Structural Engineering Practice Research Articles

The effect of viscous drag on damped simple harmonic motion

Dynamic viscosity is a quantity that describes the magnitude of a fluid’s internal friction or thickness. Traditionally, scientists measure this quantity by either calculating the terminal velocity of a falling sphere or the time a liquid takes to flow through a capillary tube. However, they have yet to conduct much research on finding this quantity through viscous damped simple harmonic motion. This phenomenon occurs when the movement of an oscillator experiencing Hooke’s law dissipates at a rate defined by the damping coefficient due to a fluid’s external drag force. The present study hypothesized that the relationship between the dynamic viscosity and the damping coefficient is positively correlated. To test this hypothesis, we computed the dynamic viscosities of glycerol-water mixtures of varying mass concentrations and filmed the oscillations of a vertical-spring mass system in each of these mixtures. We then determined the system’s damping coefficients through Vernier’s Logger Pro video analysis feature and implemented inferential statistics on a regression between these damping coefficients and the mixtures’ dynamic viscosities. The results through these methods demonstrated not only compelling evidence in favor of this hypothesis but also an alternative way to estimate a fluid’s dynamic viscosity through a least-squares regression line. With future experimentation, these results can help prepare shock absorbers for vehicle and structural engineering practices.

Efficient inner-outer decoupling scheme for non-probabilistic model updating with high dimensional model representation and Chebyshev approximation

Interval arithmetic offers a powerful tool for structural model updating when uncertain-but-bounded parameters are considered. However, the application of interval model updating for practical engineering structure is hindered due to model complexity and huge computational burden involved in the repeated evaluations of non-probabilistic constraints. In this light, an efficient inner-outer decoupling scheme is proposed for non-probabilistic model updating in this study. The mathematical operation of interval model updating is decomposed into two layers labelled as inner layer with the operation of uncertainty propagation and outer layer with the operation of interval optimization. In the inner uncertainty propagation, the High Dimensional Model Representation (HDMR) is utilized to enable the decomposition of the model outputs in terms of multivariate inputs into the sum of multiple single-variate functions, which is further approximated by Chebyshev polynomials so that the stationary points of each function can be derived. In the outer layer, a fast-running optimization strategy based on the stationary points of Chebyshev polynomial approximation is proposed to accelerate tracking the bounds of model parameters by avoiding time-consuming brute-force interval optimization. As a result, the original non-probabilistic updating process with two interacted layers can be completely decoupled into two independent operations of the inner uncertainty propagation and outer interval optimization so as to enhance the search efficiency and convergence rate significantly. Two numerical case studies illustrate capability of the proposed method in updating the structural parameters intervals efficiently with the model outputs intervals agreeing well with the testing outputs intervals. Two experimental cases of steel plates and the Canton Tower also demonstrate the efficiency and advantages of the method in interval model updating.

Uneven distribution of interfacial bond stress in steel fiber-reinforced concrete-encased steel composite structures

To solve the congestion of reinforcement and the difficulty of concrete pouring in concrete-encased steel (CES) structure, steel fiber-reinforced concrete-encased steel (SFRCES) structure was proposed. Push-out tests of 34 SFRCES specimens were carried out in this paper to study the interfacial bond stress distribution, and load-displacement curves were obtained. The interfacial ultimate bond strength calculated based on load-displacement curve is much greater than 0.2 MPa which is the interfacial design shear strength of composite steel and concrete structure in Eurocode 4. This illustrates that the design of SFRCES structure is partial to safety. Furthermore, different from the previous method using the assumption of uniform distribution of interfacial bond stress, the interfacial local bond stress was obtained based on strain data and mechanical derivation in this paper. Moreover, the influence of steel fiber volume rate, embedded length of steel, and thickness of concrete on the distribution of interfacial bond stress was analyzed by defining the uneven coefficient of interfacial bond stress distribution. Analysis results provide a theoretical basis for the design of SFRCES structure and lay a foundation for the application of SFRCES structure in practical engineering.

