Rebar Shaft Grate Spec_FINAL (1).pdf

Rebar Shaft Grate Installation

PART 1 DESCRIPTION

This work shall consist of fabricating and installing a rebar shaft grate closure within specific mine adits and shafts. Work shall include excavation of loose material and trimming of the mine opening; drilling, placing, and grouting anchors; concrete footers; and fabrication, installation, and welding of steel gates or grates in accordance with these specifications. Refer to the Drawings for construction details.

The dimensions shown on Standard Drawings are generic and based upon a standard design.

Actual dimensions will be determined by the mine opening size and site preparation. The CONTRACTOR shall make the necessary measurements and adjustments to ensure that a competent gate or grate is constructed that will prevent human access. Very large or irregularly shaped openings may require custom fitting or modification of the generic design in consultation with the OWNER. Minor variations in the location of the bat gate will be allowed so that the CONTRACTOR may select a stable location for the bat gate, with the approval of the OWNER.

PART 2 – PRODUCTS/MATERIALS

Steel Grating shall conform to grating sizes specified in Table 8.1. Cross bars shall be resistance welded at right angles to the bearing bars and spaced as specified in Table 8.1, (type WXA bar as manufactured by AMICO type 19-W-4-53, or equivalent).

Structural Steel shall conform to the requirements of ASTM A36, all-purpose steel.

Rock Bolts shall be expansion type with a minimum pullout strength of 2,000 pounds at an embedded depth of 4.5 inches. The rock bolts shall be Hilti Heavy Duty Expansion Anchor, Kwik Bolt or equivalent.

Anchor Bars shall be Number 6 (3/4") rebar in accordance with ASTM A615, Grade 60, anchored a minimum depth of 8 inches (8") into competent rock with ET Epoxy-Tie epoxy or equivalent, or with an interference fit in drilled holes in solid rock.

Concrete shall have a minimum compressive strength of 3500 psi at 28 days.

Cement shall be Type II Portland cement, conforming to ASTM C150, unless otherwise approved by

PROJECT MANAGER.

Fine and Coarse Aggregate shall conform to ASTM C33.

Water shall be potable.

Admixtures shall conform to ASTM C494. Calcium chloride will not be permitted.

Reinforcing Steel (rebar) shall be made of deformed new billet stock and shall conform to ASTM A615, Grade 60. All reinforcing steel shall be free from heavy rust, scale or other coatings that will destroy or reduce the bond.

2.03 REBAR SHAFT GRATE I-BEAM SUPPORTS

Steel used for supplemental I-beam supports for shaft grates (see Part 3.03.E) shall be rolled steel and shall meet the requirements of ASTM A 992. I-beams shall have a minimum yield strength of 50 ksi. I-beam size is dependent on the length of the span. I-beams shall be sized as scheduled in the following table:

Beam Span Length (feet) I-Beam Size

0 – 9 Not Required 10 – 15 W8 x 10 15 – 20 W10 x 15 20 – 25 W10 x 22 25 – 30 W10 x 33

30+ Consult engineer

PART 3 - EXECUTION

3.01 GENERAL

CONTRACTOR shall construct steel gate closures in adits and steel grate closures in shafts as specified below, as shown on the Drawings The final design, fabrication, and erection of the gate or grate closure shall conform to the guidelines established with these specifications and the drawings.

On sites where bedrock is near the ground surface the framework will be anchored using six inch (6”) minimum rock bolts or anchor bars inserted into a hole drilled eight inch (8") deep minimum, to accommodate the bolt or bar with a non shrink grout, such as ET Epoxy-Tie® or equivalent. Rock bolts or anchor bars will be twelve inches (12") center to center with a minimum two feet (2') setback from the edge of the opening. The bolts or bars shall then be welded to the framework.

3.02 REBAR SHAFT GRATE INSTALLATION

A. Location. Variation of the location of the shaft grate will be allowed so that CONTRACTOR can select a suitable location for the shaft grate, with approval of OWNER. Parameters for suitable location of the rebar shaft grate shall be as follows:

1. Select an area in which competent rock is found around the collar of the shaft, if possible.

2. Select an area with minimum irregularities in the collar to avoid excessive site preparation for the construction of the grade beam around the collar.

