• Ocean Systems Engineering
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• v.5 no.2
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• pp.77-89
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• 2015

As the exploitation of oil and gas resources advances into deeper waters and harsher environments, the design and analysis of the flexible risers has become the research focus in the offshore engineering filed. Due to the complexity of the components and the sliding between the adjacent layers, the bending response of the flexible risers is highly non-linear. This paper presents the finite element analysis of the flexible risers under bending loads. The detailed finite element model of the flexible riser is established in ABAQUS software. This finite element model incorporates all the fine details of the riser to accurately predict its nonlinear structural behavior. Based on the finite element model, the bending moment-curvature relationships of a flexible riser under various axisymmetric loads have been investigated. The results have been compared with the analytical ones obtained from the literature and good agreements have been found. Moreover, the stress of the tendon armors has been studied. The non-linear relationship between the armor tendons' stress and the bending loads has been obtained.

• Computers and Concrete
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• v.15 no.1
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• pp.55-71
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• 2015

This paper presents a novel harmony search (HS)-based data-driven single input rule modules (SIRMs)-connected fuzzy inference system (FIS) for the prediction of stress in externally prestressed tendon. The proposed method attempts to extract causal relationship of a system from an input-output pairs of data even without knowing the complete physical knowledge of the system. The monotonicity property is then exploited as an additional qualitative information to obtain a meaningful SIRMs-connected FIS model. This method is then validated using results from test data of the literature. Several parameters, such as initial tendon depth to beam ratio; deviators spacing to the initial tendon depth ratio; and distance of a concentrated load from the nearest support to the effective beam span are considered. A computer simulation for estimating the stress increase in externally prestressed tendon, ${\Delta}f_{ps}$, is then reported. The contributions of this paper is two folds; (i) it contributes towards a new monotonicity-preserving data-driven FIS model in fuzzy modeling and (ii) it provides a novel solution for estimating the ${\Delta}f_{ps}$ even without a complete physical knowledge of unbonded tendons.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.353-361
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• 1989

A parametric study of load distribution in bolt-nut joints is performed by the method of finite element contact analysis. The contacting surface is assumed unbonded and frictionless. Multi-body contact analysis is performed in elastic region under the assumption of axi-symmetric stress state. Load acting on the first thread from the fastened plate is much greater than that on the other threads in the standard setting. But the load distribution is shown to be improved by making the center of contact force acting on the nut surface move outwards. Such a modification is possible by enlarging the gap between bolt shank and fastened plate or by inserting suitable washers. Shape modification of the standard nut by the making a groove and a step on the nut surface is also suggested, which results in almost uniform load distribution and considerable decrease in the maximum stress of the joint.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.140-148
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• 2012

Recently there are many attempts to introduce PC construction method in buildings. But the study on PC structural wall has been made progress so slowly because it is very difficult to develop new items. In this study, we have developed new vertical joint on PC wall in order to upgrade constructivity and structural performance of the existing connections, then we have evaluated the seismic resistance performance. As a result of the cyclic loading tests for two specimens, proposed vertical joint on PC wall has shown that it behave the excellent structural performance in comparison to PC wall having no joint. Therefore, we think that proposed vertical joint is the system to apply buliding structure.

• Structural Engineering and Mechanics
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• v.73 no.4
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• pp.447-454
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• 2020

Seismic isolation technology has a wide application to protect bridges from earthquake damage, a new designed bridge pier with seismic isolation are provided for railways in seismic regions of China. The pier with rocking isolation is a self-centering system under small and moderate earthquakes, and the unbonded prestressed tendons are used to prevent overturning under strong earthquakes. A numerical model based on pseudo-static testing results is presented to evaluate the seismic performance of isolation bridge piers, and is validated by the shaking table test. It is found that the rocking response and the loss of prestressing for the bridge pier increase with the increase of earthquake intensity. Besides, the intensity and spectral characteristics of input ground motion have great influence on displacement of the top and bottom of the bridge pier, while have less influence on the bending moment of the pier bottom. Experimental and numerical results show that the rocking-isolated piers presented in this study have good seismic performance, and it provides an alternative way for the railway bridge in the regions with high occurrence of earthquakes. Therefore, we provide the detailed procedures for seismic design of the rocking-isolated bridge pier, and a case study of the seismic isolation design with rocking piers is carried out to popularize the seismic isolation methods.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.1
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• pp.3-10
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• 2018

