• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.421-430
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• 2013

To predict behaviors of offshore wind turbines which are highly laterally loaded structures and to design them rationally, evaluating the soil-foundation interaction is important. Nowadays, there are many soil modeling methods for structural analysis of general structures subjected to vertical loads, but using the methods without any consideration for design of a monopile foundation is eschewed because it might cause wrong structural design due to the deferent loading state. In this paper, we identify the differences of the member forces and displacements by design methods. The results show that fixed end method is barely suitable for monopile design in terms of checking the serviceability because it underestimate the lateral displacement. Fixed end method and stiffness matrix method underestimate the member forces, whereas virtual fixed end method overestimates them. The results of p-y curve method and coefficient of subgrade reaction method are similar to the results of 3D soil modeling method, and 2D soil modeling method overestimates the displacement and member forces as compared with other methods.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.7-15
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• 2021

In this study, we developed Void Plywood Slab (VPS) that improved the shape of existing hollow materials. Its performance was evaluated through one-way flexural and one-way shear tests using the developed VPS. As a result of the one-way flexural performance tests of VPS, the yield load value for FPS series(longitudinal direction specimens with hollow materials) was approximately 97.5% compared to FPS-00(without hollow materials) specimen. The tests showed that the yield load was not much different. In addition, FNS series(transverse direction specimens with hollow materials) also represented about 97% of FPS-00 specimen. The one-way flexural performance was shown to have little impact from void materials. Therefore, it is confirmed that the presented system is applicable to the VPS to the slab design. The results of the one-way shear performance tests of VPS showed that it was about 92% compared to the SS-00(without hollow materials) specimen. These results were somewhat insufficient for the SS-00 specimen. Shear strength equation is expressed as the sum of shear force by concrete and shear force by reinforcement. However, in the case of void slab, it is believed that the concrete section has been deleted by the void material. However, the strength of the structure applied to the shear design, as with the flexural design, is also applied to the design based on the yield load value.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.29-39
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• 2023

As the intensity of urban underground space development increases, more and more tunnels are planned and constructed, and sometimes it is inevitable to encounter situations where tunnels have to underpass the river embankments. Most previous studies involved tunnels passing river embankments perpendicularly or with large intersection angle. In this study, a project case where two EPB shield tunnels with 8.82 m diameter run parallelly underneath a river embankment was reported. The parallel length is 380 m and tunnel were mainly buried in the moderate / slightly weathered clastic rock layer. The field monitoring result was presented and discussed. Three-dimensional back-analysis were then carried out to gain a better understanding the interaction mechanisms between shield tunnel and embankment and further to predict the ultimate settlement of embankment due to twin-tunnel excavation. Parametrical studies considering effect of tunnel face pressure, tail grouting pressure and volume loss were also conducted. The measured embankment settlement after the single tunnel excavation was 4.53 mm ~ 7.43 mm. Neither new crack on the pavement or cavity under the roadbed was observed. It is found that the more degree of weathering of the rock around the tunnel, the greater the embankment settlement and wider the settlement trough. Besides, the latter tunnel excavation might cause larger deformation than the former tunnel excavation if the mobilized plastic zone overlapped. With given geometry and stratigraphic condition in this study, the safety or serviceability of the river embankment would hardly be affected since the ultimate settlement of the embankment after the twin-tunnel excavation is within the allowable limit. Reasonable tunnel face pressure and tail grouting pressure can to some extent suppress the settlement of the embankment. The recommended tunnel face pressure and tail grouting pressure are 300 kPa and 550 kPa in this study, respectively. However, the volume loss plays the crucial role in the tunnel-embankment interaction. Controlling and compensating the tunneling induced volume loss is the most effective measure for river embankment protection. Additionally, reinforcing the embankment with cement mixing pile in advance is an alternative option in case the predicted settlement exceeds allowable limit.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.25-34
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• 2009

RC flat plate, which has no large flexural stiffness by boundary beams, may be governed by serviceability as well as strength condition. A construction sequence and its impact on distributions of construction loads among slabs tied by shores are decisive factors on immediate and long term performances of flat plate. The over-loading and tensile cracking in early-aged slabs significantly increase the deflection of flat plate system. In this study, for slab deflections, the practical analysis scheme using a linear analysis program is formulated with considering construction sequence and concrete cracking effects. The concept of the effective moment of inertia in calculating deflections of one-way bending member, that is presented in structural design codes, is extended to the finite element analysis of the two-way slab system of flat plates. Effects of over-loads during construction on deflections of flat plate system are analyzed by applying the proposed practical analysis scheme into the critical construction load conditions calculated from the simplified method.

