• Structural Engineering and Mechanics
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• v.78 no.1
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• pp.41-52
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• 2021

Inelastic static pushover analysis has been used in the academic-research widely for seismic analysis of structures. Nowadays, the variety pushover analysis methods have been developed, including Modal pushover, Adaptive pushover, and Cyclic pushover, in which some weaknesses of the conventional pushover method have been rectified. In the conventional pushover analysis method, the effects of cumulative growth of cracks are not considered on the reduction of strength and stiffness of RC members that occur during earthquake or cyclic loading. Therefore, the Cyclic Pushover Analysis Method (CPA) has been proposed. This method is a powerful technique for seismic evaluation of regular reinforced concrete buildings in which the first mode of them is dominant. Since the bridges have different structures than buildings, their results cannot necessarily be attributed to bridges, and more research is needed. In this study, a cyclic pushover analysis with four loading protocols (suggested by valid references) by the Opensees software was conducted for seismic evaluation of two regular reinforce concrete bridges. The modeling method was validated with the comparison of the analytical and experimental results under both cyclic and dynamic loading. The failure mode of the piers was considered in two-mode of flexural failure and also a flexural-shear failure. Along with the cyclic analysis, conventional analysis has been studied. Also, the nonlinear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. The time history of 20 far-field earthquake records was used to conduct IDA. After analysis, the base shear vs. displacement in the middle of the deck was drawn. The obtained results show that the cyclic pushover analysis method is able to evaluate an accurate seismic behavior of the reinforced concrete piers of the bridges. Based on the results, the cyclic pushover has proper convergence with IDA. Its accuracy was much higher than the conventional pushover, in which the bridge piers failed in flexural-shear mode. But, in the flexural failure mode, the results of each two pushover methods were close approximately. Besides, the cyclic pushover method with ACI loading protocol, and ATC-24 loading protocol, can provided more accurate results for evaluating the seismic investigation of the bridges, specially if the bridge piers are failed in flexural-shear failure mode.

• Structural Engineering and Mechanics
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• v.20 no.1
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• pp.21-43
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• 2005

Masonry is a composite non-homogeneous structural material, whose mechanical properties depend on the properties of and the interaction between the composite components - brick and mortar, their volume ratio, the properties of their bond, and any cracking in the masonry. The mechanical properties of masonry depend on the orientation of the bed joints and the stress state of the joints, and so the values of the shear modulus, as well as the stiffness of masonry structural elements can depend on various factors. An extensive testing programme in several countries addresses the problem of measurement of the stiffness properties of masonry. These testing programs have provided sufficient data to permit a review of the influence of different testing techniques (mono and bi-axial tests), the variations caused by distinct loading conditions (monotonic and cyclic), the impact of the mortar type, as well as influence of the reinforcement. This review considers the impact of the measurement devices used for determining the shear modulus and stiffness of walls on the results. The results clearly indicate a need to re-assess the values stated in almost all national codes for the shear modulus of the masonry, especially for masonry made with lime mortar, where strong anisotropic behaviour is in the stiffness properties.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.72-72
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• 2018

A dynamic fatigue characteristic of dental implant system has been evaluated with applying single axial compressive shear loading based on the ISO 14801 standard. For the advanced dynamic fatigue test, multi-directional force and motion needed to be accompanied for more information of mechanical properties as based on mastication in oral environment. In this study, we have prepared loading and motion protocol for the multi-directional fatigue test of dental implant system with single (Apical/Occlusal; AO), and additional mastication motion (Lingual/Facial; LF, Mesial/Distal; MD). As following the prepared protocol (with modification of ISO 14801), fatigue test was conducted to verify the worst case results for the development of highly stabilized dental implant system. Mechanical testing was performed using an universal testing machine (MTS Bionix 858, MN, USA) for static compression and single directional loading fatigue, while the multi-directional loading was performed with joint simulator (ADL-Force 5, MA, USA) under load control. Basically, all mechanical test was performed according to the ISO 14801:2016 standard. Static compression test was performed to identify the maximum fracture force with loading speed of 1.0 mm/min. A dynamic fatigue test was performed with 40 % value of maximum fracture force and 5 Hz loading frequency. A single directional fatigue test was performed with only apical/occlusal (AO) force application, while multi directional fatigue tests were applied $2^{\circ}$ of facial/lingual (FL) or mesial/distal (MD) movement. Fatigue failure cycles were entirely different between applying single-directional loading and multi-directional loading. As a comparison of these loading factor, the failure cycle was around 5 times lower than single-directional loading while applied multi-directional loading. Also, the displacement change with accumulated multi-directional fatigue cycles was higher than that of single directional cycles.

