• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.233-240
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• 1999

It is well known that the ultimate compressive strength of concrete filled tubular stub-column is higher than that of the simplified evaluating value because of the confinement effect of infilled concrete. In this paper, It is compared the experimental results of other researchers with estimated ones by using the formulae. Finally, It is shown that the predicted equation is obtained by using the numerical analysis.

• Computers and Concrete
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• v.9 no.2
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.82-89
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• 2014

The purpose of this study is to propose a simple model to evaluate the compressive strength development of concrete with various supplementary cementitious materials (SCMs) and cured under different temperatures. For the generalization of the model, the ACI 209 parabola equation was modified based on the maturity function and then experimental constants A and B and 28-day compressive strength were determined from the regression analysis using a total of 265 data-sets compiled from the available literature. To verify the proposed model, concrete specimens classified into 3 Groups were prepared according to the SCM level as a partial replacement of cement and curing temperature. The analysis of existing data clearly revealed that the 28-day compressive strength decreases when the curing temperature is higher and/or lower than the reference curing temperature ($20^{\circ}C$). Furthermore, test results showed that the compressive strength development of concrete cured under $20^{\circ}C$ until an early age of 3 days was marginally affected by the curing temperature afterward. The proposed model accurately predicts the compressive strength development of concrete tested, indicating that the mean and standard deviation of the ratios between predictions and experiments are 1.00 and 0.08, respectively.

• Journal of the Korea Institute of Building Construction
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• v.23 no.1
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• pp.35-43
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• 2023

In this study, the mechanical properties of concrete mixed with non-sintered hwangto(NHT) as an alternate material for cement were evaluated, and the compressive strength prediction equation of concrete based on ultrasonic pulse velocity analysis was proposed. Cement replacement rates for mixed NHT were set to 0, 15, and 30%, and design compressive strength was set to 30 and 45MPa to evaluate the effect on the amount of cement and NHT powder. The mechanical properties items analyzed were compressive strength, ultrasonic pulse velocity, and elastic modulus, and were measured on days 1, 3, 7, and 28. As the replacement rate of NHT increased, the mechanical properties tended to decrease. In addition, as a result of analyzing the correlation between compressive strength and ultrasonic pulse velocity, the correlation coefficient(R²) showed a high relationship(R²=0.95) on concrete mixed with NHT.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.145-148
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• 2006

Schmidt hammer and ultra-sonic method are commonly used for crushed sand concrete compressive strength test in a construction field. At present, various of equations for prediction of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between prediction strength by presentation equations and destructive strength to test specimen, and find out which is a suitable equation for the construction site, In this study, a strength test was carried out destructive test by means of core sampling and traditional test. Non-destructive test was conducted Schmidt hammer and ultra-sonic method, the experimental parameter were concrete age, curing condition, test method and strength level. It is demonstrated that the correlation behavior of crushed sand concrete strength in this study good due to the perform analysis of correlation between core, destructive strength and non-destructive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.767-772
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• 1998

schumidt hammer and ultra-sonic method are commonly used for concrete compressive strength test in a construction field. At present, various kinds of equations for estimation of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between estimation strength by presentation equations and destructive strength to test specimen, and find out which is a suitable equation for this construction site. In this study, a strength test was carried out destructive test by means of core sampling. Non destructive test was conducted Schumidt hammer and ultra-sonic method, the experimental parameter were concrete age, test method and strength level. It is demonstrated that the correlation behavior of concrete strength in this study good due to the performs analysis of correlation between core strength and nondestructive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.184-189
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• 1993

This is an experimental investigation the shear behavior of reinforced concrete with stirrup of which stress ranges 0.0㎏/㎠ to 7.0㎏/㎠. Five rectangular beams which concrete strengths are 287㎏/㎠ and 380㎏/㎠, a/d=3, and main steel ratio equal to 1.96% was tested. Those were designed to fail in shear. The shear cracking load and failure load were measured and compared with ACI's equation and Zutty's proposed equation. The results are following : ACI equation and Zutty's equation are consertive. As the concrete compressive strength increased, reserved shear strength of beams with minimum web reinforcement decreases. According to increase of web reinforcement , the rate of increases of shear strength is decreased. The failure modes of specimen with minimum web reinforcement are shear compression failure which is reached after diagonal shear cracking.

• Tunnel and Underground Space
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• v.9 no.3
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• pp.221-229
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• 1999

Parameters of failure criteria, compressive strength and elastic modulus are most important for design and stability analysis of rock structure using numerical analysis. In this study, it suggests that the application of input data for numerical analysis by the literature study and the result of the 150 sets of triaxial compressive test. There was much different between parameters of failure criterion suggested by Hoek-Brown and parameters resulted from the analysis using 150 sets of triaxial compressive test. But the converting equations of compressive strength have had an interrelation with RMR. However, the converting of elastic of elastic modulus were different as chosen of equation, and the equation by Nicholson et at was more useful than others.

• Journal of the Korean Society of Safety
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• v.23 no.4
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• pp.67-71
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• 2008

Formwork is a temporary structure that supports its weight and that of fresh concrete as well as construction live loads. Slab formwork consists of sheathing, stringer, hanger and shore. In construction site, pipe supports are usually used as shores which are consisted of the slab formwork. In this study, compressive strength of 80 pipe supports was measured by knife edge test and plate test. Buckling load of pipe supports was analyzed by structural analysis program(MlDAS). Theoretical buckling load with/without initial deformation was got by theoretical analysis. According to these results, buckling load which was analyzed by structural analysis program(MlDAS) was larger than compressive strength of knife edge test and plate test. Theoretical buckling load without initial deformation was larger than compressive strength of knife edge test and plate test. But Theoretical buckling load with initial deformation was lower than compressive strength of knife edge test and plate test. Initial deformation equation for test method according to the pipe support length was suggested. Therefore, the present study results will be used to design the slab formwork safely.

• International Journal of Advanced Culture Technology
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• v.6 no.3
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• pp.163-172
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• 2018

The power train of hydro-mechanical continuously variable transmission(HMCVT) for the middle class forklift makes use of an hydro-static unit, hydraulic multi-wet disc brake & clutches and complex helical & planetary gears. The complex helical & planetary gears are a very important part of the transmission because of strength problems. The helical & planetary gears belong to the very important part of the HMCVT's power train where strength problems are the main concerns including the gear bending stress, the gear compressive stress and scoring failures. The present study, calculates specifications of the complex helical & planetary gear train and analyzes the gear bending and compressive stresses of the gears. It is necessary to analyze gear bending and compressive stresses confidently for an optimal design of the complex helical & planetary gears in respect of cost and reliability. This paper not only analyzes actual gear bending and compressive stresses of complex helical & planetary gears using Lewes & Hertz equation, but also verifies the calculated specifications of the complex helical & planetary gears by evaluating the results with the data of allowable bending and compressive stress from the Stress - No. of cycles curves of gears. In addition, this paper explains actual gear scoring and evaluates the possibility of scoring failure of complex helical & planetary gear train of hydro-mechanical continuously variable transmission for the forklift.