| Connected structure refers to structures with upper connecting bodies(including corridors)between two or more towers,apart from bottom podiums.In recent years,the trend of structural form has grown more complex and diversified,besides satisfying the basic functions of buildings.Connected high-rise structures have received extensive attention and are widely used due to its outstanding features,grand momentum,and flexibility for air traffic.Due to the existence of the connecting body,the force behavior of a connected structure is much more complicated than that of an independent single-tower structure.It is prone to problems such as obvious torsional effects under earthquake and concentrated force on supports of connecting bodies.Defining connected structure as complex high-rise structure,the design code suggests similar stiffness and symmetrical layout for connected structures.However,complexity of connected structure force behavior became higher,as the need for asymmetrical connected structures grew in the industry.This paper is based on an actual engineering project.A research is conducted on the connection scheme selection and seismic performance of an asymmetric double-tower connected structure.Referring to our country’s design codes,analysis software such as YJK,ETABS,Perform-3D are used for calculation and comparative analysis.The main research contents and conclusions are as follows:1)Four representative types of rigid connection system are selected based on characteristics of force behaviors of connected structures: large-span steel beams,vierendeel trusses,multi-story trusses and bottom trusses.Structural models are built respectively for calculation and analysis.2)The influence of the diagonal members extending into the inner tower structure on the mechanical performance of the structure is compared.The results indicate that the connection body can form a rigid connection with the tower without having its diagonal members extending in the tower,as long as the top and bottom floor slabs of the connecting body can reliably transmit lateral forces between the towers connected.With a lower lateral stiffness of the truss comes a reduction in abrupt change of seismic force.As a result,a structure with no diagonal members extending in the tower has better seismic performance,along with a greater advantage in meeting the building function.3)The article discussed the seismic performance objectives of floor slabs at critical locations.It also summarized the advantages and disadvantages of the current engineering design calculation and analysis methods for floor slabs under lateral forces.The bearing capacity checking method and the design of reinforcement of floor slabs based on principal stresses is studied and applied to seismic design of floor slabs in connected structures.This design method can be used not only for floor slabs under earthquake,but also for that under the effect of temperature,lateral earth pressure,and horizontal components of inclined columns.4)A comparison of the four types of connected structure was conducted based on their influences on main structural evaluation indexes such as deformation,seismic shear,vertical regularity,and material consumption.The results indicated that although diagonal truss system is more cost effective,it causes obvious abrupt changes in the force behavior of other structural members.Moreover,the diagonal members would have a great impact on the architectural function.Therefore a vierendeel truss connection scheme is the most suitable for the connected structure of this project.5)Seismic design and performance analysis were conducted for the selected vierendeel truss connected structure.Four high-rise irregular criterions were found in the project,and the seismic performance objective was determined to be Class C.The specific component seismic performance objectives and bearing capacity checking method were listed.Light earthquake elastic response spectrum calculation and time-history elastic analysis,moderate earthquake equivalent elastic response spectrum calculation,severe earthquake equivalent elastic response spectrum calculation and dynamic elastoplastic time history analysis are carried out.Evaluation indexes of the structure and bearing capacity of members are reviewed and analyzed.The analysis results show that,with reasonable design and reinforcement,the asymmetrical connected structure of this project can reach the predetermined seismic performance target.This article draws some general conclusions and general design methods on the basis of calculation and analysis.These results can provide references for the research and design of similar complex high-rise buildings. |
