Browsing by Author "Demir A."

Now showing 1 - 20 of 50
  • No Thumbnail Available
    Item
    Synovial chondromatosis of the temporomandibular joint extending to temporalis, masticator, and parotid spaces
    (Lippincott Williams and Wilkins, 2001) Yildiz S.T.; Demir A.; Kaya A.
    Synovial chondromatosis of the temporomandibular joint (TMJ) is very rare. We report a case of synovial chondromatosis of the TMJ with extraarticular extension that was diagnosed with MRI and CT. Histopathologic evaluation indicated that this case was synovial chondromatosis in intermediate phase.
  • No Thumbnail Available
    Item
    A case of large mucinous adenocarcinoma arising in a long-standing fistula-in-ano
    (2003) Erhan Y.; Sakarya A.; Aydede H.; Demir A.; Seyhan A.; Atici E.
    Background: Chronic anal fistulas are not rare conditions, however, the development of a carcinoma in a long-standing fistula-in-ano is rare. Methods: The case of a 77-year-old male with a large perianal mucinous adenocarcinoma arising in a long-standing fistula-in-ano is presented. Results: Perianal biopsy revealed mucinous adenocarcinoma. Abdominal CT, double contrast barium examination and flexible sigmoidoscopy revealed no other tumoral lesion in the colon and rectum. Conclusion: The patient underwent abdominoperineal resection including wide tumor excision on the gluteal region. The final reconstruction was performed by bilateral gracilis musculocutaneous flaps. Due to clinical and histopathological evidence it was thought that a curative resection had been performed. To date he is clinically disease free. Copyright © 2003 S. Karger AG, Basel.
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    Item
    Correction of node mapping distortions using universal serendipity elements in dynamical problems
    (Techno-Press, 2011) Küçükarslan S.; Demir A.
    In this paper, the use of universal serendipity elements (USE) to eliminate node mapping distortions for dynamic problem is presented. Rectangular shaped elements for USE are being introduced by using a flexible master element with an adjustable edge node location. The shape functions of the universal serendipity formulation are used to derive the mass and damping matrices for the dynamic analyses. These matrices eliminate the node mapping distortion errors that occurs incase of the standard shape function formulations. The verification of new formulation will be tested and the errors encountered in the standard formulation will be studied for a dynamically loaded deep cantilever.
  • No Thumbnail Available
    Item
    Strengthening of reinforced concrete (RC) beams with prefabricated reinforced concrete (RC) plates
    (Academic Journals, 2011) Demir A.; Tekin M.
    Reinforced concrete (RC) beams which are insufficient in terms of shear and flexural capacities are strengthened by various methods. Steel and fibre reinforced polymer (FRP) plate bonding methods are very widely used in strengthening of beams. Strengthening methods such as bonding steel and FRP plates have deficiencies as corrosion, fire and buckling. In this work, it is aimed strengthening of damaged RC beams using prefabricated RC rectangular and U cross-sectional plates. The rectangular cross-sectional plates were bonded to the bottom sides of the beams by rods and epoxy. The plates having U cross-section were bonded to the three sides of the beams. The strengthened beams were incrementally loaded up to maximum load capacities. The load carrying capacity of the beams increased 41% with the strengthening rectangular cross-sectional plates, however when the U cross-sectional plates were used, the capacity increased up to 76%. The experimental results were compared with the theoretical values. In addition, post-elastic strength enhancement and displacement ductility of beams were investigated. The advantages of this method do not require shuttering, concrete and steel workmanships in situ. Also, the application of this method is very easy and economic. For these reasons, this method should be preferred against other methods. © 2011 Academic Journals.
  • No Thumbnail Available
    Item
    Strengthening of Rc beams with prefabricated RC rectangular cross-sectional plates
    (Association for Scientific Research, 2011) Tekin M.; Demir A.; Turali T.; Nohutçu H.; Bagci M.
