Optimal finite element size in reinforced high-strength concrete beams

Açıklık ortasında tekil yüklü betonarme kirişlerde kesme ve eğilme mukavemetleri; doğrusal olmayan (Drucker-Prager akma kriteri) çözüm yöntemleri temel alınarak deneylerle uyumlu tahmin edilebilmektedir. Bu çalışmada; kesme mukavemetini hesaplamak için kiriş ortasından tekil yükle yüklenmiş donatılı, yüksek mukavemetli beton kirişlerde, deney sonuçları ile tutarlı yük-yerdeğiştirme eğrisini veren uygun sonlu eleman boyutları araştırılmıştır. Karşılaştırmaya tabi tutulan deney serilerinde değişkenler; beton basınç mukavemeti, kesme açıklığının kiriş etkili derinliğine oranı (a/d) ve enine donatı oranıdır. Kirişler doğrusal olmayan çözümlemeye tabi tutulmuş ve sonlu eleman boyutlarının uygun değerleri araştırılmıştır.Anahtar Kelimeler: Kesme mukavemeti, boyut etkisi, yüksek mukavemetli beton, kesme donatısı oran, sonlu elemanlar.Ever since the finite element method was applied to nonlinear problems in the field of reinforced concrete, many researchers have tried to predict the shear and bending strengths of reinforced concrete beams by using various material models for concrete.  In this study; to determine shear strength of reinforced high-strength concrete beams with shear span to depth ratios between 1.5 and 2.5, under concentrated loads at midspan, finite element size effect on load carrying capacity has been investigated analytically. In order to obtain more accurate numerical solutions from the finite element simulation of the reinforced high-strength concrete beams, the beams are evaluated for the different mesh size. Providing a larger size than optimum mesh size configuration for the nonlinear analysis, the whole load-deflection behavior of the beams have been analyzed and the main results of the numerical analyses were compared with the results of reinforced high-strength concrete beams experimental results reported in literature (Shin et al. 1999) to demonstrate how accurately the present mesh size predicts the load carrying capacity. The test variables were compressive strength of concrete, the shear span to depth ratio (a/d) and vertical shear reinforcement ratio for the comparison.  The elasto-plastic analyses of the beams, employing the Drucker-Prager yield criterion for concrete, have been performed and reasonable mesh size has been investigated. Keywords: Shear strength, size effect, high-strength concrete, shear reinforcement ratio, finite element

Contribution of concrete to shear strength of rc beams failing in shear

Reinforced concrete (RC) beams with light transverse reinforcement are vulnerable to shear failure during seismic response. In order to prevent brittle shear failures at beam plastic hinge regions of earthquake-resistant structures, the Turkish Earthquake Code and ACI318 require the use of sufficient transverse reinforcement to resist the total expected shear demand. These codes tend to be excessively conservative and, in some cases, the contribution of the concrete to the shear strength is neglected. The aim of this study is to investigate the contribution of concrete to shear strength of RC beams failing in shear experimentally. The beams were tested under monotonically increasing reversed cyclic loading to determine the concrete contribution to shear strength. It is observed that the concrete contribution to the shear strength at ultimate state ranges from 18% to 69% of the ultimate strength

The relationship between oxidative stress and coronary artery ectasia

Background: Whereas coronary artery ectasia (CAE) is a rare abnormality of the coronary arteries, co-existent coronary artery disease (CAD) is commonly seen in CAE patients. Since a causative relationship has been shown to exist between oxidative stress and CAD, we sought to determine whether any relationship exists between oxidative stress and CAE. Methods: Fourty four patients with CAE (without CAD) and 86 controls (without any coronary disease) were recruited from among 1,520 patients undergoing coronary angiography. CAE subgroups were determined in accordance with the Markis classification system. Mean values for serum total oxidant status (TOS), total antioxidant status (TAS) and the oxidative stress index (OSI) were statistically compared between these two study groups and among CAE subgroups, with p = 0.05 set as the threshold for statistical significance. Results: TOS and OSI were significantly increased (p = 0.018 and 0.0002) and TAS decreased (p = 0.031) in the CAE versus control group. TOS and TAS were independently related to CAE (p = 0.037 and 0.039), with an r2 of 0.127. Interestingly, however, among CAE subgroups, no differences were observed. Conclusions: Oxidative stress might be implicated in the pathogenesis of CAE. Clinically-defined CAE subgroups did not differ in terms of oxidative stress status. However, the clinical implications of these findings are unclear and warrant further investigation. (Cardiol J 2010; 17, 5: 488-494

