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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]

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]

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]

• The rust layer characteristics of steel pipes are analyzed after 25-year service. • The corrosion mechanism of corroded steel pipes is elucidated after 25-year service. • The corrosion model of corroded steel pipes is assessed after long-term corrosion. • Thickness loss and max pit depth have profound effects on mechanical properties. Since the period required for testing the atmospheric corrosion of steel is long, most studies have focused on the corrosion behavior in less than three years, making exploring long-term atmospheric corrosion particularly valuable. This study investigates the corrosion behaviors, corrosion models, and mechanical properties of Q235 welded steel pipes collapsing due to corrosion after 25-year service in an urban industrial atmospheric environment using SEM, XRD, electrochemical methods, 3-D noncontact surface profilometry, and static tensile testing. The typical morphologies of α-FeOOH, γ-FeOOH, and Fe 3 O 4 and the effect of the content of various corrosive materials on the corrosion rate of the steel pipes are identified and analyzed. Then, the influence of different corrosion degrees on the mechanical properties of the steel pipes is examined by considering the morphologies of the rust pits. The results show that the wetting–drying cycles affect the structures of the rust layers and their protective properties. The rust layers on the sheltered surface are thicker but less protective than those on the exposed surface. In the wet state, FeSO 4 accelerates ion transfer, while Fe 3 O 4 facilitates electron transfer. These processes collectively contribute to the corrosion of Q235 steel. Moreover, as the time-of-wetness of the rust layers on sheltered specimens increases, the corrosion rate of Q235 steel also accelerates. The corrosion model combines pitting and uniform corrosion and gradually changes from predominated by pitting to thickness as the corrosion degree increases. The corrosion morphology impacts the mechanical properties of the welded steel pipes, and the influences of the thickness loss and maximum rust pit depth on these properties are profound. [ABSTRACT FROM AUTHOR]

• A new configuration of Geiger-type cable domes with sliding continuous ridge cables is proposed. • A general energy-based computational framework is proposed for the analysis of the structure. • The new cable dome has better construction features and feasible mechanical properties. Cable domes have been widely used in the field of structural engineering for their lightweight feature that is fit for large-span structures. Geiger-type cable domes have gained much attention due to their simple configurations. This paper proposes a modified Geiger-type cable dome with sliding ridge cables. Compared to conventional forms, the pre-stresses in the cables are more uniform, and the number of cables is fewer. An energy-based method is adopted to derive the equilibrium equations for the form-finding and load response analysis of the sliding cable system. The Levenberg-Marquardt algorithm is used to solve the non-linear equilibrium equations. A numerical example is employed to demonstrate the feasibility of the proposed structural form in terms of structural strength, stiffness, and stability. The influence of two design parameters, i.e., the force ratio of the hoop and ridge cables and the strut length, on the structural performance is investigated. In general, the new cable dome has better construction features and feasible mechanical properties and is believed to have the potential for practical applications. [ABSTRACT FROM AUTHOR]

• A compressive sampling matching pursuit (CoSaMP) algorithm was developed. • The algorithm was used to solve the restoration problem of lossy admittance signatures. • Approach validation was conducted on artificial crack identification of concrete structure. • The approach was compared with iterative shrinkage-thresholding algorithm (ISTA). • Impacts of different loss ratios on restoration accuracy were additionally discussed. • The approach showed effective damage identification using restored admittance signatures. Effective restoration of lossy data is prerequisite to guarantee the reliability of early warning information for damage diagnosis, considering large amounts of sensor data to be collected, transmitted and stored in long-term structural health monitoring (SHM) process. In this study, a compressive sampling matching pursuit (CoSaMP) algorithm was developed for solving the restoration problem of electromechanical admittance (EMA, inverse of impedance) signatures-based damage identification. Observed vectors through a random matrix projection were collected as a substitute of the EMA signatures used in conventional method, and EMA signature restorations from incomplete observed vectors were transformed into solving constrained optimization problems. Then the CoSaMP algorithm was utilized to recover EMA signatures with loss in observed vectors. Validation of the approach was conducted by a series of tests on artificial crack identification for a standardized concrete cube under laboratory conditions, which was compared with that using iterative shrinkage-thresholding algorithm (ISTA)-based algorithm. Additionally, impacts of different loss ratios on restoration accuracy were discussed. The proposed approach showed promising availability for damage identification using EMA technique encountered with lossy data. [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]

