برآورد ظرفيت نهايي اتصالات RBS تحت بار يكنواخت و سيكلي با استفاده از مكانيزم شكست شكل پذير

ESTIMATED ULTIMATE CAPACITY OF RBS CONNECTIONS UNDER MONOTONIC an‎d CYCLIC LOAD USING DUCTILE FRACTURE MECHANISM

جهت تعيين سطح عملكرد واقعي سازه ها تحت زلزله، لازم است ظرفيت نهايي اتصال هاي تحت بار سيكلي مشخص شود. از طرف ديگر، در سال هاي اخير انهدام موضعي اعضا و ايجاد خرابي پيش رونده در سازه ها در اثر انفجار و يا آتش سوزي، تعيين ظرفيت نهايي اتصال ها تحت بار يكنواخت را اجتناب ناپذير كرده است. در پژوهش حاضر، ظرفيت نهايي اتصال هاي داراي تير با مقطع كاهش يافته ي RBS تحت بارگذاري يكنواخت با استفاده از سناريوي حذف ستون و با استفاده از مدل تنش مشخص كرنش بحراني مشخص شد. سپس ظرفيت نهايي اتصال هاي موردبررسي تحت بارگذاري سيكلي با استفاده از مدل رشد و به هم پيوستگي حفره ها تحت بار سيكلي به دست آمد تا در مواقعي كه امكان انجام آزمون هاي آزمايشگاهي نيست، بتوان با استفاده از مدل هاي مذكور، ظرفيت اتصال RBS را تعيين كرد. نتايج پژوهش حاضر نشان مي دهند ظرفيت چرخش اتصال هاي RBS تحت بار سيكلي كمتر از اعداد ذكر شده در نشريه ي 350FEMA است، ولي ظرفيت چرخش اتصال هاي ذكر شده تحت بار يكنواخت تقريبا 2 برابر ظرفيت چرخش آن ها تحت بار سيكلي است.

The basis of the modern design of earthquake resistant structures is based on the structural ductility for absorption of earthquake energy and stability in large-scale displacement. Although metal materials are highly ductile, the Northridge earthquake showed that moment connections have a certain rotational capacity under cyclic load, and severe earthquakes can lead to failure in the area with low ductility. Therefore, in order to determine the level of actual performance of structures under earthquake, such as the life safety or Collapse Prevention, it is necessary to carry out more serious studies to determine the final cyclic capacity of connections. On the other hand, after the collapse of the Alfred P. Murrah Federal building, a truck explosion in 1995, as well as the collapse of the World Trade Towers caused by the 2001 airplane collapse;Determination of final capacity or failure of fittings under uniform load; to investigate the structural behavior before the destruction or complete destruction began. Since most of the tests carried out on the connections have not been completed due to the limitations of the laboratory facilities and have not been performed until the failure phase of the connection; hence, it does not determine the final capacity of the connection. Mathematical studies are also in the early stages due to the lack of reliable failure mechanism to determine the time and how to start and spread the failure under monotonic and cyclic loading. In this research,it has been attempted to be evaluated the final capacity of the RBS connections under the monotonic and cyclic load . Also, the place of the start of defect in this type of connection is evaluated. In this regard, the final capacity of the reduced-sectional beam (RBS) connections under uniform loading was determined using a column-removing scenario with the SMCS model and the theory of growth and expansion of void under uniform load. Then, the final capacity of the reduced-beam section (RBS) connections under cyclic loading (SAC) was obtained by using the Cyclic Void Growth Model (CVGM) and compared with the proposed final capacity of FEMA350 for RBS connection. The results of this study show that the cyclic rotational capacity of the RBS connections provided in FEMA350 is far more than actual. Also, the results show that the rotational capacity of the RBS connection under monotonic load is almost twice the amount given in FEMA350.