• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.41-47
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• 2004

The objective of this paper is to monitor damage in beam-type structures by using time history of natural frequencies. First, numerical experiments on test beams are described, Dynamic responses of the test structures are obtained for several damage scenarios in a consequent order. Next, the time history of natural frequencies are extracted for the first four modes from the dynamic responses of the test structures. Finally, damage detection in the test structures is performed using the time-history of natural frequencies.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.721-725
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• 1996

The microfabricated test structures were used in order to evaluate the stress characteristics in films. The test structures were fabricated using surface micromachining technique, including HF vapor phase etching as an effective release method. The fabricated structures were micro strain gauge, cantilever-type vernier gauge and bridge for stress measurement, and cantilever for stress gradient measurement. The strain was measures by observing the deformation of the structures occurred after release etching and the amount of deformation can be detected by micro vernier gauge, which has gauge resolution of 0.2${\mu}{\textrm}{m}$. The detection principles and the degree of precision for the measured strain were also discussed. The characteristics of residual stress in LPCVD polysilicon films were studied using these test structures. The stress gradient due to the stress variation through the film thickness was calculated by measuring the deflection at the cantilever free end.

• Journal of Ocean Engineering and Technology
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• v.21 no.4
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• pp.21-27
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• 2007

The multiplication equipment of marine products with artificial upwelling structures could be useful in the fishing grounds near coastal areas. Artificial upwelling structures could move the inorganic nutrients from the bottom to the surface. Artificial upwelling structures have been used to improve the productivity of fishing grounds. Until now, research on artificial upwelling structures has been related to the distribution of the upwelling region, upwelling structures, and the marine environment. However, little work on the optimum design of the rubber-mound artificial upwelling structures has been done to increase the efficiency of drawing up the inorganic nutrients. This study investigated the optimum cross-section of rubber-mound artificial upwelling structures by means of hydraulic experiments. The hydraulic experiments include the falling test of rubber. Based on the results of the falling test, the relationship between the length of the rubber mound and water velocity, and the relationship between the shape of the rubber and the stratification parameter were established. In addition, the effect of the void ratio of various artificial structures on the stratification parameter was studied. From the experiment, it was found that upwelling could be enhanced when the ratio of structure height to water depth was 0.3 and stratification parameter was 3.0. The upwelling was not improved when the void ratio exceeded 0.43. The optimum size of rubber mounds was determined when the incident velocity was influenced by the mean horizontal length rather than size of block.

• Computers and Concrete
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• v.31 no.3
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• pp.241-252
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• 2023

Corrosion of rebar is one of the major deteriorating mechanisms that affect the durability of reinforced concrete (RC) structures. The increase in CO₂ concentration in the atmosphere leads to early carbonation and deterioration due to corrosion in RC structures. In the present study, an attempt has been made to modify the existing carbonation depth prediction empirical model. The modified empirical model is verified from the carbonation data collected from selected RC structures of CSIR-SERC campus, Chennai and carbonation data available from the reported literature on in-situ RC structures. Attempt also made to study the carbonation depth in the laboratory specimens using oxygen permeability index (OPI) test. The carbonation depth measured from RC structures and laboratory specimens are compared with estimated carbonation depth obtained from OPI test data. The modified empirical model shows good correlation with measured carbonation depth from the identified RC structures and the reported RC structures from the literature. The carbonation depth estimated from OPI values for both in-situ and laboratory specimens show lesser percentage of error compared to measured carbonation depth. From the present investigation it can be said that the OPI test is the suitable test method for both new and existing RC structures and laboratory RC specimens.

• Journal of Korean Association for Spatial Structures
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• v.15 no.4
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• pp.107-114
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• 2015

Large spatial structures can not easily predict the dynamic behavior due to the lack of construction and design practices. The spatial structures are generally analyzed through the numerical simulation and experimental test in order to investigate the seismic response of large spatial structures. In the case of analysis for seismic response of large spatial structure, the many studies by the numerical analysis was carried out, researches by the shaking table test are very rare. In this study, a shaking table test of a small-scale arch structure was conducted and the dynamic characteristics of arch structure are analyzed. And the dynamic characteristics of arch structures are investigated according to the various column cross-section and length. It is found that the natural vibration periods of the small-scaled arch structure that have large column stiffness are very similar to the natural vibration period of the non-column arch structure. And in case of arch structure with large column stiffness, primary natural frequency period by numerical analysis is very similar to the primary natural frequency period of by shaking table test. These are because the dynamic characteristics of the roof structure are affected by the column stiffness of the spatial structure.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.148-153
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• 1993

