Theoretical Analysis And Seismic Performance Study For Transfer Story Of Reinforced Concrete Structure With Haunch Braces

To the application status of transfer structure in tall buildings, based on the beam-type transfer,a new transfer structure with haunch braces and between the slant column transfer andbeam-type transfer is presented. The features of the structure are that the additional braces areset in the junction between the column and the beam, thus the force transmission mode of thestructure is changed, the shear force, the moment at the end of the beam and the span of thebeam is reduced, thereby the cross-section size and reinforcement of the transfer beam aregreatly reduced. The structure can meet the increasing demand for architectural arts andarchitectural features very well. Currently, few studies are carried on the structure of transferwith haunch braces. The studies to this complex transfer structure with haunch braces includethe following aspects of work.(1) According to the characteristics of transfer structure with haunch braces, theå…«-typeand V-type of the transfer structure with haunch braces are selected to study by finite elementnumerical simulation. Taking a simple plane transfer frame structure as example, the forcecharacteristics of the transfer structure under the vertical load and horizontal load areanalyzed, and the effects of the haunch braces angle and the stiffness of transfer structuremember on internal forces of the transfer structure are analyzed. Based on ABAQUSnonlinear finite element analysis, the deformation, the stress distribution of concrete and steelof theå…«-type and V-type direct-transfer frame structure under loads are analyzed andsummarized in detail.(2) Because the lateral stiffness of transfer structure with haunch braces changes unevenlyalong the vertical direction, it will lead to a certain degree of force mutation in structuralelements. In order to avoid the formation of weak links in structural members, it is practicallysignificant to evaluate the seismic performance of the transfer structure. Push-over analysis onan example structure against the transfer structure with haunch braces is conducted to revealthe characteristics of the formation of plastic hinges in elements of transfer structure withhaunch braces, and to discuss the development feature of the plastic deformation of the structure and the responses of the force and displacement during elasto-plastic stage of thestructure. The hinge sequence, failure mechanism and the reaction force and displacementduring elasto-plastic stage are studied. Based on the deformation damaged criteria, the overallseismic resistance performance for transfer structure with haunch braces is assessed usingCapacity Spectrum Method, and reliable earthquake-resistant measures are proposed.(3) Applying the nonlinear structural analysis method, the earthquake damage of thetransfer structure with haunch braces is predicted based on elasto-plastic displacement angle.According to performance-based seismic design theory and taking the elasto-plasticdisplacement angle of the structure as the overall performance index, through the seismicanalysis of the structure, a method was investigated to find the weak links in the elements ofreinforced concrete transfer structure with haunch braces and to evaluate the ductility andseismic capacity of the structure by the earthquake damage prediction analysis. The analyticalresults of an example show that for the earthquake damage prediction of a single or smallnumber of reinforced concrete frame building structures, based on the method of Push-overanalysis, to determine the structural damage state according to the deformation indexes of theweak floor, it is a viable earthquake damage prediction method for transfer structure withhaunch braces.(4) Based on the nonlinear beam-column element of fiber cross-section, the effects ofseismic control of the reinforced concrete haunch braces are analyzed by using the method ofincremental dynamic analysis.The transfer structure as micro-hazard-affected bodies, themethod of vulnerability analysis is used, and by the analysis of the probability of the capacityand the seismic demand, the seismic limit state and the probability of seismic demand of thetransfer structure are determined. The conditional probability of the transfer structure underdifferent seismic intensity when earthquake demand conditions beyond the limit state isestablished, and the vulnerability curve of the common transfer structure and the reinforcedconcrete structure with haunch braces is given.(5) In the reinforced concrete transfer structure with inclined column or haunch brace, thetransfer beam between the inclined column or haunch brace and the transfer column will havea great axial tension force, how to ensure the transfer beam satisfies "strong shear weak bending" design under eccentric tension has become the focus of the structural design. Toarchieve the concept design of "strong shear weak bending", the design parameters of transferbeam as random variables, using Monte Carlo method for reliability analysis, and taking thetransfer beam as the series connected system of the eccentric tensile failure and shear failure,the "strong shear weak bending" seismic reliability analysis is carried out for reinforcedconcrete transfer beams under eccentric tension designed according to the current buildingstructure specification. The different effections to the reliability of eccentric tension beams arediscussed for different load ratio such as the ratio of seismic action and gravity load, differentsections, strength grade of materials and different reinforcement ratio. For the "strong shearweak bending" design of eccentric tension transfer beams on the basis of seismic class oneand two, the target reliability index for shear enhancement factor is checked to providereference for reasonable analysis.