Structural Behavior Of Pretensioned Double-Tee Beams And Full-Scale Experimental Research

The application of pretensioned beams in small and medium-span bridges has its own economic and technical advantages,although the application of post-tensioned beams in bridge engineering in China is more common.However,combined with the current development of new bridge technologies and facing green construction,the research and application of pretensioned prestressed double T beams with larger spans is of great significance for promoting the progress of bridge industrialization technology.This paper takes the new 30 m pretensioned double Tee beam as the research object,through the full-scale model test,3D finite element simulation and theoretical analysis,the basic structural behavior and design method of the pretensioned prestressed double T beam are systematically studied.The main research conclusions are as follows:(1)Analyzed the basic structural behavior of pretensioned prestressed beams from tensioning,decompression,cracking to ultimate bearing state;summarized the mechanical mechanism and related calculation formulas of pretensioned prestressed tendon transfer length;sorted out pretensioned double T beams The calculation method and influencing factors of prestress loss at each stage,especially for the existing beam making process,put forward measures such as adding anti-slip jacket at the end of steel strand to reduce prestress loss.(2)The full-scale model test of the 30 m pre-tensioned prestressed double T beam was carried out.In the test loading technology,the mixed loading method of "heaping on the beam+ jack loading" was used;using a variety of sensor testing methods,the results were obtained.The stress distribution and deflection development of key sections at each stage show that the design parameters of the new pre-tensioned double-T beam structure are reasonable and can meet the stiffness and bearing capacity requirements of the current bridge gauge.(3)The elastic and solid finite element analysis of the new 30 m pre-tensioned double-T beam was carried out,and the results were compared with the full-scale model test results.Based on the experimental study,some structural measures to improve the crack resistance of beam ends are proposed.(4)From the point of view of thrust line and force flow spreading and transmission,the change law of internal force of pre-tensioned double T beams is studied.The position of the full-section thrust line is calculated for each loading condition,and the thrust line is decomposed into the top plate thrust line and the web thrust line,and the force flow transmission between the top plate and the web plate is observed respectively.On this basis,a tensioncompression rod model in which the prestressing of the beam end is gradually diffused in the roof is proposed,which can provide a reference for the design of transverse reinforcement of the roof.(5)Taking the Magnel feasible region as the theoretical basis,the design method of the steel strand distribution of the pretensioned prestressed double T beam is studied,and the Magnel feasible region of each characteristic section of the pretensioned double T beam is calculated,and the prestressed tendons are obtained.Arrangement of cable bounds;according to the reinforcement characteristics of pre-tensioned prestressed double T beams,a design method of broken line reinforcement is proposed based on the determination of straight reinforcement.