• Geomechanics and Engineering
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• v.31 no.2
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• pp.129-147
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• 2022

The properties of soil are naturally highly variable and thus, to ensure proper safety and reliability, we need to test a large number of samples across the length and depth. In pile foundations, conducting field tests are highly expensive and the traditional empirical relations too have been proven to be poor in performance. The study proposes a state-of-art Particle Swarm Optimization (PSO) hybridized Artificial Neural Network (ANN), Extreme Learning Machine (ELM) and Adaptive Neuro Fuzzy Inference System (ANFIS); and comparative analysis of metaheuristic models (ANN-PSO, ELM-PSO, ANFIS-PSO) for prediction of bearing capacity of pile foundation trained and tested on dataset of nearly 300 dynamic pile tests from the literature. A novel ensemble model of three hybrid models is constructed to combine and enhance the predictions of the individual models effectively. The authenticity of the dataset is confirmed using descriptive statistics, correlation matrix and sensitivity analysis. Ram weight and diameter of pile are found to be most influential input parameter. The comparative analysis reveals that ANFIS-PSO is the best performing model in testing phase (R² = 0.85, RMSE = 0.01) while ELM-PSO performs best in training phase (R² = 0.88, RMSE = 0.08); while the ensemble provided overall best performance based on the rank score. The performance of ANN-PSO is least satisfactory compared to the other two models. The findings were confirmed using Taylor diagram, error matrix and uncertainty analysis. Based on the results ELM-PSO and ANFIS-PSO is proposed to be used for the prediction of bearing capacity of piles and ensemble learning method of joining the outputs of individual models should be encouraged. The study possesses the potential to assist geotechnical engineers in the design phase of civil engineering projects.

• Earthquakes and Structures
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• v.25 no.4
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• pp.249-267
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• 2023

Various methods for determining the damping ratio have been proposed by scholars both domestically and abroad. However, no comparative analysis of different determination methods has been seen yet. In this study, typical sand (Fujian standard sand) and cohesive soils were selected as experimental objects, and undrained strain-controlled dynamic triaxial tests were conducted. The differences between existing damping ratio determination methods were theoretically compared and analyzed. The results showed that the hysteresis curve of cohesive soils had better symmetry and more closely conformed to the definition of equivalent linear viscoelasticity. For non-cohesive soils, the differences in damping ratio determined by six methods were significant. The differences decreased with increasing confining pressure and relative density, but increased gradually with increasing shear strain, especially at high shear strains, where the maximum relative error reached 200%. For cohesive soils, the differences in damping ratio determined by six methods were relatively small, with a maximum relative error of about 50%. Moreover, they were less affected by effective confining pressure and had the same changing trend under different effective confining pressures. The damping ratio determination method has a large effect on the seismic response of soils distributed by non-cohesive soils, with a maximum relative error of about 15% for the PGA and up to about 30% for the Sa. However, for soil layers distributed by cohesive soils, the damping ratio determination method has less influence on the seismic response. Therefore, it is necessary to adopt a unified damping ratio determination method for non-cohesive soils, which can effectively avoid artificial errors caused by different determination methods.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1412-1419
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• 2002

Dynamic shear tests for the tough-pitch copper at high strain and high strain rate was performed. The Split Hopkinson Pressure Bar (SHPB) compression test system was modified to yield a shear deformation in the specimen. Hat-shaped specimens for the tough-pitch copper were adopted to generate high strain of γ=3～4 and high strain-rate of γ= 10$^4$/s. The dynamic analysis by ABAQUS 5.5/EXPLICIT code verified that shear zone can be localized in hat-shaped specimens. A proper impact velocity and the axial length of the shear localization region wert determined through the elastic wave analysis. The displacement in a hat-shaped specimen is limited by a spacer ring which was installed between the specimen and the incident bar. The shear bands were obtained by measuring the direction of shear deformation and the width of deformed grain in the shear zone. The decrease of specimen length has been measured on the optical displacement transducer. Dynamic shear stress-strain relations in the tough-pitch copper were obtained at two strain-rates.

• Structural Engineering and Mechanics
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• v.25 no.5
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• pp.519-540
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• 2007

In this paper, the energy-based plastic-damage model previously proposed by the authors [International Journal of Solids and Structures, 43(3-4): 583-612] is first simplified with an empirically defined evolution law for the irreversible strains, and then it is extended to its rate-dependent version to account for the strain rate effect. Regarding the energy dissipation by the motion of the structure under dynamic loadings, within the framework of continuum damage mechanics a new damping model is proposed and incorporated into the developed rate-dependent plastic-damage mode, leading to a unified constitutive model which is capable of directly considering the damping on the material scale. Pertinent computational aspects concerning the numerical implementation and the algorithmic consistent modulus for the unified model are also discussed in details, through which the dynamic nonlinear analysis of damping structures can be coped with by the same procedures as those without damping. The proposed unified plastic-damage model is verfied by the simulations of concrete specimens under different quasistatic and high rate straining loading conditions, and is then applied to the Koyna dam under earthquake motions. The numerical predictions agree fairly well with the results obtained from experimental tests and/or reported by other investigators, demonstrating its capability for reproducing most of the typical nonlinear performances of concrete under quasi-static and dynamic loading conditions.

