Mechanism of Elasto-Plastic Behavior of Composite Beam Connected to RHS Column

Mohammadreza Eslami,Hisashi Namba 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3

Following to the experimental test of full-scale beam-to-RHS column sub-assemblies, it was observed that in the composite beam considerable reduction of rotation capacity occurs due to the increase of strain at the lower flange. In the case of bare beam-to-RHS column connection, it is already known that occurrence of out-of-plane deformation in the column web, results in the reduction of rotation capacity of beam. However, in the composite beam-to-RHS column connection due to slab axial force, web connection is in more severe stress condition. Further comprehensive understanding of effect of out-of-plane deformation of RHS column on the behavior of composite beam is needed. In this paper results of finite element analysis and limit analysis are presented to clarify the structural condition of web connection. The force flow pattern and ultimate flexural capacity are evaluated by considering main parameters affecting the deformation. Correspondence between FEA, limit analysis and experimental data is shown, mechanism of mechanical stress transfer and strain concentration is explained.

Elasto-Plastic Behavior of Composite Beam Connected to RHS Column, Experimental Test Results

Mohammadreza Eslami,Hisashi Namba 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3

This paper presents results of study on the elasto-plastic behavior of composite beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. In order to investigate the effects of width-to-thickness ratio (B/t) of RHS column on the rotation capacity of composite beam, cyclic loading test were conducted on three full scale beam-to-column subassemblies. Detail study on the different steel beam damages and concrete slab damages are presented. Experimental test showed the importance of this parameter of RHS column, on the seismic behavior of composite beam. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the lower flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with composite and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

Nanostructured Hydroxyapatite for Biomedical Applications: From Powder to Bioceramic

Eslami, Hossein,Tahriri, Mohammadreza,Moztarzadeh, Fathollah,Bader, Rizwan,Tayebi, Lobat The Korean Ceramic Society 2018 한국세라믹학회지 Vol.55 No.6

In this study, a wet chemical method was used to synthesize nanostructured hydroxyapatite for biomedical applications. Diammonium hydrogen phosphate and calcium nitrate 4-hydrate were used as starting materials with a sodium hydroxide solution as an agent for pH adjustment. Scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, differential thermal analysis, thermal gravimetric analysis, atomic absorption spectroscopy, and ethylenediaminetetraacetic acid (EDTA) titration analysis were used to characterize the synthesized powders. Having been uniaxially pressed, the powders formed a disk-like shape. The sinterability and electrical properties of the samples were examined, and the three-point bending test allowed for the measurement of their mechanical properties. Sedimentation analysis was used to analyze the slurry ability of hydroxyapatite. As in-vitro biological properties of the samples, biocompatibility and cytotoxicity were assessed using osteoblast-like cells and the L929 cell line, respectively. Solubility was assessed by employing a simulated body fluid.

Synthesis and characterization of nanocrystalline fluorinated hydroxyapatite powder by a modified wet-chemical process

Hossein Eslami,Mehran Solati-Hashjin,Mohammadreza Tahriri 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.3

Fluorinated hydroxyapatite (FHA; fluorhydroxyapatite) powder was synthesized through a pH-cycling method by varying the sodium fluoride [NaF] concentration in a hydroxyapatite suspension as a modified wet-chemical process. The powder sample was characterized by the commonly used bulk techniques of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), F-selective electrode, atomic absorption spectroscopy (AAS) and EDTA titration analyses. SEM was used to estimate the particles size of the powder and observe the morphology and agglomeration state of the powder. The functional groups presented in the synthesized powder were ascertained by FTIR investigations. AAS and EDTA titration techniques were employed for calculation of the Ca/P molar ratio. F-selective electrode analysis also was used to measure the fluorine (F) content in the crystalline network of the synthesized powder. Finally, the FHA and other phases according to processing parameters were observed by XRD analysis Fluorinated hydroxyapatite (FHA; fluorhydroxyapatite) powder was synthesized through a pH-cycling method by varying the sodium fluoride [NaF] concentration in a hydroxyapatite suspension as a modified wet-chemical process. The powder sample was characterized by the commonly used bulk techniques of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), F-selective electrode, atomic absorption spectroscopy (AAS) and EDTA titration analyses. SEM was used to estimate the particles size of the powder and observe the morphology and agglomeration state of the powder. The functional groups presented in the synthesized powder were ascertained by FTIR investigations. AAS and EDTA titration techniques were employed for calculation of the Ca/P molar ratio. F-selective electrode analysis also was used to measure the fluorine (F) content in the crystalline network of the synthesized powder. Finally, the FHA and other phases according to processing parameters were observed by XRD analysis

Rotation capacity of composite beam connected to RHS column, experimental test results

Hisashi Namba,Mohammadreza Eslami 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.1

Commonly in steel frames, steel beam and concrete slab are connected together by shear keys to work as a unit member which is called composite beam. When a composite beam is subjected to positive bending, flexural strength and stiffness of the beam can be increased due to "composite action". At the same time despite these advantages, composite action increases the strain at the beam bottom flange and it might affect beam plastic rotation capacity. This paper presents results of study on the rotation capacity of composite beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. Due to out-of-plane deformation of column flange, moment transfer efficiency of web connection is reduced and this results in reduction of beam plastic rotation capacity. In order to investigate the effects of width-to-thickness ratio (<i>B</i>/<i>t</i>) of RHS column on the rotation capacity of composite beam, cyclic loading tests were conducted on three full scale beam-to-column subassemblies. Detailed study on the different steel beam damages and concrete slab damages are presented. Experimental data showed the importance of this parameter of RHS column on the seismic behavior of composite beams. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the bottom flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with composite and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

Effects of incorporation of 2.5 and 5 wt% TiO2 nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA)

Sahar Abdulrazzaq Naji,Marjan Behroozibakhsh,Tahereh Sadat Jafarzadeh Kashi,Hossein Eslami,Reza Masaeli,Hosseinali Mahgoli,Mohammadreza Tahriri,Mehrsima Ghavvami Lahiji,Vahid Rakhshan 대한치과보철학회 2018 The Journal of Advanced Prosthodontics Vol.10 No.2

PURPOSE. The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes (n-TiO2) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS. TiO2 nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each TiO2:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of n-TiO2 addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS. SEM images of n-TiO2 exhibited the presence of elongated tubular structures. The XRD pattern of synthesized n-TiO2 represented the anatase crystal phase of TiO2. Moderate to very strong significant positive correlations were observed between the concentration of n-TiO2 and each of the 3 physicomechanical properties of PMMA (Pearson’s P value ≤.001, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% n-TiO2 were significantly higher than those of control (P≤.001). Fracture toughness of samples reinforced with 5 wt% n-TiO2 (but not those of 2.5% n-TiO2) was higher than control (P=.002). CONCLUSION. Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.