• 한국터널지하공간학회 논문집
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• 제22권2호
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• pp.145-154
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• 2020

NATM 공법에 있어서 강지보재는 숏크리트가 타설되어 라이닝을 완전히 구성할 때까지 터널의 안정화를 확보하는 구조체로서, 숏크리트의 타설 전 뿐만 아니라 타설 후 숏크리트와의 일체 거동을 통해 라이닝의 강도를 더해주는 역할을 수행한다. 본 연구에서는 새로운 형식의 사변형 격자지보재를 터널의 안정해석에 적용하기 위한 방안으로 체적비 기반의 숏크리트와 강지보재 합성부재의 등가 물성치 결정법을 제시하였다. 사변형 격자지보재는 수직 및 수평 보강재의 존재로 면적비 기반으로 등가 물성치를 산정할 경우 선택한 단면에 따라 물성치가 상이 할 수 있다. 따라서 본 연구에서는 체적비 기반의 등가 물성치 결정법을 제시하였으며, 격자지보재와 숏크리트로 구성된 합성부재 요소에 대한 상세모델과 등가물성치를 사용한 등가모델의 비교를 통하여 등가탄성계수를 보정할 수 있는 방법을 제시하였다. 상세모델과 등가모델을 비교한 결과등가모델은 상세모델에 비해 평균적으로 130% 작은 휨 강도를 나타내었다. 본 연구에서는 휨강도의 오차율을 고려하여 등가탄성계수를 보정할 수 있는 방법을 제시하였고, 보정된 등가탄성계수를 적용한 등가모델의 휨강도는 상세모델과 평균오차율 1% 이내로 나타났다.

• 한국강구조학회 논문집
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• 제22권5호
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• pp.435-443
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• 2010

현행 송전강관철탑의 경우 허용응력 설계개념을 도입한 철탑설계기준을 적용하여 설계, 제작되고 있다. 이 철탑설계기준의 압축재의 설계 강도 결정은 압축재의 허용좌굴응력에 의하여 결정되고 있으나 이는 접합부의 내력을 고려치 않은 값이다. 부재가 압축좌굴내력에 도달하기 전에 접합부의 변형으로 인하여 국부변형에 의한 접합부 파괴가 발생할 수 있다. 따라서 본 연구에서는 접합부의 보강형태별로 접합부내력을 산출하고 이를 데이터베이스화한 후 지난 연구에서 도출한 등가비선형해석기법의 부재내력과의 상호 비교를 통하여 부재파괴와 접합부파괴의 선행 여부를 판별할 수 있는 실용적인 평가 및 설계 기법을 제시하였다.

• Journal of Welding and Joining
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• 제21권7호
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• pp.49-58
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• 2003

It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.

• 한국구조물진단유지관리공학회 논문집
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• 제17권5호
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• pp.49-58
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• 2013

축소모형 원형기둥 실험체 8개를 제작하여 일정한 축력 하에서 반복 횡하중을 가력하는 실험을 수행하였다. 실험체들은 형상비 4.5인 실험체로 설계되었다. 실험체의 주요변수는 횡방향철근비, 축방향철근비, 축방향철근 항복강도와 축력비이다. 기둥 실험체들의 실험결과들은 축방향철근비, 횡철근비와 축력비에 따라 등가점성비, 잔류변형, 유효강성등과 같은 내진성능이 다르게 나타났다. 낮은 항복강도의 축방향철근이 적용된 실험체는 등가점성감쇠비와 잔류변형과 같은 내진성능이 낮게 나타났다. 국내의 도로교설계기준에 휨 초과강도 규정이 2012년에 채택되었다. 실험결과들은 공칭강도, 비선형 모멘트-곡률 해석 결과, AASHTO LRFD 및 도로교설계기준 (한계상태설계법)과 같은 기준들과 비교하였다.

• 한국공간구조학회논문집
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• 제20권1호
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• pp.87-94
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• 2020

A corrugated steel plate wall (CSPW) system is advantageous to secure the strength and stiffness required for lateral force resistance because of its high out-of-plane stability. It can also stably dissipate large amounts of energy even after peak strength. In this paper, a preliminary study has been carried out to use the CSPW system in the seismic retrofit of existing reinforced concrete (RC) moment frame buildings. The seismic performance for an example building was evaluated, and then a step-by-step retrofit design procedure for the CSPW was proposed. An equivalent analytical model of the CSPW was also introduced for a practical analysis of the retrofitted building, and the strengthening effect was finally evaluated based on the results of nonlinear analysis.

