Collapse of steel cantilever roof of tribune induced by snow loads

Ahmet C. Altunışık,Şevket Ateş,Metin Hüsem,Ali F. Genç 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.3

In this paper, it is aimed to present a detail investigation related to structural behavior of laterally unrestrained steel cantilever roof of tribune with slender cross section. The structure is located in Tutak town in A&$287;rı and collapsed on October 25, 2015 at eastern part of Turkey is considered as a case study. This mild sloped roof structure was built from a variable I beam, and supported on steel columns of 5.5 m height covering totally 240 m² closed area in plan. The roof of tribune collapsed completely without any indication during first snowfall after construction at midnight a winter day, fortunately before the opening hours. The meteorological records and observations of local persons are combined together to estimate the intensity of snow load in the region and it is compared with the code specified values. Also, the wide/thickness and height/thickness ratios for flange and web are evaluated according to the design codes. Three dimensional finite element model of the existing steel tribune roof is generated considering project drawings and site investigations using commercially available software ANSYS. The displacements, principal stresses and strains along to the cantilever length and column height are given as contour diagrams and graph format. In addition to site investigation, the numerical and analytical works conducted in this study indicate that the unequivocal reasons of the collapse are overloading action of snow load intensity, some mistakes made in the design of steel cantilever beams, insufficient strength and rigidity of the main structural elements, and construction workmanship errors.

Effect of Repeated Quenching Heat Treatment on Microstructure and Dry Sliding Wear Behaviour of Low Carbon PM Steel

Gural Ahmet,Tekeli Suleyman,Ozyurek Dursun,Guru Metin 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The mixed atomized iron powders with 0.3% graphite and 1% Ni powders were cold pressed and sintered at for 30 min under pure Ar gas atmosphere. Some of the sintered specimens were intercritically annealed at and quenched in water (single quenching). The other sintered specimens were first fully austenized at and water quenched. These specimens were then intercritically annealed at and re-quenched in water. The experimental results showed that the wear coefficient effectively decreased in the double quenched specimen.

ZnO nanostructures for photocatalytic degradation of methylene blue: effect of different anodization parameters

Oksuz Ahmet Emrecan,Yurddaskal Metin,Kartal Ugur,Dikici Tuncay,Erol Mustafa 한국세라믹학회 2022 한국세라믹학회지 Vol.59 No.6

In this paper, the photocatalytic activity of ZnO nanostructures formed by anodization method with diff erent parameters was investigated. The synthesis of ZnO nanostructures with diff erent morphology by varying anodic oxidation parameters containing electrolytes, molarity, voltage, and duration was analyzed. ZnO nanostructures were prepared through diff erent parameters consisting of six samples. The produced ZnO nanostructures were investigated by using X-ray diff raction, scan- ning electron microscopy, diff use refl ectance spectroscopy, and UV–Vis spectrophotometer. It was found that the morphology of ZnO structures was formed as nanorods, needle-like, fl ower-like, heterogeneous, and homogeneous of mixed structures. ZnO nanostructures were identified by matching X-Ray diffraction peaks due to the international center for diffraction data database. Experiments on photocatalytic degradation of methylene blue demonstrated that the photocatalytic activity of ZnO samples. The best photocatalytic performance was observed by the sample anodized for an hour in 0.05 M of KHCO 3 electrolytes with 40 V electrical potential. It was observed that the removal of methylene blue increased 3 times (photocatalytic degradation efficiency ~ 31% for methylene blue vs ~ 90% by the best sample) thanks to the obtained ZnO nanostructured photocatalysts. The results showed that an increment of the voltage has a significant effect on the photocatalytic activity of ZnO while keeping other parameters including molarity, time, and electrolyte type constant.

Intussusception: As the Cause of Mechanical Bowel Obstruction in Adults

( Murat Cakir ),( Ahmet Tekin ),( Tevfik Kucukkartallar ),( Metin Belviranli ),( Ebubekir Gundes ),( Yahya Paksoy ) 대한소화기학회 2013 대한소화기학회지 Vol.61 No.1

Background/Aims: Intussusception in adults is rarely seen and causes misdiagnosis due to its appearance with various clinical findings. The cause of intussusception in adults is frequently organic lesions. In this study, the underlying etiologic factors, diagnostic methods and alternative methods of treatment are discussed in the light of the literature. Methods: In this study, a retrospective evaluation was performed on 47 cases with the diagnoses of intussusception, who were operated on for bowel obstruction between 1990-2011 in Department of Surgery of Necmettin Erbakan University Meram Medical Faculty. Data related to presentation, diagnosis, treatment and pathology were analyzed. Results: Twenty-four of the patients (51%) were female, and 23 were male (49%). Mean age (year) was 49 (range: 23-78) in female group, and 50 (range: 17-72) in male group. All patients presented mechanical bowel obstruction findings and underwent operation. Intussusception was caused by benign and malignant tumors in 38 patients, and other reasons in 3 cases. No reason could be determined in the other 6 cases. Only small intestine resection was applied in 29 cases, and large intestine resection was also applied in 17 cases. Reduction and fixation surgery was performed in one patient. No postoperative mortality was observed. Conclusions: Adult intussusception remains a rare cause of abdominal pain. Diagnosis of intussusception in adults is still difficult. Main treatment was surgical in most cases. (Korean J Gastroenterol 2013;61:17-21)

Free transverse vibrations of an elastically connected simply supported twin pipe system

Müge Balkaya,Metin O. Kaya,Ahmet Sa lamer 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.5

In this paper, free vibration analyses of a parallel placed twin pipe system simulated by simply supported-simply supported and fixed-fixed Euler-Bernoulli beams resting on Winkler elastic soil are presented. The motion of the system is described by a homogenous set of two partial differential equations, which is solved by a simulation method called the Differential Transform Method (DTM). Free vibrations of an elastically connected twin pipe system are realized by synchronous and asynchronous deflections. The results of the presented theoretical analyses for simply supported Euler-Bernoulli beams are compared with existing ones in open literature and very good agreement is demonstrated.

