Overload permit rules applicable to H-type and HS-type bridges

Abstract

This document defines standards for issuing permits for overweight vehicles crossing standard H-type and HS-type Texas highway bridges. A general formula and a bridge specific formula have been developed for simple spans of both bridge types. Several reinforced concrete continuous span slab bridges were then evaluated according to the proposed criteria to ensure the validity of the proposed formulae for continuous spans as well as simple spans. The general formula will limit the axle group weight according to only the "X" rating and the vehicle dimensions while the bridge specific formulae also include the span length. Currently, the vehicle dimensions are the only criteria used by the Texas Department of Transportation (TXDOT) to determine whether or not an overweight permit will be issued. The proposed restrictions allow only one permit vehicle on the bridge at a time and ensure that the maximum stress does not exceed the operational stress level. In addition to determining the maximum weight which may be safely carried by a given axle configuration over either a specific bridge or an unknown bridge, the proposed formulae may also yield the "X" rating for any specific truck. Being able to quickly convert any truck to an equivalent HX or HSX rating will greatly simplify and increase the accuracy of the permitting process.