    The topic of this study is to strengthen cracked beams with prefabricated RC rectangular cross-sectional plates. The damaged beams were repaired by epoxy based glue. The repaired beams were strengthened using prefabricated RC rectangular crosssectional plates. The strengthening plates were bonded to the bottom face of the beams by anchorage rods and epoxy. The strengthened beams were incrementally loaded up to maximum load capacities. The experimental results were satisfactory since the load carrying capacities of damaged beams were increased approximately 47% due to strengthening. The post-elastic strength enhancement and the displacement ductility of all the beams are researched during the experiments. The experimental program was supported by a three-dimensional nonlinear finite element analysis. The experimental results were compared with the results obtained from the beam modeled with ANSYS finite element program. © Association for Scientific Research.
  • No Thumbnail Available
    Item
    A comparative evaluation of performance based analysis procedures according to 2007 Turkish Earthquake Code and FEMA-440
    (Association for Scientific Research, 2011) Erdem R.T.; Baǧci M.; Demir A.
    Chapter 7 of the 2007 Turkish Earthquake Code (TEC) entitled "Assessment and Strengthening of Existing Buildings" sets standards for assessment and rehabilitation of existing buildings. Linear elastic and non-linear evaluation procedures of 2007 TEC are applied to reinforced concrete buildings. 2007 TEC gives two methods for assessment and rehabilitation of existing buildings. Linear elastic and non-linear static evaluation procedures are proposed for structural evaluation. A performance-based evaluation methodology is used under three levels of earthquake ground motion intensities with different return periods. The performance acceptance criteria are based on demand to capacity ratios at critical sections for the linear evaluation procedures (equivalent seismic load method and mode superposition method) and material strains for the non-linear evaluation procedures (the non-linear static pushover analysis). Member performance limits are described for three damage levels, considering the anticipated failure mode and ductility capacity of each member. Structural performance is then calculated by accounting for the distribution of member damages over the building.. Consistency between the results of the methods used for seismic evaluation of existing buildings is of prime importance. For this purpose, an irregular structure of in plane (A3 type) and 3 story is considered. The target performance level of the building is obtained by applying the linear and the non-linear evaluation procedures. The results are given comparatively on the target performance level of the building. Furthermore non-linear procedure results are compared between 2007TEC and FEMA-440 Capacity-Spectrum Method (CSM) and Displacement- Coefficient Method (DCM). © Association for Scientific Research.
  • No Thumbnail Available
    Item
    Comparison of nonlinear static and dynamic analyses on a R/C building
    (Association for Scientific Research, 2013) Tekin M.; Gürbüz A.; Demir A.
    In recent years, nonlinear calculation methods can be easily carried out by means of developing computer technologies. In this way, comparisons of the nonlinear methods have started to increase rapidly and more studies are carried out on regular and irregular buildings. However, it is most important to compare consistency of the methods on buildings. In this study, most common nonlinear static (pushover) and nonlinear dynamic analysis (time history analysis) methods were compared on an asymmetric planned reinforced concrete (R/C) building. Building having horizontal and vertical irregularities was 5-story. Analyses were carried out by using SAP2000 program. The results are discussed in terms of base shear, lateral displacements and top displacement ratios.
  • No Thumbnail Available
    Item
    The behavior of masonry walls with reinforced plaster mortar
    (2013) Basaran H.; Demir A.; Bagci M.
    The purpose of this study is the improvement of the behaviors of walls constructed with masonry bricks using reinforced plaster mortars. In this study, 400 × 400 × 100 mm sized walls were constructed using 1: 2 scaled 100 × 50 × 30 mm sized masonry bricks. The walls were plastered using normal and various proportions of polypropylene and steel fiber reinforced plaster mortars and were subjected to vertical loads at 30°, 45°, 60°, and 90° angles. As a result of the experiments, attempts were made to present the strength, stiffness, and ductility of all of the walls. At the end of the study, an evaluation concerning failure envelope curve (σ - τ) obtained from test results according to plastered masonry walls types was performed. © 2013 Hakan Basaran et al.
