The National Academies

NCHRP 10-57 [Completed]

Structural Safety Evaluation Guidelines for Suspension Bridge Parallel-Wire Cables

  Project Data
Funds: $448,752
Research Agency: Weidlinger Associates
Principal Investigator: Ronald Mayrbaurl
Effective Date: 3/10/2000
Completion Date: 4/30/2004

Background: There are nearly 50 major suspension bridges in the United States, and more than half of these are more than 50 years old. These represent major investments and essential transportation links for regional and national commerce and lifelines. As this group of major structures advances in age, the number of in-depth evaluations to determine their ability to safely carry increasing traffic is expected to increase. The need to estimate remaining service life and to take preventative steps to extend service life will also increase.

There is no reliable and nationally recognized procedure, either practical or theoretical, to inspect and evaluate the condition, strength, and safety of suspension bridge parallel-wire cables. Typically, inspections are visual and do not necessarily reveal the condition of the entire cable. Several significant suspension bridges have undergone in-depth inspections and evaluations in recent years by various engineering organizations, each performing the inspection and evaluation in its own way. At the NCHRP-sponsored "Workshop on Safety Appraisal of Suspension Bridge Main Cables" held in Newark, New Jersey, in 1998, the highest priority research needs identified were the development of cable inspection, sampling, and testing guidelines and the development of models to predict the strength of deteriorated cables.

Unreliable methods of inspection and evaluation could result in unnecessary replacement or in unexpected failures. Developing and improving the inspection and analytical tools for a better understanding of immediate and long-term needs are essential for planning effective strategies for preservation, rehabilitation, and, ultimately, replacement. The savings to owners and users could be in the tens of millions of dollars for each bridge. There is a pressing need to develop a manual of recommended practice defining reliable procedures for inspection and evaluation of parallel-wire cables of suspension bridges.

Objective: The objective of this research is to develop a manual of recommended practice for inspection and evaluation of suspension bridge parallel-wire cables. This manual shall be in a form suitable for consideration for adoption by the AASHTO Highway Subcommittee on Bridges and Structures.

Tasks: Achievement of this objective is expected to require the completion of the following tasks: (1) Review relevant domestic and international practice, performance data, research findings, sampling methods, laboratory testing, and other information related to inspection and evaluation of suspension bridge parallel-wire cables. This information shall be assembled from technical literature and from unpublished experiences of engineers, bridge owners, and others. Review and assess the inspection techniques and analytical methods used in current evaluations. (2) Identify and evaluate all factors that affect long-term cable durability and capacity. This should include, but not be limited to, current cable condition and the effects of design, construction, maintenance practices, and environment. (3) Propose for consideration by the panel one or more analytical models for practical application in estimating current cable capacity and for predicting future degradation and capacity. (4) Identify and evaluate non-destructive evaluation (NDE) methods for determining cable condition. (5) Submit an interim report within 6 months of the contract effective date documenting Tasks 1 through 4 for review by the NCHRP. The report shall also contain a detailed work plan for the remaining tasks. The contractor will be expected to meet with the NCHRP project panel approximately 1 month later. NCHRP approval of the interim report and work plan will be required before work begins on the remaining tasks. (6) Develop a model for practical application in estimating current cable capacity and for predicting future degradation and capacity. Apply the model to available data. (7) Develop a draft manual and commentary for suspension bridge cable inspection and evaluation in a format suitable for consideration by the AASHTO Highway Subcommittee on Bridges and Structures. (8) Plan and conduct a workshop on the background and use of the manual. It is expected that the workshop will last not longer than 2 1/2 days, with approximately 25 invited participants. The NCHRP will select workshop participants, provide the facility, and cover the costs for the travel and subsistence of invited workshop participants except for contractor personnel. The contractor will be responsible for all other activities and costs. (9) Submit a final report documenting the research effort. The manual, revised to reflect comments from the workshop, shall constitute an appendix to the report.

Status: The contract is complete.

Product Availability: The product of this research has been published as NCHRP Report 534: Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel-Wire Cables. A companion CD-ROM, bound with the guidelines, provides details of the research program undertaken to develop the guidelines and explanations of the guidelines' recommendations.

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