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Civil structures may deteriorate during their service life due to degradation or damage imposed by natural hazards such as earthquakes, wind, and impact. Structural performance anomaly detection is essential to provide an early warning of structural degradation limit states in order to prevent potential catastrophic failure. Data-driven machine learning approaches have been widely used for this, due to their capability in capturing features sensitive to damage-induced anomalies from structural health monitoring (SHM) data, assuming that such data are available. Although machine learning models have been used, many are challenged by the vast operational and environmental variability that can corrupt SHM data and by (typically) strongly correlated information from different sensors in the SHM data. This paper proposes an unsupervised deep learning approach for the detection of structural anomaly based on a deep convolutional variational autoencoder (DCVAE) for feature extraction coupled with support vector data description (SVDD) for anomaly detection. The proposed DCVAE-SVDD method has several appealing strengths. First, the variational latent encoding is used to capture the features of monitoring data through a probability distribution. The integration of the Kullback–Leibler divergence in the loss function provides accurate estimation of the probability distributions. Second, the DCVAE designed with convolutional and deconvolutional operations utilizes the correlation among multisensor data to avoid loss of correlation features and achieve better performance in feature extraction. Third, the SVDD is utilized to create a minimum-volume hypersphere that contains the anomaly-sensitive statistical features of the state. The hypersphere accurately separates anomaly-sensitive statistical features of reference states of structure from the anomalous ones. A computational frame model and a laboratory grandstand model are used to evaluate the performance of the proposed method for detecting structural anomaly. The results demonstrate the superiority of the proposed DCVAE-SVDD in detection accuracy over the other commonly used structural anomaly detection methods (deep autoencoder combined with SVDD autoregressive model with one-class support vector machine, and principal component analysis). [ABSTRACT FROM AUTHOR]

This work presents an investigation of robotic technologies' effectiveness in construction activities. Sixty‐four highly relevant publications were identified from the database. By systematically reviewing the publications, the secondary data that are of interest to the review theme were retrieved and further evaluated. It is found that robotic technologies for automated construction is a growing field, where the taxonomy of robot was reflected in a diversified manner in the existing studies, ranging from the muscular guy—robotic manipulator—to the dexterous ones—unmanned aerial vehicle, autonomous mobile robot, automated guided vehicle, autonomous construction machinery and quadruped robot. In addition, the existing studies have provided substantial evidence to reveal the robotic technologies' effectiveness against traditional human methods in construction scenarios, and the measures for effectiveness consisted of productivity, precision, and success rate. With the evidence, it seems that the construction sector could benefit from robotic technologies to achieve intelligent workflows. Furthermore, based on the existing knowledge foundation in the current literature, a theoretical framework for future research direction is proposed. The framework envisages the integration of large models with construction robots to address operational inefficiencies, reduce costs, and simplify management. [ABSTRACT FROM AUTHOR]

Structural health monitoring obtains data reflecting the service status of grid structures through sensors. One of the issues to consider in optimal sensor placement is how to obtain as much information as possible with a limited number of sensors. In this paper, a sensor placement method is proposed based on damage sensitivity and correlation analysis, which is based on strain energy calculation and is suitable for grid structures. Specifically, with the sensor locations as optimization variables, a mathematical optimization model is established by considering the damage sensitivity and redundancy of the monitoring scheme, and a genetic algorithm is employed for computation. Two examples, including a lattice shell and a flat grid, are provided to illustrate the method, followed by a discussion of the sensitivity of parameters such as stiffness reduction degree and load form. The results indicate that the redundancy of the optimized schemes for the two examples decreased by approximately 80% and 30%, respectively. The proposed method ensures a certain degree of damage sensitivity while significantly reducing redundancy, demonstrating its applicability and robustness in sensor placement for grid structures. [ABSTRACT FROM AUTHOR]

Crack detection is significant to building repair and maintenance; however, conventional inspection is a labor-intensive and time-consuming process for field engineers. This paper proposes a three-step computer vision-based framework to quickly recognize concrete cracks and automatically identify their length, maximum width, and area in damage images. In step one, a region-based convolutional neural network (YOLOv8) is applied to train the crack localizing model. In step two, Gaussian filtering, Canny, and FindContours are integrated to extract the reference contour (a pre-designed seal) to obtain the conversion scale between pixels and millimeter-wise sizes. In step three, the recognized crack bounding box is cropped, and the ApproxPolyDP function and Hough transform are performed to quantify crack dimensions based on the conversion ratio. The developed framework was validated on a dataset of 4630 crack images, and the model training took 150 epochs. Results show that the average crack detection accuracy reaches 95.7%, and the precision of quantified dimensions is over 90%, while the error increases as the crack size grows smaller (increasing to 8% when the crack width is within 1 mm). The proposed method can help engineers to efficiently achieve crack information at building inspection sites, while the reference frame must be pre-marked near the crack, which may limit the scope of application scenarios. In addition, the robustness and accuracy of the developed image processing techniques-based crack quantification algorithm need to be further improved to meet the requirements in real cases when the crack is located within a complex background. [ABSTRACT FROM AUTHOR]

Bennett linkage has broad application prospects in civil engineering, aerospace engineering, mechanical engineering, etc. The existence of clearance in the revolute joints makes the journal collide with the bearing and thus affects the dynamic responses of the Bennett linkage. Based on the finite particle method, an effective approach is proposed for the dynamics analysis of the deployment process of the Bennett linkage with revolute clearance joints. Firstly, a simplified computational model of the Bennett linkage is proposed to consider the size effects and contacts. The corresponding beam element, torsion spring element, and face-to-face contact element are derived. Subsequently, the detection method of the axial and radial contact states of revolute clearance joints is presented, and the calculation model of the contact force is depicted. Finally, dynamics analysis of a typical Bennett linkage with clearance joints is carried out. The results of the simplified model are consistent with the higher-fidelity model, demonstrating the effectiveness of the proposed method. The Bennett linkage with clearance joints is observed to exhibit more oscillations than that with ideal joints during deployment, and its energy is dissipated due to the existence of clearance. The increase of the number of the revolute clearance joints leads to more dynamic effects of the mechanism. The increase of clearance size causes more oscillations in the mechanism. The increase of the friction coefficient in revolute clearance joints reduces the oscillations of the mechanism. The growth of the damping coefficient results in more energy dissipation and weakens the additional dynamic response caused by clearance. [ABSTRACT FROM AUTHOR]

