كليدواژه :
اتصالات تير به ستون , سازه هاي بتن مسلح , مدل سازي المان محدود , بارگذاري يكطرفه و بارگذاري چرخه اي
چكيده فارسي :
در ساختمان ها با سيستم باربر لرزه اي قاب خمشي، اتصالات تير به ستون عامل عمده ي خرابي ها بعد از زلزله مي باشد. ميزان شكل پذيري و جذب انرژي مطلوب سازه ي قاب خمشي وابسته به طراحي و اجراي بدون نقص اتصالات تير به ستون آن است. در اتصالات تير به ستون سازه هاي بتن مسلح، عدم امتداد آرماتور مثبت تير در ناحيه اتصال و عدم امتداد خاموت ستون در ناحيه مشترك، نقص هاي رايجي هستند كه جزييات لرزه اي اتصالات مطابق با آيين نامه هاي جديد آنها را پوشش مي دهد. در اين تحقيق به منظور صحت سنجي مدل هاي اجزا محدود ، مطابق با نمونه هاي آزمايشگاهي، مدل هايي با جزييات لرزه اي و بدون جزييات لرزه اي در نظر گرفته شد و سپس همان مدل ها با تغيير مدل تنش و كرنش، اثر لغزش آرماتور هاي طولي تير در ناحيه اتصال شبيه سازي شد و مقايسه اي بين رفتار بارگذاري يكطرفه و بارگذاري چرخه اي و پوش حاصل از آن انجام شد. و سپس تاثير شرايط مختلف تيرهاي عرضي در پيرامون اتصال در نظر گرفته شد. نتايج به خوبي نشان داد كه مدل سخت اجزا محدود زماني كه اثرات لغزش آرماتور هاي طولي تير درنظر گرفته مي شود، رفتار مدل هاي عددي با نتايج آزمايشگاهي مطابقت بيشتري پيدا مي كند. و همچنين مقايسه نتايج مدل ها با شرايط مختلف تيرهاي عرضي نشان داد كه محصور كردن اتصالات غير پيشتنيده تا يك حدي مي تواند باعث افزايش مقاومت اتصال در برابر بارهاي جانبي بشود.
چكيده لاتين :
Beam–column connections in reinforced concrete (RC) structures play an important role when the frame is subjected to seismic loading. The overall stability of the structure and the formation of the optimal energy absorption mechanism in the beam plastic hinge zone depends on the role of the beam-column joints. The non-seismic detailing in the joint panel area can cause a partial or total collapse of the structure. Beam-column connections with non-seismic detailing in buildings with moment resisting lateral load bearing systems, are the major cause of post-earthquake damage. The optimal shape and energy absorption of the moment frame structure is dependent on the design and perfect execution of the beam-column connections. In the beam-column connections, the lack of positive reinforcement of the beam in the joint area and non-extension of the column stirrup in the joint area are common defects of the joints in accordance with new regulations. Researchers have provided a lot of experimental studies on beam–column connections, while experimental studies are usually costly and time consuming, and can be restricted by the test facilities and space. The behaviour of the RC beam–column joint is very complex and several parameters such as axial load ratio, reinforcement detailing, concrete strength have significant influences on its seismic performance, it is impractical to fully investigate all parameters through a limited number of experimental tests. Finite element modelling using ABAQUS software platform can provide an opportunity to study the various parameters governing the monotonic and cyclic behaviour of the beam–column joints. In this study, by examining several parameters in the finite element model of the RC Beam–column connections in ABAQUS software, such as specifications of strain-hardening for steel, bushinger effects, concrete damaged plasticity (CDP) in tensile and compression, concrete confinement effects, presence of lateral beam, and also bond-slip of reinforcing bars was investigated and leads to provides recommendations for finite element modelling of the RC frames. For this purpose, the behaviours of the seismically and the non-seismically detailed beam–column joints under monotonic and cyclic lateral loading were evaluated in different conditions of the presence of lateral beam. The finite element models with seismic and non-seismic detail were considered and validate with laboratory tests by considering sliding effect of longitudinal beam reinforcement using modified steel stress-strain curve. Then, the effect of different lateral beam conditions around the joint was considered. The results showed well that the finite element model is more consistent with the experimental results when considering the slip effects of the longitudinal beam reinforcement. Also comparing the results of the models with the different lateral beam conditions showed that confining the non-seismic joints can increase the joint strength against lateral loads. The general behaviour mode for the seismically detailed specimen was flexural yielding in the beam at the column face whereas for the non-seismically detailed specimens joint shear failure occurred generally before the beam section reached its ultimate flexural strength. The finite element model of beam-column joint specimens was calibrated by test results and good agreement was found between the experimental and numerical hysteretic behaviour. The model was able to capture the modes of failure, peak load and initial stiffness of the tested specimens.
