Study Of MPA Method On Frame Structures Supported By Stepped Foundation In Mountainous City

There are a lot of research on the mechanical characteristics of frame structures supported by stepped foundation in mountainous city, Part of the study show that higher mode has a great influence on the design and analysis for this kind of structures at present. It is different from the assumptions of pushover analysis method. So far, we don’t know how serious the higher modes of down-floors affect the traditional pushover analysis method. MPA method become a choice. This article, the time-history analysis results is regarded as correct, research on the influence of higher modes on the downslope direction, and compared to traditional Pushover method, further research on the precision of MPA method for the frame structures supported by stepped foundation in mountainous city.Based on the conventional seismic analysis method on regular frame structure: mode-shape decomposition response spectrum, static pushover analysis method and dynamic elastic-plastic time history analysis method, Thesis aims to research on higher modes effects on structures supported by stepped foundation and difference between modal pushover analysis(MPA) and traditional static pushover analysis method. These researches may provide theoretical basis for the forthcoming industry norms: REGULATIONS FOR DESIGN OF MOUNTAINOUS BUILDING STRUCTURES. This thesis includes following contents:(1) the introduction of the equivalent model of structures supported by stepped foundation;(2) verify the existence of the higher modes;(3) the comparative research on two modal control methods;(4) the influence of different structure arrangement in the elastic analysis, and main variable consist of the number of dropped stories, stiffness ratio and mass ratio;(5) the influence of different structural arrangement in the plastic analysis, and have added the change of seismic intensity;(6) the influence of different performance point solving method;(7) based on dynamic elastic-plastic time history analysis, research on the drift and story shear under different lateral load pattern such as MPA, MMPA and others.According to the analysis in this thesis, main conclusions are as follows:(1) Double gourd string can be equivalent to structures supported by stepped foundation. According to regular frame, structures supported by stepped foundation are more highly influenced by higher modes.(2) For the same frame, the number of modal displacement control method is far more than that of modal mass participation coefficient method. The latter one is more close to reliable values. Under certain conditions, increasing 1-2 mode number for calculation is recommended.(3) In the elastic analysis phase, different structural arrangement has huge impact on the higher modes: increasing the number of dropped stories and mass ratio will enlarge higher modes influence, and increasing stiffness ratio will reduce higher modes influence in the local place. In dynamic elastic-plastic analysis, the direction of Pushover have a smaller effect on the target displacement. The error of shear force and displacement is bigger under different vibration mode combination. Higher mode have a greater influence to shear relative to story drift. Structural arrangement and seismic intensity have a greater influence to the result of combination different modes. Higher mode have main impact on 1-1 and the lower ground plane.(4) Target displacement could be predicted by Yanghong method, fixed target displacement method and FEMA440 linearization method. For the capacity spectrum method has a good predicted results just when the seismic intensity is low.(5) Predicted values of every distributed force are relatively accurate. With the rise of floor, distribution trend of every distributed force is fixed and dispersion degree increase: MPA and MMPA are the best, and compared with the former MMPA method is not improve prediction accuracy significantly, followed by SRSS distribution, exponential distribution, mode1 distribution and inverted-triangle distribution. The result of uniform distribution undervalued internal force and deformation significantly and error is the largest. Internal force and deformation of 1-1 story and dropped stories are more sensitive to the change of the structure arrangement.(6) For prediction of weak layer, the change of structural arrangement may the transfer of weak layer. Uniform distribution is the worst and maximum story drift is larger than others. Results of MPA, MMPA, exponential distribution, SRSS distribution are reasonable.