Lattice Girders 3 Bar / 4 Bar
Advantages with the use of Lattice Girders
Lattice girders provide the following advantages:
- Immediate roof support over the excavated section.
- Act as a template assuring a minimum thickness when applying shotcrete.
- Become part of the reinforcement in the shotcrete lining.
- Provide support for spilling, if needed, over the next excavation.
- Work equally well with machine mining or drill and shoot tunneling - no need for major investment in special equipment
- Are practical supports for a wide range of ground conditions.
- Can be erected within a few minutes by a small crew without special handling equipment.
Fabrication of Lattice Girders
1. Lattice girder segments shall be composed of a low alloy steel used for concrete reinforcement and intended for special applications where bending and welding are of importance.
2. Minimum physical properties of steel:
- Tensile strength minimum of 80 ksi
- Yield strength minimum of 70 ksi
- Ultimate elongation minimum of 10%
3. The connection elements shall be constructed of structural steel meeting the minimum properties of ASTM A 36. Bolts and nutes shall meet the requirements of ASTM A 325 unless otherwise noted.
4. Welding process to meet the requirements set forth by AWS for gas metal arc welding (GMAW). All welders must be certified in accordance with AWS D1.1. All welds will run parallel to the retaining bars with a minimum length of 1 inch.