Post-fire Repair of Concrete Structural Members: A Review on Fire Conditions and Recovered Performance

Qiu, Jin,Jiang, Liming,Usmani, Asif Council on Tall Building and Urban Habitat Korea 2021 International journal of high-rise buildings Vol.10 No.4

Concrete structures may rarely collapse in fire incidents but fire induced damage to structural members is inevitable as a result of material degradation and thermal expansion. This requires certain repairing measures to be applied to restore the performance of post-fire members. A brief review on investigation of post-fire damage of concrete material and concrete structural members is presented in this paper, followed by a review of post-fire repair research regarding various types of repairing techniques (FRP, steel plate, and concrete section enlargement) and different type of structural members including columns, beams, and slabs. Particularly, the fire scenarios adopted in these studies leading to damage are categorized as three levels according to the duration of gas-phase temperature above 600℃ (t₆₀₀). The repair effectiveness in terms of recovered performance of concrete structural members compared to the initial undamaged performance has been summarized and compared regarding the repairing techniques and fire intensity levels. The complied results have shown that recovering the ultimate strength is achievable but the stiffness recovery is difficult. Moreover, the current fire loading scenarios adopted in the post-fire repair research are mostly idealized as constant heating rates or standard fire curves, which may have produced unrealistic fire damage patterns and the associated repairing techniques may be not practical. For future studies, the realistic fire impact and the system-level structural damage investigation are necessary.

금속-세라믹용 Pd-Cu-Ga-Zn계 합금의 산화처리 시 냉각 속도가 모의 소성 후 후열처리에 따른 경도 변화에 미치는 영향

김민정(Min-Jung Kim),신혜정(Hye-Jeong Shin),권용훈(Yong-Hoon Kwon),김형일(Hyung-Il Kim),설효정(Hyo-Joung Seol) 대한치과재료학회 2018 대한치과재료학회지 Vol.45 No.1

Effect of cooling rate during oxidation treatment on the hardness change by post firing heat treatment of a Pd-Cu-Ga-Zn alloy after simulated porcelain firing was investigated and the following results were obtained. In the firing simulated specimens after quenching during the oxidation treatment, the hardness did not increase by post-firing heat treatment. However, in the firing simulated specimens after slow cooling during the oxidation treatment, post-firing heat treatment for 25 minutes was effective in increasing the hardness (p<0.05). In the firing simulated specimens after quenching during the oxidation treatment, the significant decrease in hardness during the post-firing heat treatment was attributed to the coarsening of fine precipitates formed in the matrix and plate-like precipitates. In the firing simulated specimens after slow cooling during the oxidation treatment, the increase in hardness during the post-firing heat treatment for 25 minutes was due to precipitation hardening. From these results, it was found that the cooling rate during the oxidation treatment affected the change of hardness by the post-firing heat treatment after the simulated firing. From these results, post-firing heat treatment increased the hardness of the Pd-Cu-Ga-Zn alloy only when the cooling rate during the oxidation treatment was slow.

