Section 4 Extension of Use and Reuse

401. Extension of Use

1. Application

This section pertains to the classification or continuance of classification of an existing structure for extension of service beyond the design life. However, if the structure is currently classed with the Society, the requirements are to be in accordance with 304. 4.

2. Extension of use

(1) The approach for the classification of an existing structure for extended service is as follows :

(A) Review original design documentation, plans, structural modification records and Survey Reports.

(B) Survey structure to establish condition of structure.

(C) Review the result of the structural analysis utilizing results of survey, original plans, special- ist geotechnical and oceanographic reports and proposed modifications which affect the dead, live, environmental and earthquake loads, if applicable, on the structures.

(D) Resurvey structure utilizing results from structural analysis. Make any alterations necessary for extending the service of the structure.

(E) Review a program of continuing surveys to as-sure the continued adequacy of the structure.

(2) Items (A) and (B) are to assess, the structure to determine the possibility of continued use. If the conclusion is favorable from this assessment, structural analyses should be carried out.

(3) The in-place analysis is to follow 5 and is to be in accordance with Ch 4, 504.

(4) The fatigue life can be calculated by means of analysis as described in Ch 4, Sec 5, 506. 2

or Sec 6, 603. 4 and the remaining fatigue lives of all the structural members and joints are

not to be less than twice the extended service life. The fatigue analysis may not be needed pro- vided all of the following conditions are satisfied.

(A) The original fatigue analysis indicates that the fatigue lives of all joints are sufficient to

cover the extension of use.

(B) The fatigue environmental data used in the original fatigue analysis remain valid or deemed to be more conservative.

(C) Cracks are not found during the condition survey or damaged joints and members are being repaired.

(D) Marine growth and corrosion is found to be within the allowable design limits.

(5)

Surveys on a periodic basis based on Sec 3 should be undertaken to ascertain the satisfactory condition of the structure.

3. Review of structure design documents

(1) Structure design information is to be collected to allow an engineering assessment of a struc- ture's overall structural integrity.

(2) The operator should ensure that any assumptions made are reasonable and information gathered

is both accurate and representative of actual conditions at the time of the assessment. If the in-

formation can not be provided, actual measurements or testings should be lish a reasonable and conservative assumption.

4. Survey of structures

(1) Surveying an existing structure witnessed and monitored by a Surveyor termine a base condition upon which justification of continued service can

carried out to estab-

is necessary to de- be made. Reports of

previous surveys and maintenance will be reviewed, and a complete underwater inspection re- quired to an accurate assessment of the structure's condition is obtained.

(2) The corrosion protection system is to be re-evaluated to ensure that existing anodes are capable

of serving the extended design life of the structure. If found necessary by the re-evaluation, re- placement of the existing anodes or additional new anodes may have to be carried out. If the increase in hydrodynamic loads due to the addition of new anodes is significant, this additional load should be taken into account in the structural analysis.

(3) The condition of protective coatings in the splash zone shall be rectified and p1aced in sat- isfactory condition.

(4) The requirements for survey are to be in accordance with 304. 4.

Ch2 Classification and Surveys Ch 2

5. Structural analyses

(1) The structural analyses of an existing structure must incorporate the results of the structure survey. Specifically, deck loads, wastage, marine growth, scour, and any structure modifications and damages must be incorporated into the analysis model.

(2) The original fabrication materials and fit-up details must be established.

(3) The pile driving records should be made available so that the foundation can be accurately modelled.

(4) For areas where the design is controlled by earthquake or ice conditions, the analyses for such

conditions should also be carried out.

(5) Possible alterations of structures to allow continued use are developed by altering the analysis model to evaluate the effect of the alterations.

(6) An analysis based on an ultimate strength method is also acceptable if the method and safety factors used are proven to be appropriate.

(7) Members and joints indicated overstressed or low in fatigue life may be improved by reducing

deck load and removing unused structures such as conductors, conductor guides framing, and boat land-ing. The results of these load reduction on the structure should be evaluated to de- termine whether the repairs/alterations is needed.

6. Repairs and reinspection

(1) A second survey may be necessary to inspect areas where the analysis results indicate as being the more highly stressed regions of the structure.

(2) Members and joints found overstressed should be strengthened. Joints with low fatigue lives

may be improved either by strengthening or grinding the welds. If grinding is used, the details of the grinding are to be submitted to the Society for review and approval.

(3) Interval of future Periodical Surveys should be determined based on the remaining fatigue lives

of these joints.

402. Reuse

1. General

(1) The classification of a structure to be reused requires special considerations with respect to the review, surveys, structural analyses, and the removal and reinstallation operation.

(2) The requirements described in 401. whenever applicable and survey requirements given in 304.

5. for structure reuse.

(3) Since the structure is to be reused at a new site, the environmental and geotechnical data used in the analysis should be in accordance with those for the new site.

(4) The structure reuse involves the structure removal and reinstallation process which requires spe- cial plans in order to achieve its intended services.

2. Removal and reinstallation operation

(1) The structure removal procedure shall be well planned and analyzed to verify that the integrity of the structure has not been compromised.

(1) Structure removal plans, procedures, sea-fastening drawings, transportation, together with the analysis calculations should be submitted to the Society for review.

(3) In general, Ch 4, Sec 9 should be followed for the reinstallation of used structures.

Ch3 Materials and Welding Ch 3