Fatigue failure is a phenomenon that often occurs in mechanical structures, especially in components that receive direct cyclic loading, e.g., marine facilities, automobiles, critical infrastructure, ...reservoirs, turbines, nuclear reactors, and features that work in extreme conditions. Several factors can affect fatigue resistance, including applied material type, environment temperature, microstructure state, residual stress, corrosion, and crack initiation. Accurately estimating fatigue life is critical. A variety of variables must be taken into the calculation to reduce the risk of dangerous failure. In this paper, a series of development and achievement reviews on the relevant phenomena and advanced research related to fatigue assessment is conducted. Consideration of fatigue assessment methodology, e.g., laboratory experiment and numerical calculation, is discussed to summarize relevant effects to characteristics of stress life, strain life, frequency-based, and fracture mechanic approaches. The review also presents the relationship of previous research and its relevance to the development of the recent study. The purpose of this paper is to provide state-of-the-art investigations as well as demonstrate the challenges of uncharted problems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The results of a geophysical survey of the technical condition of the lighthouse are presented. The stress–strain state, the residual resource, the tension of the fastening cables, the fixation of ...piles in the ground (rigid/non-rigid), and the immersion depth of the historical study object, the Sukhumi Lighthouse built in 1861 were determined. The passive seismic standing method based on the extraction of the natural vibrations of the object from noise records, as well as the tapping method, based on the recording of a reflected seismic wave passing along the structure were used to solve the above problems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An implicit limit state function is predicted with a support vector machine (SVM) for reliability analysis of engineering structures to reduce the number of finite element analyses. The accuracy and ...predictability of the SVM method are reduced considerably by noise in data. In this paper, density-based spatial clustering of applications with noise (DBSCAN) is applied to reduce the noise in training samples for SVM regression. Then, the SVM model is linked with Monte Carlo simulation (MCS) to find out the reliability of the engineering structures. Four different examples of static and dynamic problems are solved to show acceptability and efficiency of the proposed method. It is observed that the proposed method is suitable for a smaller number of performance function calls. Direct MCS, artificial neural network-based MCS and response surface methods have been used to examine the effectiveness of the algorithm.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
This study explores the use of a recent metaheuristic algorithm called a reptile search algorithm (RSA) to handle engineering design optimization problems. It is the first application of the RSA to ...engineering design problems in literature. The RSA optimizer is first applied to the design of a bolted rim, which is constrained optimization. The developed algorithm is then used to solve the optimization problem of a vehicle suspension arm, which aims to solve the weight reduction under natural frequency constraints. As function evaluations are achieved by finite element analysis, the Kriging surrogate model is integrated into the RSA algorithm. It is revealed that the optimum result gives a 13% weight reduction compared to the original structure. This study shows that RSA is an efficient metaheuristic as other metaheuristics such as the mayfly optimization algorithm, battle royale optimization algorithm, multi-level cross-entropy optimizer, and red fox optimization algorithm.
•A creep model of ETFE foils in terms of T, σ and t is proposed and validated.•Two cushions with inverse T and P are compared with experiments and simulations.•Ratios (height to edge) larger than ...suggested ratio result in proper structural forms.•Cushions with low P/high T is easier to achieve forms than Cushions with high P/low T.
Ethylene tetrafluoroethylene (ETFE) cushion structures with excellent building aesthetics and reasonable structural behavior can be utilized as roofs and facades of large-span building structures. The form and force of such structures interact due to structural flexibility and complexity. The determination of a suitable form needs form-finding and cutting pattern for conventional ETFE cushions, which incorporates complex theoretical analysis and fabrications. To obtain a structural form without complex cutting pattern, a flat-patterning ETFE cushion is proposed based on creep properties of polymer materials. This methodology facilitates to achieve desired forms using creep models of ETFE foils. Moreover, time-temperature superposition of polymer materials is employed to improve this method. Therefore, this paper focuses on a modified creep model of ETFE foils and utilizes it to assess form and force of flat-patterning ETFE cushion structures.
