Evaluation of Reliability for the Tensile Strength of the Flexible Pavement System

이봉학,김광우,윤경구,Lee, Bong Hak,Kim, Kwang Woo,Yun, Kyeong Gu Korean Society of Civil Engeneers 1988 대한토목학회논문집 Vol.8 No.2

층상구조(層狀構造)로 이루어진 아스팔트 포장도로(鋪裝道路)의 안전성(安全性)은 교통하중(交通荷重)과 아스팔트 콘크리트의 층별강도(層別觸强度)와의 함수관계(函數關係)에 의하여 평가된다. 본(本) 논문(論文)은 아스팔트 포장도로(鋪裝道路)의 신뢰도(信賴度)를 고찰(考察)하기 위하여 확률론적(確率論的) 방법(方法)을 적용시켰는데 이에 사용(使用)된 자료(資料)들은 현장(現場) 또는 문헌(文獻)으로부터 수집하였다. 각층(各層)의 임계인장강도(臨界引張强度)를 목표신뢰도(目標信賴度)에 근거(根據)하여 시뮬레이션 방법(方法)으로 산정(算定)하였는데 이 값을 실제로 표면(表面)에 손상(損傷)이 일어난 시료강도(試料强度)와 비교(比較), 고찰(考察)하였다. 확률론적방법(確率論的方法)으로 산정(算定)한 임계강도(臨界强度)는 현행(現行)의 도로조건(道路條件)에 적합(適合)한 값임을 알 수 있었다. The flexible highway pavement is a layered structure. The safety of the pavement is a function of the load induced by traffic and the layer strength of asphaltic concrete mixture. Therefore, the probabilistic approach was applied to the pavement system to evaluate the reliability. Monte Carlo simulation technique was used for the reliability study. Data used were colleted from the field or literature. A critical tensile strength for each layer was estimated based on a target reliability from the simulation. The critical strength was evaluated by comparing the strengths with the actual surface distress. The result shows that the critical strength estimated in the probabilistic approach is valid for the current highway condition.

불확실성(不確實性) 요인(要因)들이 포장공사(鋪裝工事) 지급액(支給額) 결정(決定)에 미치는 영향(影響)

이봉학,김광우,Lee, Bong Hak,Kim, Kwang Woo 대한토목학회 1992 대한토목학회논문집 Vol.12 No.4

아스팔트 포장공사의 판정에 있어 품목집단 특성치의 측정시 공정평균(工程平均)이 규정에 합당해도 표본(標本) 선정이나 측정상의 고유분산치(固有分散値)가 규정한계를 벗어나기도 한다. 그러나 많은 규정들이 이러한 점을 간과(看過)하고 있어 충실한 시공자라도 고유의 불확실성(不確實性)때문에 불이익을 당한다. 따라서 본 연구는 이러한 점에 착안하여 선정된 판정기준에 의하여 시뮬레이션으로 얻은 품목집단의 특성치를 검정하고 이때 재료와 측정상의 불확실성(不確實性)이 지급비율 결정에 미치는 영향을 분석하였다. 각 추정치를 검사특성곡선(檢査特性曲線)으로 도시한 결과 재료 및 측정이 지급비에 영향을 주며 특히 고유측정오차가 그 영향이 가장 큰 것으로 나타났다. 따라서 각 기관의 지급 규정은 측정시 불확실성의 고유치로 인한 시공자의 불이익을 고려하여 제정 및 정비되어야 할 것으로 사료된다. The objective of the study is to evaluate the effect of variabilities (uncertainties) in materials and testing on contractor payment and to suggest a base for adjusting the unsuitable specification. Most commonly used acceptance plans were used to estimate payment using simulation. Simulation results that were graphically illustrated by means of operating characteristics (OC) curves in terms of expected payment showed that contractor received a reduced payment due to intrinsic sampling and test variabilies. The most significant reduction was caused due to relatively large magnitude of the testing variability. Therefore, the tolerance range in acceptance plan should be revised as compared with typical testing variability.

강섬유보강 초속경시멘트 콘크리트의 휨인성 및 피로거동

이봉학,홍창우,김동호,Lee, Bong-Hak,Hong, Chang-Woo,Kim, Dong-Ho 강원대학교 산업기술연구소 1999 産業技術硏究 Vol.19 No.-

This study is conducted on the flexural toughness and flexural fatigue test to fine the mechanical properties of steel fiber reinforced rapid-set cement concrete. Experimental investigation is examined according to fiber contents(0, 0.4, 0.7, 1.0, 1.5%), fiber aspect ratio(58, 60, 83), fiber type (hooked, crimped fiber), and cement type (normal portland & rapid-set cement). The principal results obtained through this study are as follows; toughness and fatigue resistance tend to considerably increase with fiber contents, fiber aspect ration. And hooked fiber is improved better than crimped fiber. Concrete using rapid set cement is increased strength properties compared with concrete using normal portland cement, but relative strength properties behavior and fatigue resistance show a tendency to decrease a little.

손상지수법을 이용한 트러스 교량의 손상추정

이봉학,김정태,장동일,Lee, Bong Hak,Kim, Jeong Tae,Chang, Dong Il 한국강구조학회 1998 韓國鋼構造學會 論文集 Vol.10 No.2

An existing Damage Index Method is verified to demonstrate its feasibility for detecting structural damage in truss bridges (1) for which modal parameters are available for a few modes of vibration and (2) for which baseline modal information is not available from its as-built state. The theory of approach to detect locations of damage and to identify baseline modal model is summarized on the basis of system identification theory and modal sensitivity theory. The feasibility of the Damage Index Method is demonstrated using a numerical example of a truss bridge with 11 subsystems of 211 members and for which only two modes of vibration were recorded for post-damaged state. 소수의 진동특성치가 실측된 삼차원 트러스 교량을 대상으로 기존의 손상추정법이 실험되었다. 첫 번째 단계로 진동모드 민감도 해석과 패턴인식기법을 사용하여 초기구조모델(baseline model)이 구성되었고, 다음 단계로 수개의 손상시나리오 수치 예를 초기구조물에 시뮬레이션하고 이를 손상지수와 패턴인식기법을 이용하여 손상위치를 예측하였다. 총 211개 요소에 11개의 부 구조계를 갖는 트러스 구조에 대하여 진동모드가 2개인 경우에 한하여 분석 검토한 결과 손상발견 알고리즘의 적합성이 입증되었다.

