806Timber Construction

806.01 Description.

This work includes heavy timber construction for bridge superstructures, roadway decks, sidewalks, railings, and other similar applications.

806.02 Materials.

Timber. Use s awn lumber, structural glued laminated timber , and wood preservative treatment that conforms to SECTION M11. Hardware. Use metal fastenings required for timber connections or for connecting timber to concrete or steel work that conform to Subsection M05.05.13.

806.03 Construction Methods.

Workmanship. Ensure that all timber is cut and framed to a close fit so that the joints have even bearing over the entire contact surfaces. Drive nails and spikes sufficiently to set the heads flush with the surface of the wood. Evidence of deep hammer marks in wood surfaces will be sufficient cause for rejection of the work. Remove timber scraps from cuts from the site on a regular basis to keep the work site neat and orderly. Preservative Treatment of Timber and Lumber. For all timber and lumber designated for treatment , use the pressure-treated process according to the standard practices of the American Wood Preservers Association (AWPA). Use the appropriate standards and specifications from AWPA for the Project conditions. Use the “empty cell” pressure-treated process, followed by an expansion bath where applicable, vacuum to 22 in. of mercury at sea level, and perform a final steam cleaning. Handling of Timber and Lumber.

Part 800 — Bridge Structures August 2025

SECTION 806 — TIMBER CONSTRUCTION 800-39 use cant hooks, peaveys, pikes , or hooks. Provide c orner protectors to prevent damage to timber bundled with metal bands or straps. ● Cuts and Abrasions. Perform all cutting, framing, and boring of treated timber before treatment as practical. Apply three brush coats of hot preservative oil to all cuts and abrasions made after treatment. Allow each coat to dry before the next coat is applied. ● Holes. Treat with preservative oil all holes, bored after treatment, with an AWPA- approved pressure bolt hole treater or with hot preservative oil by other methods approved by AWPA. Plug any unfilled holes, after being treated with preservative oil, with treated plugs. ● Temporary Attachments. Forms or temporary braces may be attached to treated timber with nails or spikes only when approved by the Engineer. Upon their removal, fill the holes by driving galvanized nails or spikes flush with the surface or by plugging as required for holes. Installation of Connectors. Install the split ring and the shear plate types in precut grooves of dimensions as recommended by the manufacturer. Force spike grids into the wood so that timbers are in firm contact. Use pressure equipment that does not damage the wood. Cut connector grooves in timber concentric with the bolt hole, conform ing to the cross-sectional shape of the rings and providing a snug fit. Ensure that the inside groove diameter is larger than nominal ring diameter so that the ring will expand slightly during installation. Perform the fabrication of all structural members using connectors before preservative treatment. When prefabricated from templates or shop details, ensure that the location of bolt holes is not more than 1/16 in. from the required placement. Ensure that b olt holes are 1/16 in. larger than the finished bolt diameter. Bore the bolt holes perpendicular to the face of the timber. Store the timber after fabrication to prevent changes in the dimensions of the members before assembly. Ensure that t imber is cured before fabrication so that its dimensions remain stable. Timber that shrinks during storage causing predrilled grooves for split rings or plates to become elliptical or causing bolt hole spacing to change will be rejected. Countersinking. Perform c ountersinking where smooth faces are required. Treat recesses formed in treated timber for countersinking as required for cuts and abrasions. Hardware. • Rods. Thread r ods connecting only sawed timbers at each end to provide tight connections, allowing only for permissible variations in the dimensions of material.