도재 모의소성시 냉각 속도와 후열처리가 Pd-Ag-In-Sn 금속-세라믹용 합금의 경도에 미치는 영향

김민정,신혜정,정지인,설효정 대한치과재료학회 2023 대한치과재료학회지 Vol.50 No.3

본연구의 목표는 냉각 속도의 차이가 소성 후 금속-세라믹용 합금의 최종 경도에 미치는 영향과, 소성을 시행한뒤 추가적인 후열처리가 합금의 최종경도에 미치는 영향을 알아보는 것이다. 이를 위해 Pd–Ag–In-Sn 합금을 사용하여도재 상부 구조 없이 두 가지 다른 냉각 속도로 모의 소성을 시행한 후 후열처리 하였다. 모의소성 및 후열처리된시편은 경도측정, 미세구조 관찰 및 결정구조 분석을 시행하여 경도변화와 관련된 원인을 분석하였다. 실험결과 모의소성시냉각 속도의 차이는 합금의 최종 경도에 영향을 미쳤으며, 가장 낮은 냉각속도(Stage 3)에서 냉각된 시편은 가장 높은냉각속도(Stage 0)에서 냉각된 시편에 비해 모든 소성단계에서 더 높은 경도를 나타냈다. 소성 공정 중 냉각 속도의차이에 관계없이 합금의 경도는 소성 후 시행된 후열처리에 의해 유의하게 증가하였다. 후열처리에 의한 경도상승은기지에 생성된 미세한 석출상에 기인하였으며, 석출 반응은 Pd–Ag-rich 기지의 (Pd, Ag, Au)3(In, Sn, Zn) 상에 대한용해한도 감소에 의해 일어났다. 본 연구의 임상적 의의는 금속-세라믹용 합금의 소성후 낮아진 경도를 높이기 위해낮은 온도에서 후열처리를 시행하는 것이 효과적임을 밝힌 것이다. The objective of this study was to investigate the effect of different cooling rates and subsequent post-firing heat treatment on the final hardness of a metal-ceramic alloy. For this, Specimens of Pd-Ag-In-Sn alloy underwent simulated firing at two different cooling rates, followed by post-firing heat treatment. Hardness measurement, microstructure observation, and crystal structure analysis were conducted on the firing simulated and post-firing heat-treated specimens to analyze the causes of hardness variations. The experimental results showed that the difference in cooling rates during simulated firing had an impact on the final hardness of the alloy, and the specimens cooled at the slowest rate (Stage 3) exhibited higher hardness at all firing Stages compared to the specimens cooled at the highest rate (Stage 0). Regardless of the difference in cooling rates during the firing process, the hardness of the alloy significantly increased by the post-firing heat treatment. The increase in hardness by the post-firing heat treatment was attributed to the formation of fine precipitates in the matrix, and the precipitation reaction occurred as a result of the decrease in solubility of (Pd, Ag, Au)3(In, Sn, Zn) phase in the Pd-Ag-rich matrix. The clinical significance of this study is that performing the post-firing heat treatment demonstrates effectiveness in increasing the reduced hardness after porcelain firing in metal-ceramic alloys.

