مطالعات عنصری تحلیلی و محدودی بر رفتار FRP تقویت کننده های پرتوهای RC تحت چرخش Analytical and finite element studies on behavior of FRP strengthened RC beams under torsion

Fiber reinforced polymer (FRP) is a widely used strengthening material for reinforced concrete members owing to its various advantages such as light weight, ease of application, high strength and stiffness. Faulty design, unexpected loads, change in usage type, construction errors are few of the reasons which necessitate the strengthening of existing structures. The behavior of FRP strengthened reinforced concrete (RC) members is more complex than the unstrengthened RC members and therefore, a clear understanding of their behavior under different types of loading is important. A plethora of studies has been conducted in the past to understand the behavior of FRP strengthened RC beams under flexure and shear [1–۲]. However, torsional behavior has not been given significant attention despite its frequent occurrence in many important engineering structures. Though torsion is considered as a secondary effect for most general cases, it becomes critical in cases such as connecting beams, outrigger bent, and bridge columns. Therefore, it is important to understand the behavior of RC members under torsional loading in detail. Moreover, the efficiency of FRP strengthening in terms of strength and stiffness improvement under torsional loading is relatively not very well understood. This is due to the complex nature of interaction effects of FRP on the softening and confinement of concrete and increased tension stiffening behavior of concrete. This study tries to fill the knowledge gap existing in this vital area of research by carrying out analytical and FE studies. Behavior of FRP strengthened RC beam can be understood from the assembly of membrane elements with additional equilibrium and compatibility conditions. Fig. 1 describes the shear flow in an FRP strengthened RC beam subjected an external torque ‘T’. Membrane element ‘E’ subjected to shear flow ‘q’ is also shown in Fig. 1.