So a few weeks ago a colleague of mine pointed out a flaw in my bridge theory. Bridges require almost constant maintenance. Salt water is especially hazardous. Cracked or worn paint can expose the steel below to corrosion. Cracks in re-bar reinforced concrete are paths for salt water to rust and corrode the supporting steel re-bar beneath. The Golden Gate bridge undergoes painting year round to prevent corrosion. A bridge near saltwater would likely suffer significant structural damage rather quickly. Freezing weather also contributes to wear and tear on bridges. As water fills cracks and voids in the structure and then freezes, it expands those voids and can gradually damage or break apart pieces of the bridge or its foundation. Obviously survivors of a zombie threat would not have time to spend painting and checking bridges for cracks and thus bridge maintenance poses a serious problem to my theory of utilizing one for a stronghold. So this raises the question, zombie attacks aside, how long would such a bridge stronghold last against the onslaught of mother nature?There are several factors to consider, namely the environment the bridge is in, its age, and the materials and design used in its construction. On a very basic level, eliminating simple environmental factors like salt and ice should help us choose which bridges would be best. A bridge inland, over a river and away from the ocean, in a temperate climate less prone to freezing weather, would likely yield a longer lasting bridge. What about age, materials used, and the design of the bridge? How can we evaluate the best bridges to use?
Fortunately the Federal Highway Administration maintains a database called the National Bridge Inventory (NBI) that contains information on all bridges and tunnels in the United States. Not only does this database detail the location, age, materials, design, and length of the bridge, it also assigns each bridge a sufficiency rating and a structural evaluation.
Sufficiency Rating:The bridge sufficiency is a method of evaluating highway bridge data by calculating four separate factors to obtain a numeric value which is indicative of bridge sufficiency to remain in service. The result of this method is a percentage in which 100 percent would represent an entirely sufficient bridge and zero percent would represent an entirely insufficient or deficient bridge.Sufficiency Rating is essentially an overall rating of a bridge’s fitness for the duty that it performs based on factors derived from over 20 NBI data fields, including fields that describe its Structural Evaluation, Functional Obsolescence, and its essentiality to the public. A low Sufficiency Rating may be due to structural defects, narrow lanes, low vertical clearance, or any of many possible issues.Structural Evaluation:Structural Evaluation is an appraisal rating that in plain English describes an overall rating of the condition of the bridge structure.This is the summary of the separately rated conditions of the structural components of the bridge. This is the truest measure in the National Bridge Inventory of the structural fitness of a bridge.
This tool would allow survivors to sort data for bridges in their immediate area and chose the most ideal bridge for a long-term stronghold… provided that they plan this out before the electrical grid goes down. The bridge stronghold may not be the ideal solution I thought it once was, but I if you chose your bridge carefully, it doesn’t have to be the rusted deathtrap my coworker makes it out to be.
Zombie DEFCON 
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