  • No Thumbnail Available
    Item
    Strengthening of RC beams with prefabricated RC U cross-sectional plates
    (Techno-Press, 2014) Demir A.; Tekin M.; Turali T.; Bagci M.
    The topic of this study is to strengthen cracked beams with prefabricated RC U cross-sectional plates. The damaged beams were repaired by epoxy based glue. The repaired beams were strengthened using prefabricated plates. The strengthening plates were bonded to the bottom and side faces of the beams by anchorage rods and epoxy. The strengthened beams were incrementally loaded up to maximum load capacities. The experimental results were satisfactory since the load carrying capacities of damaged beams were increased approximately 76% due to strengthening. It was observed that strengthening plates had a dominant effect on the performance of beams in terms of both the post-elastic strength enhancement and the ductility. The experimental program was supported by a three-dimensional nonlinear finite element analysis. The experimental results were compared with the results obtained from the beam modeled with ANSYS finite element program. Copyright © 2014 Techno-Press, Ltd.
  • No Thumbnail Available
    Item
    The association between insulin resistance and hepatic fibrosis in patients with chronic hepatitis C: An observational, multicenter study in Turkey
    (Turkish Society of Gastroenterology, 2014) Dökmeci A.; Üstündaʇ Y.; Hulagu S.; Tuncer I.; Akdoʇan M.; Demirsoy H.; Köklü S.; Güzelbulut F.; Doʇan I.; Demir A.; Akarsu M.; Yüceyar H.; Özdogan O.C.; Özdener F.; Erdoʇan S.
    Background/Aims: To evaluate the association between insulin resistance and hepatic fibrosis in patients with chronic hepatitis C.; Materials and Methods: A total of 104 chronic hepatitis C patients were included in this non-interventional, open-label, observational, multicenter, cross-sectional study conducted at 20 gastroenterology clinics in Turkey. The primary end point was the correlation between stage of hepatic fibrosis and insulin resistance evaluated via the homeostasis model of assessment-insulin resistance index. Confounders of hepatic fibrosis and insulin resistance were the secondary end points.; Results: The mean age of patients was 52.8 years; 65.4% were female. Type 2 diabetes was present in 6.8% and insulin resistance noted in 38.0% of patients. Further, 45.7% of the patients had mild (A0/A1) and the remaining had moderate/severe (A2/A3) hepatic necroinflammatory activity. Patient distribution according to Metavir fibrosis stage was as follows: F0/F1 (57.0%); F2 (6.5%); F3 (23.7%); and F4 (12.9%). A univariate analysis revealed significant positive correlations between Metavir fibrosis stage and insulin resistance (r=0.297; p=0.007). Logistic regression analysis showed that significant predictors of insulin resistance were high alanine transaminase levels (odds ratio, 0.97; 95% confidence interval, 0.944-0.997) and liver fibrosis stage (odds ratio, 0.114; 95% confidence interval, 0.021-0.607).; Conclusion: Our findings revealed significant associations between insulin resistance and hepatic fibrosis. © 2014 by The Turkish Society of Gastroenterology.
  • No Thumbnail Available
    Item
    Pulsed Nd: YAG laser shock processing effects on mechanical properties of 6061-T6 alloy
    (2014) Gencalp Irizalp S.; Saklakoglu N.; Akman E.; Demir A.
    The aim of this paper is to investigate effects of single and double shot Nd:YAG laser shock processing (LSP) on residual stress, micro-hardness and tensile properties of 6061-T6 aluminum alloy. The X-ray diffraction technique was used to measure surface residual stress in LSP-treated 6061-T6 samples. The magnitude and directional dependence of the surface residual stress after single shot and double shot LSP were investigated with the sin2 Ψ method. The results show that laser shock processing can significantly increase surface compressive residual stress. In addition, micro-hardness of the LSP-treated sample was measured using a Vickers diamond indenter depending on the depth. The tensile tests of the single shot and double shot LSP-treated and untreated samples were carried out by the Schimadzu tensile testing machine having a video extensometer. Experimental results show that the values of micro-hardness, tensile strength and uniform elongation increase by LSP. © 2013 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Shaking table study of masonry buildings with reinforced plaster; [Ispitivanje zidanih gradevina s armiranom žbukom na vibracijskom stolu]
    (Union of Croatian Civil Engineers and Technicians, 2014) Ba̧aran H.; Demir A.; Bagci M.; Ercan E.
