Damage Identification Method And Experimental Study Of Beam String Structure Based On Modal Parameters

The beam string structure is a kind of spatial hybrid structure formed by the combination of the upper rigid arch truss and the lower flexible cable through the strut,which is widely used in large-span steel roof structure such as gymnasium and station hall.With the increase of operating time,an increasing number of beam string structures will experience the demand for the safety assessment and maintenance reinforcement,especially when the damage on such a structure may have a great impact on the safety of important projects,furthermore,the damage may even cause a continuous collapse.Therefore,there is a great practical significance to study the damage identification of the beam string structure during the operating time.However,there are different types of rods,such as cable,pole and truss,which lead to a more complicated mechanism of the structure,and its damage identification is different from that of conventional bridge structure or multi-storey building.As the relevant theoretical and experimental research is still insufficient.The damage identification method based on the modal parameters of the beam string structure with considering the structural characteristics of the beam string structure and the sensitivity analysis of the lower cable system and the upper truss bar is proposed in this paper.The damage identification experiments of different types of damage conditions and the numerical simulation of damage identification are also carried out for practical engineering application.The main contents include:(1)The advantages and disadvantages and applicability for the three kinds of damage identification indexes are studied by theoretical analysis of the regularized frequency change rate,curvature modal difference and modal flexibility difference curvature to lay the theoretical basis for selecting the appropriate damage identification index for the lower support system and the upper truss bar respectively.(2)The ANSYS finite element analysis model of the string truss structure is established,and the susceptibility design module(PDS)is used to analyze the sensitivity of each part of the finite element model.The influence of parameters such as upper truss structure part,lower cable structure part,chord weld part and cable pre-stress on the natural frequency of the structure is studied,which can provide the basis for selecting appropriate damage identification and determining the damage location of structural damage.(3)A method of damage combination recognition for beam string structure is proposed based on the results of rod sensitivity analysis and the applicability of each damage identification method,and the damage degree identification of the lower part is carried out by using the regularized frequency change rate index.The damage degree identification of the upper truss section carried out by using curvature mode difference and modal flexibility difference curvature index.The finite element model is used to simulate the damage of the truss,the partial damage of the support,the damage of the weld and the pre-stress loss of the cable.To carry out the analysis of the damage identification under different damage conditions and verify the feasibility of the damage identification of damage identification index of each part of the beam string structure,which verified the effectiveness of truss string structure damage identification method of combination.(4)’The damage identification test of two-piece truss structure model with 6m span is designed and tested.The two models with different cross-sectional dimensions is verified by the method of damage combination identification.In this paper,the damage location of the rods of the test structures is determined by the analysis of the sensitivity of the rods in the finite element model.A variety of damage conditions are designed,including the damage of the trusses,the damage of the cable part and the pre-stress loss of the cable.The damage mode is to replace the different cross-section bar.According to the order of each condition,the structural model is tested and modal analysis is carried out.The impact hammer is used to energize the structure.The modal data obtained from the non-destructive condition of the experimental structure are compared with the finite element model,and the correctness of the model is verified.The damage identification index is verified by the experimental data.The validity of damage identification,and provide the basis for subsequent engineering application.(5)The damage identification analysis of actual engineering of beam string structure in a train station is carried out.Firstly,the modal analysis of the structure is carried out to unriddle its dynamic characteristics.The frequency fingerprint library of the lower part is constructed,and the partial vibration data of the trusses are obtained.The curvature modal difference index and modal flexibility difference curvature index are used to obtain the truss partial damage identification verification and it has a better recognition effect.