Showing papers by "Dong-Soo Kim published in 2006"

IE-SASW method for nondestructive evaluation of concrete structure

Abstract: The Impact–Echo (IE) method has been widely used to evaluate the integrity of concrete structures. In this method, the P-wave velocity of concrete is a crucial parameter in determining the thickness of concrete slab and the location of cracks or other defects. To determine P-wave velocity of concrete, in this paper, Spectral Analysis of Surface Wave (SASW) method was employed, and IE–SASW method was suggested by combining two nondestructive testing methods. IE method was used for the detailed nondestructive evaluation of concrete whereas SASW method was employed for the measurement of the average P-wave velocity and for the status evaluation of concrete. The feasibility study of SASW method was performed by using finite element method. Experimental studies were also performed in the slab type concrete model specimens in which various types of defects or boundaries were included at known locations. SASW tests showed the potential of determining the P-wave velocity of concrete accurately and IE tests were able to determine the thickness of structures and locations of defects. Based on both experimental and numerical studies, the feasibility of the proposed method was verified.

Development of new site classification system for the regions of shallow bedrock in korea

Abstract: In the current Korean code, the site classification and the corresponding site coefficients were determined similar to the UBC 1997, which were revised based on the results from the investigation of the 1989 Loma Prieta earthquakes in the western United States. Since the site effects are directly dependent on the local site conditions, the use of site coefficients derived from earthquake records which occurred in different site conditions may mislead the earthquake ground motion. Therefore, it is important to compare the local site conditions in Korea to those in the western United States and assess their effects on site coefficients, for the reliable estimation of earthquake ground motions in Korea. In this paper, site response analyses were performed based on equivalent linear technique using the shear wave velocity profiles of 162 sites collected around the Korean peninsula. The site characteristics, particularly the shear wave velocities and the depth to the bedrock, are compared to those in western U...

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (III) - Modification of Desing Response Specra

Abstract: In the companion paper (II, Development of Site Classification System), new size classification system based on site periods was recommended for legions of shallow bedrock depth in Korea. Despite the site classification method was improved, the response spectrum would be required to be modified by adjusting the integration interval to calculate the site coefficients because the response spectra did not match well the average spectral accelerations obtained by site response analyses in the range of long periods. In this paper, new response spectra for each site categories were determined by adjusting the integration interval of long period site coefficient second. It matched well the average spectral accelerations and new response spectrum, and it was also improved compared to the current she classification system.

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (I) - Problem Statements of the Current Seismic Design Code

Abstract: Site response analyses were peformed based on equivalent linear technique using the shear wave velocity profiles of 162 sites collected around the Korean Peninsula. The she characteristics, particularly the shear wave velocities and the depth to bedrock, are compared to those in the western United States. The site coefficients of short period and the long period obtained from this study were significantly different compared to 1997 Uniform Building Code (1997 UBC). underestimated the motion in shot period ranges and overestimated the motion in mid period ranges in Korean seismic guideline. It is found that the existing Korean seismic design code were is required to be modified considering geological site conditions in Korea for the reliable estimation of sue amplification. Problems of the current seismic design code were dicussed in this paper and the development of site classification method and modification of desing response spectra were discussed in the companion papers(II-Development of Site Classification System and III-Modification of Dosing Response Specra).

Cyclic threshold shear strains of sands based on pore water pressure buildup and variation of deformation characteristics

Abstract: The cyclic threshold shear strain c th is defined as the cyclic strain amplitude above which the pore water pressure in saturated sandy soil increases and/or the modulus and damping values vary with the number of loading cycles during cyclic loadings. In this paper, the cyclic threshold shear strains are thoroughly investigated on sands using torsional shear tests. Toyoura sand is tested at various densities, drainage conditions (dry, saturated drained, and saturated undrained), and effective confining pressures. Based on the test results, the cyclic threshold strains above which the excess pore water pressure increases and/or shear modulus and damping ratio vary with the number of cycles are determined. Cyclic hardening in dry and saturated drained conditions, and cyclic degradation in an undrained condition, are observed for the same sample, using identical testing equipment. c th for cyclic degradation is compared with c th for cyclic hardening. The variation of damping ratio with the number of cycles is observed at different drainage conditions, and c th for damping ratio is also investigated.

