Transient Response Of Pre-stressed Steel Strand When Subjected To Impact Loading

With the rapid development of China’s economy,large-scale public buildings such as airport terminals and bridges have been rapidly developed.However,the buildings may be seriously damaged by factors such as earthquakes,tsunamis and terrorist attacks.Pre-stressed steel strand are widely used in many large-span buildings due to their high bearing capacity and good relaxation performance.However,there are few studies on the mechanical response of pre-stressed steel strand subjected to strong dynamic loads such as impact.Therefore,this thesis focuses on the study of transient response of pre-stressed steel strand when subjected to impact loading.In this thesis transient response of pre-stressed steel strand when subjected to impact loading is studied by tests and finite element analysis.The main contents include:(1)The stress-strain relationship curve and key material parameters are obtained by carrying out the tensile test specification of metal materials of the pre-stressed steel strand.On this basis,the finite element analysis software ABAQUS was used to carry out the finite element simulation of the pre-stressed steel strand tensile test,whose process is repeated by defining the material properties.Finite element analysis results show that during the tensile process of the strand,the contact area between the center wire and the outer wire and the outer wire is in a complex stress state,and the other free end regions of the outer wire are still in a uniaxial tensile stress state.(2)The axial loading device was invented to support the drop hammer system and apply impact kinetic energy to strands of different pre-stressed states.In this way,the impact mechanical behavior is studied.Tests have found that sparks are present in the process of impact fracture of pre-stressed steel strands.When the impact load is small,the impact process is divided into three stages:elastic-plastic bending wave propagation,axial force stretching and elastic rebound.As the impact kinetic energy increases,the strand may break.The breakage of the strands is carried out in a root-to-root failure mode.The presence and increase of axial pre-stress does not significantly change the critical kinetic energy value,but significantly reduces the lateral displacement at break.(3)Beam unit,solid unit,beam and solid coupling models are used separately when applying the finite element program ABAQUS package.The application of the spring unit to simulate the slip relationship between the steel strand and the anchor is developed and compared with the experimental results.Numerical results show that the mid-span area consumes the most energy and absorbs a large amount of energy instantaneously when it breaks.In addition,it was found that the steel strand was first controlled by the bending moment,then controlled by the axial force,and finally broken.The slip of steel strands and anchors can significantly affect the impact mechanics.Multi-scale model can accurately predict the dynamic behavior of steel strands on the basis of keeping computational efficiency.Through the research in this thesis,a new understanding of the mechanical response of pre-stressed steel strand under impact loads has been made.Provide an effective basis for the safety evaluation of pre-stressed steel strand.It is of great significance to theoretical research and engineering design in the future.