• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.643-646
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• 2003

This study concerns the new estimated strength equation of concrete by penetration test. There are not only few estimate strength equations of concrete, but also many problems to apply them because of time, cost, easiness, structural damage, reliability and so on. In this study, there performed a series of test for one year and estimated strength equation of concrete as follows; Linear: fck =3.38d - 95.1 ($$r^2$$=88.6%) Quadratic: fck =0.188$$d^2$$- 10.76d + 166.3 ($$r^2$$=96.7%) here, fck : estimated compressive strength of concrete by Mpa d: exposed probe length by mm.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.129-132
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• 2004

This study concerns the new strength equation of concrete by ultrasonic pulse velocity test. There are not only few estimate strength equations of concrete by ultrasonic pulse velocity test, but also many problems to apply them because of time, cost, easiness, structural damage, reliability and so on. For this study, there performed a series of test and proposed equations as follows; $$Linear\;:\;f_{kc}=65.43Vp-207.18\;r^2=80.8\%$$ $$Quadratic\;:\;f_{ck}=42.35Vp^2-250.71Vp+378.8\;r^2=83.7\%$$ here, fck : Estimated compressive strength of concrete by MPa Vp: Ultrasonic Pulse Velocity of concrete by km/sec.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.133-136
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• 2004

This study concerns the. new equation of concrete strength by schmidt hammer test. There are not only few estimate strength equations of concrete by schmidt hammer test, but also many problems to apply them because of time, cost, easiness, structural damage, reliability and so on. For this study, there performed a series of schmidt hammer test with in existing 730days' concrete structures and proposed equations as follows; $$Linear\;:\;f_{ck}=2.18R-40.54\;(r^2=77.7\%)$$ $$Quadratic\;:\;f_{ck}=0.076R^2-2.92R+40.04\;(R^2= 85.5\%)$$ here, fck : Estimated compressive strength of concrete by MPa, R : Rebound index of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.125-128
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• 2004

This study concerns the new estimated strength equation of concrete by penetration test. There are not only few estimate strength equations of concrete, but also many problems to apply them because of time, cost, easiness, structural damage, reliability and so on. In this study, there performed a series of penetration test with in 730days' concrete structures and proposed equations as follows; $$Linear\;:\;f_{ck}=2.95d-80.0(r^2= 69.8\%)$$ $$Quadratic\;:\;f_{ck}=0.204d^2-12.15d+193.2(r^2=83.6\%)$$ here, fck : Estimated compressive strength of concrete by MPa d: exposed probe length by mm.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.105-111
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• 2023

In this study, the mechanical properties of high-strength concrete according to the substitution rate of NSH(Non-sintered Hwangto) as an alternative material for cement were measured and evaluated. Through UPV(Ultrasonic pulse velocity) analysis, the compressive strength prediction equation was proposed, and the substitution rate of NSH was set at 15 % and 30 %. The evaluation items were compressive strength and UPV, and the curing period was set to 24 hours. In compressive strength and UPV, as the NSH substitution rate increased, lower strength and lower UPV were shown. In addition, the correlation number(R² ) between compressive strength and UPV was 0.99 for NC(Normal Concrete), 0.97 for NSHC(Non-sintered Hwangto Concrete)33-15, and 0.94 for NSHC33-30.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.233-240
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• 1998

A rational expression, developed to predict the shear strength of reinforced concrete beams, is derived from the relationship between shear and the rate of change of bending moment along a beam coupled with experimental findings for the arch action. The proposed ultimate shear strength equation, arising from analytical premises and then calibrated with experimental data, is a similar form to the ACI 318 equation derived mainly from empirical approach. The proposed equation depends on the concrete compressive strength, amount of longitudinal steel content, and the shear span-to-depth ratio, and rationally reflects the shear resistance mechanism of combined beam action and arch action in reinforced concrete beams. The proposed equation applied to existing test data and the results were compared with those predicted by the ACI 318 equation and the Zsutty's equation.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.659-666
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• 2010