Long-term monitoring of spatial structures is of great importance for the full understanding of their performance and safety. The missing part of the monitoring data link will affect the data analysis and safety assessment of the structure. Based on the long-term monitoring data of the steel structure of the Hangzhou Olympic Center Stadium, the correlation between the stress change of the measuring points is studied, and an interpolation method of the missing stress data is proposed. Stress data of correlated measuring points are selected in the 3 months of the season when missing data is required for fitting correlation. Data of daytime and nighttime are fitted separately for interpolation. For a simple linear regression when single point’s correlation coefficient is 0.9 or more, the average error of interpolation is about 5%. For multiple linear regression, the interpolation accuracy is not significantly increased after the number of correlated points is more than 6. Stress baseline value of construction step should be calculated before interpolating missing data in the construction stage, and the average error is within 10%. The interpolation error of continuous missing data is slightly larger than that of the discrete missing data. The data missing rate of this method should better not exceed 30%. Finally, a measuring point’s missing monitoring data is restored to verify the validity of the method. [ABSTRACT FROM AUTHOR]

With the aid of self-developed wireless sensors of structural stress and temperature, long-term measurement of stress and temperature was applied to steel structure of the National Stadium. Based on the measured data, this paper analyzes the distribution of the temperature field, and according to the non-uniformity of the temperature field, the actions of temperature field consists of two parts, uniform and non-uniform. Then this paper studies the performance of the structure under temperature action, during which a comparison was made between the actions of uniform and non-uniform temperature field. With the measured data throughout a whole year, it is indicated that: 1) there is obvious difference between different parts of the structure, and also, the temperature of the structure differs from the air temperature; 2) the stress variation was notable under uniform temperature field action, and the member stress is linear to its temperature ; 3) the non-uniform temperature field makes the stress variation grow larger. At some parts such as the top chords, stress variation caused by non-uniform temperature field is larger than that caused by uniform temperature field action. [ABSTRACT FROM AUTHOR]

• The control system is designed based on the singular values of a sensitivity matrix. • The method to determine control strategy is robust to noise. • The pre-stress error is greatly reduced by adjusting a small number of members. The pre-stress errors caused by construction affect the structural performance of cable-strut structures. The pre-stress errors can be reduced by adjusting the lengths of the structural members. Previous studies did not consider the computational robustness and sparseness of adjusted elements. This paper proposes a robust approach for the pre-stress adjustment of cable-strut structures based on sparse regression. The sensitivity matrix relating the element elongations to the relative pre-stress variations is derived. The active and measured elements are selected based on the physical meaning of the singular values of the sensitivity matrix. Sparse regression is used to obtain the element elongations, and a modified orthogonal matching pursuit method is proposed to obtain the sparse solution. The effectiveness of the proposed approach is demonstrated using a typical numerical example. It shows that the proposed approach can significantly decrease the pre-stress errors by adjusting a small number of active elements and is robust to noise. [ABSTRACT FROM AUTHOR]

Tensegrity structures have been intensively studied since they appeared in the 1950s. Their applications have been extended from architecture to other areas including aerospace structures, cell mechanics, and robotics. In this paper, an interesting characteristic, the so-called multistability, is reported. A detailed investigation on a multistable tensegrity structure whose basic stable configuration corresponds to the expanded octahedron tensegrity is presented. Using an evolutionary form-finding scheme, together with the dynamic relaxation method, two other self-equilibrated configurations with higher strain energies are found. The stabilities of these configurations are verified by a matrix analysis process. Then, an investigation on the actuations and the corresponding threshold energies triggering the transformations between the different configurations is carried out. A typical set of actuation loads and the corresponding threshold energies for the state transformations are identified. The existence and the stability of the multistable configurations are verified by physical models. This study provides a theoretical basis for the further applications of multistable tensegrity structures. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the form-finding problem of nonregular tensegrities was converted into a constrained optimization problem. A genetic algorithm was used to solve this problem. Two cases of form-finding were considered. In the first case, the number of members, the rest lengths of members, the elastic moduli of members and the connectivity of members were given, and the only variables are the initial locations of nodes. In the second case, the elastic moduli of members were also treated as variables besides the initial locations of nodes. Typical examples were carried out to verify the proposed method. [Copyright &y& Elsevier]

