Mechanical Properties Of Rubber Isolators Reinforced By Novel Reinforcement Plates And Practical Seismic Isolation Technology

The earthquakes in recent years have caused numerous rural buildings to damage and collapse.Under the same earthquake intensity,the losses suffered by rural buildings are always greater than those by urban buildings,which is called the ‘small earthquake,big disaster’ phenomenon.The problem of safety of rural buildings in China is extensive,as most these buildings are constructed by residents themselves.It is a long-term and complex subject to improve seismic capacity of these buildings considering farmers’ economical capacity at the same time.Laminated steel rubber isolation technology is an increasingly mature anti-seismic technology,which has been widely used worldwide and has withstood many earthquakes.It is a new solution for the problem.However,traditional isolators are complex,heavy and expensive and need high construction quality.They are hardly to be popularized in rural areas.In this paper,an isolator reinforced by a novel type of plate-short cut glass fiber reinforced polyacrylate plate was developed.The steel plate of conventional isolators was replaced by the engineering plastic plate,and the connecting steel plates are removed,and a new simple connection construction was proposed.Comparing to conventional isolators,the new isolator is simple,light,cheap and easy to be installed.The following researches were carried out in this paper,focusing on the novel type of isolator:(1)The theoretical formulas of stiffness and strength of the isolator were derived.Firstly,the available theoretical formulas of conventional isolators and a type of fiber-reinforced isolators were reviewed and analyzed.It was found that these formulas were not applicable to the proposed isolator.As the rigid reinforcement assumption of conventional isolators makes the calculated stiffness too high,and the incompressible rubber assumption and the assumption of reinforcement decoupling of fiber-reinforcement isolators makes the calculated stiffness too low.In this paper,the orthotropic constitutive relationship of the reinforcement,rubber compressibility and Poisson effect of the reinforcement were considered at the same time,and the solutions for distribution of rubber stress of a layer model of the isolator under either compression or pure bending was derived.And the analytical formulas of compressive and bending modulus were obtained.Furthermore,the formulas of compression stiffness,shear stiffness,compressive strength,roll-off deformation and limit roll-out deformation were derived.The proposed formulas were proved to be more accurate than the existed theoretical formulas,and was suitable for all the isolators employing orthotropic reinforcing materials.In addition,the proposed formulas can be degraded to the theoretical formulas of the conventional isolators and fiber-reinforced isolators by making reasonable assumption of the parameters of elastic modulus,Poisson’s ratio and the bulk modulus.(2)The proposed isolator was manufactured and experimentally investigated,and the theoretical results were compared with the test results.The isolator consists of short cut glass fiber reinforced polyacrylate plates and rubber layers bonded to the plates.The extrusion process of the engineering plastic plates and the forming process of the isolator were studied.Systematically experiments were carried out including tests on axial compression stiffness,basic shear stiffness,compressive stress relevance,shear strain relevance,frequency relevance,damping characteristics and ultimate performance.Another nine type of isolators of different parameters were also tested for axial compression stiffness and the basic shear stiffness to verify the proposed theoretical formulas.The test results showed that the proposed isolator had stable stiffness and good damping characteristics,and its compressive strength and shear deformation ability could meet the requirements of building isolation design.The theoretical stiffness of different isolators was in good agreement with the experimental results,which verified the accuracy of the proposed formulas.(3)Finite element analysis(FEA)and parameter optimization of the proposed isolator were carried out.The isolator was modeled using ABAQUS.The stress distribution and stiffness of the isolator model were analyzed under axial compression and compression-shear.The FEA stiffness was compared with the experimental results to verify the rationality of the FEA model.Then the variation of the compression and bending modulus with the elastic modulus of the reinforcement of a single layer model was analyzed,and it was compared with the proposed formulas to verify their accuracy.Then the stress distribution and roll-off deformation of the isolator under large deformation were analyzed.Based on the FEA results,the assumption of the effective compression area and the assumption of parabolic distribution of the compressive stress were proposed,which provided basis for theoretical analysis of stiffness degradation and roll-out instability.Finally,parameter optimization was conducted based on four isolators with different parameters.The effect of the number of layers,the thickness of reinforcement and the thickness of rubber on the maximum stress of the reinforcement were analyzed.The results showed that only the increase of the thickness ratio of the reinforcement to the rubber could significantly reduce the maximum stress.Considering that the strength of the proposed isolator was generally decided by the strength of the reinforcement,the optimal parameters of the isolator were proposed.(4)Simplified formulas for the stiffness and strength of the proposed isolators were derived.The steps of the weighted residual method of solving partial differential equations were introduced and the method was introduced to solve the equilibrium equation of the rubber stress.Taking three isolators of different shapes and reinforcement materials as examples,simplified formulas based on polynomial test functions were derived using collocation method.And simplified formulas of stiffness and strength of the isolators were derived.The simplified formulas were compared with the theoretical formulas and parameter analysis were conducted to give the applicable ranges of the simplified formulas.Results showed that the simplified formulas based on the weighted residual method had much simpler form than the theoretical ones,which greatly improved the computational efficiency.For the proposed isolators of common values of parameters,the error of the simplified formulas was within 10%.And it was proved that this simplifying method could be extended to the isolators with different shapes and reinforce materials.(5)A practical isolation design method and construction method were proposed based on the proposed isolator.The seismic reduction coefficient and isolation layer displacement of the isolated buildings were calculated using base shear method,under different sites and fortification intensity,based on the rigid assumption of low-rise masonry structures.The basic design procedure of the design method was introduced,and its applicable range based on the minimum damping ratio of the isolation layer was proposed.Based on the proposed isolator,the connection structure and the construction method for the isolation of rural buildings were proposed.All these research work provided basis for the ‘Code of Design for seismic isolation buildings’(under review).Finally,based on a demonstration project,the rationality of the practical design method was verified by comparison with FEA results,and the construction technology was introduced in details.