History of AASHTO Design Specifications

Through 1930

Through 1930 each state bridge engineer/consultant could decide how they wanted bridges designed


1st Publication of Standard Specifications for Highway Bridges. It followed the WS philosophy

  • Fraction or a Percentage of material's load-carrying capacity was determined
  • Actual load effects compared


HS20 testing vehicle introduced


In early 1970's Load Factor Design (LFD)

  • Recognized the predictability of Live and Wind Loads
  • Applied different factors to the loads and checked against material yield


Standing Committee started a two-year process to review foreign design specifications and codes and identify gaps in the US Code


1994 1st edition of AASHTO LRFD (Load and Resistance Factor Design) Bridge Construction Specifications published in 1994

  • Different materials act differently
  • Different members act differently (tension versus compression versus moment)
  • Extensive use of statistical methods
  • HL-93 Vehicle was established (HS20 vehicle no longer was accepted)


Final 17th edition was published in 2002

In 2005, the 17th edition was retired for all new bridges (AASHTO decided to no longer maintain or update).

After 2005, the 17th edition was only to be used to analyze existing bridges which were being refurbished, but had been designed prior to 2005.


4th edition published in 2004 finally gets LRFD correct FHWA and States agree that all new bridges designed after 2007 will follow LRFD criteria

From 1994 to 2007 could use any of the three methods:

  • WS
  • LFD
  • LRFD

A very confusing time especially since LRFD had a lot of holes in it.
4th edition published in 2004 finally gets LRFD correct


Current standard: 2018 LRFD

To Top