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Chapter 10
Uplift bearings—selection and design considerations
G. Moor
Mageba USA, New York, USA
T. Spuler, N. Meng & C. O’Suilleabhain
Mageba SA, Bulach, Switzerland
ABSTRACT: The vertical forces exerted by bridge decks and other structures on their sup-
ports are not always downwards; uplift can occur for a variety of reasons. Upward forces
are generally transient, lasting no longer, for example, than the duration of a strong wind
or of live loading of the relevant section of the structure. Although the structure’s bearings
must typically still be capable of carrying downward forces, facilitating rotations, and resist-
ing horizontal forces and/or accommodating displacements, they must now be able to do
all of this even under uplift conditions. And if the frequency of load reversal is high, then
the uplift load condition may become fatigue-relevant, adding yet another dimension to the
design—especially if the load reversals would cause hammering of interfaces such as the slid-
ing surfaces of a sliding bearing. This paper describes key issues which must be considered in
selecting and designing bearings for uplift conditions.
1 INTRODUCTION
A structure’s bearings play a critical role in its proper functioning and performance, typically
accommodating movements and rotations while carrying loads and resisting other forces. In
doing this, they generally enable the structure to function far more efficiently than it would in
the absence of bearings, allowing bending moments and stresses to dissipate in a controlled
manner.
Most bridges require their bearings to resist downward forces, with resultant upward forces
never arising. If no horizontal forces must be resisted, the basic design of the bearing may be
relatively simple, as shown in Figure 1 for the case of a spherical bearing. If horizontal forces
are to be resisted (in the longitudinal or transverse direction, or both), this can generally be
achieved by the addition of stops or guide bars, for example as shown in Figure 2.
However, the design becomes significantly more complicated if any type of uplift force
must be considered, as described below.
Figure 1. Cross-section of a typical spherical
bearing (free sliding type), which must not resist
uplift forces.
Figure 2. Cross-section of a typical spherical
bearing (guided sliding type, with guide bars on
sides allowing horizontal sliding movements).
NYBRIDGE_Book.indb 105NYBRIDGE_Book.indb 105 7/17/2013 8:42:10 AM7/17/2013 8:42:10 AM

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