Reliability on timber columns under fire situation

Timber structures in fire situation are subject to intrinsic uncertainties from the material and the actions on the structure and their probabilistic behavior has not being studied exhaustively. In this paper, four limit state equations using the reduced cross-section method are developed for timber columns in fire situation. The security criteria taken into account in these equations are the compression, the lateral stability and the combined bending and compression, according to the NBR 7190:1997 standard. The structural reliability analysis of five simply supported timber columns with rectangular cross-section in fire situation and different base and height ratios where performed using the first order reliability method. The overall probability of failure of the column was obtained by associating the failure criteria in a series system. The reliability behavior of the different base to height ratios was evaluated, leading to different results for the distinct ratios and the criteria used. Also, a sensitivity analysis was performed indicating the timber charring rate as the most important random variable in the reliability analysis for these limit state equations.