• Computers and Concrete
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• v.23 no.5
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• pp.335-349
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• 2019

A low-cycle loading experiment of 16 transfer column specimens was conducted to study the influence of parameters, likes the extension length of shape steel, the ratio of shape steel, the axial compression ratio and the volumetric ratio of stirrups, on the shear distribution between steel and concrete, the concrete damage state and the degradation of lateral stiffness. Shear force of shape steel reacted at the core area of concrete section and led to tension effect which accelerated the damage of concrete. At the same time, the damage of concrete diminished its shear capacity and resulted in the shear enlargement of shape steel. The interplay between concrete damage and shear force of shape steel ultimately made for the failures of transfer columns. With the increase of extension length, the lateral stiffness first increases and then decreases, but the stiffness degradation gets faster; With the increase of steel ratio, the lateral stiffness remains the same, but the degradation gets faster; With the increase of the axial compression ratio, the lateral stiffness increases, and the degradation is more significant. Using more stirrups can effectively restrain the development of cracks and increase the lateral stiffness at the yielding point. Also, a formula for calculating the yielding lateral stiffness is obtained by a regression analysis of the test data.

• Journal of International Academy of Physical Therapy Research
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• v.10 no.1
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• pp.1695-1699
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• 2019

Background : Although plank exercises is reported to the changes in muscle activity of the deep muscles and superficial muscles among the core muscles. However, no study has examined the effects of forearm plank exercise on tone and stiffness in the superficial back line muscle. Objective: To compare the effects of sling forearm plank exercises and mat forearm plank exercises on the superficial back line muscle tone and stiffness. Design: Randomized controlled clinical trial (single blind) Methods: The subjects were randomized to sling forearm plank exercise group (N = 8) or mat forearm plank exercise group (N = 8). The measurements were taken for each research group following exercises: the muscle tone and stiffness of upper lumbar muscles, lower lumbar muscles, long head of biceps femoris, and medial part of gastrocnemius among the superficial back line muscles. Results: Sling forearm plank exercise group Indicated statistically significant increases in stiffness of medial part of gastrocnemius (p<.05). However, mat forearm plank exercise group reported no statistically significant in muscle tone and stiffness of all measured muscles. No significant differences in measured variables were found between the groups. Conclusions: These results suggest that the forearm plank exercise performed with an unstable surface in the defined sling can increase the stiffness of calf muscle, but it is unlikely to achieve increases in muscle tone and stiffness of the overall superficial back line muscles.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.293-304
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• 2021

Structural failure due to seismic pounding between two adjacent buildings is one of the major concerns in the context of structural damage. Pounding between adjacent structures is a commonly observed phenomenon during major earthquakes. When modelling the structural response, stiffness of impact spring elements is considered to be one of the most important parameters when the impact force during collision of adjacent buildings is calculated. Determining valid and realistic stiffness values is essential in numerical simulations of pounding forces between adjacent buildings in order to achieve reasonable results. Several impact model stiffness values have been presented by various researchers to simulate pounding forces between adjacent structures. These values were mathematically calculated or estimated. In this study, a linear spring impact element model is used to simulate the pounding forces between two adjacent structures. An experimental model reported in literature was adopted to investigate the effect of different impact element stiffness k on the force intensity and number of impacts simulated by Finite Element (FE) analysis. Several numerical analyses have been conducted using SAP2000 and the collected results were used for further mathematical evaluations. The results of this study concluded the major factors that may actualise the stiffness value for impact element models. The number of impacts and the maximum impact force were found to be the core concept for finding the optimal range of stiffness values. For the experimental model investigated, the range of optimal stiffness values has also been presented and discussed.

• PNF and Movement
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• v.20 no.3
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• pp.321-329
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• 2022

Purpose: The purpose of this study was to compare the immediate effect on the change in muscle stiffness in the common extensor muscle (CEM) when using the spiral taping method to promote proprioception. Methods: There were 18 participants in this study. CEM stiffness was measured using a MyotonePRO device with the subject in a sitting position and according to the proprioceptive neuromuscular facilitation (PNF) arm pattern. Elastic tape was used as the material for the three taping methods employed in the study: kinesiotaping (KT), right spiral taping (RST), and left spiral taping (LST). The taping methods were applied to the wrist extensor muscle with elongation position. Additionally, when performing PNF arm patterns, spiral taping in diagonal and spiral directions was used to promote CEM proprioceptors. The change in CEM stiffness was compared with the initial data values. Results: The results of this study were obtained by comparing and measuring changes in CEM stiffness using three different tapings. It was found that the stiffness change of the CEM was significant compared to the initial value, and the increase in stiffness of the CEM after RST application was also significant. Conclusion: The results of this study show that by affecting the strength and activation of the extensor muscle, taping performed through the RST method had the most positive effect on the change in CEM stiffness.