Transcatheter Closure of a Residual Patent Ductus Arteriosus After Surgical Ligation in Children

Osman Baspinar,Metin Kilinc,Mehmet Kervancioglu,Ahmet Irdem 대한심장학회 2011 Korean Circulation Journal Vol.41 No.11

Background and Objectives: To assess the safety and efficacy of transcatheter closure of residual ductal flow after initial surgical ligation of the arterial duct. Subjects and Methods: Between June 2005 and December 2009, transcatheter occlusion of residual postsurgical ductus arteriosus was performed in six children. Results: The mean patient age was 10±5.5 years; mean post-procedural time since the initial surgical closure was 6.3±4.5 years. The mean diameter of the patent ductus arteriosus on angiography was 1.3±0.5 mm (range, 0.8 to 2.4 mm). Three different types of coils were used successfully without any complications. Conclusion: Transcatheter occlusion of residual postsurgical arterial duct is a safe and successful procedure. However, attention should be paid due to the distorting shape of the arterial duct.

Total Serum Oxidant/Antioxidant Status and Arylesterase Activity in Recurrent Aphthous Stomatitis

Gulsen Akoglu,Ahmet Metin,Fadime Kilinc,Suzan Demir Pektas,Semra Isikoglu,Ayse Akbas,Sertac Sener 대한피부과학회 2013 Annals of Dermatology Vol.25 No.3

Background: Recurrent aphthous stomatitis (RAS) is a chronic relapsing inflammatory disorder of the oral mucosa with unknown etiology. Oxidative stress (OS) is suggested to play a main role in the etiopathogenesis in RAS. Objective: In this study, we hypothesize that a systemic OS is present in patients with RAS. Methods: Forty-four patients with active RAS lesions and 38 healthy controls were being included in the study. Serum total oxidant status (TOS), total antioxidant status (TAS), oxidative stress index (OSI), and paraoxonase 1arylesterase (ARES) activity were being determined. Results:RAS patients had significantly lower TAS levels and higher TOS and OSI values than controls. The patients had a lower ARES activity when compared to healthy controls. No correlations were observed between OS parameters and age,gender, duration of disease or frequency of RAS attacks per month. Conclusion: A systemic OS is determined with an imbalance in oxidant/antioxidant status and lower ARES activity in RAS. Systemic OS may have an important role in the pathogenesis of RAS formation.

Clinical challenges associated with the endovascular treatment of acute stroke in a patient with infective endocarditis

Emil Settarzade,Ahmet Peker,M. Akif Topcuoglu,E. Murat Arsava,Metin Demircin,Anıl Arat 대한뇌혈관외과학회 2020 Journal of Cerebrovascular and Endovascular Neuros Vol.22 No.3

Although stroke is common in infective endocarditis (IE), only 26 cases of thrombectomy have been reported to date for IE-related acute stroke. We report a 40-year-old man who presented with left middle cerebral artery occlusion of unknown cause. Multiple attempts of mechanical aspiration thrombectomy and stentrievers failed to recanalize the artery. Effective revascularization was eventually achieved by placing a self-expanding intracranial stent. Post-procedurally the patient was diagnosed with IE with mitral valve insufficiency, mandating emergent valvular replacement while the patient was still on tirofiban infusion. On follow-up, the patient had a modified Rankin’s score of 0, had no recurrent stroke, and the intracranial stent remained patent yet stenosed. Based on the use of a self-expanding intracranial stent in the setting of IE, we discuss the consequences of the fibrotic and inflammatory content of the embolus and the associated high risk of intracranial hemorrhage which complicates clinical decision making.

Influence of Tempering Temperature and Microstructure on Wear Properties of Low Alloy PM Steel with 1-2% Ni Addition

Tekeli Suleyman,Gural Ahmet,Guru Metin 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The effect of tempering temperature and microstructure on dry sliding wear behavior of quenched and tempered PM with 0.3% graphite and 1-2% Ni steels was investigated. The sintered specimens were quenched from 890℃ and then tempered at 200℃ and 600℃ for 1 hr. Wear tests were carried out on the quenched+tempered specimens under dry sliding wear conditions using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively increased with increasing tempering temperature and decreased with increasing Ni content.

Free transverse vibrations of an elastically connected simply supported twin pipe system

Balkaya, Muge,Kaya, Metin O.,Saglamer, Ahmet Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.5

In this paper, free vibration analyses of a parallel placed twin pipe system simulated by simply supported-simply supported and fixed-fixed Euler-Bernoulli beams resting on Winkler elastic soil are presented. The motion of the system is described by a homogenous set of two partial differential equations, which is solved by a simulation method called the Differential Transform Method (DTM). Free vibrations of an elastically connected twin pipe system are realized by synchronous and asynchronous deflections. The results of the presented theoretical analyses for simply supported Euler-Bernoulli beams are compared with existing ones in open literature and very good agreement is demonstrated.