• Architectural research
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• v.19 no.4
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• pp.117-124
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• 2017

In this research, we carried out finite element analysis depends on the variations such as the strength of the main bar, concrete, shear-span ratio(a/d) and existence of shear reinforcing bar. Throughout the results of FEM analysis, we were able to figure out how each variation can effect on shear performance. As the strength of concrete increased, the maximum shear force enhancement effect of each specimen was evaluated. As a result, the shear strengthening effect was 51~97% for shear reinforced specimens, and 26~44% for non-shear reinforced specimens. As the yield strength of reinforcing bars increases, the shear reinforcement effect of the specimen the specimens without shear reinforcement were 3%~6% higher than those with shear reinforcement. Theoretical and analytical values were compared using the design equations obtained from the CEB code. Theoretical and analytical values were compared using the design equations obtained from the CEB code. As a result, the error rate was the highest at 3.64 in the S1.0-C0 series and the lowest at 1.46 in the S1.7-C1 series. Therefore, the design equation of the CEB code is estimated to underestimate the actual shear strength of deep beams that are not subjected to shear reinforcement.

• Corrosion Science and Technology
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• v.3 no.6
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• pp.245-250
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• 2004

A series of classical G109 type concrete specimens was exposed to cyclic wet and dry ponding with 15 w/o NaCl solution for approximately five years. Mix design variables included 1) three cement alkalinities (EqA of 0.97, 0.52, and 0.36) and 2) three water-cement ratios (0.50, 0.41, and 0.37). To determine the corrosion initiation time, corrosion potential and macro-cell current between top and bottom bars were monitored. Subsequent to corrosion initiation, specimens were autopsied and visually inspected. Concrete powder samples were collected from top rebar trace and chloride concentration was measured. Also, time-to-corrosion, $T_i$, for specimens of the individual mix designs was represented using Weibull analysis. Time-to-corrosion was a distributed parameter; and because of this, corrosion initiation of four identical specimens for each mix varied, often over a relatively wide range. Specimens fabricated using the lowest water cement ratio and the highest alkalinity cement exhibited the longest time-to-corrosion initiation and the highest chloride threshold levels. Time-to-corrosion did not increase monotonically with cement alkalinity, however, presumably as a consequence of relatively high $Cl^-$ binding in the lower pore water pH range. The chloride threshold level, $Cl_{th}$, increased with increasing $T_i$ and, consequently, was greatest for the highest cement alkalinity specimens.

• Journal of Korean Association for Spatial Structures
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• v.14 no.2
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• pp.79-86
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• 2014

The purpose of this study is intended to determine the validity of shear reinforcement by evaluating flexural performance in the hollow slab. The hollow slab is relatively light and second moment of inertia is large. Due to these characteristics, it can be used to slab system efficiently. Therefore the prediction of the structural behaviors is very important because of decrease of shear and flexural strength which is caused by hollow section of slab interior. In this study, the flexural test were performed to analyze the flexural capacity of the hollow slab w/ or w/o shear reinforcement. A total of six full scale specimens were tested. These specimens have three cases of reinforcing bar ratio, 0.009, 0.018 and 0.024. To verify the flexural behavior such as ultimate load, load-deflection and crack pattern, the flexural experiment were tested by using loading frame. Experimental results have shown that the flexural behavior are depend on the reinforcing bar ratio. Also the hollow slab with shear reinforcement have shown flexural behavior. Therefore, it is appropriate that the hollow slab is reinforced by shear reinforcement to improve the flexural performance of the hollow slab.

• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.95-110
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• 2011

This paper presents a tri-uniform bond stress model for predicting the lap splice strength of reinforcing bar at the critical bond splitting failure. The proposed bond distribution model consists of three zones, namely, splitting zone, post-splitting zone and yielding zone. In each zone, the bond stress is assumed to be constant. The models for bond strength in each zone are adopted from previous studies. Combining the equilibrium, strain-slip relation and the bond strength model in each zone, the steel stress-slip model can be derived, which can be used in the nonlinear frame analysis of the column. The proposed model is applied to derive explicit equations for predicting the strength of the lap splice strengthened by fiber reinforced polymer (FRP) in both elastic and post-yield ranges. For design purpose, a procedure to calculate the required FRP thickness and the number of FRP sheets is also presented. A parametric investigation was conducted to study the relation between lap splice strength and lap splice length, number and thickness of FRP sheets and the ratio of concrete cover to bar diameter. The study shows that the lap splice strength can be enhanced by increasing one of these parameters: lap splice length, number or thickness of FRP sheets and concrete cover to bar diameter ratio. Verification of the model has been conducted using experimental data available in literature.

