Variable Stiffness Level Application In The High-rise Building Design

With the development of high-rise buildings, pile foundation has been widelyapplied. It has exerted the bearing capacity of pile foundation greatly and had goodeconomic and social benefits. However, traditional design method was naturalfoundation and uniform arrangement of pile, and initial vertical bearing stiffness weredistributed evenly. When the finite stiffness foundation was under uniform distributedload, because of soil and pile, pile and pile interaction, the foundation or pile verticalbearing stiffness distribution changed strongly inside weakly. Its settlement appearedbig in small butterfly distribution, and it would cause additional bending and shear forcein the upper structure and itself or crack. Its basal reaction also appeared small outsidebig saddle distribution, and it would increase the integral moment of foundation. Whenthe upper structure was frame-core tube structure, which load and stiffness was bigoutside small, the butterfly settlement would be more obvious. In order to avoid thenegative effect, using variable rigidity leveling concept design instead of traditionaldesign concept, adjust vertical bearing stiffness distribution of foundation or pile, as aresult of least differential settlement of the building and reducing internal force of thepile caps and secondary stress of the upper structure. Then it can conserve resources,improve the service life of buildings, receive good economic benefit.On the basis of previous studies, this paper expounded the principle, method andapplication in Engineering of variable rigidity leveling design, summarized methods ofgroup pile composite foundation settlement calculation. Combined with engineeringexample, use the variable rigidity leveling concept design and settlement calculationmethod of composite pile foundation, and Flac3D was adopted to analyze the settlementof the frame-core tube structure after variable rigidity leveling, and it can meet thespecification requirements and reduce the additional internal force of pile caps.The engineering example results can show that the frame-core tube structure of thehigh-rise building pile foundation should strengthen the core area of the pile foundationrigidity, such as a change in increasing pile length, pile spacing and pile diameter, etc.,and weaken peripheral frame rigidity of pile foundation, such as using compound sparsepile foundation. Then it can effectively decrease the uneven settlement and reduce theraft of internal force and secondary stress of upper structure, and get good economic benefit.