# Seismic Behavior of RC Beam Column Joints with 600 MPa High Strength Steel Bars
## 1 Introduction  
Reinforcement concrete frame systems are widely used in concrete structures for earthquake-resistant design because of their structural efficiency and architectural flexibility [1; 2; 3; 4]. However, large beam and column sections often make it difficult for architectural designs to meet the structural requirements. Hence, beam and column sections are often designed to be as compact as possible to provide more available space in buildings, which often encounter steel congestion at beam-column joints [5; 6; 7]. Now, congested reinforcement has become the key problem for several complications, including the honeycomb phenomenon and hard concrete placement during construction, which will reduce the quality of the construction. In an attempt to solve these problems, a great amount of attention has been recently paid to the use of high strength materials, including high strength concrete [8; 9; 10; 11; 12; 13; 14] and high strength steel bars [15; 16; 17; 18; 19] in designs and constructions. The use of high-strength steel bars not only reduces the consumption of steel bars, which is convenient for construction, but also reduces construction cost, with a greater impact on building structures in highly seismic regions [20; 21]. Nevertheless, the ACI Committee 318 [22] and Ministry of Housing and Urban-Rural Development of the People's Republic of China [23] restricted the employment of high strength steel bars, stating that with the development of yield strength, higher shear and bond stresses may cause brittle failure. Further experimental research is required to evaluate the seismic performance of longitudinal high strength steel bars used in different frame elements, including interior beam-column joints. The main challenges in the design of interior beam-column joints with high strength steel bars are the bond and shear failures, which are mainly caused by insufficient anchorage length and higher strains [6; 24]. Four full-scale exterior and interior beam-column joints with 600 MPa yield strength steel bars, were investigated and compared by [PERSON] et al. [25]. The importance of the sufficient development length of steel bars in compression and tension for deformation capacity and energy dissipation capacity were demonstrated and emphasized. In order to study the seismic behavior of reactive powder concrete beam-column joints reinforced with high strength steel bars, an experimental investigation was carried out by [PERSON] et al. [26]. A total of five exterior joint specimens were tested, including two specimens with HRB600 steel bars. There are lower degradation of strength and stiffness, residual deformation, but higher deformation capacity and energy dissipation capacity in the beam-column joints with HRB600 steel bars. Five exterior beam-column joints reinforced with Grades 500 MPa and 700 MPa steel bars were tested to study the seismic behavior of [PERSON] et al. [27]. The results showed that utilizing high strength steel bars resulted in a slight decrease in bond strength and energy dissipation capacity. After that, seismic performance of exterior beam-column joints with high strength steel bars of Grade 600 MPa and high strength concrete of 70 MPa were discussed by [PERSON] et al. [15]. It was reported that failure mode, energy dissipation capacity, pinching behavior, and stiffness of joints with high strength steel bars were similar to those with nominal steel bars. Furthermore, the combination of high strength steel bars and strength concrete can improve the cumulative energy dissipation. Three full-scale reinforcement concrete frame subassemblies with high strength materials were tested to evaluate the seismic performance by [PERSON] et al. [28]. The results showed joints with high strength steel bars and concrete exhibited excellent lateral deformation capacity. Analytical investigations of reinforced concrete beam-column joints constructed using high-strength materials were conducted by [PERSON] and [PERSON] [29] to analyze the shear deformation and bond-slip behavior of the joints.