بررسی پارامترهای موثر بر رفتار تیرهای بتن‌آرمه برش کنترل با احتساب اندرکنش برش- خمش

در تحلیل و طراحی‌های متعارف تیر‌های بتن‌آرمه مطابق با اکثر آیین‌نامه‌ها، طراحی برای خمش و برش، بدون در نظر گرفتن اثرات اندرکنشی میان آنها انجام می‌شود. جهت برآورد یک دیدگاه دقیق از رفتار تیر‌های بتن‌آرمه می بایستی حتماً اثرات اندرکنشی میان برش و خمش نیز در نظر گرفته شود. در این پژوهش با روشی ابتکاری، تعداد 27 تیر بتن‌آرمه دو سر مفصل برش-کنترل، مورد آنالیز و ارزیابی توالی خرابی با احتساب اندرکنش برش-خمش قرار گرفته و دوران برشی مفصل پلاستیک بحرانی هر یک از تیر‌ها محاسبه شد. اساس کار به این صورت است که در ابتدا برای هر یک از تیر‌ها نرخ افزایش بار برش-خمش محاسبه شده و پس از تحلیل به روش میدان فشاری اصلاح شده mcft، منحنی کامل رفتاری برشی و خمشی تیر به دست آمد. مقادیر دوران پلاستیک برشی مربوط به مفصل بحرانی هر یک از تیر‌های مدل شده، بر اساس متغیر‌های طول تیر، فواصل تنگ‌ها و مقاومت فشاری بتن محاسبه شد. در تیرهای با طول کوتاه، افزایش مقاومت فشاری بتن و کاهش فواصل میان تنگ‌ها موجب دوران پلاستیک برشی بیشتری شده، اما در تیرهای با طول بلند تر به دلیل رفتار خمشی تیر، افزایش فواصل میان تنگ‌ها موجب دوران پلاستیک برشی بیشتری شد. با توجه به نتایج پژوهش، مقادیر پیشنهادی برای دوران پلاستیک برشی تیر‌های بتن‌آرمه با طبقه‌بندی مشخص ارائه گردید که می‌تواند در تحلیل‌های غیرخطی به روش مفصل پلاستیک و پروژه‌های مقاوم‌سازی و بهسازی لرزه‌ای مورد استفاده قرار گیرد.

investigation of effective parameters on the behavior of shear control reinforced concrete beams including shear-flexure interaction

in conventional analysis and design of reinforced concrete beams in accordance with most codes, the design for flexure and shear is done separately and without considering the interaction effects between them. uncertainty about shear in reinforced concrete beams due to the brittle nature of concrete in shear behavior causes the shear ductility of beams not to be used in linear analyzes and considering a large safety margin for the shear ductility of these beams in non-linear analyses using the plastic hinge method. axial force and shear force have a significant impact on the flexural behavior of a concrete element. axial force and shear force can be either constant due to gravity loads and... or variable due to seismic loads. the seismic standard asce 41-17 in table 7-10 provides values ​​as the shear plastic rotation for use in the nonlinear analysis of shear-controlled reinforced concrete beams, based on a single division (only the distance between the stirrups) and a high margin of confidence. by providing a more realistic classification, if necessary, shear ductility can also be utilized in non-linear analyses and seismic retrofitting and rehabilitation projects to meet seismic requirements. in this paper, by an innovative method, 27 reinforced concrete beams with simply-supported and shear-control are analyzed and evaluated for damage sequences in response2000, excel, sap2000 software, taking into account the shear-flexure interaction, and the critical shear plastic hinge rotation values of each one of the beams was calculated. the fiber model will be accurate enough when it correctly simulates the interaction between v-m-p. response2000 software is one of the user-friendly software that performs these calculations for limited sections. the basis of the work is that at first for each beam, the rate of increment loads of shear-flexure is calculated and after fiber analysis, the complete shear and flexural behavior curve of the beam is obtained. after ensuring that the shear behavior of the beams is controlled by shear, the values of the shear plastic rotation related to the critical hinge of each of the modeled beams have been calculated and graphed based on the beam length variables, stirrup distances and the compressive strength of the concrete. the shorter the length of the beam, due to the increase in moment stiffness, it is possible to use stirrups with shorter intervals for more shear plastic rotation. in this case, increasing the compressive strength of concrete also helps to increase the shear plastic rotation. in short-length beams, if they are not considered deep beams, the distances between the stirrups have an inverse relationship with the amount of shear plastic rotation, and in longer-length beams, the relationship between the mentioned parameters will be direct. the longer the length of the beam becomes, because the concrete of the beam must also serve in moment in addition to shear, it does not have enough strength to yield and tensile the stirrups with close distances, and in such a situation, by increasing the distance between the stirrups, the shear plastic rotation can be relatively increased. the maximum amount of shear plastic rotation in reinforced concrete beam occurs when the length of the beam is short and the distances between the transverse reinforcements are small. increasing the compressive strength of concrete also increases the amount of shear plastic rotation in the beam. in short-length beams, with a small increase in the compressive strength of the concrete, the amount of shear plastic rotation increases, and in medium and long beams, this increase in compressive strength to increase the shear plastic rotation requires a significant change. according to the results of the research, values for the shear plastic rotation of rc beams were presented that can be used in nonlinear analyzes by the plastic hinge method and seismic retrofitting projects.