Safety and stability analysis of variable cross-section disc-buckle type steel pipe high support system

In order to solve the problems of poor safety and difficult determination of construction scheme in the construction process of variable cross-section disc-buckle type steel pipe high support system, based on the stress state of the normal working of the disc-buckle type formwork support, the stability bearing capacity of vertical poles under three working conditions of central pole, side pole and corner pole were experimentally carried out, and the correctness were verified by comparing with the results of the experiment and finite element analysis. Based on the verified finite element model and the characteristics of semi-rigid connection joints, the first-order buckling mode and nonlinear buckling analysis of the stability bearing capacity of the variable cross-section disc-buckle type steel pipe high support system were carried out in the construction period with special structure in practical engineering, the stability bearing capacity and deformation law of the variable cross-section disc-buckle type steel pipe high support system in the construction process were mastered. Through parametric analysis of the influencing factors such as the joint bending stiffness, the setting parameters and the initial imperfections, the influence law of the relevant parameters on the overall stability of the variable cross-section disc-buckle type steel pipe high support system was grasped. The results showed that the corner poles at the higher variable section and the lower variable section of the weak stiffness direction support system were prone to instability and failure. The overall stability bearing capacity was mainly affected by the lift height. The vertical diagonal bracing plays an important role in improving the overall stability, the larger the lift height was, the more obvious the improvement was. The overall stability bearing capacity decreases with increasing top extension length, and the top extension length should be controlled within 0.45 m. When the extension length of the top was greater than 0.45 m, the initial imperfection cannot control the overall stability bearing capacity, and the overall structural stability bearing capacity was determined by the buckling behavior of the top vertical pole. When the joint bending stiffness was greater than 2.0 K, the stability bearing capacity does not change. The higher the support system was, the smaller the influence of joint bending stiffness on the overall stability was.

Wave motion of spinning periodically multi-stepped pipes — Dynamics of a novel motional 2D phononic crystal structure

With the rapid development of processing technology, phononic crystals (PCs) have been gradually applied from conceptual model to practical engineering structure. In this paper, a novel motional two-dimensional (2D) PC structure — spinning periodically multi-stepped pipes is proposed. Due to the spinning motion, there will be two flexural waves respectively in the orthogonally transverse directions, forming such a planar PC structure. Considering a constant internal flow, the wave propagation and self-attenuation characteristics of the system are explored. Improved spectral element method and transfer matrix method are applied to treat such spatial wave motion. Based on the attained band structure in conjunction with the frequency response and wave shape, a significant mechanism is revealed that for a spinning periodically multi-stepped pipe conveying fluid, there are two sets of pseudo band gaps (BGs) generated owing to the gyroscopic effect, which do not exist in a static PC structure. However, the effective BG regions, where both the flexural waves truly attenuate, are actually located in their coincident frequency areas. Furthermore, the effects of number and geometry of sub-segments and motional parameters on the BG are discussed in detail. The present research will develop the PC dynamics in motional structures, and provide an in-depth theoretical basis for vibration suppression of engineering pipe system.

Research on Mechanical and Carbonization Properties of Hybrid Fiber Iron Tailings Concrete Based on Deep Learning.

Iron tailings sand is a kind of mineral waste, and open-air storage is a common treatment method for iron tailings, which not only has a huge impact on the ecological environment but also occupies a lot of land resources. Therefore, the preparation of high-ductility fiber reinforced iron tailings concrete and its application in practical engineering structures have good application prospects. This paper is based on the deep learning research on the mechanical and carbonization properties of hybrid fiber iron tailings concrete. Therefore, tailings sands with different substitution rates, single-mixed steel fiber, and mixed steel-PVA fiber concrete were prepared in this paper. Its compressive strength, split tensile strength, axial compressive strength, elastic modulus, strain, and carbonization depth were tested. Through the existing concrete compressive stress-strain curve equations, the nonlinear calculation of each group of concrete compressive stress-strain curve equations in this paper is carried out, some parameters are determined, and the carbonation depth equation is established. The results show that, with the increase of tailings content, the properties of concrete increase first and then decrease and the addition of fibers can effectively improve the strength, elastic modulus, peak strain, and carbonization depth of concrete. However, with the increase of PVA fiber content, its performance enhancement effect decreased.