유한요소해석을 이용한 현장 덧씌우기 콘크리트의 부착강도 평가 방법 제안

이봉학(Lee Bong Hak),홍창우(Hong chang Woo),이주형(Lee Joo Hyung),김성환(Kim Seong Hwan) 강원대학교 산업기술연구소 2001 産業技術硏究 Vol.21 No.1

Significant improvements in bond strength between new and existing concrete can be achieved through the modification of the new concrete by latex modification. But, no test method has been adopted as a standard to measure the bond strength between the concrete used to repair and the substrate being repaired. The performance of old and the new concrete construction defends upon band strength between old and the new concrete. Current adhesion strength measurement method is inaccurate method that ignore effect of stress concentration by shape of specimens. Therefore, this research calculates stress concentration coefficient using finite element analysis and direction tensile strength test (pull-off test). The result shows that the required core depth is 2.5cm. Elastic modulus and overlay thickness do not influence in stress concentration.

철근 콘크리트 부재의 인장강성 효과에 관한 연구

이봉학(Lee. Bong-Hak),윤경구(Yun. Kyong-Ku),홍창우(Hong. Chang-Woo) 한국콘크리트학회 1999 콘크리트학회논문집 Vol.11 No.4

철근콘크리트 인장부재의 인장강성에 관한 실험적 연구

이봉학 ( Lee Bong Hak ),윤경구 ( Yun Kyong Ku ),장동일 ( Chang Dong Il ) 한국농공학회 1998 韓國農工學會誌 : 전원과 자원 Vol.40 No.4

The tension stiffening in reinforced concrete member means increase of stiffness caused by the effective tensile stress between cracks and the tension softening behavior of concrete. This paper presents on the tensile behavior and tension stiffening of RC tension members. Direct tension tests were performed with a main experimental variables such as concrete strength, rebar diameter and strength. The tension stiffening was analyzed from the load-displacement relationship and was compared with ACI code, CEB model and the proposed by Collins & Mitchell. The results are as follows ; The tension behaviors of RC members were quite different from those of bare bar and were characterized by loading and concrete cracking steps. The effect of tension stiffening decreased rapidly as the rebar diameter and strength increased, and the concrete strength increased. The proposed by Collins & Mitchell described well the experimental results, regardless of rebar types and concrete. But, ACI code and CEB model described a little differently, depending on the types. The effect of tension stiffening in RC member was the biggest near at concrete cracking step and decreased gradually to the bare bar's behavior as loading closed to the breaking point. Thus, tension stiffening in RC members should be taken into account when the load-deflection characteristics of a member are required or a precise analysis near the load of concrete clacking is needed.

부순모래를 사용한 고강도 콘크리트의 배합설계에 관한 연구

이봉학(Lee Bong Hak),김동호(Kim Dong Ho),홍창우(Hong Chang Woo),이주형(Lee Joo Hyung) 강원대학교 산업기술연구소 2001 産業技術硏究 Vol.21 No.1

The amount used of aggregates for concrete is increasing rapidly since the mid-1980s in Korea. The natural gravels from river are already displaced with crushed stone, and use of crushed sand as a substitute of natural river sands, also, is getting increased day by day. This paper is presented for mixture of high strength concrete using crushed sands. Mixing design of concretes are various water-cement ratios(w/c) such as 25%, 40%, 55% and different replacement ratio of crushed sands to natural sands such as 0%, 20%, 40%, 60%. As a results, it has been shown that compressive strength of concretes with w/c lower than 40% and 25% is higher than 400 kgf/㎠ and 600 kgf/㎠ respectively.

재생 폐콘크리트의 성능향상에 관한 연구

이봉학(Lee, Bong-Hak),김광우(Kim, Kwnag-Woo),박제선(Park, Je-Seon),김진영(Kim, Jin-Young) 한국콘크리트학회 1995 콘크리트학회논문집 Vol.7 No.2

소포제 종류 및 혼입률에 따른 초속경 라텍스개질 모르타르의 역학적 특성

이봉학(Lee Bong Hak),홍창우(Hong Chang Woo),이주형(Lee Joo Hyung),김동호(Kim Dong Ho) 강원대학교 산업기술연구소 2001 産業技術硏究 Vol.21 No.1

The purpose of this study was to remove the excessive air foaming which was produced in mixing the RSLMC(latex-modified concrete with rapid-setting cement) by choosing the best antifoam agent type. A series of RSLMM(latex-modified mortar with rapid-setting cement) experiments were carried out as a basic experiments for RSLMC with the main experimental variables such as antifiamer types (A, B, C, D), antifoamer contents(0, 1, 2, 3%), and latex contents(10, 15%). Air content test and compressive strength tests were carried out to measure the improved properties of RSLMM. SEM analysis, also, was carried to observe the formation of latex film. The results of RSLMM showed that the decrease of 50% air content was obtained by admixturing an antifoam agent by 1%. This made the strength enhanced and the workability be within the purposed. The best properties of compressive strengths was obtained at latex content of 15% and D antifoam agent of 1%. compressive strength increased about 32.6%. The analysis of SEM results no difference in a formation of later film.