Strength and structural safety of long-span light wood roof trusses. Reliability analysis using safety index

The results of the full-scale testing, previously carried out, of 75 light wood trusses are analysed to evaluate their compliance with strength and serviceability requirements. Size effects were studied considering span length and chord size. Test data were grouped into 15 case studies according to span lengths, chord size, and mode of failure. For the study of a strength limit state, the safety index, β, was calculated for a range of values of the ratio of maximum lifetime to nominal snow load. For the study of a serviceability limit state, the safety index was calculated for a range of values of allowable mid-span deflection as a function of the span. A size effect was observed for both span length and chord size. Short-span trusses with small chords exhibited acceptable levels of safety when their strength safety index is compared with recommended target values. Long-span trusses with large chords, with an improved heel joint detail, exhibited values of β slightly below target values. All trusses showe...