Analysis of Permit Vehicle Loads in Wisconsin

Quarterly Reports Other Documents Final Report
September 2008
December 2008
March 2009
June 2009
Research Brief Final Report

Primary Investigator

Jian Zhao
Department of Civil Engineering and Mechanics
University of Wisconsin – Milwaukee

Abstract

Trucking accounts for 80% of expenditures on freight transportation in the United States; thus, allowing heavy trucks to operate will improve the efficiency of the highway system and benefit the economy. More than 230 oversize/overweight (OSOW) permits on average are issued by the Wisconsin Department of Transportation (WisDOT) everyday. As the truck weight increases, permit review and decision making become a concern for WisDOT. Wisconsin statutes usually allow non-divisible trucks (category AA) with a gross vehicle weight (GVW) between 80 kips and 170 kips for annual permits. Heavier non-divisible trucks (up to 250 kips) may be issued single-trip permits with predetermined routes. The impact of these heavier trucks on the state highway bridges has not been fully studied.

WisDOT has used the AASHTO HS20-44 design vehicle as well as the Standard Permit Vehicle for many years to describe the maximum safe load carrying capacity of highway bridges. The Standard Permit Vehicle is an important guide for issuing annual permits and/or single-trip permits. The Standard Permit Vehicle load also has been used as a design parameter because all newly designed bridges are required to safely carry this load. The Standard Permit Vehicle load was increased from 190 kips to 250 kips in 1999 to accommodate the increase in truck sizes in Wisconsin. The axle configuration, on the other hand, remained the same to facilitate the transition. Such permit vehicle load increase may be viable as indicated by the results of several load tests.

Both the configuration and the gross weight of the vehicles have impact on highway bridges. The truck load effects (i.e., moments and shear in bridge elements) can be greatly affected by the axle spacing, axle weights, and vehicle length as shown later in a typical line-girder analysis. Similar variations may exist in the configurations of the permit vehicles in Wisconsin; the Standard Permit Vehicle represents an “average” configuration of non-divisible permit vehicles with a high GVW. In addition, longer combination vehicles with large gross vehicle weights also are allowed on WISCONSIN Interstate highways. Thus, to ensure highway safety while keeping competitive business capability in Wisconsin, an investigation is needed for a clear understanding of permit vehicles and their impact on the state highway infrastructure.

Objectives

  • Gather and evaluate the representative OSOW permit vehicles that WisDOT process in recent years. A database will be created for overweight permit vehicles with detailed configuration information, such as statistical distribution of gross vehicle weights, axle weights, and axle spacing.
  • Identify vehicle configurations that best envelop the permit vehicles in Wisconsin. Propose modification to Standard Permit Vehicle(s) based on moment and shear in representative bridge spns caused by the collected permit vehicles.
  • Provide modifications to Chapter 45 of the WIsconsin Bridge Manual; provide examples to bridge rating and permit vehicle checking for the Bridge Manual; and provide counterpart information consistent with the AASHTO LRFD Specifications.
  • Establish guidelines for future evaluation and adaptation of further increased permit vehicle weights and future overweight vehicle configurations.
  • Collect and document existing research and state-of-practice on OSOW premit issuance, with a focus on other state DOT practices and the latest federal regulations and documents.

Tasks

  1. Collect representative OSOW permit records in Wisconsin
  2. Review literature and other state’s DOT practices
  3. Analyze typical bridges under permit vehicle loads
  4. Develop supplemental materials for the Wisconsin Bridge Manual
  5. Final report/Implementation plan

Project Information

  • Duration: 12 months
  • Dates: October 1, 2007 – October 1, 2008
  • Budget: CFIRE: $25,000; Total: $74,595
  • Modal Orientation: Highway
  • Project ID: CFIRE 01-02
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