Earthquake performance of FRP retrofitting of short columns around band-type windows

Ali Koçak 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.1

Due to design codes and regulations and the variety of building plans in Turkey, it is very often seen that band-type windows are left for ventilation and lightening of the basements of buildings which are used for various purposes such as workplaces and storage. Therefore when the necessary support measurescannot be given, short columns are subjected to very high shear forces and so damage occurs. One of the precautions to avoid the damage of short column mechanisms in buildings where band-type windows are in the basement is to strengthen the short columns with fiber reinforced polymer (FRP). In this study, the effect of the FRP retrofitting process of the short columns around band-windowed structures, which are found especially in basement areas, is analyzed in accordance with Turkish Seismic Code 2007 (TSC 2007). Three different models which are bare frame, frame with short columns andretrofitted short columns with FRP, are created and analyzed according to TSC 2007 performance analysis methods to understand the effects of band windows in basements and the effect of FRP retrofitting.

The effect of short columns on the performance of existing buildings

Ali Koçak 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.4

In this study, the seismic performance of a residential building which was damaged in the 1992Erzincan (Turkey) Earthquake (Ms = 6.8) is performed. Damages on columns due to short columns are estimated analytically implementing the shear hinges and results are compared with the observed damages on the building after the earthquake. In seismic performance evaluation, a deformation based approach is adopted, whereby the structural behavior under external and seismic loads is evaluated. Furthermore, the effects of short columns formed by band windows in basement floors are investigated analytically. The sizes of band windows are parametrically changed in order to understand the effects of short columns on overall building behavior.

Ambient vibration testing and seismic performance of precast I beam bridges on a high-speed railway line

Burak Toydemir,Ali Koçak,Barış Sevim,Basak Zengin 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.5

In this study, the seismic performance levels of four bridges are determined using finite element modeling based on ambient vibration testing. The study includes finite element modeling, analytical modal analyses, ambient vibration testing and earthquake analyses of the bridges. For the purpose, four prestressed precast I beam bridges that were constructed for the Ankara-Sivas high speed railway line are selected for analytical and experimental studies. In the study, firstly a literature review related to the dynamic behavior of bridges especially precast beam bridges is given and then the formulation part related to ambient vibration testing and structural performance according to Turkish Seismic Code (2007) is presented. Next, 3D finite element models of the bridge are described and modeled using LARSA 4D software, and analytical dynamic characteristics are obtained. Then ambient vibration testing conducted on the bridges under natural excitations and experimental natural frequencies are estimated. Lastly, time history analyses of the bridges under the 1999 Kocaeli, 1992 Erzincan, and 1999 Düzce Earthquakes are performed and seismic performance levels according to TSC2007 are determined. The results show that the damage on the bridges is all under the minimum damage limit which is in the minimum damage region under all three earthquakes.

Evaluation of Dry Eye Syndrome in Patients With Familial Mediterranean Fever: A Cross-sectional Study

( Senem Sas ),( Ali Kurt ),( Emine Eda Kurt ),( Fatmanur Aybala Koçak ),( Hatice Rana Erdem ) 대한류마티스학회 2020 대한류마티스학회지 Vol.27 No.4

Objective. It has been reported that some autoimmune diseases are associated with dry eye syndrome. There are limited studies that relates dry eye syndrome in patients with Familial Mediterranean fever (FMF). The aim of this study is to evaluate the relationship between dry eye syndrome in patients with FMF comparing with healthy controls. Methods. Prospective cross-sectional study was carried out in departments of physical medicine and rehabilitation and ophthalmology clinics in a tertiary public institution with a sample of 46 participants including 23 FMF patients and 23 healthy controls. Detailed eye examination was performed in all cases and indicators of xerophthalmia were assessed by Schirmer-I test, tear break-up time (TBUT) and ocular surface disease index (OSDI). In patient group; results of FMF gene analysis, acute phase reactants, concomitant diseases and number of FMF attacks were noted. Results. The average Schirmer-I test results for right-eye were recorded as 14.74±8.38 for the FMF group and 13.09±10.54 for the healthy group; the TBUT scores were 14.69±5.32 in FMF group and 15±6.45 in the healthy group; and OSDI scores were 9.04±2.75 and 10.86±1.77 in the FMF group and the healthy control, respectively. There were no statistically significant differences between FMF and control groups in terms of Schirmer-I, TBUT, and OSDI scores (all p>0.05). No correlation was identified between acute phase reactants and the OSDI, TBUT and Schirmer-I tests for right-eye (all p>0.05). Conclusion. This study identified no correlation between dry eye and FMF. Ocular pathology is rare and infrequently reported in FMF. (J Rheum Dis 2020;27:270-276)

Automated Analysis Approach for the Detection of High Survivable Ransomware

( Yahye Abukar Ahmed ),( Barış Koçer ),( Bander Ali Saleh Al-rimy ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.5

Ransomware is malicious software that encrypts the user-related files and data and holds them to ransom. Such attacks have become one of the serious threats to cyberspace. The avoidance techniques that ransomware employs such as obfuscation and/or packing makes it difficult to analyze such programs statically. Although many ransomware detection studies have been conducted, they are limited to a small portion of the attack's characteristics. To this end, this paper proposed a framework for the behavioral-based dynamic analysis of high survivable ransomware (HSR) with integrated valuable feature sets. Term Frequency-Inverse document frequency (TF-IDF) was employed to select the most useful features from the analyzed samples. Support Vector Machine (SVM) and Artificial Neural Network (ANN) were utilized to develop and implement a machine learning-based detection model able to recognize certain behavioral traits of high survivable ransomware attacks. Experimental evaluation indicates that the proposed framework achieved an area under the ROC curve of 0.987 and a few false positive rates 0.007. The experimental results indicate that the proposed framework can detect high survivable ransomware in the early stage accurately.

