## 1 Introduction  
Precast concrete frame structures are elements prefabricated in the factory and then erected at the site. Precast concrete structures are widely used as an alternative to conventional cast-in-situ structures, mainly due to the speed of construction, better quality control, lower manpower requirements, and less activity at the site [1]. According to an Armenian earthquake report, numerous poor connections have contributed to the collapse of precast frame buildings, as they were insufficient to resist the seismic loads [2]. The poor performance of precast structures in the 2012 Emilia-Romagna earthquake was also due to an insufficient understanding of connections [3, 4]. The connection between different precast elements is important, and it significantly governs the response of the structure [5]. To address this issue, the Precast Seismic Structural Systems (PRESSS) research program began in 1989 for the development of efficient precast connections in seismic zones [6]. The program was initiated to provide design recommendations for precast structures [7]. The hybrid connection was successfully developed during this program, and contained unbonded post/tensioning steel and bonded mild steel bars. The performance of precast concrete frame structures subjected to earthquake loads depends on the beam column connection strength, stiffness, energy dissipation, and ductility [8]. A comprehensive review of the performance of hybrid post-tensioned connectionsbased on various parameters is presented. This will help structural engineers and researchers to develop an in-depth knowledge of connection behavior of precast frames under seismic loads. Previous earthquakes [2; 9] showed that connections should not be used without a proper understanding of their complex behavior. In the present study, the code requirements of precast structures in seismic zones are discussed. Further, the development of hybrid connections by the PRESSS is also mentioned. This will serve as a real example for researchers to develop more efficient connections. Hybrid connections have self-centering capabilities if post-tensioning steel remains elastic [10]. Since the plastic hinge is in the connection region, damage to the structural components is minimal. Moreover, dry connections provide optimum speed in precast construction [11]. The major drawback in hybrid connections is energy dissipation. Post-tensioning steel does not provide enough energy dissipation [12]. Mild steel was first used by [PERSON] and [PERSON] [13] as an energy dissipator. Experimental results showed that with mild steel bars, the energy dissipation was low compared to that of their monolithic counterparts. With low energy dissipation, the drift of the structure increases [14]. Several attempts were made to improve energy dissipation to reduce displacement demands [15]. The unique gap opening phenomenon at the beam-column interface of hybrid connections allows the use of several types of energy dissipators. Some of the energy dissipators in literature include metallic yielding devices [16; 17], friction devices [18], bracing systems [19], and smart materials [20]. Hybrid connections with different energy dissipators are evaluated based on performance. Apart from performance, connections are also examined based on their feasibility in the precast construction industry. A connection that is simple, economical, and efficient will help the precast industry to benefit from precast construction technology. A lack of feasibility is the main reason that few connections found in the literature are put to practical use. One example is the connection proposed by [PERSON] et al. [21], which contained several components, including column plates, steel I sections, friction devices, and beam plates. [PERSON] [11] states that the connection must be economical or else it will not be used. Connection feasibility includes a simple assembly process, easy and economical production, the accommodation of production, and erection tolerances.