Calculation Method Of Shear Capacity Of Brick Walls Strengthened With Reinforced Mortar Layers

There are large numbers of masonry buildings in China. It has been proved by huge amount of earthquake damage that masonry buildings which have not been reasonably designed for seismic loads have poor structure integrity and seismic performance. As the earth is currently entering another seismic active period and China is a country where earthquake frequently happens, it is of great significance to investigate theory for the design of seismic strengthening of masonry structures and provide theoretical support for seismic retrofitting of brick masonry structures.Strengthening with reinforced mortar layers is one of the most widely used conventional retrofitting techniques for brick masonry walls. There have been some experimental studies completed, and the methods to calculate the shear capacity of brick walls strengthened with reinforced mortar layers have been proposed based on the experiment results. However, the influence of aspect ratio and axial compression ratio on the shear capacity of brick walls strengthened with this technique has not been taken into consideration by the existing calculation methods. Moreover, the impact of aspect ratio has also not been considered in the method of calculating the shear strength of brick walls before strengthening. Besides, the existing calculation methods are established based on the tests in which both the vertical and horizontal loads are applied to the wall after the completion of strengthening with reinforced mortar layers. On the contrary, in practical engineering, vertical loads are borne by the brick wall prior to its strengthening, therefore the reinforced mortar layers used for the strengthening bears approximately no vertical loads and only resists the horizontal loads together with the original brick wall.In this thesis, quasi-static tests of six brick walls are analyzed based on the finite element software ABAQUS, and the calculated results show fairly good consistency with the experiments, which proves the feasibility of applying this software and the selected brick masonry constitutive model to the seismic behavior analysis of brick walls. The shear capacity of brick walls with aspect ratio ranging from 0.4 to 2.5 and axial compression ratio ranging from 0.1 to 0.8, before and after strengthened with the reinforced mortar layers of which the reinforcement ratio ranges from 0.0% to 0.5% and the strength grade of the mortar ranges from M5 to M15, is analyzed. It is found that the shear strength of the brick walls before strengthened decreases as aspect ratio increases, on the other hand, it increases firstly and then decreases with the increase of the axial compression ratio and a maximum value is achieved at the axial compression ratio of 0.6. For strengthened walls, with the axial compression ratio between 0.1~0.2, the shear capacity increment increases firstly and then decreases, with the maximum value obtained at the aspect ratio of 0.8. Whereas when the axial compression ratio is between 0.3~0.8, the shear capacity increment ascends with the increase of the aspect ratio but remains almost the same while the aspect ratio is above 0.6. The shear capacity increment of the strengthened walls firstly decreases and then increases as the axial compression ratio of the walls before strengthening rises, and the minimum increment is found at the axial compression ratio of 0.3. A linearly increasing relationship is found between the shear capacity increment and the arithmetic square root of the value of strength grade of the mortar used for the layers as well as the reinforcement ratio of the layers. The axial compression ratio of the original brick wall has direct influence on the failure pattern of the strengthened walls analyzed in this paper. With the axial compression ratio between 0.1 and 0.8, the shear capacity provided by the mortar increases linearly with the axial compression ratio, while that provided by the steel meshes varies according to a down concave parabolic curve.The calculation method for the shear capacity of brick masonry walls with the influence of aspect ratio and axial compression ratio taken into consideration is proposed based on the analyzed results, and a formula considering the influence of aspect ratio, axial compression ratio of the original brick wall, reinforcement ratio of the layers as well as the strength of the mortar used for the layers is put forward for the calculation of the shear capacity of brick masonry walls strengthened with reinforced mortar layers. Besides, construction details for seismic design for strengthening brick masonry walls with reinforced mortar layers are presented.