1、Report on Flexural Live Load Distribution Methods for Evaluating Exisiting BridgesReported by ACI Committee 342ACI 342R-16First PrintingJanuary 2016ISBN: 978-0-87031-947-1Report on Flexural Live Load Distribution Methods for Evaluating Existing BridgesCopyright by the American Concrete Institute, Fa
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11、athered together in the annually revised ACI Manual of Concrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis report provides a synthesis of the topic of flexural live load distribution and i
12、ts applicability to concrete bridges. Flexural live load distribution is critical to describing how loads are transmitted through a bridge system. This report is intended to provide engi-neers, including load rating engineers, with basic guidance on the methods and tools available for determining li
13、ve load distri-bution behavior of in-service bridges. Included in the 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. A series of case studies are presented i
14、n the latter part of the report to serve as a comparison summary of commonly used live load distribu-tion methods and their performance in describing the behavior of in-service structures. The report also provides performing bridge load ratings with a practical synopsis of the various methods avail-
15、able for determining the live load distribution factor. While this report is limited to flexural live load distribution, it provides the foundation for a future committee guide on the in-service evalua-tion of concrete bridges.Keywords: bridge analysis; bridge load rating; distribution factor; equiv
16、a-lent beam analysis; finite element; grillage analysis; live load testing; load resistance; transverse flexural load distribution.CONTENTSCHAPTER 1INTRODUCTION AND SCOPE, p. 21.1Introduction, p. 21.2Scope, p. 2CHAPTER 2NOTATION AND DEFINITIONS, p. 32.1Notation, p. 32.2Definitions, p. 3CHAPTER 3BASI
17、S OF CODE CRITERIA FOR TRANSVERSE LIVE LOAD DISTRIBUTION, p. 43.1Introduction, p. 43.2Transverse load distribution, p. 43.3Empirical formulas for transverse live load distribu-tion, p. 43.4AASHTO Standard Specification for Highway Bridges, p. 43.5AASHTO LRFD Bridge Design Specifications, p. 53.6Cana
18、dian Highway Bridge Design Code, p. 63.7American Railway Engineering and Maintenance-of-Way Association, p. 73.8Summary, p. 8CHAPTER 4SUMMARY AND USE OF REFINED METHODS OF ANALYSIS, p. 84.1Introduction, p. 84.2General approach, p. 94.3Equivalent beam line method, p. 9Jeffrey L. Smith, ChairRiyadh A.
19、 Hindi, SecretaryRita K. Oglesby, SecretaryACI 342R-16Report on Flexural Live Load Distribution Methods for Evaluating Existing BridgesReported by ACI Committee 342Om P. DixitAndrew J. FodenAndre G. GarnerDevin K. HarrisMohamed A. MahgoubBruno MassicotteJohn J. MyersLarry D. OlsonAyman E. SalamaJoha
20、n L. SilfwerbrandMark Erik WilliamsConsulting MembersF. Michael BartlettFernando A. BrancoAngel E. HerreraBarney T. Martin Jr.Madhwesh RaghavendracharJaroslav SimekACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction
21、. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsib
22、ility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be
23、restated in mandatory language for incorporation by the Architect/Engineer.ACI 342R-16 was adopted and published January 2016.Copyright 2016, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any ph
24、oto process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.14.4Grillage analogy method, p. 104.5Three-
25、dimensional frame analysis method, p. 114.6Finite element method, p. 114.7Summary, p. 12CHAPTER 5IN-SERVICE EVALUATION AND LOAD RATING OF CONCRETE BRIDGES, p. 125.1Introduction, p. 125.2Load rating for concrete bridges, p. 125.3Load distribution for in-service evaluation and load rating, p. 135.4Loa
26、d testing, p. 135.5Characterizing lateral load distribution from load testing, p. 145.6Summary, p. 15CHAPTER 6CASE STUDIES OF ANALYSIS METHODS AND LOAD TESTS, p. 156.1Introduction, p. 156.2Literature survey, p. 156.3Slab bridges, p. 166.4Simply supported concrete girder bridges (with concrete decks)
27、, p. 186.5Continuous concrete girder bridges (with concrete decks), p. 216.6Steel girder bridges (with concrete decks), p. 236.7Summary, p. 256.8Synthesis of case studies, p. 256.9Recommendations from findings, p. 26CHAPTER 7SUMMARY AND CONCLUSIONS, p. 267.1Refined analysis methods, p. 277.2Load tes
28、ting and instrumentation, p. 277.3Bridge types, p. 277.4Correlation of distribution factors, p. 27CHAPTER 8REFERENCES, p. 27Authored documents, p. 27CHAPTER 1INTRODUCTION AND SCOPE1.1IntroductionMaintenance of an aging transportation infrastructure, including concrete bridges, is essential to the su
29、stainability of resources and economic prosperity. With a national inven-tory of more than 600,000 bridges in the United States, 66 percent of which are concrete, maintenance and preservation represent a challenge for transportation agencies (Federal Highway Administration 2014). For these agencies,
