THE BRIDGE IN THE ENVIRONMENT - Bridges

Civil Engineering Reference

In-Depth Information

Even more importantly, bridge durability matters. In dry climates, both

steel and concrete are very durable. In damper climates, concrete is far more

durable than steel, especially if the concrete is properly maintained (as to

keep out penetration by chlorine). In principle, a deck-arch bridge made

of concrete and well maintained can last a thousand years, as compared to

the typical 75 to 100 years for a standard bridge.

CONCLUSION: THE THOUSAND-YEAR BRIDGE

The value of the EIS method is that it catalogs a project's harmful envi-

ronmental impacts, allows agencies and stakeholders to compare them, and

provides options for mitigation of impacts. It provides penalties for a harm-

ful bridge; it does not usually provide incentives for positively contributing

to the health of the environment. Broadly defined, a sustainable bridge is

one that both minimizes bad effects and contributes to good effects on the

environment.

It has good effects in part through the positioning and role of the

physical bridge in the community. Say that the proposed bridge at Great

Lake City makes attractive residential land available near downtown. If

people then settle there, and are there more likely to walk to stores and

downtown jobs and make use of newly connected outdoor areas for recre-

ation, instead of settling in suburbs and having to drive to work, the bridge

has succeeded in compacting activity and reducing sprawl.

Even more, a bridge has good effects on environmental health if it is

a net avoider of the embodiment of nonrenewable resources. Odd as that

may seem, that is just what a very durable bridge is. Take as an illustration a

concrete deck-arch bridge (the deck rests on top of the arch) that has been

shown, from EIS studies, to have little by way of harmful environmental

impact. The concrete material in the bridge is not a glutton for embod-

ied energy. Most interestingly, like the Roman arch bridges and aqueducts

of old, it can last a thousand years. Over the millennium, it helps avoid

the embodied energy from nine replacement bridges with conventional life

spans. Though it is oversimplified to say so, there is a legitimate sense in

which the bridge makes the environment healthier by saving the energy

value of nine bridges. That is the greenest possible bridge.