Proper maintenance can extend the life of waterfront facilities, no matter what building material is selected. With proper maintenance and prompt repair when indicated, structural steel is a highly durable material.
As part of our ongoing series of guidelines from the U.S. Department of Defense’s Unified Facilities Management manuals, here is “the book” on maintaining steel in a marine environment.
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.
• Other items such as utility lines, grating, opening frames, space manhole covers, fences, bolts and nuts, handrails, and concrete reinforcement.
• 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;
• clamping template for cutting piles;
• special clamping equipment;
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.
1. PROTECTING STEEL PILES BY COATING OR JACKETING
Problem: A new steel pile has been installed or an existing pile has experienced slight deterioration (less than 15 percent) of the cross-sectional area at some point. Protection against further corrosion is required.
Description of Repairs: Clean steel above water with abrasive blasting equipment and underwater with water jet cleaning equipment.
Epoxy-Polyamide Coating: See the Paragraph entitled, “Protective Coatings for Steel” (see Figure 8-1).
Fiberglass Jacket: Place jacketing around pile and secure. Pour epoxy grout inside sleeve if grout is used. Seal the top and bottom of the pile to prevent water entering inside jacket, if mortar is placed between pile and jacket (see Figure 8- 1).
Concrete Jacket: During installation of steel pile, place a concrete pipe jacket around pile after it is driven. Fill the annular space between concrete jacket and pile with concrete (see Figure 8-1). The pile must be accessible from the top.
Application: These methods can be used to prevent further rusting. Economics will govern which method is used based on the extent of overall facility deterioration, access to pile, and availability of alternatives.
Future Inspection Requirement: Increased inspections may be required, particularly in areas where ice may be present, to detect signs of abrasion of the mastic or jacketing and renewed corrosion of the pile.
2. CATHODIC PROTECTION FOR STEEL BEARING PILES
Problem: New steel bearing piles have been installed or existing piles have experienced slight surface deterioration. Anticipated corrosion is high. Protection against further corrosion is required.
Description of Repairs: Two methods are available for providing cathodic protection for steel bearing piles:
Sacrificial Anode System: Secure sacrificial anodes below low water on steel by welding or bolting. Size, type, and spacing of anodes must be determined to suit structure and environment (see Figure 8-2). A good electrical connection between elements must be maintained.
Impressed Current System: Install the cathodic protection system as shown in Figure 8-2. Basic components include:
• Anode: Material to be consumed over a long period of time.
• Electrical potential: Power source (rectifier) to provide constant electrical potential between anode and steel pile.
• Ground between piles and power source to provide closed cell.
Application: Requires careful design and installation. System is not effective for mitigating corrosion above mean low water.
Future Inspection Requirements: The cathodic protection system must be carefully monitored and maintained. If anodes for an impressed current system are placed between bents, special inspections must be made to ensure that floating debris has not damaged or removed the individual anodes.
3. PARTIAL REPLACEMENT OF STEEL PILE
Problem: Moderate to heavy deterioration (greater than 35 percent) of the upper cross-sectional area of the H-pile has occurred.
Description of Repairs: Cut out the corroded section of pile; be sure that the bottom cut and top cut (if applicable) are square. Temporary supports may be needed to transfer the load from the pile being repaired to adjacent piles. Fabricate a welded assembly consisting of: a 1-inch (25 mm) steel bearing plate, two 2/5-inch (10 mm) steel side plates, and four steel angles. Place over the bottom cut. Drill and bolt the bearing assembly to the remaining lower steel pile using 1 ¼-inch (32 mm) galvanized steel bolts. Add cathodic protection to new the section.
Intermediate Replacement (see Figure 8-3): Cut a section of new H-pile to fit the missing length of pile and weld a 1-inch (25 mm) steel bottom bearing plate to the new section. Place the intermediate section into position and bolt the bearing plates together. Weld the upper joint and four 5/8- inch (16 mm) steel splice plates to both old upper and new H-pile sections.
Total Upper Section Replacement (see Figure 8-3): Cut a new section similar to that required for intermediate replacement, except cut to fit under the concrete cap using a 1-inch (25 mm) steel bearing plate bolted to the cap. This arrangement is necessary when the steel has corroded extensively at the concrete-steel interface. All new metal should be cleaned and coated before installation. Welded joints should be cleaned and coated after welding. All welded joints should be watertight.
