A typical 3-hinged timber portal frame is designed to Eurocode 5 design specification and the safety level of the members assessed using the First Order Reliability Method (FORM). The failure modes associated with the members were identified and limit state equations related to each mode of failure is generated and written as subroutines using FORTRAN language in FORM. The safety index (β) for each failure mode was computed at varying load ratios, α (dead to live load ratio) from 0.2 to 1.0. It t was observed that for the varying load ratio’s (α), the predominant failure in the rafter member is bending failure with computed safety indices, β of 2.089 to 0.661; shear failure was identified for the column member with β- values of 2.230 to 0.675; failure mode (i) for both eaves and apex joints with β-values of 1.791 to 0.294 and -0.453 to -1.996 respectively for the α values considered. The results suggest that structural failure is most likely to occur at the apex joint for all possible loading conditions and more attention should be given to it during design.
Key words: Eurocode 5, First order reliability method (FORM), load ratio, Safety level index, Three hinged Portal frame, Timber.
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