• 한국도로학회논문집
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• 제9권4호
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• pp.205-213
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• 2007

본 연구에서는 포장용 콘크리트의 강도실험을 통해 강도간의 상관관계식을 도출하는 것을 목적으로 하였다. 강도로서 재령별 압축강도, 휨강도, 할렬인장강도와 탄성계수를 측정하였다. 배합변수는 조골재(화강암, 석회암, 사암), 세골재(자연사, 세척사, 부순모래) 및 단위시멘트량(315-375kg)을 변수로 하였다. 전체적으로 골재나 단위시멘트량보다는 재령에 의해 전형적인 강도곡선을 따라 뚜렷하게 변화함을 보여준다. 이러한 강도결과를 바탕으로 휨강도와 압축강도, 할렬인장강도와 압축강도, 탄성계수와 압축강도, 할렬인장강도와 휨강도의 상관관계를 분석한 결과 휨강도와 압축강도, 탄성계수와 압축강도는 기존의 관례대로 제곱근(n=0.5)의 상관관계식이 잘 맞음을 알 수 있었다. 할렬인장강도와 휨강도는 선형의 상관관계식으로 표현하였고, 할렬인장강도와 압축강도는 n=0.87의 지수승을 사용한 경우가 가장 적합한 것으로 나타났다.

• 국제초고층학회논문집
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• 제7권4호
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• pp.287-298
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• 2018

High strength steels have been widely applied in recent years due to high strength and good working performance. When subjected to fire conditions, the strength and elastic modulus of high strength steels deteriorate significantly and hence the load bearing capacity of structures reduces at elevated temperatures. The reduction factors of mechanical properties of high strength steels are quite different from mild steels. Therefore, the fire design methods deduced from mild steel structures are not applicable to high strength steel structures. In recent ten years, the first author of this paper has carried out a lot of fundamental research on fire behavior of high strength steels and structures. Summary of these research is presented in this paper, including mechanical properties of high strength steels at elevated temperature and after fire exposure, creep response of high strength steels at elevated temperature, residual stresses of welded high strength steel member after fire exposure, fire resistance of high strength steel columns, fire resistance of high strength steel beams, local buckling of high strength steel members, and residual strength of high strength steel columns after fire exposure. The results show that the mechanical properties of high strength steel in fire condition and the corresponding fire resistance of high strength steel structures are different from those of mild steel and structures, and the fire design methods recommended in current design codes are not applicable to high strength steel structures.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 가을 학술논문 발표대회
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• pp.193-194
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• 2022

The use of high-strength grout for facility foundations and bridges has recently been expanding in offshore wind farms. Offshore wind farms require a bearing capacity for horizontal loads such as wind, waves. Therefore, in this study, the strength of the high-strength grout discharged through pump pressure was measured and compared with the existing strength to secure the strength after the underwater pump pressure of the high-strength grout used in the offshore wind connection. The compressive strength measurement showed that the strength difference at each position of the core specimen was 1% higher than that of the other specimens, and there was almost no change in the strength according to the height. The strength of the core specimen decreased by 23% compared to the existing strength, which is similar to the result of this study because the strength of the core specimen decreased by approximately 25% compared to the general specimen according to related research. Therefore, it is believed that there is no decrease in strength due to underwater pumping.

• 한국의류학회지
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• 제23권7호
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• pp.998-1006
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• 1999

This study has investigated the relation between the sewing speed and seam breaking strength applied perpendicular to the seam direction. Breaking strength efficiency breaking mode of seams were examined under various sewing conditions using three kinds of sewing threads and four kinds of fabrics. The results obtained are as follows : 1. According to the increase in sewing speed seam strength was remarkably decreased. Seam strength and its loss difference were shown variously as threads and fabrics were mixed. 2. In case of fabrics with higher strength seam strength showed higher. And the seam strength was determined by the loop strength. 3. In case of fabrics with lower strength seam strength and its difference for every sample showed lower. So the strength of fabrics dominated the seam strength than those of threads. 4. In the experiment using various fabrics and sewing threads there was a type of thread appropriate to each fabric. Fabrics and threads with have similar physical properties were shown proper seam efficiency. 5. The breaking mode was different for every sample seam that was tested.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.245-253
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• 2002