Modal Parameter Estimation of Tall Structures using HHT with Improved EMD

In this paper, identification of the natural frequencies, damping ratios and mode shapes of the structures using the measured ambient responses are proposed using time-frequency analysis. The impulse responses are obtained from the measured acceleration time history data through cross-correlations. Empirical Mode Decomposition (EMD) is employed on these generated impulse responses to obtain Intrinsic Mode Functions (IMFs). Finally, modal identification of the structure is carried out by performing Hilbert Transform (HT) on these generated IMFs. To avoid the problem of mode mixing during EMD of the signal, an improved version with intermittency criteria along with treatment to end effects during sifting is proposed in this paper. Experimentally measured data of Guangzhou New TV (GNTV) Tower is used to test and verify the proposed algorithm. The studies indicate that the proposed HHT based algorithm can be applied quite effectively for the modal identification of practical engineering structures.

An improved fatigue life prediction model based on loading sequence

PurposeIn view of the difficulty in determining the key parameters d in the Corten-Dolan model, based on the introduction of small loads, damage degrees and stress states to the Corten-Dolan model and the existing improved model, the sequential effects of the adjacent two-stage load were further considered.Design/methodology/approachTwo improved Corten-Dolan models were established on the basis of modifying the parameter d by two different methods, namely, increasing stress ratio coefficient as well as considering the effects of loading sequence and damage degree as independent influencing factors respectively. According to the test data of the welded joints of common materials (standard 45 steel), alloy materials (standard 16Mn steel) and Q235B steel, the validity and feasibility of the above two improved models for fatigue life prediction were verified.FindingsResults show that, compared with the traditional Miner model and the existing Corten-Dolan improved model, the two improved models have higher prediction accuracy in the fatigue life prediction of welding materials whether under two-stage load or multi-stage load.Originality/valueBecause the mathematical expressions of the models are relatively simple and need no multi-layer iterative calculation, it is convenient to predict the fatigue life of welded structure in practical engineering.

Evaluation of the fresh and mechanical properties of nano-engineered self compacting concrete containing graphite nano/micro platelets

The graphite nano/micro platelets (GNMPs) offer distinct features for the effective reinforcement of cementitious matrices in the behaviors of concrete. The thoroughly dispersed and well-bonded nanomaterials provide effective control of the size and propagation of defects (microcracks) in the matrix and also act as closely spaced barriers against diffusion of moisture and aggressive solutions into the concrete. Graphite nanomaterials can play multi-faceted roles in enhancing the mechanical and physical attributes of concrete materials. The GNMPs have to exhibit enhanced mechanical and other functionalities to be suitable for emerging structural applications. Although GNMPs improved some of the mechanical performance of concrete but less information is available particular the influence of (GNMPs) in self-compacting concrete (SSC). Therefore, in this research an innovative nano-engineered self-compacting concrete was prepared using 0.1%, 0.2%, 0.3%, 0.4% and 0.5% GNMPs. The rheological properties were assessed through slump flow, v funnel, v funnel at T5 minute, L box test while mechanical performance was assessed through compressive and tensile tests. The microstructural properties of the self-compacting concrete (SSC) with GNMPs were investigated through Scanning Electron Microscopy (SEM). The results indicate that the filling and passing ability of SCC improved with GNMPs. Furthermore, 0.3% addition of GNMPs shows 42% and 21.3% enhancement in compressive and tensile strength as compared to reference concrete respectively. Overall, the study demonstrated the effectiveness of GNMPs in SCC and may be applied in practical structural engineering applications.

Reliability‐based topology optimization of continuum structure under buckling and compliance constraints

AbstractBuckling failure mainly occurs in slender rod structure under pressure, which incurs great concern and should be addressed in topology optimization (TO). However, due to the internal defects of material and the external environment interference of engineering system, the practical engineering structure inevitably produces many uncertain factors in the manufacturing and service stages. Therefore, a reliability‐based topology optimization (RBTO) model under buckling and compliance constraints is established to operate the structural lightweight design considering reliability and stability requirements. To reduce the number of probabilistic constraints, the Kreisselmeier–Steinhauser aggregation function is adopted for combining the multiple constraints into a single smooth and differentiable constraint. Then, a single‐loop approach combining modified chaos control strategy is applied to guarantee the robustness, effectiveness, and computational efficiency of RBTO. In addition, the sensitivities of the probabilistic constraint with respect to design and random variables are deduced, and the accuracy of sensitivities is verified by finite difference method. Finally, the validity of the RBTO method is verified by comparing with deterministic TO, in which three numerical examples are employed to demonstrate the robustness and computational accuracy.

