• Journal of Advanced Marine Engineering and Technology
• /
• 제26권1호
• /
• pp.59-67
• /
• 2002

The comparison of $J_{Rice}$-resistance considering a few strength ratio in Rice J-integral formula and $J_{\delta}$-resistance curves converted from experimental CTOD using appropriate strength chosen according to strain hardening level, n=10.6 (A533B steel) and n=8.1 (BS4360 steel) is carried out. The optimal dimensionless strength ratio like the factor of revision, (see full text)reflecting strain hardening level in Rice\`s experimental formula is found out and the reliability of appropriate reference strength chosen according to strain hardening level in different materials is investigated through doing that CTOD is transformed from $J_{\delta}$-integral using relationship between J-integral and CTOD. The results are as follows; 1) The optimal factor of revision is when m equals to 3 in (see full text) for Rice's and the above optimal factor of revision multiplies by coefficient, η in Rice's experimental formula instead of n=2, 2) and the pertinent reference strength for high strain hardening material like BS4360 steel is ultimate strength, $\sigma_{u}$ and for material like A533B steel is ultimate-flow strength, $\sigma_{u-f}$. The incompatible of the behavior of both experimental J-resistance curves using Rice's formula and CTOD-resistance curves for A533B and BS4360 steel by Gordon, et al., could be corrected using the optimal factor of revision in Rice\`s and the pertinent reference strength in J=$m_{j}$${\times}$$\sigma_{i}$${\times}$CTOD.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
• /
• pp.73-78
• /
• 2002

This study examines self-compacting of concrete using Ground Calcium Carbonate(GCC) gathering in limestone mine of Banyans district in order to make self-compacting concrete in the range of design strength 300kgf/cm$^2$ and the optimal mix proportion of self-compacting concrete that can use in field structure. The result shows that the optimal GCC replacement ratio is 45$\pm$5% in the normal strength of design strength 300kgf/cm$^2$ and that the volume ratio of the optimal fine aggregate used as the way satisfying both viscosity and compacting ability without separating materials is 46%. The optimal volume ratio of the coarse aggregate considering the economical aspect of concrete is 50%. It is desirable that the optimal mix proportion satisfying self-compacting for replacement of GCC is decided through mix design according to each replacement ratio.

• 한국건축시공학회지
• /
• 제5권2호
• /
• pp.153-159
• /
• 2005

This study is to choose the optimal mixture and to analyze the sensibility properties of High strength concrete and mass concrete to apply the high rising building. The main experimental variables were water/binder ratio $39\%,\;33\%,\;35\%\;and\;37\%$, replacement ratio of fly ash $5\%,\;10\%\;and\;15\%$, in the high strength concrete and water/binder ratio $39\%,\;41\%\;and\;43\%$, replacement ratio of fly ash $10\%,\;20\%\;and\;30\%$, in the man concrete. According to the test results, the principal conclusions are summarized as follows. 1) The slump(or slump flow) and air content of fresh concrete were found to be the highest in the elapsed time 30 minutes. 2) The optimal mixture conditions are W/B $40\%$, FA $25\%$ in the mass concrete and W/B $33.4\%$, FA $15\%$ in the high strength concrete. 3) The ranges of sensibility are satisfied in the moisture content ${\pm}l\%\;and\;S/a\;{\pm}2\%$.

• 한국구조물진단유지관리공학회 논문집
• /
• 제11권4호
• /
• pp.152-158
• /
• 2007

본 연구는 알칼리 활성시멘트(Alkali Activated Cement)를 콘크리트에 활용하기 위한 기초적인 연구로서 잔골재 및 굵은골재의 혼합비는 일정하게 하고, 활성화제/플라이 애쉬의 혼합비, 그리고 활성화제 중 물유리, 수산화나트륨, 물의 혼합비를 변화시킨 AAC 콘크리트에 대한 압축강도를 측정하였다. 또한 각 변수에 따른 압축강도의 특성을 분석하고, AAC 콘크리트의 최적 혼합비를 구하였다. 그 결과 최대 압축강도 발현을 위한 활성화제 중 물유리, 수산화나트륨, 물의 최적 혼합비는 4.0:1.0:2.5 이었으며, 활성화제/플라이 애쉬의 최적 혼합비는 0.7 이었다.

• Structural Engineering and Mechanics
• /
• 제58권2호
• /
• pp.259-276
• /
• 2016

Lead-rubber bearings (LRBs) have been used worldwide in seismic design of buildings and bridges owing to their stable mechanical properties and good isolation effect. We have investigated the effectiveness of LRBs in framed underground structures on controlling structural seismic responses. Nonlinear dynamic time history analyses were carried out on the well-documented Daikai Station, which collapsed during the 1995 Hyogoken-Nanbu earthquake. Influences of strength ratio (ratio of yield strength of LRBs to yield strength of central column) and shear modulus of rubber on structural seismic responses were studied. As a displacement-based passive energy dissipation device, LRBs reduce dynamic internal forces of framed underground structures and improve their seismic performance. An optimal range of strength ratios was proposed for the case presented. Within this range, LRBs can dissipate maximum input earthquake energy. The maximum shear and moment of the central column can achieve more than 50% reduction, whereas the maximum shear displacement of LRBs is acceptable.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
• /
• pp.519-523
• /
• 2009

In this study, the base mixing ratio was determinated to estimate the optimal mixing ratio of material with a change of mixing ratio of micro cement, sand, foaming agent, plasticizer by testing the unconfined compressive strength test. The unconfined compressive strength test was performed to grasp a engineering characteristics of with a change of micro cement, bubble. The results of test, the unconfined compressive strength increased with a micro cement's increase and bubble's decrease. In the future, it will be secured that is reliable datas from laboratory of various condition and in-situ tests to develop optimal lightweight foamed concrete.