The magnetic shielding device, made of high-permeability soft magnetic material, is sensitive to external influences and requires a protective steel enclosure. A steel enclosure, being strongly ferrimagnetic, can alter the surrounding magnetic field distribution, thus impacting the shielding effectiveness. This study proposes a novel analytical approach to quantify this effect, which has not been previously researched. The method develops a simplified finite element simulation model based on the structural symmetry of the steel enclosure. By using this model, this study analyzes the impact of steel structures with varying heights, widths, and remanent magnetization values. The validity of the method is confirmed through experimental tests on steel buildings. The findings offer insights into the optimal placement of magnetic shielding systems and provide theoretical guidance for designing large-scale magnetic shielding devices. [ABSTRACT FROM AUTHOR]

Space grid structures are widely used in the field of structural engineering due to their good mechanical properties and simple construction procedures. This paper reviews the development of space grid structures and mainly introduces the development of space grid structures in China in recent years. Some typical applications of space grid structures are introduced and the technical developments are summarized. It shows that China not only has a large number of engineering applications of space grid structures, but also a rapid development of related technologies. Finally, some prospects for space grid structures are discussed. [ABSTRACT FROM AUTHOR]

A beam string structure is an efficient hybrid system comprising beams, cables, and struts. This study proposes an active beam string structure that adapts to external loading for deflection control, achieved by replacing passive struts with telescopic ones. An optimization-based model is created to minimize deflection, with the maximum deflection of beams serving as the optimization objective. A deflection control framework is constructed by using a hybrid genetic algorithm and back-propagation neural network. The former combines the strengths of the genetic and gradient descent algorithms, and the latter trains a prediction network applying mechanical responses, resulting in quick output of control schemes. To assess the control framework's performance, a scaled model is designed and fabricated, including a measuring system for deflection and stress, an actuating system with telescopic struts, and a PC-based decision-making system. Experimental and numerical studies are carried out for the model. The control schemes using the hybrid genetic algorithm and back-propagation neural network successfully reduced the deflection responses by at least 80% in simulations and experiments. The results validate the accuracy of the algorithm and reliability of the network, further demonstrating the effectiveness of the control framework. In addition, the deflection control process also optimizes the internal forces of the beam, with a maximum decline rate of stress response approaching 60%. [ABSTRACT FROM AUTHOR]

The large-span, relaxed antenna network is a large deformation flexible structure due to its low pre-tension level of the wires. Its dynamic analysis under a wind load belongs to dynamic and geometric nonlinear problems, which is very complex to accurately calculate and solve. This paper explores the possibility of the finite particle method (FPM) to the aeolian vibration analysis of a large-span, low stress-tensioned antenna cable net. In the FPM, the antenna network structure is discretized into a group of finite particles, where the motions of all particles follow Newton's second law and can be solved dynamically using a central difference scheme. The effectiveness and applicability of the FPM were verified by comparing the calculation results of the finite element method and FPM. The FPM was used to study the effects of wind speed and the distribution of vibration on the aeolian vibration of antenna cable nets. The results showed that this method is suitable for studying the aeolian vibration of a large-span, low stress-tensioned antenna network and has high computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

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A comparative study of composite floor systems with I-beams and corrugated web beams is performed based on non-linear programming (NLP) algorithm. The optimization is conducted to find the most economical design with minimum steel consumption considering variables associated with the cross-sectional dimensions and multiple constraints from standards, specifications and engineering practices. Various parameters of live loads ranging from 2 to 10 kN/m2 and spans ranging from 20 to 100 m are considered. The optimization results reveal that composite floors with corrugated web beams have reasonable and economical cross-sections with less steel consumption, owing to the high performance of the corrugated web in shear resistance and stability. Further comparative studies show that composite floors with corrugated web beams are economically competitive for spans larger than 30 m with a steel saving of 20–60%, and composite floors with welded I-beams can be applicable for spans less than 30 m considering the simpler configuration and construction. In addition, a spatially structured cable-supported steel–concrete composite floor system is proposed and recommended for super-large-span floor structures considering the cost-effectiveness of the analyzed floor systems reduces as the span further increases. [ABSTRACT FROM AUTHOR]

This study develops stability conditions for general tensegrity regarding the three stability criteria (e.g., prestress stability, general stability, and super stability) based on an energy approach. The coupling relations of specific nodal degrees of freedom caused by the rigid bodies are described by a set of constraint functions and incorporated into the potential energy function by the Lagrangian multiplier method. Stiffness matrices of general tensegrity systems are derived from the augmented potential energy function. It shows that the stability of general tensegrity can be evaluated through the stiffness matrices expressed in the constrained motion space generated by the constraint functions. Elegant formulations are developed for the evaluation of the three types of stability conditions for general tensegrity systems. Moreover, it turns out that the formulations developed in this study will degenerate into those for the stability analysis of classic tensegrity if no rigid bodies exist in the system, which indicates that the proposed approach is a general framework for the stability analysis of any type of tensegrity systems. [ABSTRACT FROM AUTHOR]

The construction site environment is quite complex with many dangerous hazards (e.g., foundation pits, holes). To avoid injuries, workers must wear helmets that are color-coded for the specific type of work, which is helpful to identify whether workers are in permitted areas. Therefore, it is possible to identify unauthorized intrusion by classifying the safety helmets. This study proposes a vision-based method called Helmet–Yolov5 to automatically detect unauthorized intrusions by workers on construction sites. Multiple improvement measures are made to enhance the model performance. First, the attention mechanism is used to enhance the weights of object regions in the image, which makes the detection of small objects more effective. Second, atrous spatial pyramid pooling is adopted to preserve the detail information of the image. Third, the universal upsampling operator is introduced to fuse image features at different scales. To verify the effectiveness of the improved model, images collected from a real construction site are used to build a large-scale image dataset of safety helmets for model testing. It shows that the proposed Helmet-Yolov5 model is more accurate than the original Yolov5 model, also with high inference speed. Compared to other state-of-the-art models (e.g., Yolov4), the Helmet-Yolov5 model has considerable advantages in term of high detection accuracy and efficiency. [ABSTRACT FROM AUTHOR]

