Okay why the push to ABC bridges? Speed of course. The most common argument for ABC is the issue of building a bridge quickly which would minimize the impact to drivers and local businesses.
This is a very strong argument. I have worked on traditional bridges that took up to a year to build. This can have a big impact on traffic patterns but typically its the businesses that are affected the most. Taking away access to businesses or reducing entrances can really disrupt the flow of traffic to a company. Drivers often avoid congested areas which means they avoid the businesses.
The irony is that disruption to drivers and businesses are considered in design but are not readily used in benefit/cost ratios for projects. So…ABC projects often look more expensive than traditional projects because we can’t quantify the costs to drivers and local businesses.
I designed a steel bridge that took 3 years to build. It turned out pretty well but high water events and staging really slowed the project down. It would have been interesting to try and design ABC piers for this project….Keosauqua Bridge Link.
Obviously ABC would be great for rapid replacement projects, but you would probably need to have the bridge already sitting on the shelf. This means of course standardized design which saves money but stifles creativity.
Here is a link to an older ABC paper (2006) by John Fowler. ABC paper. It contains a good overview of the ABC reasoning and has PICTURES! Couple that with the fact that it is from Canada (where I grew up) and you can’t go wrong.(what no mention of hockey?)
The new I35 bridge was built fairly quickly. I guess it qualifies as an ABC bridge because it was built faster than a “normal” bridge. So that begs the question, how much faster does the construction of a bridge have to be to qualify as accelerated construction?
One of the ABC projects I worked on used precast abutments and pier caps. It was a good project but the funny thing was that we did not impose time restrictions so the bridge took almost the normal amount of time to build.
We replaced a beautiful Marsh Arch bridge with a three span precast beam bridge.
Since this a new blog and Google has not placed it in it’s search engine yet, I can pretty much talk about anything because no one is reading it anyway….
Why Accelerated Bridge Construction?
Despite all the hype it is difficult to change the direction of bridge construction to ABC. Critics of ABC will quote the higher up front costs, but this will be dealt with as standards and mass production come to ABC designs. The real problem with ABC is that typical cast-in-place techniques usually provide a better final product than ABC.
When you build a bridge the old fashioned way, and I am speaking primarily of concrete bridges, you get a bridge that increases in strength due to integral construction. Meaning, the bridge is “locked” together by the cast-in-place concrete.
Accelerated Bridge Construction will always be appealing for its speed and eventually it will have the longevity of its cast-in-place cousins. As I learned in my steel design class, its all in the connections!