Study On Mechanical Behavior Of Prefabricated High-strength Foamed Concrete Self-insulation Shear Wall

Because of the many problems existing in the building thermal insulation mode in China,comprehensively considering the development goals of carbon peaking and carbon neutrality,combined with the development needs of rural buildings,a kind of prefabricated high strength foamed concrete self-insulation shear wall(HFSW)structure with vertically distributed steel bars disconnected was proposed based on the newly developed high strength and high heat resistance foamed concrete.This new type of shear wall structure has many advantages as better thermal and sound insulation property,lightweight,good fire-resistant and seismic performance,and it could realize the same life cycle of building insulation and structure.The shear wall integrates structural self-insulation and building industrialization,which is of great significance to the improvement and development of multi-storey rural buildings in china.Based on the development of the foam concrete with high strength and high heat resistance,the vertical loadbearing properties and seismic capacity of the HFSW shear wall were analyzed through experimental studies,finite element parameter analysis and theoretical derivation.The main research works and research results are as follows:1.By adding polypropylene(PP)fiber,fly ash to the foam concrete and using composite foaming agent as well as polycarboxylic acid water reducer,the compression strength of5.2MPa and thermal conductivity of 0.14W/(m.K)foam concrete with A08 density grade was developed based on the optimization of the mix proportion.Compared with the same density grade foam concrete,the compressive strength was increased by more than 70%,and the thermal conductivity was reduced by more than 30%.The water absorption rate and carbide coefficient of this foam concrete meet the relevant specifications in China,and its dry shrinkage level is at a medium level compared with previous studies,the freezing resistance performance meets the requirements of hot-summer and warm(or cold)-winter zone specifications for the use of exterior wall materials.2.Under the action of axial compressive load,the bottom connection of the HFSW shear wall is safe and reliable.The damage is mainly manifested in the cracking of the interface between the prefabricated wall piece and the post-cast column,and the horizontal wrinkles and vertical cracks of the wall are developed in large numbers.The final damage is due to the local crushing of foam concrete on the top side of the wall.Increasing the reinforcement rate of distribution reinforcement could significantly reduce the number of horizontal wrinkles,and has a positive effect in delaying wall cracking,improving vertical bearing capacity as well as vertical stiffness.The failure mode of the cast-in-place wall was almost the same as the prefabricated ones,and the difference in the peak carrying capacity was small.The out-of-plane angles were between 1/162～1/300,and global bulking did not occur during the loading process.3.Through the shear strength test of the wall under cyclic loading,the ductility coefficient of HFSW shear wall is relatively small,which is between 1.8 and 2.5 as a whole.Different from the traditional concrete shear wall,a large number of shear inclined cracks were developed on the wall body,and formed an obvious "X" shape network distribution.There is no interface separation phenomenon in the sizing layer,and the bottom connection is safe and reliable.When the peak bearing capacity is reached,the longitudinal reinforcement of the side column has yielded,and the distributed reinforcement generally does not yield.Similar to the traditional concrete shear wall,the foam concrete diagonal compression struts were locally crushed at the bottom sides of the wall while it reached the peak load-bearing capacity.The use of a low distribution steel reinforcement ratio could still ensure the structural integrity,and the two work well in coordination.Due to the development of a large number of cracks as well as the relative slippage between the steel rebar and foam concrete,the hysteresis curves of the specimens exhibited obvious pinching characteristics.Increasing the width of the wall had an obvious effect on improving the shear bearing capacity,and the unit size bearing capacity of the wall showed a trend of first increasing and then decreasing as the width of the specimen increased.The axial compression ratio has a significant effect on the lateral stiffness of the specimens with a large shear-span ratio,but has little effect on the specimens with a small shear-span ratio.The shear strength of cast-in-place components was improved within 20% compared with the prefabricated ones.4.Large shear-span ratio(two-story)HFSW wall behaved as bending controlled failure mode under cyclic load.Local crushing of the column bottom on both sides occurred when the peak load was reached.Due to the low strength of foamed concrete,a large number of shear cracks also appeared at the bottom of the wall.A large number of horizontal oblique downward bending cracks were generated at the bottom of the bottom-storey and obvious local crushing occurred at the bottom of the columns of the bottom-storey because of bending action.The vertical joints on both sides of the bottom-storey of the wall were completely cracked,but no interface separation occurred,and the interface separation phenomenon occurred in the tension zone of the mortar layer at the bottom of the wall.Compared with the shear failure controlled specimen,the deformation capacity of the bending failure specimen was improved to a certain extent,and the peak load carrying capacity was not significantly reduced.The characteristic stiffness of the wall at each stage was lower than that of the single-storey wall with shearcontrolled failure.The ductility coefficient of the bottom storey of the two-storey specimen was slightly smaller than that of the single-storey wall,but the difference was not obvious,and its energy dissipation capacity was slightly better than that of the shear failure controlled ones.5.By using the plastic damage model,comprehensively considering the material stressstrain relationship,and boundary conditions,as well as interface relationship and other factors,the HFSW shear wall finite element model was established.The calculated shearing-controlled and bending-controlled failures were all consistent with the experimental failure modes.The peak point calculation results were in good agreement with the test results,and the differences between them were within 10%.Parameter analysis showed that the peak load-bearing capacity of cast-in-place shear specimens was improved by an average of 15.8% compared to fabricated ones,and the degree of influence of each parameter on the bearing capacity from high to low was wall width,side column reinforcement ratio,and wall thickness.Whether cast-in-place or not has no obvious effect on the flexural strength of HFSW shear walls,while the average increasement was 5.7%.6.According to the test results,combined with the finite element force transmission path analysis results,the softened Strut and Tie model and the corresponding simplified calculation method for predicting the shear capacity of the wall were first established based on redefining the calculation method of the diagonal compression strut and the reduction ratio of the effective area of the reinforcement tie,and the average calculating precision of the model was 1.04 and0.94,respectively.Then,based on the structural characteristics of the wall,a relatively conservative frame-softened Strut and Tie model and the simplified calculation method were further proposed,and the average calculation accuracy was 0.93 and 0.86,respectively.Finally,based on the actual stress situation of cast-in-place components,the calculation model was reasonably modified to make a more accurate prediction.7.According to the failure mechanism of the axial compression test,the design formula for the axial compression bearing capacity of the HFSW shear wall was modified and obtained,and the calculation deviation was within 5%.On the basis of the frame-softened Strut and Tie model,semi-empirical design methods for the prediction of shear strength of cast-in-place and fabricated HFSW shear walls were proposed through force balance and parameter fitting method,respectively,as the average calculation accuracy was 0.96 and 0.95,the maximum calculation deviation was within 10%.Referring to the calculation method of the load-bearing capacity of the large eccentric compression member,combined with the stress analysis of the normal section of the test member,the calculation methods of the flexural capacity of the castin-place and fabricated HFSW shear walls were respectively proposed,and the maximum calculation deviation in the two cases were all within 10%,and the calculation accuracy was above 0.9.8.In this paper,the four-line skeleton curve model that can accurately reflect the stress characteristics of the fabricated HFSW shear wall at each stage was proposed,and the calculation method of each characteristic node was given.In addition,according to the "pinch" feature of the wall hysteresis loop,the dynamic calculation methods of the slip points in the ascending section and descending section related to the loading stage were respectively proposed.On the basis of comprehensive consideration of unloading stiffness degradation and strength degradation,a good fit HFSW shear wall restoring force model and specific calculation process were proposed.