Hearted Youtube comments on IT'S HISTORY (@ITSHISTORY) channel.
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My wife and I enjoy all your videos. You do a great job with basic history overviews of many subjects. Prior to putting this video together, however, it would have been wise to check with some of the engineers at the Chicago DPW and/or with consulting engineer firms such as HNTB Corporation, Parsons Brinkerhoff, CTE, etc., who provide condition inspections and designs for rehabilitation of these old bridges when needed, as you missed an important point -- one that is easily missed by not doing so. There are major differences between a Chicago Type Trunnion Bascule Bridge, which pivots around large diameter trunnion shafts located at fixed points on each shore (truly similar to a seesaw), and a Scherzer Rolling Lift Type Bascule Bridge which actually rolls back away from the river on large tracks and treads as it lifts (hence the name, rolling lift). They are not the same. The rolling lift bridge provides more clearance for navigation than the trunnion bascule bridge type can, and the rolling lift type remains a viable movable bridge design today, as do various types of trunnion bascule bridges. However, the early Scherzer rolling lift bridges had serious structural issues that were not overcome for a couple decades. This led the City of Chicago to develop the Chicago Type Trunnion Bascule, with assistance from Ralph Modjeski and others, in the first decade of the 1900s, and they established it as their standard. All Chicago bascule bridges designed and built for the Chicago DPW over the past 120 years or so have therefore been Chicago Type Trunnion Bascules, not Scherzer Rolling Lift bascules.
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