Development of Modulus-Soil Moisture Model for Subgrade Soils Using Suction Control Testing System

Abstract: In a pavement structure, moisture is an environmentally driven variable that can significantly affect the resilient modulus of subgrade soils. In this study, the variations of deformational modulus with post compaction moisture content were investigated for three subgrade soils using suction control resonant column and torsional shear (RC/TS) tests. A series of tests were performed to evaluate the modulus values using specimens compacted at various moisture contents and compared to the results obtained by post compaction method by suction controlling. Applicability of existing models which relate the modulus and soil moisture was assessed using test results, and a model which relates the modulus and soil suction was newly proposed.

Non-Destructive Pile Integrity Test Using HWAW Method

Abstract: The evaluation of soundness of pile is very important for safety of super structure. In this paper, the HWAW(Harmonic Wavelet Analysis of Wave) method is modified and applied to evaluate soundness of pile non-destructively. The proposed method can evaluate pile integrity such as pile length, material quality represented by wave velocity and pile end condition which are very important factors for pile behavior. To verify the applicability of proposed method, the numerical simulation test using ABAQUS was performed. A model pile was made and the proposed method was applied to evaluate soundness of model pile. Through numerical simulation and model tests, it is shown that the HWAW method has good potential of applying in the evaluation of pile integrity.

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (II) - Development of Site Classification System

Abstract: In the companion paper (I-Problem Statements of the Current Seismic Design Code), the current Korean seismic design code is required to be modified considering site characteristics in Korea for the reliable estimation of site amplification. In this paper, three site classification methods based on the mean shear wave velocity of the top 30m , fundamental site periods and bedrock depth were investigated and compared with each other to determine the best classification system. Not enough of a difference in the standard deviation of site coefficients to determine the best system, and neither is the difference between the average spectral accelerations and the design response spectrum of each system. However, the amplification range of RRS values based on were definitely concentrated on a narrow band than other classification system. It means that sites which have a similar behavior during earthquake will be classified as the same site category at the site classification system based on . The regression curves between site coefficients and described the effect of soil non linearity well as the rock shaking intensity increases than the current method based on . Furthermore, it is unambiguous to determine sue category based on when the site investigation is performed to shallower depth less than 30m, whereas the current is usually calculated fallaciously by extrapolating the of bedrock to 30m. From the results of this study, new site classification system based on was recommended for legions of shallow bedrock depth in Korea.

Determination of Mode Dispersion Curves of Surface Wave Using HWAW Method

Abstract: The evaluation of shear modulus is very important in various fields of civil engineering. Non-destructive seismic methods can be used to determine shear wave velocity () profile. Non-destructive seismic methods geneally consist of three steps: field testing, evaluation of dispersion curve, and determination of Vs profile by inversion process. Non-destructive seismic methods can be divided into two categories according to the number of receivers used for data reduction: two-channel tests and multi-channel tests. Two channel tests use apparent velocity dispersion curve and multi-channel tests use mode dispersion curves. Multi-channel tests using mode dispersion curve can reduce calculation time to determine soil profile and uncertainties in inversion process. So far, only multi-channel tests can determine mode dispersion curves but multi-channel test needs many receivers to determine reasonable mode dispersion curves. In this paper, HWAW (Harmonic Wavelet Analysis of Wave) method is applied to determine mode dispersion curves. HWAW method uses short test setup which consists of two receivers with a spacing of 1 to 3 m. Through numerical simulations and field application, it is shown that HWAW can determine resonable mode disperson curves.

Development of Torsional Shear Testing System to Measure P-wave Velocity, S-wave Velocity and Pore Water Pressure Buildup on Fully and Partially Saturated Sands

Abstract: Laboratory tests have revealed that the liquefaction resistance of sands depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The velocity of compression waves(i.e. P-waves), which have been known to be influenced largely by the degree of saturation and can be measured conveniently in the field, appears as an indicator of saturation. In this paper, the Stokoe type torsional shear(TS) testing equipment is modified to saturate the specimen and measure the velocities of P-wave and S-wave and pore pressure buildup. The velocities of P-wave and S-wave for Toyoura sand from Japan is measured and compared at the various B-value (degree of saturation) which are partially saturated to fully saturated conditions. Additionally, the variation of the pore water pressure induced during undrained TS tests at the various B-value is measured and analyzed.

A Study on the Elastic Wave Propagation in the Telecommunication Pole Having Different Subsurface End Condition

Abstract: Alternative construction methods and a simple method for identifying pole’s subsurface end condition using elastic wave propagation test were proposed. After twelve prototypes of poles having different subsurface end conditions were constructed, horizontal loading tests and elastic wave propagation tests were performed. It was found that there was a close correlation between the 1st resonant frequency and maximum pulling force. The results of this study will provide a key to identify the telecommunication pole’s foundation.