• Journal of Ocean Engineering and Technology
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• v.33 no.6
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• pp.547-555
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• 2019

The purpose of this study was to establish a numerical model of polyurethane foam (PUF) to simulate the dynamic response and strength of membrane-type Liquefied natural gas (LNG) Cargo containment system (CCS) under the impact load. To do this, initially, the visco-plastic behavior of PUF was characterized by testing the response of the PUF to the impact loads with various strain rates as well as PUF densities at room temperature and at cryogenic conditions. A PUF material model was established using the test results of the material and the FE analysis. To verify the validation of the established material model, simulations were performed for experimental applications, e.g., the dry drop test, and the results of FEA were compared to the experimental results. Based on this comparison, it was found that the dynamic response of PUF in dry drop tests, such as the reaction force and fracture behaviors, could be simulated successfully by the material model proposed in this study.

• Transactions of Materials Processing
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• v.10 no.4
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• pp.347-354
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• 2001

Compression tests were carried out to investigate the hot-deformation behavior of Ti-6Al-4V alloy in the temperature range of $915^{\circ}C$ to $1015^{\circ}C$ and the strain rate range of $10^{-3}s^{-i}$ to $10s^{-1}$. Under the given test conditions, the hot-deformation of Ti-6Al-4V alloy was mainly led by dynamic recovery rather than by dynamic recrystallization. The activation energy for the plastic deformation in $\alpha+\beta$ field was about 894 kJ/mol and $\beta$ field was 332kJ/mo1. Processing map for hot working are developed on the basis of the variations of efficiency of power dissipation($\eta$=2m/m＋1) and flow instability criterion using the dynamic material model. The optimum process condition in the ($\alpha＋\beta$) field was obtained at the temperature ranges of $930^{\circ}C$ to $955^{\circ}C$$^{\circ}C$ and a strain rate of $10^{-3}s{-1}$.

• KCI Concrete Journal
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• v.14 no.1
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• pp.23-29
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• 2002

Recent construction activities have given rise to civil petitions associated with vibration-induced damages or nuisances. To mitigate unfavorable effects of construction activities, the measures to reduce or isolate from vibration need to be adopted. In this research, a vibration-mitigated concrete, which is one of the active measures for reducing vibration in concrete structures, was investigated. Concrete was mixed with vibration-reducing materials (i.e. latex, rubber power, plastic resin, and polystyrofoam) to reduce vibration and tested to evaluate dynamic material properties and structural characteristics. Normal and high strength concrete specimens with a certain level of damage were also tested for comparisons. In addition, recycling tires and plastic materials were added to produce a vibration-reducing concrete. A total of 32 concrete bars and eight concrete beams were tested to investigate the dynamic material properties and structural characteristics. Wave measurements on concrete bars showed that vibration-mitigated concrete has larger material damping ratio than normal or high strength concrete. Styrofoam turned out to be the most effective vibration-reducing mixture. Flexural vibration tests on eight flexural concrete beams also revealed that material damping ratio of the concrete beams is much smaller than structural damping ratio for all the cases.

• International Journal of Automotive Technology
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• v.8 no.3
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• pp.309-317
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• 2007

In this study, we conducted a vibration fatigue analysis of the lower control arm in a vehicle suspension system. The vehicle was driven during the tests so that the dynamic effects could be taken into account. The dynamic load of the frequency domain was superimposed on the frequency response analysis. We performed a virtual proving ground test using multi-body dynamics, along with a finite element analysis and fatigue life predictions. Shape optimization was also considered using the design of the experimental approach, and a response surface analysis was performed to improve the durability performance of the lower control arm. We identified the elements that had the most influence on the optimal shape of the finite element model and analyzed the sensitivity of those elements. Then the optimal points that minimized the amount of damage to the areas of interest were determined through a response surface analysis. The results suggested that the fatigue life of the model increased as its mass was not increased excessively, and demonstrated that these design procedures yielded an appropriate optimized lower control arm model.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.4
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• pp.118-125
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• 2009

Bumper is designed to protect the automotive frame without damage at low velocity. Expanded polypropylene (EPP) foam is used in the bumper as an energy absorbing material. In order to exactly predict the energy absorbing performance of the foam material under impact loading condition, it is important to use high strain rate material properties. In this study, a new apparatus for dynamic compression tests was developed to investigate the high strain rate behavior of EPP foams. Three kinds of EPP foams which have different expansion ratios were tested to investigate the quasi-static and dynamic compression behavior. Quasi-static compressions were performed at low strain rates of 0.001/s, 0.1/s and 1/s. The dynamic compressions were carried out at high strain rates of 50/s and 100/s with the developed apparatus. It was observed that the EPP foam has significant strain rate effect as compared to quasi-static behavior.

• Smart Structures and Systems
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• v.16 no.2
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• pp.263-280
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• 2015

Microwave remote sensing is probably the most recent experimental technique suitable to the non-contact measurement of deflections on large structures, in static or dynamic conditions. In the first part of the paper, the main techniques adopted in microwave remote sensing are described, so that advantages and potential issues of these techniques are presented and discussed. Subsequently, the paper addresses the application of the radar technology to the measurement of the vibration response on the stay cables of two cable-stayed bridges. The dynamic tests were performed in operational conditions (i.e. with the excitation being mainly provided by micro-tremors, wind and traffic) and the maximum deflections of the cables were generally lower than 5.0 mm. The investigation clearly highlights: (a) the safe and simple use of the radar on site and its effectiveness to simultaneously measure the dynamic response of all the stay cables of an array; (b) the negligible effects of the typical issues and uncertainties that might affect the radar measurements; (c) the accuracy of the results provided by the microwave remote sensing in terms of natural frequencies and tension forces of the stay cables; (d) the suitability of microwave interferometry to the repeated application within Structural Health Monitoring programmes.