Research On Mechanical Properties Of Masonry Wall Considering Rotational Deformation

Masonry structure is widely distributed in China due to its convenient material acquisition and low cost.However,the masonry structure is seriously damaged in the earthquake and the existing seismic design theory of masonry structure develops slowly for a long time and has some deficiencies.Therefore,the seismic design theory of masonry structure needs to be further improved.The results show that the deformation of the wall under horizontal load includes not only bending deformation and shear deformation,but also rotational deformation.The rotational deformation of masonry structure occurs when the wall cracking generates horizontal cracks and enters into the elastic-plastic stress stage.Masonry structures are prone to crack and enter into the elastoplastic stage under the action of earthquake,while the lateral stiffness and horizontal bearing capacity of existing masonry structures in China are still based on the elastic theory,ignoring the effect of wall rotation on mechanical properties.In order to improve the theoretical design of masonry structure,the rotational deformation theory of masonry structure is studied in this paper.The main research contents fall into the following aspects:(1)Integral finite element model of masonry structure is established by ABAQUS for numerical analysis and compared with test data to verify the feasibility of the integral model.Then finite element analysis is carried out for walls with different parameters by changing the height-width ratio of wall between windows,the height-width ratio of wall joints(load-bearing wall part under windows),the pressure stress and the presence or absence of side constraints.Through finite element analysis,it is found that the ratio of height-width of wall between windows and the pressure stress have great influence on the rotation and mechanical properties of the wall.(2)Through theoretical analysis,the calculation method of rotational horizontal bearing capacity of masonry walls under different failure modes is presented.In addition to the typical shear failure mode,there are also shear failure with rotational participation,diagonal crack rotational failure along the joints of wall limbs and horizontal crack rotational failure along the bottom of the wall.For shear failure with rotation,the height-width ratio influence factor is introduced to take the influence of rotation into account.It is found that the wall rotation has little influence on the horizontal bearing capacity.Therefore,the horizontal bearing capacity can be calculated according to the current seismic code.For rotational failure along diagonal cracks ofwall limb joints,since the cracking load of the wall along the wall limb joints is close to the ultimate load,the horizontal bearing capacity of this failure mode is obtained by deducing the cracking load of the wall along the wall limb joints and making it equal to the ultimate load.For rotational failure along horizontal cracks at the bottom of the wall,the horizontal bearing capacity of the wall in this failure mode is obtained based on the principle of moment balance.(3)Based on the attenuation law of rotating wall in elastic-plastic stage,the normalized stiffness attenuation model of rotating wall is established.As the attenuation of stiffness is mainly caused by rotational deformation,the stiffness in the elastic stage of the wall is reduced by using the ratio of height to width of the rotating part of the wall.By substituting the reduced stiffness into the normalized attenuation stiffness equation,the lateral stiffness in the elastic-plastic stage of the masonry is obtained and compared with the test results of rotating wall in other people's tests,the feasibility of the stiffness model proposed in this paper is verified.