Structural Vulnerability Evaluation Considering Material Elastic-plastic Properties,Parameter Randomness And The Contributions Of In-ternal Forces Of Components

In order to avoid the continuous damage of structures in emergencies,the vulnerability of structures must be considered in the design,and the existing vulnerability analysis theory still needs to be improved in quantitative analysis.Therefore,it is of great theoretical and practical significance to develop a vulnerability index system and quantitative calculation method for describing the structure under different static and dynamic loads by studying the vulnerability of structure.Due to it,four structural vulnerability analysis methods have been proposed for truss structures and frame structures,and the effects of plastic properties,static and dynamic loads on the internal forces of components and uncertainties have been considered in these methods.The main research contents and achievements and are listed below.Firstly,in order to present structural vulnerability analysis close to practical failure situations,a practical method based on the plastic properties of materials has been developed for calculating the component importance coefficients of a truss structure.The design of the truss structure was further optimized using the proposed method.The component material was assumed to possess both elastic and plastic properties.The plastic situations and failure patterns of truss components were defined according to their stiffness loss.Meanwhile,the bearing capacity of a truss structure was considered by means of additional loads during the plastic analysis.Then the relationship between structural stiffness matrix and deformation stiffness matrix was established in order to seek for the inherent connection between components' displacements and corresponding deformations.After that,the plastic importance coefficient of each component was deduced.Lastly,through predefining the worst loading scenario and the failure pattern of the truss structure,its component design was optimized with the aid of the developed method.The analysis results demonstrate that after involving the plastic properties of materials,the importance coefficients are different from those calculated by considering only the elastic properties.However,the failure patterns become more rational.At the same time,the components of an optimized truss show better mechanical performance under external loads.In addition,the validity and reliability of the method have been verified by the example of steel truss.Secondly,taking into account the possible randomness(uncertainties)existing in structural parameters,a concept of relative sensitivity based on reliability indices has been proposed.Furthermore,a method for calculating the component importance coefficient was developed by integrating the plastic importance coefficients and the relative sensitivity theory.After that,the feasibility of the proposed method was validated using the aforementioned experimental steel truss.Thirdly,a component importance evaluation method for frame structures under horizontal and vertical loads is developed in this paper.The strain energy equation,together with the node-external force relationships of frame components,is first used to calculate the axial forces,shear forces and bending moments of beams and columns.Then component-level partial importance coefficients are defined based on the ratios between the calculated internal forces of components and their resisting forces.The coefficients embody the utilization levels of the resisting forces of components.Subsequently integrated importance coefficients are defined using the combinations of different partial coefficients,which reflect the component contributions to the entire load capacity of a frame structure.Lastly,the feasibility of the developed method is verified against two different frame structures.The analysis results demonstrate the method can provide quantitative evaluations for the optimal design and the progressive collapse design of frame structures.Lastly,due to the randomness of seismic excitations and uncertainties existing in structural seismic fragility analysis,a new concept of partial coefficients of seismic effects has been proposed for the purpose of quantitative seismic collapse analysis of multi-story RC frame structures.seismic excitations were defined as seismic motion parameters,by which means a dynamic solution procedure was simplified into a static one.Then partial coefficients of seismic effects were used to embody the importance of each beam or column of an RC frame.Collapse judgment criterions were also given for subsequent analysis.Meanwhile,an inverse analysis procedure was adopted and the critical values of seismic motion parameters were obtained according to the collapse critical state of the frame.After that,specific collapse criterion formulas were established according to which the collapse situation of the frame was quantitatively determined.Lastly,dynamic time-history analysis was used to calculate the equivalent values for interstory drift ratios with respect to the critical values.The accuracy of the aforementioned critical values was defined by deviation rates.A 7-story RC frame was adopted to validate the feasibility of the proposed method.