From: The Living Islands Project THE LANCE MITAN SUSPENSION BRIDGE Trinidad

Replacing The Lance Mitan Suspension Bridge

   For 99 years the Lance Mitan suspension bridge provided both an elegant and decorous solution to crossing a significantly wide river. Its main drawback, as with any suspension type bridge, is the requirement of ‘preventative maintenance’ needed to keep the bridge in good order. Any replacement bridge will have the same factors that existed 100 years ago, to be considered in the equation of cost, before any decision to rebuild it can be made.

   Provided that the necessity for a bridge can be sanctioned in the first place; the ‘cost balances’ should begin to drive the next part of the decision making process. The fact that the river is ‘significantly wide’ translates to a ‘significant cost’ factor and also presses the suitability of a Bailey type bridge; as some may have prematurely suggested. To arrive at an acceptable ‘balance’, requires not only some engineering input to derive what type of bridge is best suited for the ‘job’, but also a dimension of ‘creativity’; to determine if there is an exciting and challenging opportunity here to make a ‘structural statement’, something that we could be proud of, something that could also become ‘a tourist attraction’ for example.

   In this light, a suspension type bridge may still be an attractive and elegant solution to this problem; further reasons follow.

What may be Reusable

   What should be noted about a suspension bridge, and a significant factor in its initial cost, is in fact that part of the bridge that is usually not noticed at all. These are the foundations that support the ‘upright’ structures over which the cables are strung; and as importantly, the ‘anchor’ foundations to which the ‘ends’ of the cables are attached to the ground. The ‘anchor’ foundations, set behind the ‘uprights’ on the bank, prevent the bridge from folding over and falling into whatever it is trying to cross. The ‘anchor’ takes up the forces that suspend the weight of the bridge, together with the mass of whatever is crossing the bridge.
   All of this is in fact already in place and reusable.

   The reusability of the riveted wrought-iron ‘upright’ structures, that remain of the Lance Mitan bridge, will require considered investigation of their present structural integrity.
   Should they prove sound; they still pose a vexing problem with their closed-box structure. They are initially difficult to clean up. Provided that a reasonable job could be made of this; an electrostatic paint process would then allow cover of all hidden recesses.
   Should they prove useless; a couple of opposing ‘reversed-C’ or ‘I’ beams per column, with suitable engineering attention to ‘crown’ and ‘footer’ loading design, would provide adequate support for a bridge of this size; together with the added advantage of an open structure for easy maintenance.

The reusability of the very clever dual solid ‘anchor’ rods, in their present condition, is also questionable; but the elegance of their utility should be kept in any new design.    This is aptly illustrated here; where the main suspension cable interface to the ‘anchor’ rods is shown.

Crossing more than just a significantly wide river

   Although there are technical areas about the remains of the Lance Mitan suspension bridge that have not been addressed in these discussions, these are details that can be considered later by others more qualified; but should not detract from the issues here. With a policy of ‘design for maintainability, suitability and asperity’, the Lance Mitan suspension bridge can and should be replaced by a similar structure.
   This is not beyond our ability nor is it unreasonable economics. It returns the same exciting and challenging elegant and decorous solution; to crossing more than just a significantly wide river.

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Images: Digital CASIO QV-100 © 1998: tobagojo@trinidad.net

The Living Islands Project © 1998: tobagojo@gmail.com - 980308 Last Update: 30 April 1998 00:00:00 Processed by: Jeremy G de Barry

 

	http://www.seetobago.org/trinidad/sbridge/lmsb4.htm	© 1997: tobagojo@gmail.com - 19980308 - 1m20071228 - 2m20140615 Historic Update: 30 April 1998; Last Update: 20 June 2014 01:30:00 TT Processed by: Jeremy G de Barry
An historic web page for this site; one of the first set by The Living Islands Projects. The page is left mostly in its origional presentation format, apart from an external update to its active eMail link; and internal coding and 'METAS' that update its compatability, list its content and records its dating history. This footer is added for update compatibility.