Why is it Needed
Most aqueducts have streams to cross or small ravines to avoid. At some point, there may be a good reason to elevate the tubes. All the bridge designs covered in this website are a variation on the same theme – tubes are attached to a suspended, taught cable that is anchored to something. In places where you can anchor to existing boulders or trees, this is preferable to creating posts and anchors because it means less concrete, which can sometimes present logistical issues in remote sites.
Most aqueducts have streams to cross or small ravines to avoid. At some point, there may be a good reason to elevate the tubes. All the bridge designs covered in this website are a variation on the same theme – tubes are attached to a suspended, taught cable that is anchored to something. In places where you can anchor to existing boulders or trees, this is preferable to creating posts and anchors because it means less concrete, which can sometimes present logistical issues in remote sites.
Design
The construction section focuses mostly on bridge crossings using trees and making anchored posts. If you have access to a hammer drill and there is an existing rock that can be used, this is an easy option. However, this is usually a rare occurrence.
The construction section focuses mostly on bridge crossings using trees and making anchored posts. If you have access to a hammer drill and there is an existing rock that can be used, this is an easy option. However, this is usually a rare occurrence.
Design resources are hard to find for this type of application. If you are a Peace Corps volunteer, consult your APCD as he/she may have some available software (excel spreadsheet) or reference documentation.
In general, these crossings do not experience high loads (no one is walking on them), so the important part is that the posts/anchors are properly sized given the type of soil. For a softer soil prone to flooding, the post should be embedded in concrete at least three feet and the anchor should have a volume of about 1.5 ft3. For rockier, more stable soil, the post and anchor can be downsized. Review the final design with an engineer if available.
If you are using rocks or large trees as anchors, the cable alone should be sufficient for bridge crossings up to 60 feet.
The handbook for gravity flow discusses bridge crossings and shows a few design examples. Though I haven't used them, Agua Para La Vida has a few resources on designing bridge crossings including a user guide and spreadsheet (Spanish).
No comments:
Post a Comment