Impact Factors for Highway Bridges

Abstract

This paper deals with the review of impact or dynamic allowance factors for highway bridges that are being implemented by various countries around the world. This review has specifically emphasized the field results of other researchers and concluded that most of the studies have noted that the current American Association of State Highways and Transportation Officials (AASHTO) Specifications grossly underestimate the impact factors for highway bridges. The review of impact factors herein has concluded further that the AASHTO Specifications on impact for highway bridges are a function only on the span length, even though many other important parameters (for example, road roughness, vehicle and bridge dynamics) play a major role in terms of bridge dynamics. Test results of two medium span steel stringer concrete deck bridges (span length approx. 100 ft.) on West Virginia's highway systems are reported herein for varying truck speeds, and for various bridge natural frequencies, dynamic strains on stringers, concrete slabs, and abutments. A deterministic procedure, based on the orthotopic plate theory that was developed at West Virginia University, has been used to compute frequencies, deformations and stresses. In addition, I-D beam theory has been used to compute natural frequencies. A comparison of these theoretical results with the experimental is found to be satisfactory.