In recent years, specialty bearings have been introduced for use in highway bridge construction. Prominent among these are the high-load multi-rotational (HLMR) types of bearings.
Current specifications for HLMR bearings have been developed from industry standards and vary widely throughout the United States. There is a need for a broad range, generic specification that reflects the best of current practice and will ensure long life, high quality, reliable bearings.
Although there is a proliferation of HLMR bearing specifications, many basic questions remain unanswered. These include questions related to: (1) the performance characteristics of such bearings subjected to induced eccentric loading while under rotation; (2) the apparent loss of full performance capabilities; (3) the long-term durability of certain materials and bearing configurations; and (4) the disparities between domestic and foreign design procedures and materials applications.
There is also inadequate information available to the bridge engineer providing concise guidance on the selection of an appropriate bearing for a specific design situation. Therefore, a selection guide is needed which will inform bridge engineers of the relative performance features for HLMR and conventional bearings used in new bridge designs in the United States.
The objectives of this research were to develop (1) a bearing selection guide for all bearings currently used in new bridge designs in the United States and (2) specifications for high-load multi-rotational bearings that can be recommended to AASHTO for consideration for adoption. Base-isolation bearings were not intended to be included in this research. PTFE slide units associated with high-load multi-rotational bearings shall be considered.
The final has been published as NCHRP Report 432. The report includes proposed specifications in load and resistance factor design (LRFD) format using customary U.S. units of measurement.