Civil Engineering Reference
In-Depth Information
Figure 6.12
Temperature stresses in box girder
Figure 6.12 (a). It will be subjected to an overall compression corresponding to its
average rise in temperature, and to a sagging moment. Both the compression and
the bending moment may be computed by considering the cross section divided into
appropriate strips, and by summing the force in each strip and its moment about the
neutral axis.
If the length restraint is released, allowing the beam to expand, effectively a tensile
force is added to the beam, cancelling the overall compression and creating a new set
of stresses that have no net normal force, Figure 6.12 (b); that is the compressive areas
of the cross section balance the tensile areas. Now rotational releases may be applied
to the beam ends allowing it to hog upwards. Effectively, a hogging moment has been
applied to the beam, modifying the stresses so that there is no overall bending moment,
