Analysis On Nonlinear Damage Of Ecological Composite Walls Filled With Different Materials Based On The Twin Shear Unified Strength Theory

The ecological composite-wall structure, which is the continuation of the multi-ribbed composite-wall structure, is a new, energy-saving and assembled monolithic residential building structure with good seismic performance. The filled material in the structure can be obtained according to the application of the local ecological wall materials. To research and develop the ecological composite-wall structure being suitable for different areas will be important to accelerating technological progress and industrial upgrading produce for traditional construction industry. Based on previous research, five ecological composite walls with different filled materials are researched by experiment research, the theory analysis and numerical simulation, and the nonlinear behavior of the ecological composite walls with different ecological blocks is interpretated from the angle of damage. The researching emphasis are the basic mechanical properties of filled materials, the seismic performance of the walls with different filled materials, elastic-plastic simplified calculation model of ecological composite wall based on unified strength theory, the twin shear damage constitutive relationship of ecological composite wall materials, the nonlinear damage performance of ecological composite wall and so on. The main research contents and the results are as follows:(1) The characteristics of the five kinds of the ecological filled materials applicated and developed by the group at presentare are summarized, and the main production process and procedure of the blocks are introduced. Through the mechanical properties test, the basic mechanical properties of the filled materials have been studied, the basic physics and mechanics properties parameters of the materials have been gotten. Then using the linear regression analysis method to fit the uniaxial compression material constitutive equations, and using two lines to structure the uniaxial tensile stress and strain constitutive relationship of the four kinds of the materials. Based on the part slope of the material’s one-way elastic-plastic stress-strain curve, the hardening function expression containing the hardening parameters is presented, and the expression of the material incremental elastic-plastic stiffness matrixis is deduced in the end.(2) A pseudo-static experiment is conducted on five ecological composite walls(filled with aerated concrete block, plant fiber soil-based block, plant fiber cement-based block, recycled EPS lightweight concrete block and cotton stalk block) with 1:2 scales entirely. The mechanical characteristics and failure mechanism are studied. The emphasis was put on the evaluation bearing capacity, hysteretic loops, ductility, deterioration of strength and stiffness and energy dissipation of ecological composite walls filled with different materials block under seismic loads. The experiment results show that the filled blocks, ribbed grid and end frame can play a role in turn in elastic stage, elastic-plastic stage and failure stage; the bending failure of "strong plate and weak column" occurred in the composite wall filled with plant fiber cement-based block, while the shear failure of "strong column and weak plate" occurred in the other composite walls; such parameters as compressive strength, anti-crack ability, elastic modulus and bonding ability with ribbed grid of infill block are the main factors affecting characteristic loading and characteristic displacement of the composite wall; these walls are with stronger ability of anti-collapse.(3) According to the previous experimental study of frame grids and composite walls, the mechanical characteristics of the ecological filled blocks and frame grids are analyzed, the rigid frame-oblique compression bar model with plastic hinges of ecological composite wall is put forward, the twin shear unified strength theory is adopted in this article, in which the influence of intermediate principal stress 2σ is considered and it is applied to various materials of different performance in tension and compression under complex stress state, based on the unified strength theory, the width expression of equivalent oblique compression strut is deduced, the calculated values and experimental values are contrastingly analyzed, the width expression is a unified form solution for ecological composite wall filled with different ecological materials on calculating and analyzing. The rigid frame-oblique compression bar model with plastic hinges of a full scale ecological composite wall filled with aerated concrete block is established, and the nonlinear dynamic reaction analysis is carried out, the numerical results and the previous pseudo-dynamic experimental results are contrastingly analyzed. The simplified model is suitable for dynamic and static nonlinear numerical analysis of ecological composite wall.(4) Based on the unified strength theory, the twin shear damage model of material is derived, and based on the uniaxial elastoplastic curve of the materials in ecological composite wall, the damage parameters in the model are determined, then the twin shear damage model subroutine is programmed with the FORTRAN language in accordance with the provisions of the finite element software ABAQUS user material subroutine format requires, while the subroutine program is implanted into the existing material software library by the UMAT subroutine interface, the examples are the effectiveness of verification models and procedures. The results show that the twin shear damage model for the ecological diversity of composite wall material provides a unified form of solution, the preparation of the model validation is good agree with the experimental results, twin shear damage model has a certain accuracy and practicality; as long as the values of parameter b and α are determined, the unified yield criterion for various materials can be determined. The constitutive model can be applied to a variety of structural dynamic and static numerical analysis.