Turkish Solar Radiation Zones for Segmental Box Girder Bridge Design Under Temperature Gradient Loading

Abstract

Solar radiation developing non-linear temperature distribution at the depth of the concrete structures may cause significant stress changes along the long span box type bridges. Segmental concrete box bridges are one of the example in which stresses change not only due to annual uniform temperature changes but also due to daily temperature changes that can develop a second type of thermal difference; namely, thermal gradient, which forces to have internal thermal stresses within a cross-section. Over the years it has been observed that nonlinear temperature distribution develop at the depth of box girder type bridges can cause bending moments as high as the ones generated due to live loads that may result in concrete cracking. American Highway Association of Transportation Officials (AASHTO) bridge specifications recognize the use of thermal gradient loads in design since 1989. In this specification, the U.S. is divided into 4 zones per the country’s solar radiation zones and gives some gradient values to be applied through the depth of the girder. The aim of this study is to construct a simple similar solar radiation map for Turkey to be used in design of segmental bridges. Temperature and solar radiation data from eight cities in different regions of Turkey are collected, and used in analysis of a box girder bridge model through a thermal finite element analysis program. Thermal differences through the depth of the girder are determined to obtain the design gradient values for the bridge that can be hypothetically constructed in different parts of Turkey. The end results are used to develop a recommendation for a simple solar map that is related to thermal gradients to be used in design of segmental bridges.