Structural Health Monitoring (SHM) for a Cable Stayed Bridge under Typhoon

주민관,박철우,김규선 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.4

Long span bridges have usually experienced natural disaster during service age. A typhoon is very specific natural phenomenon which has a great impact on human life, including civil structures themselves. Combined with IT, operation of these monitoring systems enables reasonable, scientific, and economic maintenance based on measured data. IN particular, as climate has changed due to global warming, unexpected natural disasters have occurred more frequently. Structural Health Monitoring (SHM) for the cable supported bridges in a typhoon can reduce maintenance efforts and costs. Scientific verification for cable supported bridge structural performance is also possible using SHM data. This can ensure a more efficient maintenance strategy is developed for bridges. This study analyzed the SHM data of a cable stayed bridge during a typhoon, with the structural capacity evaluated respective to the safety ratio for Fracture Critical Member (FCM). Finally, some strategies for cable supported bridge maintenance during a typhoon were suggested and its applicability was discussed.

Predictability Evaluation of the Existing Punching Shear Formulas using Failure Test and Probability-based Approach

주민관,박철우,황의승,심종성 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.5

This study is to investigate the predictability of the existing punching shear formulas and to evaluate the best predictable punching shear formula including probabilistic evaluation method including the level of 95% probability. The considered punching shear formulas are existing 10 formulas, which are based on the standard codes and newly developed and verified by experimental data. For FRP reinforced concrete slabs, it is more important that the probable uncertainty of predicting formulas for material characteristics, structural dimension, and modeling errors should be considered. The random variables for probabilistic analysis were simulated by Monte Carlo Simulation. The best predictable punching shear formula and its components were analyzed with two analysis methods; the test-to-predicted ratio of punching shear strength and the nominal-to-95% probability ratio which is the ratio of nominal punching shear strength to that at the level of 95% probability. From the test-to-predicted ratio analysis, the important effect of modulus of elasticity of the reinforcement for predicting formulas was found. As using the resulted formula, this study provides a preliminary approach for suggesting a new punching shear formula of concrete slabs reinforced by either FRP or steel bar.

Assessment of reliability-based FRP reinforcement ratio for concrete structures with recycled coarse aggregate

주민관,박경수,이기홍,안기용,Jongsung Sim 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.4

The present study assessed the reliability-based reinforcement ratio of FRP reinforced concrete structure applying recycled coarse aggregate (RCA) concrete. The statistical characteristics of FRP bars and RCA concrete were investigated from the previous literatures and the mean value and standard deviation were employed for the reliability analysis. The statistics can be regarded as the material uncertainty for configuring the probability distribution model. The target bridge structure is the railway bridge with double T-beam section. The replacement ratios of RCA were 0%, 30%, 50%, and 100%. From the probability distribution analysis, the reliability-based reinforcement ratios of FRP bars were assessed with four cases according to the replacement ratio of RCA. The reinforcement ratio of FRP bars at RCA 100% showed about 17.3% higher than the RCA 0%, where the compressive strength at RCA 100% decreased up to 27.5% than RCA 0%. It was found that the decreased effect of the compressive strength of RCA concrete could be compensated with increase of the reinforcement ratio of FRP bars. This relationship obtained by the reliability analysis can be utilized as a useful information in structural design for FRP bar reinforced concrete structures applying RCA concrete.

Flexural behavior and a modified prediction of deflection of concrete beam reinforced with a ribbed GFRP bars

주민관,박철우,김용재 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.6

This study experimentally investigated the flexural capacity of a concrete beam reinforced with a newly developed GFRP bar that overcomes the lower modulus of elasticity and bond strength compared to a steel bar. The GFRP bar was fabricated by thermosetting a braided pultrusion process to form the outer fiber ribs. The mechanical properties of the modulus of elasticity and bond strength were enhanced compared with those of commercial GFRP bars. In the four-point bending test results, all specimens failed according to the intended failure mode due to flexural design in compliance with ACI 440.1R-15. The effects of the reinforcement ratio and concrete compressive strength were investigated. Equations from the code were used to predict the deflection, and they overestimated the deflection compared with the experimental results. A modified model using two coefficients was developed to provide much better predictive ability, even when the effective moment of inertia was less than the theoretical Icr. The deformability of the test beams satisfied the specified value of 4.0 in compliance with CSA S6-10. A modified effective moment of inertia with two correction factors was proposed and it could provide much better predictability in prediction even at the effective moment of inertia less than that of theoretical cracked moment of inertia.