Application: This method restores the structural strength lost in the deteriorated upper section. Corrosion can again occur once the coating fails. Economics will govern approach.
Future Inspection Requirement: Same as for new steel pile sections.
4. REPAIRING STEEL PILE WITH CONCRETE ENCASEMENT
Problem: Slight to moderate deterioration (less than 35 percent) of the cross- sectional area has occurred; or protection against corrosion and abrasion is required.
Description of Repairs: Clean the steel pile of all marine growth and loose rust using a high-pressure water blaster. Two methods may be used to provide the concrete encasement: flexible and rigid form. In addition, steel angles may be used with the rigid form, to regain some of the reinforcement in the steel pile where greater levels of deterioration have occurred (see Figure 8-4). After the piles have been thoroughly cleaned, place a 6- by 6-inch (150- by 150-mm) reinforcing mesh around the pile, using spacers to maintain clearance between the pile, reinforcing, and fabric form. The fabric form should be placed around the pile.
For the flexible form, the zipper should be closed, and the form secured to the pile at the top and bottom with mechanical fasteners (see Figure 8-4).
For the fiberboard form, the straps are installed and secured every 12-inch (300- mm). Maintain a 1 ½-inch (38-mm) space between the pile and reinforcing and between the reinforcing and form (see Figure 8-4).
The annular space between the pile and the form is then filled to overflowing with concrete grout using a tube or hose extending down to the lowest point of the form. The form is left in place and the base is backfilled to above the concrete.
Application: This method can be used as a repair or as a protection technique to prevent further rusting or abrasion. The method will not restore bearing capacity lost by the deterioration of the steel cross section. Partial restoration of compressive strength may be gained by the using steel angles with the concrete encasement. This is not a generally accepted practice, however, so care must be used to ensure that the connections are made to sound metal. Many times, posting the existing pile with a new H-pile section may be more cost effective. Economics would normally govern the decision.
Future Inspection Requirement: Increased inspections may be required to detect signs of potential failure of the repair.
5. COMPLETE REPLACEMENT OF STEEL PILE
Problem: Moderate to heavy deterioration (greater than 35 percent) of the cross sectional area, or damage has occurred to a steel H-pile.
Description of Repairs:
Using Existing Pile Cap. Cut an opening in the concrete deck adjacent to the damaged pile. Drive the new steel pile and cut to fit under the existing pile cap. Pull the pile laterally into place (see Figure 8-5). Shim between the pile and pile cap and secure the pile to the pile cap using 1 ¼-inch (32-mm) expansion bolts.
With New Pile Cap. Cut an opening in the concrete deck between existing pile locations. Drive the new steel pile through the hole cut in the deck and cut off below the top of the concrete deck (see Figure 8-5). Weld horizontal reinforcing bars to the top of the steel replacement pile or provide suitable reinforcing steel transitions with concrete piles, to ensure load transfer. Form the pile capital under the deck and around the new pile, and fill the form and deck space with concrete. Ensure that new and existing piles are electrically isolated otherwise accelerated corrosion may be experienced with the new piles.
Application: This method restores the structural strength lost with the deteriorated pile. The same corrosion can occur, however, with the new pile. Concrete encasement or cathodic protection can be used to extend life expectancy. Economics will govern approach.
Future Inspection Requirement: Same as for new steel or concrete pile sections.
6. COATING/CATHODIC PROTECTION OF STEEL SHEET PILE WALL
Problem: Sheet pile wall has surface deterioration. Protection against further corrosion is required.
Description of Repairs: Two procedures provide corrosion protection for steel sheet piling:
Coatings. See Figure 8-6.
Cathodic Protection: For sacrificial anode system, weld or bolt anodes below low water on the steel. Determine size, type, and spacing of anodes to suit structure and environment. A low resistance electrical connection between adjacent piling must be made (see Figure 8-6). For impressed current systems, place anodes off the face of the sheet pile wall.
