• Journal of the Korean Society of Safety
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• v.31 no.6
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• pp.52-57
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• 2016

In this study, a restoring viscous damper is introduced for X-type damper system which is designed for the seismic response control of large spatial structures. A nonlinear numerical model for its behavior is developed using the result of dynamic loading tests. The X-type damper system is composed of restoring viscous dampers and connecting devices such as adjustable wire bracing, where the damping capacity of the system is controllable by changing the number of the dampers. The restoring viscous damper is devised to exert main damping force in tension direction, which is effective to prevent the buckling of bracing subjected to compressive axial force. To evaluate the performance of the proposed damper, dynamic cyclic loading tests are performed by using manufactured dampers at full scale. In order to construct the numerical model of the damper system, its model parameters are first identified using a nonlinear curve fitting method with the test data. The numerical simulations are then performed to validate the accuracy of the numerical model in comparison with the experimental test results. It is expected that the proposed system is effectively applicable to various building structures for seismic performance enhancement.

• Journal of the Korean Geotechnical Society
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• v.33 no.2
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• pp.17-26
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• 2017

Pile foundations that support offshore structures or transmission towers are dominantly subjected to cyclic lateral loads due to wind and waves, causing permanent displacement which can severely affect stability of the structures. In this study, a series of cyclic lateral load tests were conducted on a pre-installed aluminum flexible pile in sandy soil with three different relative densities (40%, 70% and 90%) in order to evaluate the permanent displacement of a cyclic laterally loaded pile. Test results showed that the cyclic lateral loads accumulated the irreversible lateral displacement, so-called permanent displacement. As the number of cyclic lateral load increased, accumulated permanent displacement increased, but the permanent displacement due to one loading cycle gradually decreased. In addition, the permanent displacement of a pile increased with decrement of relative density and decreased by soil saturation. From the test results, the normalized permanent displacement defined as the cumulative permanent displacement to the initial permanent displacement ratio was investigated, and empirical equations for predicting the normalized permanent displacement was developed in terms of relative density of the soil and the number of cyclic lateral load.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.263-275
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• 2014

In this study, connection of steel reinforced concrete(SRC) column and composite beam which consists of H-section and U-section members were tested under cyclic loading. An essential point of the composite beam is the structural performance of welded joint between the H-section and the U-section members. To improve the structural performance of joint of two beam members, vertical stiffeners, trapezoidal stiffeners, and top bars were used. Five full-scaled specimens were designed to study the effect of a number of parameters on cyclic performance of connections such as H-section beam size($H-500{\times}200{\times}10{\times}16$, $H-600{\times}200{\times}11{\times}17$), the presence of stiffeners and top bars, and the presence of no weld access hole(WAH) method. Based on the test results, deformation capacity of the specimens with H-500 series beam and H-600 series beam were 4% and 3% rotation angle, which is the requirement for the Special Moment Frame and Intermediate Moment Frame(IMF), respectively. Test result showed that deformation capacity of connection with stiffeners and top bars is greater than that of connection without stiffeners and top bars. Finally, energy dissipation capacity and strain profile of specimens were summarized.

• Smart Structures and Systems
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• v.1 no.2
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• pp.141-158
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• 2005

A new design of distributed crack sensors based on the topological change of transmission line cables is presented for the condition assessment of reinforced concrete (RC) structures during and immediately after an earthquake event. This study is primarily focused on the performance of cable sensors under dynamic loading, particularly a feature that allows for some "memory" of the crack history of an RC member. This feature enables the post-earthquake condition assessment of structural members such as RC columns, in which the earthquake-induced cracks are closed immediately after an earthquake event due to gravity loads, and are visually undetectable. Factors affecting the onset of the feature were investigated experimentally with small-scale RC beams under cyclic loading. Test results indicated that both crack width and the number of loading cycles were instrumental in the onset of the memory feature of cable sensors. Practical issues related to dynamic acquisition with the sensors are discussed. The sensors were proven to be fatigue resistant from shake table tests of RC columns. The sensors continued to show useful performance after the columns can no longer support additional loads.

• Steel and Composite Structures
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• v.24 no.4
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• pp.409-423
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• 2017

This paper presents an experimental study on damage evolution laws of solid-web steel reinforced concrete (SRC) T-shaped columns along the direction of the web under various loadings. Ten specimens with a scale ratio of 1/2 and a shear span ratio of 2.5 were designed and fabricated. The influences of various parameters, including the axial compression ratio, steel ratio, and loading mode, were examined. The mechanical performances including load-displacement curve and energy dissipation capacity under the monotonic and low cyclic loadings were analyzed. Compared with the monotonic loading, bearing capacity, ultimate deformation capacity, and energy dissipation capacity of the specimens decrease to some extent with the increase of the displacement amplitude and the number of loading cycle. The results show that the damage process of the SRC T-shaped column can be divided into five stages, namely non-damage, slight-damage, steadily-developing-damage, severe-damage and complete-damage. Finally, based on the Park-Ang model, a modified nonlinear damage model which combines the maximum deformation with hysteretic energy dissipation is proposed by taking into account the dynamic influence of the aforementioned parameters. The results show that the modified model in this paper is more accurate than Park-Ang model and can better describe the damage evolution of SRC T-shaped columns.

