• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.4
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• pp.350-357
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• 2017

This study was conducted as a post - study on the development of a centralized controller and a hydraulic lift system including structural analysis and remote control for the development of a vertically elevated car. The safety review was carried out through the structural modification of the elevator lift which was developed during the previous research. 3D modeling was performed with Solidworks, and a model of finite element was created through Hypermesh S / W. In addition, the loading environment of the work vehicle for the evaluation is a condition in which the loading amount is 250 kg per position (total, upper, upper, lower, and lower) on the work table, ), The structural analysis was carried out under the condition that the load was 600 kg, and safety was examined in various aspects. As a result, when the allowable load of 250 kg and the excess load of 600 kg are excluded (except Case-11), the stress level is below the yield strength. In the case of Case-11, there is a region exceeding the yield strength at the center support portion of the safety bar at the upper end even after excluding the component which generates the maximum stress, but it does not affect the safety aspect of the whole structure Respectively. Looking at the deflection results, it can be seen that in all cases the maximum deflection occurs in the same table, and the tendency of sagging in both 250 kg and 600 kg is the same.

• The korean journal of orthodontics
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• v.40 no.1
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• pp.40-49
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• 2010

Objective: The aim of this research was to evaluate the mechanical properties (MP) and degree of the phase transformation (PT) of martensitic (M-NiTi), austenitic (A-NiTi) and thermodynamic nickel-titanium wire (T-NiTi). Methods: The samples consisted of $0.016\;{\times}\;0.022$ inch M-NiTi (Nitinol Classic, NC), A-NiTi (Optimalloy, OPTI) and T-NiTi (Neo-Sentalloy, NEO). Differential scanning calorimetry (DSC), three-point bending test, X-ray diffraction (XRD), and microstructure examination were used. Statistical evaluation was undertaken using ANOVA test. Results: In DSC analysis, OPTI and NEO showed two peaks in the heating curves and one peak in the cooling curves. However, NC revealed one single broad and weak peak in the heating and cooling curves. Austenite finishing ($A_f$) temperatures were $19.7^{\circ}C$ for OPTI, $24.6^{\circ}C$ for NEO and $52.4^{\circ}C$ for NC. In the three-point bending test, residual deflection was observed for NC, OPTI and NEO. The load ranges of NC and OPTI were broader and higher than NEO. XRD and microstructure analyses showed that OPTI and NEO had a mixture of martensite and austenite at temperatures below Martensite finishing ($M_f$). NEO and OPTI showed improved MP and PT behavior than NC. Conclusions: The mechanical and thermal behaviors of NiTi wire cannot be completely explained by the expected degree of PT because of complicated martensite variants and independent PT induced by heat and stress.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.393-404
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• 2008

The approaches in many design codes for the estimation of the deflection of flexural reinforced concrete (RC) members utilize the concept of the effective moment of inertia which considers the reduction of flexural rigidity of RC beams after cracking. However, the effective moment of inertia in design codes are primarily based on the ratio of maximum moment and cracking moment of beam subjected to loading without proper consideration on many other possible influencing factors such as span length, member end condition, sectional size, loading geometry, materials, sectional properties, amount of cracks and its distribution, and etc. In this study, therefore, an experimental investigation was conducted to provide fundamental test data on the effective moment of inertia of RC beams for the evaluation of flexural deflection, and to develop a modified method on the estimation of the effective moment of inertia based on test results. 14 specimens were fabricated with the primary test parameters of concrete strength, cover thickness, reinforcement ratio, and bar diameters, and the effective moments of inertia obtained from the test results were compared with those by design codes, existing equations, and the modified equation proposed in this study. The proposed method considered the effect of the length of cracking region, reinforcement ratio, and the effective concrete area per bar on the effective moment of inertia, which estimated the effective moment of inertia more close to the test results compared to other approaches.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.61-69
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• 2011

Fiber Reinforced Plastic (FRP) sheets have been widely used to retrofit and rehabilitate RC structures, while in case of retrofitting steel structures, there are no codes and researches. It stems from configuration of member and characteristics of bonding behavior. This study focused on the static behavior of steel beams reinforcement by AFRP sheets. The main objective of the experimental programme was the evaluation of the force transfer mechanism, the increment of the beam load carrying capacity and the bending stiffness. A bending test was conducted on a H-shaped steel beam, with aramid FRP sheets bonded to its flanges. The mid-span deflection and the strain from three points along AFRP sheets were recorded Test results exhibit that the increment of the load-carrying capacity with reference to a mid-span deflection level of 15 mm(1/125mm of the clear span) was equal to 9.4% and for the two layers case, an elastic stiffness increment is slightly higher than one layer case.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.393-400
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• 2011

The needs for high strength structural materials have recently increased, because construction and cost efficiencies are demanded by the costumers. But, the use of high strength reinforcing bars requires longer development and splice lengths compared to normal strength bars. This restriction may cause reduction in construction efficiency and require more complicated details. The purpose of this paper is to evaluate the bond strength on the rib shape of reinforcing bars to decrease development and splice lengths of high strength reinforcements. Total of 5 simple beam specimens were tested, and the main test variable was a rib shape of reinforcing bars. Test data was analyzed in the viewpoint of bond strength, load-deflection relationship, and crack pattern. Test results indicated that the bond strength of high relative rib area reinforcing bars increased up to 11% compared to normal strength reinforcements. And the improved rib shape reinforcements, which were formed with high and low height rib, increased the bond strength up to 23% even though the relative rib area was same as the high relative rib area reinforcements. Serviceability performances such as deflection number of cracking, and maximum crack width were similar in all specimens, so it is safe to conclude that the improved rib shape reinforcements can be applied to the structural members.

