EFFECTS OF INCREASED SUPERSTRUCTURE FLEXIBILITY ON DYNAMIC RESPONSE OF CONCRETE BRIDGES

A study of the effects of design changes in the 1994 Load and Resistance Factor Design (LRFD) version of the American Association of State Highway and Transportation Officials (AASHTO) design code for prestressed concrete bridges is carried out in comparison with the earlier 1989 version of the AASHTO code. In the first part of this study, a detailed review of the design changes in the new LRFD code is 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. Coupled dynamic equations for interaction between the bridge and traversing vehicles are developed to predict the dynamic responses of the bridge girder. Dynamic characteristics of the bridges are determined using a finite element computer program. A number of vehicle models are developed for simulation of heavy truck loads. A modal condensation technique is used to reduce the degrees of freedom of the bridge models. Numerical simulations are performed for cases in which different vehicle models are used. Dynamic amplification factors are calculated and compared for the cases involving different vehicle speeds and traffic patterns. 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.

• Supplemental Notes:
  • This report contained no publication date; date shown is the date the report was entered in the TRIS data base.
• Corporate Authors:

  University of Central Florida, Orlando

  Department of Civil and Environmental Engineering
  P.O. Box 162450
  Orlando, FL  United States  32816-2450

  Florida Department of Transportation

  Haydon Burns Building, 605 Suwanee Street
  Tallahassee, FL  United States  32301
• Authors:
  • Kunnath, S K
  • Chopra, M B
• Publication Date: 1997

Language

• English

Media Info

• Features: Appendices; Figures; Tables;
• Pagination: v.p.

Subject/Index Terms

• TRT Terms: Box girders; Computer programs; Dynamic loads; Dynamics; Finite element method; Girder bridges; Girders; Heavy vehicles; I beams; Live loads; Prestressed concrete bridges; Simulation; Specifications; Spreadsheets
• Identifier Terms: American Association of State Highway and Transportation Officials
• Uncontrolled Terms: Dynamic characteristics; Dynamic response; I girders
• Subject Areas: Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 00738020
• Record Type: Publication
• Report/Paper Numbers: WPI 0510734, Final Report
• Contract Numbers: B-9909
• Files: TRIS, STATEDOT
• Created Date: Jun 27 1997 12:00AM