ارائه مدل تجربی تاثیر اندازه نمونه بتنی مسلح به الیافماکروسینتتیک بر عمر خستگی

بتن به عنوان یکی از پرکاربردترین مصالح ساختمانی رفتاری شکننده دارد. افزودن الیاف به بتن بر رفتار شکل پذیری مقاومت کششی ، مقاومت خمشی ، مدول الاستیسیته ، مقاومت ضربه و برخی مشخصات مکانیکی دیگر بتن اثر میگذارد. به همین منظور پژوهشی آزمایشگاهی جهت ارائه مدل تجربی عمر خستگی خمشی بتن مسلح به الیاف ماکروسینتتیک با ساخت تیرچه بتنی با سه ضخامت مختلف 80، 100 و 150 میلیمتر انجام شد و مدل های s-n (سطح تنش-بارگذاری) و h-n (ضخامت-بارگذاری ) ارائه شد. نتایج نشان داد که با افزایش ضخامت نمونه های بتنی و افزودن الیاف به مخلوط بتنی مقدار عمر خستگی افزایش می یابد. همچنین اضافه نمودن الیاف به نمونه های بتنی ضخامت نمونه را برای سطح تنش 0.7 تنش نهایی به میزان 12.45-8.24 % ، برای سطح تنش 0.8 تنش نهایی به میزان 22.15-5.45 % و برای سطح تنش 0.9 تنش نهایی به میزان 22.95-10.18 % کاهش می یابد.

the effect of specimen size on Flexural Fatigue Life of macro-synthetic-fiber-reinforced concretes

Concrete is one of the most widely used building materials for fragile behavior. The addition of fiber to concrete affects the behavior of tensile strength, tensile strength, flexural strength, modulus of elasticity, impact resistance and some other mechanical properties of concrete. For this purpose, an experimental research was carried out to provide an experimental model of the flexural fatigue life of reinforced concrete with macrosynthetic fibers by constructing concrete joists with three different thicknesses of 80, 100 and 150 mm. SN models (stressloading) and HN (thicknessloading) was presented. The results showed that increasing the thickness of concrete samples and adding fibers to concrete mixture increases the fatigue life. Also, the addition of fibers to concrete samples measured the thickness of the sample for the stress level of 0.7 final stresses at 12.458.24%, for the stress level of 0.8, the final stress was 22.155.45%, and for the stress level of 0.9, the final stress decreased to 22.15% 10.18% Finds. Fiberreinforced concrete is a type of concrete that is mixed with fiber. Various types of fibers are used to produce fiberreinforced concrete, which include glass, polymer, carbon and steel. In the present research, macrosynthetic polymer fibers were used. Some of the consequences of applying macrosynthetic fibers in concrete include reduced shrinkage of fresh and hardened concrete, increased ductility, increased strength against fatigue stresses, increased durability and lifetime of concrete, improved concrete mechanical properties (tensile strength, flexural strength, etc.), control of secondary/thermal cracks of concrete, preventing the indepth propagation of cracks, postcracking chargeability and reduced permeability against chloride and sulfate ions .In most of the studies, the concrete samplechr('39')s thickness is increased along with the increase in the beamchr('39')s length; however, in the present work, only thickness of the beam samples with and without fibers was changed and other dimensions of the samples were kept constant in order to investigate merely the effect of increased thickness. Accordingly, effect of the size of macrosynthetic fiberreinforced concrete sample at different thicknesses was assessed via fatigue life variations. The intertwisted fibers were added to the concrete mixture by 0.4 vol.%. Then, from each sample, three specimens were made. The obtained results were averaged and, then, recorded in the relevant tables. The following cases were considered as the research objectives: Effect of sample size on fatigue life of concrete samples Effect of adding macrosynthetic fibers on fatigue life In order to determine flexural fatigue of the concrete samples with the abovementioned geometric properties, UTM device was used. The test was performed with constant sinusoidal loading at the frequency of 10 Hz. The input information for the test included loading curve shape, minimum and maximum loading values, loading frequency, and maximum number of loadings, all of which were defined as the input. To measure the values of stress levels in order for measuring the loading values, first, the average of the sampleschr('39') flexural strength had to be determined; then, the stress levels could be calculated from the obtained results. also A cross sectional analysis of the broken sample showed that most of the sample failure was from aggregate and the mixture design was suitable.