• Journal of Urban Science
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• v.7 no.2
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• pp.21-27
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• 2018

With the increase of the skyscraper center, the development of large-diameter and high-strength reinforcing bars is being carried out to solve the dense reinforcement. In case of the steel reinforced concrete with a small cross section such as beam-column joints, the development length becomes short when straight bars are used. Therefore, it is possible to solve the problem that the development length becomes short by using the bearing strength of the hooked bar and headed bar. In this study, the exterior beam-column joint test of SD700 hooked bar and headed bar with anchorage length of 20db was conducted to extend the development length limitation of hooked bar and headed bar. As a result of the evaluation of the anchorage strength using the design equation by KCI, the average of the [measured value]/[predicted value] ratio was 1.31 for the hooked reinforcing bars. In the case of headed bars, the average of the [measured value]/[predicted value] ratio was 1.12. In addition, in order to compare the anchorage performance of the hooked bar and the headed bar, the measured values were divided by the square root of the compressive strength of the concrete to compare the anchorage strength. Under the same conditions, the anchorage strength of headed bars was 8.5% higher than the hooked bars.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.439-444
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• 2019

It is generally known that high strength soil is indicative of well-graded particle size distribution. However, there are some special cases of firm ground despite poor grade distribution, especially a specific gap-graded soil. Based on these discoveries, this study investigated the development of an additive of gap-graded soils designed to increase soil strength. This theoretical concept was used to calculate the mixed ratio required for optimal soil strength of the ground sample. The gap-graded aggregate was added according to Plato's polyhedral theory and subsequently calculated ratio and soil strength characteristics were then compared to characteristics of the original soil sample through various test results. In addition, the underground stress transfer rate was measured according to the test conditions. The test results showed that the ground settlement and stress limit thickness were reduced with the incorporation of gap-graded soil. Further field tests would confirm the reproducibility and reliability of the technology by using gap-graded soil to reinforce soft ground of a new construction site. Gap-graded soil has the potential to reduce the construction cost and time of construction compared to other reinforcing methods.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.1
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• pp.21-28
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• 2019

This study investigates the applicability of composite polyurea to contain fiber reinforcement like fiber glass, steel fiber and carbon nanotube. Polyurea as elastomer is an excellent water-proofing material with many mechanical characteristics such as high tensile strength, ductility, high rate of expansion and contraction, and so on. The reinforcing fibers can be utilized for improving the load-carrying capacity of concrete structures. The polyurea plays a role to improve the ductility and toughness. Composite polyurea takes the mechanical advantages of the fibers and the polyurea. The test variables include the type of reinforcing fiber, its spraying thickness, and its weight ratio contained in the composite polyurea. It is observed that the load-carrying capacity, and the ductility and toughness are improved with the increase in the spraying thickness and the weight ratio contained in the composite polyurea. It is expected that the composite polyurea can be widely utilized in enhancing the structural and seismic performance.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.1-10
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• 2022

In Korea, accidents related to the collapse of deteriorated aging reservoirs occur every year. The grouting method is generally applied to reinforce an aging reservoir. However, when using this method, different reinforcing effects appear depending on the ground conditions. Thus, new construction methods and materials capable of providing consistent reinforcing effects are required. In this study, the direct shear test (DST), model test, and simulation analysis were performed to evaluate the impact of surface stabilizers, generally used to reinforce roads, rivers, and slopes of roads, applied using surface curtain walls on aging reservoirs. The DST results indicate that when the surface stabilizer was mixed with in-situ soil, the increase in cohesion was the highest at a mixing ratio of 9%. No changes in the friction angle were evident; therefore, 9% was determined to be the optimal mixing ratio. In addition, the model test and simulation analysis showed that when 9% of the surface stabilizer was mixed and applied to the aging reservoir, the seepage quantity of water and the saturated area were reduced by approximately 42% and 73%, respectively. Moreover, the comprehensive analysis of results showed that the grouting method could be completely replaced by surface stabilizers applied through surface curtain walls because the technique could secure stability by decreasing the seepage in the aging reservoir.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.105-113
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• 2011

This study evaluated the effects of fibers on the mechanical properties and chemical solution resistance of porous concrete with fiber type (jute, pulp, PVA and nylon fiber) and fiber volume fraction (0.0%, 0.1%, 0.2%, 0.3%). The tests that were carried out to analysis the properties of porous concrete included compressive strength, void ratio, pH value, and chemical solution exposure with varying type and volume fraction of fiber were conducted. The type and volume fraction of fiber also affected the void ratio, compressive strength, flexural strength and chemical solution exposure. Increased volume fractions of fiber resulted in improved properties of the compressive strength, flexural strength and void ratio. However, the difference between the measured pH value and chemical resistance of porous concrete with fiber type and volume fraction was not significant.

• Fire Science and Engineering
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• v.25 no.1
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• pp.63-71
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• 2011

When it comes to slim floor using asymmetric H-beam, it was designed that the steel member is embedded in concrete with relatively low thermal conductivity so as to minimize the deterioration of rigidity of steel member in fire. But given the bottom flange of asymmetric H-beam is directly exposed to the fire, the measure of applying the fireproof coating to improve the fire rate performance of slim floor beam was sought. The test was aimed at comparing the fireproof performance by adjusting the load ratio of 0.4 and 0.3, and The test was carried out to identify the 3-hour fire performance by reinforcing the beam as well as applying the fireproof coat, In the wake of comparing the specimen depending on variation of load ratio, lowering load ratio by 0.1 resulted in difference of 12 minutes and deflection was 39 mm. It was able to improve 12 minutes by reinforcing the beam and up to 102.4 mm in deflection.