Research And Application Of Mechanical Properties Of Continuous Cantilever Concrete Structure Support Platfor

With the diversification of building functional requirements,cantilever structures are becoming more prevalent in high-rise buildings.Simultaneously,as building technology advances,the variety of cantilever structures continues to expand.Support platforms,an essential construction measure for concrete cantilever structures,must bear the permanent and live loads during the construction of these structures to prevent potential safety hazards.To address safety,efficiency,and economic issues in the construction of concrete cantilever structures,while also studying the mechanical properties of the structure and the support platforms,this thesis investigates and practically applies the load transfer rules of continuous cantilever concrete structures and the types and mechanical properties of their support platforms.The primary research content and outcomes are as follows:(1)Studying the characteristics and applicability of different types of cantilever support platforms.The construction of ground support platforms,pure cantilever support platforms,and combination cantilever support platforms are modeled in three dimensions using Revit software.By examining the design,construction,dismantling techniques,and economic features of these three types of cantilever support platforms,we analyzed and summarized their suitable application scope.For lower-height cantilever structures,ground support platforms may be utilized;for higher-height cantilever structures with a cantilever span not exceeding 2m,pure cantilever support platforms are suitable;for higher-height cantilever structures with a cantilever span exceeding 2m,combined cantilever support platforms should be employed.For continuous cantilever concrete structures,due to the issue of transferring the load from the upper part,it is advisable to use ground support platforms or combined cantilever support platforms.(2)The study examines the load transfer rules during the step-by-step casting of continuous cantilever concrete structures under three conditions: normal temperature,high summer temperature,and low winter temperature.Using ANSYS finite element software,a model of a three-story continuous cantilever concrete structure and its supporting frame was established,with a construction rate of one level every seven days.The simulation results indicate:At normal temperatures: 77% of the load of the second layer is carried by the concrete structure of the first layer,and 23% is transferred to the bottom supporting frame.The third layer’s load is shared by the first and second layers,accounting for 87%,with 13% transferred to the bottom supporting frame.At high summer temperatures: 81% of the load of the second layer is borne by the concrete structure of the first layer,with 19% transferred to the bottom supporting frame.The load of the third layer is shared by the structures of the first and second layers,accounting for88%,with 12% transferred to the bottom supporting frame.At low winter temperatures: 76% of the load of the second layer is borne by the concrete structure of the first layer,with 24% transferred to the bottom supporting frame.The load of the third layer is shared by the structures of the first and second layers,accounting for 84%,with 16% transferred to the bottom supporting frame.From the analysis results,it is concluded that with identical curing time,the load-bearing capacity of the concrete under high summer temperatures increases by approximately 5%compared to that under low winter temperatures,and by approximately 4% compared to that under normal temperatures.(3)In conjunction with a specific case of a six-story continuous cantilevered concrete beam and slab construction,a comparative analysis of multiple methods was conducted,leading to the selection of a stay-cable combined cantilever support platform as the primary structural support.The construction season is summer,and the load application method adopts the transfer rule under high summer temperature.Through the application of finite element numerical analysis of the cantilevered structure and the supporting platform during the construction process,the theoretical computation indicated that the maximum stress of 179 MPa occurred at the interface between the stay-cable of the platform and the cantilevered beam.The maximum vertical displacement was recorded at the mid-span of the platform,measuring 4.578 mm.At the bottom of the platform,on the cantilevered steel,vertical displacement monitoring points were set.Upon completion of the casting of the first-layer concrete cantilever structure,the maximum vertical displacement was recorded at 3.7 mm.Following the completion of casting from the second to the sixth layers,the maximum vertical displacements were observed to be 4.0 mm,4.2 mm,4.3 mm,4.4 mm,and 4.4 mm respectively,with corresponding increments of 8%,5%,2%,2%,and 0%.The analysis of the monitoring data post-casting revealed that from the fifth layer onwards,the upper construction load was completely supported by the lower completed concrete structure.