TOPSIS Decision Analysis for Inventory Management Including Blast Loading on Critical Bridges
Open AccessCurrent bridge inventory management process does not take the infrastructure’s vulnerability to an explosion into consideration despite the severe consequences of a bridge collapse (Winget, 2015; BDIS 2016). Bridge inventory management is conducted by the owner of a bridge structure, usually a Department of Transportation in a state or local government agency. Bridge inventory management is the process by which the owner stores data about and allocates resources for repair, replacement and/or inspection of bridges in their jurisdiction. Current inventory management tools simply organize user inputs but do not provide suggested actions or prioritization which can result in critical repairs not occurring due to limited funds (BDIS 2016, USDOT 2015). The purpose of this praxis is to expand the current bridge inventory management process to include blast loading, and to develop a decision tool using TOPSIS that includes blast loading. The decision tool determines what, if any, mitigation is suggested (rehab, other, nothing, etc.) to reduce risk of the consequences of an event (earthquake, storm, explosion) while keeping cost outlay below the potential revenue loss of the Event. This decision tool quantifies a bridge’s vulnerability to collapse from an explosion by evaluating how likely it is to be targeted and how well it is expected to perform under blast loading. The decision tool then assesses the consequences of an event (e.g. potential loss of life, toll revenue) against the cost to early action (e.g. repair, replacement, etc.) and provides a suggested action. This tool provides guidance for master planning at Department of Transportations to understand which structures are vulnerable and how to allocate funding for project planning.To address the lack of risk prioritization and blast loading assessment, this research uses the National Bridge Inventory database, which is publicly available from the FHWA and vulnerability manuals available on the New York State Department of Transportation (NYSDOT) website to perform a hydraulic and seismic risk assessment per the NYSDOT Hydraulic Vulnerability Manual and the NYSDOT Seismic Vulnerability Manual. The research then proposes a blast risk assessment protocol to get a vulnerability risk group. The model is validated against the NYSDOT database with abstracted data. Finally, the research takes these classifications and prioritizes funding based on best value for investment cost and risk mitigation. Two TOPSIS models were developed for comparison. The first TOPSIS model, Current Model, included BIN and associated ratings, one to six, that came out of the model developed in Chapter 3 for seismic and hydraulic vulnerabilities only in accordance with the procedure and equations developed by Hwang and Yoon (1981). The second TOPSIS model, Blast Model, was identical to the first model with the exception of including the associated ratings, one to six, that came out of the model developed in Chapter 3 for blast loading. Using a TOPSIS MCDA decision model that includes blast loading will yield at least 10% cost savings compared to the current model (without blast loading), was tested using the total project costs reported, NBI Database Item 96, between the two TOPSIS and was rejected in favor of the alternate hypothesis there was not a ten percent cost saving. The cross-correlation coefficient was used to determine that the order of the two datasets was not correlated. Mood’s median test showed that the there was a difference between the two project costs. The one sample sign test was used to test if the ratio of total cost in the bridge model to the total cost in current model for bridge’s was 0.9 representing a 10 percent cost savings. The cost to mitigate the risk of an explosion to an existing bridge is less than lost revenue associated with a bridge collapse, was tested using the total bridge cost reported, NBI Database Item 94, against toll revenue generated for each bridge was not rejected.. Only toll bridges as defined by NBI Database Item 20 were used. Toll revenue is the minimum economic impact associated with a bridge closure. The non-parametric sign test was used to determine the median of ratio of toll revenue to the bridge project costs was not equal to zero. To test if the lost toll revenue was greater than the bridge project cost, the non-parametric sign confidence interval was used to determine the lost toll revenue was greater than the bridge project cost.
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