Numerical prediction based on XFEM for mixed-mode crack growth path and fatigue life under cyclic overload

The numerical prediction based on the extended finite element method (XFEM) is carried out in this paper, where the mixed-mode crack propagation process is simulated accurately and the fatigue life considering the cyclic overload effect is calculated conveniently by using the proposed novel method. In this method, a simple crack surface updating strategy that can simulate the through-thickness crack in a three-dimensional structure is proposed, and it replaces the complex level set updating algorithm. Meanwhile, the cycle-by-cycle method for overload fatigue life is also proposed. The prediction is implemented based on the ABAQUS software by Python codes and the corresponding functional modules are developed. Compared with the built-in crack propagation modules of XFEM in ABAQUS, the method in this paper contains the complete crack tip enhancement functions and presents strong robustness in computational convergence and excellent calculation efficiency. The accuracy in calculating stress intensity factors (SIFs) and predicting mixed-mode crack growth paths is verified through examples. In addition, the fatigue life under cyclic overload is also predicted accurately by the developed modules. The effects from different parameters of load spectrum with overload are obtained according to the numerical results. Moreover, combined with the shell-to-solid coupling method, the large and complex practical engineering structure is simulated and analyzed in detail.

ANN-based Lagrange optimization for RC circular columns having multi-objective functions

Structural engineers must encounter multi-objective optimization (MOO) problems in designs including a design of reinforced concrete (RC) columns, where several design objectives must be satisfied to meet contractors’ interests and produce a sustainable design. MOO applications in structural engineering practice are uncommon despite their high demand. Multi-objective population methods have been mainly investigated. However, previous studies have mostly neglected the stopping criteria and convergence of these algorithms. This study proposes a novel gradient-based algorithm - ANN-based Lagrange optimization and its implementation in designs of circular reinforced concrete columns where three objectives, such as cost, CO2 emissions, and column weight, are minimized simultaneously. This study integrates each single-objective function extracted from an artificial neural network (ANN) into a global Lagrange function, a unified function of objectives (UFO), using the tradeoff-fractions. Lagrange multiplier method is adopted to deal with constrained conditions by using Newton–Raphson iteration to solve Karush-Kuhn-Turker (KKT) conditions. The proposed algorithm brought in a set of optimal results capturing multiple objectives, known as a Pareto frontier, which is compared with those obtained using the Nondominated Sorting Genetic Algorithm – II (NSGA-II), showed that two algorithms calibrated to each other. Overall, the ANN-based Lagrange optimization algorithm exhibited better convergence than NSGA-II.

Tensile Performance of Headed Anchors in Steel Fiber Reinforced and Conventional Concrete in Uncracked and Cracked State.

Steel fiber reinforced concrete (SFRC) is currently the material of choice for a broad range of structural components. Through the use of SFRC, the entire, or a large portion of, conventional rebar reinforcement can be replaced, in order to improve the load-bearing behavior but also the serviceability and durability characteristics of engineering structures. The use of fiber reinforcement therefore plays a vital role in acute current and future construction industry objectives, these being a simultaneous increase in the service life of structures and the reduction of their environmental impact, in addition to resilience to extreme loads and environmental actions. Next to the extended use of SFRC, modern construction relies heavily on structural connections and assembly technologies, typically by use of bolt-type cast-in and post-installed concrete anchors. This paper addresses the influence of fiber reinforcement on the structural performance of such anchors in SFRC and, particularly, the load bearing behavior of single headed anchors under axial static loads in uncracked and cracked concrete. Along with a presentation of background information on previous studies of SFRC with a focus on anchor concrete breakout failure, the experimental investigations are described, and their results are presented and elaborated on by consideration of various research parameters. A comparison with current design approaches is also provided. The conclusions are deemed useful for structural engineering research and practice.

