Numerical Analysis Of Damage And Collapse Of Concrete-filled Steel Tube Frame Structure Under Blast Load

With the development of China's economy and the promotion of its political status,the probability of accidental explosions and terrorist attacks will inevitably increase,and the study of explosion and shock resistance of building structures has been paid more and more attention by scholars in the field of disaster prevention and mitigation engineering.At present,concrete filled steel tube(CFST)columns are widely used in bridges,multi-storey buildings and underground space.It is of great theoretical and practical value to study the anti-explosion and anti-collapse performance of CFST composite frame structures.Based on the test of CFST column members and the joint test to be carried out by our research group,damage and collapse dynamic response of CFST frame and multi-storey structures under blast load are numerically simulated by using the non-linear dynamic finite element analysis software ANSYS/LS-DYNA,in order to discuss the damage analysis process and design suggestions.The main research work and achievements are as follows:Firstly,the dynamic characteristics of blast loads and materials in frame structures are sorted out and the numerical simulation is realized by ANSYS/LS-DYNA.By comparing the failure modes and displacement responses of the tests,the applicability and accuracy of the software are verified.Two damage criteria for composite frame are compared and analyzed which shows the criterion based on deflection damage is fast and direct,while the criterion based on bearing capacity is comprehensive but error is large.For small equivalent blast,the fomer is more conservative.It is necessary to choose suitable damage criteria for different structural forms based on actual conditions.Secondly,according to the above scale parameter system to establish a multi-storey CFST composite frame structure model.The dynamic response and damage degree of beams,reinforcement rings and structures are studied under blast load.The results show that there are two kinds of damage modes of frame beams including axial compression and lateral bending and the damage wave height ranges from the first to fourth floor.By equivalent plastic strain damage,it can be judged that the most vulnerable fracture surface of the joint is connection between lower ring plate and beam.The steel yielded,but the joint did not break at last.The explosion resistance of frame corner column is better than that of side column but the stiffness of floor makes the energy dissipation in longitudinal direction of frame structure stronger than that in transverse direction.The displacement of corner columns are higher than those of side columns.Judging the interlayer damage according to elasto-plastic interstory displacement angle limit of frame structures.When the explosion occurs at the side and corner separately,the plastic damage height ranges from the 1-3 floor and the 1-4 floorThirdly,considering the advantages and disadvantages,internal and external factors,setting up three sets of parameters: scale distance,floor load and steel strength,flexible application of direct simulation method and demolition component method to analyze factors affecting collapse response of CFST frame structure.The results show that the scale distance has a significant impact,with the decrease of it(the increase of explosive equivalent),the range of frame increases,the trend of collapse is faster and the degree is greater.The failure mode of the frame structure is the integral collapse of the upper part due to the tie-up effect.Vertical collapse response is proportional to floor load.The collapse range is fan-shaped with the failure column top node as the center of the circle.The resistance of corner column to catenary mechanism is weaker than that of side column.Increasing the strength of steel can effectively improve the bearing capacity of joints.For side column,the increment is 15.11%.But has limited effects on corner.Lastly,the evaluation and design method of explosion resistance and collapse resistance of CFST frame structures are proposed.Anti-explosion design starts with strengthening the lateral resistance of components,and collapse resistance is based on increasing axial bearing capacity of columns and ductility or redundancy of structures.