• Ocean Systems Engineering
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• v.1 no.4
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• pp.263-283
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• 2011

The performance of a rig tie-down system on a TLP (Tension Leg Platform) is investigated for 10-year, 100-year, and 1000-year hurricane environments. The inertia loading on the derrick is obtained from the three-hour time histories of the platform motions and accelerations, and the dynamic wind forces as well as the time-dependent heel-induced gravitational forces are also applied. Then, the connection loads between the derrick and its substructure as well as the substructure and deck are obtained to assess the safety of the tie-down system. Both linear and nonlinear inertia loads on the derrick are included. The resultant external forces are subsequently used to calculate the loads on the tie-down clamps at every time step with the assumption of rigid derrick. The exact dynamic equations including nonlinear terms are used with all the linear and second-order wave forces considering that some dynamic contributions, such as rotational inertia, centripetal forces, and the nonlinear excitations, have not been accounted for in the conventional engineering practices. From the numerical simulations, it is seen that the contributions of the second-order sum-frequency (or springing) accelerations can be appreciable in certain hurricane conditions. Finally, the maximum reaction loads on the clamps are obtained and used to check the possibility of slip, shear, and tensile failure of the tie-down system for any given environment.

• Computers and Concrete
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• v.6 no.5
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• pp.377-390
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• 2009

In this paper an improved one-dimensional frame element for modelling of reinforced concrete beams and columns subjected to impact is presented. The model is developed in the framework of a flexibility fibre element formulation that ignores the shear effect at material level. However, a simple shear cap is introduced at section level to take account of possible shear failure. The effect of strain rate at the fibre level is taken into account by using the dynamic increase factor (DIF) concept for steel and concrete. The capability of the formulation for estimating the element response history is demonstrated by some numerical examples and it is shown that the developed 1D element has the potential to be used for dynamic analysis of large framed structures subjected to impact of air blast and rigid objects.

• Advances in aircraft and spacecraft science
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• v.5 no.3
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• pp.385-400
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• 2018

In this paper dynamic behavior (modal analysis and dynamic transient response) of a novel sandwich T-joint is numerically and experimentally investigated. An epoxy adhesive is selected for bonding purpose and making the step wise graded behavior of adhesive region. The effect of the step graded behavior of the adhesive zone on dynamic behavior of a sandwich T-joint is numerically studied. Finite element analysis (FEA) of the T-joints with carbon fiber reinforced polymer (CFRP) face-sheets is performed by ABAQUS 6.12-1 FEM code software. Modal analysis and dynamic half-sine transient response of the sandwich T-joint are presented in this paper. Two verification processes employed to verify the dynamic modeling of the manufactured sandwich panels and T-joint modeling. It has been shown that the step wise graded adhesive zone cases have changed the second natural frequency by about 5%. Also, it has been shown that the different arranges in the step wise graded adhesive zone significantly affect the maximum stresses due to transient dynamic loading by 1112% decrease in maximum peel stress and 691.9% decrease in maximum shear stress on the adhesive region.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.607-616
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• 2006

More strict construction control of railway roadbeds is demanded in high speed railway system because of heavier repeated dynamic loading than conventional railways. The aim of this study is to propose a compaction control methodology of crushed-rock-soil-fills including as large particles as $200\sim300mm$ in diameter, which are easily encountered in high speed railway roadbed. Field tensity evaluation and in turn compaction control of such crushed-rock-soil-fills are almost impossible by conventional methods such as in-situ density measurements or plate loading tests. The proposed method consists of shear wave measurements of compaction specimens in laboratory and in-situ measurements of fills. In other words, compaction control can be carried out by comparing laboratory and field shear wave velocities using as a compaction control parameter. The proposed method was implemented at a soil site in the beginning and will be expanded to crushed-rock-soil-fills in future. One interesting result is that similar relationship of shear wave velocity and water content was obtained as that of density and water content with the maximum value at the optimum moisture content.

• Computers and Concrete
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• v.30 no.1
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• pp.19-32
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• 2022

This paper presents an investigation into the failure of RC columns under impact loadings. A numerical simulation of 19 identical RC columns subjected to single and repeated impact loadings was performed. A free-falling hammer was dropped at midspan with the same total kinetic energy input but varying mass and momentum. The specimens under the repeated impact test were struck two times at the same location. The colliding index, defined as the impact energy-momentum ratio, was proposed to explain the different impact responses under equal-energy impacts. The increase of colliding index from low to high indicates the transition of the impact response from static to dynamic and failure mode from flexure to shear. This phenomenon was more evident when the column had a greater axial load and was impacted with a high colliding index. The existence of the axial load had an inhibitory effect on the crack development and increased the shear resistance. The second impact changes the failure mode from flexural to brittle shear as found in the specimen with 20% axial load subjected to high a colliding index. Moreover, a deflection prediction equation based on the impact energy and force was limited to the low colliding index impact.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.25-32
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• 2018

This paper investigates the effect of rock discontinuities on a shear stress wave that is induced by earthquake or blasting and provides the result of numerical parametric studies. The numerical tests of different conditions of rock and discontinuity have been carried out after confirming that the numerical approach is valid throughout a verification analysis from which the test results were compared with a theoretical solution. In-situ stress condition was considered as a rock condition and internal friction angle and cohesive value, which are the shear strength parameters, were considered as discontinuities condition. The joint inclination angle was also taken into account as a parameter. With the various conditions of different parameters, the test results showed that a shear stress wave propagating through a mass is highly influenced by the shear strength of discontinuities and the condition of joint inclination angle as well as in-situ stress. The study results indicate that when earthquake or blasting-induced dynamic loading propagates through a jointed rock mass or a stratified soil ground the effect of in-situ stress and discontinuities including a stratum boundary should be taken into account when evaluating the dynamic effect on nearby facilities and structures.