• Computers and Concrete
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• 제3권5호
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• pp.357-373
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• 2006

The concepts of four parameters of nominal water-cement ratio, equivalent water-cement ratio, average paste thickness, fly ash-binder ratio were introduced. It was verified that the four parameters and the mix proportion of mortar can be transformed each other. The behaviors (strength, workability, et al.) of mortar primarily determined by the mix proportion of mortar now depend on the four parameters. The prediction models of strength and workability of mortar were built based on artificial neural networks (ANNs). The calculation models of average paste thickness and equivalent water-cement ratio of mortar can be obtained by the reversal deduction of the two prediction models, respectively. A mortar mix proportion design algorithm was proposed. The proposed mortar mix proportion design algorithm is expected to reduce the number of trial and error, save cost, laborers and time.

• 한국안전학회지
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• 제23권1호
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• pp.1-11
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• 2008

In this study, small punch test and tensile test were performed with specimens directly machined from an ASTM A53 grade B carbon steel pipe at which an explosion accident was occurred in the Heavy Oil Unit. Main damage mechanism of the pipe was known as a high temperature hydrogen attack(HTHA). Effects of HTHA on the mechanical strength change of the A53B steel were studied in detail. Small punch test results have showed that maximum reaction forces, SP energy and ductility were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Yield strength and tensile ultimate strength were calculated with the obtained small punch test curve results using different methods and compared the estimation methods. Small punch test simulation has been also performed with the finite element method and then mechanical strength, equivalent strain and fracture toughness were calculated with the obtained numerical analysis results. It was shown that the fracture toughness data calculated from small punch equivalent energy obtained by the finite element analysis for SP test was very low at the hydrogen attacked part.

• 한국안전학회지
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• 제21권5호
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• pp.17-21
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• 2006

In this study, SPCC cross-tension type specimens produced under various spot welding conditions were tensile and fatigue tested. Decrease of 2 kA in normal current condition of 10 kA caused a large amount of reduction in both static joining strength and fatigue life. And 2 kA increase resulted in increase of static joining strength and an increase in low cycle regime but a decrease in high cycle regime, revealing the fact that fatigue strength rather than static joining strength would be a major factor during design process in view of the body endurance. As a results of estimating the fatigue lifetimes of various types of spot weld specimens. equivalent stress intensity factor is the proper parameter for predicting the lifetimes of various types of specimens. which can be expressed as ${\Delta}K_{eq}(N/nm^{1.5})=11550N^{-0.36}_{f}$.

• Earthquakes and Structures
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• 제2권1호
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• pp.65-88
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• 2011

A new method for the seismic design of plane steel moment resisting frames is developed. This method determines the design base shear of a plane steel frame through modal synthesis and spectrum analysis utilizing different values of the strength reduction (behavior) factor for the modes considered instead of a single common value of that factor for all these modes as it is the case with current seismic codes. The values of these modal strength reduction factors are derived with the aid of a) design equations that provide equivalent linear modal damping ratios for steel moment resisting frames as functions of period, allowable interstorey drift and damage levels and b) the damping reduction factor that modifies elastic acceleration spectra for high levels of damping. Thus, a new performance-based design method is established. The direct dependence of the modal strength reduction factor on desired interstorey drift and damage levels permits the control of deformations without their determination and secures that deformations will not exceed these levels. By means of certain seismic design examples presented herein, it is demonstrated that the use of different values for the strength reduction factor per mode instead of a single common value for all modes, leads to more accurate results in a more rational way than the code-based ones.

• 한국건축시공학회지
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• 제8권1호
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• pp.43-48
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• 2008

Fifteen concrete specimens were mixed and tested to explore the significance and limitation of appling the polyvinyl alcohol (PVA) fiber and steel fiber with end hook to concrete. Main parameters investigated were volume fraction and length of the fibers. The measured mechanical properties of fiber reinforced concrete are analyzed according to the equivalent fiber amount index explaining the adding amount and length of fibers. Test results showed that compressive strength of fiber reinforced concrete was higher than that of concrete with no fiber by $10{\sim}20%$. The normalized splitting tensile strength and flexural strength of PVA fiber reinforced concrete were similar to those of concrete with no fiber, whereas those of steel fiber reinforced concrete increased with the increase of the equivalent fiber amount index. In particular, much higher ductile behavior was observed in steel fiber reinforced concrete than in PVA reinforced concrete, indicating that the slope of descending branch of load-displacement relationship of steel fiber reinforced concrete decreased with the increase of the volume fraction and length of the fiber.