Investigation On Dynamic Response Of CFST Columns Subjected To Blast Loading

Except for static load, building structure might also experience explosive dynamicimpacts, such as terrorist bomb attack, gas explosion and etc. Because of sound stress balance,high bearing capacity, and convenient construction method, Concrete Filled Steel Tube (CFST)are comprehensively utilized in civil engineering. Therefore, academic researches on how theCFST would respond to dynamic changes carry significant theoretical meanings as well asapplication values. This essay employs methods of theoretical analysis, experimental studyand numerical modeling to facilitate the whole process; dynamic response, damage modes anddestruction mechanism are thoroughly discussed, using the methods mentioned above. Majorresearch work and outcomes are listed below:(1)2shells,3tubes of static explosive experiments on CFST are deployed for differentexplosive amount and in predetermined distances. The researcher measured the overpressuredistribution (on top, in the middle and at the bottom), the vibrating acceleration and thedisplacement lengths on both the plane facing explosion and the one opposite; these dataprovides grounds for predicting explosive load and for evaluating damage modes, destructionmechanism of the CFST. As the experience states, for the structure of comparatively highstiffness, impacts to the negative pressure region of the front plane and the back plane isrelatively small and is neglectable; when the environment is simple, the overpressure put onthe front plane approximately equals to reflecting overpressure in the free field.(2) This research studies the interaction between explosive blast and CFST. Bycomparing the facing-explosive overpressure distribution in the experiment with the existingoverpressure formula and by setting explosive characteristic parameter of TM5-1300as aprediction standard, the research provides reliable explosive load prediction for studyingCFST’s dynamic responding when facing explosive load.(3) This dissertation develops numerical simulation for the interaction between explosiveblast and CFST. Based on explicit dynamic program ANSYS/LS-DYNA and employingfluid-solid coupling algorithm, the researcher forms the numerical model for the interactionbetween explosive blast and the CFST surface through choosing sound material model, applying hourglass control method and considering boundary conditions. The results provethe numerical reasoning right. After analyzing the parameters, the result states that steel ratiohas barely influence on the interaction, while shape and scale of the section has strong effects.In another word, under the same explosive extent, explosive load on the round section issmaller than the one on the rectangle section.(4) This dissertation relies on equivalent single-degree-of-freedom system to study thedynamic response of the CFST. The author introduces the notion of equivalentexplosive-facing plane for CFST and applies ductility coefficient to calculate the maximumdynamic displacement under the triangle pulse load. The above process verifies the equivalentexplosive-facing plane method and the feasibility of theoretical calculation.(5) This essay establishes numerical simulative method for the dynamic response andcross-over analyzes the simulative results, the experimental results and the theoreticalcalculation. After massive numerical simulation and parameter analysis, the finals show that,as the scale distance grows, the horizontal maximum displacement and the residualdisplacement drops significantly. When the scale distance is over0.3m/kg1/3, its influence onhorizontal displacement can be ruled out. Lowering loading rate and reducing the size of thesection can evidently bring down the column horizontal displacement. Improving thecompressive strength of concrete and steel and enlarging steel ratio would optimize antiknockperformance of the CFST. Although rectangle CFST has nearly twice the moment of inertiathan round CFST, it is hard for explosive load to diffraction; the plane facing explosive is fourtime of the round one. Thus, round section tube has higher explosive resistance.(6) Typical destruction paradigm, according to various load type, can be categorized intoshear fracture, flexural mode and flexural damage. The results show that when the column issubjected to impulsive blast load, the column is inclined to be damage by shear; in thequasi-static region, however, the column is likely damage by flexural mode; and in the regionof dynamic loading, the failure of the column might be a combination of shear and flexuraldamage.