30、 the challenge is to avoid or minimize bridge replacement and rehabilitation in the face of increased traffic volume and truck loads, along with dwindling financial resources.Transportation agencies are responsible for ensuring both the safety and functionality of these bridges, and meeting this cha
31、llenge requires a realistic measure of the actual behavior and in-service performance. This characterization of behavior is essential to determine the actual load-carrying capacity or remaining capacity of a bridge, which is typi-cally determined through a processed called load rating. Load rating o
32、f a bridge defines the expected resistance or capacity based on its existing condition state and operating environment. As with bridge design, a challenge that exists for describing a bridges capacity is the complex system interaction that exists amongst the superstructure compo-nents. For example,
33、in a beam-slab bridge, the complexity is derived from the coupled interaction of two-way plate behavior within the bridge deck and the one-way beam behavior inherent to the girders. For both design and evalu-ation, a methodology for transverse distribution of loads, or live load distribution, is typ
34、ically used to represent this phenomenon and provide a method to quantify relative load sharing behavior within the system.In practice, this phenomenon is typically defined using prescriptive formulas that simplify the complex behavior into simple factors, but in recent decades, several refined meth
35、ods for determining live load distribution have evolved. These methods provide alternative mechanisms to describe live load distribution behavior, which can often be more representative than the empirical methods included in most bridge design codes and specifications. The advantage of considering t
36、hese methods is that they have the potential to describe the physical phenomenon and actual load distri-bution behavior, which in turn provides the bridge engi-neer with a mechanisms to make more informed decisions regarding load restrictions, maintenance, and replacement of existing bridges.1.2Scop
37、eThis report is intended for the bridge engineering commu-nity, 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 avail
38、able methods for determining live load distribu-tion, including approximate formulas, structural analysis, or load testing. The selection of a particular method of anal-ysis is presented within the context of the intended level of refinement and bridge type, such as slab, beam-slab, and box girder.
39、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 distribu-tion, including the
40、ir 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 distrib
41、ution 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 gu
42、ide on the in-service evaluation of concrete bridges, but is beyond the scope of this report. For a treatment of shear load distribution, the American Concrete Institute Copyrighted Material www.concrete.org2 REPORT ON FLEXURAL LIVE LOAD DISTRIBUTION METHODS FOR EVALUATING EXISTING BRIDGES (ACI 342R
43、-16)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).CHAPTER 2NOTATION AND DEFINITIONS2.1NotationB = width of bridge, ft (m)C = capacityDC = dead load effect d
44、ue to structural components and attachmentsDF = lateral load distribution factor (also designated as g)DW = dead load effect due to wearing surfaces and utilitiesde= roadway part of overhangF = amplification factorIM = dynamic load allowancek = number of girdersL = span of the bridge, ft (m)LL = liv
45、e load effectMg,ave= average moment per girderm = multiple presence factorn = number of wheel lines of applied loadingP = permanent loads other than dead loadsS = center-to-center spacing of longitudinal web lines or girders, ft (m); also spacing of floor beams, ft (m)wj= ratio section modulus of th
46、e i-th girder to section modulus of typical interior girderj= bottom flange strain at the i-th girderDC= LRFD load factor for structural components and attachmentsDW= LRFD load factor for wearing surfaces and utilitiesLL= evaluation live load factorP= LRFD load factor for permanent loads other than
47、dead loads2.2DefinitionsACI provides a comprehensive list of definitions through an online resource, “ACI Concrete Terminology,” https:/www.concrete.org/store/productdetail.aspx?ItemID=CT13. Definitions provided herein complement that resource.beam slabbridge system where the concrete slab or bridge
48、 deck is not supported by beams or girders and serves as the primary superstructure element or load-resisting component of the posite beam-slabmember produced by inter-connecting separate beam and slab; the connections have sufficient stiffness to ensure strain compatibility between components under
49、 service and sufficient strength to ensure the member strength is limited by material capacities in the individual components.diaphragmtransverse member placed between the primary load-carrying elements of a superstructure system to distribute stresses and improve strength and rigidity.dynamic load allowance (impact factor)increase in the applied static live load force effects that account for the dynamic interaction between the bridge and moving vehicles.effective widthreduced width of a concrete slab with
