Section 557 — Timber Structures

Description

557.01This work consists of fabricating, treating, erecting, and coating structural timber.

Material

557.02Conform to the following Section and Subsections: Galvanized coatings 717.07 Gray iron castings 717.04(c) Malleable iron castings 717.04(d) Material for timber structures 716 Structural carbon steel 717.01(a)

Construction Requirements

557.03General. Excavate and backfill according to Section 208. Use slings or other devices to protect the corners of heavy timbers and banded packages of lighter timber. Cut and form lumber and timber so joints have even bearing over their entire contact surface. Do not use shims in making joints. Close all joints. Drive nail and s pike heads flush with the wood surface. Use the same end, face, and edge of the timber member for all layout dimensions. Bore holes from mating faces.

557.04Storing Material. Store material in an area cleared of weeds, rubbish, or other deleterious mater ial. Elevate material at least 8 inches above the ground. Provide sufficient support to prevent sagging. Open -stack untreated material to shed water. Allow for free air circulation by stacking material in layers on stickers that extend across the full widt h of the stack. Align stickers vertically and space them at regular intervals. Close -stack treated material to shed water. Protect material from the elements. Use water- resistant paper or opaque polyethylene film if material is be covered. Do not use imper vious membranes (such as polyethylene film) during dry weather. Slit or puncture individual wrappings full length on the lower side to allow water drainage. Store and protect glued laminated timber according to AITC 111, Recommended Practice for Protection of Structural Glued Laminated Timber During Transit, Storage and Erection. 557.05 Holes for Drift Pins, Dowels, Bolts, and Lag Screws. Bore holes before preservative treatment. Bore holes for round drift pins and dowels to a diameter ⅟ 16 inch less than t he diameter of the pin or dowel. Bore holes for square drift pins and dowels to a diameter equal to the side dimension of the pin or dowel. Bore holes for galvanized bolts to a diameter ⅟ 16 inch larger than the diameter of the bolt. Bore holes for lag screws to a bit not larger than the body of the screw at the base of the thread.

557.06Treating Timber. Indicate the preservative used, penetration in inches, and the retention in pounds per cubic foot (assay method). Cut, frame, and bore timbers before trea tment. Do not cut or bore timber below the high- water mark in coastal waters. Handle treated timber according to AWPA M4, Standard for the Handling, Storage, Field Fabrication, and Field Treatment of Preservative -Treated Wood Products . Do not drip or spill preservative into an aquatic environment or onto the ground. Handle treated timbers to prevent damage to their surfaces. Do not use cant hooks or pike poles. Field treat cuts or abrasions with preservative. Dip, soak, spray, or apply three brush coat s of the same preservative according to AWPA M4. Impregnate holes bored after treatment with the same preservative using tools suitable for proper application. Plug unused holes with the same treated timber.

557.07Hardware. Galvanize hardware and fasteners, including nails, spikes, bolts, washers, and timber connectors according to AASHTO M 232. Use washers under bolt heads and nuts in contact with wood. Fabricate washers from gray iron or malleable iron castings. Use malleable iron washers with a diameter approximately three times the bolt diameter. Use steel washers only when specified. Use cut or round wire nails of standard form. Use cut, round, or boat spikes as specified. Cut off excess bolt lengths of more than 1 inch. After final tightening, check or burr bolts with a pointing tool to prevent loosening of the nuts. Use split -ring or shear -plate timber connectors conforming to Section 16.2.6 of AASHTO, LRFD Bridge Construction Specifications. For fasteners in contact with wood treated with copper- based preservatives, use Type 316 stainless steel or hot -dipped galvanized steel that conforms to ASTM A153 or A653, Class G185. For wood structures immersed in or within one mile of salt or brackish water, use Type 316 stainless steel fasteners and hardware.

557.08Countersinking. Countersink screws, bolts, and nuts where required. Treat countersunk recesses with an approved preservative before filling, except in railings. Fill the recess with hot pitch or other approved filler after bolts, screws, an d nuts are in place.

557.09Framing. Do not slab or trim treated piles when fitting sway or sash braces. Securely fasten braces to smaller piles using treated blocks to fill the gaps.

557.10Framed Bents. For mud sills, firmly and evenly bed mud blocks to solid bearing. Tamp in place. Finish concrete pedestals supporting framed bents so that sills or posts bear evenly on the pedestals. When concrete is cast, set dowels for anchoring sills and posts to project at least 6 inches above the tops of the pede stals. Make sills bear evenly and true on mud blocks, piles, or pedestals. Bolt sills into place with drift bolts that extend into the mud blocks or piles for at least 6 inches. Where possible, remove material in contact with sills for circulation of air a round the sills.

557.11Bent Caps. Make timber caps bear evenly and uniformly over the tops of aligned supporting posts or piles. Secure caps with drift bolts extending at least 9 inches into the approximate center of each post or pile.