The corrosion mechanism and characteristics of steel in typical atmospheric environments directly affect the rationality of corrosion protection methods. This study investigates the corrosion evolution law of Q235 steel that has been exposed to the urban industrial atmosphere for seven years. The mass loss is used for corrosion dynamics analysis. The rust layers have been characterized by SEM, EDS, and XRD. Finally, the corrosion mechanism was analyzed through a combination of electrochemical methods, corrosion kinetics, and rust layer characteristics. The mass loss results indicate that a two-stage corrosion power function law can still effectively describe the corrosion rate of a seven-year exposure that complies with the power function law. The short-term corrosion results fail to fully reflect the corrosion performance of Q235 steel. The typical morphological structures of γ-FeOOH and α-FeOOH are identified, and the rust layers change from a loose and flat form to a granular and, finally, compact into a smooth surface. The crystalline phases of the rust layers include α-FeOOH, γ-FeOOH, Fe3O4/γ-Fe2O3 and α-Fe2O3. Corrosion products in the initial period are mainly γ-FeOOH, followed by α-FeOOH, and a small amount of Fe3O4/γ-Fe2O3. With the increase in exposure time, α-FeOOH and Fe3O4/γ-Fe2O3 in the rust layer increase. SO2 and Fe3O4/γ-Fe2O3 are the primary factors accelerating steel corrosion. During the first three years of atmospheric corrosion, the primary corrosion mechanism was governed by the acid cycle reaction mechanism. However, from the fifth year of atmospheric corrosion, oxygen-absorbing corrosion began to gradually dominate, specifically oxygen-absorbing corrosion. [ABSTRACT FROM AUTHOR]

Locomotive robot based on tensegrity has recently drawn much attention due to its lightweight and flexibility. This article presents an improved numerical model for locomotive tensegrities. The previously used bar element for struts is replaced by beam element, and rigid joint element is used to consider more details of the tendon–strut connections. The vector form intrinsic finite element (VFIFE) method is adopted to formulate the numerical model and carry out the simulation. The improvement of the proposed model on the prediction of feasible rolling gaits is quantitatively verified by experiments on a six-strut locomotive tensegrity. Mann–Whitney U test is adopted, and the p value between the experimental success rates of the gait primitives generated by the improved model and the rates of the gait primitives generated by the previous model is 1.46 × 10 − 12 . It is shown that the improved model is more consistent with the experiment by considering the details of the tendon–strut connection. [ABSTRACT FROM AUTHOR]

The residual magnetic field in a magnetic shielding device with a multilayer high permeability material (permalloy) structure can be obtained at the nanotesla (nT) level or even lower. At present, in the process of designing a magnetic shielding device, most of the external environmental magnetic field settings are set at the size of the Earth's environmental magnetic field, but the instruments inside the magnetic shielding device need to be powered, the active compensation coil needs to be powered, and the degaussing coil of passive shielding layer needs to be powered, so substations need to be used around magnetic shielding devices. The magnetic field generated by the substation will affect the magnetic shielding device, so this paper analyzes and measures the magnetic field generated by the substation. Firstly, the finite element model of a substation is established, and the influence of different substations on the environmental magnetic field is analyzed by changing the power. Secondly, the test method of a substation environment magnetic field is determined. Finally, the site test was carried out to measure the influence of different power substations and different distances on the magnetic field, and its influence on the magnetic shielding device was analyzed, which provided an important basis for the construction of the magnetic shielding device. [ABSTRACT FROM AUTHOR]

Structural anomaly detection based on the structural health monitoring (SHM) data has attracted significant attention owing to its important role in the early warning of structural damage to existing civil structures. Data-driven approaches, where damage-sensitive features are extracted directly from the SHM data using statistical pattern recognition (SPR) techniques without physical models of structures, have been widely studied. Principal component analysis (PCA) and probabilistic PCA (PPCA) are powerful and efficient SPR methods for linear or weakly nonlinear cases. However, some special structures may be subjected to multiple operational conditions, wherein structural configurations such as geometry and mass distribution may change due to the movement of parts or the whole structure, as in retractable roof structures. These changes may give erroneous results in the SPR of the SHM data and eventually in the anomaly detection by a single PCA or PPCA model. This paper presents an improved approach using a mixture of probabilistic principal component analysis (MPPCA) for the anomaly detection of structures under multiple operational conditions with missing measurement data. First, the baseline MPPCA model was constructed for stress data collected under healthy conditions, where the estimation of the MPPCA parameters was reformulated for the missing data cases. Second, three anomaly statistics were presented for newly monitored incomplete data to detect and localize structural anomalies. The probability distributions of the anomaly statistics were estimated to obtain thresholds for outlier detection. Finally, the effectiveness of the MPPCA-based method was investigated by applying the method to the anomaly detection of a retractable roof structure with numerically simulated and real monitored stress data. [ABSTRACT FROM AUTHOR]

The cover image is based on the Article From muscular to dexterous: A systematic review to understand the robotic taxonomy in construction and effectiveness by Yifan Gao et al., https://doi.org/10.1002/rob.22409.By Yifan Gao; Jiangpeng Shu; Zhe Xia and Yaozhi LuoReported by Author; Author; Author; Author [Extracted from the article]

Continuous cables are widespread in various fields, and mechanical analysis is an important issue in their application. The structural responses of frictional continuous cable systems under external loads are related to the load path. The influence of load path has seldom been considered in the existing analysis methods. This paper proposes a novel approach for the mechanical analysis of continuous cable systems considering the influence of load path. The constitutive relation of the frictional continuous cables was derived, in which the sliding amount parameters were eliminated. The computational frameworks for both definite and indefinite load path cases were proposed. For a definite load path, the structural responses can be uniquely determined by successively trials and modifications of the nodal sliding state. For an indefinite load path, a formula of all the possible structural responses was derived, and the ranges of the structural responses can be obtained. All computations in the approach were converted to matrix operations. The effectiveness and practicability of the proposed approach were demonstrated by two typical numerical examples. [ABSTRACT FROM AUTHOR]

