## 1 Introduction  
Demolished concrete is used to make RAC, which has the advantages of being energy-saving and environment-friendly. Moreover, the steel reinforced concrete (SRC) structure has the advantages of high bearing load capacity and good seismic performance. And SRC can combined with the RAC [1; 2; 3] to form the SRRAC structure. SRRAC meets the development direction of modern architecture, which has many advantages, such as being energy-saving and environment-friendly, sustainable development, having good mechanical performance. Therefore, SRRAC has broad application prospects. However, the porosity of recycled aggregate is higher than that of natural aggregate [4]. And the coarse aggregate surface in RAC attaches the cement-based or mortar, and its initial defects are more than natural aggregate, thus, those will affect the mechanical properties of RAC [5; 6]. Therefore, many studies were carried out by scholars for RAC. The results show that inferior waste concrete reduces the quality of recycled coarse aggregate and consequently reduces the strength of RAC [7]. The mechanical properties of RAC can be improved by Polyvinyl alcohol (PVA) after soaking in polyvinyl alcohol solution, which the optimum concentration of PVA solution is 10% [8]. The compressive strength of RAC increases when cement is replaced by fly ash [9]. Recycled fine aggregate with demolished concrete has little effect on the mechanical properties of RAC, when the replacement percentage is less than 30% [10]. Meanwhile, [PERSON], [PERSON] et al. [11] conclude that the compressive strength of RAC columns meets the American Certification Institute (ACI) design criteria. [PERSON], [PERSON] et al. [12] consider that the bond strength of RAC is 9 to 19% lower than natural aggregate concrete. [PERSON], [PERSON] et al. [13] conclude that the seismic performance of recycled concrete frame structure is reduced with the increase of replacement percentage. [PERSON], [PERSON] et al. [14] suggest that the stiffness and cracking load of RAC slabs are slightly lower than those of natural aggregate concrete. According to the literature [15; 16; 17], the content of recycled coarse aggregate has an insignificant effect on the flexural or shear properties of RAC beams. Secondly, in order to improve the utilization ratio of RAC in high-rise and super-high-rise buildings, a large number of scholars pay attention to the structure of SRRAC. The results show that the flexural strength [18; 19] and shear strength [20] of SRRAC beams are similar to those of SRC beams. SRRAC frame has good seismic performance [21], and the seismic performance of SRRAC components decreases in varying degrees with the replacement percentage of recycled aggregate increases [22; 23; 24]. The seismic performance of three beam-column joints with ordinary concrete is similar to the RAC, for which the replacement percentage of the specimens is 30% [25]. The SRRAC structure can be used in high-rise and super-high-rise buildings after reasonable preparation and design. Fire is one of the major hazards that can affect engineering structures. It is necessary to study the fire behavior of RAC structures. The results show that the residual performance of RAC after exposure to elevated temperature is optimal level when replacement percentage is 50% [26]. The performance of RAC is similar to ordinary concrete after exposure to elevated temperature [27; 28]. With the increase of elevated temperature, the elastic modulus of RAC decreases [29]. And its compressive strength increases slightly at first under the temperature of 400 degrees centigrade and then decreases with the temperature increases [30]. The ductility and cracking performance of RAC are improved after exposure to elevated temperature when the steel fibers are added [31]. Meanwhile, the energy dissipation and anti-spalling properties of RAC can improve by the rubber powder [32]. The increase of RAC strength can improve its impact behaviors when the temperature is lower than 500 degrees centigrade.