Cyclic behavior of FRP - crumb rubber concrete - steel double skin tubular columns and beams

Danda Li,Reza Hassanli,Yue Su,Yan Zhuge,Xing Ma 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.5

This paper presents experimental and analytical studies to understand the behavior of crumb rubber concrete (CRC)-filled fiber reinforced polymer (FRP) and steel tube double skin column (DSC) and beam (DSB) members under cyclic loading. The main test variable was the percentage of rubber which ranged from 0 to 40%. For column members, different heights corresponding to different aspect ratios were examined to understand the to understand the effect of DSCs’ slenderness on the cyclic response of the columns. the. The behavior of the specimens in terms of failure mode, strain development, energy dissipation, load-displacement response were presented and compared. The ability of the current provisions of the Australian codes to predict the capacity of such double skin members was also evaluated based on the test results. This study concluded that the reduction in the concrete strength was more severe at the material level compared to structural level. Also, as the load changed from axial compression in columns to pure moment in beams the negative effect of rubber percentage on the strength became less significant.

A Field Deployable Real-Time Loop-Mediated Isothermal Amplification Targeting Five Copy nrdB Gene for the Detection of ‘Candidatus Liberibacter asiaticus’ in Citrus

Tirumalareddy Danda,Jong-Won Park,Kimberly L. Timmons,Mamoudou Sétamou,Eliezer S. Louzada,Madhurababu Kunta 한국식물병리학회 2023 Plant Pathology Journal Vol.39 No.4

Huanglongbing (HLB) is one of the most destructive diseases in citrus, which imperils the sustainability of citriculture worldwide. The presumed causal agent of HLB, ‘Candidatus Liberibacter asiaticus’ (CLas) is a non-culturable phloem-limited α-proteobacterium transmitted by Asian citrus psyllids (ACP, Diaphorina citri Kuwayama). A widely adopted method for HLB diagnosis is based on quantitative real-time polymerase chain reaction (qPCR). Although HLB diagnostic qPCR provides high sensitivity and good reproducibility, it is limited by time-consuming DNA preparation from plant tissue or ACP and the requirement of proper lab instruments including a thermal cycler to conduct qPCR. In an attempt to develop a quick assay that can be deployed in the field for CLas detection, we developed a real-time loop-mediated isothermal amplification (rt-LAMP) assay by targeting the CLas five copy nrdB gene. The rt-LAMP assay using various plant sample types and psyllids successfully detected the nrdB target as low as ~2.6 Log10 copies. Although the rt-LAMP assay was less sensitive than laboratorybased qPCR (detection limit ~10 copies), the data obtained with citrus leaf and bark and ACP showed that the rt-LAMP assay has >96% CLas detection rate, compared to that of laboratory-based qPCR. However, the CLas detection rate in fibrous roots was significantly decreased compared to qPCR due to low CLas titer in some root DNA sample. We also demonstrated that the rt-LAMP assay can be used with a crude leaf DNA extract which is fully deployable in the field for quick and reliable HLB screening.

Numerical Simulation of Degradation Behavior of Concrete Piles in Sulfate Saline Soils

Wei Shao,Danda Shi 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.1

In this study, an integrated numerical approach is developed to simulate the damage and degradation behaviors of concrete piles in sulfate saline soils. The governing equations for modeling the sulfate diffusion-reaction mechanism are presented. The diffusion properties of sulfate ions are modified by taking into account the effects of pore filling and expansion cracking on the diffusivity of sulfate ions. The model for simulating the volumetric expansion and damage evolution is presented. The developed numerical method is verified by comparison with experimental results of linear expansion. Numerical analysis results show that the sulfate concentration tends to increase with the exposure time at the same diffusion depth, but the growth rate gradually slows with increasing diffusion depth. The concentration of the reacted calcium aluminates increases gradually with the exposure time, while reduces with the increasing diffusion depth. The effective diffusion coefficient decreases sharply at the interface depth, and then increases gradually with an increase in diffusion depth at the same exposure time. The higher environmental sulfate concentration and water-cement ratio can accelerate the degradation of structural capacity of concrete piles.

