• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.35-50
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• 2013

Rapid and effective repair methods are desired to enable quick reopening of damaged bridges after an earthquake occurs, especially for those bridges that are critical for emergency response and other essential functions. This paper presents results of tests conducted as a proof-of-concept in the effectiveness of a proposed method using externally bonded carbon fiber reinforced polymer (CFRP) composites to rapidly repair severely damaged RC columns with different damage conditions. The experimental work included five large-scale severely damaged square RC columns with the same geometry and material properties but with different damage conditions due to different loading combinations of bending, shear, and torsion in the previous tests. Over a three-day period, each column was repaired and retested under the same loading combination as the corresponding original column. Quickset repair mortar was used to replace the removed loose concrete. Without any treatment to damaged reinforcing bars, longitudinal and transverse CFRP sheets were externally bonded to the prepared surface to restore the column strength. Measured data were analyzed to investigate the performance of the repaired columns compared to the corresponding original column responses. It was concluded that the technique can be successful for severely damaged columns with damage to the concrete and transverse reinforcement. For severely damaged columns with damaged longitudinal reinforcement, the technique was found to be successful if the damaged longitudinal reinforcement is able to provide tensile resistance, or if the damage is located at a section where longitudinal CFRP strength can be developed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.53-60
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• 2003

Large sized marine structures are used under corrosion environment of seawater and applied by severe service loading such as an ocean current, a billow and a tempest. Marine structures are usually constructed by lots of thick wall steel pipes joining welded joints. The thickness of such as steel pipes is usually more than 40mm. The such as steels are called "Thermo-Mechanical Control Process steel (TMCP steel)" strengthened by a heat treatment in process of steel manufactures. The failure, especially crack initiation, of marine structures was starting at weld joints under service condition. Then they should be designed by basis of the fatigue strength under seawater corrosion environment of weld joints. To clarity the fatigue crack initiation behavior is important more than to clarify the crack propagation behavior on the strength design of marine structures, because it is very difficult to find out the crack initiation and propagation phenomena and then even if it will be able to find out, it is considered that the refit of the damaged parts of welded joints have a technical difficulty under the sea. Therefore, it is most important to clarify the corrosion fatigue crack initiation behavior under the seawater condition. But, there is one big difficulty to make a test for thick plate specimen, for example thicker than 40mm. Because, it is need large capacity loading apparatus to test such as thick plate specimen. In this research, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the fatigue clack initiation tests with relatively low cyclic loading and to observe a fatigue crack initiation behavior.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.25-33
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• 2018

In regard to modular systems, new methods, as well as middle and high-story unit design ideas, are currently being studied. These studies need to focus on the enhanced stiffness and seismic performance of these connections, and see that the development of fully restrained moment connections can improve the seismic performance. For this reason, this study evaluates the performance of the connections of the ceiling bracket-typed modular system through repeated loading tests and analyses. In order to compare them with these modular units, new unit specimens with the bracket connection being different from that of the traditional modular unit specimens were designed, and the results of repeated loading tests were analyzed. In the traditional units, the structural performances of both welding connection and bolt connection were evaluated. In regard to the testing results, the initial stiffness of the hysteresis curve was compared with the theoretical initial stiffness, and the features of all specimens were also analyzed with regard to the maximum moment. In addition, the test results were examined with regard to the connection flexural strength of the steel special moment frame specified under the construction criteria KBC2016. The connections, which were proposed in the test results, were found to be fully restrained moment connections for designing strong column-weak beams and meeting the requirements of seismic performance of special moment frames.

• Steel and Composite Structures
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• v.34 no.4
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• pp.547-559
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• 2020

Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. The first part of this paper presents the results of the experimental program which included sub-assemblage tests on ten full-scale BRBs and uniaxial tests on components materials (steel and concrete). Two different solutions of the core were investigated: milled from a plate and fabricated from a square steel profile. The strength of the buckling restraining mechanism was also investigated. The influence of gravity loading on the unsymmetrical deformations in the two plastic segments of the core was assessed, and the response of the bolted connections was evaluated. The cyclic response of BRBs was evaluated with respect to a set of performance parameters, and recommendations for design were given.

• Geomechanics and Engineering
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• v.9 no.6
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• pp.729-742
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• 2015

The aim of the present work was the study of instability in a loose sand from Les Dunes beach in Ain Beninan, Algeria, where the Boumerdes earthquake occurred in 2003. This earthquake caused significant structural damages and claimed the lives of many people. Damages caused to infrastructures were strongly related to phenomena of liquefaction. The study was based on the results of two drained and six undrained triaxial tests over a local sand collected in a region where liquefaction occurred. All the tests hereby analyzed followed compression stress-paths in monotonic conditions and the specimens were isotropically consolidated, since the objective was to study the instability due to static loading as part of a more general project, which also included cyclic studies. The instability was modeled with the second-order work increment criterion. The definition of the instability line for Les Dunes sand and its relation with yield surfaces allowed the identification of the region of potential instability and helped in the evaluation of the susceptibility of soils to liquefy under undrained conditions and its modeling. The dilatancy rate was studied in the points where instability began. Some mixed tests were also simulated, starting with drained conditions and then changing to undrained conditions at different time steps.

