• Journal of Korean Society of Steel Construction
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• v.21 no.2
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• pp.135-144
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• 2009

This study aims to suggest an appropriate flexural reinforcement technique by evaluating the reinforcement capacity of specimens that underwent flexural reinforcement according to the post-tension method with the anchoring position of an unbonded tension member on the conventional SC composite beam and the applied tension level as variables. For the experiment, up to a predetermined yield load was applied to each type of specimen and then, unbounded post-tensioning was additionally conducted to examine its reinforcement capacity. The analysis of the said experiment showed that the post-reinforced SC composite beam was characterized by significantly improved yield stress and initial stiffness, compared with the pre-reinforced one and the experimental measurements/theoretical values of maximum stress ranged from 0.95 to 1.13 following reinforcement. There was little or no change depending on the maximum stress and tension in the specimen (D160, Class 240) whose neutral axis and upper part had anchoring devices mounted prior to reinforcement. Rather, the ductility decreased with the increasing tension. On the contrary, in the case of the other specimen (Class D120) whose neutral axis had anchoring devices mounted after reinforcement, both the maximum stress and ductility increased with increasing tension, which indicates that the latter tension reinforcement was reasonably appropriate and effective for the neutral axis reinforcement.

• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.23-33
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• 2008

The moment redistribution in continuous reinforced concrete beams is very feasible phenomenon, by which the efficiency and the economy in designing reinforced concrete members can be enhanced. However, to understand the structural behavior by moment redistribution phenomenon, it is desirable to verify its mechanism experimentally considering tension stiffening effect, the relationship of moment redistribution and beam deflection, crack pattern, and effective stiffness. Six reinforced concrete continuous beam specimens were fabricated, and each specimen had a dimension of 250 mm $\times$ 350 mm and 7,000 mm long. The location of de-bonding was taken as the primary test parameter to investigate tension stiffening effect. The moment redistribution ratio of the specimens was different depending on the position of de-bonding, and in particular no moment redistribution was observed when de-bonding exist at both ends, the maximum negative moment region and the maximum positive moment region.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.88-98
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• 2011

Masonry structure is a style of building which has been widely applied as residential facilities of low and middle stories, commercial and public facilities etc. But it is possible to destroy by loss of adhesive strength or sliding when lateral forces, such as earthquake, occurs. This study proposes a seismic retrofit method for masonry structure and its seismic performance is demonstrated by shaking table test. Two specimens per each shaking direction were made, having out-of-plane(weak axis) and in-plane(strong axis) direction. External load of 1 ton was also applied for each specimen during the test, to model the behavior of reinforced masonry wall. As a result of shaking table tests, it is shown that the specimen applying the proposed seismic retrofit method showed acceptable behaviors in both of Korea building design criteria(0.14g) and USA seismic criteria suggested by IBC(0.4g). However, it was observed that stiffness of the specimen toward out-of-plane was rapidly decreasing when seismic excitations over 0.14g were loaded. In comparison of relative displacements, maximum relative displacement of specimens which were accelerated toward out-of-plane with 0.4g at once was 29~31% of maximum relative displacement when specimens were gradually accelerated from 0.08g to 0.4g, while the maximum relative displacement of specimens accelerated toward in-plane has similar value in both cases. Therefore, it is concluded that the wall accelerated toward out-of-plane is more affected by hair crack or possible fatigues caused by seismic excitation.

• Journal of the Korean Geosynthetics Society
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• v.19 no.2
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• pp.1-11
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• 2020

The lateral bearing characteristics of large diameter drilled shaft depend greatly on the stiffness of the pile, horizontal subgrade reaction of adjacent ground. In particular, the empirical evaluation results of the horizontal subgrade reaction coefficient which are widely used in pile design are very important factors in evaluating the lateral bearing capacity of drilled shaft because the difference in bearing capacity depends on the estimated result. Nevertheless, the evaluation of the horizontal subgrade reaction coefficient on the large diameter drilled shaft is insufficient. In addition, although the range of influence and the location of the maximum moment which is the weaken zone on the pile may be correlated and relationship of these are major consideration in determining the reinforced zone of drilled shaft, the previous studies have not been evaluated it. In this study, the field test and nonlinear analysis of large diameter drilled shaft were performed to evaluate the horizontal subgrade reaction coefficient and to investigate the relationship between the influence range 1/β of the pile and the location of the maximum moment z_m. In the result, the lateral bearing capacity of drilled shaft showed a difference in results by about 190% according to the empirical equation on the horizontal subgrade reaction coefficient. And the relationship between the influence range of the pile and the location of the maximum moment was evaluated as a linear relationship depending on the soil density.

• Journal of Korean Society of Steel Construction
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• v.17 no.5 s.78
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• pp.569-580
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• 2005

The postbeam joint connection of the existing steel structure moment flexible frame system did not produce sufficient seismic resistance during the earthquakes in Northridge and Kobe, and it sustained brittle fracturing on the joint connection. This study was performed to execute the high-tensile bolt share connection of H-beams web and the full-scale experiment as a parameter of the existing reinforcement of H-flange rib, by making the shape of the existing joint connection. This experiment was performed to determine the extent of the decrease of the number of high-tensile bolts and how to improve workability of the two-phase shear connection of web beam. In addition, this study was performed to enhance the seismic resistant capacity through the enforcement of rib plates. As a result of the experiment of two-phase shear connection of H-beam web and of joint connection to be reinforced by rib plates, the results of this study showed that the initial stiffness, energy-dissipation capacity, and rotational capacity of plasticity was higher than the existing joint connection. As to the rate of increasing the strength and deformation capacity, there were differences between the tension side and compression side because of the position of shear tap. However, as a whole, they have shown excellent seismic resistant capacity. Also, all the test subjects exceeded 4% (rate of delamination), about 0.029 rad (total plastic capacity), and about 130% (maximum strength of joint connection) of fully plastic moment for the original section. Accordingly, this study was considered as it would be available in the design more than the intermediate-level of moment flexible frame.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.796-803
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• 2002