• 한국조경학회지
• /
• 제38권5호
• /
• pp.93-101
• /
• 2010

탄성포장은 보행자의 만족감이 매우 높아 수요가 지속적으로 증가할 것으로 예상되나, 탄성포장의 재료 배합기준 즉, 합성고무 칩(EPDM chip)과 폴리우레탄 바인더의 적정배합기준이 미비하여 시공 시 많은 시행착오를 겪고 있는 실정이다. 따라서, 본 연구는 조경용 탄성포장의 폴리우레탄 바인더 배합비에 따른 결합력과 반발탄성의 변화를 실험을 통해 분석하고, 이를 바탕으로 적정한 재료배합 비율을 제시하고자 하였으며, 실험결과는 다음과 같다. 인장실험에서는 시료 B와 시료 C가 바인더 배합비율과 인장강도 간에 강한 양의 상관관계가 있는 것으로 나타나, 배합비율이 증가하면 인장강도가 증가한다는 것을 알 수 있다. 경도실험에서는 시료 A,시료 B,시료 C모두 바인더 배합비율과 경도 간에 통계적으로 상관관계가 없는 것으로 나타나, 탄성포장재의 경도는 바인더의 배합비율에 따라 달라지지는 않는 것으로 판단된다. 반발탄성실험에서는 시료 A와 시료 B가 배합비율과 반발탄성 간에 강한 음의 상관관계가 있는 것으로 나타나, 배합비율이 증가하면 반발탄성이 낮아진다는 것을 알 수 있다. 실험결과를 바탕으로 적정배합비율을 분석해 보면 인장강도의 경우, 인장강도의 증가가 둔화되거나 오히려 감소하는 배합비율 포인트는 20%이며, 반발탄성의 경우, 반발탄성이 급격하게 감소하는 배합비율 포인트는 22%이다. 따라서 두가지 요인을 감안할 때, 적정 배합비는 20~22% 사이로 판단된다. 본 연구의 결과는 조경용 탄성포장 시공 시 결합력과 탄성을 제고할 수 있는 재료배합의 지침을 제공할 수 있을 것으로 기대된다.

• 한국정밀공학회지
• /
• 제15권1호
• /
• pp.130-136
• /
• 1998

A procedure of stress and strength analysis has been proposed for the centrifuge rotor of composite materials of quasi-isotropic laminates. The goal in this study is to maximize the allowable rotating speed, that is, to minimize maximum strength ratio with the given path length by changing the geometric parameter-outer radius and ply angles in quasi-isotropic laminates. Optimum values of the geometric parameter-outer radius and ply angles are obtained by multilevel optimization. All the geometric dimensions and stresses are normalized such that the result can be extended to a general case. Two dimensional analysis at each cross section with an elliptic tube hole subjected to internal hydrostatic pressures by samples as well as the centrifugal body forces has been performed along the height to calculate the stress distribution with the plane stress assumption, and Tsai-Wu failure criterion is used to calculate the strength ratio. The maximum allowable rotating speed can be increased by changing the radii of the outer surface along the height with the maximum strength ratio under the unit value : The optimal number of ply angles maximizing the allowable rotating speed in quasi-isotropic laminates is found to be the half number of tube hole, and the optimal laminate rotation angle is the half of $[{\pi}/m]$. A $[{\pi}/3]$ laminate, for instance, is stronger than a $[{\pi}/4]$ laminate for the centrifuge rotor of 6 tube hole number even though they have the same stiffness.

• 제어로봇시스템학회논문지
• /
• 제20권1호
• /
• pp.58-69
• /
• 2014

This paper proposes a method for predicting maximum friction coefficients and optimal slip ratios as optimal control parameters for traction control or slip control of autonomous mobile robots on rough terrain. This paper focuses on strength of ground surface which indicates different characteristics depending on material types on surface. Strength of various material types can be estimated by Willoughby sinkage model and by a developed testbed which can measure forces, velocities, and displacements generated by wheel-terrain interaction. Estimated strength is collaborated on building improved Brixius model with friction-slip data from experiments with the testbed over sand and grass material. Improved Brixius model covers widespread material types in outdoor environments on predicting friction-slip characteristics depending on strength of ground surface. Thus, a prediction model for obtaining optimal control parameters is derived by partial differentiation of the improved Brixius model with respect to slip. This prediction model can be applied to autonomous mobile robots and finally gives secure maneuverability on rough terrain. Proposed method is verified by various experiments under similar conditions with the ones for real outdoor robots.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2002년도 봄 학술발표회 논문집
• /
• pp.731-738
• /
• 2002

Recently, as large constructions on the coast are performed frequently, surface layer stabilization method which Is one of the improvement methods for dredged soft clay has been applied. However, there have been few studies about the surface layer stabilization method. The purpose of this study is to clarify characteristics of ultra-soft marine clay and hardening agent. Also, optimal mixture ratio of hardening agent was verified through the laboratory tests such as statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil and standard mixing tables of hardening agent were determined according to ground conditions through statistical analysis. Also, applicability of surface layer stabilization method to field was verified by pilot tests. From the results of the tests, it was found that hardening agent materials such as cement, slag, fly-ash, inorganic salts, arwin, gypsum etc. affect on the appearing compressive strength. It was defined optimal mixture ratio which satisfies the required compressive strength from the statistical analysis. Also, It was compared the effect of ground improvement by cements and hardening agents through the pilot tests. This study will serve as data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.