Semisequicentennial Transportation Conference Proceedings
May 1996, Iowa State University, Ames, Iowa

Condition Assessment of Navigation Lock and Dam Structures

Lowell Greimann, James Stecker, and Kevin Rens

L. Greimann and J. Stecker,
Department of Civil and Construction Engineering,
Iowa State University,
Ames, Iowa 50011.

K. Rens, Civil Engineering,
University of Colorado at Denver,
Denver, Colorado 80217-3364.

As part of the U.S. Army Corps of Engineers Repair, Evaluation, Maintenance, and Rehabilitation (REMR) program, Iowa State University has been involved in the development of a condition assessment program for navigation lock and dam structures. For each structure a set of distresses were identified that characterize its current condition. Inspection procedures have been created to measure and describe the current state of each of the distresses. Using the information collected during the inspection, a set of rating rules yield a condition index that ranges between zero and 100. Key words: condition assessment, distresses, condition index.


The U.S. Army Corps of Engineers (US-COE) operates more than 600 hydraulic structures (lock chambers, flood control dams, power houses, etc.), many of which are nearing the end of their design life. To meet the challenge of deteriorating structures, the US-COE initiated a Repair, Evaluation, Maintenance, and Rehabilitation (REMR) research program (1), the overall objective of which is to identify and develop effective technology for maintaining and extending the service life. As part of the REMR program, an Iowa State University research team has focused on: steel sheet pile structures (2), miter and sector gates (3,4), filling and emptying valves (5), dam gates (6,7), and equipment which operates gates and valves (8). During the course of developing condition assessment procedures, the project team held meetings with Corps personnel and conducted site visits and field investigations at lock and dam facilities. Corps experts conveyed their opinions about the critical components of the operation and repair of the structures and suggested means of quantifying and relating these components to the overall condition. The project team then took the experts' comments and formulated them into an inspection procedure and a tentative set of rating rules. Field tests of the inspection form and rating rules were conducted at several locations. At each test site, experts suggested improvements to the rules and inspection process.

FIELD INSPECTION

The entire condition assessment process is based on a field inspection of the structure. Inspectors record current attributes of the structure such as the location of the structure, inspection history, historical water level, and maintenance history. In addition, they record several field measurements, such as anchorage movements, elevation changes, deflections, misalignments, cracks, dents, and corrosion.

The two basic ideas behind the inspection procedure are simplicity and adaptability. In general, the field inspection is based on data that are obtainable with minimal disturbance to lock traffic. All data are measured by a tape measure, a level, a ruler, dial gauges, cameras, and subjective observations.

CONDITION INDEX

One outcome of the inspection is a condition index (CI). The CI is primarily a planning tool which ranges from zero to 100 and is meant to focus management attention on those structures most likely to warrant immediate repair or further evaluation. To group structures, the CI is divided into three basic zones: 70 to 100 means no action is required; 40 to 69 means maintenance action may be necessary if economically feasible; and 0 to 39 means maintenance is probably required—after further investigation.

A series of distresses are identified for each structure. For example, in the sector gate module, a total of ten distresses have been identified (Table 1). Each distress is quantified by a measurement X. For example, anchorage movement in sector gates is quantified by the relative motion between the steel and the concrete at the connection to the concrete wall. The individual distress CI is quantified by:

x

CI = 100(0.4) x max [1]

where Xmax is some limiting value of X. Experts have selected Xmax to be the point at which the gate requires immediate repair or, at least, a more detailed inspection and CI evaluation.

EXAMPLE: ANCHORAGE MOVEMENT OF SECTOR GATES

Anchorage movement is a parallel and perpendicular displacement of the embedded anchorage system. Anchorage movement can be caused by several factors: corrosion of the embedded steel anchorage, concrete cracks in the anchorage region, steel elongation or movement, additional load, or movement at shims or nuts. The presence of anchorage movement may indicate a significant structural problem, or it can eventually introduce structural problems into other gate components.

For sector lock gates, anchorage movement is measured while the gates are open, closed, closed with full head, and jacked while half open. A dial gauge is placed such that the relative motion between the embedded steel and concrete interface can be measured.

Inspectors also record the presence of cracked or spalled concrete at the concrete interface and the existence of severe corrosion pitting in a dense pattern or thickness reduction in a local area. Each of these conditions reduces the CI by a factor of 0.85. For rigid anchorage systems, a limiting displacement has been selected as:

Xmax = 0.03 in. [2]

Numerical Example: Suppose that jacking was a part of the sector gate inspection. From measurements at four gate positions, a sector gate leaf has the following maximum movement.

X = 0.015 in. [3]

Inspectors observed that the anchorage steel had corrosion pitting of at least 1/8 in. (severe pitting). Thus the CI for anchorage movement is

CI = [100(0.4)0.015/0.030]0.85 = 54 [4]

where the 0.85 factor has been used because anchorage corrosion has been observed and the Xmax value of Eq. [2] has been used.

OTHER DISTRESSES

For sector gates measurements will also be recorded for the nine other distresses in Table 1. When several types of distress occur simultaneously the CIs are combined into a single value using weighting factors. Anchorage movement is the most important and dents the least important.

STRUCTURAL CONSIDERATIONS

Safety is taken into account by the experts in a subjective manner as they formulate the CI rules. For example, excessive movement of the anchorage embedment may indicate a potential safety problem. The embedded anchorage may have corroded and be approaching a failure condition. Only a more detailed inspection, perhaps requiring concrete removal or ultrasonic inspections, will reveal the true cause. The distresses in Table 1 that relate most directly to safety were identified by the experts and are listed in Table 2.

ACKNOWLEDGMENTS

This study was authorized by Headquarters, U.S. Army Corps of Engineers (HQUSACE), under Civil Works Research Units 32672 and 32673, "Development of Uniform Evaluation for Procedures/Condition Index for Civil Works Structures" and "Development of Maintenance and Repair Guidelines and Management Systems," respectively.

REFERENCES

  1. An Overview of the Repair, Evaluation, Maintenance, and Rehabilitation (REMR) Research Program 1984 - 1989. Washington D.C. 20314-1000. U. S. Army Corps of Engineers.
  2. L. Greimann and J. Stecker. Maintenance and Repair of Steel Sheet Pile Structures. Technical Report REMR-OM-9. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1990.
  3. L. Greimann, J. Stecker, and K. Rens. Management System for Miter Lock Gates. Technical Report REMR-OM-08. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1990.
  4. L. Greimann, J. Stecker, and K. Rens. Condition Rating Procedures for Sector Gates. Technical Report REMR-OM-112. U.S. Army Corps of Engineers, Washington, D. C. 20314-1000, 1992.
  5. L. Greimann, J. Stecker, and J. Veenstra. Condition Rating Procedures for Tainter and Butterfly Valves. Technical Report REMR-OM-14. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1993.
  6. L. Greimann, J. Stecker, and M. Nop. Condition Rating Procedures for Tainter Dam and Lock Gates. Technical Report REMR-OM-17. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1994.
  7. L. Greimann, J. Stecker, and T. Kraal. Condition Rating Procedures for Roller Dam Gates. Technical Report REMR-OM-118. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1996.
  8. J. Stecker, L. Greimann, S. Mellema, and K. Rens. Condition Rating Procedures for Lock and Dam Operating Equipment. Technical Report REMR-OM-119. U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, 1996.

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