Mechanical Investigation and Durability of HDPE-confined SCC Columns Exposed to Severe Environment

Ahmet Emin Kurtoglu,Ali Khalid Hussein,Mehmet Eren Gulsan,Mehmet Fatih Altan,Abdulkadir Cevik 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.12

This paper aims at investigating the mechanical properties and short term durability performance of Self-Compacting Concrete (SCC) – filled High Density Polyethylene (HDPE) tubes with and without steel fibers. A total of 45 cylinder specimens were prepared and subjected to aggressive substances such as sulfate or acid contents. At the end of each exposure, the specimens were instrumented and tested under axial compression. Test variables included the environmental exposure conditions, tube thickness, inside diameter, tube height and steel fiber presence. The load-strain behavior was inspected to evaluate the effect of each exposure. The results indicated that peak load reduction in HDPE-confined specimens is only about 0.3-1% whereas this reduction is around 45 -50% for unconfined specimens. In addition, increasing tube thickness by 30% results in up to 50% higher fracture energy. Results also indicate that steel fiber addition has little contribution (0.3-1%) in load capacity whereas the energy absorption capacity is increased up to 20%.

Mechanical and durability properties of fly ash and slag based geopolymer concrete

Kurtoglu, Ahmet Emin,Alzeebaree, Radhwan,Aljumaili, Omar,Nis, Anil,Gulsan, Mehmet Eren,Humur, Ghassan,Cevik, Abdulkadir Techno-Press 2018 Advances in concrete construction Vol.6 No.4

In this paper, mechanical and short-term durability properties of fly ash and slag based geopolymer concretes (FAGPC-SGPC) were investigated. The alkaline solution was prepared with a mixture of sodium silicate solution ($Na_2SiO_3$) and sodium hydroxide solution (NaOH) for geopolymer concretes. Ordinary Portland Cement (OPC) concrete was also produced for comparison. Main objective of the study was to examine the usability of geopolymer concretes instead of the ordinary Portland cement concrete for structural use. In addition to this, this study was aimed to make a contribution to standardization process of the geopolymer concretes in the construction industry. For this purpose; SGPC, FAGPC and OPC specimens were exposed to sulfuric acid ($H_2SO_4$), magnesium sulfate ($MgSO_4$) and sea water (NaCl) solutions with concentrations of 5%, 5% and 3.5%, respectively. Visual inspection and weight change of the specimens were evaluated in terms of durability aspects. For the mechanical aspects; compression, splitting tensile and flexural strength tests were conducted before and after the chemical attacks to investigate the residual mechanical strengths of geopolymer concretes under chemical attacks. Results indicated that SGPC (100% slag) is stronger and durable than the FAGPC due to more stable and strong cross-linked alumina-silicate polymer structure. In addition, FAGPC specimens (100% fly ash) showed better durability resistance than the OPC specimens. However, FAGPC specimens (100% fly ash) demonstrated lower mechanical performance as compared to OPC specimens due to low reactivity of fly ash particles, low amount of calcium and more porous structure. Among the chemical environments, sulfuric acid ($H_2SO_4$) was most dangerous environment for all concrete types.

Is Surgical Staging Necessary for Patients with Low-risk Endometrial Cancer? A Retrospective Clinical Analysis

Kokcu, Arif,Kurtoglu, Emel,Celik, Handan,Kefeli, Mehmet,Tosun, Migraci,Onal, Mesut Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.13