The paper presents the results of shaking table test conducted on the 1/3.3 scaled large concrete panel model. The behaviors of large concrete panel structures subjected to seismic excitations are controlled by capacity of horizontal and vertical joints. To Study the seismic capacity of the large concrete panel structures, experimental researches for joints and structural assemblage are needed. Especially, since the magnitude of seismic loads are depended on the variation of time, period and accelerations, dynamic test is needed for estimating the seismic resistance of large concrete panel structures. The objective of this paper is to study the behaviors of large concrete panel structures on seismic excitations and to estimate the safety. Test results are as follows : 1) Test model was critically damaged in the first floor horizontal joint by rocking. 2) Elastic limit(0.12kg) of test model was 5times higher than that of korean seismic design code. 3) Maxium base shear of test model at the ground acceleration of 0.12g was 3.5 times higher than the result of equivalent static analysis. 4) Damping ratio of test model turned out 3.9~5.3% and the period at 0.12g was 0.065sec.

• Earthquakes and Structures
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• v.9 no.3
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• pp.541-562
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• 2015

This paper aims at developing the knowledge on the seismic behavior of dowel beam-to-column connections, typically employed in precast buildings in Europe. Despite the large diffusion of the industrial buildings, a high seismic vulnerability was exhibited by these structures, mostly due to the connection systems deficiencies, during some recent earthquakes (Emilia 2012, Turkey 2011). An experimental campaign was conducted on a typical dowel connection between an external column and a roof beam. In this paper, the performed cyclic shear test is described. According to the experimental results, the seismic response of the system is evaluated in terms of strength, stiffness and failure mechanism. Moreover, the complete damage pattern of the test is described by means of the instrumentations records. The connection failure occurred due to the concrete cover failure in the column (splitting failure). Such a mechanism corresponds to a negligible energy dissipation capacity of the connection, compared to the overall seismic response of the structure. The experimental results are also compared with the results of a similar monotonic shear test, as well as with some literature relationships for predicting the strength of dowel connections under horizontal (seismic) loads.

• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.801-811
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• 2011

A new experimental technique was developed on the plate-inserted welded tubular joints of spatial grid structures. In the experimental technique, a microcomputer controlling instrument of moire intervention (MCIMI) was adopted. A test was designed on the plate-inserted welded tubular joints of spatial grid structures to show the effectiveness of the MCIMI technique. Both traditional electrical measuring technique and MCIMI technique were employed in the test. The test results showed that the MCIMI technique was feasible in the case of the complicated tests on steel structures. The MCIMI technique not only implemented the limitation of traditional electrical measuring technique, but also improved the accuracy of the test. According to the test results, we further examined the plate-inserted welded tubular joints in the cable-stayed spatial grids of the Binhai International Convention & Exhibition in Tianjin, China. The analysis showed the joints are safely designed with adequate conservatism. The research provided a new application of MCIMI in the field of large-scale structure engineering.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.759-762
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• 1999

The concrete structures possessing good structural integrity can face durability problems due to deteriorations of concrete structures under various environmental conditions. The durability problems weaken the structural integrity in the long run. Especially, the excessive use of sea sand causes serious reinforcement corrosion and carbonation in concrete structures. An accelerated test is often used to predict deterioration as a qualitative measure, but without long term exposure test results or understanding of the relationship between the accelerated test and the long term exposure test, the accelerated test result alone can not be used effectively as a quantitative measure. In this paper, a methodology is proposed to predict the long term deteriorations, based on the result of the short-term accelerated test, of concrete containing different contents of chloride ions. Then, the correlation between two results on the steel corrosion ratio and the carbonation depth is analyzed for concrete with different chloride contents.

• Journal of Korean Association for Spatial Structures
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• v.7 no.3 s.25
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• pp.87-95
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• 2007

The recent completions of free-form spatial structures provide us a very attractive form. To realize such an extraordinary shape, it is absolutely necessary that the connector systems have to be investigated the characteristics of the systems and analyzed with a practicable method. In this context, this research consists of not only literature research but also numerical analysis with selected connector systems, which was adopted in real free-form spatial structures. For numerical analysis, especially, finite element analysis (FEA) is performed with a various test parameter using a commercial program ANSYS. Consequently, the general characteristics of node connectors the moment-rotation-curves are presented by considering a large deformation effect as well as a multi-linear material properties.