## 1 Introduction  
The beam-column joint is the important element in the reinforced concrete (RC) frame structure, which carries large horizontal and vertical shear forces as the internal forces of beam and column transfers through joints. Earthquake damage demonstrates that beam-column joints are susceptible to shear failure. In order avoid shear failure, a high percentage of transverse stirrups are required in the joint core [1], which may lead to reinforcement congestion and, thus, construction difficulties in casting concrete in the joint regions [2; 3]. Fiber RC may be a feasible solution to reduce the congestion of stirrups in the beam-column joint core [4; 5]. The main objective of this research is to provide experimental evidence of the behavior of beam-column joints with UHPFRC under earthquake loads and with various design parameters, and determine the effect of UHPFRC on the shear bearing capacity of beam-column joints.  
Since the mid-1960s, numerous researchers have conducted a series of studies on the calculation of the shear carrying capacity of beam-column joints, and proposed certain analytical models; for instance, the diagonal strut mechanism, truss mechanism [6], softened strut-and-tie model, simplified softened strut-and-tie model [7; 8], general analytical model [9], and two diagonal axial springs model [10]. Those models and their parameters were mainly developed based on the experimental results of beam-column joints with normal concrete (NC); however, the mechanical properties vary significantly between UHPFRC and NC. The compressive strength of UHPFRC ranges from 120 to 800 MPa; its fracture energy can reach 40,000 J/m\({}^{2}\), its toughness index (TI) can reach 3.5, and its ultimate tensile strain can reach up to 0.0003 [11; 12; 13]. The improvement of UHPFRC in terms of strength, toughness, and deformation capacity will influence the failure characteristics of the structure, which may affect the load-carrying capacity. [PERSON] et al. [14] conducted a test on the torsional behavior of the UHPFRC beam and investigated the effect of the transverse and longitudinal reinforcement ratio on the angle of the diagonal compressive stresses. [PERSON] et al. [15] investigated the bearing features of UHPFRC columns under eccentric compression and developed a simple analytical method for calculating the ultimate loads of UHPFRC columns. Existing test result of UHPFRC beam and column components indicated that the existing models or parameters are not completely suitable for UHPFRC structures. Very little research has been done on seismic behavior and shear-bearing capacity UHPFRC beam-column joints. The compressive strength, tensile strength, and ultimate strain of UHPFRC are all higher than that of NC, so the cracking load and ultimate bearing capacities of the UHPFRC joint should be different to those of the NC joint. On the other hand, the UHPFRC usually contain no coarse aggregates, and the aggregate interlock forces are nearly nonexistent. However, the steel fiber that exists in UHPFRC may change the failure process and modes, and lead to change the load bearing capacity. Therefore, it is necessary to investigate the behavior and failure mechanism of the UHPFRC joint under earthquake loads through experiments, analyze the components of shear resistance, and suggest a formula for calculating the shear bearing capacity of UHPFRC beam-column joints.