770.8 Maintenance of Bridge Substructure
Substructure maintenance involves maintenance to bents, tubes, piers and abutments. Many types of designs are being used for these units and the materials commonly employed in their construction are concrete, steel, timber, or combinations thereof.
770.8.1 Concrete Caps
It is usually advantageous to seal the concrete caps of all substructure units under open joints or expansion devices in the deck. It may also be desirable to seal the caps of the other substructure units. The caps should be sandblasted and loose concrete removed prior to sealing. The modified elastomeric urethane used to seal these caps should be carried a minimum of 1/2 in. up on the bearing plates. Ensure proper drainage is maintained so water will not pond on cap.
770.8.2 Timber Piling and Caps
Untreated piles and timbers have a relatively short life because of decay or termite damage unless they are in a dry location or permanently below the water line. Treated piling will give excellent service if constructed properly of sound materials and adequately maintained. Early decay in the treated piling can usually be traced to faulty construction practices, such as leaving the metal cap off the top of the piling, cutting below the treated depth for framing purposes, or to a poor grade of timber and improper preservative treatment. Decay will eventually occur, and experience indicates the point of decay is usually at or just below the ground line.
Treated piles which have decayed or been damaged by fire or impact, and where the portion below the ground is still sound may be repaired without the necessity of driving new piling. After the necessary falsework is in place, the old pile should be cut off below the decayed or damaged area. The decayed pile section is replaced by a new section of steel H-pile to take the place of the deteriorated piling. Care must be taken so that the new section of H piling will result in the bent cap being raised from the adjacent timber piling. Steel rebar are installed into the top of the existing timber pile to allow it to be tied into the concrete collar that will be used to encase the old piling and the steel H pile. The falsework may be removed after the concrete collar around the timber piling and H pile has cured.
Where it is not practical to replace the piling as outlined above, a new section of piling can be spliced to the old section by using a steel pipe or band to hold the two butt ends together.
If water surrounds the area, coffer dams may be used to keep water from the work area.
Because of the fire hazard, it is essential that the area around timber pile bents and abutments be scalped and all weeds and brush be removed from the vicinity.
Where timber pilings are subject to frequent damage from ice they should be protected with used motorgrader blades banded around piling or other forms of armor. Scour of the stream may lower the flow line or widen the channel to a degree where additional crossbracing may become necessary. Crossbracing may be 3 in. x 8 in. treated timber or 3 1/2 in. x 5 in. x 3/8 in. angle.
Timber pile caps which have deteriorated may be replaced by twelve inch steel bearing piles. Stiffeners must be welded between the flanges directly under the stringers and directly over the piling. The steel cap is secured to the piling with a piece of 3 in. flat stock bent to encircle the top of the pile and welded to the bottom of the cap.
770.8.3 Concrete Piling
Precast concrete piling may be damaged by fire, drift, ice or collision. If the damage is not excessive, it probably can be repaired by removing all loose and weakened concrete, squaring up the ends, and placing new minimum shrinkage concrete or epoxy mortar. It may be desirable in some cases to make the new portion larger than the original dimensions to provide additional resistance to impact.
Cracks in concrete piling can be repaired by epoxy injection.
Should the need arise, Central Office bridge maintenance can recommend various materials to use for these repairs.
770.8.4 Steel Piling and Cast-In-Place (CIP) Piling
Maintenance of steel piling and cast-in-place (CIP) concrete piling consist of painting to prevent corrosion and repairs necessitated by reason of fire or impact.
Painting is to be performed in accordance with standard bridge painting procedures. Painting at the ground line should be performed using approved bituminous coating.
Damaged or weakened sections of the piling may be repaired by straightening bent sections, by adding reinforcement, or by placing a collar around the pile. Fenders may be installed on the upstream side where damage from ice or drift is frequent. Additional cross bracing may also be necessary when erosion has occurred. See EPG 7126.96.36.199 Steel HP Pile Maintenance and Repair.
770.8.5 Concrete Substructure
Maintenance of concrete abutments, piers, and bents consists of repairs necessitated by deterioration and damage caused by fire, impact or erosion.
Superficial damage may be repaired by removing the deteriorated or damaged concrete and applying patching materials developed for those areas of application. Epoxy mortars may also be used, but in all cases the affected areas must first be thoroughly cleaned by sandblasting to remove all dirt and loose material.
Deeper damage or deterioration may be repaired by replacing the areas involved or even entire sections with low shrinkage concrete.