• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.38-39
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• 2015

For the purpose of reducing defects (cracking) in topping concretes cast as artificial greening layer base, synthetic macro fibers were mixed. The flexural strength of synthetic macro fiber mixed topping concretes was tested via comparing its performance with current topping concrete. According to the results of the testing, topping concrete with adjusted mixing ratio after mixing with 1kg of synthetic macro fiber showed approximately 15% higher flexural strength compared to the current topping concrete.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.61-65
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• 2008

A 4-story reinforced concrete structure built above an underground parking garage shows some slab deflections, and the deflections of the concrete floor slabs are proposed to be alleviated by the application of light-weight topping material in conjunction with localized strengthening of the slabs. The application of light-weight concrete topping on the existing slab has been simulated and its performance to anticipated loads has been analyzed. The application of light-weight topping material imposes additional weight on the exiting floor slabs. This added weight on the existing slabs causes over-stressing of the slabs. This over-stressing can be alleviated by enhancing the load carrying capacity of the existing slabs. Additional load carrying capacity in the existing slabs can be developed by localized strengthening of the slabs utilizing techniques such as the application of fiber-reinforced composites on the bottom surface of the slabs, and application of fiber-reinforced composites adequately complements the capacity of the existing slabs to bear the additional load imposed by light-weight leveling material. Additional moments in the beam and columns induced by the application of the light-weight topping material were tabulated and compared with capacity. The moment D/C ratios of the beam and columns are well the range of acceptable limits, and the beam and columns are not overstressed by the application of the surcharge.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.31-37
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• 2017

The use of half PC slab has been increasing to shorten construction period. Because the drying shrinkage of topping concrete is restrained by PC slab, the tensile stress is generated at the topping concrete and the cracks can be occurred at the topping concrete due to drying shrinkage. Therefore, it is important to predict the tensile strain of half PC slab due to drying shrinkage to improve the quality of half PC slab. However, there is no studies on prediction of shrinkage behavior of half PC slab yet. Therefore, in this study, half PC slab was made, and the predictability of tensile strain generated at half PC slab due to drying shrinkage was investigated. The step by step method considering creep was used to estimate the tensile strain of half PC slab. In result, good agreement was obtained between the analytical and experimental values.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.7-8
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• 2016

The use of half PC slab is increasing to shorten construction period. Because the drying shrinkage of topping concrete is restrained by PC slab, the tensile stress is generated at the topping concrete and the cracks can be occurred at the topping concrete due to drying shrinkage. Therefore, it is important to predict the tensile strain of half PC slab due to drying shrinkage to improve the quality of half PC slab. However, there is no studies on prediction of shrinkage behavior of half PC slab yet. Therefore, in this study, half PC slab was made, and the predictability of tensile strain generated at half PC slab due to drying shrinkage was investigated. The step by step method considering creep was used to estimate the tensile strain of half PC slab. In result, good agreement was obtained between the analytical and experimental values.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.741-749
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• 2014

Prestressed hollow-core (PHC) slabs are structurally-optimized lightweight precast floor members for long-span concrete structures, which are widely used in construction markets. In Korea, the PHC slabs have been often used with cast-in-place (CIP) topping concrete as a composite slab system. However, the PHC slab members produced by extrusion method use concrete having very low slump, and it is very difficult to make sufficient roughness on the surface as well as to provide shear connectors. In this study, a large number of push-off tests was conducted to evaluate interfacial shear strengths between PHC slabs and CIP topping concrete with the key variable of surface roughness. In addition, the horizontal shear strengths specified in the various design codes were evaluated by comparing to the test results that were collected from literature.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.505-512
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• 1998

