Performance Evaluation of Existing Reinforced Concrete Bridge In Kombolcha Town Crossing Borkena River

Abstract

Bridge deterioration may take place over time due to aging of materials, varying environmental conditions, damage due to impact of heavy vehicles and the number of vehicles has been increased due to the growth of related industries. River Borkena Bridge in Kombolcha is one of those deteriorated bridge which is also subjected to a vehicular load that generates dynamic forces and corresponding deflections and stress on the bridge components. The evaluation of existing bridges is an important task in the sustainable management of infrastructures. The most common approach to assess the safety of a bridge in bridge management is the determination of its load-carrying capacity. The load-carrying capacity directly affects the serviceability of the bridge. Performance assessment of bridge can be expressed in terms of load rating. One of several uses of bridge load rating is identifying those bridges that do not have adequate capacity for normal operation and consider such bridges for posting. The study demonstrates the comparison of maximum absolute deflection of River Borkena Bridge the strain gauge results from the field test, analytical results and the finite element analysis. Maximum deflection occurred at the mid-span of the bridge from strain gauge results of field test which is 18mm.The maximum permissible deflection for River Borkena Bridge is 24.21% greater value than the field test deflection result, 18.10% greater value than effective moment of inertia deflection, 21.68% greater value than finite element analysis deflection result. The section of River Borkena Bridge resists the Flexural cracks in Exterior and Interior Girder by satisfied amount of reinforcement 5.41% and 9.61% greater in that of required amount. This means that the crack width obtained from the field measurement using the crack scale is 40% to 60% less than the allowable limit value. River Borkena Bridge steel reinforcements tensile stress at the service limit state are 46.42% greater value for positive moment and 38.78% for negative moment than actual stress in the reinforcing steel due to service limit state moment. In this study, the mode shape and corresponding frequencies of River Borkena Bridge was determined by using 6 different load condition. Mode shapes and deflection shapes are interrelated. Indeed, one is always measured to obtain the other. Yet, they are quite different from one another in a number of ways. The relationships between the maximum span length of bridges and the fundamental frequency was discussed in this thesis. The minimum estimated frequency value is 19.31%, 20.20%, 20.55%, 7.03%, 8.34% and 8.85% greater than minimum frequency of case-A, Case-B, Case-C, Case-D , Case- E and Case-F loading respectively. The maximum estimated frequency value is 23.53%, 24.86%, 25.39%, 1.13%, 3.96% and 5.06%greater than maximum frequency of case-A, Case-B, Case-C, Case-D , Case- E and Case-F loading respectively. The result of this thesis shows that the condition of the exterior girder differs from the interior girder the rating value of the one differs from the other. As it can be seen that the interior girder rating factor for shear is below 1.0. After conducting the load post analysis on the bridge safe load capacity for interior girder section which is below 20 ton.