Effects of temperature - Concrete Structures: Stresses and Deformations - page 352

4 orientation of the bridge axis, latitude and altitude of the location;

5 time of the day and the season;

6 diurnal variations of ambient air temperature and wind speed;

7 degree of cloudiness and turbidity of the atmosphere.

In daytime, especially in summer, heat gain is greater than heat loss, result-
ing in a rise of temperature. The reverse occurs in winter nights and the
temperature of the structure drops. Figure 10.1 is a schematic representation
of heat

ow for a bridge deck during daytime in summer. Incident solar
radiation is partly absorbed and the rest is re

fl

ected. The absorbed energy
heats the surface and produces a temperature gradient through the deck. The
amount of absorbed radiation depends upon the nature and colour of the
surface: the absorptivity is higher in a dark rough surface compared to a
smooth surface of light colour. Some of the absorbed heat of radiation is lost
to the air by convection and re-radiation from the surface. The amount of
convection depends upon wind velocity and the temperatures of the air and
the surface.

fl

10.3 Shape of temperature distribution in bridge
cross-sections
Bridges are generally provided with bearings which allow free longitudinal
translation of the superstructure. A change in temperature, which varies lin-
early over the cross-section of a simply supported bridge, produces no
stresses. When the temperature variation is non-linear, the same bridge will be
subjected to stresses, because any fi bre, being attached to other fi bres, cannot

Figure 10.1 Heat transfer processes for a bridge deck in daytime in summer.