Research On The Creep Effect Of PC Box Girder Structure Under Variable Temperature And Humidity Conditions

The change of ambient temperature and humidity is an important factor affecting the creep effect of concrete structures,but in the existing creep prediction model,the influence on ambient temperature and humidity is considered according to the annual average temperature and humidity,and the change of ambient temperature and humidity is ignored,resulting in low creep prediction accuracy.In this thesis,the creep effect of concrete structures under changing ambient temperature and humidity is studied,and the main research contents are as follows:(1)The creep test of eccentric compression members of reinforced concrete in outdoor environment was carried out,the influence of variable temperature and humidity environment on the strain of reinforced concrete components was analyzed,and a correction method considering the variable temperature and humidity conditions was proposed for the calculation method of creep coefficient in the current specification.(2)A creep analysis algorithm for concrete structures considering variable temperature and humidity is proposed,the expression form of the creep function is improved,and the functional relationship between creep parameters and environmental temperature and humidity changes is obtained by parametric fitting.Based on the ANSYS software secondary development tool UPFs,the user subprogram USERMAT.F was modified to implement the relevant algorithm.The accuracy of the calculation of the creep subroutine is verified by example analysis.(3)In order to consider the influence of different theoretical thicknesses of different parts of the box girder section on the creep coefficient,a calculation method considering different theoretical thicknesses of any part of the box girder structure is proposed.Through the analysis of examples,it is found that when the theoretical thickness increases from 100 mm to 200 mm,the creep coefficient decreases by 15.07% and the deformation decreases by 12.49%.When the theoretical thickness increased from 200 mm to 300 mm,the creep coefficient decreased by 9.51% and the deformation of the specimen decreased by 7.88%.(4)Through the analysis of the spatial creep effect of a prestressed concrete box girder bridge,the effects of environmental temperature change,humidity change and theoretical thickness change on the long-term deformation and time-varying stress of the structure were studied.When considering the change of ambient temperature,the longterm deformation of the box girder increased by about 9%,and the axial stress of the top and bottom plates changed by 0.4Mpa and 0.58 Mpa,respectively.When considering the change of ambient humidity,the long-term deformation of the box girder increased by27.9%,and the axial stress relaxation of the top and bottom plates increased by 16.6%and 25%,respectively,compared with the humidity change.When considering the theoretical thickness change,the long-term deformation of the box girder increased by16.9mm,and the axial stress on the inner surface of the roof plate decreased by 3.1%compared with the outer surface.