Study On The Effects Of Basement Fixed Ways On Seismic Performance Of Symmetrical Two-tower Structure With Non-fixed Enlarged Base

Recently, the multi-tower structure with enlarged base is widely used in China. As people's demands varies, the structure becomes more complicated and emerges more urgent problems.The basement is commonly fixed in all directions so the analysis of models is conducted in regular ways by consolidating certain basement story to simulate the bounding effect. Due to the big size of base flat and the uncertainty of complicated topography, the basement maybe non-fixed around by earth(with one or more directions no fixed). So far China regulations have not set the ways online to simulate the bounding effect under the condition. Few documents study on the problem and several papers only deal with one-tower and not deeply. So the research of multi-tower on this aspect is urgently demanded.This paper study on the effects of different basement fixed ways on seismic performance of symmetrical two-tower structure with earth fixed in only three directions. Writer applies Midas/building to conduct 36 groups analysis models in different base spans and each group composes 3 models with same structure but in consolidated bases, consolidated basement and basement with soil spring.(Basement with soil spring is referenced from Technical Code for Building Pile Foundations.) There are 108 models in all and 24 storeys for each symmetrical tower. The results of 36 groups' response spectrum analysis and reinforcement calculation are as follows :1. Dynamic characteristics of three kinds of models are similar. The fundamental periods of the structure with soil spring is decreased than that under consolidated bases condition and increased than that under consolidated basement condition. They are in slight differences within 0.06 s and can be neglected in practical engineering.2. The maximum inter-storey drift angel of the structure with consolidated bases(consolidated basement) is increased 30%(decreased 19%) of that under soil spring condition.The results under consolidated basement condition are more similar with that under soil spring condition, but unsafe. The writer suggests that designers simulate structure with the model with soil spring if conditions permit, otherwise with the model under consolidated bases condition which is more conservative.3. The bottom floor shear of tower of structure with consolidated bases(consolidated basement) is increased 20%(decreased 35%) of that under soil spring condition. The results under consolidated bases condition are more similar with that under soil spring condition. The author advises that designers simulate structure with the model with soil spring if conditions permit, otherwise with the model under consolidated bases condition which is more conservative.4. The steel amount of 3 models are in slight differences within 2% and the effect on engineering cost will be limited in practical engineering.