| Inadequate flexural strength and ductility, or shear strength, of concrete bridge columns have resulted in collapse or severe damage of a number of California bridges in recent moderate earth-quakes. In general, these bridges were designed prior to the new seismic design methods which were implemented in the mid-seventies. Bridges constructed in accordance with the new design methods have performed well in recent earthquakes. However, the large number of older bridges that are still in service, particularly freeway overpasses designed and constructed in the 1950's to 1970's, are now recognized to have substandard design details and to constitute a cause for major concern.; The principal objective of this study is to provide basic knowledge on the performance of circular columns with noncontact lap splices at their maximum moment sections. As part of that work the validity of existing equations, (Darwin et al, 1995), for calculating the maximum bar stress (or bond strength of lap splice) at failure along the splice length is examined. Then a simple model is used to provide reasonable predictions of the response to seismic loadings of bridge columns with inadequate length lap splices at the column to foundation connection.; This study involved both field and laboratory investigations. The field work involved the reversed cyclic lateral load testing to failure of four as--built large diameter circular columns which formed parts of existing bridge piers. However, due to the wide irregularities in the details of the field columns, it was not possible to determine the relative importance of the various parameters. Therefore, a laboratory investigation to examine physically what effects concrete cover, bar spacing and bar lap separation had on the behavior of columns with splices at the maximum moment region at their bases was undertaken in the Newmark Civil Engineering Laboratory. |