Cyclic behaviour of concrete encased steel (CES) column-steel beam joints with concrete slabs

Liusheng Chu,Danda Li,Xing Ma,Jun Zhao 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.6

In this paper, the cyclic behavior of steel beam-concrete encased steel (CES) column joints was investigated experimentally and numerically. Three frame middle joint samples with varying concrete slab widths were constructed. Anti-symmetrical low-frequency cyclic load was applied at two beam ends to simulate the earthquake action. The failure modes, hysteretic behavior, ultimate load, stiffness degradation, load carrying capacity degradation, displacement ductility and strain response were investigated in details. The three composite joints exhibited excellent seismic performance in experimental tests, showing high load-carrying capacity, good ductility and superior energy dissipation ability. All three joint samples reached their ultimate loads due to shear failure. Numerical results from ABAQUS modelling agreed well with the test results. Finally, the effect of the concrete slab on ultimate load was analyzed through a parametric study on concrete strength, slab thickness, as well as slab width. Numerical simulation showed that slab width and thickness played an important role in the load-carrying capacity of such joints. As a comparison, the influence of concrete grade was not significant.

Probabilistic Analysis of the Durability of Piles with Microcracks Under Chloride Attack

Wei Shao,Danda Shi 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.6

A probabilistic analysis approach for estimating the durability of piles with microcracks under chloride attack is presented. The chloride ingress model is obtained by considering the time-dependent diffusion process. The equivalent diffusion coefficient is derived to investigate the crack effect by introducing the crack effect factor. The fitting formula between the chloride diffusion coefficients and crack widths is established through experimental results, and the proposed equivalent diffusion coefficient is verified by comparison with the experimental results. The probabilistic evaluation of durability of piles with microcracks is performed, and then the parametric analysis is performed to study the effect of main parameters on the failure probability and durability life. The results indicate that the chloride concentration increases rapidly as the crack width increases at the same number of cracks. The durability life greatly reduces with increasing crack density of pile. The durability life predicted by probabilistic method is always less than those by deterministic method at the same condition. The deterministic approach may underestimate the threat of reinforcement corrosion induced by chloride attack, owing to the omission of probabilistic nature of main influencing parameters.

Extraction of copper from copper slag: Mineralogical insights, physical beneficiation and bioleaching studies

Sandeep Panda,Srabani Mishra,Danda Srinivas Rao,Nilotpala Pradhan,Umaballava Mohapatra,Shivakumar Angadi,Barada Kanta Mishra 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.4

Copper slag was subjected to in-depth mineralogical characterization by integrated instrumental techniquesand evaluated for the efficacy of physical beneficiation and mixed meso-acidophilic bioleaching tests towardsrecovery of copper. Point-to-point mineral chemistry of the copper slag is discussed in detail to give better insight intothe association of copper in slag. Characterization studies of the representative sample revealed the presence of fayaliteand magnetite along with metallic copper disseminated within the iron and silicate phases. Physical beneficiation of thefeed slag (~0.6% Cu) in a 2 L working volume flotation cell using sodium isopropyl xanthate resulted in Cu beneficiationup to 2-4% and final recovery within 42-46%. On the other hand, a mixed meso-acidophilic bacterial consortiumcomprised of a group of iron and/or sulfur oxidizing bacteria resulted in enhanced recovery of Cu (~92-96%) from theslag sample. SEM characterization of the bioleached slag residue also showed massive coagulated texture with severeweathered structures. FE-SEM elemental mapping with EDS analysis indicated that the bioleached residues were devoidof copper.

Synthesis and Biological Evaluation of Some Novel [4-(1H-Benzoimidazol-2-yl)-thiazol-2-yl]-benzylidene-amines and N-[4-(1H-Benzoimidazol-2-yl)-thiazol-2-yl]-N'-benzylidene-hydrazines

Mekala, Raghu Vardhan Reddy,Danda, Ravinder Reddy,Gadegoni, Hemalatha Korean Chemical Society 2013 대한화학회지 Vol.57 No.1

A new family of thiazole heterocycles, namely [4-(1H-benzoimidazol-2-yl)-thiazol-2-yl]-benzylidene-amines has been synthesized by the condensation of 4-(1H-Benzoimidazol-2-yl)-thiazol-2-ylamine with various aromatic aldehydes and N-[4-(1H-benzoimidazol-2-yl)-thiazol-2-yl]-N'-benzylidene-hydrazines through the cyclization of 1-(1H-benzoimidazol-2-yl)-2-bromo-ethanone with arylthiosemicarbazones. The target compounds are achieved by using 1-(1H-Benzoimidazol-2-yl)-ethanone as starting material. The chemical structures of all newly synthesized compounds were confirmed by their IR, $^1H$ NMR and Mass spectral data. Further the compounds were used to evaluate their antimicrobial activity and found that the appreciable antimicrobial activity by some of the title compounds.

