Effects of Increased Superstructure Flexibility on Dynamic Response of ConcreteBridges

摘要

A study of the effects of design changes in the 1994 LRFD version of the AASHTOdesign code for prestressed concrete bridges is carried out in comparison with the earlier 1989 version at the AASHTO code. In the first part of this study, a detailed review of the design changes in the new LRFD code are outlined. An automated spreadsheet program is developed for the analysis of simply-supported standard AASHTO I-girder bridges and post-tensioned box girder bridges. The spreadsheet program is used to generate a set of typical bridge designs with varying spans and girder spacing to be used in the second phase of the study. Based on the study of typical designs using both versions of the code, a critical evaluation of the LRFD provisions is presented. In the second phase of the study, the dynamic characteristics of typical bridges designed by the 1989 and 1994 LRFD versions of the AASHTO code were evaluated. The response of I-girder and box-girder bridges to moving loads with and without vehicle interaction is investigated. Results of phase I investigation indicate that the new LRFD provisions result in generally more conservative designs. Results of phase II investigation show that there is no significant change in dynamic properties of I-girder bridges designed by either AASHTO (1989) or LRFD (1994). Box girder bridges designed with the new code do exhibit more flexibility than previous AASHTO (1989) based designs.