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Upgradeable Bridge

A bridge that cen be easily upgraded when it no longer is sufficient to handle traffic.
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Any of you that live in big cities no that bridges often go through extremely costly upgrades. It is often cheaper and less disruptive than building a new bridge, which is why they upgrade them. It is also often rather half-assed, and no nearly sufficient. As well, there are often safety concerns on the new bridge. Yes it is "safe" enough by some study, but it certainly isn't as safe as the original after they cram another lane in.

Now, in a perfect world, the bridges would just be built good enough in the first place. However, often what is needed isn't the only factor in what gets built. Other concerns, such as cost, public image, politics, etc. all come into play. Even though they know a bridge will only be sufficient for 25 years, it is hard to convince people that they should pay for something that they will never utilize when the hospitals need money too.

So in comes the "upgradeable bridge." Say they are looking at a 4-lane bridge. If they buy the upgradeable version, then it is more expensive than a regular 4-lane, by some percentage, however not too much, say 10-20%. The major load bearing pieces (supports, cables, etc.) are engineered to be able to hold much more than the 4 lane bridge.

The public sees this as a bridge that solves/helps there current traffic problems, and isn't unreasonably expensive.

Go down 25 years down the road, and traffic is again a problem. So at that point, you upgrade the bridge to the 6-lane version. You have to do very little alterations to what is already there, maybe change an on-ramp a little or move a divider. New support for the extra lanes attach in predetermined places to the original supports, and things go in, fitting properly and safely. The cost here may be something like 110-120% of the original difference between a 4 and 6 lane bridge.

So when it is all said and done, the city has bought a 6 lane bridge for ~130% of a standard ones cost. However, they have done it in distinct stages spending money at different times, appeasing the public. This results in less "one-time" money needed. The public is happy because they don't see a giant bridge that is not being used. When the upgrade is made, safety is not compromised because the original plan calls for the extra lanes.

Depending on the bridge, the extra lanes could be a second level, or on the outside of the current lanes. As well even if the city never upgrades the bridge, the company making still makes money on the original. This isn't something that little one horse towns use, it would be something for major cities where it is extremely unlikely that growth is going to stop, so there is definite appeal to knowing that a bridge can be upgraded in the future.

PK, May 16 2002

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       "Go down 25 years down the road..."   

       No thanks. But I'll vote for your idea if you tell me how it can be applied to tunnels.
phoenix, May 17 2002
  

       Here in UK, our bridges are currently being upgraded because of a Euro-Regulation that allows trucks to have a max weight of 44 tonnes (up from 38 tonnes, I think). The original bridge design was OK at the time, but who could have foreseen the future requirement? Should they now be modified to withstand 178 tonnes, in case someone decides to increase maximum vehicle weight again?
angel, May 17 2002
  

       I am not talking about heavier vehicles. I am not expecting people to forsee the vehicle size rules of the future. I am talking about traffic in major cities. Growth in such cities, as well as traffic growth, is very predictable.   

       This isn't something that can be applied to existing bridges, or tunnels as the major factor of tunnels is not the wieght it holds, but the hole you need to dig.   

       This would be ideal for a growing city of say 1-5 million. Continued growth is almost certain, and that is where this comes into play.
PK, May 17 2002
  

       Depending upon the technology used to build the original bridge, major overhauls may be needed every 25 years or so anyway. Unfortunately, many of the cheaper techniques used to build bridges (reinforced concrete) are not very repairable nor even really inspectable. On the other hand, if something that will last 25 years can be had for half the cost of something that could last forever, it will in many cases be a better bargain.
supercat, May 17 2002
  

       Maybe it could be made from lego also?
bbglas007, Nov 10 2009
  
      
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