In this paper, a three-member tensegrity structure is used as a conceptual model for the dendritic actin network in living cells. The pre and postbuckling behavior of the tensegrity is analyzed basing on the energy method. Analytical simulations are carried out on the tensegrity by using the experimentally obtained scales and mechanic properties of actin-filaments for the structural members of the tensegrity. The model exhibits a stress stiffening regime followed by a stress softening regime in the load-stiffness relationship, which qualitatively tallies with the experimentally observed response of actin networks. Due to the simplicity of the model, there is only a single compressed member and the structure buckles abruptly, which results a softening regime much steeper than that observed in the actin network. To take the member length variety into account, we propose a conceptual large-scale tensegrity system with various member lengths, and its behavior is approximately estimated by the mean response of a large number of three-member tensegrity cells with their member length varying in the range of filament lengths. The obtained mean response exhibits a much better fitness to the response of actin networks than those exhibited by the single tensegrity model. The findings reported in this paper indicate that the dendritic actin network may work as a complex tensegrity system, when it is subjected to a stress. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the planar closed loop double chain linkages consisting of a series of scissor like pairs connected by hinges. The chain is made of a serious of loop parallelograms, i.e., in the assemblies each set of four neighbouring hinges form a parallelogram. Three cases of mobile assemblies have been identified: the chains with intersecting and non-intersecting pairs as well as a mixture of both pairs. The corresponding mobility conditions are derived. Physical models were made which demonstrates that our proofs are correct. [Copyright &y& Elsevier]

Abstract: Stress fibers are contractile bundles in the cytoskeleton that stabilize cell structure by exerting traction forces on the extracellular matrix. Individual stress fibers are molecular bundles composed of parallel actin and myosin filaments linked by various actin-binding proteins, which are organized end-on-end in a sarcomere-like pattern within an elongated three-dimensional network. While measurements of single stress fibers in living cells show that they behave like tensed viscoelastic fibers, precisely how this mechanical behavior arises from this complex supramolecular arrangement of protein components remains unclear. Here we show that computationally modeling a stress fiber as a multi-modular tensegrity network can predict several key behaviors of stress fibers measured in living cells, including viscoelastic retraction, fiber splaying after severing, non-uniform contraction, and elliptical strain of a puncture wound within the fiber. The tensegrity model can also explain how they simultaneously experience passive tension and generate active contraction forces; in contrast, a tensed cable net model predicts some, but not all, of these properties. Thus, tensegrity models may provide a useful link between molecular and cellular scale mechanical behaviors and represent a new handle on multi-scale modeling of living materials. [Copyright &y& Elsevier]

Abstract: Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented. [Copyright &y& Elsevier]

Abstract: The radially retractable plate structures (RPS) are a family of new retractable structures consisting of a set of cover plates connected by revolute hinges. The concept evolves from the foldable bar structures (FBS) by replacing the beams in an FBS with cover plates. With a single degree of freedom, the structures close to form a covered enclosure and expand to reveal a large central opening space, which makes them ideal for use as retractable roofs. In designing the plates of an RPS, two primary requirements have to be met. First, the boundary of these plates must be designed such that they form an enclosure without any gaps or overlaps in both closed and open configurations, and the plates do not interfere with each other during deployment. Second, all of the pivots of a beam must remain within the boundary of its corresponding RPS plate. This paper tackles the second problem. To meet the requirement, an analytical method is proposed. A feasible design area, defined by closed and open angles of the corresponding FBS, can be identified under this approach. The designers are no longer limited to use the empirical or numerical means to determine whether all of the pivots of a multi-angulated beam are within its corresponding plate. The analytical approach can be used regardless of the boundary’s profile. The approach can be extended into both symmetrical and non-symmetrical structures. Physical models built to validate our approach have shown that the analysis is correct. [Copyright &y& Elsevier]

Abstract: This paper proposes a force method based structural analysis algorithm for geometrically non-linear bar assemblies. Like the linear force method, the method is suitable for both statically and kinematically indeterminate assemblies, which have been widely used in non-traditional structures such as tension structures and tensegrities. The geometrically non-linear force method is able to produce much more accurate solutions when the infinitesimal mechanisms exist in the assembly, which has been illustrated by a number of examples. [Copyright &y& Elsevier]

