• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.357-373
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• 2022

The high-temperature gas-cooled reactor pebble-bed module project is the first commercial Generation-IV NPP(Nuclear Power Plant) in China. A new joint is used for the vertical support of RPV(Reactor Pressure Vessel). The steel corbel is integrally embedded into the reactor-cabin wall through eight asymmetrically arranged pre-stressed high-strength bolts, achieving the different path transmission of shear force and moment. The vertical monotonic loading test of two specimens is conducted. The results show that the failure mode of the joint is bolt fracture. There is no prominent yield stage in the whole loading process. The stress of bolts is linearly distributed along the height of corbel at initial loading. As the load increases, the height of neutral axis of bolts gradually decreases. The upper and lower edges of the wall opening contact the corbel plate to restrict the rotation of the corbel. During the loading, the pre-stress of some bolts decreases. The increase of the pre-stress strength ratio of bolts has no noticeable effect on the structure stiffness, but it reduces the ultimate bearing capacity of the joint. A simplified calculation model for the elastic stage of the joint is established, and the estimation results are in good agreement with the experimental results.

• Steel and Composite Structures
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• v.45 no.1
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• pp.101-118
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• 2022

The seismic performance of the reinforced concrete (RC) special-shaped column to steel beam connections with steel jacket used in the RC column to steel beam fabricated frame structures was investigated in this study. The three full-scale specimens were subjected to cyclic loading. The failure mode, ultimate bearing capacity, shear strength capacity, stiffness degradation, energy dissipation capacity, and strain distribution of the specimens were studied by varying the steel jacket thickness parameters. Test results indicate that the RC special-shaped column to steel beam connection with steel jacket is reliable and has excellent seismic performance. The hysteresis curve is full and has excellent energy dissipation capacity. The thickness of the steel jacket is an important parameter affecting the seismic performance of the proposed connections, and the shear strength capacity, ductility, and initial stiffness of the specimens improve with the increase in the thickness of the steel jacket. The calculation formula for the shear strength capacity of RC special-shaped column to steel beam connections with steel jacket is proposed on the basis of the experimental results and numerical simulation analysis. The theoretical values of the formula are in good agreement with the experimental values.

• Journal of Wind Energy
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• v.13 no.4
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• pp.80-89
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• 2022

In this paper, a study was conducted to evaluate the safety of pitch reducers for 8 MW class wind turbines. The housing and carrier of the pitch reducer were subjected to structural analysis for the ultimate load by load duration distribution (LDD). As a result of the finite element analysis of the housing parts, the part with the highest stress was the output housing, and the equivalent stress was 522.4 MPa and the safety factor was 1.14. As a result of finite analysis of the carrier, the highest stress occurred at 80.5 MPa in the first carrier, and the safety factor was 10.3. In addition, extreme strength and life analysis by LDD load were performed for gears and bearings included in each stage. The strength analysis of the planetary gear train was conducted based on ISO 6336, and the stability evaluation of the bearings through life analysis based on ISO 281 found all to be safe.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1406-1416
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• 2008

Soil nailing is used as a method of slope stabilization and excavation support. The design method of soil nail are based on experience or assumption of interaction between soil and reinforcement. Most design methods simply considers the tension of reinforcement for analysis of slope stabilization. Soil nails interact with soils under combined loading of shear and tension. Jewell & Pedley(1990) suggested a design equation of shear force with bending stiffness and discussed that the magnitude of the maximum shear force is small in comparison with the maximum axal force. However, they have used a very conservative limiting bearing stress on nails. This paper discusses that the shear strength of soil nails should not be disregarded with proper bearing stresses on nails. The modified FHWA design method was proposed by considering shear forces on nails with bending stiffness.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.335-341
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• 1994

Laboratory model test results for bearing capacity of a square shallow foundation supported by a sand layer reinforced with layers of geogrid have been presented. Use of geogrids provides an economical and time efficient method for improving load-settlement, and strength characteristics of weak soils. Especially the geogrid reinforced soil will be necessary in the case of foundations supporting machines, embankments for railroads, and foundations of structures in earthquake-prone areas. Based on the present model test results, the bearing capacity ratio (BCR) with respect to the ultimate bearing capacity (UBC), at levels of limited settlement of the shallow foundation. has been determined. Also, it appears that significant improvement in the UBC of medium sands can be achieved by reinforcing elements which shows promise for future work.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.56-62
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• 2018

In this study, an artificially formed Gap graded soil, designed to increase its shear strength, was analyzed to determine the strength parameters through direct shear tests. Uniform and fine grain size samples were compared to the Gap graded soil to investigate the increase in the shear strength. Plate loading tests were conducted using 13mm and 19mm aggregates to confirm the reproducibility of the strength enhanced samples for site application. This test confirmed that the particle size ratio and the internal friction angle are correlated to the shear strength, and the shear resistance angle significantly increased in the specific particle size ratio range. The calculation of the ultimate bearing capacity by the plate load test demonstrated that the grain size adjustment method greatly influences the strength increase rate. Therefore, the findings were verified and it was confirmed that a high shear strength is achievable despite the existence of a poor particle size distribution.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.74-81
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• 2014

