Reliability Assessment of Three Selected Timber Species Strength for Bridge Beams in Bending and Shearing Forces

This study investigated the reliability of three timber species from the Niger Delta—Mansonia (Mansonia altissima), Ububa Red (Berlinia grandiflora), and Angala (Rhizophora racemosa) as bridge beams to Eurocode 5 design rules. The strength classes for Mansonia, Ububa Red and Angala timber species were established in accordance with the provisions of EN 338 (2009). The study classified Mansonia as D50, Ububa Red as D60 and Angala as D70 respectively. The limit state functions were developed considering the failure of the beams in bending and shear respectively. Reliability analysis was used to assess the structural performance of each timber species, and sensitivity analyses were conducted by varying design parameters to observe their effect on reliability indices. The reliability indices were computed using custom MATLAB programs based on the First Order Reliability Method. It was shown that the reliability indices generally decreased with increasing beam span and live load on beams for both bending and shear failure modes respectively. The timber beams showed the capacity to support live loads of 11.5 KN/m, 14 KN/m, and 16.5 KN/m over a 50-year reference period, meeting the target reliability index of 3.8 recommended by Eurocode 0 (1978). It is also found that the reliability of the beam increased with increase in depth and width of the beams. For this period, required beam depths were identified as 350 mm for Mansonia, 325 mm for Ububa Red, and 300 mm for Angala timber beam respectively. It is also found that Mansonia, Ububa Red and Angala timber beams are very safe for a span of 6.8m, 7.5m and 8m respectively. The Mansonia, Ububa Red and Angala timber beams are generally very safe in bending and shear.