Study On The Axial Compressive Performance Of Brick Masonry Column Strengthened By Angle Steel Considering The Size Effect

Brick masonry structures are widely distributed in China.However,brick masonry columns also have some shortcomings such as low strength and poor seismic performance,which need to be strengthened to meet the security requirements of structural components.Compressive strength is one of the most important basic mechanical properties of brick masonry.However,the brick masonry columns or walls are not necessarily the same size.Whether the compressive strength of brick masonry is affected by the sectional dimensions of components is worth exploring.Besides,the technology of strengthening brick masonry columns by angle steel is mature,but there is still little research on the calculation method of compressive bearing capacity of brick masonry columns strengthened by angle steel,and the influence of section size on the compressive bearing capacity of composite column is not clear as well.Therefore,it is necessary to study the axial compressive performance of brick masonry column strengthened by angle steel considering the size effect.A total of twelve axial compression tests of unstrengthened masonry columns and brick masonry columns strengthened by angle steel with different sizes were designed and conducted in this paper.The failure characteristics of the specimens and the experimental data such as curves of load-displacement,nominal peak stress,nominal peak strain,strain of angle steel and batten plate were analyzed.The results showed that increasing the section size of unstrengthened brick columns had no effect on the axial compressive strength under the condition that the ratio of height to side length was 3.The nominal peak strain of brick masonry columns increased firstly and then decreased.The compressive bearing capacity and deformation capacity of brick masonry columns could be greatly improved by using the technology of envelop angle steel.Under the same steel ratio and volume stirrup ratio and aspect ratio,compared with the unstrengthened specimens,the axial compressive bearing capacity of small-sized composite brick columns with side length of 240 mm,medium-sized composite brick masonry columns with side length of 370 mm and large-sized composite brick masonry columns with side length of 490 mm increased by 234.7%,152.3% and 176.9%respectively.And the initial axial stiffness increased by 112.1%,238.0% and 76.2%respectively.Nominal peak stress and nominal peak strain of composite columns with different sizes are also not the same.Compared with small-sized composite brick masonry columns,the nominal peak stress of medium-sized composite brick masonry columns and large-sized composite brick masonry columns decreased by 23.9% and 20.1% respectively,and the nominal peak strain decreased by 17.6% and 35.3% respectively.On the basis of experimental research,based on the concept of effective restraint area in Mander’s confined concrete model,the mechanism of strengthening brick masonry columns with external angle steel were analyzed.The calculation method of effective restraint area and corresponding effective restraint coefficient of confined brick masonry columns were deduced.Based on the assumption of deformation coordination,the calculation method of lateral restraint stress on brick masonry columns was also obtained.Combined with the calculation formula of maximum strength under constraint stress,considering the utilization coefficient of angle steel and the initial state of columns,the calculation formula of compressive bearing capacity of brick masonry columns strengthened with angle steel was proposed.Finally,finite element models for extended analysis were established by ABAQUS.The finite element simulation results and theoretical results showed that in the compression simulation of brick masonry columns strengthened by angle steel,changing the thickness of batten plate had little effect on the bearing capacity,while the compressive bearing capacity of the model with properly increased batten plate’s height could be improved slightly.Decreasing the spacing of batten plate had the most significant effect on improving the bearing capacity of axial compression.Based on the proposed formula,the steel consumption for composite column was analyzed,and the minimum steel consumption scheme for brick masonry columns with different sizes strengthened by angle steel under different conditions was given.