T-shaped walls have different strength, stiffness and ductility in the two opposite directions parallel to the web when subjected to horizontal in-plane loads. When the flange is in tension, the extent that the flange reinforcement contributes to the flexural strength will be subjected to shear-lag effect. Because of this shear-lag effect, the flange may not participate fully in the action with the web, and the effective flange width is needed for predicting the actual strength and stiffness of structures. The objective of this paper is to evaluate the effective flange width and actual strength of the T-shaped wall with Korean code specified detailing of the wall web. Three specimens were tested with cyclic lateral loading applied at top of the wall. A constant axial load of approximately 0.1f$\_$ck/$.$A$\_$g/ is maintained during the testing. Test results show that the effective flange width increases with increasing drift level, such that the entire overhanging flange of h/3 is effective at the maximum strength level. Therefore, the use of PCI or KBC(Korean Building Code) value of h/10 is unconservative with respect to detailing at the wall web boundary.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.12-17
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• 2018

In order to enhance the realism of a virtual environment, a method of maximizing the stiffness of the virtual environment model is needed, which maintains the stability of the haptic system. In our previous research, we proposed a haptic system with a first order hold, instead of a zero order hold, and showed that the maximum available stiffness of a virtual spring with the first-order hold is larger than that with the zero-order hold. However, in terms of real system implementation, the zero order hold is a more common and easy method. In this paper, we propose an extrapolation method and a high frequency zero-order-hold output method in order to obtain the stability region using a zero order hold, which is equivalent to the method using the first-order-hold. The simulation results shows that the stability range of the virtual spring becomes almost the same as that of the method using the first order hold when the sampling period of the high frequency zero-order-hold method is decreased. Moreover, the stability range of the proposed method is several times to several tens of times greater than that of the method using the zero order hold only. Therefore, it is expected that the proposed method can enhance the realism of rigid bodies in a virtual environment.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.833-840
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• 2008

The time and cost can be reduced when applying partial precast concrete to the stair system in comparison to the cast-in-place or precast method. Because the performance of staircase which is used for evacuation can be largely different from connection types of precast concrete member, we tried to know structural behavior and performance evaluation according to each type of stair joints by experimental study. In the cast-in-place rigid joint, much reinforcement is needed in the end portion because much stress is concentrated in the middle portion. Also, in the pin joint which is used in the connection point, the maximum stress occurs in the middle point, so not only the amount of re-bar is increased but also the serviceability is largely decreased. The bolt type of semi-rigid joints proposed in this study had been increased strength and serviceability which is similar to the rigid joints. Also, its ductility was shown about 0.7 times in comparison to the rigid type and was about 2.8 times for the pin joint type. According to the classification of joint in Eurocode, it can be considered that it is one of the semi-rigid joints which are in the semi-rigid-full strength, and the structural behavior can be expected by using a model which applied to stiffness value decreased by 40 percent.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.37-45
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• 2014

An embedded length of monopile caused by a scouring should be evaluated to monitor the stability of offshore foundations, because offshore foundations are affected by horizontal load. The objective of this study is to evaluate the scouring around offshore foundation by using electrical resistivity and to estimate ground stiffness by using shear wave tomography. The electrical resistivity profiles and shear wave tomography were measured according to the scour depth of model ground prepared with sand and cement. Several electrodes and bender elements were used to measure the electrical resistivity and shear waves, respectively. The electrode sets are attached on the monopile surface and bender elements are arranged in $7{\times}7$ arrays by using nylone frames. The electrical resistivity profiles and shear wave tomography are acquired by laboratory experiment. Maximum scour depth was estimated by electrical resistivity profiles and the ground stiffness of model ground was estimated by shear wave tomography. This study suggests that the electrical resistivity profiles and shear wave tomography may be useful for monitoring the stability of the offshore foundations.

• Smart Structures and Systems
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• v.26 no.5
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• pp.575-589
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• 2020

For vibration control of stay cables in cable-stayed bridges, viscous dampers are frequently used, and they are regularly installed between the cable and the bridge deck. In practice, neoprene rubber bushings (or of other types) are also widely installed inside the cable guide pipe, mainly for reducing the bending stresses of the cable near its anchorages. Therefore, it is important to understand the effect of the bushings on the performance of the external damper. Besides, for long cables, external dampers installed at a single position near a cable end can no longer provide enough damping due to the sag effect and the limited installation distance. It is thus of interest to improve cable damping by additionally installing dampers inside the guide pipe. This paper hence studies the combined effects of an external damper and an internal damper (which can also model the bushings) on a stay cable. The internal damper is assumed to be a High Damping Rubber (HDR) damper, and the external damper is considered to be a viscous damper with intrinsic stiffness, and the cable sag is also considered. Both the cases when the two dampers are installed close to one cable end and respectively close to the two cable ends are studied. Asymptotic design formulas are derived for both cases considering that the dampers are close to the cable ends. It is shown that when the two dampers are placed close to different cable ends, their combined damping effects are approximately the sum of their separate contributions, regardless of small cable sag and damper intrinsic stiffness. When the two dampers are installed close to the same end, maximum damping that can be achieved by the external damper is generally degraded, regardless of properties of the HDR damper. Field tests on an existing cable-stayed bridge have further validated the influence of the internal damper on the performance of the external damper. The results suggest that the HDR is optimally placed in the guide pipe of the cable-pylon anchorage when installing viscous dampers at one position is insufficient. When an HDR damper or the bushing has to be installed near the external damper, their combined damping effects need to be evaluated using the presented methods.