كاربرد اتصال برشي – اصطكاكي در اتصال مفصلي تير ميان طبقه راه پله بتني به ستون

APPLICATION OF SHEAR-FRICTION HINGE CONNECTION IN MID-STORY STAIR SLABS TO COLUMN JOINT

امروزه در ساختمان هاي قاب خمشي بتني اتصال پله در ميان طبقه به ستون ها يكي از مشكلات طراحي و اجرايي محسوب مي شود. اين مشكل از آنجا ناشي مي شود كه اتصال تيرميان طبقه به ستون، در نرم‌افزار به صورت مفصل مدل‌سازي مي شود اين در حالي است كه اجراي اين اتصال مفصلي به‌علت عدم جزييات اجرايي مناسب با فرض اوليه (اتصال مفصلي) تطابق ندارد. آشكار است اين اتصال غيراصولي تيرميان طبقه به ستون از نظر تغيير بارگذاري و در آخر تغيير رفتار چند ستون متصل به دال نيم طبقه پله، ضعفي آشكار براي اين ستون ها و كل سازه محسوب مي‌شود. هدف از اين پژوهش ارايه جزييات اتصالي ساده و اجرايي است كه با عملكردي برشي – اصطكاكي براي اتصال دال پله در ميان طبقه به ستون ها قابل استفاده است. اين اتصال براساس ظرفيت‌هاي موجود در ضوابط و مقررات ملي ساختمان، مبحث 9 تعريف شده و مي‌تواند راهكاري مناسب براي تطبيق طراحي با اجرا باشد.

Reinforced concrete buildings are considered as one of the most important types of structures. According to the implementation nature of these buildings, mainly as in place construction, usually their connections are performed as fixed connections. Because of restraint form of girder-column connection in the reinforced concrete buildings, their participation in the lateral load bearing will be in the form of moment frame system. Nowadays stair -column connection in the middle of story is considered as one of the design and implementation problems. Since using of multiple arm stairs is the best method in terms of performance, cost and safety to make an appropriate connection between stories, different methods will be used to transfer landing plate (stations) load to structural members in order to increase stability and safety of the stairs. Two general methods of landing plate load transfer include: A) transfer of stations load to lower or upper balanced beam of the floor B) transfer of stations load to columns around the stair. In our country more attention is paid to the second method (B) due to the ease of implementation and financial and time savings. Fixed and unchangeable behavior of landing plate- column connections in the middle of story is one of the most important properties of a good connection. This target can be achieved largely through designing and implementing of joint connections of landing plates to columns. It is a long time that this connection is designed in our country as joint connection but there are no appropriate details of implementation for the given assumptions. Always in the typical methods there is a considerable moment imposed on the column because of restraint nature of in place reinforced concrete practice. It is clear that this unusual beam – column connection in the middle of story is considered practically an obvious weakness for these columns and the whole structure in terms of loading and final variable behaviors of several columns connected to half-height slab of the stairs. Purpose of the present study is to introduce a new joint connection that is consistent with national building regulations, part 9 and also can be easily performed and designed. Suggested connection with a shear – friction function can be applied in the connection of slab stairs in the middle of the story to columns. It can also be considered as a suitable method for consistent relationship of design and implementation. Force transmission in this connection is just in a shear form (because moment arm is not formed) and mainly takes place by reinforcement bars. Although concrete connection friction can transmit substantial shear force; it is recommended to ignore this capacity. However, friction connection capacity is predictable and applicable in the theoretical relationships. Implementation of this connection is very simple and can be created just by preparation of several bars as antennae (dowel) with appropriate and minimum aanchorage length. Implementation of suggested connection leads to removal of the beam in the middle of the story staircase. Finally, it causes high amount of savings in the use of concrete, bars and shuttering and increases the accuracy and speed of implementation. According to loading of each staircase, amount of required reinforcement will be calculated based on shear force as well as tensile force.