Abstract:
Concrete bridge structures, which are exposed to the sun are subjected to complex thermal
stresses, which may vary continuously with time. The magnitude of these stresses depends
mainly upon the temperature variations that occur within the cross section of the bridge
deck. The nonlinear temperature variation created over the cross section of a simply
supported bridge produces longitudinal self-equilibrating stresses (eigen stresses). These
can be determined by restraining the simply supported beam and then releasing the
restrained structure by reversing and applying the stress resultants. Using the Principle of
superposition gives the desired stresses. The resulting internal forces are unaffected but
there is a re-distribution of stresses in different components of a cross-section under
thermal loading. In a continuous bridge, additional continuity stresses also develop. In this
situation internal forces as well as external reactions change. Overall results can be
obtained using superposition of self-equilibrating stresses and continuity stresses. The
procedure described can be used for any practical situation as long as there is symmetry of
the cross section about a vertical axis. A section containing several layers made out of
different materials can also be handled in a similar way. In the situation of a complex
bridge deck consisting of a grid structure the above results can be combined with a normal
grillage analysis to enhance the comprehensive nature of the approach.
