Standards > Monitoring

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1.0 Iintroduction

This article outlines the criteria that must be considered for the systematic planning and implementation of a monitoring program. The extensive bibliography serves as a source of detailed information on specific methods, experimental techniques and equipment referenced within this article.

1.1 Definition

Monitoring is the task of collecting and recording data in a systematic and repetitive manner for the purpose of correlating and comparing the physical performance and condition of the quantity being examined to related quantities. Unlike inspection, monitoring has an identified objective and is clearly defined in terms of what is to be measured, when and how this is to be accomplished for how long and who is responsible for the execution of the program and for interpreting and using the results.

Monitoring is one on-site method of assessing changing structural, material, geotechnical and environmental conditions which affect the conservation and maintenance of historic structures and sites. The results obtained contribute to the evaluation of restoration and maintenance techniques and the assessment of problems and suspected changes of condition.

Regular and repetitive maintenance functions such as seasonal inspections are not considered monitoring programs (see Section .2.3 “Maintenance Procedures: Periodic Works”). However, the need to establish a monitoring program could be identified during regular cyclic inspections.

1.2 Scope

Monitoring may be an independent maintenance or project activity, form part of a wider investigation and analysis pro-gram or be incorporated into the regular maintenance activities of the site. Correspondingly, it can be contracted out to a consultant or carried out entirely by the area superintendent and staff; the arrangement depends on the scope and complexity of the work to be accomplished and the skills and availability of the required resources.

2.0 Establishing a Monitoring Program

2.1 Objectives

For those directly involved in projects related to site development a monitoring program could be identified to:

  1. assess the possible presence and causes of deterioration and instability;
  2. understand situational behaviour of structural form and material characteristics; and
  3. assess the effect of changes to the original loading, member configuration or environment and the use of new technology on the performance behaviour of the structure. These post-development assessment requirements would generally be identified by the design team in the maintenance manual developed for the site.

For those concerned with the continuing on-site maintenance and operation of the site, such a program could provide:

  1. assessment of deterioration and instability problems identified during the routine maintenance work; and
  2. assessment of the effects of conservation and maintenance procedures on the overall performance and appearance.

2.2 Implementation

The routine for implementation varies with the scope of work. In general, project managers and area superintendents can best recognize the need to initiate these types of programs. The reports, recommendations and requests they receive from their staff will form the basis for judging the program’s importance, scope and objectives.

3.0 Planning A Monitoring Program

3.1 General Considerations

A monitoring operation is a chain of potential weak links. The need for reliable techniques is only one consideration. Careful planning is essential and should encompass such aspects as definition of objectives and quantities to be measured and decisions on the type, number, location and frequency of measurements and on the organization of personnel, equipment, measurements and reporting procedures. Only if each of these aspects is considered in detail before the start of the project will there be any certainty of accomplishing the objectives.

3.2 Terms of Reference

Regardless of the program complexity and whether or not the work is to be done by site personnel, regional staff or outside consultants, the following steps should be taken:

  1. Define clearly the monitoring objectives, including relationships to other project work and the anticipated use of results. This provides a guide for the appropriate level of resource expenditure and requirements for precision.
  2. Define “normal” and “acceptable” behaviour and assess anticipated behavior.
  3. If safety considerations exist, establish emergency contingency plans (see Section 3 “Emergency Works”).
  4. Determine which behavioural or material properties and characteristics are to be examined in order to achieve objectives. This requires isolating prime phenomena and identifying all factors which would influence results and which might require simultaneous measurement and establishing viable range and precision requirements.
  5. Identify locations to be examined and, if required, establish a priority list of critical areas to be monitored. Often it is sufficient to provide an extensive area of low precision and low frequency of measurement, with a provision for more accurate, concentrated and frequent monitoring whenever the results indicate a change.
  6. Estimate the duration of the project and frequency of measurements. Although a minimum number of readings should be predetermined, it is important to be able to match reading frequency to progress rather than to time elapsed.
  7. Ensure that personnel with appropriate levels of experience and familiarity with the method and equipment employed are directly responsible for interpreting results and making recommendations.

3.3 Monitoring Program Considerations

3.3.1 Personnel

Depending on the requirements of the program, maintenance staff, professional and technical personnel or consultants might form an on-site monitoring team. One individual representing the team should co-ordinate the monitoring. Establishing liaison channels in advance ensures continuity and communication gathering, between those requiring the information and those performing the work. Unless specifically indicated in the terms of reference, the team is usually responsible for the readings but not for interpretation or action that may be required by the results. This aspect of the work is not considered part of the monitoring, which is essentially a data-gathering exercise.

3.3.2 Equipment and Methods of Measurement

  1. For each parameter to be measured, there are usually several methods and types of equipment that might be suitable. All have advantages and limitations. The following factors will influence the final selection:
  2. Reliability The success of the program relies on the repeatability of the measurements. In general, selection of methods and equipment which are more sophisticated than necessary should be avoided. For every instrument selected there should be calibration methods and equipment to ensure that the instrument continues to function correctly through-out the duration of the project. Calibration helps ensure that the interpretation of the data is appropriate for the material and conditions being examined. This can be obtained from a variety of sources, including available calibration charts from equipment manufacturers, established procedures and technical literature and experimenting with the instrument to evaluate its performance relative to a known set of conditions.
  3. Precision Requirements for precision usually reflect the objectives of the program. The more stringent the requirement, the more sophisticated, costly and time-consuming the monitoring project becomes. If, for example, a comparative visual observation will provide the information necessary to arrive at a decision, then more sophisticated methods of recording the data are redundant. A clear understanding of the precision requirements is necessary to satisfy program objectives.
  4. Ease of use
  5. Cost
  6. Durability
  7. Ease of repeatability of technique or method on-site
  8. Personnel requirements. This applies to the expertise required to use the equipment and to record and interpret the results.

3.3.3 Measurement Plans

General guidelines for personnel, time requirements and frequency of each measurement should be established at the initial stage. It is advisable to assess the data on an ongoing basis in order to adjust the frequency of readings and to evaluate the validity of the recorded results. One should always establish routines for calibration checks of the equipment.

3.3.4 Processing Results

It is here that errors, delays and ambiguities can often occur. To avoid these;

  1. process data as it becomes available. This provides a constant picture of the changing nature of the problem;
  2. allocate responsibilities for calculation and plotting before the project starts: and
  3. prepare results carefully, thereby assisting in interpretation of the behaviour under examination.

3.3.5 Reporting

Monitoring results forms a basis for action or for informed inaction. The report itself should establish a reference for the interpretation of the results (if not included as part of the terms of reference for the program) and include details on the equipment used, numbering systems employed, instrumentation performance, tests, calibration methods, data processing techniques and pertinent comments and observations which may have a bearing on the interpretation.

4.0 Monitoring Techniques

(See Vol. 111.10 “Special Investigation and Analysis” and the bibliography attached to this publication.)

Unlike dimension and weight, many parameters cannot be measured directly without altering or destroying the material or structural form. Fortunately, methods have been developed which provide an indirect means of assessment. These depend on the interrelationship among certain physical and mechanical properties of the materials of configuration being examined such as hardness, resistance to penetration and ability to transmit ultrasonic pulses and X-rays.

Once a specific program objective is determined, there is often more than one method of gathering the required data. The selection of the most appropriate technique should be based on the criteria outlined in 3.3.2 above.

The Appendix groups some of the commonly used methods according to the quantity to be measured. The lists are not meant to be exclusive, but to illustrate potential solutions. Details of each technique are not provided, although the general comments are extended to provide guidance.

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