• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.139-148
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• 1998

Internal and external heat sources will cause to deform to machine elements in the contact joint of structure, which results in the change of contact pressure distribution different from initial assembly. Heat induced variations of contact pressure will change the static and dynamic properties such as contact stiffness, damping as well as contact heat conduction in the structure In order to design and control the intelligent machine tool operating in variant conditions more sophisticatedly, the good prediction for the changes of prescribed properties are strongly required especially in the contact elements adjacent to the rotational or linear bearing. This paper presents some computational and experimental results in regard to static and dynamic characteristics of the press-fitted bush and shaft assembly which is a model of the bearing innerrace and shaft assembly. In the condition of heat generation on the outer surface of the bush, the effects of changes in the negative clearance and the heat flux on pressure distribution and dynamic properties are investigated. Results of this study show that the edge effect of the bush and the initial clearance have effects on the transient dynamic characteristics significantly.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.441-452
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• 2014

In this paper, steel reinforced concrete(SRC) column and composite beam connections were statically tested under gravity loading. The composite beam consists of H-section and U-section members. Five full-scaled specimens were designed to investigate the effect of a number of parameters on behavior of connections such as H-section size, the presence of stud connector, the presence of stiffeners and top bars. In addition, structural performance of welded joint between the H-section and the U-section members is mainly discussed, with an emphasis on initial stiffness, strength, deformation capacity.

• Computers and Concrete
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• v.21 no.4
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• pp.441-449
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• 2018

FE models for complex or large-scaled structures that need detailed modeling of structural components are usually constructed using commercial analysis softwares. Updating of such FE model by conventional sensitivity-based methods is difficult since repeated computation for perturbed parameters and manual calculations are needed to obtain sensitivity matrix in each iteration. In this study, an FE model updating procedure avoiding such difficulties by using response surface (RS) method and a Pareto-based multiobjective optimization (MOO) was formulated and applied to FE models constructed with a commercial analysis package. The test building is a low-rise reinforced concrete building that has been seismically retrofitted. Dynamic properties of the building were extracted from vibration tests performed before and after the seismic retrofits, respectively. The elastic modulus of concrete and masonry, and spring constants for the expansion joint were updated. Two RS functions representing the errors in the natural frequencies and mode shape, respectively, were obtained and used as the objective functions for MOO. Among the Pareto solutions, the best compromise solution was determined using the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) procedure. A similar task was performed for retrofitted building by taking the updating parameters as the stiffness of modified or added members. Obtained parameters of the existing building were reasonably comparable with the current code provisions. However, the stiffness of added concrete shear walls and steel section jacketed members were considerably lower than expectation. Such low values are seemingly because the bond between new and existing concrete was not as good as the monolithically casted members, even though they were connected by the anchoring bars.

• Korean Journal of Applied Biomechanics
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• v.31 no.2
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• pp.126-132
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• 2021

Objective: The purpose of this study was to investigate how three gaze directions (bottom, normal, up) affects the coordination and stability of the lower limb during drop landing. Method: 20 female adults (age: 21.1±1.1 yrs, height: 165.7±6.2 cm, weight: 59.4±5.9 kg) participated in this study. Participants performed single-leg drop landing task on a 30 cm height and 20 cm horizontal distance away from the force plate. Kinetic and kinematic data were obtained using 8 motion capture cameras and 1 force plates and leg stiffness, loading rate, DPSI were calculated. All statistical analyses were computed by using SPSS 25.0 program. One-way repeated ANOVA was used to compared the differences between the variables in the direction of gaze. To locate the differences, Bonferroni post hoc was applied if significance was observed. Results: The hip flexion angle and ankle plantar flexion angle were significantly smaller when the gaze direction was up. In the kinetic variables, when the gaze direction was up, the loading rate and DPSI were significantly higher than those of other gaze directions. Conclusion: Our results indicated that decreased hip and ankle flexion angles, increased loading rate and DPSI when the gaze direction was up. This suggests that the difference in visual information can increase the risk of injury to the lower limb during landing.

• Advances in concrete construction
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• v.8 no.2
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• pp.77-90
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• 2019

This paper aims to investigate vibration frequency decrease (vibration period elongation) of reinforced concrete (RC) structure with unreinforced infill wall and reinforced infill wall exposed to progressively increased artificial earthquake load on shaking table. For this purpose, two shaking table experiments were selected as a case study. Shaking table experiments were carried on 1:1 scaled prototype one bay one storey RC structure with infill walls. The purpose of this shaking table experiment sequence is to assess local behavior and progressive collapse mechanism. Frequency decrease and eigen-vector evolution are directly related to in-plane and out-of-plane bearing capacities of infill wall enclosure with reinforced concrete frame. Firstly, frequency decrease-damage relationship was evaluated on the base of experiment results. Then, frequency decrease and stiffness degradation were evaluated with applied Peak Ground Acceleration (PGA) by considering strength deterioration. Lastly, eigenvector evolution-local damage and eigenvector evolution-frequency decrease relationship was investigated. Five modes were considered while evaluating damage and frequency decrease of the tested specimens. The relationship between frequency decrease, stiffness degradation and damage level were presented while comparing with Unreinforced Brick Infill (URB) and Reinforced Infill wall with Bed Joint Reinforcement (BJR) on the base of natural vibration frequency.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.399-408
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• 2018

