Precast concrete frame construction is not used extensively in high seismic regions, despite its potential benefits in construction speed and quality control. The new type of frame has been developed recently for resisting seismic loads in buildings. It consists of precast concrete beams and columns that are joined by a combination of conventional steel reinforcing bars and unbounded post tensioned tendons. The clamping force between the beam and the column provides vertical shear force transfer at the interface between the beam and the column, so the corbel is not needed. The mild steel bars are placed in ducts and grouted into sleeves at the top and bottom of the beam, which extended through the columns. They are placed at the top and bottom of the beams, because this would maximize the dissipation of energy through cyclic yielding in tension and compression. This study focuses on analytical investigation of hybrid precast beam-column concrete connections subjected to lateral loading. 3-D nonlinear finite element was developed to study the response and predict and validate experimental results for O-P-Z4 specimen. The experiments were conducted at NIST. The results from the FE model accurately predicted actual strain levels in the mild steels and force in the PT tendon. The force-displacement envelope was also in satisfactory agreement with experimental result. Upon the validation of experimental work, the behavior of monolithic and hybrid specimens with identical characteristic were evaluated. Furthermore, effective functions in the behavior of hybrid connections, including the amount of the PT tendons contribution in beam moment strength and initial post-tensioning force were investigated. The results from nonlinear analysis in ANSYS showed that elastic and plastic stiffness of hybrid frames, with any amount of PT tendons contribution in beam moment strength or initial post-tensioning force, were greater than monolithic frame. Also, the elastic stiffness of hybrid frames increased with growing of initial post-tensioning force and decreased with raising the amount of the PT tendons contribution. The plastic stiffness of hybrid frames increased with increasing the amount of PT tendons contribution and decreased with raising the initial post-tensioning force. Hybrid frames yield load, with any arrangement of mild steel bars and PT tendons, were greater than monolithic frame and with raising the strand effective stress, the yield load decreased. The same results were obtained for post yield loads. In a new approach, rotation analysis was used in order to compare the ANSYS results with this new method. The results from this method showed good agreement with software results. The post yield prediction of this method from the behavior of hybrid connections was conservative and leaded to smaller post yield stiffness than software.
