• Geomechanics and Engineering
• /
• v.19 no.1
• /
• pp.79-91
• /
• 2019

Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

• Steel and Composite Structures
• /
• v.43 no.6
• /
• pp.809-819
• /
• 2022

This paper proposes a method to predict the deflection of prestressed concrete (PC) beams with corrugated steel web (CSW) under constant load concerning time-dependent variation in concrete material. Over time, the top and bottom concrete slabs subjected to asymmetric compression experience shrinkage and creep deformations. Here, the classical Euler-Bernoulli beam theory assumption that the plane sections remain plane is not valid due to shear deformation of CSW. Therefore, this study presents a method based on the first-order shear deformation to find the long-term deflection of the composite beams under bending by considering time effects. Two experimental prestressed beams of this type were monitored under their self-weight over time, and the theoretical results were compared with those data. Additionally, 3D analytical models of the experimental beams were used according to material properties, and the results were compared with two previous cases. There was good consistency between the analytical and numerical results with low error, which increased by wave radius. It is concluded that the proposed method could reliably be used for design purposes.

• Journal of Navigation and Port Research
• /
• v.44 no.2
• /
• pp.128-135
• /
• 2020

Long-term shipping contracts represent the cooperative and coexisting relationships between the shipping and steel industries. Yet, differences between the contract forms for iron ore and steel products have emerged. Specifically, the large proportion of consecutive voyage charters (CVC) is being applied in the iron ore trade, whereas the contract of affreightment (COA) is proportionally higher for shipping steel products. The literature review and in-depth interviews in this study identified through the research model, the characteristics of the shipping and market structure in both markets have significantly contributed to the preference of different long-term contracts. It has been determined that the mutual oligopoly market structure and the characteristics of shipping such as, the small number of suitable vessels in the market, the single fixed load/discharge ports, the long-distance voyages, and the potential risks for fatal accidents because of cargo liquefaction, for the iron ore trade, provide higher contribution to the preference of CVC contracts. In contrast, the consignor oligopoly market structure and the shipping characteristics, such as the greater number of suitable vessels available in the market, the variation in ports, the cargo quantity per shipment, the various load/discharge ports, and the need for experienced carriers for steel product loading in the steel product trade has shown higher preference on the COA contracts as the consignors with superiority over the shipowners, resulting in favorable contract types and conditions for the consignors.

• Journal of Ocean Engineering and Technology
• /
• v.25 no.6
• /
• pp.110-115
• /
• 2011

Numerouslong-term consolidation and secondary compression settlements may occur in Busan clay, which is astructured soft clay and consists of a thick clay deposit. As a surcharge load is applied to soils, soils experience different stress paths with depth. Therefore, it is necessary to study the long-term consolidation behavior of Busan clay considering stress conditions such as OC or NC states. In this study, a series of long-term consolidation tests were performed to investigate the consolidation characteristics of Busan clay for 20 days. The undisturbed clay samples were taken from 3 sites located in the Nakdong River estuary. The results showed that the creep rate of the Busan clay gradually decreased with time, which indicated that the secondary compression settlement decreased with time. In addition, the experimental results for 3 samples showed that the ratios were about 0.0363 and 0.051, respectively.

• International journal of steel structures
• /
• v.18 no.4
• /
• pp.1252-1264
• /
• 2018

Long span bridges such as steel cable stayed and suspension bridges are usually more flexible than short to medium span bridges and expected to have large deformations. Deflections due to live load for long span bridges are important since it controls the overall heights of the bridge for securing the clearance under the bridge and serviceability for securing the comfort of passengers or pedestrians. In case of sea-crossing bridges, the clearance of bridges is determined considering the height of the ship master from the surface of the water, the trim of the ship, the psychological free space, the tide height, and live load deflection. In the design of bridges, live load deflection is limited to a certain value to minimize the vibrations. However, there are not much studies that consider the live load deflection and its effects for long span bridges. The purpose of this study is to investigate the suitability of live load deflection limit and its actual effects on serviceability of bridges for steel cable-stayed and suspension bridges. Analytical study is performed to calculate the natural frequencies and deflections by design live load. Results are compared with various design limits and related studies by Barker et al. (2011) and Saadeghvaziri et al. (2012). Two long span bridges are selected for the case study, Yi Sun-Sin grand bridge (suspension bridge, main span length = 1545 m) and Young-Hung grand bridge (cable stayed bridge, main span length = 240 m). Long-term measured deflection data by GNSS system are collected from Yi Sun-Sin grand bridge and compared with the theoretical values. Probability of exceedance against various deflection limits are calculated from probability distribution of 10-min maximum deflection. The results of the study on the limitation of live load deflection are expected to be useful reference for the design, the proper planning and deflection review of the long span bridges around the world.