Structural performance of reinforced concrete wall with boundary columns under shear load

Liusheng Chu,Yuexi He,Danda Li,Xing Ma,Zhanqi Cheng 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.4

This paper proposed a novel form of reinforced concrete (RC) shear wall confined with boundary columns. The structural effect of applying steel fiber reinforced concrete (SFRC) in the wall-column systems was studied. Three full-scale wall samples were constructed including two RC wall-RC column samples with different stirrup ratios and one RC wall-SFRC column sample. Low frequency cyclic testing was carried out to investigate the failure modes, hysteretic behavior, load-bearing capacity, ductility, stiffness degradation and energy dissipation. ABAQUS models were set up to simulate the structural behavior of tested samples, and good agreement was achieved between numerical simulation and experimental results. A further supplementary parametric study was conducted based on ABAQUS models. Both experimental and numerical results showed that increasing stirrup ratio in boundary columns did not affect much on load bearing capacity or stiffness degradation of the system. However, applying SFRC in boundary columns showed significant enhancement on load bearing capacity. Numerical simulation also shows that the structural performances of RC wall-SFRC column system were comparable to a wall-column system fully with SFRC.

Jugular foramen paragangliomas: preoperative transcatheter particle embolization

Charbel Ishak,Varun Danda 대한뇌혈관외과학회 2020 Journal of Cerebrovascular and Endovascular Neuros Vol.22 No.4

Jugular foramen paragangliomas (JFP) are benign tumors of neural crest origin that are located along the temporal bone in the region of the jugular bulb and middle ear. The optimal management of these lesions includes surgical excision with or without preoperative embolization as well as stereotactic radiotherapy. The use of preoperative embolization in the treatment of JFP has shown great promise to bridge patients to surgery by diminishing complication rates and decreasing intraoperative bleeding. We present three successful polyvinyl alcohol (PVA) particle embolizations of patients presenting with symptomatic JFPs. All patients recovered completely in the short term with no bleeding during or after resection of paragangliomas and they were discharged free of their presenting symptoms. Early clinical and imaging diagnosis followed by adequate treatment including preoperative transcatheter particle embolization and surgical or radiosurgical interventions can lead to excellent outcomes.

Studies on removal of lead ions from aqueous solutions using iron ore slimes as adsorbent

Laxmipriya Panda,Bisweswar Das,Danda Srinivas Rao 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.10

Iron ore slimes, a waste material generated during iron ore mining have been employed for the removal of lead ions from aqueous solutions by a batch adsorption technique. The slime sample contains 45.8% Fe, 13.6% SiO_2,and 13.9% Al_2O_3. It is characterized by X-ray diffraction (XRD) and optical microscopy to determine the presence of different phases such as hematite, goethite, limonite, quartz and kaolinite. It is assumed that the adsorption of lead ions is mainly due to the presence of pores and cavities in goethite mineral. The FTIR studies showed the presence of Si-OH and Fe-OH sites responsible for adsorption. Furthermore, the point of zero charge (pzc) of iron ore slime is shifted from 6.2 to 5.8 due to the adsorption of lead ions. Batch adsorption experiments have been conducted to study the sorption behavior of lead ions on iron ore slime. The effects of agitation time, concentration of lead ions, adsorbent doses, solution pH, other metal ions and temperature on the amount of lead ions adsorbed have been investigated. Lead ion adsorption is fast, and equilibrium could be achieved within 15 minutes of time. The adsorption increased with increase in temperature suggesting an endothermic adsorption. Under the conditions, it is possible to remove 95%lead from an aqueous solution bearing ~20 mg/l at pH~5.1. The equilibrium adsorption isotherm data fitted very well to both Langmuir and Freundlich adsorption models.