Part 800 — Bridge Structures August 2025

800-40 SECTION 806 — TIMBER CONSTRUCTION • Bolts. The length specified is the length measured under the head. Bolts may be substituted for rods for timber connections where the length of the threaded portion provided by the bolt is sufficient. • Lag S crews . Install lag screws by turning them into place. The screws may be driven sufficiently to start them into the holes and hold them firmly in place for turning. P erform pre-drilling according to Subsection 806.03.7. • N uts and Washers . Use w ashers or plate washers under all nuts, bolt heads, and lag screws that would otherwise contact with wood, except under large diameter heads of specially designed flat head bolts. Always use standard square nuts. Tighten the nuts to prevent the rods or bolts from becoming loose during service. A fter being tightened, secure the nuts from backing off by the burring of the rod or bolt threads. • N ails and Spikes . Do not allow nails to extend through all material into which they pass unless approved by the Engineer. Ensure that distance and spacing adhere to the currently adopted versions of the AASHTO LRFD Bridge Design Specifications and the National Design Specification (NDS) for Wood Construction. Drive nails or spikes through the thinner member into the thicker member. Ensure that the nails and spikes are flush or countersunk to the member surface. Drill pre-bored holes according to Subsection 806.03.7. Holes for Bolts, Dowels, Rods, Lag Screws, Nails, and Spikes. Bore holes for round drift bolts and dowels with a bit sized 1/16 in. less in diameter than the bolt or dowel to be used. Ensure that the diameter of holes for square drift bolts or dowels is equal to the least dimension of the bolt or dowels. Bore holes for machine bolts with a bit of the same diameter as the bolt up to 1/16 in. greater than the bolt diameter. Bore holes for rods with a bit 1/16 in. greater in diameter than the rod. Bore holes for lag screws with a bit not larger than the body of the screw at the base of the thread. To prevent splitting or stripping of the threads, bore a lead hole for the shank with a bit of the same diameter and to the same depth as the shank. Ensure that the depth of holes for lag screws are 1 in. less than the length under the thread. Do not drive lag screws into the lead hole with a hammer. Instead, turn the screw in with a wrench. Spikes and nails are generally hand- driven but may be power driven for the smaller diameters and lengths. Pre-bore holes for large diameter spikes and nails (generally greater than ¼ in.) to prevent the wood from splitting during driving. Ensure that the diameter of the lead hole does not exceed 0.9 times the diameter of the fasteners for wood species with specific gravities greater than 0.6 and no more than 0.75 times the diameter of the fastener for wood species with specific gravities less than 0.6. Do not allow p re-bored holes to extend into the members that will be holding the point of the nail or spike.

Part 800 — Bridge Structures August 2025

SECTION 806 — TIMBER CONSTRUCTION 800-41 Framing. Cut and frame all lumber and timber to a close fit so that the joints have even bearing over the entire contact surfaces. Ensure that mortises are true to size for their full depth and that tenons fit snugly. Do not use shimming to make joints. Open joints will be rejected. Framed Bents. • Mud Sills . Firmly and evenly bed m ud sills to solid bearing and tamp in place. Use pressure preservative treated mud sills for ground contact. Where untreated timber is permitted for mud sills, use heart cedar, heart cypress, redwood, or other durable timber as approved by the Engineer. • C oncrete Pedestals . Finish concrete pedestals for the support of framed bents so that the sills or posts will take even bearing. Ensure that dowels for anchoring sills or posts are not less than ¾ in. in diameter and project at least 6 in. above the tops of the pedestals. Cast the dowels into the concrete pedestals. • S ills . Install sills that have true and even bearing on mud sills, piles, or pedestals. Ensure that sills are drift-bolted to mud sills or piles with bolts of not less than ¾-in. diameter and extend into the mud sills or piles at least 6 in . When practical, remove all earth from contact with sills so that there is free air circulation around the sills. • Po sts . Fasten posts to pedestals with dowels of not less than ¾- in. diameter, extending at least 6 in. into the posts. Fasten posts to sills by one of the following methods as indicated on the Plans: ○ By dowels of not less than ¾-in. diameter, extending at least 6 in. into posts and sills ○ By drift-bolts of not less than ¾-in. diameter driven diagonally through the base of the post and extending at least 9 in. into the sill. Drive drift bolts into holes at a 45-degree angle to enter the post at least 6 in. above the post base. ○ By other types of connectors as detailed on the Plans. • Caps. Place timber caps, with ends aligned, to secure an even and uniform bearing over the tops of the supporting posts or piles. Secure all caps by drift-bolts of not less than ¾- in. diameter, extending at least 9 in. into the posts or piles. Ensure that the drift bolts are approximately in the center of the post or pile. • B racing. Bolt bracing through the pile, post, or cap at the ends and at all intermediate intersections using a bolt of not less than ⅝ in. in diameter. Ensure that bracing has sufficient length to provide a minimum distance of 8 in. between the outside bolt and the end of the brace. Stringers. Size the stringers at bearings and place them in position so that knots near edges are in the top portions of the stringers. Other stringers may have butt joints with the ends cut on a taper, but lap interior stringers to take bearing over the full width of the floor beam or cap at each end. Separate t he lapped ends of

