Performance of timber girders with end-notch: Experimental and numerical investigation

Many bridges built during the colonial times in Australia have timber girders as load transferring elements and they are still in service with increased traffic loads and consistent deterioration. Most of the timber girders in those bridges are notched at the ends for better seating arrangement. Therefore, it is necessary to quantify the strength characteristics of notched girders in order to ensure structural safety and make necessary intervention to extend their service lives. Hence experimental tests were conducted on the notched rectangular timber girder samples with three different notch depths (i.e.10%, 15% and 30% of the depth of beam) having the notched angle of 1:4. Consequently, detailed finite element models were developed for notched timber girders, and the models were validated with experimental results. The validated model was used to predict the shear and flexural strengths and stiffnesses of typical circular and rectangular timber girders with two different spans (i.e. 6 m and 9 m), three different notch angles (i.e. 1: 0, 1:2 and 1:4) and three depths (i.e.15%, 30% and 45% o of the depth of beam). Strength data developed for notched timber were used to compare the applicability of the design provisions in various timber design standards. Experimental and finite element model test results show that when the notch depth increased from 15% to 45%, the load carrying capacity of rectangular timber girder was reduced by 50%. Whilst, the reduction of the load carrying capacity of the corresponding circular timber girder was slightly low (i.e. 37%). Further, when the notched angle changes from 1:0 to 1:4, the load carrying capacity of circular and rectangular girders increased about 50%, 69% and 110% for the notch depths 15%, 30% and 45%, respectively.