Study On Material Mechanical Properties And Seismic Performance Of Modern Rammed Earth Structure

As a traditional architectural style,there are large number of rammed earth(RE)buildings,which is also widely used in underdeveloped rural areas in China.In recent years,in order to achieve the strategic requirements of sustainable development,implement the rural revitalization plan,and realize the concept of green building design with low energy consumption and low pollution,rammed earth building has been paid attention again for its unique advantages of low environmental pollution,high living comfort and low construction cost.The traditional RE structure is mainly composed of soil-based materials with low strength,poor deformability and durability,and weak seismic performance,which makes it difficult to meet people’s demand for the performance of RE structure.Based on these conditions,this study makes a series of improvements to the traditional RE,including optimizing and adjusting the proportion of rammed building materials.The standard of "clay content is the main factor,gradation curve is the auxiliary factor" is established.Modern ramming machines and formwork are used to improve construction quality and seismic structural measures are also proposed.Finally,a modern RE structure system is established.In order to study the seismic performance of modern RE structures,this paper studies the influence of different factors on the mechanical properties of RE materials,and explores the seismic performance of modern RE wall through quasi-static test.Finally,the overall seismic performance of modern RE structures is tested by shaking table test.On these basis,the seismic design and construction research of modern RE structures are put forward.This study establishes the evaluation standard of modern RE mixtures,explores the influence of size effect and solidification efficiency on the strength of RE cube specimens,studies the mechanism of compressive failure of RE earth prisms,establishes the compressive constitutive model,discusses the seismic performance of modern RE wall and restrained RE structure,and puts forward the seismic design and construction theory of modern RE structure.The main research contents of this paper includes:(1)Taking loess in the suburb of Xi’an as an example,the criterion of "clay content is the main factor,gradation curve is the auxiliary factor" is put forward to measure whether RE mixtures are suitable for ramming.Furthermore,the influence of size effect on the compressive strength of compacted soil cube specimens is studied.The formation process and failure mechanism of different modern compacted soil strength are compared.Finally,the content and gradation of clay,the size of cubic specimen and the content of curing agent were determined.(2)The uniaxial compressive properties of modern RE prism specimens were studied.The development of cracks,failure pattern,compression strength,elastic modulus E and Poisson’s ratio (?) of different modern RE prism specimens were compared.The compressive failure mechanism and stress-strain relationship of different modern RE prisms are established,typical failure modes of modern RE prisms are including: entire shear failure;shear failure along bedding;collapse of bottom layer;splitting tension failure;crushing failure with peeling area;entire crushing expansion failure.(3)Based on horizontal pseudo-static test of modern RE wall,the key parameters of seismic performance,such as damage development,failure mechanism,hysteretic characteristics,stiffness degradation and energy dissipation are compared.The restoring force model and non-linear calculation model of RE wall are established.Typical failure modes of RE wall include brittle shear failure and dilatancy characteristics,and cement stabilized RE wall exhibits a rocking failure mode.Comparing these parameters,it is found that the stabilized RE wall has better seismic performance than the unstable RE wall.The validity of the model is examined by comparing the finite element calculation with the pseudo-static test results.(4)Two 1/2 scaled shaking table tests are conducted,and the crack distribution,failure mechanism,dynamic characteristics and displacement response are compared,the seismic performance of two typical confined modern RE structures is studied.Model 1 and model 2 reach the moderate damage stage at 8 degrees and 7 degrees(0.15g),respectively.It also proves that the restraint measures of the built-in reinforced thin beam and column are effective in restraining the deformation of the structure.And the wood roof with poor integrity is more compatible with the deformation of restrained RE structure than the cast-in-place concrete slab roof.(5)Based on the results of horizontal quasi-static test of modern RE wall and shaking table test of single-story modern RE structure,the shear bearing capacity of RE wall is calculated.Combined with engineering design examples,the seismic conceptual design parameters such as height-thickness ratio and local size of modern RE wall are given,which provide basis for the design of seismic structural measures,foundation and roof of modern RE structure.And the basic theory of construction and maintenance of modern RE structure is established to provide reference for future engineering application of modern RE structure.