This experimental investigation was conducted to observe the shear strengthening behavior of pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. A total of six simply supported beams - two control beams and four post-tensioned beams using external steel rods - were tested to failure in shear. The external steel rods of 18 mm or 28 mm diameter were respectively employed as post-tensioning material. The four post-tensioned beams have a V-shaped profile with a deviator (or saddle pin) located at mid-span, and the post-tensioning system increased the low load-carrying capacity and overcame a little bit of deflection caused by damage. Concretely, the load-carrying capacity and flexural stiffness were respectively increased by about 25~57% and 263~387% due to the post-tensioning when compared with the unstrengthened control beams.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.2
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• pp.11-17
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• 2018

Concrete is the well-used material in many architectural and civil structures. The behavior of concrete does exhibit a different characteristic in compression and tension, and it also shows an inelastic-nonlinear behavior. In addition, the concrete properties vary slightly depending on the environmental factor and manufacturer. These properties of concrete make the modeling or simulation of concrete material difficult. In reinforced concrete, particularly, there is a difficulty in bond-slip relationship between concrete and steel. However, in this paper, reserving remainder of these limits the finite element analysis for reinforced concrete beams through ABAQUS simulation has been carried out with some assumptions. Assumptions include the perfect bond of steel and concrete as well as the concrete damaged plasticity (CDP) in concrete property. There is a reasonable agreement between the experimental and numerical results, although the analytical strength and external rod deformation are slightly overestimated. The average and standard deviation between two results are 1.05 and 0.05, respectively. And the models and the computations lead to the evolution of fracture in bending beam.

• Steel and Composite Structures
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• v.38 no.2
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• pp.165-176
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• 2021

Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

• Computers and Concrete
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• v.30 no.1
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• pp.75-83
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• 2022

This study introduced a post-tensioned precast concrete system that was developed and designed to improve the performance of joints by post-tensioning. Full-scaled specimens were tested to investigate flexural performances at the negative moment region, where the test variables were the presence of slabs, tendon types, and post-tensioned lengths. A specimen with slabs exhibited significantly higher stiffness and strength values than a specimen without slabs. Thus, it would be reasonable to consider the effects of a slab on the flexural strength for an economical design. A specimen with unbonded mono-tendons had slightly lower initial stiffness and flexural strength values than a specimen with bonded multi-tendons but showed greater flexural strength than the value specified in the design codes. The post-tensioned length was found to have no significant impact on the flexural behavior of the proposed post-tensioned precast concrete system. In addition, a finite element analysis was conducted on the proposed post-tensioned precast concrete system, and the tests and analysis results were compared in detail.

• Structural Engineering and Mechanics
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• v.84 no.2
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• pp.225-238
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• 2022

In order to improve the cracking resistance of reinforced concrete and give full play to the advantages of prefabricated assembly structure in construction, prestressed reinforced concrete composite beam (PRCC) is proposed. Through the bending static test of seven I-shaped beam specimens, the bending failure modes and bearing capacity of PRCC and reinforced concrete composite beam are compared and analyzed, and the effects of prestress size, prestressed reinforcement layout and prestress application sequence on the flexural behavior of PRCC beams are studied. The results show that the cracking load and ultimate load of PRCC beams significantly increased after prestressing, and prestressed tendons can effectively control the crack development. With the increase of prestressing degree, the deformation resistance and bending stiffness of PRCC beams are increased. The application sequence of prestress has little influence on the mechanical properties of PRCC beams. The crack width, stiffness and normal section bearing capacity of PRCC beam are analyzed, and the calculated results are in good agreement with the experimental results.