Purpose: The aim of this study was to compare the tumor-free and overall survival rates between patients with low-risk endometrial cancer who underwent surgical staging and those who did not undergo surgical staging. Materials and Methods: Data, including demographic characteristics, grade of the tumor, myometrial invasion, cervical involvement, peritoneal washing, lymph node involvement, lymphovascular space invasion, postoperative complication, adjuvant treatment, cancer recurrence, and tumor-free and overall survival rates, for patients with low-risk endometrioid endometrial cancer who were treated surgically with and without pelvic and paraaortic lymph node dissection (LND) were analyzed retrospectively. The patients diagnosed with endometrioid endometrial cancer including the following criteria were considered low-risk: 1) a grade 1 (G1) or grade 2 (G2) endometrioid histology; 2) myometrial invasion of <50% upon magnetic resonance imaging (MRI); 3) no stromal glandular or stromal invasion upon MRI; and 4) no evidence of intra-abdominal metastasis. Then the patients at low-risk were divided into two groups; group 1 (n=117): patients treated surgically with pelvic and paraaortic LND and group 2 (n=170): patients treated surgically without pelvic and paraaortic LND. Results: There was no statistical significance when the groups were compared in terms of lymphovascular space invasion, cervical involvement, positive cytology, and recurrence, whereas the administration of an adjuvant therapy was higher in group 2 (p<0.005). The number of patients with positive pelvic nodes and the number of metastatic pelvic nodes were significantly higher in the group with positive LVI than in the group without LVI (p<0.005). No statistically significant differences were detected between the groups in terms of tumor-free survival (p=0.981) and overall survival (p=0.166). Conclusions: Total hysterectomy with bilateral salpingo-oophorectomy and stage-adapted postoperative adjuvant therapy without pelvic and/or paraaortic lymphadenectomy may be safe and efficient treatments for low-risk endometrial cancer.

Reliability-based modeling of punching shear capacity of FRP-reinforced two-way slabs

Ahmet Emin Kurtoglu,Abdulkadir Cevik,Hasan M. Albegmprli,Mehmet Eren Gulsan,Mahmut Bilgehan 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.1

This paper deals with the reliability analysis of design formulations derived for predicting the punching shear capacity of FRP-reinforced two-way slabs. Firstly, a new design code formulation was derived by means of gene expression programming. This formulation differs from the existing ones as the slab length (L) was introduced in the equation. Next, the proposed formulation was tested for its generalization capability by a parametric study. Then, the stochastic analyses of derived and existing formulations were performed by Monte Carlo simulation. Finally, the reliability analyses of these equations were carried out based on the results of stochastic analysis and the ultimate state function of ASCE-7 and ACI-318 (2011). The results indicate that the prediction performance of new formulation is significantly higher as compared to available design equations and its reliability index is within acceptable limits.

Fiber reinforced concrete corbels: Modeling shear strength via symbolic regression

Ahmet E Kurtoglu,Mehmet E Gulsan,Hussein A Abdi,Mohammed A Kamil,Abdulkadir Cevik 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.1

In this study, a novel application of symbolic regression (SR) is employed for the prediction of ultimate shear strength of steel fiber reinforced (SFRC) and glass fiber reinforced (GFRC) corbels without stirrups, for the first time in the literature. A database is created using the test results (42 tests) conducted by the authors of current paper as well as the previous studies available in the literature. A symbolic regression based empirical formulation is proposed using this database. The formulation is unique in a way that it has the capability to predict the shear strength of both SFRC and GFRC corbels. The performance of proposed model is tested against randomly selected testing set. Additionally, a parametric study with a wide range of variables is carried out to test the effect of each parameter on the shear strength. The results confirm the high prediction capacity of proposed model.

Single Stage Repair for Aortic Coarctation associated with Intracardiac Defects Using Extra-Anatomic Bypass Graft in Adults

Ibrahim Duvan,Mehmet Sanser Ates,Burak Emre Onuk,Beyhan Bakkaloglu,Umit Pinar Sungur,Murat Kurtoglu,Yahya Halidun Karagoz 대한심장학회 2016 Korean Circulation Journal Vol.46 No.4