Abstract: A new form of space structure, polyhedron frames, was developed recently. In polyhedron frame structures, most structural members are under multi-loads of compression, bending and torsion. A new type of tapered member that is obtained by axially connecting a constant-section tube to two tapered and relatively short tubes was proposed to be the structural member of polyhedron frame structures. We named this kind of tapered member a tapered-end tube. This paper has analytically and experimentally proved that tapered-end tubes can restrict the plastic hinge to the interface of the constant-section part and the tapered part, and the location of the plastic hinge can be arranged by correctly choosing the ratio of slope of the tapered ends. Corresponding tests and simulations are done to verify the analytical prediction, and these also reveal that the strength of the tubes is significantly improved by the tapered ends. [Copyright &y& Elsevier]

Abstract: By axially connecting a constant-section circular tube to two tapered circular tubes, a so-called circular tube with tapered ends structural member is obtained. To get the element stiffness matrix of a tube with tapered ends, a transfer matrix method is introduced in this paper. Transfer matrices for the constant-section tube and tapered tubes are derived firstly, and then the element stiffness matrix for a tube with tapered ends is obtained on the basis of the relationship of the transfer matrices. Two typical examples are given to verify the element stiffness matrix. And the stiffness matrix for a tube with tapered ends can be treated as a modification of the stiffness matrix for a constant-section tube. Stiffness modified coefficients are introduced to represent the modification, and a table of stiffness modified coefficients for tubes of frequently used dimensions is given at the end of the paper. [Copyright &y& Elsevier]

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]

• A Lorentz force-based SH-typed EMAT was developed and systematic tested. • A specially design of the flexible circumferential printed circuit was presented. • The designed CPC-EMAT is easy to be assembled and fabricated in real application. • It can generate omnidirectional SH 0 waves with desirable central frequencies. Structural health monitoring (SHM) of in-service structures is becoming increasingly important. The fundamental shear horizontal (SH 0) guided wave mode in plate-like structures shows great potential in damage detection due to its non-dispersive and in-plane vibration properties. In order to generate SH 0 waves, a practical Lorentz force-based electromagnetic acoustic transducer (EMAT) was introduced in this study using the flexible circumferential printed circuit (CPC). The designed principle of CPC-EMAT was similar to that of the circumferential magnet array (CMA)-based EMAT. However, the structure of the CMA-EMAT is complex, and it is difficult to assemble for generating high frequency and uniformly distributed omnidirectional SH 0 waves. Firstly, the performance of the CMA-EMAT with different numbers of magnets was investigated by finite element simulations. Then, the CPC was proposed to replace the CMA with an optimized designed on its size. The CPC-EMAT is easier to fabricate compared to the CMA-EMAT. Finally, experimental tests were conducted for systematic validations on the transducer properties. Simulation and experimental results show that the CPC-EMAT can successfully generate the desirable and acceptable omnidirectional SH 0 waves. The proposed CPC-EMAT is anticipated to find widespread application in SH-typed guided wave-based SHM. [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]

Passive dynamic control with integrated dampers is an efficient strategy for the vibration of a cable-strut system. Except the rigid components, the flexible components are also a triable direction as the integrated damper, especially for the continuous cable systems. This paper proposes a novel dynamic control method for pre-stressed cable systems by using frictional sliding cables. Firstly, a simplified dynamic simulation method is introduced. The friction of sliding cables can be considered in the dynamic analysis of a continuous cable system. Secondly, two numerical examples with sliding cables including the types of Levy and Geiger are established. The results show that frictional sliding cables can reduce the structural dynamic response. Thirdly, a dynamic experiment of a Geiger-type cable dome with sliding ridge cables is carried out. The acceleration of the structure during vibration is recorded and compared with the results of the conventional configuration. The dome with sliding cables exhibits higher damping ratios, indicating superior vibration reduction capabilities. The frictional energy dissipation of this study can be taken as a dynamic control strategy for continuous cable structures during the design and analysis process. • A novel dynamic control method for pre-stressed cable systems is proposed. • An improved method for the dynamic analysis of frictional continuous cables is developed. • A physical model experiment of a Geiger-type cable dome with sliding ridge cables is built. [ABSTRACT FROM AUTHOR]

