General
Steel is used extensively in construction and repair of waterfront facilities due to availability, cost, ease of fabrication, physical and mechanical properties, and the design experience with its use. Structural steel and cast or fabricated steel are used in all areas of the waterfront. Typical applications requiring maintenance include:
- Piers, wharves, bulkheads, and quaywalls using steel H-piles or pipe piles to support or brace the structure; steel sheet piling used to retain fill; structural steel shapes used for framing.
- Fender systems incorporating steel H-piles.
- Mooring hardware such as cleats, bollards, bitts, and chocks made from cast or fabricated steel.
- Mooring hardware such as cleats, bollards, bitts, and chocks made from cast or fabricated steel.
- Steel components of camels.
Corrosion is the major cause of deterioration of steel structures and components. The extent or severity of corrosion will vary with the exposure zone of the material; that is, whether it is in the atmospheric zone, the splash or tidal zone, or the submerged zone. Selection of the repair technique must consider each of these varied conditions and such other elements as:
- Facility mission and required life.
- Extent of damage and deterioration.
- Estimated life expectancy with repairs and without repairs.
- Projected load capacities.
- Problems associated with mobilization of equipment, personnel, and materials to accomplish repairs/maintenance.
- Tides and currents
- Economics and trade-offs.
Maintenance and repair of steel structures and components fall into five general categories: coating and wrapping, cathodic protection, concrete encasement, partial replacement, and complete replacement.
PLANNING THE REPAIRS.
Repairing steel structures are often controlled by the availability of skilled personnel and equipment. In many cases, structural repairs, particularly of bearing piles and sheet piling, will be done by contract.
The initial planning step for establishing the repair approach must involve review of prior inspection reports to determine the scope of damage or deterioration, the rate of deterioration, and specific operational constraints placed upon the facilities because of the deterioration. Once the scope of repair requirements, including priorities, is established, how the work will be done, whether in-house or by contract, must be determined.
Special Skill Requirements.
Repairing the pier decking and curbs, pile caps, fender system, and deck hardware involves having skills common to
in-house shop forces. Underwater repairs require special skill levels that may not be available with in-house forces. These include general diving capability plus knowledge of:
- removing marine growth
- jetting or air lifting procedures
- underwater cutting, welding and drilling techniques
- underwater lifting procedures
- application techniques for underwater protection coatings
- wrapping materials used in underwater construction
Equipment Requirements.
Repairing pier decking and curbs, pile caps, fender system and deck hardware requires equipment common to in-house shop forces. Equipment for bearing or sheet piling repairs, however, may include:
- high-pressure water blaster
- hydraulic grinders with barnacle buster attachment
- hydraulic drill with bits
- hydraulic power unit
- oxygen arc cutting and oxy-acetylene torch equipment
- protective clothing and gloves for personnel handling epoxy coatings for steel
- concrete pump with hose
- jetting pump and hose
- rigging equipment
- float stage and scaffolding
- cofferdams
- clamping template for cutting piles
- special clamping equipment
- crane
REPAIR PROCEDURES.
Selecting a technique must address both immediate repairs necessary to restore the structure to full (or other designated) usage and protective measures needed to prevent further corrosion. Selecting a means for restoring the structural capacity of the facility may be straightforward, being generally controlled by the level and rate of deterioration. Decisions on the level of protection needed to inhibit future corrosion may be more difficult. Generally, these decisions are economically driven.
Each repair decision must carefully weigh the long-term operational requirements and existing environmental factors (tides and currents) that can help accelerate corrosion before evaluating initial and life cycle costs. In many cases, combining cathodic protection and protective coating in the repair decision may be the most cost effective in the long term.
Damaged steel hardware such as cleats and bollards in general should be replaced in kind. Care should be taken that the engineer determine the cause of failure and that the replacement item conforms to current engineered specifications.
