Study On Mechanical Characteristics Of Prestressed Concrete Special-shaped Continuous Box Girder

Urban elevated interchange structure has the characteristics of wide width,skew and curved,which will lead to more problems in the construction and operation of the wide oblique box girder bridge.Among them,The shear lag effect,lateral distribution of effect and temperature effect and other aspects caused by the load and environmental effects of the special-shaped continuous box girder bridge need further analysis.Based on the b-ramp viaduct in the terminal of Chongqing Jiangbei International Airport,it has a large width(transverse bridge radial width 54m),oblique(maximum slope 24),curve(circular curve radius 227.5m)and other structural features,this paper studies the mechanical properties of the super-wide oblique bending prestressed concrete continuous box girder.The purpose of this paper can be concluded as following aspects: study the temperature field and strain variation of concrete special-shaped continuous box girder in early age;the long-term temperature variation law of concrete special-shaped continuous box girder;The longitudinal and transverse deflection of concrete special-shaped continuous box girder with time;Combined with finite element analysis,the mechanical properties of special-shaped continuous box girder are revealed.The main research contents and results of this paper are described as followings:Through the field test of early age hydration heat of concrete special-shaped continuous box girder,the temperature field and strain variation law of early age concrete box girder are analyzed.And combined with finite element analysis,the temperature field variation of hydration heat in early age is analyzed.The main conclusion can be summarized: Due to the bending and large lateral width,there is a significant difference in the temperature field between the ten chambers of the box girder.The second pouring will cause the concrete the secondary heating,and the heating rate is much larger than the cooling rate.The longitudinal and transverse strains of the early age concrete of the span,3/4 span,pier top section showed a certain change law.Through the long-term hydration heat field test of the concrete special-shaped continuous box girder,the distribution of the lateral and vertical temperature fields of the special-shaped box girder is analyzed from two angles for the box girder temperature field.The main conclusion can be summarized: The temperature inside the curve of the span,3/4 span section of the box girder in spring(March to May)is sinusoidal,the temperature outside the curve is small,and the temperature is lower than the outside of the curve.The temperature changes inside and outside the curve are almost the same.The pier top section has a sinusoidal change in spring and summer,and the temperature inside the curve box girder is slightly higher than the outside,and the vertical temperature difference of the box girder reaches 7 °C.Through the long-term test of the stress characteristics of the concrete special-shaped continuous box girder,the strain and deflection data of the span,3/4 span,pier top section of the box girder are collected,and the long-term deflection and strain time-varying law are analyzed.The main conclusion are as follows: In span section,the longitudinal compressive strain on the inner and outer sides of the curve is higher than the middle,but the transverse strain is smaller than the intermediate point when the bridge is in the state.In 3/4 span section,the longitudinal compressive strain on the inner and outer sides of the curve is lower than the middle,but the transverse strain is higher than the intermediate measurement point,and the lateral strain distribution of the intermediate measurement point is concentrated.In pier top section the longitudinal strain at both curve ends is much larger than the intermediate measurement point,and the longitudinal strain changes more than the other two test sections.The transverse strain at both ends of the curve is larger than the intermediate measurement point.The deflection of the three sections is basically the same,showing a downward deflection trend.Using finite element software,the finite element grillage model and solid model of concrete special-shaped continuous box girder are established,and the mechanical effects such as long-term deflection and strain of the whole structure are calculated.The longitudinal bridge and transverse bridge(diameter)effect and shear lag distribution time-varying laws are analyzed.The main conclusion are as follows: Due to the bending and skewing of the box girder,the lateral reaction force of the outside curve is higher than the inner side of the curve;the deflection of the outer side of the curve is greater than the inner side,which proves that the the influence of box girder width and the bending characteristics is large;the cross beams,webs and bottom plates are in the state of compressive stress after completion,and there is a certain regularity in the stress distribution of the longitudinal bridge and the transverse bridge;the middle beam exhibits obvious shear lag effect.Through the analysis of a large number of data in field test,combined with theoretical calculation and finite element analysis,the mechanical properties of concrete special-shaped continuous box girder are revealed,which is helpful to optimize the theoretical calculation and design of concrete special-shaped continuous box girder.It is applied to construction projects such as the interchange hub project,the airport terminal building and the three-dimensional traffic integrated hub project.