However, steel-only bearings (e.g., Figure 13.1b) suffered from long-term problems, such as corrosion or dust and debris collection; they were of high costs due to the need of expensive sliding surfaces and had ultimately poor performance. New trends led to the design of continuous bridges with fewer joints, widespread use of curved and skewed bridges with increased demands on bearings. This has led after 1950 to the development of modern bearings, where other materials as plastics or elastomers are used in combination with steel. Bearings are sensitive components of a bridge. As industrial products, they need certification and require manufacturing, transportation, temporary storage, and on-site installation in accordance with specifications and by qualified personnel. Such issues are covered in Europe by EN 1337 [13.5] that describes in its 11 parts the current types of bearings, gives a design methodology, and includes provisions for installation. The most common types of bearings are reinforced elastomeric bearings. However, the appropriate type of bearings must be chosen with due consideration of the design requirements, the initial and maintenance costs, the availability, or other parameters. EN 1337 includes in several parts provisions for some types of bearings as follows:
• Reinforced elastomeric bearings • Roller bearings • Pot bearings • Rocker bearings • Spherical and cylindrical bearings • Guided bearings and restrained bearings
The most usual type, reinforced elastomeric bearings, is described in Section 13.2, while spherical and pot bearings are described in Sections 13.3 and 13.4. For other types, reference is made to the code and the manufacturer’s specifications (see [13.9] and [13.10]).