• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.119-125
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• 2020

Research on high-attenuation concrete for the vibration reduction performance by mixing epoxy-based synthetic resins and aggregates is actively being conducted. The curing time of high-attenuation concrete is very short because water is not used, and the physical and dynamic properties are very excellent. therefore, it is expected to be widely used in building structures requiring reduction of interior-floor noise and vibration. Furthermore, A way to expand the applicability of the high-damping concrete mixed with polymer in the field of reinforcement material have been variously studied. In order to replace polymer concrete with ordirnary concrete and existing anti-vibration reinforcement material, it is necessary to review overall vibration reduction performance considering physical properties, dynamic properties, productivity and field applicability. In this study, the physical and dynamic properties of polymer concrete by epoxy mixing ratio compared with ordirnary concrete. As a result, the elastic modulus was similar. On the other hand, polymer concrete for the compressive, tensile, and flexural strengths was quite more excellent. In particular, the measured tensile strength of polymer concrete was 4-10 times higher than that of ordirnary concrete. it was a big difference, and the frequency response function and damping ratio was studied through modal test and finite element analysis model. The dynamic stiffness of polymer concrete was 20% greater than that of ordirnary concrete, and the damping ratio of polymer concrete was approximately 3 times more than that of ordirnary concrete.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.677-684
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• 2012

In recent years, extension of life span of buildings is becoming an important issue in our society. To improve the life span of buildings, rhamen structure construction and long-spanned structures are advantageous. And in order to achieve this goal, structural elements of buildings must be light and slender. As an alternative method, general porous slabs are used frequently domestically and internationally. But the study on the porous slabs using T-deck plate and assembly of light weight precast construction is insufficient at present. In this study, flexural and fatigue tests were performed on six specimens to verify structural performance and serviceability. The main parameters of the specimens were light weight and T-deck plate construction possibility as well as slab thickness. The test results indicated that the strength of porous slabs using T-deck plate and assembly of light weight were much better than general RC slabs and porous slabs without T-deck plate. And stiffness was much better than that of other tested slabs.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.325-333
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• 2010

In this study, new moment-resisting precast concrete beam-column joint made up of hybrid steel concrete was developed and tested. This beam-column joint is proposed for use in moderate seismic regions. It has square hollow tubular section in concrete column and connecting plate in precast U-beam. The steel elements in column and beam members were connected using bolt. Furthermore, in order to prevent the premature failure of concrete in hybrid steel-concrete connection, ECC(engineered cementitious composite) was used. An experimental study was carried out investigating the joint behavior subjected to reversed cyclic loading and constant axial compressive load. Two precast beam-column joint specimens and monolithic reinforced concrete joint specimen were tested. The variables for interior joints were cast-in-situ concrete area and transverse reinforcement within the joint. Tests were carried out under displacement controlled reverse cyclic load with a constant axial load. Joint performance is evaluated on the basis of connection strength, stiffness, energy dissipation, and displacement capacity. The test results showed that significant differences in structural behavior between the two types of connection because of different bonding characteristics between steel and concrete; steel and ECC. The proposed joint detail can induce to move the plastic hinge out of the ECC and steel plate. And proposed precast connection showed better performance than the monolithic connection by providing sufficient moment-resisting behavior suitable for applications in moderate seismic regions.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.797-804
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• 2009

The structural designs of RC flat plates that have insufficient flexural stiffness due to lack of support from boundary beams may be governed by serviceability as well as a strength criteira. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of calculating slab deflections considering construction sequences and concrete cracking effects is proposed. The construction steps and the construction loads are defined by the simplified method, and then the slab moments, elastic deflections, and the effective moment of inertia are calculated in each construction step. The elastic deflections in column and middle strips are magnified to inelastic deflections by the effective moment of inertia, and the center deflection of slab are calculated by the crossing beam method. The proposed method is verified by comparisons with the existing test result and the nonlinear analysis result. Also, by applications of the proposed method, the effects of the slab construction cycle and the number of shored floors on the deflections of flat plates under construction are analyzed.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.273-283
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• 2003

Fissured rock and soft ground always suggest, problems in the construction of the underground space. The stress release of the weak underground material by opening the underground space with a soft ground, fissures and joints can lead to the failure of the opening. Grouting of the weak rock and the soft ground, which is a process of injecting some bonding agents into the soft ground, is one of the measures to reinforce the soft ground and to prohibit the failure of the underground construction due to the stress release. The proper installation of the grouting is essential to ensuring the safety of the tunneling operation, so that the evaluation of the grouting performance is very significant. The general procedure of evaluating the grouting is coring the grouted section and measuring the compression strength of the core. However, sometimes when the grouted section is at the crown of the tunnel and the grouting is installed at a wide section, the coring is not good enough. This study is oriented to propose a new and a non-destructive procedure of evaluating the grouting performance. The proposed method is based on the wave propagation of elastic waves, and evaluates the shear stiffness of the ground and investigates the anomalies such as voids and cracks. The SASW ( Spectral-Analysis-of-Surface-Waves) method is one of the candidate s to make the inspection of the pouting performance, and is adopted in this study. The practical grouting activity was monitored by SASW method, and the proposed method was applied to the inspection of the grouting performance to check the verification of the proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.359-366
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• 2019

