| The reduced or reinforced beam section joint with the flange of steel frame possesses superior extension and energy-dissipating capacities, which have been proved by a lot of steel frame joint tests and finite element researches. However, the research aimed at the seismic performance of joint cannot fully simulate the true circumstance of the whole frame structure under seismic load, especially that space cooperating effect, the rod end’s development mechanism of plastic hinge, P-Δ effect and the binding effect of secondary beam on girder cannot be fully reflected. Therefore, in-depth research has to be made to further explore the seismic performance of the whole steel frame with the application of reduced or reinforced joint of beam section with the flange.According to the similarity theory and the reduced scale of 1: 3, the author of this paper designed and produced two large spatial steel frame specimens with ductile beam column joints. The specimen was 2-layer 2-truss 1-span type, and the joint of beam column was respectively reduced beam section type(RBF specimen) and symmetrical haunched plate type(SHF specimen). In the structure laboratory of Qingdao University of Technology, the quasi-static loading test was conducted to research the seismic performance of specimens, such as hysteretic performance, damage degeneration, plastic hinge mechanism, ductility, energy dissipation, failure mechanism. The test results were compared with ANSYS finite element simulation results to verify the accuracy of test results and the reliability of testing equipment. In addition, depending on the testing equipment and load characteristics, the author studied the influence of P-Δ effect on seismic performance of steel frame structure.Experimental research shows that obvious plastic deformation occurred in the weakened area at the flange of main beam for all of the 8 joints on RBF specimen, and plastic hinge occurred at the height of 0.5 time of the beam at the end of axillary plate from the main beam, for the 8 joints on SHF specimen. The experimental research has reached the expected goal. The ductility factor for both RBF and SHF steel frame specimens is in between 0.04~0.06, which demonstrates the sound plasticity and energy-dissipating capacity for both steel frame specimens; the angle between the story of both specimens is in between 0.04~0.06, which is able to meet the design requirement of minimum story drift of 0.04 and has further demonstrated the strong plastic deformation capacity. After adopting new joints, all space steel-frame specimens have achieved the designing purpose of shift-away of plastic hinge, thus enabling the well protection of all attachment welds at the beam-column joints.Relevant test and ANSYS finite element analysis show that, due to the influence of testing apparatus, measuring error and the idealization of finite element modeling etc., a distinct gap exists among hysteresis curve, skeleton curve, energy-dissipating capacity curve, curve of rigidity degeneration and bearing capacity degeneration in the structural elastic stage, but the gap is greatly narrowed in the plastic stage- presenting an overall same law of development; especially in the stage of structural failure, the position of plastic hinge and deformation are almost consistent with each other.Taking RBF steel frame specimen as an example, a research referring to field test data of deformeter and research results of finite element has been conducted on the 8 joints on RBF steel frame specimen in to compare the development and change of each joint’s internal force in elastic stage and of each stress-strain on the critical path. The research shows that the stress at the weakened center of circular arc flange gradually surpasses the stress level of the welded joint at the beam end with the increase of load, thus effectively unloading the stress of the welded joint at the beam end and avoiding the phenomenon of ultrahigh stress. Relevant test and ANSYS comparative research have verified that the reduced beam section joint with the flange still possesses superior shift-away of plastic hinge in space steel frame, which further indicates its superior anti-seismic and dissipation capacity under synergistic effect, P-Δ effect, internal force redistribution, etc.Through establishing an OSF finite element model and adopting the same loading system for RBF and SHF steel frame models, ANSYS finite element numerical simulation is conducted again to make in-depth contrastive analysis. Research results show that all plastic deformations of OSF space steel frame model occur in the weld position that connects the column and beam flange, with apparent brittle failure. SHF steel frame model enjoys the biggest yield load and ultimate load, followed respectively by OSF model, and RBF model- with the least yield and ultimate loads but the biggest ductility factor. SHF model is the second to RBF in terms of ductility factor, and OSF model is the last one; this indicates that new ductile joint has enhanced the ductility of steel frame: RBF model’s ductility is able to be greatly enhanced, while SHF model’s ductility is unable to be greatly enhanced due to its initial rigidity that has been enhanced by its symmetric axillary plate.A research has been conducted for P-Δ effect on steel frame’s seismic performance, with the combination of field testing apparatus, testing program and loading condition. Numerical simulation has been conducted for RBF and SHF models established under three different working conditions using ANSYS finite element software. Results show that P-Δ effect causes steel frame a huge degeneration in terms of bearing capacity, resulting in the bearing capacity of RBF steel frame down 21.8% and 20.1%, and that of SHF steel frame down 40.4% and 40.0%, which further indicates the severe deterioration of P-Δ effect on steel frame’s bearing capacity and deformability. This should be given serious consideration during experimental research or when a great horizontal displacement exists in the design of steel structure. |
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