Magnetic shielding devices with a grid structure of multiple layers of highly magnetically permeable materials (such as permalloy) can achieve remanent magnetic fields at the nanotesla (nT) level or even lower. The remanence of the material inside the magnetic shield, such as the building materials used in the support structure, can cause serious damage to the internal remanence of the magnetic shield. Therefore, it is of great significance to detect the remanence of the materials used inside the magnetic shielding device. The existing test methods do not limit the test environment, the test process is vulnerable to additional magnetic field interference and did not consider the real results of the material in the weak magnetic environment. In this paper, a novel method of measuring the remanence of materials in a magnetic shielding cylinder is proposed, which prevents the interference of the earth's magnetic field and reduces the measurement error. This method is used to test concrete components, composite materials and metal materials commonly applicated in magnetic shielding devices and determine the materials that can be used for magnetic shielding devices with 1 nT, 10 nT and 100 nT as residual magnetic field targets. [ABSTRACT FROM AUTHOR]

Gaussian process modeling (GPM) is widely used to replace physical models for uncertainty quantification (UQ). The fidelity of training samples has a major impact on the prediction performance of the GPM, and the computational time of obtaining high‐fidelity (HF) samples from simulations may be very prohibitively expensive. Therefore, this study proposes the use of the multi‐fidelity GPM for UQ to make a trade‐off between the computational cost and accuracy by combining a few HF samples with many computationally‐cheaper low‐fidelity (LF) ones. Currently, the co‐Gaussian process model (co‐GPM, also known as multi‐fidelity GPM) requires that the LF and HF samples be nested. A generalized co‐Gaussian process model (GC‐GPM) is developed that can mix LF and HF samples under both nested and un‐nested conditions. In addition, to further alleviate the computational cost, an adaptive sampling strategy is introduced into GC‐GPM to reduce the number of training samples using a new infill criterion. Within the adaptive GC‐GPM framework, the high dimensional integrals associated with the statistical moments (mean and variance) of structural response can be decomposed to single dimensional ones that are analytically tractable, which finally allows for analytical calculation of the mean and variance. Three full‐scale structures are adopted to verify the reliability and efficiency of the proposed adaptive GC‐GPM method, and traditional GC‐GPM and Monte Carlo simulation (MCS) are used for comparison purpose. The comparison results show that the UQ results of the adaptive GC‐GPM match well with those of the MCS and compared to the traditional GC‐GPM, the adaptive GC‐GPM owns higher computational accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Summary: The roof of a large‐span structure is vulnerable to strong winds, and thus, wind‐induced damage of the roof happens occasionally. Structural condition assessment from structural health monitoring (SHM) data provides a good means to analyze the structural safety condition and detect the damage. An accurate state space model is the key point to structural system identification and condition assessment as well. Because the wind loadings on the roof are frequently nonzero and non‐Gaussian, they cannot be directly simplified as random noise for the stochastic subspace identification. Data‐driven combined deterministic‐stochastic subspace identification (CSI) is adopted to identify the state of the wind‐induced vibrating roof structure, in which the wind loadings of the roof are considered as input parameters instead of noise term. Then, a novel specific damage‐sensitive feature is proposed to extract the damage information directly using the system matrices from the identified state space model, which overcomes the diversity at the state matrices. Combined with the statistical pattern recognition (SPR) technique, a statistics‐based damage index is defined to detect the change of the structural state. The proposed method is verified by a numerical simulation of a roof structure, in which the influence of different levels of wind excitation on the methodology is investigated. The results show that the proposed method is sensitive to the change of the structural state but insensitive to wind loading variations. Subsequently, a wind tunnel test performing on a real double‐layer metal roof model further demonstrates the effectiveness of the proposed method for practical application. [ABSTRACT FROM AUTHOR]

In this study, the mechanical responses of a functionally graded thick-walled tube simultaneously under magnetic, thermal and mechanical loads are studied. Based on the assumption that the volume fraction of each phase material is distributed as a power function, the Voigt method is used to obtain the stress–strain relationship of the functionally graded materials (FGMs). The influences of the relevant material parameters including volume fraction, thermal expansion coefficient, and Poisson's ratio on the magneto-thermo-elastic theoretical solution are deeply studied and discussed. Furthermore, when some of the parameters are set as special values, the research results can be degenerated to two coupled loads which are consistent with the existing researches. The results of this paper provide theoretical support for the practical design and application of the FGM tube under the combined action of magnetic, thermal and mechanical loads. [ABSTRACT FROM AUTHOR]

Fatigue cracks are typical damage of threaded steel rods under dynamic loads. This paper presents a study on ultrasonic guided waves-based, fatigue-crack detection of threaded rods. A threaded rod with given sizes is theoretically simplified as a cylindrical rod. The propagation characteristics of ultrasonic guided waves in the cylindrical rod are investigated by semi-analytical finite element method and the longitudinal L(0, 1) modal ultrasonic guided waves in low frequency band is proposed for damage detection of the rod. Numerical simulation on the propagation of the proposed ultrasonic guided waves in the threaded rod without damage shows that the thread causes echoes of the ultrasonic guided waves. A numerical study on the propagation of the proposed ultrasonic guided waves in the threaded rod with a crack on the intersection of the smooth segment and the threaded segment shows that both linear indexes ( R f and ARS) and nonlinear indexes ( β r e ′ and β ′ ) are able to detect the crack. A constant-amplitude tensile fatigue experiment was conducted on a specimen of the threaded rod to generate fatigue cracks in the specimen. After every 20,000 loading cycles, the specimen was tested by the proposed ultrasonic guided waves and evaluated by the linear indexes and nonlinear indexes. Experimental results show that both the linear and nonlinear indexes of the ultrasonic guided waves are able to identify the crack before it enters the rapid growth stage and the nonlinear indexes detect the crack easier than the linear indexes. [ABSTRACT FROM AUTHOR]

Lightweight and flexible membranes offer different façades for buildings (suitability, competitive costs, durability, and other benefits) compared to traditional building materials. Increasing attention is being paid to membrane structures in the civil and industrial sectors. Acquiring response data or environmental characteristics directly from a model or building is the most straightforward approach to analyzing the properties of membrane structures, which also contributes to the development of theoretical studies and simulation methods along with the enactment of specifications. This paper provides a comprehensive overview of membrane structure performance, including mechanical, thermal, and energetic aspects, alongside the deployment and deflation of inflatable types. Furthermore, the devices used to monitor the structural response are summarized. The constitution of the structure is the most critical factor affecting its performance. A proper design would offer enhanced mechanical properties and thermal environments with a reduction in energy consumption. Non-contact measurement technology has the advantage of causing no structural disturbance and is low cost, but it lacks practical application in membrane buildings. The achievements and limitations of previous studies are also discussed. Finally, some potential directions for future work are suggested. [ABSTRACT FROM AUTHOR]

