ITEM 402 – TIMBER STRUCTURES

402.1 Description

This Item shall consist of the construction of timber structures to the dimensions, lines and grades as shown on the Plans or as ordered by the Engineer in accordance with these Specifications. The timber shall be treated or untreated as called for on the Plans or Special Provisions.

402.2 Material Requirements

402.2.1 Timber

It shall conform to the requirements of Item 713, Treated and Untreated Timber.

402.2.2 Hardware

All hardware shall be of the kind and size specified on the Plans. All bolts, including drift bolts, shall be either wrought iron or medium steel. Washers shall be either ogee gray iron casting or malleable cast iron unless cut washers are specified on the Plans.

Bolts shall have square heads and nuts, unless otherwise specified. Nails shall be cut or round wire of standard form. Spikes shall be cut wire or spikes, or boat spikes, as specified. All hardware shall be galvanized in conformity with AASHTO M 232 or cadmium plated per ASTM M 165 Type OS, unless otherwise specified on the Plans or Special Provisions.

402.2.3 Paint

It shall conform to the requirements of Item 709, Paints or Item 411, Paint.

402.2.4 Structural Steel

It shall conform to the applicable requirements of Item 712, Structural Metal.

402.2.5 Preservatives

The preservative shall be creosote oil or creosote petroleum oil blend as called for on the Plans or by the Special Provisions, and shall conform to the Specifications for timber preservatives of the AASHTO M 133.

When timber is intended for marine use, creosote petroleum oil blend shall not be used.

402.3 Construction Requirements

402.3.1 Storage of Materials

All timber which is to be stored on the job for any length of time prior to its use in the structure shall be neatly stacked in piles to prevent warping or distortion. Untreated timber shall be open-stacked at least 300mm above the ground and the stack shall be sloped so as to shed water. Creosote-treated timber shall be close-stacked and piled to prevent warping. The ground underneath and in the vicinity of all material piles shall be cleared of all weeds and rubbish.

402.3.2 Treated Timber

All treated timber shall be framed prior to treating. Care shall be exercised in handling all treated timber so as not to break or penetrate the treatment with any tool or handling equipment. Any piece of timber that has been damaged by the Contractor shall be replaced by him without extra compensation.

Any cut made or hole bored in treated timber that shall expose untreated wood shall be given three coats of hot creosote or carbolineum before the exposed part is assembled.

402.3.3 Timber Treatment

Treatment shall consist of the forcing of either creosote oil or a creosote-petroleum oil mixture into the outer fibers of the timber by a heat and pressure process. The treatment shall be so regulated that the curing process will not induce excessive checking.

The minimum penetration of the preservative with the surface of the timber shall be 20 mm. The minimum retention of preservative per cubic meter of timber shall be as follows:

For general use, 195 kg by empty cell process

For marine use, 320 kg by full cell process

The Engineer shall be notified at least ten (10) days in advance of the date that the treating process will be performed in order that the untreated timber, the treatment process, and the finished treated timber may all be inspected. The Engineer will inspect the timber prior to treatment to determine conformance with the Specifications and suitability of conditions for treatment. He shall be permitted free access to the plant in order that temperatures, pressures and quantities and types of treatment materials used may be observed. Samples of the creosote or creosote-petroleum mixture shall be furnished as required for tests.

After completion of the treatment, the timber shall be checked to determine penetration of treatment, amount of checking, quantity of free preservative remaining of the timber and any other visual evidence that the treatment has been performed in a satisfactory manner. The penetration of treatment shall be determined by boring a sufficient number of well-distributed holes to determine the average penetration. All such holes shall be plugged with plugs approximately 2 mm larger in diameter than the bit used in boring the holes.

If the penetration of preservative is less than the required amount, the entire charge, or such parts thereof as are determined by the Engineer or his authorized representative to be unsatisfactory, may be retreated. If after retreatment, the penetration is still insufficient, the retreatment pieces shall be rejected.

Any excessive checking caused by the treating process shall be cause for rejection of the pieces in which the excessive checking occurs.

The treating plant shall be equipped with adequate thermometers and pressure gages so that the process can be accurately controlled and a continuous record made of stages of the treating process. If requested by the Engineer, records shall be furnished showing the duration, maximum and minimum temperatures and pressures used during all stages of the process.

402.3.4 Untreated Timber

In structures of untreated timber, all of the following surfaces shall be coated thoroughly with two (2) coats of hot creosote oil or carbolineum before the timber are assembled: ends, tops and all contact surfaces of posts, sills, caps, floor beams and stringers, all ends, joints and contact surfaces of bracing. The back surface of all bulkheads and any other timber in direct contact with earth shall be similarly treated.

