Influence of Loading Conditions on the Residual Flexural Capacity of Reinforced Concrete T-beams after Fire Exposure

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.

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.

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.

Effect of Stirrup Corrosion and Fire on Shear Behavior of Reinforced Concrete Beams

Jialiang Liu,Jijun Miao,Guangzhong Ba,Jiangzhuang Xiao,Dongshuai Hou 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.9

This article presents an investigation on corrosion damage effects on the shear bearing capacity of reinforced concrete (RC) beams after a fire. Accelerated corrosion tests were conducted using four RC beams designed with corrosion crack widths ranging from 0.1 mm to 0.3 mm to simulate an aggressive corrosion-prone environment. One control beam (B1) did not undergo accelerated corrosion. The fire test was conducted separately on each beam for two hours to explore how the different widths of corrosive cracks affect heat propagation at elevated fire-induced temperatures. A residual capacity test determined the effects of corrosion on the beams’ residual shear strength after a fire. The experimental results showed that corrosion cracks accelerate the heat propagation in concrete during a fire; moreover, the post-fire residual shear strength for corroded RC beams slightly decreased with an increasing degree of corrosion on the stirrups. The authors also developed a corresponding simplified calculating method to determine residual shear strength, which showed shear design provisions that could improve some existing codes.

Sorption behavior of Eu(III) on Tamusu clay under strong ionic strength: Batch experiments and BSE/EDS analysis

Zhang, Han,He, Hanyi,Liu, Jun,Li, Honghui,Zhao, Shuaiwei,Jia, Meilan,Yang, Jijun,Liu, Ning,Yang, Yuanyou,Liao, Jiali Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.1

The europium sorption on Tamusu clay was investigated by batch sorption experiments and spectroscopic study under the condition of strong ionic strength. The results demonstrated that europium sorption on Tamusu clay increased rapidly with pH value, but decreased with the ionic strength of solution increased. The europium sorption also increased in the presence of humic acid, especially at low pH value. The sorption could be fitted by Freundlich isotherm model and the europium sorption on clay was spontaneous and endothermic reaction. Besides, the result indicates that ion exchange was the main process at low pH value, while inner-sphere surface complexation dominated the sorption process at high pH value. The Backscatter electron scanning/Energy Dispersive Spectrometer(BSE/EDS) and the effect of Na for europium sorption results further suggested that europium sorption on Tamusu clay mainly competed with Na at low pH value. Overall, the results in this research were of significance to understand the sorption behavior of europium on the geological media under high ionic strength.

Yellow pigment from gardenia fruit: structural identification and evaluation of cytotoxic activity in HepG2 cells by induction of apoptosis

Liqin Tang,Haocheng Liu,Manqin Fu,Yujuan Xu,Jing Wen,Jijun Wu,Yuanshan Yu,Xian Lin,Lu Li,Zhibin Bu,Wanyuan Yang 한국식품과학회 2022 Food Science and Biotechnology Vol.31 No.11

The preparation process of yellow pigment (YP) from gardenia (Gardenia jasminoides) fruit was investigated, and the main components of YP were characterized by liquid chromatography-time of flight-mass spectrometer/mass spectrometer (LC-TOF–MS/MS). Furthermore, cytotoxic activity in HepG2 cells by induction of apoptosis was also evaluated. The preparation results indicated that the color value of YP was 498.34, which was 8.6 times higher than crude YP. Fifteen compounds in YP were identified, and crocins were the predominant compounds. The cell experiment results showed that YP inhibited the proliferation of HepG2 cells in a time- and dose-dependent manner. Moreover, YP also inhibited HepG2 cells in G2/M stage, increased the level of intracellular reactive oxygen species (ROS), and enhanced cell apoptosis. Real-time quantitative polymerase chain reaction (RT-PCR) analysis revealed the up-regulation of caspase-3, 8, 9, and bax and down-regulation of bcl-2 in HepG2 cells. Overall, these findings suggested that YP had potential cytotoxic activity in HepG2 cells by induction of apoptosis, which might be beneficial to human health.

Spectrum Cartography Based on Dynamic Compressed Sensing by Using Multiple Domains Information

Xia, Haiyang,Huang, Jijun,Liu, Jibin,Liu, Peiguo,Zha, Song 한국통신학회 2023 Journal of communications and networks Vol.25 No.4

Radio maps have experienced their success in ap-plications of wireless communications for years by offeringmetrics of radio frequency (RF) information, e.g., power spectraldensity (PSD), within a geographical region of interest. Spectrumcartography technique constructs radio maps to expand theabilities of RF awareness. However, seldom of existing methodsaim at constructing radio maps by utilizing multiple domains in-formation. In this paper, a novel framework inspired by dynamiccompressed sensing (DCS) has been proposed firstly to solve thisproblem. This flexible framework first to apply joint group-Lassofor PSD map construction based on the different sparse patternsbetween space and frequency domains as well as innovativelyutilizes transmitters’ mobility patterns for support prediction ofDCS. Simulation experiments have been processed to assess theperformance of methods within the proposed framework andframework’s superiority has been proven.