• 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 Korean Society of Steel Construction
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• v.20 no.2
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• pp.289-301
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• 2008

Double skin composite (DSC) wall is a structural wall that is filed with concrete between two steel plate skins connected by tie bars. This type of wall was developed to enhance the structural performance of wall, to reduce wall thickness, and to enhance constructibility, eliminating the use of formwork and re-bars. In this study, cyclic tests were performed to investigate the inelastic behavior and earthquake resistance of isolated and coupled DSC walls with rectangular and T-shapedcross-sections. The DSC walls showed stable cyclic behaviors, exhibiting excellent energy dissipation capacity. The te st specimens failed by the tensile fracture of welded joints at the wall base and coupling beam and by the severe local buckling of the steel plate. The deformation capacity of the walls varied with the connection details at the wall base and their cross-sectional shapes. The specimens with well-detailed connections at the wall base showed relatively god deformation capacity ranging from 2.0% to 3.7% drift ratio. The load-carrying capacities of the isolated and coupled wall specimens were evaluated considering their inelastic behavior. The results were compared with the test results.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.33-41
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• 2014

Fretting is a kind of surface degradation mechanism observed in mechanical components and structures. When two pieces of materials, pressed together by an external static load, are subjected to a transverse cyclic loading or various vibrations, so that one contacting face is relatively displaced cyclically parallel to the other face, wear of the mating surfaces occurs. These fretting damages may be observed in electrical connectors for automotive components, where there are special environments and various vibration conditions. This study aims to evaluate the usefulness of fretting test equipment that was developed for reliability test of electrical connector. Fretting tests were carried out using tin coated connectors and friction force, contact resistance, contact area and roughness of contact region were investigated. The following results that will be helpful to understand the fretting wear mechanism, increase process the contact resistance and contact area were obtained. (1) In the same frequency and slip amplitude, the friction force, roughness and contact area increased rapidly until about $10^3$ cycles, after which it was slightly changed. (2) In the various frequency and slip amplitude, the contact area increased with slip amplitude and cyclic numbers, but it did not depend on cyclic frequency. (3) The surface roughness of contact region did not depend on the cyclic frequency. From these results, the applicability of the fretting wear test equipment and reliability of connector were discussed.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.529-540
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• 2020

The mechanical properties of timber construction have drawn more attention after the 2013 Lushan earthquake. A strong desire to preserve this ancient architectural styles has sprung up in recent years, especially for residential buildings of the mountainous areas. In the column-and-tie timber construction, continuous-tenon joints are the most common structural form to connect the chuanfang (similar to the beam in conventional structures) and the column. To study the cyclic performance of the continuous-tenon joints in column-and-tie timber construction, the reversed lateral cyclic loading tests were carried out on three 3/4 scale specimens with different section heights of the chuanfang. The mechanical behavior was assessed by studying the ultimate bending capacity, deformation ductility and energy dissipation capacity. Test results showed that the slippage of chuanfang occurred when the specimens entered the plastic stage, and the slippage degree increased with the increase of the section height of chuanfang. An obvious plastic deformation of the chuanfang occurred due to the mutual squeezing between the column and chuanfang. A significant pinching was observed on the bending moment-rotation curves, and it was more pronounced as the section height of chuanfang increased. The further numerical investigations showed that the flexural capacity and initial stiffness of the continuous-tenon joints increased with the increase of friction coefficient between the chuanfang and the column, and a more obvious increasing of bending moment occurred after the material yielding. The compressive strength perpendicular to grain of the material played a more significant role in the ultimate bending capacity of continuous-tenon joints than the compressive strength parallel to grain.

• Journal of Biosystems Engineering
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• v.17 no.1
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• pp.79-90
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• 1992

Viscoelastic characteristics of agricultural products may be determined through three basic tests ; stress relaxation, creep, and dynamic test. Considering the changeability of living materials, dynamic test in which information is derived in a relatively short time appears to be highly desirable, in which either cyclic stress or cyclic strain is imposed and the remaining quantity (strain or stress) is measured. The periodically varying stress will also result in periodically varying strain which in a viscoelastic material should theoretically be out of phase with the stress, because part of the energy subjected to sample is stored in the material as potential energy and part is dissipated as heat. This behavior results in a complex frequency-dependent compliance denoted by J($i{\omega}$). The complex compliance and therefore the storage compliance, the loss compliance, the phase angle, and percent energy loss for the sample should be obtainable with a given static viscoelastic property of the material under static load. The complex compliance of the rough rice kernel were computed from the Burger's model describing creep behavior of the material which were obtained in the previous study. Also, the effects of cyclic load and moisture content of grain on the dynamic viscoelastic behavior of the samples were analyized. The results obtained from this study were summarized as follows ; 1. The storage compliance of the rough rice kernel slightly decreased with the frequency applied but at above the frequency of 0.1 Hz it was nearly constant with the frequency, and the loss compliance of the sample very rapidly decreased with increase in the frequency on those frequency ranges. 2. It was shown that the storage compliance and the loss compliance of the sample increased with increase in grain moisture content. Effect of grain moisture content on the storage compliance of the sample was highly significant than effect of the frequency applied, but effect of the frequency on the loss compliance of the sample was more significant than effect of grain moisture content. 3. In low moisture content, the percent energy loss of Japonica-type rough rice was much higher than that of Indica-type rough rice, but, in high moisture content, vice versa.