Sylwia Stawska

Excessive weight and a growing number of permit vehicles can cause an accelerated bridge damage. Therefore, there is a need to better control operation of heavy permit vehicles. This paper presents an approach to assess bridge life consumption by permit loads. An economic lifetime of a bridge is considered in terms of the number of load cycles to failure so that the structure has to be replaced. Each passage of a truck causes one or more load cycles and thus reduces or consumes a part of the total remaining fatigue life. An incremental consumption equation is derived, and it allows to convert fatigue damage to dollar damage by considering the bridge construction cost, traffic volume, and bridge parameters. The incremental consumption covers only weight exceeding the legal limits. This consumption approach is presented for representative average values and the individual consumption approach with the GIS system using Florida as an example. A developed approach can help state agencies to establish a rational and fair permit fee structure. The methodology is transparent and can be used by any state utilizing the available databases.

This study aims to develop Load and Resistance Factor Design (LRFD) provisions for movable bridges’ mechanical components. It requires the formulation of the limit state functions, determination of the statistical parameters of loads and resistances, development of the reliability analysis method, selection of target reliability indices, and calibration of load and resistance factors. The service and overload limit states for electric and hydraulic motors were considered. Movable bridge owners and operators were surveyed to gather information about the bridge’s condition. The survey results helped to define the limit state functions and the acceptability limits. The target reliability index was established based on movable bridge performance determined by the bridge owner survey. It was concluded that the target reliability index is the same as is used in current practice. Finally, load and resistance factors were calculated and verified so that designed movable bridges’ mechanical components meet minimum safety requirements. The project results will be submitted for consideration as updates to the AASHTO LRFD Movable Highway Bridge Design Specification.

To ensure bridge safety under vehicular traffic, the owners must systematically verify the adequacy of bridge live load-carrying capacity. Bridges are evaluated for design, legal, and permit loading. The legal load rating uses AASHTO legal trucks, which meet the Federal Bridge Formula requirements. However, each state has a federal law exemption for truck weight and size. The state-specific grandfather provisions allow the operation of legally overloaded vehicles. Thus, the objective of this study is to determine whether the current live load factors provide adequate safety for exempted vehicles because there are no provisions for overloaded vehicles under grandfather provisions. This study presents a reliability-based analysis to determine state-specific live load factor for bridge rating on an example of Montana’s 20% overload allowance for agricultural vehicles. This approach does not require a reanalysis of the state bridge inventory. Linear scaling of existing rating results from bridge records can be used to determine ratings for agricultural vehicles. The study provides a calibration method to maintain the required minimum safety level with the minimum cost and effort.

Roads and bridges are designed to meet the transportation demands for traffic volume and loading. Knowledge of the actual traffic is needed for a rational management of highway infrastructure. There are various procedures and equipment for measuring truck weight, including static and in weigh-in-motion techniques. This paper aims to compare four systems: portable scale, stationary truck weigh station, pavement weigh-in-motion system (WIM), and bridge weigh-in-motion system (B-WIM). The first two are reliable, but they have limitations as they can measure only a small fraction of the highway traffic. Weigh-in-motion (WIM) measurements allow for a continuous recording of vehicles. The presented study database was obtained at a location that allowed for recording the same traffic using all four measurement systems. For individual vehicles captured on a portable scale, the results were directly compared with the three other systems’ measurements. The conclusion is that all four systems produce the results that are within the required and expected accuracy. The recommendation for an application depends on other constraints such as continuous measurement, installation and operation costs, and traffic obstruction.