EFFECT OF 85 YEARS OF SERVICE ON MECHANICAL-PROPERTIES OF TIMBER ROOFMEMBERS - PART III - RELIABILITY STUDY

The first two parts of this series (Fridley et al. 1996a, b) presented a comprehensive experimental and analytical duration of load (DOL) st udy of Purdue University's Peirce Hall, an 85-year-old, turn-of-the-ce ntury building razed in 1989. In this part of the research, we approac h the structure from a probabilistic standpoint. We treat the material properties and loading as random variables in order to answer the fol lowing questions: Would we have ever seen any DOL effects in Peirce Ha ll? If not, and recognizing that the structure was in general conforma nce with current design practice, are we overly conservative in curren t design considering DOL? If yes, how often, and how does this relate to the level of safety we currently assume in design? We found that Pe irce Hall, with randomness of loading and material properties, had a f inite probability of experiencing a DOL failure, but not as high as as sumed in current design. That is, the probability of Peirce Hall exper iencing a DOL failure was less than what would be predicted using curr ent DOL-analysis procedures. The major reason for this lower probabili ty of failure is not due to an ''over-designed'' Peirce Hall, but is c ontributed to differences in real loading and assumed loading. Specifi cally, the snow load process assumed in current DOL-analysis procedure s utilizes a rectangular representation of snow events, when a triangu lar representation is more appropriate. The rectangular event produces greater damage and higher probabilities of failure than the triangula r event.