A Case of Emetophobia Responding to Mirtazapine and Propranolol Treatment

Merve Köksal,Gökçe Koçak,Yusuf Öztürk,Ali Evren Tufan 대한소화기 기능성질환∙운동학회 2022 Journal of Neurogastroenterology and Motility (JNM Vol.28 No.4

Endoscopic ultrasound-guided gastrojejunostomy with a direct technique without previous intestinal filling using a tubular fully covered self-expandable metallic stent

Hakan Şentürk,İbrahim Hakkı Köker,Koray Koçhan,Sercan Kiremitçi,Gülseren Seven,Ali Tüzün İnce 대한소화기내시경학회 2024 Clinical Endoscopy Vol.57 No.2

Background/Aims: Endoscopic ultrasonography-guided gastrojejunostomy is a minimally invasive method for the management of gastric outlet obstruction. Conventionally, a lumen-apposing metal stent (LAMS) is used to create an anastomosis. However, LAMS is expensive and not widely available. In this report, we described a tubular fully covered self-expandable metallic stent (T-FCSEMS) for this purpose. Methods: Twenty-one patients (15 men [71.4%]; median age, 66 years; range, 40–87 years) were included in this study. A total of 19 malignant (12 pancreatic, 6 gastric, and 1 metastatic rectal cancer) and 2 benign cases were observed. The proximal jejunum was punctured with a 19 G needle. The stomach and jejunum walls were dilated with a 6 F cystotome, and a 20×80 mm polytetrafluoroethylene T-FCSEMS (Hilzo) was deployed. Oral feeding was initiated after 12 to 18 hours and solid foods after 48 hours. Results: The median procedure time was 33 minutes (range, 23–55 minutes). After two weeks, 19 patients tolerated oral feeding. In patients with malignancy, the median survival time was 118 days (range, 41–194 days). No serious complications or deaths occurred. All patients with malignancy tolerated oral food intake until they expired. Conclusions: T-FCSEMS is safe and effective. This stent should be considered as an alternative to LAMS for gastric outlet obstruction.

An Experimental Investigation on Flexural Behavior of RC Beams Strengthened with Different Techniques

M. Mustafa Önal,Bas¸ak Zengin,Ali Koçak,Bilge Doran 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7

In in many earthquake-prone regions and countries including Mediterranean area, India, the Middle East, Southeast Asia, existing buildings with its structural elements such as Reinforced Concrete (RC) beams and columns, which show little ductility, have consistently exhibited poor performance during past earthquakes and consequently unavoidable earthquake damages on these structures led to a significant loss of world cultural heritage. Therefore, appropriate strengthening techniques have to be implemented in order to improve load carrying capacities and overall ductility. This paper summarizes experimental investigations of damaged and undamaged RC beams. In this context, twenty-seven beams were tested under combined bending and shear. Eighteen RC beams were damaged and then strengthened with four different methods while nine were kept undamaged. The behavior of damaged and undamaged RC beams is discussed with emphasis on the load deflection and strain characteristics. The results indicate that the specimens strengthened with full jacketing had slightly higher load carrying capacity than the reference beams strengthened with other techniques. The experimental results can also be used for understanding the most convenient strengthened technique for damaged beams.

Experimental and numerical investigations on spray structure under the effect of cavitation phenomenon in a microchannel

Morteza Ghorbani,Abdolali Khalili Sadaghiani,Mehmet Yidiz,Ali Koşar 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

In this study, the effect of upstream pressure on cavitation flows inside a microchannel with an inner diameter of 152 µm and resulting spray structure were experimentally and numerically investigated. The effects of bubble number density on two-phase flow hydrodynamics were studied using the numerical approach, where transient model was utilized to obtain the changes in vapor quality inside the microchannel and velocity field near the inlet and outlet of the nozzle. Spray visualization was carried out at a distance of 4.5 mm from the tip of the microchannel using the high speed visualization system. The experimental results showed that the spray cone angle increased with upstream pressure, and beyond the upstream pressure of 50 bar, the liquid jet flow changed to the cloudy spray flow. The bubble collapse was recorded at upstream pressures of 100 and 120 bar, where the cavitation bubbles extended to the outlet of the microchannel, and their collapse took place around the spray.

Experimental and numerical analysis of RC structure with two leaf cavity wall subjected to shake table

Onur Onat,Paulo B. Lourenço,Ali Koçak 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.5

This paper presents finite element (FE) based pushover analysis of a reinforced concrete structure with a two-leaf cavity wall (TLCW) to estimate the performance level of this structure. In addition to this, an unreinforced masonry (URM) model was selected for comparison. Simulations and analyses of these structures were performed using the DIANA FE program. The mentioned structures were selected as two storeys and two bays. The dimensions of the structures were scaled 1:1.5 according to the Cauchy Froude similitude law. A shake table experiment was implemented on the reinforced concrete structure with the two-leaf cavity wall (TLCW) at the National Civil Engineering Laboratory (LNEC) in Lisbon, Portugal. The model that simulates URM was not experimentally studied. This structure was modelled in the same manner as the TLCW. The purpose of this virtual model is to compare the respective performances. Two nonlinear analyses were performed and compared with the experimental test results. These analyses were carried out in two phases. The research addresses first the analysis of a structure with only reinforced concrete elements, and secondly the analysis of the same structure with reinforced concrete elements and infill walls. Both researches consider static loading and pushover analysis. The experimental pushover curve was plotted by the envelope of the experimental curve obtained on the basis of the shake table records. Crack patterns, failure modes and performance curves were plotted for both models. Finally, results were evaluated on the basis of the current regulation ASCE/SEI 41-06.