다목적용 Ag-Pd-Zn-In-Sn계 합금의 모의소성 시 냉각속도의 조절이 소성 및 후열처리에 따른 경도변화에 미치는 영향

신혜정,김민정,권용훈,김형일,설효정 대한치과재료학회 2017 대한치과재료학회지 Vol.44 No.4

In this study, the effect of cooling rate control on the change in hardness of the multi-purpose Ag-Pd-Zn-In-Sn alloy during porcelain firing simulation and post-firing heat treatment was investigated, and the following results were obtained. Softening of the multi-purpose Ag-Pd-Zn-In-Sn alloy during porcelain firing simulation was suppressed by controlling the cooling rate. When the cooling rate was adjusted to stage 0(firing chamber moves immediately to upper end position), the alloy was softened during porcelain firing simulation, and the hardness was greatly increased by the additional post-firing heat treatment. When the cooling rate was adjusted to stage 3(firing chamber remains closed), the alloy was not softened even after porcelain firing simulation, and the hardness was apparently lowered by the additional post-firing heat treatment. The apparent increase in hardness in the post-firing heat treated alloy after porcelain firing simulation at cooling rate of stage 0 attributed to the active precipitation. The apparent decrease in hardness in the post-firing heat treated alloy after porcelain firing simulation at cooling rate of stage 3 attributed to the fact that the precipitates were solutionized into the matrix by the post-firing heat treatment. 본 연구에서는 소성 시 냉각속도를 조절하는 것과 동시에 소성 후 추가적인 후열처리를 시행하는 것이 후열처리를 시행하지 않는 것보다 합금의 경도 상승에 더욱 효과적인지 알아보고자, 다목적용 Ag-Pd-Zn-In-Sn계 합금을 이용하여 모의소성 시 냉각속도의 조절이 소성 및 후열처리에 따른 합금의 경도변화에 미치는 영향을 조사하여 다음과 같은 결과를 얻었다. 다목적 용 Ag-Pd-Zn-In-Sn계 합금의 모의소성 시 냉각속도를 조절함에 따라 합금의 연화가 억제되었다. Stage 0(4단계의 냉각속도 중 가장 빠른 속도; 소성로 챔버가 소성 종료 즉시 전체가 열린 상태로 냉각되는 단계)으로 냉각속도를 조절하여 합금을 소성한 경우, 모의소성 과정에서 합금이 연화되었으며, 적절한 시간동안의 후열처리가 경도상승에 효과적이었다. Stage 3(4단계의 냉각속도 중 가장 느린 속도; 소성로 챔버가 소성완료 후 닫혀진 상태로 냉각되는 상태)으로 냉각속도를 조절하여 합금을 소성한 경우, 모의소성 과정에서 합금이 연화되지 않았으며, 추가적인 후열처리는 합금의 경도를 하강시켰다. Stage 0으로 모의소성 된 합금에서 30분간의 후열처리에 의해 경도가 크게 상승한 원인은 소성에 의해 기지 내로 고용되었던 석출물이 다시 기지 밖으로 활발하게 석출된 것에 기인하였다. Stage 3으로 모의소성 된 합금에서는 후열처리에 의해 석출물이 기지 내로 다시 고용되었고, 새로운 석출상의 생성이 미미하여 후열처리가 경도 상승에 기여하지 못하였다

Recovery of mortar-aggregate interface of fire-damaged concrete after post-fire curing

Lang Li,Hong Zhang,Jiangfeng Dong,Hongen Zhang,Pu Jia,Qingyuan Wang,Yongjie Liu 사단법인 한국계산역학회 2019 Computers and Concrete, An International Journal Vol.24 No.3

In order to investigate the strength recovery of fire-damaged concrete after post-fire curing, concrete specimens were heating at 2°C/min or 5°C/min to 400, 600 and 800°C, and these exposed specimens were soaked in the water for 24 hours and following by 29-day post-fire curing. The compressive strength and split tensile strength of the high-temperature-exposed specimens before and after post-fire curing were tested. The proportion of split aggregate in the split surfaces was analyzed to evaluate the mortar-aggregate interfacial strength. After the post-fire curing process, the split tensile strength of specimens exposed to all temperatures was recovered significantly, while the recovery of compressive strength was only obvious within the specimens exposed to 600°C. The tensile strength is more sensitive to the mortar-aggregate interfacial cracks, which caused that the split tensile strength decreased more after high-temperature exposure and recovery more after post-fire curing than the compressive strength. The mortar-aggregate interfacial strength also showed remarkable recovery after post-fire curing, and it contributed to the recovery of split tensile strength.

Au-Pt-Pd계 금속-세라믹 합금의 모의소성 후 후열처리에 따른 석출경화

김성민(Sung-Min Kim),전병욱(Byung-Wook Jeon),유영준(Young-Jun Yu),권용훈(Yong-Hoon Kwon),김형일(Hyung-Il Kim),설효정(Hyo-Joung Seol) 대한치과재료학회 2014 대한치과재료학회지 Vol.41 No.3

The precipitation hardening by post-firing heat treatment after simulated firing of an Au-Pt-Pd metal-ceramic alloy was examined by observing the change in hardness, crystal structure and microstructure. By post-firing heat treatment of a completely fired specimen at 650℃, the hardness increased rapidly within 10 minutes to the maximum value. The maximum hardness value was maintained until 40 minutes, then the hardness decreased gradually. The apparent hardening by post-firing heat treatment after simulated porcelain firing was attributed to the lattice strains which were formed by the grain interior- and grain boundary precipitates. The precipitated phase from the parent Au-rich α phase by the post-firing heat treatment after simulated firing was an AuCu<SUB>3</SUB>-type (Pt, Pd)<SUB>3</SUB>(In, Sn) phase with a lattice parameter of a<SUB>220</SUB>=3.9986 Å. From the above results, appropriate post-firing heat treatment in order to support the hardness of metal substructure of metal-ceramic prosthesis was expected to bring positive effects to durability of the prosthesis.