A two-step topology-finding method based on mixed integer programming and nonlinear programming is proposed for tensegrity structures. In the first step, feasible and symmetric strut connectivities are obtained through a ground structure method combined with mixed integer programming; in the second step, the cable connectivities are optimized through nonlinear programming to obtain a feasible tensegrity structure. The same ground structure used in the first step is adopted in the second step, which is beneficial to find a more symmetric cable layout. The independent continuous mapping method is used in the second step to convert the 0–1 binary variables of cable connectivities to continuous variables to transform the combinatorial optimization problem into a nonlinear programming problem. The number of strut lengths is adopted as a control parameter and a symmetry objective function is proposed to generate a variety of regular and symmetric tensegrity structures. A multi-stage computation scheme is proposed to improve the computational efficiency. Typical examples are carried out to validate the proposed method. The computational efficiency of the method is benchmarked with existing methods fully based on mixed integer programming. Results demonstrate that the computational efficiency of the proposed method is significantly improved compared to the existing methods. [ABSTRACT FROM AUTHOR]

Wireless sensor networks usually suffer from the issue of time synchronization discrepancy due to environmental effects or clock management collapse. This will result in time delays between the dynamic responses collected by wireless sensors. If non-synchronized dynamic response data are directly used for structural modal identification, it leads to the misestimation of modal parameters. To overcome the non-synchronization issue, this study proposes a time synchronization approach to detect and correct asynchronous dynamic responses based on frequency domain decomposition (FDD) with frequency-squeezing processing (FSP). By imposing the expected relationship between modal phase angles extracted from the first-order singular value spectrum, the time lags between different sensors can be estimated, and synchronization can be achieved. The effectiveness of the proposed approach is fully demonstrated by numerical and experimental studies, as well as field measurement of a large-span spatial structure. The results verify that the proposed approach is effective for the time synchronization of wireless accelerometer sensors. [ABSTRACT FROM AUTHOR]

Axially loaded steel tubes are widely used as primary structural members in civil engineering structures. In this paper, a stress measurement method for axially loaded steel tubes is developed based on the linear relationship between the group velocity of guided waves in the steel tube and the stress of the steel tube. The propagation modes of guided waves in a typical steel tube are analyzed using semi-analytical finite element method. A torsional mode T(0,1) is adopted to conduct the measurement. Experiments are carried out to calibrate the linear relationship between the group velocity of guided waves in a steel tube and the stress of the steel tube. The calibrated linear relationship is verified by another round of experiments on the same steel tube specimen. There is an average error of 8.2% between the stresses predicted by the calibrated linear equation and those obtained from strain gauges. Via this study, the guided wave-based stress measurement method has been successfully extended to axially loaded steel tubes. [ABSTRACT FROM AUTHOR]

Prestressed structures have gained popularity in large-span buildings due to their great spanning capacity and light self-weights. This kind of structure is normally subjected to multiple types of loads, such as temperature load, wind load, and construction load. The determination of different load effects not only guides the design of similar structures but also helps reveal the damage-induced variation that would be concealed by the environmental loads. To determine the different load effects, separation of the load effects collected by structural health monitoring (SHM) is needed. This study presents an enhanced approach for load effect separation based on independent component analysis (ICA) and ensemble empirical mode decomposition (EEMD), called EEMD-ICA*. The proposed method is to minimize manual tuning of user-defined parameters, which makes the EEMD-ICA suitable for separating load effects from the different measured data. Specifically, an optimization method is developed to determine the appropriate level of the added white noise in the EEMD using the relative root-mean-square error (RMSE) index. A logarithm form of Bayesian information criterion (BIC) is employed for the robust estimation of the number of load effects in the ICA. Simulated structural responses from a square orthogonal cable-net are used to validate the effectiveness of the EEMD-ICA*. Then, the proposed methodology is employed to extract various load effects from the SHM data of the National Speed Skating Oval (NSSO), which is the largest single-layer cable-net structure in the world. [ABSTRACT FROM AUTHOR]

Explosion overpressure and its duration are important parameters describing blast loading. However, their values obtained using the currently available methods differ significantly. To address this problem, we simulated the overpressure reflection coefficient (i.e., the ratio of reflection overpressure to incident overpressure) and fitted the analytical expressions to the test data. We then collected a large amount of theoretical and experimental blast loading data from literature and studied the probability distribution of blast loading for different scaled distances. The results show that the probability density function of explosion overpressure obeys an exponential distribution when the scaled distance is between 0.1 m / kg 1 / 3 and 0.5 m / kg 1 / 3 . On the other hand, it obeys a normal distribution when the scaled distance is greater than 0.5 m / kg 1 / 3 . The coefficient of variation reaches the maximum value of 1 when the scaled distance is between 0.1 m / kg 1 / 3 and 0.5 m / kg 1 / 3 , while it is between 0.13 and 0.2 when the scaled distance is from 1.5 m / kg 1 / 3 to 6 m / kg 1 / 3 . The coefficient of variation of reflected overpressure is slightly bigger than that of incident overpressure. Nevertheless, the coefficient of variation of proportional duration (i.e., the ratio of actual duration to cubic root of charge mass) is generally smaller, between 0.408 and 1.017. It was also found that there is no clear probability distribution for the blast loading duration. Finally, formulas for the explosion overpressure and proportional duration were determined together with their 95% confidence level bounds. [ABSTRACT FROM AUTHOR]

