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- 저자 : Caiwei Liu (검색결과 5 건)
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Caiwei Liu,Xiuliang Lu,Guangzhong Ba,Hao Liu,Jijun Miao 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.12
To explore the influence of the loading conditions and fire exposure time on the residual mechanical properties of concrete T-beams, 10 concrete T-shaped beams were designed and manufactured. Three levels of loading were applied to the concrete T-beams during fire tests, namely, unloaded, loaded without concrete cracking and normal service conditions. The fire test durations were 60 min, 90 min, and 120 min. After the fire tests, static loading tests were carried out on the fire-damaged T-beams to determine the residual flexural capacity. The test results showed that with an increase in load ratio and fire time, the maximum temperature experienced by the concrete and steel bar increased. For example, for the specimens that underwent 120 minutes of fire exposure, the temperature of the specimen with a load ratio of 0.44 was larger than that with load ratios of 0.12 and 0, and the difference was 60°C and 80°C, respectively. During the fire tests, the mid-span deflection also increased significantly with an increase in load ratio and fire duration. In addition, the flexural load-bearing capacity after fire exposure decreased with an increase in load ratio and fire time. Compared with the bearing capacity, the degradation of the flexural rigidity was more obvious. For example, when the fire exposure time was 120 minutes, the bending capacity of the beam with a load ratio of 0.44 was approximately 4.5% lower and 5.1% lower than that with a load ratio of 0.12 and 0, respectively, and the reduction in flexural rigidity became 6.8% and 15%, respectively. Considering the effect of cracking, ANSYS was used to analyze the temperature field, deflection, and bearing capacity of the T-beams. It was determined that the calculation model that considers the effects of cracks was more accurate than the calculation model that disregards the appearance of cracks. This study can provide a basis for the assessment of fire damage and the repair of concrete structures.
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A Fractal-Interpolation Model for Diagnosing Spalling Risk in Concrete at Elevated Temperatures
Caiwei Liu,Chaofeng Liu,Wenlong Xu,Xiaobo Zhang,Yue Lan 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.12
Spalling risk analysis and assessment of fire-loaded concrete structures is an essential part of research on fire-resistant behavior of concrete structures. In this work, the authors developed a stochastic interpolation-based fractal model capable of quickly assessing spalling risk in concrete at high temperatures based on mainly factors affecting explosive spalling. The preliminary grading standard of the factors elected in the study was established based on the data from literature. Test samples were then generated by the stochastic interpolation method according to uniform distribution. A spalling risk diagnosis model was built based on fractal dimension weights. In addition, 10 specimens were assessed with the presented model. The evaluation results obtained by the model in this study were in good agreement with those obtained by the fuzzy pattern recognition approach and coincided well with the actual fire test results. The applicability and reliability of the proposed model were verified and can provide theoretical support for identification of the spalling risk of concrete at elevated temperatures.
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Fire Damage Identification in RC Beams based on Support Vector Machines considering Vibration Test
Chaofeng Liu,Caiwei Liu,Chengxin Liu,Xuhong Huang,Jijun Miao,Wenlong Xu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.10
In order to obtain the degree of damage in reinforced concrete (RC) beams exposed to fire, using the equivalent fire exposure time as the damage index, a new method of damage identification based on the support vector machine technology was proposed. Firstly, the feasibility analysis was conducted based on finite element models of simply supported beams. Thereafter, four RC simply supported beams were designed for fire test and vibration test, which were used to amend the finite element model and the SVM-based identification method. Fire tests were carried out on 4 beams for 60, 90, 120, and 150 min, respectively. During and after the fire tests, structural modal information were recorded. The first two order modal information, as SVM input paraments, was used to predict the equivalent fire exposure time based on SVM. The predicted results were very close to the actual fire exposure time. The residual bearing capacities of the beams after fire were calculated according to the predicted fire exposure time, which were close to experimental results. It indicated that the equivalent fire exposure time as the output parameter for damage identification was reliable. Finally, on the basis of damage identification method for simply supported beams, a new three-step positioning method was established for identifing the degree of damage in continuous beams. The method was applied to a thress-span continuous beam. The numercial situlation results revealed that the three-step positioning method was accurate.
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Calculation of Thermal Fields of Cracked Concrete at Elevated Temperatures
Yanchun Liu,Jijun Miao,Jialiang Liu,Guangzhong Ba,Caiwei Liu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.1
This paper analyzes the effects of cracking on the thermal field of concrete at elevated temperatures. In four concrete specimens with pre-made cracks, fire tests were performed. Then finite element analysis and theoretical analysis were conducted, which have indicated that heat conduction was the primary source of heat transfer in cracked concrete. At last mathematical software MATLAB was used to calculate the temperatures distributions of a simplified model based on theoretical analysis, which were compared with the test results. The results show that as the thermal diffusion of air is far greater than that of concrete, there is an increase in the thermal propagation through the cracked regions in comparison with undamaged regions, and the temperatures increase with the increase of cracks’ widths. The temperature of concrete farther away from a crack was less affected because concrete has a lower thermal diffusion coefficient. The water content of concrete has an impact on the temperature distributions, which should be considered at the early stage of fire when determining the concrete temperature distributions.
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Numerical study on the impact response of SC walls under elevated temperatures
Lin Wang,Weiyi Zhao,Caiwei Liu,Qinghong Pang 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.3
A thermal-mechanical coupling finite element model of the steel-plate concrete composite (SC) wall is established, taking into account the strain rate effect and variation in mechanical and thermal properties under different temperatures. Verifications of the model against previous fire test and impact test results are carried out. The impact response of the SC wall under elevated temperatures is further investigated. The influences of the fire exposure time on the impact force and displacement histories are discussed. The results show that as the fire exposure time increases, the deflection increases and the impact resistance decreases. A formula is proposed to calculate the reduction of the allowable impact energy considering the fire exposure time.
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