A Numerical Study on the Thermo-mechanical Response of a Composite Beam Exposed to Fire

박홍락,강문수,강준원,기성훈,최병정 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.4

This study presents an analytical framework for estimating the thermo-mechanical behavior of a composite beam exposed to fi re. The framework involves: a fi re simulation from which the evolution of temperature on the structure surface is obtained; data transfer by an interface model, whereby the surface temperature is assigned to the fi nite element model of the structure for thermo-mechanical analysis; and nonlinear thermo-mechanical analysis for predicting the structural response under high temperatures. We use a plastic-damage model for calculating the response of concrete slabs, and propose a method to determine the stiff ness degradation parameter of the plastic-damage model by a nonlinear regression of concrete cylinder test data. To validate simulation results, structural fi re experiments have been performed on a real-scale steel–concrete composite beam using the fi re load prescribed by ASTM E119 standard fi re curve. The calculated evolution of defl ection at the center of the beam shows good agreement with experimental results. The local test results as well as the eff ective plastic strain distribution and section rotation of the composite beam at elevated temperatures are also investigated.

화재 열 유동을 고려한 구조물의 열응력해석

박홍락,강준원,이진우 한국전산구조공학회 2016 한국전산구조공학회논문집 Vol.29 No.4

이 연구는 화재에 노출된 구조물의 역학적 거동을 평가하기 위한 기반연구로서 화재 유동해석과 열응력해석의 통합 프레 임워크를 확립하고 이를 강재와 콘크리트로 이루어진 대표체적에 적용한 결과를 제시하였다. 먼저 Fire Dynamics Simulator(FDS)를 이용해 임의의 화재곡선으로 모델링되는 화원으로부터 구조물 표면까지 유동해석을 실시하였다. 이를 통 해 구조물 표면에서 시간에 따른 온도 분포를 계산하였고, 이 결과를 비선형 열응력해석에 경계조건으로 적용하였다. 이후의 과정은 화재의 성장 또는 감소에 따라 구조물 표면온도의 변화를 반영하는 열전달해석과 구조해석으로 이루어진다. 제시한 통합 프레임워크에 의해 화재 구조해석을 수행한 결과, 강재와 콘크리트의 대표체적 모두 동일한 하중이 작용할 때 상온 조 건에서는 탄성 거동을 보였지만 화재로 인한 온도 조건을 고려할 경우 소성 거동을 보였다. 이는 구조물이 화재에 노출되는 경우 설계하중보다 작은 하중에서도 한계상태에 이를 수 있다는 것을 의미하며, 따라서 원전구조물이나 교량과 같은 중요 사회기반구조물의 설계 시 구조물의 화재거동 평가가 고려되어야 한다고 할 수 있다. In this study, a numerical analysis framework for investigating the nonlinear behavior of structures under fire conditions is presented. In particular, analysis procedure combining fire-driven flow simulation and thermo-mechanical analysis is discussed to investigate the mechanical behavior of fire-exposed representative volume structures made of steel and concrete, respectively. First of all, fire-driven flow analysis is conducted using Fire Dynamics Simulator(FDS) in a rectangular parallelepiped domain containing the structure. The FDS simulation yields the time history of temperature on the surface of the structure under fire conditions. Second, mechanical responses of the fire-exposed structure with respect to prescribed uniformly distributed loads are calculated by a coupled thermo-mechanical analysis using the time-varying surface temperature as boundary conditions. Material nonlinearities of steel and concrete have been considered in the thermo-mechanical analysis. A series of numerical results are presented to demonstrate the feasibility of the multiphysics structural fire analysis for investigating the structural behavior under fire conditions.

Fibronectin처리 탈회상아질편 이식이 골결손부 치유에 미치는 영향

박홍락,김진수 慶北大學校 齒科大學 1990 慶北齒大論文集 Vol.8 No.1

The purpose of this investigation was histologic evaluation of the fibronectin treated-decalcified dentin for the repair of bony defects. Thirty holes, 10㎜ in diameter and 5㎜ in depth were made in the mandibles of 8 adult dogs weighing about 15㎏. The decalcified dentin were prepared as descrebed by Inoue. Ten empty holes without any implant were served as control 1 group. The dentin cubes treated without fibronectin were implanted into the 10 holes, that was classified as control 2 group, and the remaining 10 holes prepared with fibronectin-treated decalcified dentin were served as experimental group. The animals were sacrificed serially at the interval of 1,2,3,5, and 8 weeks. Serial sections of all specimens were prepared and examined by routine histologic methods. The results were as follows: 1. During early experimental periods, there was a little evidence of specific inflammatory and rejective reponses caused by fibronectin-treated decalicified dentin allografts. 2. The bony repair of fibronectin treated, decalcified dentin allografts implanted wounds was more favorable than fibronectin nontreated, decalcified dentin allografts implanted wounds; by early replacement of fibrin mesh, increased connective cell proliferation, and reduction of the inflammatory response. 3. Fibronectin treated, decalcified dentin allografts revealed good osteoinductive potential. From 3 weeks after implantation, direct osteogenesis around the dentin allografts was remarkable, and with time the dentin allografts were gradually replaced by mature bone. 4. The above findings confirm the value of fibronectin treated, decalcified dentin allograts in promoting regeneration of bone and support their clinical use in treatment of bony defects. J. Kyungpook Nat. Univ. Sch. Dent. Vol.8, No.1, 75∼89, 1991.