Cable supported structures have been widely used in civil engineering. Cable tension estimation has great importance in cable supported structures' analysis, ranging from design to construction and from inspection to maintenance. Even though the Bernoulli-Euler beam element is commonly used in the traditional finite element method for calculation of frequency and cable tension estimation, many elements must be meshed to achieve accurate results, leading to expensive computation. To improve the accuracy and efficiency, a dynamic finite element method for estimation of cable tension is proposed. In this method, following the dynamic stiffness matrix method, frequency-dependent shape functions are adopted to derive the stiffness and mass matrices of an exact beam element that can be used for natural frequency calculation and cable tension estimation. An iterative algorithm is used for the exact beam element to determine both the exact natural frequencies and the cable tension. Illustrative examples show that, compared with the cable tension estimation method using the conventional beam element, the proposed method has a distinct advantage regarding the accuracy and the computational time.

• Journal of Korean Society of Steel Construction
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• v.11 no.3 s.40
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• pp.271-279
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• 1999

Recently, studies on semi-rigid beam-to-column connections have been done to develop a T-stub element with separators between column face and T-stub flange. In this paper, inelastic analyses for the improved T-stub element are performed, and their results are compared with existing experimental results. The inelastic analyses using gap elements between column face and the separator, and initial stresses at the high-tension bolts result in good agreement with experimental results. Simplified design methods estimating the initial stiffness and the strength of the semi-rigid connection for compression force are proposed.

• Journal of muscle and joint health
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• v.14 no.1
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• pp.77-84
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• 2007

Purpose: The purpose of the study was to compare the effects of Tai Chi exercise, Tai Chi self help program, and self help management program on arthritic pain, stiffness, fatigue and difficulties in performing daily activities in patients with osteoarthritis. Method: The pre-post experimental design was utilized with convenient sampling at Public Health Centers. Total of 38 subjects agreed to participate in the study with the inclusion criteria of being diagnosed as osteoarthritis and no previous regular exercise. The 12 subjects were assigned to Tai Chi exercise group, 13 subjects to Tai Chi exercise combined with self help management program, and the other 13 to self help management program. Tai Chi exercise group performed exercise twice a week for one hour per each session. Tai Chi self help management group came to the class twice a week, one hour for Tai Chi exercise, and another hour for self help management program. The third group came to the class once a week for one hour to participate self help management program. At the completion of 6 week programs, 10 subjects from Tai Chi exercise, 9 from Tai Chi self help, another 10 from self help management groups completed the post-test measures. The data were analyzed by SPSSWIN 11.0. The homogeneity tests for three experimental groups were conducted by $X^2-test$, Fisher's exact test, Kruskal-Wallis test. The final analysis of the post-test measures was conducted by ANCOVA with fatigue, pain, stiffness, and difficulties in daily activities of the pretest measures as covariates. Results: The results were as follows. There were no significant differences in fatigue, pain, and difficulties of daily activities among three groups for the pretest measures. The score of arthritic stiffness was significantly different among groups after controlled for covariates, but the post-hoc tests showed no group differences. Conclusion: The nursing interventions applied for osteoarthritis patients have been previously tested to show the cost effectiveness of symptoms management of this population.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.93-100
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• 2015

Modern wooden structures usually are connected with steel fastener type connectors. And joints using multiple connectors in wooden structures will form semi-rigid connection. If connection in wooden structure would be designed to be pinned joint, the underestimate for loads transmitted through connection, would result in the deficient capacity of resistance in connection. And if joints in wooden structures would be assumed to be fully-rigid joint, amount of fasteners needed at the connection could be excessively increased. It will give a bad effect in the view of beauty, constructability and economy. Estimate for the reasonable stiffness of connection might be essential in design of reasonable connection in wooden structure. This paper will suggest analysis modelling technique that can represent approximate stiffness of connections using a common analysis program for double shear connection in order to give help in performing easily the design of wooden structure. It is verified that the suggested approximate analysis modelling technique could represent the behavior in connection by comparing the analysis results with test results for tensile, bending moment.

• Steel and Composite Structures
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• v.29 no.5
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• pp.603-622
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• 2018

Precast concrete structures are erected from individual prefabricated components, which are assembled on-site using different types of connections. In the present design of these structures, beam-to-column connections are assumed pin jointed. Bolted billet beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is currently limited information concerning their detailed structural behaviour under vertical loadings. The experimental work has involved the determination of moment-relative rotation relationships for semi-rigid precast concrete connections in full-scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and bolt arrangements conformed to successful commercial practice. Proprietary hollow core floor slabs were tied to the beams by 2T25 tensile reinforcing bars, which also provide the in-plane continuity across the connections. The contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. The flexural strength of the connections in the double-sided tests was at least 0.93 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.94 to 1.94 times the flexural stiffness of the attached beam. In general, the double-sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided bolted billet connection test results are presented in this paper. The behaviour of single sided bolted billet connection test results is the subject of another paper.