Research On Seismic Performance Of An Isolated Frame-shear Wall Structure

Currently, the common isolation form is base isolation which requires inerratic shape of upper structure and the position of isolation floor located in the top of the foundation or the basement. During the engineering practice of base isolation structure, a new type of isolation structure form is developed, called story isolation. The isolation floor of story isolation structure is set between two floors in the building for structural seismic response control. Because of the flexibility and variety superiority of story isolation, it can widely used in engineering. This research is based on one practical engineering, considering the elastic-plastic character of upper structure, with the purpose of study the seismic performance of both base isolation and story isolation structure. The main work accomplished includes the following:(1) Summarize the present situation of the research and development of base isolation technology and story isolation technology, and elaborate the vibration reduction mechanism of isolation structure.(2) Establish the base isolation model, select three satisfactory seismic wave and carry on the elastc-plastic time history analysis under rare earthquake, considering the section and reinforcements of beam, plate, column and wall.(3)Without changing the building using function, alter the isolation layer to a higher floor, select three satisfactory seismic wave and conduct the time-history analysis in rare earthquake.(4)Compare the results between base isolation structure and story isolation structure.(5)Finally, come to the conclusions and prospects of the paper.The main research results of this paper are as follows:(1)The story shear force is gradually decreased with the increasing of floor in base isolation structure and story isolation structure. The interlaminar shear force coefficient of the isolation building is fully meet the demand of codes and the peak of base shear force is happened after the acceleration peak of earthquake waves. The peak number of story shear time history curve is about 5 in lower structure, but it will reach 10 in upper structure, which means the vibrational frequency is higher in upper structure. The distribution regularity of seismic force at different times remains unchanged, and the interlaminar shear force is triangular from the top down.(2)Under rare earthquake, the maximal interlaminar displacement angle of base isolation structure and story isolation structure are 1/317 and 1/312 respectively, proved that the maximal interlaminar displacement angle of the structure meets the requirement of 1/100, from which we can see that the limit of codes is much bigger with high safety coefficient. By making comparison and analysis the calculations of linear elastic and plastic solutions, it would draw the definite conclusions that under rare earthquakes the structure enter into the elasto-plastic state and the location of the maximum interstory drift will be changed. The peak of top horizontal displacement is happened after the acceleration peak of earthquake waves.(3)The peak acceleration value of top floor is happened after the acceleration peak of earthquake waves. For base isolation building, compared with the acceleration peak of earthquake waves, the percentage of average peak acceleration value of top floor in X direction and in Y direction are 61.08% and 60.00% respectively. For story isolation building, the stiffness in X direction is lower than it in Y direction and the percentage are 61.00% and 62.00% respectively.(4) Under rare earthquake isolation structure turns into plastic yielding phase, but it can still keep the structure from collapsing. The plasticity status have little difference between base isolation structure and story isolation structure. There is no plastic hinge under the isolated floor in the story isolation structure, which means it still in the range of elasticity under the rare earthquake. Mode of structure failure is conform to the codes of frame-shear-wall structure failure mode.(5) The comparison results between the research of base isolation structure and story isolation structure are shown in below. The difference of interlayer shear force is less than 5% between floor 2 and floor 16 and the higher the floor the bigger the difference value; the isolation layer of base isolation structure and story isolation structure are the first floor and the negative floor respectively and the difference is less than 10%; the peak value of base shear force of story isolation structure is greater than that of base isolation structure. The maximum layer displacement angle of story isolation structure between floor 5 and floor 16 is greater than that of base isolation structure and between fool 2 and floor 4 the result is the exact contrary; the maximum top horizontal displacement of base isolation structure is greater than that of story isolation structure. The peak of time-history curve of acceleration of story isolation structure is a little more than that of base isolation structure and the peak value are 1.56m/s2 and 1.51m/s2 respectively, with the difference of 3.21%.(6)According to the codes, the structure below the isolation layer should meet embedded stiffness ratio, the seismic bearing capacity under moderate earthquake and Shear bearing capacity under rare earthquake. The design methods which require the structure below the isolation layer to maintain elastic under rare earthquake is too conservative with a big security reserve rates.