Various damper forces and dynamic excitation nonparametric identification with a double Chebyshev polynomial using limited fused measurements

By introducting a double Chebyshev polynomial as a general nonparametric model for various nonlinear restorying forces (NRFs) and an updated observation equation, and with the help of an Updated Extended Kalman filter with unknown input (UEKF-UI) algorithm and a data fusion technology, a nonparametric identification approach for both NRFs at multiple locations and excitation for multi-degree-of-freedom (MDOF) lumped mass structures is presented. In order to investigate the generality of the proposed identification method, both numerical and experimental studies on different MDOF structure models equipped with a shape memory alloy (SMA) damper and/or a magnetorheological (MR) damper mimicking different types of nonlinearities that widely exist in practical engineering structures under unknown excitation are carried out. Identification results considering different initial estimation errors and measurement noise show that the NRF provided by different types of dampers at multiple locations, excitation and unmeasured dynamic responses can be identified nonparametrically with acceptable accuracy.

Stress state of hydrotechnical facilities resistant to natural disasters

The equations of the theory of the stress-strain state of an elastic body for practical engineering structures of the agro-industrial complex do not have analytical solutions. Therefore, the development of numerical methods for determining the strength parameters of agricultural facilities is an urgent task. Among the numerical methods of strength calculations, the finite element method is currently widely used. In a Cartesian coordinate system, a finite element of a hexahedral shape is used to determine the stress-strain state of an elastic body under bulk loading in two formulations: in the formulation of the method of displacements with nodal unknowns in the form of displacements and their derivatives, and in a mixed formulation with nodal unknowns in the form of displacements and stresses. Approximation of displacements through nodal unknowns in obtaining the finite element stiffness matrix was performed using a form function, the elements of which were Hermite polynomials of the third degree. When obtaining the deformation matrix, displacements and stresses of the internal points of the finite element were approximated in terms of nodal unknowns using bilinear functions. The calculation example shows a significant advantage of using a finite element in a mixed formulation.

Simultaneous outline shape and size optimization for stiffeners in practical engineering structures

This article presents an engineering method to optimize the stiffener outline shape and cross-sectional sizes simultaneously for stiffened plate structures. A new optimization model for stiffened plate is established, and a hierarchical algorithm including external and internal optimization module is proposed to tackle the shape and size variables respectively. In external optimization, genetic algorithm (GA) is utilized to optimize binary-coded shape variables, and when calculating individual fitness values in GA, an internal optimization only involving size variables is carried out. For each individual, the stiffener outline shape is determined by a given shape variable vector and a reasonable finite element model could be automatically built with a parametric modeling method. The solution of internal optimization problem can be obtained by size optimization method, and an offset vector which updates during each cycle is created to modify the relative position of plate and stiffeners, ensuring the practicality of the optimal results in engineering. The presented approach is firstly verified through a typical example and then it is applied to the structural design of a micro-satellite. The results show that the method is effective in dealing with the simultaneous outline shape and size optimization problem of stiffeners, and the optimal results could be directly applied in practical engineering structures.

Simultaneous Multi-Objective Optimal Sizing of Energy Dissipative Steel Cushions for Transversal Loading

Current practice in structural engineering requires dissipating some part of seismic energy by sacrificial elements rather than structural members and/or joints. As an easy-to-produce and plug-and-play damper with stable hysteretic loops and large displacement capacity, steel cushion (SC) is a significant device to improve the seismic performance of the structures. It was stated in the previous studies that SC is less effective in the transversal direction. Hence, the efficiency of the damper is improved by optimal sizing through intelligent optimization techniques in this study. The complex optimization problem could be converted to a relatively simple mathematical problem since closed-form equations of the damper are exist in the literature. The optimal sizing problem was solved using two distinct methods namely the [Formula: see text]-constraint method and the elitist non-dominated sorting genetic algorithm (NSGA-II). The employed optimization methods were verified by each other as almost similar geometric ratios were obtained. The efficiency of the optimization is evaluated through finite element analysis (FEA). It is shown that the optimally sized SC is superior in terms of energy dissipation.

Analysis of Fire Resistance of Square-Cased Square Steel Tube Reinforced Concrete (ST-RC) Columns.

