Keywords: bridges, bearings, partial fixity, temperature effect.

Bridges are not static structures, they are continually in motion. Temperature changes, imbalances in dead loads, the moving of vehicles or trains and other types of dynamic loads cause linear and rotational movements to take place in bridge elements. To allow for these movements to occur, a bridge has bearing devices which transmit loads from the superstructure to the substructures. Defects and problems of bridge bearings result in the restriction of their movements and partially fixation of their rotations. Once these movements and, or rotations are restricted or prevented, a build up of forces will cause undesirable movements and generate harmful stresses in different bridge elements. These detrimental stresses must be quantified and studied. The aim of this work is to study the effect of partial fixation of bearings on the structural behaviour of bridges. The finite element method is used to perform the desired analysis. The three cases studied represent the most common types of roadway bridges that are analyzed and investigated. The first study case is a composite steel-concrete bridge; the second is a reinforced concrete while the third is a pre-cast concrete bridge. The analysis for each case is done for statical systems that represent different degrees of partial fixity of the bearing rotations and complete locking of its movements. Also, the analysis is performed for both the bridge self weight and a 25°C uniform rise in temperature of bridge superstructure. The obtained results are studied versus the analysis results of the statical system considered in the design. The study indicates that partial fixity of bearings generates significant stresses, not considered in the design, in different bridge elements. Hence, a great attention must be directed towards the maintenance, repair and replacement of the bridge bearings.

As a result of this work the following conclusions and recommendations can be drawn:

1. Partial fixation of bearings occurs in all types of concrete and steel bridges due to defects and problems of bearings such as:
   • Rusting of bearings due to the accumulation of dirt and debris.
   • Misalignment of bearings due to construction errors.
   • Loose of some elements of bearings.
   • Splitting, tearing, cracking or hardening in neoprene bearings.
2. The effect of partial fixity of bearings on the bridge behaviour is significant on the bridge superstructure and substructure due to both the bridge own weight and uniform rise in temperature.
3. Very large moments, not considered in the design, will be generated in the bridge girders, piers and foundations due to partial fixation of bearings.
4. To reduce the great effect of partial fixation of bearings on the bridge behaviour, the following precautions must be considered:
   • Periodic maintenance of the bridge bearings must be done.
   • Replacement of neoprene bearings must be done when hardening is noticed.
   • Any construction errors lead to restriction of rotation of bearings must be avoided.

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