557.12Bracing. Bolt the ends of bracing through the pile, post, cap, or sill. Bolt intermediate intersections and spike with wire or boat spikes. Use galvanized spikes in addition to bolts. Make bracing bear firmly against the pile or cap to which it is bolted. Provide and place shims as necessary to prevent bending of the bracing more than 1 inch out of true when bracing bolts are tightened. Shim based on the spacing between the bracing and cap or pile as follows:

(a)Less than 1 inch, shims are not needed;

(b)From 1 to 2 inches , place two ogee washers with their narrow faces together or other approved washers on each bolt that passes through the space; or

(c)Over 2 inches, use wooden shims of the proper thickness. Fabricate the wooden shims from the same treated wood used in the structure. Do not use built -up wooden shims. Make wooden shims from a single piece of lumber with the width at least 4 inches and the length at least the width of the bracing measured along the cap or pile. Do not adze, trim, or cut treated members to avoid the use of shims.

557.13Stringers. Size stringers at bearings. Position stringers so knots near edges are in the top portion of the stringer. Outside stringers may have butt joints with ends cut on a taper. Lap interior stringers so both stringer ends have full length bearing on a floor beam or cap. Stagger joints where stringers are two panels in length. Separate lapped ends of untreated stringers by at least ½ inch for air circulation. Use drift bolts to securely fasten the lapped ends. Place cross- bridging at the center of each span. Cut cross -bridging members to provide full bearing on the stinger sides at each end. Securely toenail the cross- bridging with at least two nails in each end. If blocking is used, make it fit snugly and securely.

557.14Plank Decks. Use planks that are surfaced on four sides (S4S). Grade plank thickness so no two adjacent planks vary in thickne ss by more than ⅛ inch. Lay the planks heart side down with ¼ inch space between them for dry, seasoned material and with no joint space for unseasoned material. Spike each plank securely to each stringer. For two -layer timber plank decks, treat the lower layer according to Subsection 557.06 . Lay the top layer either diagonally or parallel to the roadway centerline. Stagger joints at least 36 inches. Securely fasten each top layer member to the lower layer. Where the top layer is placed parallel to the centerline of the roadway, use special care to securely fasten the ends of the flooring. Bevel the ends of top layer members at each end of the structure.

557.15Transversely Nail Laminated Decks. Use 2 -inch nominal thickness laminations, surfaced on one side and one edge. Place the laminations on edge parallel to the skew as shown in plans with the surfaced edge facing downwards. Attach each piece to the preceding piece using spikes of sufficient length to pass through two pieces and at least halfway through the third piece. Drive spikes at each end and at approximately 18- inch intervals alternately driving near the top and bottom edges. Securely attach the deck to stringers using approved galvanized metal clips. Use pieces of sufficient length to bear on at least four stringers. Do not splice pi eces between stringers. Space end joints on a stringer no closer than every third piece. Space end joints in adjoining pieces no closer than every second stringer.

557.16Glue Laminated Panel Decks. When handling and transporting, avoid bending panels, es pecially transverse to the laminated pieces. When lifting a panel, support it at a sufficient number of points to prevent damage and distortion. Do not drag or skid panels. Protect the panel edges from damage. When dowels are used between panels, use a tem plate or drilling jig to properly space dowel holes. Drill holes the same diameter as the dowel and ¼ inch deeper than one- half of the dowel length. Slightly taper or round dowel tips and lubricate dowels to facilitate the connection process. Start the tip s of the dowels partially and equally in the holes of the panels to be joined. Draw the panels together, keeping the edges parallel, until the panels abut tightly. Securely fasten each panel to each stringer.

557.17Wheel Guards and Railings. Use S4S timb er for wheel guards, rails, and posts. Place wheel guards in at least 12-foot lengths. Squarely butt- joint rails at posts.

557.18Trusses. Avoid irregularities in alignment. In horizontal projection, fabricate chords straight and true from end -to-end. In vertical projection, fabricate chords to a smooth, corded curve through panel points conforming to the correct camber. Make bearing surfaces fit accurately. Do not make uneven or rough cuts at the points of bearing.

557.19Coating. If requ ired, coat according to Section 563.

557.20Acceptance Material for timber structures will be evaluated under Subsections 106.02 and 106.03. Submit a produc tion certification with each shipment of structural timber and lumber. If treated, indicate the preservative used, penetration inches, retention in pounds per cubic foot (assay method), and the BMP used in treating timber members. Construction of timber structures will be evaluated under Subsections 106.02 and 106.04. Coatings will be evaluated under Section 563. Excavation and backfill will be evaluated under Section 208.

Measurement

557.21Measure the Section 557 pay items listed in the bid schedule according to Sub section 109.02 and the following as applicable: When measuring untreated and treated structural timber and lumber by the thousand board feet measure, measure in the structure. Compute the quantities from nominal dimensions and actual lengths, except for transversely nail laminated decks and glue laminated panel decks. Measure transversely nail laminated decks and glue laminated panel decks in place after dressing.

Payment

557.22The accepted quantities will be paid at the contract price per unit of measurement for the Section 557 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 .