19 June 2001
TR-1: REPAIRING TIMBER PIER SUPERSTRUCTURE
Problem: Wood components are damaged and no longer fully serve intended
purpose or present a safety risk.
Description of Repair:
Decking. Replace decking with properly treated quarter-sawn timber
or other suitable material when its top surface becomes uneven, hazardous, or
worn to a point of possible failure. Spacing between decking planks is normally
provided for ventilation and drainage. Blacktopping of decking may not provide a
completely protective cover against rain wetting beneath it because cracks often
develop in the material. Limit washing decks with freshwater as this promotes
Pile Caps. Replace decayed or damaged pile caps with properly
treated wood (including glulam) or other suitable material. Replacement caps
should be the same size and length as the original caps unless redesigned.
Curbs, Chocks, and Wales. Replace these members with properly
treated lumber (including glulam) or other suitable material when decay or other
damage renders them unfit for service. Make butt-type joints, not lap-type joints,
in connecting wood curbs and wales to reduce decay damage potential.
Replacement sections should be long enough to reach a minimum of two bents.
Place new preservative-treated wood blocks or other suitable material, 5 to 8 cm
(2 to 3 inches) thick, under each curb (upper string piece) replacement section at
intervals of about 1 meter (3.3 feet) to provide for drainage (Figure 6-1).
Braces. Replace diagonal braces that are broken or attacked by fungi
or marine borers with wood or other suitable material. Place pressure-treated
wood braces well above high water and treat all bolt holes with a preservative.
An alternative to using pretreated wood is plastic barriers, either polyethylene or
polyvinyl chloride plastic wraps or polyurethane coatings. The braces, with bolt
holes, can be fashioned to fit and the plastic applied before the braces are
attached to the pier piling. Where braces are fastened to a piling, the pile should
not be cut or dapped to obtain a flush fit. Where decking has been removed for
repairs, it is often possible to drive diagonal brace piles to provide lateral
stiffness. This procedure eliminates all bolt holes except those at the top of the
structure immediately below the decking.
Stringers. Replace decayed or damaged short stringers with properly
treated wood or other suitable material. Replace decayed or damaged areas of
long stringers with new sections. Make connections between replacement and
existing stringers directly over a pile cap and stringers. Tightly bolt or pin the
stringers to the pile cap (Figure 6-1). Stagger the splices in adjacent stringers
where possible. Avoid checks and splits, which promote decay, when driving
deck spikes by pre-drilling small holes.