Dynamic Response And Damage Assessment Of FRP-CFST Columns Under Blast Loading

Currently,explosion accidents caused by terrorist attacks and improper operation occur frequently.The performance of structures to resist blast load has become a hot topic in structural dynamics area.The fiber reinforced polymer-concrete-filled steel tube(FRP-CFST)column is that restraining with FRP sheets on the outer wall of the traditional CFST column.On one hand,FRP-CFST can be regarded as a new type of composite structure in design and construction phase.On another hand,FRP can be used to reinforce and protect existing CFST columns.The current research of FRP-CFST column mainly focuses on its static performance,but the research of its blast performance is very limited.Therefore,it is necessary to systematically study the dynamic response and damage assessment of FRP-CFST column under blast load,and it is of great significance to anti-blast design of FRP-CFST column.Moreover,it also has important engineering application value for blast mitigation and protection of CFST column with FRP material.In this paper,the dynamic response and damage assessment of FRP-CFST columns under blast load are systematically studied by combining theoretical research and numerical simulation.The main research work and innovative findings are presented as follows:(1)A numerical model of FRP-CFST column under blast load based on Arbitrary Lagrangian Euler(ALE)fluid-structure interaction is established,and its displacement and equivalent stress are analyzed.The results show that compared with the traditional CFST columns,the FRP-CFST columns exhibit better anti-blast performance.According to the parameter analysis,the deformation of FRP-CFST column can be reduced by increasing the strength of steel tube,increasing the strength of concrete or decreasing the axial load.Under the same section size,the blast resistance of FRP-CFST column with circular cross-section is better than that of square-section columns.(2)Retrofitting schemes of CFST column with FRP are proposed considering the type of FRP,the number of FRP layers and the retrofitting position.The numerical models of 33 different retrofitting schemes are generated based on CONWEP loading method.According to the comparison of displacement response,if the anti-blast protection effect is considered without considering the retrofitting cost,the use of multi-layer carbon fiber reinforced polymer(CFRP)material to strengthen the whole column performs the best for blast mitigation.If the retrofitting cost is considered,it is more economical to use glass fiber reinforced polymer(GFRP)material.Local retrofitting on the middle part or both middle part and two ends of the column is recommended with increasing the thickness of GFRP material.(3)The statistical parameters of the empirical calculation formulas for the peak overpressure,peak reflected overpressure and the duration in positive phase are fitted.By using the maximum response graph of equivalent single-degree-of-freedom(SDOF)under triangular load in UFC 3-340-02,the calculation steps for the maximum displacement of FRP-CFST column with different constraints is derived.The results calculated by theoretical approach are compared with the results analyzed by numerical solution,and the rationality of the two methods is mutually verified.(4)The support rotation angle is selected as the criterion for damage assessment of the structure.The damage degree of all cases in this paper is assessed based on the criterion.The P-I diagram of typical FRP-CFST column is drawn according to the SDOF methods,and nonlinear fitting of P-I curves is implemented.The proposed P-I curve can be used for damage assessment and prediction of FRP-CFST column.The influences of steel strength,concrete strength,axial load,steel ratio,FRP ratio,outer diameter of steel tube and height of the column on the P-I curve are discussed.The theoretical analyses and a series of numerical simulation and have shown the superiority of FRP-CFST and the FRP retrofitting schemes for blast mitigation.The work of this paper also provides numerical basis and theoretical guidance for the anti-blast design of FRP-CFST column and the prediction of damage degree of column under arbitrary blast load.