Energy-based Seismic Design For Self-centering Concrete Frame Structures

The concept of structural resilience and the enhancement of seismic performance demands promote the development of novel resilient components and systems,so as corresponding design theories.The self-centering concrete frames are introduced to satisfy with the seismic resilient demand,which have been proved to exhibit superior performance of damage controllability,functional partition and post-earthquake resilience.The constraints between beam-column ends are reduced and allowed opening-closing behaviors under earthquakes.It can protect beam-column joints from sever damages and ensure elastic performance states for critical components.The prestress mechanism and energy-dissipation devices are introduced to provide selfcentering and energy dissipation capacities for structures.The force-and displacementbased design methods are commonly adopted for self-centering systems.Although these approaches can guarantee structural strength and deformation within limitations and prevent systems from collapse,influences of seismic characteristics(frequency and duration),cumulative damages and residual deformations on structural performance and post-earthquake resilience cannot be considered.The energy concept can present reasonable elaboration of structural behaviors and damage development under earthquakes through the transformation and dissipation of earthquake energy.The seismic characteristics and structural features can be considered in the energy-balanced concept simultaneously.Therefore,it provides prospective values to conduct energyrelated analyses and proposed practical design procedures for self-centering concrete frames.In this thesis,the energy-based seismic analyses are performed on self-centering concrete frames.Practical design energy spectra are constructed through numerical simulations and statistical analyses.Development and distribution of energy responses in structures are investigated.The damage-based performance evaluation is performed based on the research of quantitative damage approach for self-centering structures.Then,the damage characteristics and development in self-centering concrete frames are analyzed.The energy-based seismic design(EBSD)method for self-centering concrete frames is established.The study expects to enrich the theoretical and design framework for the new structural system and provide references for practical engineering.The main contents of the thesis are summarized as follow:(1)The establishment of the design input energy spectrum and the hysteretic energy spectrum.Dynamic responses and energy parameters of self-centering singledegree-of-freedom systems are calculated by coding programs with ground motions selected based on soil types stipulated in the Chinese code.The influences of ground motion features and structural characteristics on the input energy and hysteretic energy are investigated.The practical energy spectra are proposed for design purposes.(2)The quantification of damages in self-centering beam-column joints.The damage model suitable for self-centering systems is proposed based on dynamic responses.The damage development and performance features of joints under cyclic loads are simulated in OpenSees.Based on the effects of structural parameters on the damage development in joints,the determination of the critical parameter in the damage model is suggested.In addition,the damage intervals are suggested based on various damage states and corresponding evaluation criteria proposed in the thesis.Multi-level performance objectives are suggested for design purposes.(3)The investigation on the energy distribution in self-centering concrete frames.The development of energy demands is analyzed by time history analyses in frames with different structural features.The influences of critical structural features on the distribution of energy demands along the vertical and horizontal directions are investigated.The quantification of energy demands for column bases and beam-column joints are proposed.Moreover,the development of damages in joints,stories and structural levels changing with seismic intensities and structure features are analyzed to furtherly understand dynamic behaviors of self-centering concrete frames.(4)The proposal of the energy-based seismic design method for self-centering concrete frames.The hysteretic energy demand is transformed as a critical design parameter based the damage model.A multi-level performance-based design methodology considering various structural responses is suggested.The approach is validated with a case study,while the seismic performance is evaluated and compared with the direct displacement-based design method.