    The objective of this study is to determine seismic behaviour of masonry buildings with reinforced plaster mortar, with a particular focus on the modification of structural response due to application of the polypropylene and steel reinforced plaster, as compared to an ordinary type of plaster. The resistance of one-storey single-span masonry buildings subjected to seismic load on the shaking table is investigated in the study. Experimental results revealed natural periods, response acceleration spectrums, and spectrum interactions of masonry buildings. In addition, finite element models of test buildings were established, and their results were compared with those obtained during experimental study.
  • No Thumbnail Available
    Item
    Near surface modification of aluminum alloy induced by laser shock processing
    (Elsevier Ltd, 2014) Saklakoglu N.; Gencalp Irizalp S.; Akman E.; Demir A.
    This paper investigates the influences of near surface modification induced in 6061-T6 aluminum alloy by laser shock processing (LSP). The present study evaluates LSP with a Q-switched Nd:YAG low power laser using water confinement medium and absorbent overlay on the workpiece. The near surface microstructural change of 6061-T6 alloy after LSP was studied. The residual stress variation throughout the depth of the workpiece was determined. The results showed an improvement of the material resistance to pit formation. This improvement may be attributed to compressive residual stress and work-hardening. The size and number of pits revealed by immersion in an NaOH-HCl solution decreased in comparison with the untreated material. © 2014 Elsevier Ltd.
  • No Thumbnail Available
    Item
    Effects of fiber reinforced plaster on the earthquake behavior of masonry buildings
    (Shiraz University, 2015) Başaran H.; Demir A.; Baǧci M.; Ercan E.
    In this paper the traditional covering plaster of masonry buildings is supplied with Polypropylene and steel fiber to enhance their seismic behavior. The plaster mix proportion is determined by some initial mortar tests. Also, one story, single span masonry building specimen plastered with different mortars is tested on a shaking table 8 times under a seismic input and the performance of the specimens with the above types of mortar is evaluated. The specimen plastered with a traditional plaster was regarded as control and its earthquake behavior was compared to that reinforced by fiber plaster. Steel fiber or polypropylene addition significantly increased stiffness, displacement ability and energy consumption ability of specimens as compared to control. The suggested reinforcement method was proven to strengthen masonry buildings in a fast, reliable and economical way. Moreover, it can easily be adapted to any masonry building without causing any negative impact. The suggested method is fire and corrosion resistant. © Shiraz University.
  • No Thumbnail Available
    Item
    Prediction of Hybrid fibre-added concrete strength using artificial neural networks
    (Techno-Press, 2015) Demir A.
    Fibre-added concretes are frequently used in large site applications such as slab and airports as well as in bearing system elements or prefabricated elements. It is very difficult to determine the mechanical properties of the fibre-added concretes by experimental methods in situ. The purpose of this study is to develop an artificial neural network (ANN) model in order to predict the compressive and bending strengths of hybrid fibre-added and non-added concretes. The strengths have been predicted by means of the data that has been obtained from destructive (DT) and non-destructive tests (NDT) on the samples. NDTs are ultrasonic pulse velocity (UPV) and Rebound Hammer Tests (RH). 105 pieces of cylinder samples with a dimension of 150 × 300 mm, 105 pieces of bending samples with a dimension of 100×100×400 mm have been manufactured. The first set has been manufactured without fibre addition, the second set with the addition of %0.5 polypropylene and %0.5 steel fibre in terms of volume, and the third set with the addition of %0.5 polypropylene, %1 steel fibre. The water/cement (w/c) ratio of samples parametrically varies between 0.3-0.9. The experimentally measured compressive and bending strengths have been compared with predicted results by use of ANN method. Copyright © 2015 Techno-Press, Ltd.
