Study And Application On Constitutive Relationship For Earth Material And Mechanical Compressed Earth Brick Masonry

Earth structure is widespread all over the world as an important part of traditional dwellings,it attracts the attention of researchers around the world because of the advantages of environment-friendly property,relatively low economic consumption,distinguished heat thermal capacity and so on.But the lack of relevant standards and computational theory has not only led to the lack of scientific guidance for the existing earth construction,but also caused poor seismic performance,and it seriously hinders the development of earth construction in the new era.Obtaining the accurate strength and mastering the stress-strain characteristics of the raw material and its components are the premise and basis for establishing the relevant standards and calculation methods for the earth structure.Based on the National Technical R&D Program 2014BAL06B04,in order to research the mechanical properties of the raw material and its components and develop the seismic performance of adobe buildings,the following jobs are done in this paper:(1)Uniaxial compressive properties of earth material are researched based on experiment.The influences of sample preparation method,specimen shape,loading rate,curing time and soil material selection on Uniaxial compressive properties of earth material are considered..There are 130 earth blocks in the test.The characteristic point parameters and stress-strain curves of the earth material are obtained.Through the analysis of the obtained curves,it is found that the stress-strain curves of earth material have an initial concave section.This characteristic is different from concrete and fired common brick.It reflects the stress-strain characteristics of earth material under uniaxial compression.(2)The constitutive relationship of earth material is established.According to measured stress-strain curve and summarized the shortcomings of existing constitutive relations of earth material,constitutive relationship expression of earth material is given with the piece-wise function.The model overcomes the defects of existing constitutive equations,and can trulyreflect the uniaxial compression stress-strain characteristics of earth material.Besides,it can be applied to all kinds of earth material based on parameter changes.(3)The problem of(Mechanical Compressed earth Brick)MCEB bonding was solved.Because the surface of MCEB is smooth,ordinary cement mortar cannot bind with it.Cellulose ether,rubber powder and fly ash were selected as admixtures to modify ordinary mortar.The mechanical properties of modified mortar were tested by tensile bond test.A special mortar that can effectively bond with MCEB is obtained.(4)The basic mechanical properties of MCEB masonry are researched.Uniaxial compression tests and shear tests along the through joints of MCEB masonry were carried out.The influences of Mortar type and strength grade,masonry method and waterproof treatment of brick surface on mechanical properties of masonry are considered.The failure mechanism of compression and shear for masonry are analyzed combined with failure modes.The uniaxial compression damage constitutive model of MCEB masonry is established based on the characteristics of earth material constitutive relation.The model can truly reflect the uniaxial compression stress-strain characteristics of MCEB masonry and can provide the basis for theoretical calculation and numerical simulation of MCEB walls.(5)The seismic performance of the MCEB wall was discussed.The seismic behavior of the wall under the action of the earthquake,such as seismic failure mode,hysteretic curve,skeleton curve,horizontal bearing capacity,deformation capacity,energy dissipation capacity and stiffness degradation,are studied according to 7 wall samples' pseudo-static testing under low cyclic loading.It is found that the MCEB walls occurred mainly shear compression failure and shearing friction failure and its bearing capacity is far higher than traditional adobe wall.Meanwhile,the shear capacity of the wall was calculated based on the constitutive equation of masonry provided in this article and calculation formula mentioned in Chinese masonry standard,respectively.It is found that the shear capacity of the wall calculated on the constitutive equation of masonry proposed aforementioned and current specification formula is in good agreement with the test results.It shows that constitutive equation of masonry and current specification formula can be used for the theoretical calculation of the wall.The mechanical performances of the earth material and its components are studied respectively from three aspects of block,masonry and wall.The compressive stress-strain characteristics of the earth material are revealed.The unified constitutive model of the earth material is proposed.The bond problem of the MCEB is solved.The failure mechanism of the MCEB masonry is discussed.The uniaxial compression damage constitutive model of the MCEB masonry is established.The research method provides a way to explore the mechanical properties of the earth material and earth structure.The results provide a basis for the rational use of earth material and scientific construction of earth structure.