• Journal of the Korean Arthroscopy Society
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• v.8 no.1
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• pp.45-50
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• 2004

Purpose: The purpose of this study is to compare the outcome of operative results in the impingement syndrome of the shoulder with and without the stiffness. Material and Method: Seventy-six patients who had the impingement syndrome without stiffness were evaluated, and treated with the subacromial decompression and 24 patients who had the impingement syndrome with stiffness, were treated with the subacromial decompression and the manipulation. The average follow-up period was 32 months. Result: The impingement syndrome of the shoulder with stiffness was more severe in the preoperative pain and worse in ASES score than without stiffness. The postoperative pain and ASES score improved in the both group. The satisfactory groups were 67% in the group with stiffness and 80% without stiffness. The satisfactory rate was 83% in the group with stiffness and 93% without stiffness. The satisfactory groups with diabetes were 47% in the group with stiffness and 81% without stiffness. Forward elevation, exeternal rotation at the side and internal rotation improved in both groups postoperatively and there were no statistically significant differences postoperatively External rotation was restricted statistically in the group with stiffness. Conclusion: Although patients may not regain the full range of motion, the technique of manipulation followed by arthroscopic subacromial decompression offers good pain relief and satisfactory functional recovery for the impingement syndrome with stiffness. However preoperative counseling is necessary for the impingement syndrome combined with diabetes and stiffness due to poor out come.

• Tribology and Lubricants
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• v.34 no.1
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• pp.23-32
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• 2018

Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic-plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.

• Steel and Composite Structures
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• v.34 no.4
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• pp.499-509
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• 2020

The purpose of this paper is to investigate the degradation law of stiffness of steel-concrete composite beams after certain fatigue loads. First, six test beams with stud connectors were designed and fabricated for static and fatigue tests. The resultant failure modes under different fatigue loading cycles were compared. And an analysis was performed for the variations in the load-deflection curves, residual deflections and relative slips of the composite beams during fatigue loading. Then, the correlations among the stiffness degradation of each test beam, the residual deflection and relative slip growth during the fatigue test were investigated, in order to clarify the primary reasons for the stiffness degradation of the composite beams. Finally, based on the stiffness degradation function under fatigue loading, a calculation model for the residual stiffness of composite beams in response to fatigue loading cycles was established by parameter fitting. The results show that the stiffness of composite beams undergoes irreversible degradation under fatigue loading. And stiffness degradation is associated with the macrobehavior of material fatigue damage and shear connection degradation. In addition, the stiffness degradation of the composite beams exhibit S-shaped monotonic decreasing trends with fatigue cycles. The general agreement between the calculation model and experiment shows good applicability of the proposed model for specific beam size and fatigue load parameters. Moreover, the research results provide a method for establishing a stiffness degradation model for composite beams after fatigue loading.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.31-43
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• 2015

A numerical analysis on the effect of increasing tensile stiffness of the geosynthetics on the soil displacement and pile efficiency was conducted. Parametric studies by changing the stiffness of soft soil, internal friction and dilatancy angles of the embankment material, and flexual stiffness of the composite layer including the geosynthetics were carried out. In general, increasing stiffness of the geosynthetics improves the pile efficiency, whereas the amount of its improvement depends on the condition of parameters. In case of the sufficiently low stiffness of the soft soil or high flexual stiffness of the composite layer including the geosynthetics, a noticeable increase in the pile efficiency can be observed. When the stiffness of the soft soil is very low, the increase in the stiffness of the geosynthetics can significantly reduce the vertical displacement in the piled embankment. When the flexual stiffness of the composite layer is sufficiently high, increasing stiffness of the geosynthetics can greatly improve the pile efficiency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.473-477
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• 2009

In general, the softer the stiffness of a linear vibration isolator the better the performance of isolation can be achieved. However, the stiffness of the isolator cannot be made too soft because it needs a sufficient stiffness to hold the load. This is the most critical limitation of a linear vibration isolator. Recently, a HSLDS (High-Static-Low-Dynamic-Stiffness) magnetic vibration isolator was proposed to overcome this fundamental limitation. The suggested isolator utilizes two pairs of attracting magnets that that introduces negative stiffness. Previously, this new type of vibration isolator was merely introduced and showed a possibility of practical use. In this paper, detailed dynamics of the HSLDS magnetic isolator are studied using computer simulations. Then, the isolation performance is examined for various design parameters to aid the practical use.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.321-321
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• 2009

This paper presents quasi-zero-stiffness (QZS) characteristic of a passive isolator using flexures under compression force. The passive isolator consists of a positive stiffness element (a vertical coil spring) and a negative stiffness element (flexures under compression force), and their proper combination of the positive and negative stiffness elements can produce both substantial static and zero dynamic stiffness, so called QZS. Firstly, a nonlinear dimensionless expression of a flexure under compression force is derived. A dynamic model of the passive isolator is developed and numerical simulations of its time and frequency response are performed. Then, undesirable nonlinear vibration is quantified using a period doubling bifurcation diagram and a Poincare's map of the isolator under forced excitation. Finally, experiments are performed to validate the QZS characteristic of the passive isolator.