3. Locate the grade beam at a reasonable distance (typically 3 feet minimum, or as directed by the OWNER) from the shaft collar to reduce the possibility of collapse of the collar of the shaft.

4. Grates at shafts with competent rock collars where grade beams are omitted shall be installed at grade or inside the opening to a maximum depth of 3 feet below grade.

B. Preparation. CONTRACTOR shall excavate to solid rock where the grade beam is to be constructed where the depth does not exceed two feet to bedrock. Any mud, clay, moss, or other materials where the grade beam is to be constructed which would be deleterious to the integrity of the grate or grade beam and would not allow good bonding of the concrete to the rock shall be removed. Historic structural features shall be preserved and maintained. Drainage shall be provided for any water that would accumulate on either side of the grade beam. Excavated materials shall be set aside for replacement later.

C. Where possible, concrete grade beams shall be constructed on competent foundation rock which is not friable, subject to deterioration, or otherwise unacceptable and the foundation rock is approved by OWNER. The grade beam shall be a minimum of 12 inches high and 12 inches wide. Grade beams for grates larger than 15 feet in either dimension (measured from the interior sides of the grade beams) shall be a minimum of 18 inches high and 12 inches wide, or as directed by OWNER. Grade beams shall be pinned to the foundation rock using #8 rebar anchor pins installed a minimum of 18 inches into the rock, grouted, and set 2 inches below the upper surface of the grade beam. Rebar anchor pins shall be located on 32-inch centers maximum.

D. Forms will be required for all grade beams. Forms shall be sufficiently braced to prevent movement or dislocation during or after setting the grate steel and rebar in place. Concrete shall be reinforced with #6 (¾-inch) rebar as shown on the Drawings. Concrete shall not be poured until the grate steel and rebar have been installed. Concrete shall be poured in one continuous operation and shall be free of cold joints. The grade beam shall be free of any voids within the beam structure and shall be 100 percent concrete construction. Concrete construction shall be done in accordance with Section 0251:

Cast-In-Place Concrete and Section 0252: Concrete Reinforcement.

E. Grates larger than 10 feet in either dimension (measured from the interior sides of the grade beam) shall be constructed with one or more supplemental supports for the grate as specified in Part 2.03 above. The supports shall be rolled steel I-beams centered or equally spaced in the long-dimension sides, and running across the short dimension of the grate. The I-beam supports shall be positioned directly beneath the crossbars and will be embedded in the grade beam 6 inches at each end. The height of the grade beam will be adjusted as needed to accommodate additional height of the I-beam supports.

F. Crossbars shall be installed in the grade beams running each direction on 8-inch centers to form a square grid. Crossbars shall be positioned a minimum of 4 inches below the top surface of the grade beam. Crossbars running the short dimension of the grate shall be placed underneath, except where there is a supplemental I-beam support. Each intersection of the crossbar grid shall be fillet welded on the upper side.

G. In shafts with competent collars, grade beams may be omitted with approval of the

OWNER. Rebar anchor pins shall be installed a minimum of 8 inches into the collar.

At least 4 anchor pins shall be installed, with a maximum spacing of 32 inches between pins. Support bars shall be welded to the anchor pins. Grate crossbars shall be installed on the support bars, running each direction on 8-inch centers to form a square grid.

Each intersection of the crossbar grid and each contact with the support bars shall be fillet welded on the upper side.

H. Crossbars shall be continuous. Lap joints, if required, shall be a minimum of 5 inches with continuous fillet welds along both sides of the lap joint.

I. All field welds shall be in accordance with the requirements of the American Welding Society (AWS) D.1.1.

J. Upon completion, the collar areas shall be cleared of all construction materials, formwork, and construction-generated trash and debris. Material excavated for the grade beam preparation shall be backfilled against the beam. Excess material shall be blended into the surrounding area. The site shall be left with a clean and finished appearance.

K. Variation in the generic design or custom fitting may be required to accommodate site-specific conditions.

PART 4 – MEASUREMENT AND PAYMENT

No measurement for payment shall be made for these bid items. Payment shall be for the lump sum bid price. The price bid shall include all of CONTRACTOR’S cost of whatever nature to provide a complete closure installation in accordance with the plans and specifications including materials, fabrication of the grated closure, excavation, welding, final grading, and revegetation of disturbed areas.