Indirect Fatigue Evaluation of CFRP-reinforced Bridge Deck Slabs under Variable Amplitude Cyclic Loading

주민관,오홍섭,심종성 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Currently, bridge deck slabs reinforced with Fiber Reinforced Polymer (FRP) bars have been widely studied and applied to the bridge deck slabs in North America. However, there is still a lack of knowledge on the structural performance of the concrete bridge slabs reinforced using FRP bars, especially Carbon Fiber Reinforced Polymer (CFRP) bars. This aim of this study was to investigate the fatigue performance of bridge deck slabs reinforced with CFRP bars. The fatigue capacity was investigated using indirect fatigue evaluation when the number of cycles to failure was unknown, by using the equivalent number of cycles. The variable amplitude cyclic loadings effectively contribute to damage acceleration even at fatigue cycles of 1,000,000. The evaluation of fatigue capacity with respect to serviceability showed that deflection and crack width under variable amplitude loading were evaluated over a reasonable range to ensure that serviceable capacity is satisfied for CFRP bar reinforced bridge slabs. For fatigue design, S-N curves were analyzed using the different fatigue life models proposed by previous studies. It was found that the fatigue limit under variable amplitude loading should be analyzed by using the fatigue life model based on the variable amplitude loading cases.

On strain measurement of smart GFRP bars with built-in fiber Bragg grating sensor

주민관,박경수,문도영,박철우,심종성 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.2

A smart glass fiber reinforced polymer (SMFRP) reinforcing bar with a fiber Bragg grating (FBG) sensor was fabricated using a pultrusion technique, while ribs were formed to improve bonding between concrete and SMFRP. Then, strain of SMFRP bars were measured for a uniaxial tension test of an SMFRP bar, and a four-point bending test of concrete beams reinforced with SMFRP bars. The results of a uniaxial tension test illustrate that the strain obtained from an FBG sensor agrees well with that obtained from electrical resistance strain gauge (ERSG). Additionally, concrete beams reinforced with SMFRP bars were fabricated, and actual flexural test were performed while the strain of with an FBG sensor was compared with that of ERSG. The experimental results demonstrate that SMFRP bars can be used as reinforcement of concrete member while providing deformation information. Furthermore, SMFRP bars may provide stronger durability and smart monitoring to reinforced concrete members under corrosive environments during a service life.

FRP 복합재료 최신 연구동향 (FRPRCS - 12)

주민관,박철우 한국콘크리트학회 2016 한국콘크리트학회 학술대회 논문집 Vol.2016 No.5

FRP 보강근 콘크리트 설계기준(안)

주민관,박철우 한국콘크리트학회 2015 한국콘크리트학회 학술대회 논문집 Vol.2015 No.5

화재 실험에 따른 철근 콘크리트 보의 재료특성 연구

주민관,박철우,오지현,서상길,심재원 한국구조물진단유지관리공학회 2016 한국구조물진단유지관리공학회 논문집 Vol.20 No.3

콘크리트는 내화재료로서 우수한 성능을 발휘하지만 화재가 지속됨에 따른 재료특성 변화 또는 성능저하의 위험을 갖는다. 이 연구는 실물모형 철근 콘크리트 (RC) 보를 활용하여 비재하 화재 실험을 수행하여 화재노출 전후의 콘크리트 및 보강철근의 재료특성을 실험적으로 분석한 연구이다. 화재실험에 사용된 보는 길이 4 m의 RC 보로서 KS F 2257 화재실험 규격에 따라 시험 체를 제작 및 화재실험을 수행하였다. 화원의 가력은 ISO 834의 표준화재 곡선을 사용하였으며 보 가열부에서의 온도를 계측하고자 하면 및 측면에 열전대를 설치하였다. 실험결과, 화재에 노출된 화재 코어 공시체의 경우 약 11 MPa로 약 66%의 강도저하가 발생하였다. 화재에 직접 노출된 철근의 경우 노출되지 않은 철근에 비해 약 17%에 해당하는 75 MPa의 항복강도 저하를 나타낸 것으로 분석되었다. 철근의 경우 콘크리트라는 내화피복에 의하여 보호되어 약 4시간의 화재 실험에서도 온도는 한계온도의 최댓값인 649°C를 크게 상회하지 않는 것으로 나타났다. Concrete is inherently a good fire-resistance material among all other constrcution materials and protects the reinforcing steel inside. This study investigates the material characteristics of concrete and steel bar inside the full scale reinforced concrete(RC) beam exposed to fire test. The fire test specimen was 4 m long and the test was conducted under no loading condition following KS F 2257. Fire source is simulated by ISO 834 and number of thermocouples were installed to measure temperature variation of surfaces and inside of the beam. The measured compressive strength of cored specimen, which was exposed to fire test, was 11 MPa, about 66% lower than the strength before exposure. The yielding strength of steel bar also decreased about 75 MPa, about 17% lower. The measured temperature of protected steel bar was around 649°C, the critical limit, after 4 hour exposure.

확률·불확실성 특성을 고려한 FRP bar로 보강된 콘크리트 슬래브의 펀칭전단강도 모델

주민관(Minkwan Ju),심종성(Jongsung Sim) 한국콘크리트학회 2017 한국콘크리트학회 학술대회 논문집 Vol.29 No.1