Based on the finite element (FE) analysis software Abaqus, an FE model of square-cased square steel tube reinforced concrete (ST-RC) columns under the hybridized action of high-temperature and load is established. The accuracy of the FE model is verified using experimental data from existing studies. This model is used to analyze the temperature change, internal force distribution, and failure characteristics of the square-cased square ST-RC columns under the action of fire, as well as the factors affecting the fire resistance limit of the column. The results of FE analysis show that under the action of fire, the maximum internal temperature of the square-cased square ST-RC columns occurs in the corner of the section. Moreover, the stress and strain reach their maximum values at the concrete corner outside the tube. During the heating process, an internal force redistribution occurs in the square-cased square ST-RC column. At the same time, the proportion of the axial force and the bending moment of the reinforced concrete outside the pipe decreases gradually, while the proportion of the internal force of the core concrete-filled steel tube (CFST) increases gradually. In essence, it is a process of load transfer from the high-temperature to the low-temperature zone. In addition, the section size, load ratio, slenderness ratio, cross-sectional core area ratio, steel content, and external concrete strength are the main parameters affecting the fire resistance limit of the square-cased square ST-RC columns. Among them, the cross-sectional core area ratio, section size, steel ratio, and external concrete strength are positively correlated with the fire resistance limit of the composite column. On the contrary, with the increase in the load ratio and the slenderness ratio, the fire resistance limit of the square-cased square ST-RC columns decreases. On this basis, a simplified formula to calculate the fire resistance limit of square-cased square ST-RC columns is proposed. The research results can be used as a theoretical reference for the fire protection design of this kind of structure in practical engineering.

Multi-Scale Structure-Mechanical Property Relations of Graphene-Based Layer Materials.

Pristine graphene is one of the strongest materials known in the world, and may play important roles in structural and functional materials. In order to utilize the extraordinary mechanical properties in practical engineering structures, graphene should be assembled into macroscopic structures such as graphene-based papers, fibers, foams, etc. However, the mechanical properties of graphene-based materials such as Young’s modulus and strength are 1–2 orders lower than those of pristine monolayer graphene. Many efforts have been made to unveil the multi-scale structure–property relations of graphene-based materials with hierarchical structures spanning the nanoscale to macroscale, and significant achievements have been obtained to improve the mechanical performance of graphene-based materials through composition and structure optimization across multi-scale. This review aims at summarizing the currently theoretical, simulation, and experimental efforts devoted to the multi-scale structure–property relation of graphene-based layer materials including defective monolayer graphene, nacre-like and laminar nanostructures of multilayer graphene, graphene-based papers, fibers, aerogels, and graphene/polymer composites. The mechanisms of mechanical property degradation across the multi-scale are discussed, based on which some multi-scale optimization strategies are presented to further improve the mechanical properties of graphene-based layer materials. We expect that this review can provide useful insights into the continuous improvement of mechanical properties of graphene-based layer materials.

A new seismic damage assessment method for single-layer steel latticed shells considering multi-modal contribution

In this paper, a new seismic damage assessment method considering multi-modal contribution is proposed to evaluate the seismic damage of single-layer steel latticed shells more accurately and efficiently. In the proposed method, the contribution of each modal damage to the structural overall seismic damage is calculated based on a specially constructed equivalent static system derived in this paper, in which the structural multi-modal damage effects can be considered. Then, the measure technics of the structural seismic damage degree is proposed in this paper according to the equivalent static displacements, and then the recommended damage index equation is derived. Considering different actual engineering requirements, the damage assessment procedures for design and appraisal are given in this paper, respectively. Since the damage assessment process is based on the static analysis results of equivalent model, the proposed method retains the conceptual simplicity and computational attractiveness. For detailed comparative evaluation, several numerical examples carried out on a Kiewitt-6 single-layer latticed shell and a practical engineering structure, named Shanghai International Convention Centre, are conducted in this paper. In numerical examples, the influence of the damage assessment direction on the assessment results, the trend characteristic of damage index curves and its comparison with structural response are all discussed in detail. For practicality, combined with the numerical analysis results, seismic damage grades of single-layer latticed shells and the recommended values of characteristic points are discussed and obtained. Furthermore, seismic damage assessment results generated by the proposed method and the other three methods are compared, which confirms the necessity of considering multi-modal contribution and the satisfying accuracy and applicability provided by the proposed method in single-layer steel latticed shell seismic damage assessment.