Jong Hwa Won

Distinct element method analysis of a retaining wall using a steel frame and fill materials

A technique is developed to clearly establish the shear resistance of a cellular structure, retaining wall composed of a steel frame and fill materials with both continuous and discontinuous characteristics. To overcome the limitation of the existing analysis approach based on continuum mechanics, in which the shear behavior and interaction between the frames and fill material of this type of structure are difficult to describe, this paper introduces displacement incremental analysis into the distinct element method. The results obtained by using the proposed approach are compared with experimental results to verify its accuracy. The results show an internal friction angle of fill materials and overburdening load are major factor determining the shear resistance of a retaining wall with a cellular structure type. From the results of the parametric study on the shear behavior of this type of structure, this paper also proposes a shear resistance moment-shear displacement formula for designing a retaining wall with a cellular structure type.

Integrated assessment for route selection of river-crossing pipeline using structural and hydraulic approach

An optimised route design procedure for a river-crossing pipeline that minimises disturbance to the structure and stream environment during its lifetime is presented in this article. The work covers both the assessment of hydrological conditions and mechanical performance of the pipeline and its protective structure. The assessment techniques for crossings involve a numerical and analytical method for simple integrity estimation. The procedure provides a feedback link to select the optimised crossing route and inform the structural repair design step. As a case study, the proposed route selecting technique is applied to a river with an exposed section in Gyeonggi Province, Korea. Complicated hydraulic flow fields are apparent in this area due to the narrow shortcut directly upstream of the pipeline. In the scour state analysis, an installed encasement, and not an alternative route, exhibits sufficient structural robustness under flood conditions.

Blast-induced dynamic response on the interface of a multilayered pipeline

This study presents an analytical vibration propagation model on a multilayered pipeline based on a full-scale field test and numerical studies. The derived analytical expressions are evaluated through comparison against 3D dynamic numerical analyses and field measurements in three-layered pipelines. In this study, the blasting test results from two sites are used for equation verification. When a wave propagates in a multilayered medium, its physical characteristics, such as velocity or pressure, change depending on the properties of the medium. Therefore, when an external wave passes through each stratum of a multilayered pipeline, the magnitude of pressure or velocity shows lower level than before. To obtain the wave pressure reduction model, the interface pressure should be defined in advance so that the stress distribution at the contact surface, derived from the Lames equation of a thick-walled cylinder, can be estimated. Using the results of experimental and analytical approaches, the obtained maximum vibration velocity of steel (inner) pipe and high density polyethylene (outer) pipe is almost the same. The distributed and reduced pressure exhibits a lower pressure state and time-delayed wave propagation when passing through thick and loose filler.

Full-Scaled Experiment for Behavior Investigation of Reinforced Concrete Columns with High-Strength Wire Ropes as Lateral Spiral Reinforcement

This study performs the test with full-scaled models for each diameter to evaluate the behavior of the reinforced concrete columns using the spiral wire rope as a lateral reinforcement of the circular columns. This study performs the quasi-static test which induced binding shear destruction to review circular concrete columns bound with high strength wire rope. Three specimens of concrete columns with 700 and 800 mm diameter each were manufactured to evaluate the movement of reinforced circular columns with the wire rope. A hoop reinforced column and 2 spiral reinforced columns were manufactured to compare the bending history and the ductility reinforced with the wire rope to existing reinforced concrete columns. The peak strain of the longitudinal reinforcements is occurred at approximately 0.75 D from the bottom of the column. The spirally confined concrete columns with high-strength wire ropes showed that improve 2.5 % of the shear strength.

Local Deformed Diameter Analysis of a Pipe in Rigid Encasement for Water-crossings Application

This article presents a new type of stress assessment method for double-layered pressure vessel. Due to its robust strength, a steel–concrete composite pipe is generally installed in poor burial conditions. However, it is difficult to directly define the stress state on pipe sections. For the convenient stress estimation of pipes encased in non-circular concrete, this article suggests a Stress Index (SI), a function of the interface pressure and changed diameter, based on the interface pressure. The ovalization characteristics of plain pipes and of pipes encased by circular and rectangular concrete are examined. The resultant stresses are replaced by the non-dimensional ratio of diameter change; thus, the stress index has the advantage of application for stress assessment irrespective of pipe characteristics.

Deformation-Based Behavior of X65 Gas Pipeline in Rectangular Concrete Encasement

The pipelines located in cold region, offshore and under riverbed are exposed and unpredictable loads and these pipelines should be protected by assistant structures. As one manner of protecting river crossing pipelines, a rectangular concrete encasement is generally used in Korea. This paper describes behavior characteristics of underground pipelines encased in rectangular concrete box in terms of deformed radius derived from occurred hoop stress. The solution for contact pressure between steel pipeline and concrete encasement is derived from the equation of Lame’s double walled cylinder. Every FEA model adopted in this study has same pipe diameter (762mm), internal pressure and cover depth. A variable is only the thickness of concrete encasement. This problem is formulated as a shrink-fit cylinder because of the inner steel pipe expanding by internal gas pressure. In order to get a deformed radius, the interface (contact) pressure was calculated, and the local deformed radius was determined based on obtained interface pressure and hoop stress. In this data processing, peculiar ovalized shape was developed in the section of the X65 steel pipeline covered with rectangular concrete encasement. The result in terms of the rate of local diameter change describes that shoulder (±45°, ±135°) part has the largest change rate over 120% and the smallest values occurred at a bottom (±180°). By using the relation of encasement size and deformed diameter, the results make stress design for the double layer pipeline be more precise and effective.Copyright