• Journal of the Korean GEO-environmental Society
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• v.16 no.2
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• pp.27-31
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• 2015

In urban area, many design projects related to geotechnical projects are controlled by serviceability rather than stability requirements. Accordingly, control of ground deformation has become more crucial and many researchers have studied soil stiffness. Recent experimental studies on the stress-strain response of Chicago glacial clays showed that the nonlinearity and anisotropy are the two key factors in evaluating the soil stiffness. In this study, experimental results are applied to analyze the deep excavation site locating in downtown Chicago. The stress paths observed from the observation points located behind and front of the supporting wall yield typical stress paths. Changes in soil stiffness nonlinearity and anisotropy were discussed by comparing experimental and computed stress paths. The stiffness anisotropy were significant even at the first few excavations. The stiffness degradation characteristics are significantly different according to relative location to the support wall even at the same elevation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.771-781
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• 1994

The heat generation of cement causes the internal temperature rise and volume change at early age, particulary in massive concrete structures. As the results of the temperature rise and restraint conditions, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction in order to control the cracks developed in mass concrete. In case of young concrete, creep effect by the temperature load is larger than that of old concrete. Thus, the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This paper is concentrated on the development of a finite element program which is capable of simulating the temperature history and the thermal stress considering creep and the modified elastic modulus due to inner temperature change and maturity. The analytical results in the inner parts highest important to control cracks are in good agreement with experimental data. Therefore this study may provide available method to control the cracks.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.655-662
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• 2011

For analyzing seismic performance of long-span bridge for multi-support excitation and preparing technically and efficiently for a variety of design demands, the new module on multiple excitation was built in a reliable non-linear analysis program(RCAHEST) by using Influence Line Method, and the study on structures was performed previously. Also, the result of the analysis through RCAHEST was compared and verified with commercial finite element analysis program SAP2000 by using the feature of Multi-Support Excitation. From these results, nonlinear time history analysis considering multi-support excitation was studied after designing FE model of Incheon cable-stayed bridge. It was proved that the maximum response of horizontal displacement decreased as the time delay was increasing at all nodes of bridge. And then the serviceability of analysis model was evaluated by performing ultimate analysis under changes in maximum acceleration of seismic load data.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.65-72
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• 2018

PURPOSE. The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials. MATERIALS AND METHODS. Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between $5^{\circ}C$ and $55^{\circ}C$. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test. RESULTS. All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed. CONCLUSION. When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.529-536
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• 2011

Recently, there has been a growing interest in expanded sidewalks for existing bridges. The cantilever beam system applied to expanded sidewalks for existing bridges are connected with the concrete structure by adhesive anchor bolts. However, the extended sidewalks are currently constructed without standardized regulations, which lead to excessive design of the beam spacing and installation and the construction difficulties due to the excessive over-weight. Moreover, there is only limited analysis and experiment data on the post-installed adhesive anchor bolts, so the excessive number of bolts is used for the connection. This paper deals with a method to increase the effectiveness of beam sections and anchor bolts geometry for expanded sidewalk of existing bridge. The study results showed that the failure of cantilever beam connected by adhesive anchor bolts was dominated by bond failure of interface between concrete and bolt. Also, the results indicated the possibilities of improving serviceability as well as safety of the sidewalks by changing of beam section and prestressing the bolts.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.50-58
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• 2018

The verification of serviceability of concrete structures requires more informations on the composite behaviors between concrete and reinforcement. Among them, the investigation of crack widths and spacings is based on the tension stiffening effects. In this paper, the tension stiffening effects of high strength concrete members with compressive strength of 80 and 100MPa are investigated experimentally. It was found that the current design code which is based on the tests of normal strength concrete may not describe the tension stiffening effects in high strength concrete correctly. The coefficient that can appropriately reflect the tension stiffening effects in the high strength concrete was proposed. Also, the crack spacing was investigated through the cracking behaviors and the crack width according to the difference of the strains in steel and concrete was estimated. The results of this paper may be used to examine the tension stiffening effects of high strength concrete members.