Reliability-based load management of the Red Deer River bridge
This thesis presents the results of an investigation into the evaluation of a selected test bridge using instrumentation to obtain site-specific factors contributing to the evaluation, with the ultimate objective of improving the estimate of the bridge’s reliability in order to assess allowable loading more accurately. The experimental portion of the research program involved instrumenting the test bridge with strain gauges, and recording field measurements using two forms of loading. The analytical portion of the research program involved the analysis of the bridge in the as-designed state, based on the design drawings and specification, followed by a re-analysis of the bridge using the site-specific factors measured on-site. The bridge was evaluated using methods outlined in the Canadian Highway Bridge Design Code CAN/CSA-S6-00 (CSA 2000). The test bridge is located near the community of Hudson Bay, Saskatchewan. The bridge is constructed of steel-reinforced concrete, and there are three, three-span arch-shaped girders. There are also external steel bars added after initial construction to increase the midspan bending moment resistance. In total, 45 strain gauges were placed on the middle spans of the three girders to record strain induced by two forms of loading: controlled loading, in which a truck of known weight and dimensions was driven over the bridge in a number of pre-determined configurations, and in-situ loading, in which normal truck traffic was used. The current allowable loading on the bridge is a gross vehicle weight of 62.5 t, although increasing the allowable loading to 110 t has been proposed, along with two strengthening alternatives to make this increased loading feasible. To provide a base-line analysis for comparison purposes, the bridge was first evaluated based strictly on information taken from the design drawings and specifications. The evaluation was performed using the load and resistance factor method, in which load and resistance factors were used to account for uncertainty, as well as by the mean load method, in which statistical properties of the variable’s parameters included in the design were used to account for uncertainty. The result of the load and resistance factor method was a live load capacity factor, indicating the overall “rating” of the bridge. In addition to the live load capacity factor, the mean load method was also used to determine the reliability index. The results of the as-designed analysis showed that the mean load method gave more conservative estimates of the bridge capacity. Furthermore, it was determined that, based on these assessments, the bridge would not have sufficient capacity to carry the proposed 110 t truck loads.The bridge was re-evaluated using site-specific factors with the mean load method. Using the measured strains, statistical parameters were determined for live load effects, distribution factors, dynamic load allowance, and resistance. Statistical parameters that could not be obtained readily through testing were obtained from the literature. The results indicated that code-predicted estimates of a number of factors were highly conservative. Flexural and shear load effects in the girders were found to be less than 15% of the theoretical predictions, as a result of apparent arching action in the girders, generating significant axial forces. For this arching action to occur, horizontal restraint was required at the supports, either through unanticipated restraint in the bearings, or tension tie action of the tensile girder reinforcement. Furthermore, the dynamic amplification was found to be less than 1.0. The resulting reliability indices indicated that the bridge would be safe under the proposed increased allowable loading (110 t). Finite element models were used to confirm the dynamic amplification observations and examine the effects of different degrees of bearing restraint. The model showed results similar to those measured for dynamic amplification. It was found that if the bearings were to become completely fixed against horizontal translation, the bridge would become overloaded as a result of increased shear effects, demonstrating the need for proper bearing maintenance. An analysis of relative costs was completed to determine the most cost-effective solution for hauling logs. Assumptions were made regarding truck and maintenance and operating costs. The results indicated that the most economic solution was to use the method outlined in the research to increase the allowable loading on the bridge to 110 t, over the strengthening alternatives and simply leaving the bridge in the current state.
DegreeMaster of Science (M.Sc.)
SupervisorSparling, Bruce F.; Sparks, Gordon A.
CommitteeWegner, Leon D.; Elshorbagy, Amin A.; El-Amoury, Tarek; Boulfiza, Mohamed
dynamic load allowance