Effects of Solar Temperature Gradient on Long-Span Concrete Box Girder during Cantilever Construction

Abstract

Three-dimensional (3D) finite-element analysis of a 106 × 200 × 106-m concrete box girder was conducted to study the effect of solar temperature gradients on long-span bridges during construction. Segments over the internal piers and at midspan were investigated to obtain temperature distributions and thermal stresses during critical times of the day. On the basis of results of the thermal analysis, temperature gradients were developed for 0600 and 1500 hrs. to be used on the entire bridge. The maximum longitudinal tensile stress in the girder was 2.67 MPa, whereas lateral tensile stress could reach 4.41 MPa. Therefore, appropriate measures must be taken during construction to avoid cracking of the box girder. A 3D model of half the entire bridge was analyzed to obtain the effects of thermal loads on the bridge in its longest cantilever construction stage. The maximum vertical deflection at the cantilever end reached 46.0 mm at 1500 hrs., when the effect of temperature was highest. It was concluded that the deflection as a result of temperature gradients should be accounted for when determining the formwork elevations in the segmental cantilever construction process.