Study On The Seismic Performance Of Masonry Structure Retrofitted With Partial RC Frame At Bottom Stories Under Rare Earthquakes

The existing masonry structure has been transformed into Masonry Structure with partial RC frame at Bottom stories.Due to the advantages in material and construction period,as the most common method of existing masonry structure retrofitting in China,it takes a place in the history of construction industry development.In recent years,many earthquakes have seriously affected this kind of buildings,but the relevant domestic codes have not put forward corresponding requirements for the seismic design of this kind of retrofitted buildings,so the study of this kind of buildings has become a top priority.In order to better study the seismic performance of this special modified structure as a whole,this paper takes a masonry structure the modified with local bottom frame structure as the main body of study.The frame element with composite cross-section and the shell element with layered sections are used to simulate the reinforced beam and column members and the boards wall members respectively.The adjusted seismic waves are selected to study the seismic performance of the modified structure under rare earthquakes.The main conclusions are as follows:Firstly,the adjusted EI-Centro wave,Borrego wave and artificial wave were selected to analyze the elastic-plastic time history of the structure before and after the modification,and the time history curves of displacement,velocity,acceleration and base shear were obtained.Through comparative analysis,it can be seen that the use of local bottom frame system for large space transformation of masonry buildings has a more obvious impact on the seismic performance of weak parts of the structure.Then,the influence of torsional effect on structure was studied by two kinds of seismic wave input methods: one-way and two-way,and the index of story displacement,story displacement angle and torsion value are obtained.Through comparison,it can be seen that the torsional effect of the structure under earthquake has a greater impact on the local bottom frame structure after the modification.The development law of plastic hinge was studied,and the typical seismic damage characteristics of this kind of modified structure under earthquake action are found.The results show that the plastic hinges of the local bottom frame structure mainly appear at the connecting beams of the original structure,and the frame beams and columns at the bottom are in the elastic state,which has good seismic energy dissipation potential.At the same time,the torsion effect will accelerate the development rate of the plastic hinge of the structure and make the structure enter the elastic-plastic state more quickly.Finally,the stress state and variation law of each strengthened member under rare earthquake were analyzed,and the typical stress characteristics of each strengthened beam-column and board wall member in this kind of modified structure were explored.The analysis shows that the stress state of the strengthened members varies regularly under earthquake,and the stress state of each layer in the board wall members was within a relatively safe range.At the same time,with the torsion effect considered,the influence on the stress state of each strengthened member is more obvious.In this paper,the seismic performance analysis of the modified partial bottom frame masonry structure was studied,which provided a reference for the design and research of this kind of project in the future.