Study On Seismic Performance Of Stone Masonry Structure Suitable For Villages

According to the Chinese and International present research status,the current research of stone masonry in southeast villages of China mainly focuses on the compressive strength,shear strength,scale walls’ seismic performance and strengthening measures of dry shedding stone masonry.The defect of dry shedding stone leads to a lower full degree of mortar at bed joint,leading to unsatisfy shear capacity.Strengthening way of dry shedding stone masonry,like grouting,rebar mesh and caulking reinforcement masonry,often leads to issues determined by low construction quality,complex construction procedure,unreplacement,delaying construction time and not guaranteed the compatibility between different materials.The previously cited techniques were recognized as not suitable for strengthening stone masonry in towns and villages.Otherwise,adopting scale walls can not reflect the real seismic performance of full-scale walls,furthermore,a specific scale procedure was not provided to replace the full-scale walls by scaling method.This thesis focuses on the mechanical properties of coarse ashlar stone masonry with shims,fine stone masonry walls and seismic resistance of walls.Compared with the dry shedding stone masonry,the coarse ashlar stone masonry including shims and fine ashlar stone masonry walls can ensure the desiderable high full degree of mortar in bed joint.However,for material,mechanical,seismic performance and working mechanism of the coarse ashlar stone masonry including shims and fine ashlar stone masonry walls are not enough.For the defects of dry shedding stone masonry strengthened,new requirements were put forward for strengthening stone masonry walls,for example,convenient,fast and effective construction.Until now,the strengthening methods of brittle stone slab mainly include pre-stressed NSM CFRP bars and reinforced mortar.For the prestressed NSM CFRP bars,prestressed method can increase the transverse axial force that forms an inverted arch effect on the slab.This mechanism is not clear for effect on the slabs,and slotting size is not considered.Furthermore,the synergic work between reinforced mortar and stone slab is not deeply investigated,leading this thesis to propose a strengthening way of near slotting mounted screw steels in the slab.The near slotting mounted CFRP in the slab will also been adressed,further studying the advantages and disadvantages of two methods’ flexural capacity.In view of the above defects and characteristics,the paper mainly carries out an integrated research of the mechanical properties of stone masonry.It analyzes the influence of factors on seismic performance of unreinforced coarse aggregate stone,proposing and analyzing strengthening measures of coarse aggregate stone to the strengthening treatment of flexural properties of stone slabs.The aim of the research is to form a systematical understanding of materials and structures behavior,leading at the same time to an improvement of theoretical understanding and tools available for practitioners.The following conclusion can be drawn from experiments and analysis.Firstly,the materials of stone is granite in southeast China,the paper carried out experiments about the compressive strength and tensile strength of stone block,compressive strength of stone masonry coarse ashlar stone masonry including shims and fine ashlar stone masonry.The main conclusions are as follows: with the increase of mortar strength,the compressive strength of coarse ashlar stone masonry including shims and fine ashlar stone masonry increases.It can be concluded that by comparison between compressive strength of coarse ashlar stone masonry including shims and fine ashlar stone masonry,the compressive strength of fine ashlar stone masonry is greater than the compressive strength of coarse ashlar stone masonry including shims,These results are justified by two reasons,one is that the thickness of bed joint of coarse ashlar stone masonry including shims is greater than fine ashlar stone masonry,the other is that coarse ashlar stone masonry includes shims,and the stiffness of shims is greater than the mortar,possibly leading to a stress concentration in the stone block.Secondly,the failure process of the shear strength of stone masonry can be divided into three stages: elastic stage,bond strength disappearance stage(elastic-plastic stage)and friction energy dissipation stage;With the increasing of vertical pressure,the initial shear stiffness of shear stress;shear displacement curve of fine stone masonry and coarse stone masonry gradually increases;At the same time,the shear strength of fine stone masonry increases.Finally,the formulas for calculating the shear strength of fine stone masonry and coarse ashlar stone masonry including shims are given based on the code and Mohr-Coulomb criterion.Thirdly,the experimental study on seismic performance of full-scale stone wall mainly investigated the influence of mortar strength,reinforced mortar band and reinforced mortar band on the seismic performance of the wall.Based on the theory of elastic uniform deformation,it can be judged whether the wall is bending or under shear failure.The main conclusions are as follows: the increasing of mortar strength has an evident impact on the seismic performance of the wall.The increasing of stiffness and load-bearing capacity of stone masonry can obviously enhance the seismic performance of stone walls with reinforced mortar belts and structural columns.It is also pointed out that the use of reinforced mortar belts alone will adversely affect the seismic performance of walls.The main reason is that when the diagonal shear crack is formed and reinforced mortar belts hinder the crack propagation,this also hinder the relative movement among stone block.When the hindering action is maximum,if increasing the loading,it will lead to the collapse of walls and subsequent loading capacity of walls abruptly descends.This goes against the earthquake resistance.The present research proposes a method to judge if the walls are under flexural failure or shear failure,which can reasonably predict the failure mode of the wall.Fourthly,through the seismic performance analysis of six full-scale tests of coarse aggregate stone,it can be seen that the deformation of coarse aggregate stone wall can be divided into three stages: linear elastic stage,elastic-plastic stage(the interface bonding force disappears completely)and friction energy dissipation stage.It is also shown that the lime joint interface of coarse aggregate stone wall has a very large energy dissipation capacity.In seismic design,the energy dissipation capacity of lime joints should be fully utilized;under the same conditions,the energy dissipation capacity of coarse stone masonry wall is worse than that of fine stone wall.The bearing capacity,ultimate displacement and initial stiffness of coarse stone wall are larger than that of fine stone wall,indicating that the coarse stone wall is designed to meet the seismic performance.In addition,a scaling method is proposed to simulate the seismic performance of full-scale walls.It can be act as a alternative scheme for experiment modeling.Finally,based on the simplified Turnsek’s model,the bearing capacity of coarse stone walls can be predicted reasonably.Fifthly,the existed tension-compression bar model has been revised,and the tension-compression bar model is unified to calculate the bearing capacity of the coarse aggregate stone model considering the failure model.Finally,the performance level of the coarse aggregate stone wall is given based on the four-stage performance level,which provides a reference for the future seismic performance design of the coarse aggregate stone structure.Sixthly,the optimal layout of prestressing tendons to reinforce coarse stone masonry is further described.It can be obtained by the arrangement of reinforcements at both ends and in the middle with a vertical compressive stress of 0.2 MPa.At the same time,using the roughness of the grey joint interface,this combined action can obviously improve the seismic capacity of the wall.Finally,the calculation method of pre-stressing tendons to reinforce the stone masonry structure is proposed.Seventhly,the stone slab is strengthened by embedding thread steel and CFRP bars.Considering the influence of groove size,reinforcement ratio and reinforcement material on the flexural capacity of the stone slab,the flexural performance is studied for the aspects of cracking load,bearing capacity and failure model.The results show that embedded thread steel and CFRP are adopted.The failure mode of reinforcement can be transformed from brittle failure to ductile failure.With the increasing of reinforcement ratio,the failure mode of stone slab is similar to that of reinforced concrete flexural members.From the above study,it can be found that the research establishes the integration research from the mechanical properties of stone materials to the seismic performance of stone masonry members.It has an important relevance for the follow-up study of the seismic capacity of stone masonry,and can be used as a basis for the seismic performance evaluation of stone masonry buildings.