An Evaluation On The Rationality Of The Column Moment Amplification Factors Based On Space Effects

It is indicated by theoretical analysis and seismic damage of structures that the essence of earthquake ground motion and the response of the structure under the seismic action are multi-dimensional. In the former seismic response research of reinforced concrete structure, as a result of the limitation of technical method, the researcher often uses the plane analysis model, considers the response that under unidirectional horizontal earthquake action only, and carries on the computation separately along two main directions of structure. In fact, regardless of regular structure or irregular structure, there are obvious differences between the responses that under unidirectional horizontal earthquake action and bidirectional horizontal earthquake action. Therefore, it's more reasonable that using the space analysis model to do the analysis under the bidirectional horizontal earthquake action for these studies.In this paper, the author firstly designed five multilayer reinforced concrete frames according to the code for seismic design of buildings (GB50011-2001) and the code for concrete structure design (GB50010-2002). Subsequently, using the non-linear analysis program OpenSees to carry the structures'three-dimensional nonlinear analysis in two perpendicular directions at the same time. Based on the global responses (such as the topmost displacement, the inner-story drift ratio etc.) and the local responses (such as the fibers'strain, the distribution of plastic hinge, the magnitude of the plastic hinge and the ductility demand etc.) of spatial frame, the availability of the column moment capacity amplification factors is evaluated in this paper. Furthermore, the rationality of plane model simplifying three-dimension frame in seismic responses analysis is evaluated. and the availability of another frame designed by the column moment capacity amplification factor 1.5 instead of 1.2 in Intensity Region 8(0.2g) with Seismic Design CategoryⅡis also evaluated.Finally, the conclusions of this paper are as following:①The global seismic responses of the spatial frame in Intensity Region 7(0.1g) with Seismic Design CategoryⅢare sufficient to the seismic performance demand under major earthquake. for the local seismic responses, although the plastic hinges at column ends and beam ends are all relatively small in quantity than that in other Intensity Region, Plastic hinges at column ends are bigger than that at beam ends in quantity, which shows that the column moment capacity amplification measures in Intensity Region 7(0.1g) are't able to avoid or defer the appearance of plastic hinges. the seismic performance of frame in this region is disadvantage. as a result of the earthquake action is relative small in Intensity Region 7(0.1g), the trend to developing a column sway mechanism is not detceted,which is implied that there have a long distance to the stucture failure.②The displacement responses of the frame in Intensity Region 7(0.15g) with Seismic Design CategoryⅢare similar to that in Intensity Region 7(0.1g), which shows that there have not evident differences of the frames in the two region. As for the local responses, the quantity of the plastic hinges at column ends are more than that in Intensity Region 7(0.1g), and the quantity of the plastic hinges at beam ends are less than that in Intensity Region 7(0.1g).since the frame starts to develop a column sway mechanism, the availability of the column moment capacity amplification measures in Intensity Region 7(0.15g) is worse than that in Intensity Region 7(0.1g).③The global seismic responses of the frame in Intensity Region 8(0.2g) with Seismic Design CategoryⅡare obviously bigger than that in Intensity Region 7, especially, the maximum inner-story drift ratio exceeds 1/50,which imply that the frame is already failure. the quantity of the plastic hinges at column ends are much more than that in Intensity Region 7.more of the column plastic hinges are yielded on two directions with big rotation. Several stories start to develop a column sway mechanism, which shows that the column moment capacity amplification measures in Intensity Region 8(0.2g) is extremely weak.④The global seismic responses of the frame in Intensity Region 8(0.3g) with Seismic Design CategoryⅡ, which are similar to that in Intensity Region 8(0.2g), are obviously bigger than that in Intensity Region 7. the maximum inner-story drift ratio is close to 1/50,which imply that the frame approach to failure. the quantity of the plastic hinges at column ends are more than that in Intensity Region 8(0.2).and also more of the column plastic hinges are yielded on two directions with big rotation. Several column sway mechanisms are developed in the frame, which is indicated that the column moment capacity amplification measures prescribed in Chinese existing codes are also weak in the extreme and should be improve.⑤The global seismic responses of the frame in Intensity Region 9(0.4g) with Seismic Design CategoryⅠ,which are obviously smaller than that in Intensity Region 8, are close to that in Intensity Region 7,which is implied that the seismic performance of the frame in Intensity Region 9(0.4g) is effective in terms of global estimate. the quantity of the plastic hinges at beam ends are much more than that at column ends. the rotation of the column plastic hinges is small, which is indicated that the column moment capacity amplification measures in Intensity Region 9(0.4g) prescribed in Chinese existing codes is positive to defer the appearance of the plastic hinges. therefore, the column moment capacity amplification measures in Intensity Region 9(0.4g) is effective to seismic performance of frame.⑥The global responses of plane model are similar to that of 3D model, it is reasonable to use plane model as the replacement of 3D model just in term of the global seismic responses. The local responses are evidently different. For plane model under unidirectional action,lots of plastic hinges develop at beam ends. Plastic hinges at column ends are much more bigger in quantity than that of beam for 3D model under bi-directional action, the frame trends to developing a column sway mechanism, which imply that simplified plane analysis model underestimates the seismic responses of 3D frame column remarkably .⑦There is not evidently deference in the global seismic responses of the frame in Intensity Region 8(0.2g) with Seismic Design CategoryⅡdesigned by the column moment capacity amplification factor 1.5 and 1.2. The plastic hinges of frame which designed by the column moment capacity amplification factor 1.5 are yielded on one or two directions, and developed the beam-column plastic hinges dissipation mechanism which the quantity of the plastic hinges at column ends are more than that at beam ends.