This study was focused on the effect of concrete strength and lateral ties of concrete columns using high-strength concrete. Thirty-six concrete columns with 20cm square cross-section were tested. Experimental parameters included the concrete strength, the distribution of longitudinal bars and the volumetric ratio, yield strength, spacing of lateral ties. From the experiments, we found that: 1) the increasing rate of the strength and ductility of concrete columns caused by confinement of lateral ties was decreasing, as the concrete strength increased. 2) The high volumetric ratio and the reduction of tie spacing had a tendency to enhance the strength and improve the ductility. 3) The high-strength concrete columns required high volumetric ratio of lateral ties to maintain the proper strength and ductility. It was observed that the current AIK design code to specify the maximum tie spacing of high-strength concrete columns led to the poor strength and ductility for seismic design.

• KCI Concrete Journal
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• 제14권2호
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• pp.81-85
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• 2002

The strength development of concrete is influenced by temperature and cement type which greatly affect hydration degree of cement. There is not pertinent concrete strength management method in korea. There are several methods for estimating the in-place strength of concrete. One such method is the maturity concept. The maturity concept is based on the fact that concrete gains strength gradually as a result of chemical reactions between cement and water; and for a specific concrete mixture, strength at any age and at normal conditions is related to the degree of hydration. The rate of hydration and, therefore, strength development of a given concrete will be a function of its temperature. Thus, strength of concrete depends on its time-temperature history. The goals of the present study are to investigate a relationship between strength of high-strength concrete and maturity that is expressed as a function of an integral of the curing period and temperature and predict strength of concrete.

• Steel and Composite Structures
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• 제29권4호
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• pp.509-526
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• 2018

The direct strength method adopted by the AISI Standard and AS/NZS 4600 is an advanced design method meant to substitute the effective width method for the design of cold-formed steel structural members accounting for local instability of thin plate elements. It was proven that the design strength formula for the direct strength method could predict the ultimate strength of medium strength steel welded section compressive and flexural members with local buckling reasonably. This paper focuses on the modification of the direct strength formula for the application to high strength and high performance steel welded section columns which have the nominal yield stress higher than 460 MPa and undergo local buckling, overall buckling or their interaction. The resistance of high strength steel welded H and Box section columns calculated by the proposed direct strength formulae were validated by comparison with various compression test results, FE results, and predictions by existing specifications.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.77-79
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• 2012

This paper intends to review possible application in the high strength area through compressive strength estimation of the simulated high strength concrete member using Rock Test Hammer and suggest it as a reference data for the strength estimation technique of the ultra high strength concrete in the future. From the results of our test, in the low strength area less than 15MPa and normal strength area in 15~60MPa, as shown on the existing studies, it is indicated that P Type Schmidt Hammer in the low strength area and N Type Schmidt Hammer in the normal strength area have high correlation of rebound-compressive strength. As the Rock Test Hammer indicated more or less reduced accuracy in the low strength area and the normal strength area but high correlation on the high strength area (50~100MPa) defined on this test, it is determined that it would be possible to make the fastest and simplest compressive strength estimation on the site where the high strength concrete is applied.

• Earthquakes and Structures
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• 제9권6호
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• 한국건축시공학회지
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• 제8권3호
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• pp.75-83
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• 2008

In this paper, concrete material tests were carried out to investigate influence of steel fiber volumn ratios on variations of workability and strength characteristics of steel fiber reinforced high-strength concrete, $50MPa{\sim}90MPa$ of compressive strength, according to increase of fiber volume. Test specimens were arranged with six levels of concrete compressive strength and fiber volumn ratios, 0.0%, 0.5%, 1.0%, 1.5%, 2.0%. The test results showed that steel fiber reinforced high-strength concrete($70MPa{\sim}90MPa$, 1.5% fiber volumn ratio) with good workability of slump 20cm could be used practically and effects of steel fiber reinforcement in improvement of concrete strength and toughness characteristics such as splitting tensile strength, flexural strength, and diagonal tensioned shear strength, were more distinguished in high-strength concrete than general strength concrete. And the test results indicated that splitting tensile strength of fiber reinforced concrete was proportioned to the product of steel fiber volumn ratios, $V_f(%)$ and sqare root of compressive strength, $\sqrt{f_{ck}}$, and the increasing rate was in contrast with that of flexural strength, and increase of diagonal tensioned shear strength was remarkable at steel fiber volumn ratio, 0.5%.