Research On Seismic Design Method Of Masonry Structure Under Rotating Mode

Masonry structure is widely used and distributed in our country.Actual earthquake disaster and seismic simulation test of masonry structures show that some walls have obvious rigid rotation besides their bending and shearing deformations under earthquakes.The masonry wall is divided into several parts under rotational deformation,and the contact surface between the parts decreases rapidly with the development of cracks,resulting in a significant decrease in the bearing capacity and stiffness of the wall.The existing design methods for lateral stiffness of masonry structures take into account both bending and shearing deformations.When the masonry wall is subjected to small earthquakes,the deformation mechanism has little influence on the horizontal bearing capacity of the masonry wall in the range of elastic stage,but it will have significant influence on the bearing capacity of the wall when the masonry enters the elastic-plastic stage or approaches the destruction stage under the medium and large earthquakes.After the wall crack enters the elastic-plastic stage,its deformation mechanism includes three types of bending,shearing and rotation.At this time,the distribution of earthquake action no longer conforms to the distribution law of elastic stiffness.As the main component of the deformation mechanism in the elastic-plastic stage,rotational deformation cannot be ignored.In order to improve the theoretical design of masonry structure,this paper studies the theory of rotational deformation of masonry structure,and the main research contents are classified into the following aspects:(1)Through quasi-static tests,the cracking mode,deformation mechanism,bearing capacity and lateral stiffness of masonry walls with typical facade shapes are studied,and the comparison with single-limb walls is analyzed.The research shows that when the asymmetric fa(?)ade shape masonry wall is subjected to loads in different horizontal directions,the seismic capacity has obvious directional characteristics,and the bearing capacity of the strong direction is greater than that of the weak direction;Bending and shearing type failure occurred,the cracks developed obliquely downward from the corners of the wall between the windows and the wall under the window,and the masonry wall was accompanied by obvious rotational deformation during the whole process of cracking to failure;It has good deformation ability.The different facade shapes and geometric dimensions of each wall pier in the double pier wall system will affect the overall bearing capacity and lateral stiffness.The performance is basically the same.(2)Based on the angle analysis of mechanical balance,the lateral stiffness of masonry wall with common elevation shape under rotational deformation is deduced.The stiffness algorithm takes into account the influence of the elevation shape of wall limbs and the loading direction under rotational deformation on the lateral stiffness of masonry wall,which conforms to the shape,stress mechanism and deformation characteristics of masonry wall elevation.On this basis,the reduction factor related to shear deformation is introduced to further improve the stiffness formula,and checked by an example and test.Compared with the standard elastic stiffness method,the calculated results of the new equivalent lateral stiffness method are closer to the measured elastic stiffness with the change trend of load and height-width ratio.The research results provide reference for further research on seismic design method of masonry structure and are of great significance for guiding seismic design of new masonry structure and seismic reinforcement of existing masonry structure.(3)Through theoretical analysis,the calculation method of horizontal bearing capacity of masonry wall in the form of rotational failure along diagonal crack is put forward.The calculation method has a good correspondence with the actual failure mode of the wall.Its principle is in accordance with the actual stress characteristics and failure characteristics of the wall,and has a more definite physical meaning compared with the shear failure of the wall between windows.The bearing capacity calculation results have a higher agreement with the test values of single wall and double-limb wall,which provides test data and basis for the seismic performance of the joint masonry wall.(4)In order to further improve the masonry code system and meet the development needs of building industry modernization,combining with existing test and theoretical research,the original masonry structure seismic design code is briefly introduced from two aspects of conceptual design and bearing capacity checking,and suggestions for improvement and revision are put forward.