Study On Mechanical Principle And Replaceability Evaluation Method For The Replaceable Members

The seismic concept of engineering structures gradually changed from preventing structural collapse to maintaining or recovering building functions after earthquake to solve the scientific problem about the poor repairable capacities of the traditional framed structure.Combined the advantages of the structural system with replaceable members and the reinforced concrete columns and steel beams(RCS)composite frame,a novel RCS hybrid frame structure with replaceable members was put forward to limit loss of economic and occupancy.The proposed hybrid frame structure is a type of earthquake resilient structures,in which the replaceable members can concentrate to dissipate the seismic energy and protect the rest of the structure remain intact or minor damage under the action of the expected earthquake.Based on the experiment,FEM and theoretical analysis methods,this paper deeply researched damage mechanism,the replaceability performance of replaceable link beams and seismic design of the whole structure.The main research works and results conducted the following:1)The hybrid frame structure consisting of energy dissipation frame and RCS composite frame was proposed.In the whole system,the energy dissipation frame is dual columns interconnected with replaceable link beams to provide inelastic behavior by having the links yield primarily in shear under the lateral load,while protecting the flexible composite RCS frames,consisting of the RC columns and steel beams,that mainly carry the gravity loads and also allow for a secondary lateral stiffness.The primary advantage of the whole frame is that the lateral response is characterized by three stages and four performance levels to concentrate damage and dissipate seismic energy.The rapid return to occupancy for the whole structure is achieved within a drift range that results in plastic deformation of only the links,which are intended to be replaced.2)The nine link specimens were designed and tested under reversed-cyclic loading.The failures process,damage characteristics,strength capacity,energy dissipation capacity and replaceability of the link specimens were studied.The tested results showed that the failure modes of specimens included two types of shear failure and bending-shear failure,and each specimen which has stable strength,excellent deformability and energy dissipation capacity.The specialized link-to-column connections of specimens can allow for easy replacement.Furthermore,the different connection details of the link specimens,especially for the link with the end plate and end web stiffeners and the link with T-bolted connection,had a better replaceability behavior after extreme lateral loading to achieve replacement conveniently.3)Based on the test of the link specimens,the finite element models during cyclic loading were conducted to research the influence of link length ratio,end web stiffeners connection,axial load and shear capacity ratio of the multi-section link beams.Results indicated that different link length ratio,end web stiffeners connection,axial load and shear capacity ratio had different influence on failure characteristic,bearing capacity,deformation,energy dissipation capacity and replaceability.Finally,some design recommendations were given according to the analyses and providing reference.4)Combining with the study in this paper and the existing research results,the recommendations of the replaceability and seismic design methods for the link beams are proposed.The permissible the residual rotation of link beam ends and permissible the residual drift levels of structure are proposed to evaluate the replaceability capacity of the link beams.In addition,various types of link-to-column connections and those of the design methods were suggested.Finally,the link beams should be designed as a shear dominated behavior and reasonable link details are given.5)To achieve the replaceability of the link beams and the resilient structure in the whole system,the performance-based design method of the hybrid frame structure is discussed.A specific four-level seismic fortification objective system for the hybrid frame structure can be summarized,which has been established to represent the lateral force distribution mode for the lateral load and estimate and control the plastic behavior of the whole structure.One three-story hybrid frame structure was designed following the proposed design principle,and validated by nonlinear static pushover analysis as well as dynamic elastic-plastic analyses.The results showed that the the hybrid frame structure had a good seismic performance and post-earthquake function resilient,which could satisfy the performance levels of no damage under minor earthquake,rapid return to occupancy under moderate earthquake,repairable under major earthquake,and collapse prevention under mega earthquake.All the links can form the shear plastic hinges to dissipate the energy and the lateral displacement for the structure relatively distributed uniform along the structural height.Additionally the development sequence and distribution state of plastic hinges were in line with expectations.