Part 800 — Bridge Structures August 2025

800-42 SECTION 806 — TIMBER CONSTRUCTION untreated stringers at least ½ in. for the circulation of air , and secure the lapped ends fastened by drift-bolting. Where stringers are two panels in length, stagger the joints. Place timber stringers in position so that the deck has an even bearing on all stringers and so that any knots near edges are in the top portions of the stringers. Outside stringers may have butt joints, centered over caps or floor beams, but lap interior stringers so that each rests completely over the full width of the cap or floor beams at each end. Toenail the stringers to caps, and spike together the intermediate stringers of adjoining spans where they lap. Properly frame the cross bridging between stringers, and ensure that the framing is securely toe- nailed with at least two nails in each end. Ensure that all cross-bridging members have full bearing at each end against the sides of stringers. Place 2 in. × 4 in. cross bridging at the center of each span. Plank Floors. Use planks for flooring that is surfaced four sides (S 4 S). Use single plank floors that include a single thickness of plank supported by stringers or joists. Lay the plank’s heart side down, with ¼-in. openings between them for seasoned material and with tight joints for unseasoned material. Securely spike each plank to each joist. Ensure that the planks are graded as to thickness and laid to ensure that no two adjacent planks vary in thickness by more than ⅛ in. Use two-ply timber floors that include two layers of flooring supported on stringers or joists. Lay the top course either diagonal or parallel to the centerline of roadway, and securely fasten each floor piece to the lower course. Stagger joints at least 3 ft. If the top flooring is placed parallel to the centerline of the roadway, securely fasten the ends of the flooring. At each end of the bridge, bevel these members. Nailed or Glued Laminated Strip Floors. Use nailed or glued laminated strip floors that include individual lumber strips. Place the strips on edge as described in the Plans to the previous strip to form a continuous surface. Construct the laminated strip floors either on top of stringers at right angles to the centerline of roadway or on top of floor beams running parallel to the roadway centerline. Use spikes that are of sufficient length to pass through two strips and at least one-half of the third strip. If timber supports are used, toenail every other strip to every other support. If steel supports are used, securely fasten the strips to the supports at the required locations and spacing. Ensure that each strip is vertical and tight against the preceding strip and bear s evenly on all supports. Laminated Panel Decks. Use laminated panel decks that include stress laminated sawn lumber strips . Place the strips with their wide side vertical and fastened together to form panels. Provide fastening as described in the Plans. Panels may be interconnected using spliced, bolted, or doweled ship-lap joints, steel

Part 800 — Bridge Structures August 2025

SECTION 806 — TIMBER CONSTRUCTION 800-43 dowels, or high strength steel stressing rods. Alternatively, panels may be assembled in a non - interconnected fashion. Panels may be u sed longitudinally with stringers, composite stringers, without stringers, or transversely across steel or wood stringers. Wheel Guards and Railings. Frame the wheel guards and railings and erect them true to line and grade. Use wheel guards, rails, and rail posts that are surfaced on four sides (S 4 S). Lay the wheel guards in sections not less than 12 ft long, except where necessary to match expansion joints or end joints. Trusses. Ensure that the trusses, when completed, have no irregularities of line. Ensure that the c hords are straight and true from end to end in horizontal projection and, in vertical projection, present a smooth curve through panel points conforming to the correct camber. Ensure that all bearing surfaces fit accurately. Uneven or rough cuts at the points of bearing will result in rejection of the piece containing the defect.