Research On Practical Method Of Crack And Reflection Control For Prestressed Concrete Frame Beams

Compared to ordinary reinforced concrete frame beams, prestressed concrete framebeams consists of high-strength materials, which causes the member section size decreasing,span-depth ratio increasing and the elements appearing more slender.So the crack anddeflection control under serviceability limit state has become an important part of thestructural design.Structure designers should attach great importance to it.Since the calculationof crack width and deflection given in the current specification is rather complicated.To someextent,the application of prestressed concrete structure is restricted.This paper focuses on thecrack and deflection control of prestressed concrete frame beams and proposes the practicalmethod of crack and deflection control.Further more, the practical method can help designprestressed concrete structures.This article mainly includes the following contents.List indicators and calculation methods for crack control of prestressed concrete flexuralmembers given in China standard.Do research on three level crack control of the prestressedconcrete frame beams.Propose the practical crack control method—Reinforced stress controlmethod.At last, give a simplified calculation method of steel stress.Through calculation andanalysis,we can draw these conclusions.When reinforced equivalent stress is controlled within190MPa under the first class environment and120MPa under the second classenvironment,the crack width will be controlled within the allowable range.The practicalmethod is tested by engineering examples,which proves to be practical and reliable.Thanks tothe practical method, tedious calculation can be avoided.List indicators and calculation methods for deflection control of prestressed concreteflexural members given in China standard.Do research on deflection control of theprestressed concrete frame beams.Propose the practical deflection control method—Loadratio method.Firstly,the factors affecting the short-term stiffness under three level crackcontrol are analyzed.With the assumption that kcr qw/q,long-term stiffness‘B’isdetermined when the value of k cris changing.Secondly,the calculation formula of deflectionis derived with diagram multiplication.Furthermore, the maximum load that the beam canbear is calculated by the deflection formula.Thirdly,With these parameters,the external loadsize,span-depth ratio,the ratio of prestressing equivalent load and external load and supportsmoment and mid-span moment ratio, a series of charts are made.By consulting thecharts,deflection can be controlled easily.At last,the practical method is tested by engineeringexamples,which proves to be practical and reliable.Because of the practical method, tediouscalculation can be avoided The practical crack and deflection control method of prestressed concrete frame beams isclear, simple and practical.To some extend,It extends the application of prestressed concretestructure.