• Propose a form-finding approach with given cable forces and strut lengths. • Transform the form-finding problem to a stationary point problem. • Define an intermediate function to solve the stationary problem. This paper presents a form-finding method for cable-strut structures with given cable forces and strut lengths. The topology of the structure, the internal force distribution of cables and the rest length of struts are given in advance. A total potential energy function in terms of nodal coordinates is derived according to the initial conditions. The equilibrium configuration satisfying the given initial conditions is essentially a stationary point of the energy function. An intermediate function is proposed and used to solve the stationary point problem. A configuration expected by the designer can be obtained when proper initial nodal coordinates are used. The effectiveness and practicability of the proposed method are verified by two typical examples. [ABSTRACT FROM AUTHOR]

Summary: Identification of earthquake ground motion from structural health monitoring (SHM) data provides a good means to reconstruct seismic loads that are essential for postearthquake safety assessments and disaster simulations of structures. Because the data measured by an SHM system are structural absolute response, they cannot be directly applied to the structural motion equation, which is established in relative coordinate system. As such, this paper originally derives the motion equation in absolute coordinate system and then expands the equation into modal space. In addition, the proposed method allows for identifying earthquake ground motion using incomplete modal information and limited measurements through the standard Kalman filter. Subsequently, a numerical two‐dimensional frame is used to validate the feasibility of the proposed method, and the influences of modal parameters and measurement noise on the identification accuracy are also fully investigated. The results show that the proposed method is sensitive to frequency and measurement noise but insensitive to modal shape and damping ratio. It is also found that the identified ground motion subjected to certain measure noise can still be reliably employed for postseismic response calculations of medium‐ and long‐period structures. Finally, a shaking table test performing on a five‐floor frame further demonstrates the effectiveness and accuracy of the proposed identification algorithm for practical application. [ABSTRACT FROM AUTHOR]

The main structure of the central detector at the Jiangmen Underground Neutrino Observatory (JUNO) is a spherical shell structure, which has a giant acrylic spherical shell connected to a stainless-steel (SS) reticulated shell with 590 SS rods. The acrylic spherical shell is submerged into water and filled with detection liquid and prone to rotation subjected to considerable buoyancy. The stability against rotation of this super-deep underground spherical shell structure needs to be fully investigated. In this study, an effective and practical method consisting of parametric analysis and optimization procedure is proposed to improve the stability against rotation. Specifically, two indicators, namely, the critical loading multiplier and the rotation angle, are proposed to evaluate the stability against rotation of the acrylic spherical shell in linear and nonlinear stability analyses, respectively. Then, parametric analysis is performed to assess the sensitivity of the stability against rotation to four parameters of interest (i.e., rod outer end constraints, liquid level difference, disc spring stiffness, and rod deviation). Based on the obtained parametric analysis results, the liquid level difference and disc spring stiffness are finally selected as design variables for the subsequent optimization process to further improve the stability against rotation. An efficient scheme combining design variable discretization and exhaustive method is adopted to identify the optimal variable values at which the acrylic spherical shell has good stability against rotation. The results indicate that the proposed method is efficient and effective for optimization of stability against rotation of such super-deep underground spherical shell structure. The proposed method is practical and easy to use for structural designers, and provides an efficient approach to the stability design of such rod-connected spherical shell structures. • An effective method is proposed to improve the stability against rotation of an underground spherical shell structure. • Two indicators are proposed to evaluate the stability against rotation of the spherical shell structure. • Influence of the parameters on the stability against rotation is fully investigated to choose the important parameters. • An efficient scheme combining design variable discretization and exhaustive method is adopted for optimization. [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]

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]

A novel type of reticulated shell structure composed of built-up plate members has been proposed based on its benefits in efficiency and precision of fabrication, as well as convenience of storage and transportation. This study aims to investigate the stability behavior of such structures by conducting numerical simulation analysis. The configuration of the structure is illustrated at first. Then, a validated numerical model is presented for parametric studies on two typical structural forms. Next, geometric nonlinear analysis is conducted, demonstrating the symmetrical characteristic of failure modes, and the results are utilized to develop practical prediction formulas for the elastic buckling load. Finally, material and geometric nonlinear analysis is performed to examine the impact of parameters on structural stability performance. The sensibilities of the material nonlinearity, geometric dimension, geometric imperfection, and joint stiffness on the structural stability are illustrated. This study provides insights into the instability mechanism of such structures and offers valuable guidance for their design and application. • A novel type of reticulated shell structure composed of built-up plate members. • Presented numerical models are validated by experimental data. • The structural stability behavior and influencing factors are revealed. • Practical prediction formulas for the elastic buckling load are developed. [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]

