ACI 342R

Abstract

Scope: This report is intended for the bridge engineering community, particularly engineers responsible for bridge load rating, to provide basic guidance on the methods and tools available for determining live load distribution behavior of in-service bridges. The objective is to present guidance on available methods for determining live load distribution, including approximate formulas, structural analysis, or load testing. The selection of a particular method of analysis is presented within the context of the intended level of refinement and bridge type, such as slab, beam-slab, and box girder. Included in this report are descriptions, a brief history, and background of the flexural load distribution phenomena and a summary of design and analysis methods used to describe the phenomena in practice. This report provides an overview of criteria for transverse load distribution, including their limitations and acceptability; a summary and description of the use of refined methods of analyses for transverse load distribution; and load test methods. A series of case studies are presented in the latter part of the report to serve as a comparative analysis of commonly used live load distribution methods and their performance in describing the behavior of in-service structures. While this distribution phenomenon is relevant to a variety of force effects, this report focuses exclusively on flexure. The treatment of shear is a topic of future work by the committee and will be part of a guide on the in-service evaluation of concrete bridges, but is beyond the scope of this report. For a treatment of shear load distribution, the reader is encouraged to review existing literature on the topic (Bakht et al. 1983; Ebeido and Kennedy 1995, 1996; Modjeski and Masters Inc. 2002; Barr and Amin 2006; Suksawang et al. 2013).