FLEXURAL BEHAVIOR OF BASE CONNECTION OF C-BENT COLUMN UNDER COMBINED CYCLIC BENDING-TORSIONAL LOADING

There is a lack of study concerning the torsional loading effect on the flexural response of column base especially cyclic behavior under combined torsional-flexural loading; many unknowns exist on this topic. A study for the flexural performance of the base connection for C-bent column subjected to seismic in the traffic direction is necessary to address the effect of the complex combination of cyclic flexural-torsional action on such a type of connection; for this purpose an extensive numerical parametric study was conducted to evaluate the flexural performance of the fixed base connection of C-bent bridge pier against combined cyclic bending and torsional loading following SAC phase II protocol. After verifying results with previous experimental works a Finite Element Analysis (FEA)  using Strand7 is performed for Finite Element Models (FEM) which simulates force transfer at major contact interfaces in the connection, and a total of six base plate connection sub-assemblages with variable base plate thicknesses (three for stiffened connection and three for un-stiffened connection) anchored by 10 bolts, were configured and analyzed to support double cantilever pier subjected to eleven loading schemes that reflect  different pairs of gravity moment and axial loads along with cyclic loading in the traffic direction eccentric from pier center of rigidity to guarantee the application of combined flexural-torsional action on the base connection. The study provided a curves for the following performance terms; strength (yield moment), deformation (yield curvature), curvature ductility, and stiffness (rotational flexural stiffness); the seismic flexural performance of the base connection under the previously mentioned loading package was evaluated by plotting the variation of the mentioned terms against the parametric values of the base plate thickness for different loading condition considered in the analysis. The study revealed that the state of gravity load weather it is concentric or eccentric has a great impact on the connection yield strength and deformation, further the level of eccentricity of the applied gravity loads has a significant impact on the connection stiffness, more over increasing base plate thickness affect deformation capacity, and strength however with less impact on the strength and remarkable impact on the deformation, study also provided the effect of adding stiffeners to the connection, which enhanced the base fixation rigidity, however in turn of that curvature ductility has suffered noticeable reduction, in the same context curvature ductility is strongly deteriorated when the torsional stresses are dominant.
يحتوي هذا البحث علي دراسة نظرية لسلوک الوصلات المعدنية لقاعدة أعمدة الکباري على شکل حرف “C”  تحت تأثير الزلازل في اتجاه حرکة المرور على الکوبري و ذلک للتحقق من تأثير إجهاد هذا النوع من الوصلات بتوليفه من أحمال عزوم انحناء مصاحب لها آنيا أحمال لي. و لهذا الغرض تم عمل تحليل بطريقه العناصر المحددة لست وصلات قاعدة بسماکات مختلفة للوح القاعده, مطبق عليها مجموعه من الأحمال ذات طبيعه دائمة لتمثيل أحمال الجاذبية من أحمال ميته و حيه و في نفس الوقت أحمال تردديه للأخذ في الاعتبار تأثير الزلازل و قد روعي في الدراسة التحليلية أيضا تأثير وجود دعائم تقويه للوصلة من عدمه.
ويتناول البحث سلوک الوصلات الانحنائي في وجود التوليفه السابق ذکرها من عزوم انحناء مصاحب لها عزوم لي و قد تم دراسة ذلک على أربعة مستويات; هي مقاومة الوصلة للإنحناء, و التشکلات الحادثه في الوصله, بالإضافه إلى مرونة الوصله و قدرتها على استيعاب الأحمال فوق المرنه قبل الانهيار التام, و أخيرا جساءة الوصله للدوران نتيجة عزوم الإنحناء. و بناء على ما سبق خلصت الدراسه لتدهور سلوک الوصلات عند زيادة اجهادات اللي المصاحبة لاجتهادات الانحناء و کذلک اهمية دعائم التقوية لتحسين سلوک الوصلات.