Study On The Effect Of Creep And Shrinkage On Concrete Members

Creep refers to the phenomenon that concrete subject to a constant force will produce an extra strain except from the instant elastic strain,which will grow as time developing,based on the initial one.Creep consists of free and constraint creep,and concrete members consist of pure concrete members and members with steel.For pure concrete members without outer constraint,when subject to force,free creep occurs,and no redistribution stress happ en,but for members with constraint,constraint creep happen and brings redistribution stress.For members with steel,for example,steel-concrete composite members,when subject to external forces,concrete creep will be hindered by the steel part and produce redistribution stress even without outer constraint.The constraint creep brings stress relaxation on the constraint part of pure concrete members and redistribution stress for steel-concrete composite members,especially when there is redistribution pressure stress transformed to the steel part of the composite members,risk of suffering buckling instability increases for the steel part,and deflection becomes larger to the point that may influence normal function ect.The shrinkage of the concrete having no relationship with the stress will result in similar effect.Generally,there are two typical ways to calculate the effect due to creep and shrinkage of the concrete: one is using differential stress-strain equation(s)based on the Dischinger theory.One can obtain analytic expression of the desired stress through solving the equation(s)and the solution is rigorous under assumptions;the other is using algebraic stress-strain equation(s)based on creep superposition principle.one can obtain redistribution stress easily once the concrete relaxation coefficient known and its accuracy depends on that of the relaxation coefficient,the relaxation coefficient can be obtained via numerical computation.Because of the complexity of solving the differential stress-strain equation,especially when t here is a multivariate equation,it is much easier to obtain stress solution through the algebraic stress-strain equation(s)based on relaxation coefficient than the Dischinger theory.There are numerous research es on the relaxation coefficient of concrete,while researches based on the domestic code Design Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG D62-2004)which is substituted for the sake of convenient in the following content by the abbreviation Domestic Highway and Bridges Culverts Code are rare and incomplete,therefore,it is the goal for this thesis to calculate the relaxation coefficient based on the Domestic Highway and Bridges Culverts Code and the key point is to introduce and study the relaxation coefficient systematically especially on the Domestic Highway and Bridges Culverts Code so as to offer a brief and effective way for the designer to compute the redistribution stress and the relative impact brought by creep and shrinkage of concrete.The main contents of this article are:1.The introduction to the formation mechanism and the influence factors of creep and shrinkage of concrete2.The introduction to the idea of relaxation coefficient and the algebraic stress-strain equation based on creep superposition principle,and the derivation of differential stress-strain equation(s)based on the Dischinger theory3.The derivation of relaxation coefficient expressions based on the creep superposition principle and Dischinger theory separately when the concre te is under rigid restraint4.The derivation of the strain increment method to calculate the changing stress when the concrete is under rigid restraint5.Calculating the relaxation coefficient based on Dischinger theory and creep superposition principle separately by using the strain increment method when the concrete is under rigid restraint,with the creep model of the Domestic Highway and Bridges Culverts Code6.Drawing the relaxation graph based on those calculated in item 5,and apply the graph to cases7.The derivation of the stress-strain equations and relaxation coefficient expressions based on the Dischinger theory and creep superposition principle when the concrete part of steel-concrete composite member is under the axis and eccentric restraint separately8.The derivation of the simplified expressions of redistribution force and relaxation coefficient on Dischinger theory9.To express the relaxation coefficient of the concrete in steel-concrete composite members under axial restraint based on the Dischinger theory through the relaxation coefficient of concrete under the rigid restraint10.To calculating the relaxation coefficient based on creep superposition principle,under the creep model of the Domestic Highway and Bridges Culverts Code when the concrete of the steel-concrete composite member is under the eccentric restraint11.Drawing the relaxation coefficient graph based on those calculated in item 10 and applying the graph to actual cases...