Although the compression splice needs not be longer than the tension slice due to existence of end bearing, current design codes impose a longer compression lap splice than a tension lap splice in high strength concrete. Hence, new criteria for the compression lap splice including the effects of concrete strength need to be sought for economical design involving ultra-high strength concrete. An experimental study has been conducted with column specimens in concrete strength of 80 and 100 MPa. Test results show that the splice strength can be evaluated to be proportional to square root of compressive strength of concrete. Bar stress developed by end bearing is not affected by splice length and is expressed with a function of the square root of concrete strength. Mean value of stresses developed by end bearing is 16.5 square root of $f_{ck}$. The stresses developed by bond in compression splices are nearly identical to those in tension splices and, therefore, strength increment of compression splices is attributed to end bearing only. From regression analysis of 58 tests, a design equation is proposed for compression lap splice in 40 to 100 MPa of compressive strength of concrete. By the proposed equation, the anomaly of lap lengths in tension and compression is got rid of. In addition, the equation has a reliability equivalent to those of the specified strengths of materials.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.3
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• pp.3815-3832
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• 1975

This study was made to investigate various engineering properties of earth materials resulting from their changes in density and moisture content. The results obtained in this study are summarized as follows: 1. The finner the grain size is, the bigger the Optimum Moisture Content(OMC) is, showing a linear relationship between percent passing of NO. 200 Sieve (n) and OMC(Wo) which can be represented by the equation Wo=0.186n+8.3 2. There is a linear relationship of inverse proportion between OMC and Maximum Dry Density (MDD) which can be represented by the equation ${\gamma}$d=2.167-0.026Wo 3. There is an exponential curve relationship between void ratio (es) and MDD whose equation can be expressed ${\gamma}$d=2.67e-0.4550.9), indicating that as MDD increases, void ratio decreases. 4. The coefficent of permeability increases in proportion to decrease of the MDD and this increase trend is more obvious in coarse material than in fine material, and more obvious in cohesionless soil than in cohesive soil. 5. Even in the same density, the coefficient of permeability is smaller in wet than in dry from the Optimum Moisture Content. 6. Showing that unconfined compressive strength increases in proportion to dry density increase, in unsaturated state the compacted in dry has bigger strength value than the compacted in wet. On the other hand, in saturated state, the compacted in dry has a trend to be smaller than the compacted in wet. 7. Even in the same density, unconfined compressive strength increases in proportion to cohesion, however, when in small density and in saturated state, this relationship are rejected. 8. In unsaturated state, cohesion force is bigger in dry than in wet from OMC. In saturated state, on the other hand, it is directly praportional to density. 9. Cohesion force decreases in proportion to compaction rate decrease. And this trend is more evident in coarse matorial than in fine material. 10. Internal friction angle of soil is not influenced evidently on the changes of moisture content and compaction rate in unsaturated state, On the other hand in saturated state it is influenced density. 11. Cohesion force is directly proportional to unconfined compressive strength(qu), indicating that it has approximately 35 percent of qu in unsaturated state and approximately 70 percent of qu in saturated state.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.591-598
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• 2014

In this study, the relationship between compressive strength and water-cement ratio according to water reducing ratio was evaluated, concrete mix was prepared according to 3 level of water reducing ratio (0%, 8% and 16%) and 3 level of water-cement ratio (40%, 45% and 50%). In addition, concrete mix was carried out repetition test of three times in order to secure the reliability. As a result, compressive strength according to water reducing ratio was shown that difference of strength was about 20% occurred, effect of compressive strength according to water reducing ratio was found more than the water-cement ratio. Therefore, reflected the effect of water reducing ratio, relationship equation between new compressive strength and water-cement ratio was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.351-354
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• 2003

Triaxial behavior of concrete cylinders wrapped with FRP material has been investigated for the increase of concrete strength by lateral confinement. Using the model by Richart et al., a modified empirical equation was proposed to estimate the strength of concrete cylinders with FRP confinement based on the linear relationship between the concrete strength and lateral confining pressure. From the experimental stress-strain result of the cylinder specimens having similar confining pressure, less ductility was observed for higher strength concrete. But the compressive strength of the specimen was linearly increased by lateral confinement. The confinement effectiveness coefficient for the strength enhancement of the cylinders by FRP wrap was obtained as 2.27 from the regression analysis.