Compensation of vertical temperature gradients on bridges using temperature induction

Climatic effects induce non-stationary temperature fields into bridges. The linear, vertical temperature portion generates bending constraints in statically indeterminate structures. In summer, for example, the associated stresses can be as large as those due to traffic. Local temperature induction offers a way out when the bottom slab is heated, and the deck slab is cooled - or vice versa. This induces an inverted gradient and compensates for external temperature stresses. A method for temperature induction of cross-sections was first developed on a scaled demonstrator (1:2) of a prestressed concrete box girder bridge and subsequently realized on the real structure. Temperature induction inside the box girder was achieved through heating mats and water cooling. Internally installed thermocouples measure the temperature distribution and validate the results of numerical computation of the non-stationary temperature field. The results indicate that the temperature gradient can be adjusted by -8.4 °C through cooling at about -30 W/m² and heating at about 90 W/m². Applying the system to a prestressed concrete bridge demonstrates its effectiveness under ambient thermal conditions, too. On this bridge, heating the bottom slab with 37 W/m² already changed the gradient by about -2.0 °C over a period of 38 hours.