Study On Mechanical Properties Of Partially Precast Partially Encased Assembled Composite Beams

In view of the characteristics of the heavy load and large span of buildings,a partially precast partially encased composite(PPEC)beam is proposed.The new beam has the advantages of high bearing capacity,better ductility,simple construction.It can also be prefabricated and assembled on site,which can greatly improve the level of construction industrialization,reduce construction costs,and has a high engineering application value.In this paper,combined with the experimental investigation,numerical simulation and theoretical analysis,the mechanical behavior and engineering application method of PPEC beams are studied to provide a basis for the application of this new composite beam.The specific work is as follows:(1)The mechanical properties of PPEC beams under static loading were systematically studied.Through the static test of bending and shearing performance of the PPEC beams,the mechanical mechanism,stress distribution characteristics,failure mode and ductility of the PPEC beams were studied,and the influence of concrete strength grade,fabrication method and other parameters on the mechanical performance of the specimens were analyzed.The results show that: I-grider,new and old concrete can work together and bear the force together;partial prefabrication and integral casting have no obvious effect on the failure mode and bearing capacity of composite beams;concrete cracking at the initial loading stage has little effect on the short-term stiffness of PPEC beams;bending failure PPEC beams have good ductility and deformation performance,and shearing failure PPEC beams have relatively good plastic deformation ability.(2)The reasonable numerical analysis model of PPEC beams was established,the script modeling program of PPEC beams was compiled,and the parameter expansion analysis of PPEC beams was carried out.Abaqus software was used to establish a reasonable numerical analysis model,and established the development module and writing process of the program based on Python language.Then,a reasonable and efficient PPEC beams script modeling program was written to realize efficient modeling and analysis of PPEC beams,and then the influence parameters of bearing capacity of PPEC beams were extended to analyze.The analysis efficiency of numerical simulation of PPEC beams is greatly improved,and the influence law of PPEC beams bearing capacity with the change of parameters is mastered.In view of the value of effective flange width of PPEC beams,the influence of width to span ratio and load properties on effective flange width was considered to carry out numerical simulation analysis,and the formula for calculating effective flange width of PPEC beams was obtained by regression analysis.At the same time,the two-stage stress behavior and stress development rule of PPEC beams were analyzed by using the birth and death element and element tracking technique.(3)The calculation method of flexural bearing capacity and deflection for PPEC beams was established.According to the test results,the formula for calculating the flexural bearing capacity of PPEC beams was deduced.Based on the analysis deformation performance of PPEC beams,the introduction of zone B(consistent with the plane section assumption),D(inconsistent with the plane section assumption)partition concept was put forward to distinguish the zone B and D with different angle of statically determinate truss model.The gauss integral model of variable angle truss was used to minimize the work under unit shear force,and the angle of diagonal compression bar in zone B was derived;the angle of diagonal compression bar in zone D was obtained using the topology optimization,and then the integral truss model considering the shear effect was constructed.On the basis of verifying the rationality of the model,the deflection calculation method of PPEC beams considering the shear effect was proposed.The calculated results were in good agreement with the experimental and numerical results.(4)The calculation method of shear bearing capacity of PPEC beams was established.Based on the modified pressure field theory,the shear bearing capacity calculation model of PPEC beams was constructed.Considering the beneficial effect of concrete in compression zone on the shear performance of PPEC beams,the shear bearing capacity calculation model of PPEC beams under the combined bending-shear action was established according to the biaxial stress relationship of concrete in compression zone.A method for calculating the shear bearing capacity of PPEC beams considering the action of the compression zone was proposed.The calculated results were in good agreement with the experimental and numerical simulation results.(5)The engineering application method of PPEC beams was established.Combined with the results of finite element analysis and the two-stage stress characteristics of PPEC beams,a systematic two-stage design and checking method of construction-using of PPEC beams was established;Combined with the characteristics of two-stage construction,the production and construction concept of "mobile factory" was put forward to develop a new prefabricated component production system of PPEC beams,and the new mold that constituted the system was developed and designed.Based on the sorting and analysis of the production process,a systematic component production solution of PPEC beams was formed.To provide support for the realization of large area and mass production of PPEC beams.By systematic research and analysis,the variation law of mechanical properties of PPEC beams is revealed,and the calculation methods of flexural and shear bearing capacity,deflection and component fabrication of PPEC beams are established,which lays a foundation for the application and development of the new composite beam.