Field Evaluation of Dynamic Load Factors for Historic Through-truss Bridges

Open Access
Newpher, Brandon James
Graduate Program:
Civil Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 20, 2013
Committee Members:
  • Jeffrey A Laman, Thesis Advisor
  • Thomas E Boothby, Thesis Advisor
  • Gordon Patrick Warn, Thesis Advisor
  • Dynamic Load Factor
  • Impact Factor
  • Dynamic Load Allowance
  • Through-Truss Bridges
  • Lenticular Arch
  • Pratt Truss
The late 1800s was a time of great innovation in bridge engineering. The advent of steel and the demand for longer spans under higher loads spurred the development of many new bridge designs. Out of this innovative time period, a wide range of historic through-truss bridges were developed and constructed. These bridges, now well beyond their design life, are being evaluated for capacity; many being demolished, few being rehabilitated. The evaluation process requires the estimation of the complex dynamic behavior of historic through-truss bridges under traffic loading. Structural engineers often evaluate complex dynamic behavior with the use of a dynamic load factor (DLF), which enables the enveloping of dynamic response values by scaling the maximum static response. For this reason the current study set out to evaluate the magnitude, distribution, and influential variables of DLF for historic through-truss bridges. This was accomplished through a combination of field evaluation of existing specimens, and digital signal processing; to produce both the maximum static and dynamic response values for instrumented bridge members for each traffic event. Scatter plots, correlation coefficients, and histograms were then created to evaluate DLF magnitude, distribution, and correlations with test variables. Correlations and trends were investigated between DLF magnitude and: maximum static strain, vehicle speed, vehicle static weight, and bridge span. The most influential variable on the magnitude of DLF was determined to be member peak static strain. The present study concludes that historic through-truss bridges exhibit DLFs with magnitudes higher than contemporary slab on girder bridge types.