• Journal of the Korean Arthroscopy Society
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• v.8 no.1
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• pp.37-44
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• 2004

Purpose: To evaluate the optimal number of additional half hitches for achieving an optimal knot-holding capacity (KHC) of Lockable sliding knots. Methods: Four configurations of arthroscopic knots (Duncan loop, Field knot, Giant knot, and SMC knot) were tested for their knot-holding capacity. For each knot configuration, 6 sequential knots were made including the initial sliding knot and additional 5 knots by incrementing one half hitches at a time. Each added half-hitch were in reversing half-hitches with alternate posts (RHAPs) fashion. For each sequential knot configuration, 12 knots were made by No. 2 braided sutures. On the servo-hydraulic material testing system (Instron 8511, MTS, Minneapolis, MN), cyclic loading, load to clinical failure (3-mm displacement), load to ultimate failure, and mode of failure were measured. Results: Most of the initial loop without additional half-hitch showed dynamic failure with cyclic loading. The mean displacement after the end of cyclic loading decreased with each additional half-hitches. SMC and Giant knot reached plateau to 0.1 mm or less displacement after one additional half-hitch, shereas Field and Duncan loop needed 3 additional half-hitches. The SMC and Duncan knots needed 1 additional half-hitch to reach greater than 80N at clinical failure, whefeas the other 2 knots needed2 additional half-hitches. For the load exceeding 100N for clinical failure, the SMC knot required 3 additional half-hitches and the other three knots needed 4 additional half-hitches. As the number of additional half-hitches incremented, the mode of failure switched from pure loop failure (slippage) to material failure (breakage). Duncan loop showed poor loop security in that even with 5 additional half-hitches, some failed by slippage (17%). On the other hand, after 3 additional half-hitches, the 3 other knots showed greater than 75% of failure by material breakage mode (SMC and Field 92%, Giant 75%). Conclusion: Even with its own locking mechanism, lockable sliding knot alone does not withstand the initial dynamic cyclic load. For all tested variables, SMC knot requires a minimum of 2 additional half-hitches. Duncan knot may need more than 3 additional half-hitches for optimal security. All knots showed a mear plateau in knot security with 3 or more additional half-hitches.

• Restorative Dentistry and Endodontics
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• v.38 no.1
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• pp.31-35
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• 2013

Objectives: This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions. Materials and Methods: ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods. Results: Spearman's rank correlation coefficient (${\rho}$ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files. Conclusions: The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.34-45
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• 2017

Cyclic loading tests for a total of nine test specimens were performed to evaluate the seismic performance of the exposed steel column-base plate connections. From the tests, flexural strength, deformation capacity, energy dissipation, and initial stiffness were investigated. The primary test parameters were the thickness of base-plate, embedment length of anchor bolt, the presence of hook, and rib plates. Test results showed that flexural behavior of column base-plate connection was substantially affected by the base-plate thickness, embedment length and the number of anchor bolts. On the other hand, the effect of rib plates on the increase of the flexural performance was not observed. The initial stiffness of the test specimens was about 15% of the flexural stiffness obtained by assuming that the support is fixed. As a result, even if the exposed column base-plate is designed in accordance with current design recommendations, in case that bond strength between concrete and the anchor bolts is not sufficient, the base-plate connection showed an unaccceptable load-displacement behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.226-234
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• 2021

The objective of this study is to establish the fundamental design data for axial load-displacement relationship under axial monotonic or cyclic responses of seismic damping·isolation (SDI) units developed for ceiling structures. The main parameters include the installation of a spring, the number of rubber layer, prestress stress of bolts for connector between the spring and rubbers, and loading type. Test results showed that SDI units with a spring in the core and higher prestress stress of bolts tended to be higher stiffness at the ascending branch and more ductile behavior at the descending branch. This trends more notable for the specimens under monotonic load rather than cyclic loads. Consequently, the energy dissipation of SDI unit can be optimally designed with the following conditions: installation of a spring within 3-layer rubbers and prestress applied to the bolts at 10% of their yielding strength . When compared with the experimental tension capacity of the developed SDI units, the predictions by JIS B 2704-1 and KDS 31 00 are conservative under monotonic loading but higher by approximately 10% under cyclic loading.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.101-116
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• 2008

The use of reinforced earth walls id permanent structures is getting its popularity. Despite a number of advantages of reinforced earth walls over conventional concrete retaining walls, there exists concerns over long-term residual deformations when subjected to repeated and/or cyclic loads, during their service period. In this investigation, the effects of pre-loading in reducing long term residual deformation of reinforced soil structures under sustained and/or repeated loading environment are investigated using a series of reduced-scale model tests. A model pier and a back-to-back (BTB) reinforced soil structures were constructed and tested under various loading and backfilling conditions. The results indicate that the pre-loading technique can be an effective means of controlling residual deformations of reinforced soils under various loading conditions.