In this paper, a new deep learning framework named encoding convolution long short-term memory (encoding ConvLSTM) is proposed to build a surrogate structural model with spatiotemporal evolution of structure, estimate the structural spatiotemporal state and predict the dynamic response under similar future dynamic load conditions. The main work of this study includes: (a) The spatiotemporal response tensor database is developed using discrete-time history data of structural dynamic response. (b) As an extension of LSTM, convolution operation is combined with LSTM network to construct structural surrogate model from the spatiotemporal evolution structural performance. (c) To enhance the anti-interference ability of structural surrogate models, a new three-layer encoding layer is added for denoising autoencoders of the hybrid network. The influence of building types and input noise on the accuracy and antinoise performance of the surrogate models are analyzed through the dynamic response prediction of a frame-shear wall, a cylindrical, and a spherical reticulated shell structure. As a testbed for the proposed network, a case study is performed on a laboratory stadium structure. The results demonstrate that the developed surrogate model can predict the structural dynamic response precisely with more under 30% noise interference. [ABSTRACT FROM AUTHOR]

Due to the features of light weight, high flexibility, and slight damping, large-scale spatial structures are very sensitive to wind load. Thus, special attention must be paid to wind effect on large-scale spatial structures. A wind pressure field measurement was carried out to characterize the actual wind pressure of a large-span spatial structure. Meanwhile, it is also intended to provide reliable full-scale measurements for verification of wind tunnel test results widely used in the design and construction of structure. In this study, both wind tunnel test and field measurement are utilized to investigate the properties of the wind pressure acting on a typical large-scale spatial structure. Specifically, wind pressure coefficients, spatial distribution, probability density distribution (PDF), non-Gaussian characteristics, and power spectral density (PSD) are fully compared and discussed based on the results of the wind tunnel test and long-term field measurement. The comparison results show that generally the results of the wind tunnel test have good agreement with those of the field measurement. In the meanwhile, the discrepancies between them are also observed. This study aims to fully investigate the wind effects on large-scale spatial structure and enhance the understanding of wind loads. [ABSTRACT FROM AUTHOR]

Previously, the contact states between the bearing and journal of a spatial revolute joint (SRJ) with both axial and radial clearances were solved in the global coordinate system (GCS), which is complex and requires iterations. In this paper, a local-coordinate representation for the SRJs with clearance is combined with a vector-form particle-element method, i.e. finite particle method (FPM), to provide a more practical means for evaluation of the dynamic effects due to clearance. Firstly, the fundamentals of the FPM for analysis of spatial mechanisms are briefed. Then, a local-coordinate representation based on the revolution axis of the bearing is proposed. Specifically, the geometry of the journal and bearing is explicitly expressed using the coordinate transformation. The axial and radial contact states are evaluated by substituting the parametric equations and transforming them to quadratic and quartic equations, respectively, which can be analytically solved without iterations. The contact forces are evaluated in the local-coordinate representation and then transformed into the GCS representation. Two numerical examples, i.e. a spatial slider-crank mechanism and a spatial double pendulum, are provided to demonstrate the feasibility of the proposed method, by which the effects of joint-joint interaction and joint-flexible component interaction are fully discussed. [ABSTRACT FROM AUTHOR]

Summary: Structures are subjected to various kinds of structural deterioration and damage with use over long periods of service life. For the safety assurance of structures, it is very important to have a long‐term monitoring system and continuous assessments of structural integrity using the measured data. The objective of this paper is to develop an anomaly detection algorithm for a long‐term structural health monitoring (SHM) system based on probabilistic principal component analysis (PPCA). Static stress data were measured and used in this monitoring system. A baseline PPCA model is built under various environmental loading conditions. Then, newly monitored data are projected onto the principal vectors. Anomaly indices and their probability distributions are evaluated to determine the presence of structural damage indicated by outliers. This method is also capable of dealing with incomplete data and recovering the missing data. First, numerical simulation studies of a revolving auditorium are carried out to validate the proposed PPCA‐based method. Then, real monitoring data collected from the SHM system are used to detect the presence and locations of anomalies in the revolving auditorium. [ABSTRACT FROM AUTHOR]

Proper deformation process is essential for forming the shape of cable net structures during construction. This highlights the importance of identifying uneven and excessive deformation when building large-scale cable net structures. As such, the deformation of large-scale cable net structures should be accurately monitored in a real-time manner during the construction process. This study is to develop a laser-based displacement monitoring system for tracing the real-time deformation of large-scale spatial structures. The developed displacement monitoring system combines wireless sensor networks (WSN) and laser ranging technology. The laser-based displacement monitoring system is implemented on the National Speed Skating Oval (NSSO), which is a large-scale cable net structure, to obtain the relative displacement change between the cable net structure and the supporting system. On the other hand, the finite element (FE) model of the NSSO is established to simulate the deformation process. Then, the measured displacement results are compared with the FE model-derived counterparts. It is shown that the simulated and measured results have a good agreement, which indicates the effectiveness of the laser-based displacement monitoring system. [ABSTRACT FROM AUTHOR]

For large-span retractable roof structures, the mechanism should be simple and efficient for the convenience of motion control. The kinematic characteristics of parallelogram closed-loop chain linkages (PCCL) show that a set of the angulated beams of PCCL rotates around the fixed points, which is suitable for retractable structures. This paper focuses on the geometrical design of the rotary retractable plate structures (RRPS), which evolves from PCCL by replacing the rotation angulated beams with cover plates. Each plate of RRPS has a fixed support and all the plates rotate simultaneously with a single DOF. The fixed points used as supports for cover plates to improve the stability and simplify the motion control of the system restrict the open area of the RRPS. By adjusting the contact boundaries of the cover plates, an optimisation method is proposed to increase the open area of the RRPS after fully deployed. The design approach is successfully extended to both symmetrical and asymmetrical RRPS. An example is carried out to demonstrate the feasibility of the approach and a simple physical model is manufactured to validate the design result in the example. [ABSTRACT FROM AUTHOR]

Locomotive robots based on tensegrities have recently drawn much attention from various communities. A common strategy to realize long-distance locomotion is combining several basic gaits that are designed in advance. Considering the unavoidable uncertainties of the environment and the real locomotive system, selecting the gaits with high robustness is essential to the implementation of long-distance locomotion of tensegrity robots. However, no quantitative approach for robustness evaluation of rolling gaits is reported in recent research work. In this study, a practical and quantitative method is proposed for the robustness evaluation of rolling gaits of tensegrity robots. A mathematical model is built to describe the evaluation process, and the success rate of rolling is adopted as an indicator of robustness. Sensitivity analysis and robust evaluation are conducted on the rolling gaits of a typical six-strut tensegrity robot. Specifically, the sensitivities of the rolling gaits to five uncertain parameters (i.e. tendon stiffness, initial tendon prestress, the equivalent mass of nodes, actuation lengths of actuators, and slope of ground) are investigated and discussed in detail, and the robustness of the rolling gaits is evaluated by correlated random sampling. Experiments on a physical prototype of the six-strut tensegrity robot are carried out to verify the proposed concept and method. [ABSTRACT FROM AUTHOR]

