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.

Over the past decade, isolation bearings have seen a dramatic increase in usage on civil engineering structures. In the early stages, specifiers relied heavily on manufacturers when it came to composing material properties, performance standards, and testing requirements for these devices. The current state of the art dealing with isolation bearing specifications is much further advanced. However, several issues remain confusing to engineers wishing to implement isolators either for seismic or force control design rationale. This paper attempts to simplify isolation bearing specification issues by identifying important design criteria. Items such as qualification, material properties, fabrication, inspection, and testing concerns are all important components in a well-structured document.

In this study, sponsored by the Texas Department of Transportation, bearing performance was analyzed on the basis of elastomer hardness, shape factor, reinforcing shim orientation, degree of taper, and compressive stress level. Emphasis was placed on comparing the behavior of flat versus tapered pads. Experimentation included shear, compressive, and rotational stiffness tests; shear and compression fatigue loading; long term compressive loading; and tests to determine compressive stress limits. Bearings were intentionally loaded nonuniformly to define safe limits for bearing/girder slope mismatches. Research showed that tapered bearings performed as well as flat bearings and that manufacturing tapered bearings with steel shims oriented parallel to one another, rather than radially, is advantageous. Bearings made from lower hardness elastomers displayed several advantages over those made from harder material, particularly, a greater ability to accommodate girder end rotations. More highly reinforced bearings performed better in compression fatigue tests and easily accommodated compressive stresses well over 7.0 MPa (1000 psi).

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.

As part of an overall study of bridge behavior, instrumented elastomeric bearings are being installed on a fully instrumented test bridge in Cincinnati, Ohio. This paper presents a summary of the completed analysis and testing and the planned laboratory and field testing of the elastomeric bearings. The role of the bearings in the behavior of the overall bridge system is explicitly considered. The primary goal is to measure the deformations of the bearings over time. The secondary goal is to determine the practicality of using instrumented bearings to assess the condition and response of the overall bridge system. Analyses have indicated that the short term movements of the bearing, due to truck loading, are large enough to practically measure. Long term movements, such as those due to temperature, are also being measured. The analyses also show that changes in the bridge deck condition can result in measurable changes in bearing deformation. Laboratory studies include shear and compression studies of prototype and one-half scale models of the bearings and instrumentation. In the field, the bearings will be instrumented to monitor long and short term deformations. Limitations to the practicality of using instrumented elastomeric bearings are discussed.