This study proposes an advanced type of a micropile system. The proposed micropile system consists of perfobond ribs installed steel rod to improve shear capacity between the thread and the grout, and partially expanded drill holes to increase resistance capacity between the grout and the ground. This study contains experimental evaluations on the proposed micropile system to verify the shear capacity of perfobond rib installed on the steel rod and the load-carrying capacity of shear key created by the partially expanded drill hole. Push-out tests were conducted on a rolled screw thread and steel rods which perfobond ribs are installed instead of rolled screw, in order to compare their load-carrying capacity and behavioral characteristics. As a result, it was confirmed that the perfobond-rib steel rods show much superior structural behavior in terms of initial stiffness, ultimate load, and ductile behavior.

• Journal of the Korean Geotechnical Society
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• v.29 no.7
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• pp.17-36
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• 2013

In this paper, the empirical relations of skin friction and end bearing resistance with the results of site investigation in soft rock are proposed through the analysis of bi-directional pile load tests of rock socketed drilled shafts performed at large offshore bridge foundations and high-rise building projects (13 test piles in 4 projects). The site investigation and drilling for bi-directional pile load tests were performed at the centers of test piles, and f-w curves for skin friction and q-w curves for end bearing were plotted based on load-transfer measurements. From the above curves, the empirical relations of skin friction and end bearing resistance with the results of site investigation depending on the mobilized displacement are determined by multiple regression analysis and compared with previous studies. Since the f-w and q-w curves of rock-socketed piles in Korea show hardening behavior according to mobilized displacement, the developed empirical relations by the mobilized displacement are more reasonable than those of previous studies which could not consider the mobilized displacement and suggested the ultimate capacity with unconfined compressive strength only. Particularly, the developed equations correlated with unconfined compressive strength show the best correlations among the equations correlated with other parameters.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.617-628
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• 2017

In order to study the failure mode and seismic behavior of the interior-joint in steel traditional-style buildings, a single beam-column joint and a double beam-column joint were produced according to the relevant building criterion of ancient architectural buildings and the engineering instances, and the dynamic horizontal loading test was conducted by controlling the displacement of the column top and the peak acceleration of the actuator. The failure process of the specimens was observed, the bearing capacity, ductility, energy dissipation capacity, strength and stiffness degradation of the specimens were analyzed by the load-displacement hysteresis curve and backbone curve. The results show that the beam end plastic hinge area deformed obviously during the loading process, and tearing fracture of the base metal at top and bottom flange of beam occurred. The hysteresis curves of the specimens are both spindle-shaped and plump. The ultimate loads of the single beam-column joint and double beam-column joint are 48.65 kN and 70.60 kN respectively, and the equivalent viscous damping coefficients are more than 0.2 when destroyed, which shows the two specimens have great energy dissipation capacity. In addition, the stiffness, bearing capacity and energy dissipation capacity of the double beam-column joint are significantly better than that of the single beam-column joint. The ductility coefficients of the single beam-column joint and double beam-column joint are 1.81 and 1.92, respectively. The cracks grow fast when subjected to dynamic loading, and the strength and stiffness degradation is also degenerated quickly.

• Computers and Concrete
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• v.31 no.3
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• pp.253-265
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• 2023

In this research, the gene expression programming (GEP) technique was employed to provide a new model for predicting the maximum loading capacity of concrete-encased steel (CES) columns. This model was developed based on 96 CES column specimens available in the literature. The six main parameters used in the model were the compressive strength of concrete (f_c), yield stress of structural steel (f_ys), yield stress of steel rebar (f_yr), and cross-sectional areas of concrete, structural steel, and steel rebar (A_c, A_s and A_r respectively). The performance of the prediction model for the ultimate load-carrying capacity was investigated using different statistical indicators such as root mean square error (RMSE), correlation coefficient (R), mean absolute error (MAE), and relative square error (RSE), the corresponding values of which for the proposed model were 620.28, 0.99, 411.8, and 0.01, respectively. Here, the predictions of the model and those of available codes including ACI ITG, AS 3600, CSA-A23, EN 1994, JGJ 138, and NZS 3101 were compared for further model assessment. The obtained results showed that the proposed model had the highest correlation with the experimental data and the lowest error. In addition, to see if the developed model matched engineering realities and corresponded to the previously developed models, a parametric study and sensitivity analysis were carried out. The sensitivity analysis results indicated that the concrete cross-sectional area (A_c) has the greatest effect on the model, while parameter (f_yr) has a negligible effect.