  • No Thumbnail Available
    Item
    Strengthening of brick masonry with PVA fiber reinforced cement stucco
    (Elsevier Ltd, 2015) Arisoy B.; Ercan E.; Demir A.
    This paper presents the behavior of masonry walls externally strengthened by poly vinyl alcohol (PVA) fiber reinforced cement plaster. Tensile weakness of masonry wall is improved by simply applying fiber reinforced cement (FRC) plaster on masonry surface. Strengthening by ductile materials, in order to maintain ductile behavior of masonry to resist shear forces would provide reduction in the crack development and crack width providing delay in failure. FRC was applied to surfaces of the masonry wall as stucco to prevent crack growth under shear effect. An experimental program was performed to study the response of unreinforced and retrofitted masonry walls with externally applied fiber reinforced cement mixture, under shear and compressive loading. The experimental results indicate that retrofitting masonry walls with PVA fiber reinforced cement stucco increases the shear strength of the wall approximately half times in solid and high strength brick walls, 2.5 times in regular brick walls. © 2015 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Effect of Hysteretic Models on Seismic Behavior of Existing RC Structures
    (American Society of Civil Engineers (ASCE), 2015) Ergun S.; Demir A.
    The aim of this study is to investigate the effect of hysteretic models on displacement demands of reinforced concrete (RC) structures having various irregularities and determine more proper hysteretic models for different types of RC structures. The RC structures having irregularities such as soft story and overhang were analyzed with nonlinear pushover and nonlinear time-history methods. Concrete compressive strength, stirrup amount, and the number of stories for the structures were variable parameters. Totally, 25,664 analyses were carried out. Displacement capacities and performance levels of structures were determined using nonlinear pushover analysis. Exceedance ratios of performance levels and displacements demanded from the structures of 100 severe ground motions that occurred worldwide were obtained using nonlinear time-history analysis (NTHA). In NTHA, various hysteretic models were used to define inelastic behavior of RC structures. The analyses show that the hysteretic models have a significant effect on displacement demands of RC structures. Finally, proper hysteretic models are suggested according to the type of structure and purpose of occupancy. © 2014 American Society of Civil Engineers.
  • No Thumbnail Available
    Item
    RC beam strengthening using precast RC plate bonding technique; [Ojačanje ab greda tehnikom povezivanja s predgotovljenom ab pločom]
    (Union of Croatian Civil Engineers and Technicians, 2015) Demir A.; Bagci M.; Tekin M.; Nuhoglu A.
    The behaviour of RC beams strengthened with precast RC plates of rectangular and U cross-section is studied in the paper. An experimental investigation was conducted to assess effectiveness of strengthening with precast plates. The investigation was supported with the 2-D nonlinear finite element analysis (NLFEA). The NLFEA results showed agood level of correlation with test results. The proposed technique is considered to be a good alternative to RC jacketing and the technique is practical, economical and reliable for buildings or bridges with a greater number sisof similar beams.
  • No Thumbnail Available
    Item
    Experimental and numerical investigation of walls strengthened with fiber plaster
    (Techno-Press, 2015) Başaran H.; Demir A.; Baʇci M.; Ergun S.
    The topic of this study is to investigate behaviors of masonry walls strengthened with reinforced fiber plaster under diagonal tensile loads. Full blend brick 100×50×30 mm in dimensions were used to make masonry walls with dimensions of 400×400×100 mm. Three different samples were manufactured by plastering masonry walls with traditional style, with 3% polypropylene or with 5% steel fiber. All the samples were tested using ASTM 1391- 81 standards. The propagation of damage on samples caused by diagonal tensile load was observed and load-displacement graphs were plotted for each sample. A finite element software (ABAQUS) was used to obtain numerical values for all samples and crack patterns and load-displacement responses were obtained. Experimental and numerical results were compared. Copyright © 2015 Techno-Press, Ltd.