Lattice Girders - 3 Bar / 4 Bar
1. All lattice girders shall consist of three or four primary retaining bars connected by stiffening elements of the manufacturer's design. The lattice girder will be designed to allow shotcrete to penetrate into and behind the girder with a minimum of shotcrete shadows.
2. DSI Underground offers various alternate stiffening element systems:
- Traditional spiders
- Romtech™ sinoidal waves
- Box systems for four-bar designs
Specific details of the above can be provided upon request.
All connections between stiffening elements and the retaining bars will be by gas metal arc welding.
3. The lattice girders will have moment properties about the neutral axis as shown. A minimum of 5% of the moment of inertia shall be provided by the stiffening elements. This percentage will be calculated as an average along a repeatable length of the girder.
4. The maximum centerline spacing of stiffening elements shall be less than three times the height of the girder to assure stability over buckling with a tolerance of plus or minus 1 inch.
5. The connection elements at the end of the girder may be made with structural plates, angles or tunular couplers. The footplates must be able to transfer the load to the soil or rock in the invert. The connecting elements must be able to transfer the full load capacity of the girder.
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 min 80 ksi, Yield Strength min 70 ksi, Ultimate Elongation min 10%.
3. The connection elements at the end of the girder shall be constructed of structural angle or plate meeting the minimum properties of A36. Bolts and nuts shall meet the requirements of A325 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.
5. All welds will run parallel to the retaining bars with a minimum length of 1".