This study presents a general approach to the topology design of tensegrities with rigid bodies. To the best of the authors' knowledge, all existing topology design methods of tensegrities focus on tensegrities that only consist of members carrying axial forces, which are referred to herein as classic tensegrities. However, another category of tensegrities, referred to as general tensegrities, contains rigid bodies aside from axially loaded members. The equilibrium and stability conditions of general tensegrities are different from those of classic tensegrities because of the existence of rigid bodies, which makes the existing topology design methods invalid for general tensegrities. In this study, the equilibrium and stability conditions of general tensegrities are first derived. A topology design approach for general tensegrities is then proposed based on a mixed-integer linear programming optimization scheme. The topology (i.e., member connectivities) is treated as a binary variable, and the member forces are treated as continuous variables. Three essential attributes, namely self-equilibrium, unilateral member force, and class- k condition, of a general tensegrity, as well as some other practical requirements, are formulated as constraints. Different objective functions are employed to design different general tensegrities. Some well-known general tensegrities are reproduced, and various numerical examples are presented to verify the effectiveness and versatility of the proposed approach. The proposed topology design method is verified to be a truly general approach for the topology design of tensegrities with or without rigid bodies. [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 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]

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]

An optimization approach based on force density method and mixed integer nonlinear programming is proposed for optimization of tensegrity structures on member connectivities and nodal positions. The member connectivities, nodal coordinates and force densities are simultaneously used as design variables and the number of nodes is the only necessary parameter needed to be given in advance. The proposed approach possesses a general-purpose formulation which can be degenerated into both conversional form-finding formulation and previous member connectivities-finding formulation. Various properties such as the number of cables, nodal coordinates and evenness of member internal forces can be controlled and optimized by introducing appropriate constraints and objective functions. Numerical examples are carried out to verify the proposed approach and illustrate that not only classical tensegrity systems but also novel tensegrity systems can be obtained by the proposed approach. [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]

Reconstruction, according to physical shape, is a novel way to generate free-form grid truss structures. 3D scanning is an effective means of acquiring physical form information and it generates dense point clouds on surfaces of objects. However, generating grid truss structures from point clouds is still a challenge. Based on the advancing front technique (AFT) which is widely used in Finite Element Method (FEM), a scheme for generating grid truss structures from 3D scanned point clouds is proposed in this paper. Based on the characteristics of point cloud data, the search box is adopted to reduce the search space in grid generating. A front advancing procedure suit for point clouds is established. Delaunay method and Laplacian method are used to improve the quality of the generated grids, and an adjustment strategy that locates grid nodes at appointed places is proposed. Several examples of generating grid truss structures from 3D scanned point clouds of seashells are carried out to verify the proposed scheme. Physical models of the grid truss structures generated in the examples are manufactured by 3D print, which solidifies the feasibility of the scheme. [ABSTRACT FROM AUTHOR]

In the past decades, the form-finding of tensegrity structures of regular geometric shapes, such as cylindrical tensegrities, polyhedral tensegrities, spherical tensegrities and so on, has been systematically studied. However, seldom studies on the form-finding of tensegrity tori have been reported. Considering the potential applications of the tensegrity tori in a number of fields, including architecture, sculpture, and other relevant fields, this paper carries out an exploration on a new kind of tensegrity tori. The topology of the new kind of tensegrity tori is based on the well-known cylindrical tensegrities and overlapping between every two adjacent tensegrity modules is allowed. Incorporating the singular value decomposition of equilibrium matrix with a force-finding algorithm, a general procedure for determining the feasible configurations for the new kind of tensegrity tori is proposed. Parametric analyses on several typical forms of the tensegrity tori are conducted and the feasible ranges of the design parameters and applicability of the feasible configurations are discussed. [ABSTRACT FROM AUTHOR]