Future Inspection Requirement: Increased inspection may be required, particularly in areas where ice may be present, in order to detect signs of abrasion of the mastic or removal of the anodes and renewed corrosion of the sheet piling.
7. PATCHING STEEL SHEET PILE WALL
Problem: Steel sheet pile wall has small to medium holes. General condition of sheet piling is otherwise sound with minimum signs of corrosion.
Description of Repairs: Clean around area to be patched. For larger holes using steel plate patches, clean sheet piling from 18-inch (460-mm) below holes to above mean low water.
Epoxy Patch: Weld wire mesh or bolt fabric mesh over holes and cover with epoxy-polyamide putty smeared on by hand (see Figure 8-7). Good for a limited number of small holes.
Steel Plate Patch: Determine size of patch plate needed. Cut plate to size and bend plate to fit over sheet pile interlocks. Weld plate in place at top, above low water. Cut holes for Tee bolts in sheet piling behind holes in plate; place and tighten Tee bolts (see Figure 8-7). Alternative is to weld plate all around, which is more appropriate for larger holes or several small holes.
Patch and Pressure Grouting: Where several small holes make pure patching cost expensive, a combination of patching and grouting may be a better solution. In this approach, cover the larger holes with epoxy or steel plate patches, then pressure grout the area behind the wall (see Figure 8-7).
Application: This approach will not prevent further corrosion and its success depends on the surrounding areas of sheet piling being relatively sound and free from rust. Continued deterioration of a weak structure, particularly near tiebacks, could lead to rapid failure and poor use of repair funds. Economics should govern final selection of the repair method.
Future Inspection Requirement: Increased inspection will be required at the patch areas to ensure that welds and bolted connections continue to hold.
8. REINFORCING TIE-BACK SYSTEMS FOR STEEL SHEET PILE WALL
Problem: Light to moderate movement of the top of the steel sheet pile wall has occurred due to tieback failure or excessive loading behind the wall. The area behind the wall is accessible to perform repairs.
Description of Repairs: Install a new wale slightly above the existing wale. Locate the new deadman anchors based on engineering calculations. Trench for the tie rods between the wall and the deadman anchors. Place the tie rods through the wale and sheet piles and secure in place to the deadman anchors (see Figure 8-8). Be sure that enough clearance is allowed through the sheet piles to electrically isolate the tie rods from the piling.
Install zinc or magnesium packaged anodes to prevent future corrosion of the rods.
Replacing an existing tieback system may involve the replacing any or all of the existing components, depending on the amount of deterioration that has taken place.
Sheet pile wall movement can also be arrested by changing the soil loading acting on the wall. For example, stone riprap dumped against the exterior toe of the wall will add resistance to the movement of the toe. Alternatively, or in addition, backfill can be removed from behind the wall and replaced with lightweight granular fill. This type of fill is free draining, which reduces the hydrostatic pressure behind the wall and allows the water level on both sides to balance.
Application: Reinforcing or replacing the tieback system may be restricted to correcting slight to moderate wall deflection. Excessive deflection may require wall replacement or major restoration.
Future Inspection Requirement: Carefully inspect the wall for further signs of continued deflection or steel member failure.
9. REPLACEMENT OF EXISTING STEEL SHEET PILE WALL
Problem: Serious deterioration of the steel sheet pile structure has occurred; patches cannot be used for repairs.
Description of Repairs: Two methods are available for replacing deteriorated steel sheet piling:
Timber Sheet Piling: Remove decking (if required) behind existing steel sheet pile wall to provide enough space to excavate and drive timber piling. Excavate to expose tie rods (usually these are above mean low water). Place new timber wales to act as template for driving timber sheeting. Drive timber sheeting (see Figure 8-9). Backfill may not be possible between steel sheeting and timber sheeting below wales. Replace decking (as applicable).
Steel Sheet Piling: Drive new steel sheet piling in front of existing sheet piling. Drill hole for tie rod and pipe casing through both walls into stiff clay, out of active zone behind old wall. Pressure grout inside casing forming bulb in clay at end of casing (see Figure 8-9). Fill space between old and new sheet piling with concrete. If stiff clay is not available, deadmen may need to be added to secure the tie rods. Ensure electrical isolation is maintained between the existing and new sheet piling, especially through tie rods.
