology and the Carrera unified formulation (CUF) method to investigate the deformation of engineering structures. Within this article, we simulate architectural structures using the CUF geometric model, which is consistent with the results of the laser tracker experiment. We aimed at constructing an intelligent and efficient CUF model which can be applied extensively in the monitoring of various constructs, such as tunnels and bridges. The innovation of this article is that high-accuracy laser tracker technology is integrated with an effective CUF model to investigate the load-displacement relationship considering lateral displacement. [ABSTRACT FROM AUTHOR]

Freeform parameterizations to reproduce structure deformation are increasingly important topics in laser-scanner-based deformation analyses. High-accuracy assurance of free-form surface approximation is extremely critical for reliable deformation analysis. One main challenge in this field is the model selection. Improper model complexity could result in under-fitting the real object shape or overfitting data noises, and thus a failure of deformation analysis. A multi-sensor system could integrate advantages of different sensors and improve the quality of mission completed. This paper combines terrestrial laser scanning (TLS) and laser tracker (LT) technologies, to enhance high-accuracy surface modeling in deformation analysis. A surface-based B-spline approximation and a multi-sensor system are investigated, the latter of which focuses mainly on the combination of TLS and LT technologies. The innovation of this paper is that the surface-based B-spline approximation is validated and optimized with LT corner cube reflectors. Hypothesis testing is adopted to select the best parameter setting by judging most consistency of TLS and LT in various epochs. In the B-spline surface modeling, both instrumental and numerical uncertainties are considered. We use the instrumental uncertainty model based on intensity value, as well as numerical uncertainty based on adjustment theories. A sampling strategy is proposed to avoid data gaps and obtain even distributed data points. [ABSTRACT FROM AUTHOR]