402.3.5 Bolts and Washers

Washers of the size and type specified shall be used under all bolt heads and nuts that would otherwise be in contact with wood. Cast iron washers shall have a thickness equal to one fourth the diameter of the bolt and the diameter of the washer shall be four times its thickness. For malleable or plate washers, the diameter or side size of the square shall be equal to four times the diameter of the bolt. Cap washers shall be used when the timber is in contact with earth. All nuts shall be checked effectively after being finally tightened.

402.3.6 Pile Bents

The pile shall be driven as indicated on the Plans, with a variation of the portion above the ground of not more than 6mm per 300mm from the vertical or batter indicated, or so that the cap may be placed in its proper location without inducing excessive stresses on the piles. Excessive manipulation of piles will not be permitted and the Contractor will be required to redrive or use other satisfactory methods to avoid such manipulations. No shimming on tops of piles will be permitted.

The piles for any one bent shall be carefully selected as to size and quality to avoid undue bending or distortion of the sway bracing. However, care shall be exercised in the distribution of piles of various sizes to secure uniform strength and rigidity in the bents of any given structure. Cut offs shall be accurately made to insure perfect hearing between caps and piles.

402.3.7 Frame Bents

Concrete pedestal for the support of framed bents shall be finished carefully so that sills or posts will take even bearing on them. Dowels for anchoring sills or posts shall be set the concrete is cast and shall project at least 150 mm above the tops of the pedestals.

Sills shall have true and even bearing on piles or pedestals. They shall be drift-bolted with bolts extending into the piles or pedestals at least 150mm. When possible, all earth shall be removed from contact with sills so that there will be free circulation of air around the sills.

402.3.8 Caps

Timber caps shall be placed to obtain even and uniform bearing over the tops of the supporting posts or piles with their ends in alignment. All caps shall be secured by drift bolts, set approximately at the center extending at least 230mminto the post or piles.

402.3.9 Bracing

Bracing shall be bolted through at intersections to the pile, posts, caps or sills.

402.3.10 Stringers

Stringers shall be sized at bearings and shall be placed in position so that knots near the edges will be in the top portions of the stringers. Outside stringers may have butt joints but interior stringers shall be lapped to take bearing over the full width of the floor beam or cap at each end. The lapped ends of untreated stringers shall be securely fastened to caps by drift bolts. When stringers are two panels in length, the joints shall be staggered. Cross-bridging between stringers shall be neatly and accurately framed and securely toe-nailed with at least two nails at each end. All cross-bridging members shall have full bearing at each end against the sides of stringers. Unless otherwise specified, cross bridging shall be placed at the center of each span.

402.3.11 Plank Floors

Roadway and sidewalk floor planks, unless otherwise stipulated, shall be surfaced one side and one edge (SISIE). The planks shall be laid heartside down, with 7 mm openings between them for seasoned materials and with tight joints for unseasoned material. Each plank shall be spiked securely to each joint or supporting member. The planks shall be graded carefully as to thickness, and so laid that no two adjacent planks shall vary in thickness by more than 1.6mm.

402.3.12 Laminated or Strip Floors

Planks for laminated or strip floors shall have a nominal thickness of 50mmand shall be surfaced to a uniform width (SIE), and when so specified, to uniform thickness (SIS). Unless otherwise stipulated, no splicing of planks will beallowed.

Planks shall be laid with the surfaced edge down and each plank shall be toe-nailed to each alternative stringer. The nailing of successive planks shall be staggered so that the spacing of nails along each stringer shall not be less than 100 mm. In addition, each piece shall be nailed horizontally to adjacent pieces at 450 mm centers, and staggered both horizontally and vertically with nails in adjacent pieces. All floors shall be cut to a straight line along the sides of the roadway.

402.3.13 Railing and Rail Posts

Railing and rail posts shall be built as shown on the Plans and shall be constructed in a workmanlike and substantial manner. All railing and rail post materials shall be surfaced on four sides (S4S). All rails shall be continuous and squarely butt-joined at the post.

402.3.14 Wheel Guards

Wheel guards shall be accurately constructed true to line and grade in accordance with the Plans. Unless otherwise specified, wheel guards shall be surfaced on one side and one edge (SISIE). Wheel guards shall be laid in sections not less than 3.60 mm long.

402.4 Method of Measurement

Timber structures shall be measured by the completed span and shall include all materials, equipment and labor used to finish the structure as called for in the Bid, Plans and Specifications.

402.5 Basis of Payment

Payment for the timber structure measured in Section 402.4, Method of Measurement, shall constitute full compensation for furnishing all materials, preservative treatment, if called for in the Contract, equipment, hardware and other metal parts, tools and labor necessary for the completion of the structure and painting, if required in a satisfactory manner and all incidentals necessary to complete the Item.

Payment will be made under:

Pay Item Number	Description	Unit of Measurement
402 (1)	Timber Structure	Span