Application: Either solution should stop the loss of backfill through the existing steel sheetpiling wall.
The timber sheet piling should be less expensive than the new steel sheetpiling wall. However, the timber piling will require access behind the existing wall, and continued corrosion of the existing steel sheet piling can be expected.
The new steel sheet piling can provide a new wall with equal or greater strength; and construction can be done without excavating behind the existing wall. This approach does, however, require grouted tie rods be secured in existing soil. If stiff clay or other suitable soil is not available, this method may not be appropriate unless deadmen are added.
Future Inspection Requirement: Normal inspection requirements should suffice for the new steel sheet pile wall. If the timber piling approach is used, more extensive annual inspections may be required to watch for signs of timber piling deterioration and failure behind the existing wall
10. INSTALLING A CONCRETE CAP/FACE ON A STEEL SHEET PILE WALL
Problem: Large-scale deterioration of the steel sheet pile structure has occurred; patches can not be used for repairs.
Description of Repairs: Excavate the soil from behind the wall to a level required for the new concrete cap or attachment of form ties for a concrete face. Remove all marine growth and deteriorated steel and clean surfaces. Two methods are available for installing a concrete cap/face:
For Concrete Cap: Build forms, place reinforcing, and pour concrete at mean low water. After curing, remove forms and backfill behind wall (see Figure 8-10).
For Concrete Face: Place and fasten blocking and low wale against existing sheet piling. Drive the timber sheet pile wall about 12 inches (300 mm) in front of existing sheet piling using wale as a guide. Attach outside wales to timber sheeting and place concrete by pumping or tremie. Leave timber sheet piling in place or remove as desired (see Figure 8-10).
For partial concrete facing of steel sheet pile wall, techniques exist to repair a deteriorated wall from the exterior side without requiring excavating. One method uses timber formwork (see Figure 8-10), welding steel studs to the steel sheet pile at locations where the metal is sound. The shear lugs help to hold the concrete in place. A temporary steel frame, which supports the timber formwork, is suspended from the top and welded to the exterior of the wall above the waterline. Blocking is used to maintain a 12-inch (300-mm) minimum space, Concrete is placed by pumping or tremie method. The form work can be removed within a few days.
Application: Used to restore structural strength at the top of the wall (cap) or prevent further loss of soil through holes in the sheet piling (face). Does not restore bending moment capacity in wall. Provides protection against further deterioration.
Future Inspection Requirements: Annually inspect the sheet piling areas immediately under the pile cap to ensure that further corrosive damage is not being weakening the support for the concrete cap. Follow similar procedures for partial concrete faces. For complete concrete facing, follow normal inspection procedures.
11. SCOUR PROTECTION FOR STEEL PILE SUPPORTED WATERFRONT STRUCTURE
Problem: Serious erosion of seabed material has occurred around a marine structure as a result of wave action and/or strong current.
Description of Repairs: Two methods are available for scour protection:
Riprap Placement: Replace the lost foundation material by dumping stones randomly into place. If stone riprap is not available, use bags of synthetic fiber woven water-permeable material filled with concrete. On sandy seabeds, a filter fabric may be required under the riprap or bags to prevent scour through the individual units (see Figure 8-11). The materials most commonly used are commercially available synthetic fiber, non-woven fabrics weighing between 8 and 12 ounces per square yard (269 and 405 grams per square meter) or woven fabrics weighing between 5 and 7 ounces per square yard (169 and 236 grams per square meter.)
Steel Sheet Piles: Drive steel sheet piling around structure to protect soil around the bearing piles (see Figure 8-11). The decision to replace the lost foundation material under the structure should be based on the strength of the exposed piles.
Application: A careful evaluation should be performed to determine if: (1) any settlement of the structure has occurred due to the scour, or (2) suitable bearing capacity exists within the remaining structural foundation to support the loading. Selecting either scour protection technique should ensure that suitable structural integrity exists before beginning the repairs.
Future Inspection Requirement: Normal inspection requirements will generally suffice. If riprap is used, annual underwater inspection will be required to ensure that material is not lost.
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U.S. DoD: Repair and Replacement of Steel Structures
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