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Deferred Cost Savings for an Inventory of Bridges Using SHM

B. WESTCOTT, D. THOMSON

Abstract


The cost of managing an inventory of bridges can be significantly reduced by deferring replacement of bridges using the combination of testing and structural health monitoring (SHM). In the US it is estimated there are 63,522 structurally deficient bridges out of a total bridge inventory of 607,751. A surprisingly small number have been placed there based on structural testing. Bridges that are structurally tested are often, but not always, found to have a higher load capacity than that estimated by analysis alone [1]. The underestimates may be due to the prudent application of safety margins due to uncertainty about materials and construction. It may also be due to over simplified structural assumptions, inaccurate modelling of boundary conditions and ignoring the load bearing capacity of “non-structural” elements. However, once results from testing are available, it is the updated estimate of the capacity that is the most appropriate to use. One can conclude that the replacement many bridges could be deferred through testing to ensure capacity and the application of monitoring to ensure ongoing capacity and safety. The economic return of deferring replacement is very high as the yearly borrowing cost for even modest structures exceeds the cost of typical SHM system. In this work, a bridge testing and SHM policy was used for model calculations on an inventory of bridges. Based on an annual model budget of $100 million for structurally deficient bridge construction and $5 million for construction per bridge. In this paper we will present cost simulations over ten years that utilize a policy of testing, monitoring or replacement to maximize the utilization of the bridge assets. The simulations predict application of SHM could reduce a ten year $1 billion budget by over $600 million.

doi: 10.12783/SHM2015/39


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