Transverse Stress Analysis Of The 3-D Prestressed Box Girder

Prestressed concrete box girder bridges are widely applied to the high-speed rail network and urban railway transport. With the development of construction technology, the box girder has developed to widened-flange and thinned-web gradually, and contains with spatial curved prestressing tendons. Part of the bridges crack obviously during construction or operation stage. Spatial curved prestressing tendons have crucial influence on the stress state of the box girder.Simply supported prestressed concrete box girder in Passenger Dedicated Line is research object of this thesis. Based on strain monitoring test, spatial model with curved prestressing tendons is created by ANSYS program to study the spatial stress distribution and mechanics characteristics of the bridge. According to the tensioning order and the initial stresses of tendons, transverse stress transformation characteristics of the box girder in the initial tensioning stages and final tensioning stages are studied. Through calculation and analysis to several sections in the initial and final tensioning stages, the spatial stress state of the box girder and the transverse stress distribution characteristics of the upper and bottom slabs are discussed. The width of crack of upper slab with spatial curved prestressing tendons are compared between experimental results and calculated value by ANSYS, main research conclusions of the thesis are drawn and listed as follows:1. After the final tensioning stages, transverse stress of bottom slab reaches to a relatively large value of 2MPa, though this value is smaller than tensile stress limits of concrete, longitudinal cracks are likely to generate under synergetic effects of various loads such as dead load, secondary dead load and live load.2. As theoretically calculated values are agreeable to experimental results, reliable data support are provided to the transverse rebar design of the box girder, the width of longitudinal cracks can be controlled effectively.3. Through analysis of the transverse stress distribution under spatial prestressing effect, significant tension stress is found in border between upper and flange slab, center line of the roof and border between bottom and flange slab, therefore the number and arrangement of the transverse prestressing tendons should be determined by section patterns and loads distribution in design.4. Through analysis of transverse stress distribution of upper slab under different load combination by the plane frame analysis method, the controlled situation of the upper slab was obtained. With the combinated effect of the "dead load" + "prestressing force" + "secondary dead load" + "special live load", the transverse rebar is controlled by single side load.Keywords:Spatial prestress; Boxgirder; Transverse stress; Passenger Dedicated Line; Experiment; Finite element model.