Evaluation of Agreement Between Sweep Visual Evoked Potential Testing and Subjective Visual Acuity

Objectives:The primary objective of this study was to evaluate the agreement of visual acuity (VA) obtained with the sweep visual evoked potential (sVEP) method with the VA obtained with the Snellen chart. The secondary objective was to examine the effect of age and gender on agreement.Materials and Methods:Best corrected VAs of subjects were recorded with the Snellen chart, and sVEP testing was performed according to the recommendations of the International Society for Clinical Electrophysiology of Vision (ISCEV). Snellen VAs and sVEP measurements were analyzed using logMAR conversion for statistical analysis. Agreement was evaluated with Bland-Altman analysis.Results:The study included 49 subjects with a mean age of 53.5±17.3 years (range: 19-75 years) and mean Snellen VA of 0.31±0.32 logMAR (range: 1.3-0.0 logMAR). In the Bland-Altman analysis, the mean differences between the VA and sVEP measurements (VA-sVEP) were significantly different and outside the limits of agreement (p=0.035). A significant proportional bias (p=0.0007) was found in the regression analysis performed between VA-sVEP and the mean VA. According to the Bland-Altman analysis of sex subgroups, there was a significant difference between VA and sVEP measurements in female subjects (p=0.006). The difference between VA and sVEP measurement increased significantly with older age (R2: 0.306, p<0.001, β: 0.05 [0.03, 0.08]).Conclusion:In conclusion, sVEP measurements and VAs did not show statistical agreement. Cranial anatomy and endocrine differences of the subjects may affect their sVEP measurements. The difference between the methods varies according to VA level. Directly using sVEP results instead of VA would not be appropriate

Characterisation and comparison of disc brake pads of heavy vehicles by experimental methods

In this study, characteristics of disc brake pads of heavy vehicles produced by three different manufacturers were compared experimentally. The former pad is the original (OEM), the latter pad is the subsidiary industrial production (SIPM), and the third pad is the Turkish production (TM). These brake pads which have different compositions; components, wear and friction characteristics, mechanical and physical properties were investigated and also the environment and usage were compared among each other. For chemical analysis, energy distribution spectroscopy (EDS) system integrated with scanning electron microscope (SEM) and X-ray fluorescence (XRF) device were used. Thermal gravimetric (TG) analysis was performed to determine the mass losses in the pad materials. Wear friction tests of pads were made according to JIS D 4411 standard. Apart from these, the hardness, density and internal shear strength values of the pads are measured

Psychometric Properties of Academic Dishonesty Tendency Scale for Graduate Students and Investigating Academic Dishonesty Tendency Levels with CHAID Analysis

The number of unethical academic dishonesty behaviours is increasing with each day in higher education. Thus, it is important to determine the level of the behaviour of academic dishonesty in the education system, the tendencies of students to perform this behaviour, and the individuals who have a tendency to show this behaviour in advance. The research has two different aims. The first one is to determine the psychometric properties of the Academic Dishonesty Tendency Scale (ADTS) originally developed for undergraduate students, not for graduate students. The second aim is to investigate the variables that best explain the academic dishonesty tendency levels of the students who continue their graduate education by using the CHAID analysis method. As a result of the analyses, it was determined that the Academic Dishonesty Tendency Scale is also a valid and reliable measurement tool for graduate students. The only significant variable explaining the students' Tendency Towards Cheating was found to be the level of graduate education. It was also determined that the most important variable affecting the "dishonesty tendency at studies as homework, project, etc.-common" is the level of graduate education. The only significant variable explaining the "dishonesty tendency at research and process of write up" was found to be the reason for receiving graduate education. The most significant variable explaining the "dishonesty tendency towards reference" of the students was found to be the level of graduate education. It was determined that the most significant variable explaining the Academic Dishonesty Tendency of the students is the level of graduate education