Jiangmen Underground Neutrino Observatory central detector is located 700 m below the ground and also submerged into an ultrapure water pool. The main structure of the Jiangmen Underground Neutrino Observatory central detector is a hybrid spherical shell that is vulnerable to rotation under the buoyancy effect. The influences of the model parameters on the rotational stability of this complex and unique structure are investigated. Since the model parameters are inevitably subjected to many sources of uncertainties (e.g. manufacturing tolerances and geometrical imperfections), the parameter uncertainty is taken into account. In addition, linear and nonlinear rotational stabilities of this super-deep underground spherical structure are also under consideration. Specifically, the critical loading multiplier is used as the evaluation indicator of linear rotational stability and the load proportionality factor- θ curve is considered as the evaluation indicator of nonlinear rotational stability. The sensitivity of linear and nonlinear rotational stabilities to uncertain parameters is systematically studied in terms of univariate and multivariate global sensitivity analyses. The univariate global sensitivity analysis is able to evaluate the effects of uncertain parameters on each evaluation indicator, whereas multivariate global sensitivity analysis enables to assess the global influence of uncertain parameters on all evaluation indicators. A polynomial chaos expansion surrogate model is utilized to replace the time-consuming simulation model for analytical implementation of the univariate and multivariate global sensitivity analyses. The present polynomial chaos expansion-based univariate and multivariate global sensitivity analyses effectively and efficiently reveal the sensitivity of the rotational stability of this super-deep underground spherical structure to uncertain parameters, and provide a practical method for comprehensive sensitivity analysis of similar structures. [ABSTRACT FROM AUTHOR]

This study proposes a general framework for topology-finding or topology optimization of tensegrity structures. The existing topology-finding formulation of tensegrity structures based on mixed-integer linear programming (MILP) was improved and transformed into a formulation based on mixed-integer semidefinite programming (MISDP) which considers the global stability condition of tensegrity. We illustrated and analyzed two undesirable phenomena, loss of prestress stability and loss of integrity, caused by the missing global stability condition in previous MILP-based approaches. A branch-and-bound algorithm combined with a primal-dual interior-point algorithm is employed to solve the proposed MISDP model. Some numerical examples illustrated the improvements and effectiveness of the proposed approach. The proposed approach successfully can avoid the two undesirable phenomena and ensure the global stability of the found tensegrity structures. By using different stability conditions in the topology-finding process, the proposed approach can find general stable tensegrity structures and superstable tensegrity structures. [ABSTRACT FROM AUTHOR]

Tensegrity structure is a prestressed self-equilibrated system consisting of compressed struts and tensioned cables. Planar truss is one of the most common forms of engineering structures with a wide application. This paper proposes a new class of planar tensegrity trusses whose prototype is unintentionally found by a topology optimization algorithm. The prototype truss is composed of two basic units which are combined alternately. In this paper, the state of prestress of the truss is analytically determined from the equilibrium conditions. The stiffness and strength of the structure are analytically formulated by using the principle of virtual work. Parametric analysis of geometrical parameters on the stiffness and strength of the structure is carried out. By changing the shape of the basic units, the uniform planar tensegrity truss is extended to a fish-bellied truss. Parametric analysis is also carried out for the fish-bellied truss. An example of extending the planar tensegrity truss into a three-dimensional latticed tensegrity truss is also given. [ABSTRACT FROM AUTHOR]

To obtain the optimal uniform prestress of a tensegrity structure with geometric configuration given, a novel method is developed for prestress design of tensegrity structures by utilizing the artificial fish swarm algorithm (AFSA). In the beginning, the form-finding process is implemented by solving a linear homogeneous system concerning the self-equilibrium system. The issue is subsequently performed as a minimum problem by regulating the value of an objective function where the unilateral condition and the stress uniformity condition are entirely considered. The AFSA is adopted to search for the global minimum, leading to a set of initial prestresses that guarantee all the above conditions. Two illustrative examples have been fully studied to prove the accuracy and efficiency of the presented approach in prestress design of tensegrities according to the practical requirements. Furthermore, the numerical examples investigated in this paper confirm that the AFSA has explicit advantages of rapid convergence and overcoming the local minima. [ABSTRACT FROM AUTHOR]

A tensegrity is a self-stressed pin-jointed system consisting of tensile members and compressive members. As its shape can be actively controlled by changing the prestress of its members, it has great potential to be used as a shape-controllable locomotive system. Particularly, the six-strut spherical tensegrity has been studied intensively as a rolling locomotive system. In this study, the rolling gaits of a strut-actuated six-strut spherical tensegrity are investigated. Specifically, a mathematical model for generating the rolling gaits of locomotive spherical tensegrities is presented, and a numerical method combining dynamic relaxation method and genetic algorithm is used to solve the model. Various rolling gaits for the strut-actuated six-strut locomotive spherical tensegrity are identified using this approach. Two basic types of touching-ground triangles, two basic distributions of payload, and six cases for the numbers of used active struts are considered. Several rolling gait primitives are noted, their motion features analyzed, and a simple path-generating strategy is proposed based on idealized rolling gait primitives. A physical prototype of the strut-actuated six-strut locomotive tensegrity is manufactured, and experiments are conducted to verify the rolling gaits and locomotion paths generated by the proposed methods. [ABSTRACT FROM AUTHOR]

A new class of tensegrity footbridges based on ring modules has been proposed and studied in the recent years. This article restudies the tensegrity footbridge and puts emphasis on some issues that are questionable or need further clarification in the previous studies. New cross-sectional sizes that satisfy the given internal space requirement are used for the tensegrity ring modules. The integral feasible prestresses of the tensegrity ring modules are determined and a new classification on the groups of members is proposed. A parametric study on the effects of cross-sectional areas of members and the level of prestress on the behavior of the tensegrity footbridge is carried out. The dominated parameters on the behavior of the tensegrity footbridge are identified. An improved structural efficiency index is proposed to evaluate the efficiency of the tensegrity footbridge. The effect of the number of modules on the structural efficiency index of the system is investigated. The reliability of the new index is verified through a comparison with the index proposed by a previous study. This article provides a more comprehensive understanding on the tensegrity footbridges based on ring modules. [ABSTRACT FROM AUTHOR]

