A Method Based On Modal Analysis For The Research Of Frame Joint Performance-Based Design

Frame joint is the key parts of frame structure, which connect the beams and columns and transfer the internal force of them. Frame joint has complex mechanical characteristics, usually, it’s difficult to control them in the structural designing. In many times in the earthquake, joint is the key of a structure destroy parts. At home and abroad, there are differences for the performance and designing method of the frame joint core and there didn’t has a quantitative index for the mechanical characteristics of the frame joint core in various countries’relevant specifications. Therefore, it’s very necessary to study the mechanical properties and the design methods of the frame jointThe vibration modes depended on the quality and rigidity is the inherent characteristic parameters of the structure, and reflects the relative relationship between the local stiffness and the quality. The order of vibration models reflects the order of the structure deformation under the action of load. Characteristic parameters can reflect the overall and partial mechanical properties of the structure, and do not involve the load combination. Therefore, it’s more convenient and direct to study the performance of joint by characteristic parameters.By the support of the National Natural Science Foundation Projects "A Research of Designing Method of the Structural Engineering Controlled by Characteristic Parameters"(50978232), this paper made the following specific work:1) Building the finite element model of frame joint, through changing the design parameters, such as the span-to-depth ratio of beam and the shear-span ratio of column, this paper takes modal analysis of the frame nodes in different sizes and summarizes the vibration changing rules of each joint. The results show that, for the joint between moderate columns and common beams, all kinds of non-bending vibration model has obviously backward, the core vibration quite gentle. With the decrease of the joint beam-column size, the core vibration more and more violent, joint of the reverse, shear such negative mode and order times more in advance. That is when the appear short column or by bending beam situation, not only component itself the stress of degradation, the mechanical properties of the shear, tend to be complex and difficult to link design, reason should be in the design to avoid as far as possible.2) By defining the participation of joint vibration model, we can take a quantitative description of the joint vibration characteristics. Through the analysis discovery, for different frame joint between beams and columns, the joint vibration model participations trend roughly the same curve. That is as beam and column across shear span ratio than the reduction of the shear vibration model participation increased gradually. Part of the shear vibration model with the component participation shear span ratio or across the obvious change than inflection point, can be used as regional concept design of quantitative node reference index.3) According to the vibration displacement, the formula based on the stress and strain of the vibration model is setted up based on the stress and strain of vibration model. We get the general rules of mechanical properties between beams and columns through the displacement projection under different loading cases of the beams and columns. In the concept design phase, we should make the favorable vibration model in front, and delay the adverse vibration model, try to avoid adverse deformation form.