The Bailey-Norton model with Modified Time Hardening effect results in a creep model that describes creep strains at high temperature. To integrate this model into software, a multi-linear model is used where parameters are determined with experimental results. The related numerical simulations demonstrate the suitability of reproducing creep strains. For structural analysis, two typical cushions with inverse temperatures and pressures are simulated with multi-linear models. It is found that the maximum stress and strain exist near middle area of long edges and propagate towards cushion center. The final deformations of two cushions are 21.2 mm and 19.4 mm; the ratios of heights to edge length are larger than the engineering ratio of 1/8, resulting in a suitable structural form. A further ratio of stress to yield stress suggests the easy operation to achieve desired forms for small pressure at high temperature than large pressure at low temperature. In general, the proposed method to reveal form and structural behavior is useful for promoting utilizations of flat-patterning ETFE cushions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To improve the accuracy and efficiency of reliability estimation for engineering structures, the adaptive optimization deep neural network framework (DNN-AO) is proposed by introducing the coati ...optimization algorithm-based disturbance strategy, momentum gradient descent, and weighted Bayesian optimization technology into the deep neural network model. In this framework, the deep neural network model is employed to establish the relationship between input variables and output response; the coati optimization algorithm-based disturbance strategy is adopted to obtain the initial weights and thresholds; the momentum gradient descent is utilized to solve the final initial weight and threshold; the weighted Bayesian optimization strategy is used to determine the optimal neural network topology. In addition, the nonlinear function approximation and aero-engine turbine blisk strain reliability analysis cases validate the effectiveness of the proposed DNN-AO with multiple methods. The reliability level of aero-engine turbine blisk strain is 0.9985 when the allowable value of strain is 5.298 × 10−4. The results show that the DNN-AO exhibits the advantages of modeling properties (i.e. modeling accuracy and efficiency) and simulation performances (i.e., simulation precision and efficiency) in various methods. The research work in this paper can enrich the reliability design theory of engineering structures and further guide the optimization design of aero-engine turbine blisk.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Dynamic response levels are critical for tall and slender civil structures. Studying the dynamic behavior of large civil structures with finite element modeling techniques requires detailed and ...accurate modeling of structural geometry, material properties, member fixities, connection types, and accompanying assumptions. Still, the finite element model results are approximations that could be away from representing the actual structural behavior. Structures are dynamically tested at their operational conditions to validate the finite element model results. This paper presents Operational Modal Analysis (OMA) and finite element model updating of a tall structure located in the West Bay area of Doha (Qatar). The structure is a reinforced concrete building with shear wall cores situated towards the center of the building plan, which was constructed between 2012 and 2016. With 53 stories above the ground and two stories below ground, the 230 m (755 ft) tall building is being used for residential and hotel purposes. For the finite element model updating and calibration tasks presented in this paper, the authors intentionally introduced drastic model changes for the first two model updates so that the results from the first two attempts guide how to proceed with a more reasonable update for the third calibration of the finite element model. While this is a non-standard technique that represents a specific condition where the initial attempts on the finite element model are very crude approximations, it is a systematized demonstration of how to operate when the structural parameters are sparse or uncertain for modeling purposes. While in theory, the finite element model updates can always be fine-tuned in a way to further decrease the error between the measured and predicted OMA results, in this paper, the authors predominantly focused on the presentation of three finite element model updates to demonstrate the way they have improved the modal assurance criteria plots and lowered the average absolute errors by visiting two drastic and then one moderate finite element model updates. The material presented here in this paper is arguably the first published work on large-scale dynamic testing of a civil structure in the State of Qatar.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Distributed optical fiber systems (DOFSs) are an emerging and innovative technology that allows long-range and continuous strain temperature monitoring with a high resolution. Sensing cables are ...either surface-mounted or embedded into civil engineering structures to ensure long-term structural monitoring and early crack detection. However, strain profiles measured in the optical fiber (OF) may differ from the actual strain in the structure due to the shear transfer through the intermediate material layers between the OF and the host material (i.e., in the protective coating of the sensing cable and in the adhesive). Therefore, OF sensors need to be qualified to provide accurate quantitative strain measurements. This study presents a methodology for the qualification of a DOFS. This qualification is achieved through the calculation of the so-called mechanical transfer function (MTF), which relates the strain profile in the OF to the actual strain profile in the structure. It is proposed to establish a numerical modeling of the system, in which the mechanical parameters are calibrated from experiments. A specific surface-mounted sensing cable connected to an optical frequency domain reflectometry interrogator is considered as a case study. It was found that (i) tensile and pull-out tests can provide detailed information about materials and interfaces of the numerical model; (ii) the calibrated model made it possible to compute strain profiles along the OF and therefore to calculate the MTF of the system; (iii) the results proved to be consistent with experimental data collected on a cracked concrete beam during a four-point bending test. This paper is organized as follows: first, the technical background related to DOFSs and interrogators is briefly recalled, the MTF is defined and the above-mentioned methodology is presented. In the second part, the methodology is applied to a specific cable. Finally, a comparison with experimental evidence validates the proposed approach.
This paper presents an experimental approach to study the durability of FRP composites used in the civil/structural engineering. Carbon epoxy (carbon/EP) and carbon vinylester (carbon/VE) composites ...were considered for accelerated ageing (thermal, hygrometric, chemical, thermochemical, hydrothermal, freezing–thawing cycles, etc.) over 18months. The accelerated ageing tests were selected to reflect the real operating conditions on natural civil engineering environment. The same composites were also subjected to environmental ageing to assess the effectiveness and the relevance of the accelerated exposure. Changes in tensile strength and viscoelastic response were evaluated through mechanical testing and Kinemat analysis. The design factors prescribed by the existing principle guidelines were applied to experimental measurements. The results revealed the presence of drawbacks inherent in these regulations based on a determinist approach.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Foundation settlement is a common problem in civil engineering. In the case of un-even settlement, it can lead to structural deformation and damage, which seriously affects the safety and reliability ...of the project. Therefore, the influence of adjusting the stiffness of the foundation on un-even settlement was analyzed through finite element analysis to effectively solve un-even settlement. By simulating the settlement of soil under different foundation stiffness and load conditions, the influence of foundation stiffness adjustment on soil deformation and settlement distribution was analyzed, and its impact on structural safety was evaluated. These studies confirmed that thickened layers could effectively solve the un-even settlement. Within the range of 0.2 to 1.0 meters, the difference in thickness was the greatest. The adjustment of differential settlement by layer thickness was phased and decreased with increasing thickness. Adjusting the stiffness of the foundation could effectively solve un-even settlement, reduce differences in soil settlement, and improve the overall stability and safety of the structure. These results have important guiding significance for the design of foundation and the solution of un-even settlement problems in engineering practice and provide certain reference and basis for further research.
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