## 1 Introduction  
The use of an externally bolted/glued steel plate system has been proven to be an effective technique for strengthening/repairing reinforced concrete (RC) structures. This method of strengthening is low-cost and efficient for improving both flexural and shear strength. It is also known to have high stiffness. In general, the plates are bonded/glued to the beams and attached at the compression and tension zones of the RC beams to provide a locking mechanism that will increase the load-bearing capacity and ductility of the section in order to avoid brittle failure [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. In the past two decades, many attempts have been made to comprehensively understand and apply steel plate systems. Most of these studies have focused on the flexural performance of bolted steel plates (BSP) on the side faces of the beams. A study by [PERSON] et al [5]. revealed that there is a partial interaction between the bolted steel plates and the RC beams. Analytical models were established for the flexural behavior of the BSP beams. It was found that there is a relationship between the longitudinal and transverse interactions of the steel plates. This relationship was derived using the identical curvatures of both steel plates [8]. Ignoring the effects of this partial interaction in theoretical computations can lead to an overestimation of the flexural performance enhancement achieved by BSP. This overestimation can be as much as 30%, as reported by [PERSON] and [PERSON] [10]. [PERSON] et al. [11] proposed a simplified \"two factor and three steps\" design method for flexural strengthening. This method was based on the combined influence of the stiffness ratio and the shear stiffness of the anchor bolts on the relative slips. However, the strengthening/repair of structural RC beams with various techniques and materials has been widely studied in recent decades. Brittle compression failure can be avoided by using proper confinement. Few studies have been done on the confinement of concrete at the compression zone in a beam. This is one of the most important methods to develop a flexural over-reinforced section by using one or two helical reinforcements with a medial span in the compression zone [16; 17]. However, the confined compression zone in beams has been developed recently based on some studies conducted on the confinement of columns [18; 19]. Based on this, further investigation is needed on the behavior of confined normal strength concrete (NSC), high strength concrete (HSC), and pre-stressed beams [20; 21]. Also, few studies have reviewed and reported on the installation of short stirrup confinement in the compression zone [22; 23]. Moreover, there are studies on the improvement of beam capacity using a system consisting of two or three layers, referred to as a hybrid system. This type of system depends on the use of different types of materials, which include HSC and light weight concrete (LWC) with steel fibres (SF) [24], and is also influenced by the strength of the materials, such as normal reinforcement (NR) and Fiber Reinforced Polymer (FRP) bars [25; 26]. To enhance the strength, stiffness, and ductility properties of concrete, the use of proper confinement is necessary to restrain lateral expansion and avoid brittle failure [16; 17; 27]. In contrast, the design of the flexural beam in the case of the brittle failure of concrete is not permitted by several international codes of practice because the member has less ductility [28; 29]. The reinforcement ratio of flexural RC beams is classified into three categories, namely, under, balance, and over, according to ACI 318-02 [28; 29]. Therefore, the development of flexural over and under RC beams can be achieved by replacing existing materials with higher quality materials that have better performance or through the addition of a structurally enhanced section with additional load-bearing materials, such as adding helical reinforced, short stirrups and bolted steel plates to the sides of RC beams.