The presence of clearance in a spherical joint makes the ball of the joint easy to collide with the socket, which causes additional dynamic effects on the motion of spatial mechanisms. The complexity of interaction between different clearance joints and that between a clearance joint and connected component requires an effective analysis method. In this paper, a practical method is proposed for evaluating the dynamic effects of spatial flexible mechanisms with multiple spherical clearance joints using finite particle method (FPM) combined with a clearance contact model. First, the equations of motion of the particles and internal force formulas of spatial beam elements in the discretized FPM model are derived, and the explicit generalized- α method is adopted for time integration. Then, the contact state is detected based on the penetration depth, using the Lankanani–Nikravesh model to calculate the contact force and the Threlfall model to calculate the friction force during collision in the clearance joint. Specifically, a method considering the particle rotations is utilized to better evaluate the direction of the friction force. A spatial four-bar mechanism with spherical clearance joints is used to demonstrate the feasibilities of the proposed method. The effects of four parameters (i.e. clearance size, friction coefficient, multiple clearance joints, and bending stiffness) on the dynamic responses of the mechanism are fully investigated. [ABSTRACT FROM AUTHOR]

Soil-structure interaction (SSI) is involved in the pile-supported structures. Such effect is mainly accounted for soil-pile interaction (SPI) driven by the deformation of pile and surrounding soil, and thus it can become significantly obvious due to large soil deformation during a severe earthquake. To capture this characteristic of simply supported bridge structure with pile foundations, a three-dimensional (3D) finite element (FE) model is developed using the computational platform OpenSees considering SPI. A two-span reinforced concrete bridge with a single pier located in multi-layered clay is employed as a test-bed. A variety of seismic responses of this coupled soil-pile-bridge system are systematically investigated. Furthermore, a parametric study is performed to explore the influences of SPI, multidirectional excitation and earthquake characteristic on the seismic responses of soil and structure. The results show that: (1) the seismic response of the bridge structure is significantly affected by its longitudinal and transversal different configuration; (2) the fixed-base support type noticeably influences the seismic response of bridge structure and (3) the direction and characteristic of base input earthquake motion greatly influence the seismic response of the bridge-soil system. [ABSTRACT FROM AUTHOR]

The central detector at the Jiangmen Underground Neutrino Observatory (JUNO) is a hybrid structure system consisting of an inner acrylic sphere and an outer stainless steel reticulated shell. The stress distributions of the acrylic joints must be accurately simulated to avoid "crazing". To balance the accuracy and efficiency of the stress analysis, a multi-scale modeling method using mixed-dimensional coupling is proposed. A framework and a generalized procedure are developed to instruct the modeling and analysis. A multi-scale model consisting of a single refined acrylic joint and equipped with simplified joints is proposed and discussed. A comparison of the results using the multi-scale model with a cluster of 3 × 3 refined joints reveals that the difference is less than 5%, while the ratio of the computation resource cost and the time consumption is approximately only 1/7 and 1/5, respectively. The stress distributions of the acrylic joints in the central detector are obtained using the proposed multi-scale model. [ABSTRACT FROM AUTHOR]

A new concept of self-centering links using post-tensioned composite tendons consisting of shape memory alloy rods and steel rods is proposed. This new concept is applicable to both short and long links and is able to fully exploit the hysteresis capacity of the used shape memory alloy material. A general scheme for preliminary design of the proposed self-centering links is developed. A typical example is used to verify the proposed concept and its design scheme. A comparison between the example using composite tendons and the previously reported example using pure shape memory alloy tendons is carried out. It is found that the system using composite tendons needs less than half of the shape memory alloy material needed by the system using pure shape memory alloy tendons to possess comparable hysteresis properties meeting the given design demands. The new concept of self-centering links is applied to a typical eccentrically braced frame system to validate its feasibility and advantages in structural systems. [ABSTRACT FROM AUTHOR]

This article presents an improved approach for topology optimization of tensegrity structures. The ground structure method is used to model the topology optimization problem of tensegrity structures into a mixed integer linear programming formulation. To improve the controllability of the found tensegrity structure, the nodes, besides the members, of the ground structure are treated as optimization variables, and direct and customized controls on the must-be-used nodes and on the number of struts connecting to each node are realized. A multi-objective function combining the previously used single objectives and a new developed single objective by weight coefficients is proposed to consider the multi-requirement on different aspects of tensegrity structures. Numerical examples are carried out to verify the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, a customized wireless sensor system (WSS) for structural health monitoring is developed toward large-scale spatial structures. Spatial structures are widely used in large public buildings which generally house thousands of people, therefore the safety of the buildings is a major concern for structural engineers. One of the characteristics of spatial structures is their steel construction and the material is homogeneous throughout. So the strain is commonly the most distinct parameter to indicate status of the structure. Another characteristic of spatial structures is their large-area scale, which brings problem for traditional wired monitoring systems, so an effective wireless sensor network (WSN) for structural monitoring is in urgent demand. Considering those features, the WSS development mainly focused on the sensor selection, hardware design and network customization. In this paper, a vibrating wire sensor is selected for strain measurement because of its stable, durable and anti-electromagnetic properties. For other parameters measurement, some commercial sensor products with digital signal output are adopted. Following the principle of modularization and extendibility, the hardware design is mainly based on the realization of several functional modules. All along, energy efficiency and measurement accuracy are the core design objective. The WSN is classified into four different types of topologies from basic to complex ones. They all have the common working mechanism, namely the collected data transfers via several relay from sensor nodes to sink nodes. Different types of networks are to be customized according to the configuration and scale of different structures. Finally, two typical applications are discussed in detail to verify the feasibility of the system. It can be concluded that the customized WSS is effective and durable, and well satisfies the requirement of structural status monitoring for large-scale spatial structures. Collected data have also shown that the structural stress variation is obvious under the effect of construction process and some other factors. [ABSTRACT FROM AUTHOR]