Experimental and analytical studies on the behavioral characteristics of a pre-stressed (PS) steel girder are conducted to investigate the effects of deviators on the non-linear inelastic properties of the PS system. In this regard, 4 test specimens consisting of a steel H-beam, a straight cable with eccentricity, anchorages, and deviators are built and failure tests are performed under two-point loading. In addition, in-plane elastic deformation theories for the PS system without a deviator, and with three deviators at regular intervals are analytically formulated and solved using a symbolic calculation technique. To verify the validity of the experimental and the proposed analytical theories, the results obtained using FEM models composed of beam elements, rigid beam elements, and truss cable elements, are compared to the experimental results and the analytical solutions. As a result, it is determined that externally installed un-bonded deviators inhibit flexural deformation of the deformed beam to such an extent that their elastic stiffness, and failure strength are significantly improved compared to those of the PS system without deviators.

• Earthquakes and Structures
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• v.23 no.4
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• pp.373-384
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• 2022

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (n_s), presence or absence of a spring, prestressed force magnitude introduced in bolts (f_ps), and mass weight (W_m) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (A_{c max}), acceleration amplification factor (α_p), relative displacement (δ_R), and increasing the damping ratio (ξ) when compared to the control specimen. The A_{c max}, α_p, and δ_R of the SDI specimens with two rubbers, spring, and f_ps of 0.1f_by, where f_by is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest ξ (=0.127). In addition, the α_p of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the α_p of the SDI specimens, a simple model was proposed based on the functions of f_ps, stiffness constant of the spring (K), W_m, and n_s.

• Journal of the Korean GEO-environmental Society
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• v.16 no.2
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• pp.45-52
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• 2015

To minimize the cost of maintenance, repair and over-design of track substructure, an accurate evaluation of strength and stiffness of the track substructure is necessary. In this study, a cone penetrometer with impact penetration rod (CPI) is developed for the evaluation of track substructure. For applicability test, the chamber and field tests were performed. As the experimental results of the CPI, dynamic cone penetration endex (DCPI), cone tip resistance ($q_c$), friction resistance ($f_s$) and friction ratio (Fr) were obtained. In the chamber test, the experimental results show reasonable values for the simulated track substructure. In the field test, the CPI clearly detects the interface between the ballast and the subgrade. Also, discontinuous layers are detected in the subgrade. It is expected that the developed CPI may be an effective tool for the evaluation of track substructure by evaluating the ballast layer by dynamic penetration and the subgrade by static penetration of the inner rod.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.880-894
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• 2010

The Grout injected precast pile is widely used in rapid-transit railway bridge recently. The existing portland cement of well used filling at injected precast method that with low strength and environmental pollution, unstable in which ground water contamination by cement flow out, ground relaxation by water down, decrease of horizontality resistance and durability and load transfer divide etc. In particular, as in rapid-transit railway bridge need to secure safety from different angle with vibration of high speed train, horizontal force when train stop and earthquake. Works of foundation construction consider to requirements of the times to coal yard green growth. Together, new green foundation method for possible economics and securing of reduce the term of works are material to developments. Therefore, we carried out study that it is using and development new concept environment - friendly filling include durability and earthquake resistance, for secure safety and minimize environment pollution. To achieve this, we carried out difference tests that new green fillings of underwater concrete, high liquidity, high viscosity, early stiffness as compared to existing portland cement fillings. As results, new green filling have outstanding application at precast pile method and micropile construction method with vertical bearing capacity, horizontal bearing capacity and many case. From now on we will be looking forward to development of new environment-friendly foundation method from various further studies.

• Journal of the Korean Wood Science and Technology
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• v.43 no.4
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• pp.456-462
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• 2015

365 pieces of domestic $38{\times}140{\times}3600mm$ Red pine structural lumber were machine graded conforming to a softwood structural lumber standard (KS F 3020). The allowable bending stresses calculated for each grade were compared with the values currently tabulated in the standard. Four calculation methods for lower $5^{th}$ percentile bending stress were non-parametric estimation with 75% confidence level, 2-parameter and 3-parameter Weibull distribution fit, and bending modulus of rupture (MOR)-modulus of elasticity (MOE) regression based method. Only the data set of Grades E8, E9, and E10 were statistically eligible for the $5^{th}$ percentile calculation. The MOR-MOE regression based method only was able to estimate the lower $5^{th}$ percentile values theoretically for the full range of grades. The results showed that all allowable bending stresses calculated were lower than the design values tabulated in the standard. This implies that the current machine grading system has the pitfall of structural safety. Improvement in current machine grading system could be achieved by introducing the bending strength and stiffness combination grade system.