Probabilistic Evaluation of Eurocode 5 Fire Design Criteria of a Timber Portal Frame

Structural reliability analysis for a three failure were identified for the frame and limit state function was formulated functions were based on the Eurocode 5 design criteria. Uncertainties in the timber material properties were generated from laboratory test results performed on five commonly used timber species in Nigeria, namely Als boonei (Ahun), Triplochiton Scleroxylon (Obeche), Terminalia Ivorensis (Idigbo), Terminalia superba (Afara) and Lophira Alata (Ekki). Uncertainties in loading and geometrical properties were obtained from international references. The limit state functions were evaluated using nonlinear constrained optimization technique. The optimization was executed using Genetic Algorithms(GA) based First Order Reliability Method (FORM) algorithm, through a developed computer programme in MATLAB. The results indica for a three-hinged timber portal frame in fire is the failure of the rafter safety levels for all the considered fire exposure times. Also, it was observed that at the criti portal frame can sustain fire for up to 50 minutes before failure, however, the target safety index of 3.8 recommended in the Eurocode can only be achieved at fire exposure time less than or equal to 25 minutes.