• Proceedings of the KIEE Conference
• /
• 2000.07a
• /
• pp.307-309
• /
• 2000

This paper presents development of program for mid-tong term load forecasting in region and district respectively. In this program, at first, the region is classified by KEPCO branch which can be analyzed in light of curl·elation between load characteristics and economic indicator and then, prediction for load density in each region was performed by scenario of economic, population and city plan. Secondly, prediction for load density in each district is performed by methodology which is based on land use method. Finally efficiency for prediction work in each KEPCO branch could be identified by applying the developed program to the Seoul city in real.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.325-328
• /
• 2008

This study is to investigate experimentally the long-term deflection of concrete beams with glass fiber reinforced polymer (GFRP) reinforcing bars subjected to the sustained flexural load for periods of up to 6 months. A total of four beams were tested. All beams were designed with net span of 2,700 mm and rectangular cross-section of 200 mm width and 300 mm depth. From the test results the time-dependent deflection of concrete beams with GFRP bars was about 40 to 70% of the initial deflection. As well as this paper compares the long-term deflection calculated by 440.1R-06 design guide and that of tested beams. The comparison indicated that the calculated long-term deflection overestimate the observed long-term deflection of concrete beams with FRP rebars.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.4
• /
• pp.343-350
• /
• 2017

The RC flat plate system has benefits such as a short construction time, an improvement of workability and a floor height reduction. In the case of long span slab, cracking damages and large deflections tend to occur due to the low flexural stiffness of flat plates. Specially, over-loading by self-weight of slab during construction increases short and long-term deflections. These problems may be solved by the use of void slab that has benefits of the reduced self-weight. In this study, to analyze an effect of self-weight reduction of void slab on slab deflections, the parametric study is performed. Including variable conditions such as a concrete strength, a slab construction cycle, the number of shored floors, a compressive reinforcement ratio and a tensile reinforcement ratio, slab construction loads and deflections are calculated by considering the construction stages, concrete cracking, and long-term effects. The short-term deflections during construction and the long-term deflections after construction of both of normal and void slabs are compared and the effects of void slab on the reduction of slab deflections are analyzed.

• Structural Engineering and Mechanics
• /
• v.20 no.6
• /
• pp.673-693
• /
• 2005

A general step-by-step simulation for the time-dependent analysis of segmentally-erected prestressed concrete box-girder bridges is presented. A three dimensional finite-element model for the balanced-cantilever construction of segmental bridges, including effects of the load history, material nonlinearity, creep, shrinkage, and aging of concrete and the relaxation of prestressing steel was developed using ABAQUS software. The models included three-dimensional shell elements to model the box-girder walls and Rebar elements representing the prestressing tendons. The step-by-step procedure allows simulating the construction stages, effects of time-dependent deformations of materials and changes in the structural system of the bridges. The structural responses during construction and throughout the service life were traced. A comparison of the developed computer simulation with available experimental results was conducted and good agreement was found. Deflection of the bridge deck, changes in stresses and strains and the redistribution of internal forces were calculated for different examples of bridges, built by the balanced-cantilever method, over thirty-year duration. Significant time-dependent effects on the bridge deflections and redistribution of internal forces and stresses were observed. The ultimate load carrying capacities of the bridges and the behavior before collapse were also determined. It was observed that the ultimate load carrying capacity of such bridges decreases with time as a result of time-dependent effects.

• Journal of the Society of Naval Architects of Korea
• /
• v.52 no.3
• /
• pp.198-205
• /
• 2015

In this study, numerical studies using a Computational Fluid Dynamics(CFD) method were carried out to estimate the green water load acting on the breakwater plate of bow deck of container carrier, KCS. For the green load water load analysis, a full load condition was considered. The relative motions at bow deck were calculated from the seakeepig analysis. Statistical analysis were carried out to estimate the long term response of the relative motions with the North Atlantic wave scatter diagram. The equivalent design wave was determined from the RAO of the relative motions at bow and the long term responses. CFD geometry modeling with three different locations and simulations for the green water loads were carried out in the equivalent design waves. A commercial CFD program, STAR-CCM+ Ver. 8.04, was used and the green water pressures on the breakwater plate were calculated successfully. The CFD analysis for green water loads can be used as a useful design tool for the evaluation of the breakwater plate of the container vessel.