A key element in the process of selecting a choice for culverts or buried bridge type structures is the determination of appropriate shapes and sizes of structure to fit a given site application. While this might seem a fairly innocuous task, it actually brings into play a number of practical and functional issues and concerns related to the decision making process. Project engineers and site developers should carefully consider these factors early on in the planning stages of a project. I will attempt to outline a number of appropriate questions necessary to the logical thought and decision-making processes related to proper structure selection to aid in such planning. This article is the first in a series and thus is intended to be a brief overview of structure type and shape selection decisions.

 

Culverts and buried bridges come in a variety of material types, structure shapes and sizes. When it comes to material choices, such structures can be corrugated metal – steel or aluminum; they can be reinforced concrete; they can be plastic. Additionally, corrugated metal culverts and buried bridges come in various corrugation profiles depending upon the size and shape of the structure. They also are available in  a variety of coating options – galvanized steel, aluminum, aluminized steel, coated steel and aluminum, etc. Selection of the appropriate material type and coating type must factor in issues such as durability, anticipated service life, site environmental issues, corrosion factors, relative economics, etc. That aspect of structure selection is a separate topic entirely and left for another discussion.

Once a material type is chosen, the size, shape and number of structures must be determined for the given site. The possibilities at first seem a bit overwhelming – one could pick a single barrel wide span structure or a battery of much smaller structures to fit a given site’s geometric characteristics. However, if you begin by ferreting out the key functional and practical needs at your site, the process can be simplified and streamlined.

Let’s start with the functionality of the structure(s) in question.

  1. Is the structure to function as a culvert carrying stream flow and stormwater runoff?
  2. Is it intended to function as a grade separation structure carrying some fixed clearance requirement (diagram) under a roadway or railroad or similar surface transportation requirement?
  3. Are hydraulic factors the primary consideration at the site?
  4. What are the headwater and tailwater conditions and limitations for the site?
  5. Would multiple barrel, smaller size culverts work or is a wider single opening needed to pass flow and debris – or traffic (vehicular or boat perhaps)?

Next, let’s address the structural design of the structure(s).

  1. What is the total available headroom at the site - - meaning the distance measured vertically from the stream bed (or traffic surface through the structure) to the traveling surface / final grade at the ground surface above the structure?
  2. What is the live load situation at the site – what type of vehicles will be crossing above the structure(s) in question? What are the axle loads, tire / wheel type and spacings of the vehicle in question?
  3. What is the required minimum depth of cover above the chosen structure for such live loading?

Following this, identify what analysis and evaluation of the site has been conducted.

  1. Has a geotechnical study or evaluation of the site been made?
  2. What is the allowable bearing capacity of the foundation under the culvert / buried bridge?
  3. If this is a potential problem, can steps be taken to improve the foundation strength and long term stability?
  4. Lastly, identify any restrictions or environmental concerns.

Often there are strict regulations as to any disturbance of existing site conditions. Permitting issues and governing regulations controlling such site development must be considered. Right of way factors also come into play. Specific areas to focus on here include:

 

  • Are closed shape structures – i.e., those with an invert / bottom – preferred or acceptable at the site?
  • Or is an arch type structure with an open bottom and installed on footings more practical and appropriate?

These are simply a few considerations that should be identified during the selection of structure, type, shape, and size for a particular culvert or buried bridge structure. The next article will go into additional detail as to how those considerations relate to the selection of structure type, shape and size.

 

Categories: Design
Written by:

Author Biography

Jim Noll is the former Director of Engineering Services for Contech’s Drainage Solutions, Plate & Specialty Products, having recently retired. He was primarily responsible for design support in the area of corrugated metal culverts, plastic pipe culvert and sewer products, corrugated structural plate (steel and aluminum structural plate), long span metal structures, retaining wall products, and tunnel liner products serving the railroad, highway and construction markets. With 40 years of design experience, he is still actively involved in the industry as a consultant. Mr. Noll is a registered professional engineer in the state of Ohio. He maintains membership on a number of technical committees and organizations, including AREMA (where he is an active member of Committee 1, serving on both the culverts and the tunnels subcommittees), NSPE, ASCE, AISI, and ASTM. He has written articles for TRB, AREMA, NCSPA and AISI publications – as well as a number of PDH technical articles for CE News magazine. He has been a presenter at a number of industry symposiums, seminars and meetings -- including AREMA sponsored symposiums, Ohio DOT seminars, TRB Annual Meeting and Vulcan Material’s Annual Meeting -- on topics related to the design, installation and inspection of corrugated metal pipe, plastic pipe, corrugated structural plate, and metal bin type retaining walls for use in the highway, railroad, mining and aggregate handling markets. He is also a contributing author for the AISI Handbook of Steel Drainage & Highway Construction Products, the AISI Modern Sewer Design Handbook, as well as the NCSPA Corrugated Steel Pipe Design Manual. Jim can be contacted at jnoll@conteches.com.

Post Rating

Comments

# Christian R. Cooper
Thursday, June 22, 2017 4:36 PM
Mr. Noll provides a good primer for any beginning engineer to read and for an experienced engineer who has gotten into a rut. I appreciated this blog.

Post Comment

Name (required)

Email (required)

Website

CAPTCHA image
Enter the code shown above:

Text/HTML