Characterization of the first tuber mustard calmodulin-like gene, BjAAR1, and its functions in responses to abiotic stress and abscisic acid in Arabidopsis

Liuxin Xiang,Yuxian Xia,Ying-Fan Cai,Jijun Liu,Xiaohong He,Quan Sun,Xiaoyan Wang,Yuyin Fu,Yonghong Fan,Daiwen Dong,Guanfan Zhou,Jinjuan Shen,Yihua Liu 한국식물학회 2013 Journal of Plant Biology Vol.56 No.3

The first tuber mustard calmodulin-like (CML) gene BjAAR1 (Brassica juncea var. tumida Tsen et Lee Abiotic stress and Abscisic acid (ABA) Responsive gene 1) was cloned and characterized. The protein encoded by BjAAR1 contains four predicted Ca2+ binding sites (EF-hand motif) and its recombinant protein can bind Ca2+ in vitro. qRT-PCR showed that the expression level of BjAAR1 was rather high in non-swollen stem of tuber mustard and largely reduced in swollen stem. Expression of BjAAR1 enhanced ABA- and stress-induced gene expression in Arabidopsis (Arabidopsis thaliana). Transgenic plants also exhibited hypersensitivity to NaCl, mannitol, and ABA during the seed germination and post-germination stages. ABA biosynthesis inhibitor, norflurazon (NF), rescued hypersensitivity phenotype of transgenic plants to NaCl and mannitol, indicating that BjAAR1 functions in multiple abiotic stresses response through ABA-dependent process.

Atypical Antipsychotics Mediate Dynamics of Intrinsic Brain Activity in Early-Stage Schizophrenia? A Preliminary Study

Yingchan Wang,Yuchao Jiang,Dengtang Liu,Jianye Zhang,Dezhong Yao,Cheng Luo,Jijun Wang 대한신경정신의학회 2021 PSYCHIATRY INVESTIGATION Vol.18 No.12

Objective Abnormalities of static brain activity have been reported in schizophrenia, but it remains to be clarified the temporal variability of intrinsic brain activities in schizophrenia and how atypical antipsychotics affect it.Methods We employed a resting-state functional magnetic resonance imaging (rs-fMRI) and a sliding-window analysis of dynamic amplitude of low-frequency fluctuation (dALFF) to evaluate the dynamic brain activities in schizophrenia (SZ) patients before and after 8-week antipsychotic treatment. Twenty-six schizophrenia individuals and 26 matched healthy controls (HC) were included in this study.Results Compared with HC, SZ showed stronger dALFF in the right inferior temporal gyrus (ITG.R) at baseline. After medication, the SZ group exhibited reduced dALFF in the right middle occipital gyrus (MOG.R) and increased dALFF in the left superior frontal gyrus (SFG.L), right middle frontal gyrus (MFG.R), and right inferior parietal lobule (IPL.R). Dynamic ALFF in IPL.R was found to significant negative correlate with the Scale for the Assessment of Negative Symptoms (SANS) scores at baseline.Conclusion Our results showed dynamic intrinsic brain activities altered in schizophrenia after short term antipsychotic treatment. The findings of this study support and expand the application of dALFF method in the study of the pathological mechanism in psychosis in the future.

U-phosphate biomineralization induced by Bacillus sp. dw-2 in the presence of organic acids

Hong Tu,Guoyuan Yuan,Changsong Zhao,Jun Liu,Feize Li,Jijun Yang,Jiali Liao,Yuanyou Yang,Ning Liu 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.5

In this paper, we systematically investigated the influence of some selected ligands on the U-phosphateprecipitation induced by soil bacteria. These organics are widely ranging from acetate, lactate, salicylateand citrate to oxalate. The results revealed that uranium could be biomineralized on bacteria asUO2HPO4$4H2O or (UO2)3(PO4)2$4H2O. The influence of organic ligands on the biomineralization hadclear-cut correlations with its complexation abilities to uranyl. It was clearly found that the U-phosphatebiomineralization was affected noticeably by the strong ligands (oxalate and citrate). Further studydiscovered that when the organic ligands were uncompetitive with biotic PO4 3 for uranyl, the transformationof uranyl species from b-UO2(OH)2 colloidal particles to free UO2 2 þ-ligands ions could facilitatethe U-phosphate biomineralization. However, when the organic ligands competed with biotic PO4 3 foruranyl, the U-phosphate biomineralization were inhibited. Our results highlight the importance ofcomplex interactions of strong organic ligands with uranyl during the bacterial precipitation of UePcompounds and thus for the mobilization and immobilization of radio-nuclides in the nature.