Background and Objectives: Coarctation of the aorta in adulthood is generally associated with other cardiovascular disorders requiring surgical management. An extra anatomic bypass grafting from the ascending to descending aorta by posterior pericardial approach via median sternotomy could be a reasonable single stage surgical strategy for these patients. Subjects and Methods: Seven male patients aged between 14-41 years underwent an extra anatomic bypass grafting for coarctation repair concomitantly with the surgical management of the associated cardiovascular disorders via median sternotomy. Preoperative mean systolic arterial blood pressure was 161.8±24.5 mmHg, although the patients were under treatment of different combinations of antihypertensive agents. Additional surgical procedures were: aortic valve replacement (n=4), ventricular septal defect (VSD) closure (n=2), ascending aortic replacement (n=3) and Bentall procedure (n=1). None of our patients have been previously diagnosed or operated on for coarctation. Data were evaluated during their hospital stay and in post-operative follow-up. Results: The post-operative course was uneventful in all but one patient was re-operated on due to bleeding. There was neither mortality nor significant morbidity during the in-hospital period and all patients were discharged within 5-9 (mean: 6.3±1.5) days. The mean follow up period was 71.83±23 months (range: 23-95 months). Unfortunately one of our patients could not be contacted for a follow up period because of invalid personal data. Conclusion: Coarctation of the aorta in adulthood associated with other cardiovascular disorders can be operated on simultaneously via an extra anatomic bypass grafting technique with low morbidity and mortality.

Optimal Selection of Arm Inductance and Switching Modulation for Three-Phase Modular Multilevel Converters in Terms of DC Voltage Utilization, Harmonics and Efficiency

Arslan, Ali Osman,Kurtoglu, Mehmet,Eroglu, Fatih,Vural, Ahmet Mete The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

The arm inductance (AI) of a modular multilevel converter (MMC) affects both the fault and circulating current magnitudes. In addition, it has an impact on the inverter efficiency and harmonic content. In this study, the AI of a three-phase MMC is optimized in a novel way in terms of DC voltage utilization, harmonics and efficiency. This MMC has 10 submodules (SM) per arm and the power circuit topology of the SM is a half-bridge. The optimum AI is adopted and verified in an MMC that has 100 SMs per arm. Then the phase shift (PS) and phase disposition (PD) pulse width modulation (PWM) methods are investigated for better DC voltage utilization, efficiency and harmonics. It is found that similar performances are obtained for both modulation techniques in terms of DC voltage utilization. However, the total harmonic distortion (THD) of the PS-PWM is found to be 0.02%, which is slightly lower than the THD of the PD-PWM at 0.16%. In efficiency calculations, the switching and conduction losses for all of the semiconductor are considered separately and the minimum efficiency of the 100-SM based MMC is found to be 99.62% for the PS-PWM and 99.64% for the PD-PWM with the optimal value of the AI. Simulation results are verified with an experimental prototype of a 6-SM based MMC.

Optimal Selection of Arm Inductance and Switching Modulation for Three-Phase Modular Multilevel Converters in Terms of DC Voltage Utilization, Harmonics and Efficiency

Ali Osman Arslan,Mehmet Kurtoglu,Fatih Eroglu,Ahmet Mete Vural 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

The arm inductance (AI) of a modular multilevel converter (MMC) affects both the fault and circulating current magnitudes. In addition, it has an impact on the inverter efficiency and harmonic content. In this study, the AI of a three-phase MMC isoptimized in a novel way in terms of DC voltage utilization, harmonics and efficiency. This MMC has 10 submodules (SM) perarm and the power circuit topology of the SM is a half-bridge. The optimum AI is adopted and verified in an MMC that has 100SMs per arm. Then the phase shift (PS) and phase disposition (PD) pulse width modulation (PWM) methods are investigated forbetter DC voltage utilization, efficiency and harmonics. It is found that similar performances are obtained for both modulationtechniques in terms of DC voltage utilization. However, the total harmonic distortion (THD) of the PS-PWM is found to be0.02%, which is slightly lower than the THD of the PD-PWM at 0.16%. In efficiency calculations, the switching and conductionlosses for all of the semiconductor are considered separately and the minimum efficiency of the 100-SM based MMC is found tobe 99.62% for the PS-PWM and 99.64% for the PD-PWM with the optimal value of the AI. Simulation results are verified withan experimental prototype of a 6-SM based MMC.

The effects of compression garments and electrostimulation on athletes’ muscle soreness and recovery

Yunus Turgay Erten,Turker Sahinkaya,Engin Dinc,Bekir Eray Kilinc,Bulent Bayraktar,Mehmet Kurtoglu 한국운동재활학회 2016 JER Vol.12 No.4