Seismic Damage Evolution And Performance Control Of Reinforced Concrete Structure And Subsystems Considering Multiple Modes

The seismic safety of concrete building structures has always been an important subject related to the safety of people’s lives and property.The performance-based seismic design method provides a new design idea to ensure the safety,reliability,and economic rationality of the structure.In the development of performance-based seismic design,one of the focuses is to reasonably quantify and effectively evaluate the seismic performance and damage state of the structure.The structural damage model is an effective way to solve this problem.Establishing a reasonable seismic damage model and quantitatively describe the damage degree of the structure under the earthquake is the basis of revealing the seismic damage evolution rule and exploring the method of structural damage control.It is of great significance to establish a reasonable seismic damage model for the structure to improve its seismic performance and ensure its safety.This dissertation focuses on two main subjects,i.e.,the quantification of global seismic damage characterization and the subsystem seismic damage.For the general reinforced concrete structure,a new global seismic damage model considering the effects of multiple modes is proposed.Based on the multiple modes global damage model,the damage quantification methods of different subsystems are established,and the relationship between the subsystem damage and global damage is revealed.By studying the evolution of the global damage and subsystem damage,and considering the latest "four-level" ground intensity classification,the quantified performance-based damage control target curves are proposed.Through the study,the innovative research achievements of this dissertation are as follows,(1)A global seismic damage model for reinforced concrete structures is proposed,considering the influence of higher-order modes.Based on the Ghobarah damage model and the concept of modal decomposition,the modal damage model of the structure is redefined by adopting modal stiffness factors.Considering the physical meaning,mathematical characteristics of modal damage,a combination rule special for the modal damage model is proposed with the assumption of the independent modal damage in-series.And the relationship between the combination rule and the SRSS rule is established with a suggested value of β.The characteristics of the modal mass contribution factor λn in the damage model are studied,which can be used to explain the influence of the change of mode shapes on the fluctuation of modal damage.The results show that the damage model can characterize the damage state of the structure well.With the increase of the PGA level and the number of modes involved,the global damage curve shows obvious convergence.Moreover,the values of the damage index at the critical collapse point have a good correlation with the IDA curves,which means the damage index can be used as the collapse criterion of the structure.(2)The shear-type structure is geometrically divided into story subsystems,the story damage description is established and the influence of the story subsystem damage on the global damage is revealed.The story damage description as well as the relationship between the story subsystem damage and the global damage are established.The influence of damage location,the damage degree,and the number of damaged stories on the modal damage index and global damage index are studied by the parameter analysis.The internal laws of damage evolution and the migration of damage among different structural levels are further revealed.The results show that the global damage considering multiple modes can reflect the importance of the bottom story.With the higher location of the damaged story,the sensitivity of the basic modal damage decreases.As the number of damaged stories increases,the higher-order modal damage also increases gradually,and the structural global damage evolution curve gradually changes from concave curve to convex curve.In addition,all stories are not able to 100%utilize the damage-resistant ability.(3)The typical dual-system,i.e.wall-frame structure,is divided into subsystems from a physical perspective,the damage quantification methods of the frame subsystem and shear wall subsystem are established,and the damage evolution and migration rules are expounded.By combining the multiple modes damage model and the generalized shear-flexure coupled model,the subsystem damage description method and the relationship between the global damage and subsystem damage are derived.Based on the derived relationship,the damage evolution and migration of subsystems are studied.The results show that the damage development of the wall-frame structure heavily depends on the relative stiffness of the frame subsystem and the shear wall subsystem.The damage index df and dw can well represent the dynamic redistribution of internal forces and the damage migration between the frame subsystem and shear wall subsystem.The damage index can be used as an effective tool to control the damage evolution path of the dual system at the macroscopic level.The case study also shows that strengthening the link beams is efficient in improving the seismic performance of the wall-frame structure.(4)The three-dimensional eccentric structures are divided into subsystems from a conceptual system perspective,and the damage characterization methods are developed for the translational subsystems and torsional systems.In terms of the constitution of structural stiffness,the mechanism of translational-torsional coupled damage is analyzed.The multi-story structure is equivalent to a series of one-story structures by using the modal stick model,which simplifies the problem while retains the higher-order modal characteristics of the original structure.Based on the equivalent one-story structures and the multiple modes damage model,the decoupled translational damage and torsional damage of eccentric structures are derived.The results show that except for torsional damage the proposed damage model can also describe the damage of the structure in the direction that exhibits no responses.And the eccentricity of the equivalent structure can be used to indicate the change of the eccentricity of the original structure,and there is a strong correction between the variation of translationaltorsional damage ratio and the variation of the eccentricity of the equivalent structure.With the increase of the nonlinearity,the eccentricity of the structure increases first and then presents a fluctuant decrease.The initial eccentricity directly affects the damage evolution of the structure in all directions.(5)The unified damage evolution equation of the structure is established,and the quantitative damage performance targets of the whole structure and the subsystems are developed by combining with the "four-level" ground motion classification.Based on two classical damage models,namely the Ghobarah damage model and the modified Park-Ang damage model,the unified mathematical expression of the structural damage evolution equation is proposed,where the Logistic curve equation is introduced and extended to describe the evolution of the multiple modes global damage and different subsystem damage.Combined the Logistic damage evolution equation and the five-segment damage characteristic points with the "four-level" ground motion classification,the structural global damage performance target curve is derived.Then,the damage performance target curves of the subsystems are determined according to the relationship between the global damage and the subsystem damage.The established quantitative damage performance target curves can be used in the structural stiffness control during the preliminary design,which provides a reference for the structural performance control.