(5) By using the twin shear damage model of materials, the numerical models of the 5 ecological composite walls filled with different materals are established and the nonlinear damage analysis is carried out to obtain the field distribution of damage of the wall. The damage degree of the walls are measured by the damage index local and global, and the damage value of typical region of the filled block, ribbed grib and frame of every wall are analyzed.According to the analysis results, a new damage index-load curve describing the structure of the tensility performance is constructed, then damage ductility index and damage ductility areas of the wall are obatained, and a method for calculating ecological composite wall ductility coefficient based on the damage is presented. According to the requirement of ductility design of structure or component, the reasonable compressive strength range of ecological composite wall filled material is obtained. The results show that the damaged area of ecological composite-wall mainly concentrated in the middle layer of blocks, the junction of ribbed beam and ribbed column and base and top of end frame. Damage of different parts of the block are different, local damage indices schedule changes is agreeable to the global, under the cumulative effect of the deformation showed the non-reducing properties; damage ductility index and damage ductility area revealed between the damage ductility of the ecological composite-wall and nonlinear response of structure, the calculated damage ductility index is closely approximate to the traditional ductility index of the five ecological composite-wall, which builds the connecting bridge between macro of the tensility performance and micro-damage evolution of the structure or components. Strengths of the filled material in ecological composite wall range from 0.5 to 2.5Mpa, and the ductility factor of which can reach 3.0 ~ 5.0.The originalities of this dissertation lie in:(1) The rigid frame-oblique compression bar model with plastic hinges based on the twin shear unified strength theory of ecological composite wall is put forward.According to the previous experimental study of frame grids and composite walls, the mechanical characteristics of the ecological filled blocks and frame grids are analyzed, the rigid frame-oblique compression bar model with plastic hinges of ecological composite wall is put forward, the twin shear unified strength theory is adopted in this article, in which the influence of intermediate principal stress 2σ is considered and it is applied to various materials of different performance in tension and compression under complex stress state, based on the unified strength theory, the width expression of equivalent oblique compression strut is deduced, the width expression is a unified form solution for ecological composite wall filled with different ecological materials on calculating and analyzing, the simplified model is suitable for nonlinear numerical calculates analysis of ecological composite wall.(2) The twin shear damage model applied to various materials subroutine is programmed by the FORTRAN language, the constitutive model can be applied to a variety of structural dynamic and static numerical analysis.Based on the unified strength theory, the twin shear damage model of material is derived, and based on the uniaxial elastoplastic curve of materials used in ecological composite wall the damage parameters in the model are determined, then the twin shear damage model subroutine is programmed with the FORTRAN language in accordance with the provisions of the finite element software ABAQUS user material subroutine format requires. The influence of intermediate principal stress 2σ and different performance in tension and compression are considered in this model, as long as the values of parameter b and α are determined, the unified yield criterion for various materials can be determined. The constitutive model can be applied to a variety of structural dynamic and static numerical analysis.(3) A method for calculating ecological composite wall ductility coefficient based on the damage is presented, the reasonable compressive strength range of ecological filled material is obtained.Five different material numerical models of the ecological composite walls are established, and the nonlinear damage analysis by using the twin shear damage model of materials is carried out. According to the analysis results, a new damage index-load curve describing the structure of the tensility performance is constructed, then damage ductility index and damage ductility areas of the wall are obatained, and a method for calculating ecological composite wall ductility coefficient based on the damage is presented. According to the requirement of ductility design of structure or component, the reasonable compressive strength and ductility factor of ecological composite wall filled material are obtained. The strength ranges from 0.5 to 2.5Mpa, and the ductility factor can reach 3.0 ~ 5.0.