• Structural Engineering and Mechanics
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• v.50 no.5
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• pp.589-603
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• 2014

Expressions for determining the value of the impact force as reported in the literature and incorporated into code provisions are essentially quasi-static forces for emulating deflection. Quasi-static forces are not to be confused with contact force which is generated in the vicinity of the point of contact between the impactor and target, and contact force is responsible for damage featuring perforation and denting. The distinction between the two types of forces in the context of impact actions is not widely understood and few guidelines have been developed for their estimation. The value of the contact force can be many times higher than that of the quasi-static force and lasts for a matter of a few milli-seconds whereas the deflection of the target can evolve over a much longer time span. The stiffer the impactor the shorter the period of time to deliver the impulsive action onto the target and consequently the higher the peak value of the contact force. This phenomenon is not taken into account by any contemporary codified method of modelling impact actions which are mostly based on the considerations of momentum and energy principles. Computer software such as LS-DYNA has the capability of predicting contact force but the dynamic stiffness parameters of the impactor material which is required for input into the program has not been documented for debris materials. The alternative, direct, approach for an accurate evaluation of the damage potential of an impact scenario is by physical experimentation. However, it can be difficult to extrapolate observations from laboratory testings to behaviour in real scenarios when the underlying principles have not been established. Contact force is also difficult to measure. Thus, the amount of useful information that can be retrieved from isolated impact experiments to guide design and to quantify risk is very limited. In this paper, practical methods for estimating the amount of contact force that can be generated by the impact of a fallen debris object are introduced along with the governing principles. An experimental-calibration procedure forming part of the assessment procedure has also been verified.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.329-338
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• 2024

Purpose: This study verified the safety of the improved box-type girder behavior by comparing and evaluating the bending behavior results of a full-scale specimen based on the analytical behavior of the splice element PSC U-shaped girder with integrated tensioning systems. Method: Based on the results of the service and strength limit state design using the bridge design standard(limit state design method), the applied load of a 40m full-scale specimen was calculated and a static loading experiment using the four-point loading method was performed. Result: When the design load, crack load, and ultimate load were applied, the specimen deflection occurred at 97.1%, 98.5%, and 79.0% of the analytical deflection value. When the design load, crack load, and ultimate load were applied, the crack gauge was measured at 0.009~0.035mm, 0.014~0.050mm, and 6.383~5.522mm at each connection. Conclusion: The specimen behaved linear-elastically until the crack load was applied, and after cracks occurred, it showed strainhardening up to the ultimate load, and it was confirmed that the resistance of bending behavior was clearly displayed against the applied load. The cracks in the dry joints were less than 25% of grade B based on the evaluation of facility condition standard. The final residual deformation after removing the ultimate load was 0.114mm, confirming the stable behavior of the segment connection.

• Structural Engineering and Mechanics
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• v.14 no.3
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• pp.331-343
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• 2002

Because of the increasing span of arch bridges, ultimate capacity analysis recently becomes more focused both on design and construction. This paper investigates the static and ultimate behavior of a long-span steel arch bridge up to failure and evaluates the overall safety of the bridge. The example bridge is a long-span steel arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any arch bridge in the world. Ultimate behavior of the example bridge is investigated using three methods. Comparisons of the accuracy and reliability of the three methods are given. The effects of material nonlinearity of individual bridge element and distribution pattern of live load and initial lateral deflection of main arch ribs as well as yield stresses of material and changes of temperature on the ultimate load-carrying capacity of the bridge have been studied. The results show that the distribution pattern of live load and yield stresses of material have important effects on bridge behavior. The critical load analyses based on the linear buckling method and geometrically nonlinear buckling method considerably overestimate the load-carrying capacity of the bridge. The ultimate load-carrying capacity analysis and overall safety evaluation of a long-span steel arch bridge should be based on the geometrically and materially nonlinear buckling method. Finally, the in-plane failure mechanism of long-span steel arch bridges is explained by tracing the spread of plastic zones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1526-1533
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• 2004

The needs of walking assistant device such as the Ankle Foot Orthosis (A.F.O) are getting greater than before. However, most of the A.F.O are generally imported rather than domestic manufacturing. The major reason of high import reliability is the rack of impact properties of domestic commercial products. Therefore, this research is going to focus on the evaluation of impact properties of the A.F.O which has the high import reliability. Unfortunately, these kinds of researches are not performed sufficiently. This research is going to evaluate impact energy behavior in composite materials such as the glass/epoxy (S-glass, [0/90]sub 2S/) and the aramid/epoxy (Kevlar-29, woven type, 8 ply) of ankle foot orthosis. The approach methods were as follows. 1) The history of impact load and impact energy due to the various velocities. 2) Relationship between the deflection and damage shape according to the impact velocities. 3) The behavior of absorbed energy and residual strength rate due to the various impact velocities.

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.9-20
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• 2011

Most of domestic expansion joint system was applied by exposed expansion joint system. There are cases where it is damaged by driving. As the result noise and impact happened, and the social cost due to frequent repair works is increasing. So based on the Asphalt Plug Joint(APJ) system that applied in the United States and Europe, new buried expansion joint system was lately developed a system of Buried Folding Lattice Joint(BFLJ) that changed substructure. In this research, we have tested for durability and flexibility performance of buried expansion joint system that based on the type of asphalt mixture. Also we have evaluated for durability of BFLJ system against vehicle load using accelerated pavement testing. As a result of the experiment, the developed BFLJ system gives high flexibility performance and resolves transformation concentration along the joint section more than APJ system. Also it could be seen that the BFLJ system could overcome the disadvantages of APJ and prevent early damage. Because surface deflection of BFLJ system against vehicle load was measured low, and sub system in the buried expansion joint system was not damaged against vehicle load.