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After 18 years of service, the pot bearings of the New Carrolton Route Section D-10, part of the Washington, D. C. Metropolitan Area Transit Authority's metro system, are being replaced. Access to the bearings is extremely limited because the bearings are architecturally sealed behind cover plates within box girders. This paper highlights the need to design bridges with access for maintenance, inspection, and bearing replacement. It also discusses issues relating to the long term performance of bearings.

Effective sealing of expansion joints in parking structures requires a thorough understanding of structural behavior and the service condition, as well as the properties and limitations of available expansion joint systems. Factors contributing to volume change, traffic conditions, detailing, and installation will all play a role in the ultimate success of the joint system selected. Commercial types of expansion joint seals commonly available include the urethane "T" joint, compression seals, steel and aluminum strip seals, winged seals with headers, and inflated structural seals. Each have certain advantages and limitations which must be considered relative to the usage condition in order to make a proper selection. Detailing considerations, such as joint opening size, movement considerations, traffic volume and loading, directional change, and termination requirements and drainage patterns all have an impact on performance. Periodic maintenance should be expected and planned for through an established program. Today, a wide variety of effective expansion joint sealing systems are available to help avoid the many problems previously associated with parking structure applications. Success depends on understanding the requirements of the service condition and the limitations of the various systems considered for use. Only with care in the specification and detailing of expansion joint requirements at the design stage will the installing contractor be positioned to most effectively install any expansion joint system.

From shortly before the entry of the U. S. in World War II and to the present, the author has been continuously involved in the design, testing, manufacturing, and observation of the performance of joints of all types, from pavements to bridges, and bearings of all types, from the old rockers to elastomeric, pot, disc, and then to earthquake isolation concepts. Starting out with load transfer devices buried in concrete pavement joints for state highways and airfield pavements to field molded sealants and then compression seals, the design trend in pavements has been from longer 100 ft panels (30 m) to relatively short panels of 15 ft (4.5 m). This has greatly simplified the sealing problem, since the distance changes between joint interfaces of shorter length panels obviously are much less in creep-shrink and thermal volume change. With respect to bridges, the design trend has been reversed, going from relatively short decks of 40 ft (12 m) to longer and longer spans, greatly complicating the sealing problem. It was in this confused design period that the writer worked toward developing sealing and bearing systems for every conceivable type pavement or bridge structure. Some lessons learned during the past 50 or more years are the subject of this paper.

The seismic performance of high type steel bridge bearings of both the fixed and expansion/rocker type were investigated. Simple seismic retrofit strategies were proposed and investigated experimentally. It was shown that by retrofitting existing high type steel bridge bearings, it is possible to provide sufficient strength and displacement capability to withstand substantial ground shaking. The weak link in the chain of force transmission may thus become the anchor bolts and/or the reinforced concrete pedestal. To understand the influence of the reinforced concrete pedestal and mild steel anchorage on the overall behavior of a high type fixed bearing assembly, a full scale reinforced concrete cap beam with pedestals was constructed. The rest results demonstrate the importance of considering the flexibility and strength of the concrete pedestal-anchor bolt system. As a retrofit method for the damaged reinforced concrete pedestal, a steel jacketing retrofit wrapped around the damaged reinforced concrete pedestal and bearing was investigated. Once retrofitted, it is shown that essentially elastic behavior may be expected in an earthquake.

SP-164 (V2) Although bearing and joint systems comprise only a small percentage of the construction cost of highways, buildings, and bridges (1 percent, typically), their importance to the functioning of those structures is vastly greater. For without adequate engineering effort in design of these vital elements to account for the many, sometimes conflicting, requirements of loading and/or movement, the integrity of the entire structure may be compromised. Our increased understanding of seismic activity has made us more aware of the wider area of this activity as the greater demand placed on support and joint systems. This Fourth (quinquennial) World Congress on Joint Sealing and Bearing Systems in Concrete Structures will enhance the general understanding of these systems and introduce entirely new concepts developed to cater to the latest seismic code requirements. As with the first two Congresses, this is V.2 of a two-volume set. V.1 contains 22 papers, plus the abstracts ofpapers presented at the Third Congress.