| In long-spans,large and heavy-duty industrial plants and high-rise building and ultra-tall building structure with high seismic fortification intensity,short columns are unavoidable vertical load-bearing components.Their seismic performance is of great significance to the safety of building structures.Because the concrete is a kind of brittle material,the concrete cover of the steel reinforced concrete short columns will still be crushed and peeled off with large area suffering from earthquake action,caused the buckling of the longitudinal reinforcement and the pull off of the stirrup,which makes the internal shape steel lose the effective restraint earlier and due to the buckling and other phenomena,thus reducing the bearing capacity,seismic performance,damage resistance and repairability of the steel reinforced concrete short columns.At the same time,the steel reinforced concrete short columns have poor fire resistance and durability,and it is easy to cause construction difficulties.Based on this,in order to give full play to the advantages of shape steel and UHTCC,UHTCC with excellent strain hardening,multi cracks cracking and high toughness characteristics will be used to replace the traditional concrete,and combined with shape steel to form steel reinforced ultra-high toughness cementitious composite(SUHTCC)composite structure.The specific work and main conclusions are as follows:Firstly,the influence of anchorage length and stud shear connectors on the bond slip behavior of UHTCC and shape steel is studied through 5 push-out tests of short columns,and compared with steel reinforced concrete specimens,the prediction formula of bond strength and bond-slip constitutive model of shape steel and UHTCC are given by regression.The following conclusions were obtained: 1)After concrete is replaced by UHTCC and combined with shape steel,the fracture morphology is more fine,and the nominal peak bond strength of shape steel and UHTCC specimens is slightly reduced,but it has high residual bearing capacity and residual bond strength,and the bond toughness and bond energy consumption are greatly increased with slightly damaged,which significantly improves the interface bond-slip performance of steel reinforced concrete.2)With the increase of anchorage length,the peak value and residual bond strength of shape steel and UHTCC specimens increased,but the nominal peak value bond strength and nominal residual bond strength decreased slightly,and the bond toughness and bond energy consumption decreased;3)After the studs are arranged on the shape steel flange,the bond slip performance of shape steel and UHTCC specimens before the peak value is obviously improved,but the bond slip performance after the peak value are reduced with especially the bond toughness and bond energy dissipation.Compared with the existing formulas used to calculate the bond strength of steel reinforced concrete,the prediction formula of bond strength of shape steel and UHTCC is given by regression;4)Combined with the tests results,an applicable bond-slip constitutive model of shape steel and UHTCC is established,and the model curves is in good agreement with the test curves.Secondly,in order to study the seismic performance of the steel reinforced ultra-high toughness cementitious composite(SUHTCC)short columns under seismic action,by changing the axial compression ratio,volume-stirrup ratio,loading system and the studs,the 8 specimens of the steel reinforced ultra-high toughness cementitious composite short columns and 1 specimen of the steel reinforced concrete short column were tested.The following conclusions were obtained: 1)After concrete is replaced by UHTCC and combined with shape steel,shape steel and UHTCC show better the deformability and seismic performance,and can improve the brittle shear failure mode of short columns,and have high damage resistance and repairability under large deformation,and make the SUHTCC short columns have a good energy consumption capacity and seismic performance even under the condition of high axial compression ratio and low stirrup ratio;2)The reversed cyclic loading mode can reduce the bearing capacity of SUHTCC short columnsx.After the peak value,the load decreases faster,and the deformability and ductility decrease;3)With the increase of the axial compression ratio,the energy dissipation capacity and ductility of the SUHTCC short columns decrease,but the SUHTCC short columns still have better nonlinear deformability and seismic performance under high axial compression ratio;4)For the SUHTCC short columns with different stirrup ratio,the hysteretic curves are full after the peak value.The SUHTCC short columns with the largest stirrup ratio show better energy consumption capacity,but the SUHTCC short columns with the smallest stirrup ratio still have good energy consumption capacity,ductility and seismic performance;5)After the studs are arranged on the shape steel flange,the bearing capacity and energy dissipation capacity of the SUHTCC short columns have been greatly improved,but the improvement of its ductility is limited.The arrangement of studs on the shape steel flange can greatly improve the hysteretic performance and energy dissipation capacity of the short columns with lower axial compression ratio,but the improvement of the SUHTCC short columns is limited with higher axial compression ratio;6)At last,the shear capacity of the tests short columns is calculated by different codes with the calculation formula of shear capacity of steel reinforced concrete columns.The results show that it is feasible to apply the Chinese code(JGJ 138-2016)to the shear analysis and design of SUHTCC short columns with shear span ratio less than 2.0.Finally,At the component level,the seismic damage assessment of steel reinforced ultra-high toughness cementitious composite columns is carried out based on deformation and damage.The following conclusions were obtained: 1)The seismic performance level of the SUHTCC short columns can be divided into six grades,and the performance targets of the composite columns under different damage and failure conditions are established;2)Taking the rotation displacement as the deformation performance control parameter,the selecting value principle of rotation displacement is also defined by two methods under different performance levels,and the value range of rotation displacement indexes limit is given.The results show that when concrete is replaced by UHTCC,the deformation limits of steel reinforced concrete can be relaxed at different performance levels;3)Combined with the existing damage index ranges corresponding to different performance levels and the damage process of the tests,damage index ranges corresponding to different performance levels of the tests SUHTCC composite column is divided;4)Based on the classical Park-Ang model and Kratzig model,the modified M-Park-Ang damage model and modified M-Kratzig damage model are proposed.The results show that the two improved seismic damage models can more truly reflect the damage behavior of the steel reinforced ultra-high toughness cementitious composite short columns. |
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