The object of this study is investigated to flexural behavior of structural deck plate composite slabs using high-strength lightweight concrete. Test variables are concrete compressive strength (normal weight concrete 210kg/$\textrm{cm}^2$, lightweight concrete 270, 350kg/$\textrm{cm}^2$), topping concrete thickness (70, 75mm when span is 3.4m), deck plate depth (50, 75mm when topping concrete thickness is 70mm and span is 3.4m) and span(3.0, 3.4m). Test results are compared with current ACI Building Code(318-95). The test results are follows ; (1) a value of Ptest/Pcal is 1.27~1.39, (2) a mean value of $\delta$test/ $\delta$ACI is, 0.60 when deflection is reatched to maximam permissible computed deflection (L/360), and (3) ductility index are 3.61~6.85.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.161-168
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• 1994

Half-P.C. slab system is the composite structural system which utilizes precast concrete for lower portion and cast in situ concrete for upper portion slab. When the composite slab using Half P.C. slab is deformed by flexural moment, horizontal shear happened at the interface between Half P.C. slab and topping concrete. To resist horizontal shear strength a scratch method has tried. To determine ultimate interface shear strength, shear stress, and shear coefficient, high and normal strength concrete are used for topping concrete. Major variables are compressive strength of topping concrete with or without shear reinforcement, quantitative roughness of the P.C. :surface and tie or untie of the stud with welded deformed wire fabric in the P.C. member. The Icross sectional area on joints is 3,200 $cm^2$ in all specimens. Test results showed that shear stress increased, as the depth of the quantitative roughness increased. The horizontal shear strength could be resisted with safe by the quantitative roughness without shear tie. A shear coefficient determinant equation is proposed such that K = 0.025918 + 0.0068894$\cdot$R – 0.000182354${\cdot}R^2$

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.167-172
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• 2001

Hollow core slabs generally have not been used for a bridge slab or a parking in Korea. In this study, high performance hollow core slabs, which has been the most thick one in domestic are re-designed and examined for practical use. Flexural tests were performed on four 315mm deep hollow core slabs to investigate adaptability for high vehicle live loadings and composite action with topping concrete. The precast slabs were reinforced with 10-l/2 inch dia-strands at the lower of slab and 4-l/2 inch dia-strands at tile upper of slab, and cast with 80mm deep topping concrete. Those tested hollow core slabs showed ductile failure behaviors which were conform to the current Ultimate Strength Design Method for a span of l0m up to the live load of 1, 000 kg/$m^2$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.235-236
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• 2023

Concrete surfaces have weak surface strength due to bleeding and laitance, and problems such as peeling, cracking, and cracking may occur. In particular, underground parking lots can be said to be more vulnerable to peeling, breaking, and cracking if excessive loading of materials and equipment movement are not managed at the initial age after placing of concrete. Cracks, peeling, and cracking problems in slab concrete in underground parking lots of apartments can lead to leakage problems and affect finishing materials constructed on top of topping concrete, reducing the performance required for waterproof materials. Therefore, in this study, the bleeding and surface strength according to the standard of topping concrete and the use of admixture were reviewed to solve the crack, peeling, and cracking problems among the types of defects in underground parking lot slab concrete. As a result, it was derived that the optimal concrete compressive strength is 30MPa or more, and it is a reasonable performance design method to prohibit the substitution of admixtures.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.156-163
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• 2002

Hollow core slabs generally have not been used for a bridge or a parking slab in Korea. In this study, high performance hollow core slabs, which have been the most thick one in domestic are re-designed and examined for practical use. Flexural tests were performed on four 315mm deep hollow core slabs to investigate adaptability for high vehicle live loadings and composite action with topping concrete. The precast slabs were pre-tensioned with ten strands of 1/2 inch diameter at the lower of slab and four strands of 1/2 inch diameter at the upper of slab, and cast with 80 mm deep topping concrete. Tested hollow core slabs showed ductile failure behaviors which were conformed to the current Ultimate Strength Design Method for a span of 10m up to the live load of 1,000 kgf/㎡. The rectangular md round shear cotters which were used for the composite action between precast and topping concrete, developed sufficient strengths because cracking, even micro had not been developed at the end of slabs up to the pure flexural tensile failure.