Finite Element Analysis and Calculation Method of Residual Flexural Capacity of Post-fire RC Beams

Bin Cai,Bo Li,Feng Fu 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.6

Fire tests and subsequent bending tests of four reinforced concrete (RC) beams were performed. Based on these tests, the post-fire performance of RC beams was further studied using finite-element simulation through reasonable selection of suitable thermal and thermodynamic parameters of steel and concrete materials. A thermodynamic model of RC beams with three sides under fire was built using finite-element analysis (FEA) software ABAQUS. The FEA model was validated with the results of fire tests. Different factors were taken into account for further parametric studies in fire using the propsed FE model. The results show that the main factors affecting the fire resistance of the beams are the thickness of the concrete cover, reinforcement ratio of longitudinal steel, the fire exposure time and the fire exposure sides. Based on the strength reduction formula at high temperature of steel and concrete and four test results, an improved section method was proposed to develop a calculation formula to calculate the flexural capacity of RC beams after fire. The theoretical calculation method proposed in this paper shows good agreement with FEA results, which can be used to calculate the flexural capacity of RC beams after fire.

Investigating the Effect of Prior Damage on the Post-earthquake Fire Resistance of Reinforced Concrete Portal Frames

Hamid Reza Ronagh,Behrouz Behnam 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.4

Post-earthquake fire (PEF) can lead to a rapid collapse of buildings that have been partially damaged as a result of a prior earthquake. Almost all standards and codes for the design of structures against earthquake ignore the risk of PEF, and thus buildings designed using those codes could be too weak when subjected to a fire after an earthquake. An investigation based on sequential analysis inspired by FEMA356 is performed here on the immediate occupancy (IO), life safety (LS) and collapse prevention (CP) performance levels of two portal frames, after they are pushed to arrive at a certain level of displacement corresponding to the mentioned performance level. This investigation is followed by a fire analysis of the damaged frames, examining the time taken for the damaged frames to collapse. As a point of reference, a fire analysis is also performed for undamaged frames and before the occurrence of earthquake. The results indicate that while there is minor difference between the fire resistances of the fire-alone situation and the frames pushed to the IO level of performance, a notable difference is observed between the fire-alone analysis and the frames pushed to arrive at LS and CP levels of performance and exposed to PEF. The results also show that exposing only the beams to fire results in a higher decline of the fire resistance, compared to exposing only the columns to fire. Furthermore, the results show that the frames pushed to arrive at LS and CP levels of performance collapse in a global collapse mode laterally, whereas at the IO level of performance and fire-alone situation, the collapse mechanism is mostly local through the collapse of beams. Whilst the investigation is conducted for a certain class of portal frames, the results confirm the need for the incorporation of PEF into the process of analysis and design, and provide some quantitative measures on the level of associated effects.

Investigating the Effect of Prior Damage on the Post-earthquake Fire Resistance of Reinforced Concrete Portal Frames

Ronagh, Hamid Reza,Behnam, Behrouz Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.4

