Whole-process Analysis And Research On Ductility Performance Of Underground Prestressed Concrete Structures Under Civil Defence Load

The prestressed concrete structure is an ideal shallow buried underground longspan structure,which has the advantages of strong bearing capacity,durability and crack resistance.However,in the current civil air defence standards,the relevant provisions on the ductility of structural members mainly come from experimental results,lacking theoretical results,and the relevant provisions of prestressed concrete structures are also lacking.Therefore,it is of great engineering application value to carry out the whole-process analysis and ductility performance of prestressed concrete structures under civil defence load.In this paper,the whole-process analysis software is developed,and the ductility performance of structures under civil defence load is studied,and the main work is as follows:(1)Based on the current Code for Design of Concrete Structures(GB50010-2010)and other standards,The whole process analysis method of reinforced concrete structure and prestressed concrete structure under static,explosion and earthquake is proposed.The first corresponding whole-process analysis and design software for reinforced concrete and prestressed concrete Structures(PCNAD)in China is developed,which is verified by static load model test,static & dynamic numerical simulation method and similar foreign software.PCNAD software meets the accuracy requirements of similar foreign software.Compared with similar foreign software,the analysis results of each control point(including initial,zero stress,cracking,steel yield,ultimate strain of uniform or non-uniform compression concrete and ultimate tensile strain of steel)in the whole-process analysis are clearly given,which is more convenient to guide the engineering design.(2)The definition of the energy ductility ratio is given,and the curvature ductility ratio and energy ductility ratio are calculated through the whole-process analysis.It solves the problem that there is no calculation formula of ductility ratio for prestressed concrete structures in the current standards and cannot be calculated by the definition in the current standards for a long time.At the same time,it solves the problem that there is no calculation method when the reinforcement ratio of the compressive steel is equal to the tensile steel,and provides a basis for the next revision of the standards.(3)The whole process analysis of the static load test of prestressed concrete box structure with densified frame is carried out,and the structure does not have sudden fracture failure under the static load,and can still maintain a certain ductility.In this test,the measured flexural capacity of the structure is higher than that calculated by PCNAD.(4)The simulation analysis of prestressed concrete simply supported beam and reinforced concrete simply supported beam under civil defence load are carried out,and the differences between PCNAD,pseudo-static method and pulse method are compared.The difference between curvature ductility ratio calculated by three methods is small,and the ductility results calculated by the pseudo-static method are safer than those calculated by the pulse method.A number of whole-process analysis examples show that the ductility index of structural members is greatly affected by the selection of yield state and limit state.When choosing the tensile strain of steel bar reaches 0.01 as the limit state,the variation law of ductility index is different from that choosing the concrete crushing as the limit state.(5)Based on the engineering examples,the whole-process analysis of prestressed concrete and reinforced concrete box structure with densified frame are carried out,and the comprehensive performance of the two structures are compared and analyzed from the aspects of bearing capacity,economic benefit,environmental benefit,ductility performance and construction difficulty,which provide a more convenient and new method for whole-process analysis of concrete structures.The influence of factors such as longitudinal reinforcement ratio,concrete strength,prestressing degree and prestressing steel elongation on the ductility performance of the structures are verified.Both prestressed concrete and reinforced concrete structures can meet the requirements of underground large-span space without columns.Under the conditions of the same net width and net height,the prestressed concrete structure has relatively good normal service performance,relatively high bearing capacity,strong comprehensive disaster resistance and continuous collapse resistance,low cost,less carbon emissions,slightly smaller ductility but can meet the requirements,and relatively good comprehensive performance.