Full-filed 3D Deformation Measurement Technology In Experimental Study Of Steel Tube-confined Concrete Under Impact

The concrete-filled steel tubes(CFST)is a combination of steel pipe and concrete.It has the characteristics of high strength,strong toughness,good stability and high carrying capacity.In recent years,CFST have been widely used in large-scale bridges,civil buildings and other important engineering areas.In addition to the normal static load,these important components in the course of the service will suffer a variety of accidental impact loadingmore or less.The impact loading is short and the strength is high,and the deformation of the member is very rapid during the loading process,which makes the response of the impacted component have many different laws and characteristics compared with the failure with the static load.With the increasing application of CFST,it is very important to study the deformation and instability of CFST under the impact.As we know the traditional strain measurement methodwith single point and single direction has been unable to meet the various complex forces in the project.In order to measure the deformation of the concrete-filled steel tube during impact,the article introduces the digital image correlation technology to complete the high speed impact test of CFST.The method has the advantages of non-contact,high precision,wide measuring range,large strain rate span and simple operation.Through the test,we explored the effect of concrete-filled height on the crashworthiness and stability of concrete-filled steel tubes(CFST),andit proved the feasibility of digital image correlation which applied for high-speed impact measurement of concrete-filled steel tubes.It providenot onlya reliable basis for the crashworthiness of CFST,but also the global data which can directly and effectively reflect the extreme value of the strain.Through this test,we provides a new idea for the safety assessment method of building structure.Firstly,the paper describes the principle of digital image correlation method,and systematically introduces the key technology of each part of the method.Aiming at the corner impact test of CFST,a speckle evaluation model suitable for engineering application is proposed,and the effectiveness of the method is verified by simulation experiment.Then we build a digital image correlation measurement systemwith two high-speed camerawhich based on binocular stereoscopic vision and digital image correlation method.By using this system,we do the test and analyze the impact deformation degree and strain distribution of the steel tube to explore the effect of concrete-filled height on the crashworthiness and stability of CFST.This paper provides the basis for the correction and improvement of the correctness and validity of the finite element model and the modification and improvement of the model.And provide effective data for providing the method of defining the level of impact resistance of CFST under load.