A Study On Seismic Behavior And Earthquake-resistant Measures Of Stilted Frame Structures

In order to use mountain resources more effectively and relieve the housing pressure because of the growing population as well as promote the development of social economy, stilted structures, regarded as a familiar kind of mountainous building structures, are born at the right moment in lots of mountain cities of China, and they are widely used in engineering practice. The special seismic damage of the stilted structures in 5.12 wenchuan earthquake exposes design defects of this kind of structures. Also, the academia and the engineering have few studies on special seismic problems of stilted structures nowadays, while most of the research achievements focus on cliff-structures, so as to make the theoretical research obviously lag behind the engineering practice. So we must consider the problem whether the structures designed by the current specifications can satisfy the seismic behavior goals of “The Three Levels”. By the finite element method, this thesis has done research on seismic behavior of stilted frame structures and put forward preliminary seismic design suggestions.Based on the above, this thesis has mainly completed the following work:Summarizing the current study achievements at home and abroad of mountainous building structures, especially of stilted structures and the seismic damage of stilted structures in 5.12 wenchuan earthquake. Making a field research on the engineering practice of stilted structures in Chongqing as well.Putting forward the new seismic design control index of “upper and lower rigidity ratio”(the rigidity ratio of the whole part above the ground floor and stilted part under the ground floor) and “storey-rigidity ratio”(the rigidity ratio of the first floor above the ground floor and stilted part under the ground floor) to discuss the dynamic characteristics of the structures because of stilted structures' congenital irregularity. Based on SAP2000 and PERFORM 3D, elastic and elastic-plastic analysis of designed stilted frame structures in different seismic intensity areas are carried out. By summarizing the forced deformation rules ? energy consumption ? damage and so on, seismic behavior and applicability of this kind of structures in different seismic intensity areas can be evaluated. Also, the seismic weak link can be found.Improving the seismic design method of stilted frame structures, offering design suggestions of this kind of structures in different seismic intensity areas, and perfecting the seismic measures design of this kind of structures in engineering practice.Through the above work, the main conclusions are as follows:“Upper and lower rigidity ratio” and “storey-rigidity ratio” are integrated and universally applicable indexes that make macroscopic evaluation indexes parameterized. And the relative value of the index can guide the structure design.Under rare earthquake, stilted frame structures in low seismic intensity areas such as 6 degrees designed by the current specifications can achieve good seismic behavior such as displacement?lateral stiffness?shear force and so on, which can meet the seismic behavior goal of ‘The Third Level'. Meanwhile, the damage of the structures are slightly less along with the increase of “upper and lower rigidity ratio” and “storey-rigidity ratio”.Along with the increase of intensity, enlarged cross section method adjusted to areas of 7 or 8 degrees can ensure the capacity of stilted short columns(shear span ratio?2), but it can lead to the transfer of weak layer when rare earthquake occurs. Especially, the components around the shortest stilted column will be badly damaged or even the whole part above it will be collapsed, which can't meet the seismic behavior goal of “The Third Level”.Summarizing the details of seismic design about stilted frame structures based on all the results from the thesis. And putting forward some preliminary seismic design suggestions in high seismic intensity areas: stilted short columns should be strengthened suitably, stilted long columns(shear span ratio>2) should be added tie-beams, the axial force of ground floor beams can't be ignored and the internal force of the first floor above the ground should be enlarged.The innovation points of this thesis can be summarized as follows:By making macroscopic evaluation indexes parameterized, the integrated and universally applicable index of “upper and lower rigidity ratio” and “storey-rigidity ratio” are proposed. And the simplified calculation formula based on the index can essentially reflect stiffness characteristics of stilted frame structures.From the research, for the ground floor beams of stilted frame structures along the slope, the nearer they are to the shortest stilted column, the bigger their axial force is, which can't be ignored in the structure design.