녹차의 추출액이 조골세포와 파골세포의 성장과 활성에 미치는 영향

박홍락,고선일,김세원 대한안면통증∙구강내과학회 2003 Journal of Oral Medicine and Pain Vol.28 No.4

LS-SVM for large data sets

박홍락,황형태,김병주 한국데이터정보과학회 2016 한국데이터정보과학회지 Vol.27 No.2

In this paper we propose multiclassication method for large data sets by ensembling least squares support vector machines (LS-SVM) with principal components instead of raw input vector. We use the revised one-vs-all method for multiclassification, which is one of voting scheme based on combining several binary classifications. The revised one-vs-all method is performed by using the hat matrix of LS-SVM ensemble, which is obtained by ensembling LS-SVMs trained using each random sample from the whole large training data. The leave-one-out cross validation (CV) function is used for the optimal values of hyper-parameters which affect the performance of multiclass LS-SVM ensemble. We present the generalized cross validation function to reduce computational burden of leave-one-out CV functions. Experimental results from real data sets are then obtained to illustrate the performance of the proposed multiclass LS-SVM ensemble.

화재에 노출된 철근콘크리트보의 비선형 열응력해석

박홍락(Pak, Hong Rak),강준원(Kang, Jun Won) 대한토목학회 2016 대한토목학회 학술대회 Vol.2016 No.10

Cement/Slag Composite 수화반응의 물리/화학적 특성분석

박홍락(Pak, Hong Rak),고명희(Ko, Myeong-Hee),배승묵(Bae, Seung-Muk),황진하(Hwang, Jin-Ha),강준원(Kang, Jun Won) 대한토목학회 2016 대한토목학회 학술대회 Vol.2016 No.10

PECVD에 의한 Sirich 산화막의 특성

강선화,이상규,박홍락,고철기,최수한,Gang, Seon-Hwa,Lee, Sang-Gyu,Park, Hong-Rak,Go, Cheol-Gi,Choe, Su-Han 한국재료학회 1993 한국재료학회지 Vol.3 No.5

SOG박막 밑에 층간 절연박으로 사용하는 PECVD산화막을 Si rich산화막으로 만들어 줌으로써 실리콘 dangling bond가 수소원자나 수분과 결합하여 SOG박막으로 부터 침투되는 수소원자나 수분의 확산을 억제하므로서 소작 열화되는 것을 방지한다. 이러한 Si rich산화막의 기본 특성을 알아보기 위하여 LF/HF power비와 $SiH_4/N_2O$ gas유량비를 변화시켜서 박막 특성을 조사하였다. 저주파 power만 변화시킨 경우, 증착속도가 감소하고 굴절율과 압축응력에 증가하며 FTIR에서 3300$\textrm{cm}^{-1}$~3800$\textrm{cm}^{-1}$영역의 수분에 의한 peak이 감소하는 것으로 보아 박막이 치밀해짐을 알 수 있고, $SiH_{4}$기체유량을 증가시킨 경우엔 증착속도, 굴절율, 식각속도는 증가하나 압축응력은 감소한다. FTIR에서 Si-O-Si peak의 세기가 감소하고 낮은 파수영역으로 이동하며, AES분석 결과에서 일반적인 oxide(Si:0=1:1.98)에서 보다 Si:O비가 1:1.23으로 낮아 PECVD산화 막내의 Si danling bond가 증가했음을 알 수 있었다. By making the inter-metal PECVD $SiO_2$ as a Si rich oxide under the SOG, the hydrogen and water related diffusants could be captured a t SI dangling bonds. This gettering process was known to prevent the device characteristics degradations related to the H, $H_20$. The basic characteristics of Si rich oxide have been studied according to changing high/low frequency power and $SiH_4/N_2O$ gas flow ratio in PECVD. As increase in low frequency power, deposition rate decreased but K.I. and compressive stress increased. Decrease of the water peaks of FTIR spectra at the wave number range of 3300~3800$\textrm{cm}^{-1}$' also indicated that intensty the films were densified. As increase in SiH, gas flow rate, deposition rate, R.I. and etch rate increased while compressive stress decreased. F'TIK spectra showed that peak intensity corresponding to Si-0-Si stretching vibration decreased and shifted to the lower wave numbers. But AES showed that Si dangl~ng bonds were increased as a result of lower Si:O(l: 1.23) ratlo inthe Si rich oxide as compared to Si : O(1 : 1.98) ratio of usual oxide.

내화피복을 적용한 강합성보의 화재구조해석

강문수(Kang, Moon Soo),박홍락(Pak, Hongrak),강준원(Kang, Jun Won) 대한토목학회 2018 대한토목학회 학술대회 Vol.2018 No.10

내화피복을 고려한 강합성보의 화재 구조거동 평가

강문수(Kang, Moon Soo),박홍락(Pak, Hongrak),강준원(Kang, Jun Won),최병정(Choi, Byung-Jeong),기성훈(Kee, Sung-Hoon) 한국강구조학회 2018 한국강구조학회 학술대회 발표집 Vol.29 No.1