Investigation of Extreme Environmental Conditions and Design Thermal Gradients during Construction for Prestressed Concrete Bridge Girders

Abstract

Current AASHTO specifications provide engineers with a temperature gradient across the depth of the cross section to predict the vertical thermal behavior of bridges. This gradient is based on one-dimensional heat flow and does not account for change in the cross section, as found in prestressed concrete girders, nor does it account for thermal effects on the sides of the girder. Furthermore, the current specifications do not provide the transverse temperature gradient that is needed to predict the lateral thermal behavior of the girders, especially during construction, before the placement of the bridge decks. To determine the transverse and vertical temperature gradients in prestressed concrete girders, experimental and analytical studies were conducted on a prestressed BT-63 concrete girder segment. The analytical results were found to be in good agreement with experimental measurements. The analytical model was then used to determine the seasonal temperature gradients in four standard PCI girder sections at selected cities in the United States. On the basis of these findings, vertical and transverse temperature gradients were developed to aid engineers in predicting the thermal behavior of prestressed girders during construction.