Blast Shock Responses Researches For Concrete-filled Steel Tubular Columns With Elastic Restraint:SDOF Model And Rapid Assessment Methods

Concrete-filled steel tubular(CFST)columns are widely used in engineering practice due to their high bearing capacity,good plasticity and toughness,and convenience in construction.The CFST structures may be subjected to blast loads caused by explosion accidents and terrorist bomb attacks during their life-cycle.It is of great academic value and engineering significance to conduct research on the dynamic response and damage assessment of CFST columns under blast loads.In this paper,the theoretical models were used to conduct a systematic study on the dynamic response and damage assessment of CFST columns under blast loading.The main work and results are as follows:1.The equivalent single-degree-of-freedom(SDOF)model of the global bending and shear responses of CFST columns was established with regard to the influence of column end constraints,axial load and non-uniformity of blast load distribution,etc.Then the improved SDOF model was validated by the existing blast tests.The results show that the end constraints of the CFST columns have an significant influence on the global bending response of the CFST columns.The influence of the end constraints of the CFST columns on the response modes and bending deformation should be included;The resistance can be calculated according to the method proposed by Han Linhai;for the calculated blast tests,the triangle load model can be used for near-field explosion and far-field explosion,and the parameters can be calculated according to the method proposed by Kingery-Bulmash;the uneven lateral distribution coefficient of the circular cross-section load can be taken as 0.7.2.Based on the validated SDOF model,the mechanism analysis and parameter analysis of the dynamic response for the CFST columns under the blast loading were carried out.Results show that both the global and shear responses can be divided into three response modes,i.e.,elastic response,elastoplastic response and plastic response.The stiffness of the end constraints of the CFST columns has a great influence in the sensitive range.The greater the stiffness of the end constraints of the CFST columns,the smaller the maximum and residual deflection.The scaled distance and the blast distance have the greatest influence on the maximum deflection,residual deflection and maximum shear strain of CFST columns.The greater the scaled distance and the blast distance,the higher the maximum deflection,the residual deflection and maximum shear strain.The influence of the axial load ratio is nonlinear.And the maximum deflection and residual deflection decrease firstly and then increase with the increase of the axial compression ratio.The influence of other factors is minor.The longer the length of the column,the larger the maximum deflection,residual deflection and maximum shear strain.The larger the steel tube size and material strength is,the smaller the maximum deflection,residual deflection and maximum shear strain.3.Based on the improved SDOF model and energy method,a damage assessment method for a CFST column under blast loading was proposed,which can rapidly establish a P-I curve.Results show that the asymptote obtained by the improved energy method is in good agreement with the results obtained by the analytical method;the CFST columns are prone to cause shear failure under impulse load and global unstability failure under quasi-static load;near the upper limit of the sensitive range,the P-I curves of the middle and bottom columns are very close.