Post-earthquake fire (PEF) can lead to a rapid collapse of buildings that have been partially damaged as a result of a prior earthquake. Almost all standards and codes for the design of structures against earthquake ignore the risk of PEF, and thus buildings designed using those codes could be too weak when subjected to a fire after an earthquake. An investigation based on sequential analysis inspired by FEMA356 is performed here on the immediate occupancy (IO), life safety (LS) and collapse prevention (CP) performance levels of two portal frames, after they are pushed to arrive at a certain level of displacement corresponding to the mentioned performance level. This investigation is followed by a fire analysis of the damaged frames, examining the time taken for the damaged frames to collapse. As a point of reference, a fire analysis is also performed for undamaged frames and before the occurrence of earthquake. The results indicate that while there is minor difference between the fire resistances of the fire-alone situation and the frames pushed to the IO level of performance, a notable difference is observed between the fire-alone analysis and the frames pushed to arrive at LS and CP levels of performance and exposed to PEF. The results also show that exposing only the beams to fire results in a higher decline of the fire resistance, compared to exposing only the columns to fire. Furthermore, the results show that the frames pushed to arrive at LS and CP levels of performance collapse in a global collapse mode laterally, whereas at the IO level of performance and fire-alone situation, the collapse mechanism is mostly local through the collapse of beams. Whilst the investigation is conducted for a certain class of portal frames, the results confirm the need for the incorporation of PEF into the process of analysis and design, and provide some quantitative measures on the level of associated effects.

2019년 강원도 대형산불지역의 열해 피해로 인한 피해강도 변화 탐색

원명수,장근창,윤석희,이훈택 대한원격탐사학회 2019 大韓遠隔探査學會誌 Vol.35 No.6

본 연구는 2019년 발생한 강원 고성·속초, 강릉·동해 대형산불 직후 산불의 영향으로 수목의 수관부가완전 연소되거나, 직간접적인 열해 피해로 인해 고사되어 가는 과정을 다목적실용위성(KOMPSAT-2호, 3호) 영상자료를 활용하여 시간경과에 따른 산불 피해강도별 피해면적의 변화를 정확하게 산정하는데 목적이 있다. 피해강도별 피해면적 산출을 위해 산불 직후 위성영상자료와 15~18일 경과 후의 두 시기 영상자료를 이용하였다. 산불 직후와 일정기간 경과 후 촬영한 위성영상자료의 산불피해강도 분석결과는 ‘수관전소(Extreme)’ 지역에서는 큰 변화가 없었으나 ‘수관열해(High)’ 지역과 ‘지표화(Low)’ 지역에서는 큰 면적차이를 보였다. 이러한 피해강도의 차이에 따른 피해면적의 변화는 산불 영향으로 인해 수관부가 서서히 갈색으로 변색되어 가는과정에 의한 것으로 판단된다. 산불피해지역의 위성영상 분석결과와 현장사진, 드론 영상을 종합해 볼 때 산불직후 3~4일 후부터 수관부의 갈변현상(Browning)이 나타나고 10~15일 경과 후엔 수관부의 갈변현상이 뚜렷해지는 것을 알 수 있었다. 본 연구결과를 통해 향후 대형산불지역의 신속한 피해면적 파악은 물론 수관열해로인한 고사 기작을 파악함으로써 산불피해지 복구계획 수립을 위한 의사결정의 기초자료로 활용할 수 있을 것으로 사료된다. The purpose of this study is to detect the burned area change by direct burning of tree canopies and post-fire mortality of trees via analyzing satellite imageries from the Korea multi-purpose satellite- 2 and -3 (KOMPSAT-2 and -3) for two large-fires over the Goseong-Sokcho and Gangneung-Donghae regions in April 2019. For each case, the burned area was compared between two dates: the day when the fire occurred and 15-18 days after it. As the results, within these two dates, there was no substantial difference in burned area of sites whose severities were marked as “Extreme”, but sites with “High” and “Low” severities showed significant differences in burned area between the two dates. These differences were resulted from the lagged post-fire browning of canopies which was detected by images from insitu observation, satellite, and the unmanned aerial vehicle. The post-fire browning started after 3-4 days and became apparent after 10-15 days. This study offers information about the timing to quantify the burned area by large fire and about the mechanism of post-fire mortality. Also, the findings can support policy makers in planning the restoration of the damaged areas.