Design Requirements for Culvert Joints

<div><span><font size="3">Traditional methods for the structural design of buried culverts ignore culvert distress emanating from longitudinal, shear, and gasket circumferential stresses at the joint. Typically, it is presumed that alignment and bedding stiffness is uniform in the longitudinal direction of the pipe and the gasket insertion pressures minimal. Accordingly, the structural design of the culvert joint is based on the assumption of in-plane loading of the pipe's cross section, that is, in-plane bending (ovaling, yielding, and cracking) and in-plane thrust (crushing and buckling). Longitudinal bending moments and shear resulting from nonuniform loading and/or variations in the bedding support along the length of the pipe or internal ring tension forces from gaskets are not traditionally considered in the design process. </font></span><span><font size="3">Contrary to traditional design practice, field observations reveal that longitudinal effects may be responsible for a large number of costly culvert failures. One very prevalent failure mode is initiated by longitudinal variations in bedding stiffness resulting in differential settlement of the pipe, which in turn generates longitudinal culvert stresses and relative joint movements. In the recent NCHRP Project 4-24 for HDPE plastic pipe, pipe cracking from the joint integrity of buried drainage pipe was observed to be extremely sensitive to differential settlement. The supposition is that nonuniform bedding stiffness included joint distress, allowing leakage of groundwater and soil into the culvert, thereby losing vast amounts of soil support, and ultimately, collapse of pipe and destruction of pavement. In like fashion, if a joint is cracked, sheared or over-deflected and opened due to circumferential tension forces from a gasket, the resulting leakage has the same effect. </font></span><span><font size="3">Another well-known longitudinal problem occurs whenever culverts (concrete, corrugated metal, or plastic) are joined into manholes or headwalls. Here the discontinuity of soil support to the stiffer manhole/headwall support is even further aggravated by the softer than normal soil support due to deeper excavations and poor compaction in the vicinity of the manhole/headwall. </font></span><span><font size="3">More installations are becoming gasketed in order to prevent infiltration of backfill into the culvert. Insertion force from the compression of a rubber gasket during the connection of two pipe exerts tensile forces on the bell and spigot end of the mating pipe. If the pipe is not structurally adequate to resist these forces, either the bell or spigot will deform, crack, or shear. The consequential opening to the backfill will permit further undermining of the culvert and embankment. Conversely, a reduction of confining stress over time in joints due to the nature of the visco-elastic materials utilized for joints also must be assessed with respect to the type of gasket and pipe employed. </font></span><span><font size="3">It has long been argued that longitudinal distress resulting from less than perfect bedding alignment and stiffness is a problem that should be cured by placing tighter controls on the construction/installation methods. Although it is correct that the engineering community should strive to enforce proper construction procedures, reality and long experience has shown that construction always will be less than perfect. Thus, in order to avoid costly repairs, it is prudent to incorporate in the culvert design process some design requirements to account for longitudinal distress resulting from less than perfect construction practices. </font></span><span><font size="3">The objective of this research is to develop joint design requirements for culvert joints to withstand reasonable variations in bedding stiffness and other nonuniform effects that are anticipated form actual construction and installation practice. All culvert materials are included in this objective, e.g. corrugated metal, reinforced concrete, and plastic pipe. </font></span><span><font size="3">Steps to achieve the objective include: Survey literature and existing culvert installations to quantify all mechanisms and practices that promote longitudinal, joint, and shear distress at culvert joints; establish design criteria for each failure mechanism, pipe type, and associated joint type, including material time effects. These design criteria are to be based, in part, on the development of anticipated loading conditions from research field and laboratory testing; develop a general design model applicable to all pipe types and joints (such as beam segments with specialized joints on yielding foundation). A sensitivity analysis to incorporate variations in material properties, stiffness, rotational movement, and insertion forces will be included as part of this task; incorporate a three-dimensional model as an optional tool in a primary culvert design program such as ANSYS; develop simplified design procedures and evaluation methods, which may be referenced by ASTM or AASHTO specifications. These procedures and methods would define such properties as joint shear strength, pull tests, maximum insertion force, beam strength, and other related items identified under the design criteria development component of this research project. </font></span><span><font size="3">It is urgent and imperative that, as pragmatic engineers, we recognized construction practices or as-built conditions invariably deviate from the ideal design world. For example, variations in bedding stiffness are a fact of life that cannot be swept under the rug with the notion it is a problem for the contractor, not the designer. Culverts will continue to fail until we incorporate concerns at joint into our design specifications. </font></span></div>

Language

  • English

Project

  • Status: Proposed
  • Funding: $370000.00
  • Contract Numbers:

    Project 15-38

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Beal, David

  • Start Date: 20090301
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 18037

Subject/Index Terms

Filing Info

  • Accession Number: 01464469
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 15-38
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:43PM