Alternate load factor (autostress) design for short to medium span continuous steel bridges

Inelastic procedures, in contrast to the commonly used elastic procedures, have been adopted as an alternate method in the AASHTO Load and Resistance Factor Design (LRFD) Specifications. The Alternate Load Factor Design (ALFD) method, or Autostress method as it is more commonly called, provides a realistic alternative by assuming that some yielding will occur in the structure and by incorporating the forces generated in the process (as Automoment) into the design procedure. On the other hand, the current AASHTO Load Factor Design (LFD) method for steel bridges is still based on elastic analysis with only implicit recognition of inelasticity by using 10% moment reduction in the negative moment region. As stated in the AASHTO LRFD Specifications commentary, in order to utilize fully this inelastic analytical method, a computer program is generally required. The AUTO-DASH program is the first program for steel bridge design to attempt to use this method. Methods for simulating the actual hinge mechanism and autostress algorithms for any number of span bridges are incorporated into the AUTO-DASH program to perform an extensive analysis. The results have shown that using ALFD gives favorable comparisons with other methods using elastic procedures.