Vibration data from physical systems, such as civil structures and machinery, often carries important information about the dynamic characteristics, but streaming acquisition of higher-frequency vibration often accrue large volumes of data, resulting in data transmission and storage challenges. Compressive sensing (CS) is a relatively newly-developed technique for efficient data representation, capable of reconstructing the target signal using only a few random measurements through sparse optimization. However, the real-world application of CS is hindered by the strong assumption of signal sparsity and a costly reconstruction process. In this work, we propose a novel deep learning method for vibration data reconstruction by using deep convolutional generative adversarial networks (DCGAN), which is composed of a generator G and a discriminator D. A modified 1D symmetric U-net architecture with shortcuts is presented for G to flexibly deal with different inputs, while a typical 1D classifier is used as D. A composite adversarial loss function is proposed considering errors in both time and frequency domains. The proposed DCGAN approach has several appealing properties. First, it directly learns the end-to-end mapping between the compressed and original signals without employing the sparsity assumption or random sampling, which fundamentally differs from existing sparsity-based CS methods. Second, the reconstruction process is highly computationally efficient as the network is fully feed-forward and no optimization is needed during data reconstruction. The proposed DCGAN approach is evaluated using the simulation data from a numerical 9-floor frame as well as experimental data collected from a large test steel grandstand. The results demonstrate the superiority of the proposed DCGAN in computational accuracy and efficiency compared to the tested sparsity-based algorithms. Furthermore, the influences of network configurations (network depth, down-sampling strategy, and shortcuts) are comprehensively explored. • A novel CS approach is proposed for vibration data reconstruction using DCGAN. • The DCGAN can reconstruct vibration data without employing sparsity assumption. • The proposed feed-forward network is highly computationally accurate and efficient. • The DCGAN is evaluated using simulated and experimental data, respectively. • The influences of network configurations are comprehensively explored. [ABSTRACT FROM AUTHOR]

• A generalized objective function is proposed for tensegrity topology-finding. • Different tensegrities can be found via adjusting the weight coefficients. • A circular computing strategy is proposed to efficiently obtain various tensegrities. • Novel tensegrity structures based on common Archimedes polyhedrons are given. This paper proposes a generalized objective function for the topology-finding of tensegrity structures to be able to assign selection priorities to different members and efficiently find multiple tensegrity structures through a single ground structure. The generalized objective function is constructed by the sum of the product of member internal forces and weight coefficients. The member weight coefficients can be defined and adjusted freely to change the selection priorities of different members in the topology-finding process. By adjusting the weight coefficients, different tensegrity structures can be generated. The weight coefficients can be determined by the designer according to the practical design requirements and preferences, e.g., member length limitations, member position requirements. In addition, a circular computing strategy is proposed for the weight coefficient adjustment to efficiently obtain a large number of tensegrity structures through a single ground structure. The topology design of typical regular tensegrity structures, as well as irregular ellipsoid tensegrity structures, are carried out to demonstrate the effectiveness of the proposed method. Furthermore, by using the proposed method, multiple novel tensegrity structures based on common Archimedes polyhedrons have been found; detailed information (e.g., member connectives, self-stress) are given as an open database for future investigation and applications. [ABSTRACT FROM AUTHOR]

Conventional eccentrically braced frames dissipate seismic energy through plastic deformation of link beams. However, large residual deformation after strong earthquakes often makes the damaged structure necessary for costly repair. This paper proposes a self-centering eccentrically braced frame system which incorporates shape memory alloy bolts and post-tensioned high strength steel tendons to provide a self-centering response behavior with moderate energy dissipation. An analytical model which has taken into account the super-elastic constitutive of shape memory alloys and the changing contact condition at the link-beam interface is formulated to predict the cyclic load behavior of the system. The feasibility of the proposed concept is demonstrated by cyclic load analysis of a prototype self-centering eccentrically braced frame. Finite element simulations are carried out to verify the analytical model and to further investigate the effects of the configuration details of the link-to-beam connection to the cyclic performance of the self-centering EBF system. [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]

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]

Link beams in seismic resistant structures are usually designed to undergo severe plastic deformation to provide required ductility and energy dissipation on the occurrence of strong seismic events. The plastic deformation of link beams results in permanently deformed structures that are costly to repair after the earthquake. To reduce permanent deformation of link beams, a new concept of self-centering link beam using post-tensioned shape memory alloy rods to simultaneously provide re-centering force and energy dissipation capacity is proposed. It has two basic configurations and is modularized for the ease of fabrication and erection. An analytical model that is able to predict the cyclic loading behavior of the self-centering modularized link beam is presented. Based on the analytical model, parametric studies are carried out to investigate the effects of design parameters on the performance of the self-centering modularized link beam and also to show the performance range of the self-centering modularized link beams under given ranges of design parameter values. Typical examples are presented to demonstrate that the proposed self-centering link beam can be designed to exhibit performance comparable to that of conventional link beams in addition to re-centering capability. [ABSTRACT FROM AUTHOR]