INVESTIGATING THE REMAINING FATIGUE RELIABILITY OF AN AGING ORTHOTROPIC STEEL PLATE DECK

Abstract

The A. Murray MacKay Bridge is an aging structure which opened to traffic over 40 years ago. With many of our structures aging, the ability to make confident management decisions supported by reliable engineering has become increasingly important. Evaluating existing structures using the design code approach contains uncertainty which affects management decisions. This thesis explores an alternate method that used structural health monitoring (SHM) coupled with laboratory testing to reduce uncertainty in these decisions. The MacKay is the first suspension bridge in North America to have an orthotropic steel plate deck (OSPD), which contains three fatigue prone details of interest. A planning decision is required for when to replace the OSPD, thus the remaining fatigue reliability of the OSPD is needed. During the summer of 2010, sections of the OSPD near the expansion joints on the MacKay were replaced and 29 specimens from the former deck were obtained for laboratory testing. These specimens were subjected to various stress ranges and number of load cycles to obtain the remaining life S-N curve. Concurrently, key details on the MacKay were instrumented with strain gauges to obtain the in-situ strain range from vehicle loads in the deck for a one year period. Numerical models were developed to determine necessary factors to adjust strain readings for both geometric location and the stress state at the fatigue details. After a limit state equation was defined for the fatigue limit state (FLS), probability distributions were used to model each variable in the limit state equation. Using the Rackwitz-Fiessler procedure, the reliability index was calculated over time for each gauge location. System reliability theory was used to combine all component reliabilities and determine the fatigue reliability of the whole OSPD.