10.2.1 Clearances for Holes for Fasteners
Bolts may be located in standard size, over size, short slotted or long slotted hole.
- a) Standard clearance hole — Except where fitted bolts, bolts in low-clearance or oversized holes are specified, the diameter of standard clearance holes for fasteners shall be as given in Table 19.
- b) Over size hole — Holes of size larger than the standard clearance holes, as given in Table 19 may be used in slip resistant connections and hold down bolted connections, only where specified, provided the over size holes in the outer ply is covered by a cover plate of sufficiently large size and thickness and having a hole not larger than the standard clearance hole (and hardened washer in slip resistant connections).
- c) Short and long slots — Slotted holes of size larger than the standard clearance hole, as given in Table 19 may be used in slip resistant connections and hold down bolted connections, only where specified, provided the over size holes in the outer ply is covered by a cover plate of sufficiently large size and thickness and having a hole of size not larger than the standard clearance hole (and hardened washer in slip resistant connection).
10.2.2 Minimum Spacing
The distance between centre of fasteners shall not be less than 2.5 times the nominal diameter of the fastener.
Table 19 Clearances for Fastener Holes
(Clause 10.2.1)
| SI No. | Nominal Size of Fastener, d mm | Size of the Hole = Nominal Diameter of the Fastener + Clearances mm | |||
|---|---|---|---|---|---|
| Standard Clearance in Diameter and Width of Slot | Over Size Clearance in Diameter | Clearance in the Length of the Slot | |||
| Short Slot | Long Slot | ||||
| (1) | (2) | (3) | (4) | (5) | (6) |
| i) | 12–14 | 1.0 | 3.0 | 4.0 | 2.5 d |
| ii) | 16–22 | 2.0 | 4.0 | 6.0 | 2.5 d |
| iii) | 24 | 2.0 | 6.0 | 8.0 | 2.5 d |
| iv) | Larger than 24 | 3.0 | 8.0 | 10.0 | 2.5 d |
10.2.3 Maximum Spacing
10.2.3.1
The distance between the centres of any two adjacent fasteners shall not exceed or 300 mm, whichever is less, where is the thickness of the thinner plate.
10.2.3.2
The distance between the centres of two adjacent fasteners (pitch) in a line lying in the direction of stress, shall not exceed 16t or 200 mm, whichever is less, in tension members and 12t or 200 mm, whichever is less, in compression members; where is the thickness of the thinner plate. In the case of compression members wherein forces are transferred through butting faces, this distance shall not exceed 4.5 times the diameter of the fasteners for a distance equal to 1.5 times the width of the member from the butting faces.
10.2.3.3
The distance between the centres of any two consecutive fasteners in a line adjacent and parallel to an edge of an outside plate shall not exceed 100 mm plus 4t or 200 mm, whichever is less, in compression and tension members; where is the thickness of the thinner outside plate.
10.2.3.4
When fasteners are staggered at equal intervals and the gauge does not exceed 75 mm, the spacing specified in 10.2.3.2 and 10.2.3.3 between centres of fasteners may be increased by 50 percent, subject to the maximum spacing specified in 10.2.3.1.
10.2.4 Edge and End Distances
10.2.4.1
The edge distance is the distance at right angles to the direction of stress from the centre of a hole to the adjacent edge. The end distance is the distance in the direction of stress from the centre of a hole to the end of the element.
In slotted holes, the edge and end distances should be measured from the edge or end of the material to the centre of its end radius or the centre line of the slot, whichever is smaller. In oversize holes, the edge and end distances should be taken as the distance from the relevant edge/end plus half the diameter of the standard clearance hole corresponding to the fastener, less the nominal diameter of the oversize hole.
10.2.4.2
The minimum edge and end distances from the centre of any hole to the nearest edge of a plate shall not be less than 1.7 times the hole diameter in case of sheared or hand-flame cut edges; and 1.5 times the hole diameter in case of rolled, machine-flame cut, sawn and planed edges.
10.2.4.3
The maximum edge distance to the nearest line of fasteners from an edge of any un-stiffened part should not exceed , where and is the thickness of the thinner outer plate. This would
not apply to fasteners interconnecting the components of back to back tension members. Where the members are exposed to corrosive influences, the maximum edge distance shall not exceed 40 mm plus 4t, where t is the thickness of thinner connected plate.
10.2.5 Tacking Fasteners
10.2.5.1
In case of members covered under 10.2.4.3, when the maximum distance between centres of two adjacent fasteners as specified in 10.2.4.3 is exceeded, tacking fasteners not subjected to calculated stress shall be used.
10.2.5.2
Tacking fasteners shall have spacing in a line not exceeding 32 times the thickness of the thinner outside plate or 300 mm, whichever is less. Where the plates are exposed to the weather, the spacing in line shall not exceed 16 times the thickness of the thinner outside plate or 200 mm, whichever is less. In both cases, the distance between the lines of fasteners shall not be greater than the respective pitches.
10.2.5.3
All the requirements specified in 10.2.5.2 shall generally apply to compression members, subject to the stipulations in Section 7 affecting the design and construction of compression members.
10.2.5.4
In tension members (see Section 6) composed of two flats, angles, channels or tees in contact back to back or separated back to back by a distance not exceeding the aggregate thickness of the connected parts, tacking fasteners with solid distance pieces shall be provided at a spacing in line not exceeding 1 000 mm.
10.2.5.5
For compression members covered in Section 7, tacking fasteners in a line shall be spaced at a distance not exceeding 600 mm.
10.2.6 Countersunk Heads
For countersunk heads, one-half of the depth of the countersinking shall be neglected in calculating the length of the fastener in bearing in accordance with 10.3.3. For fasteners in tension having countersunk heads, the tensile strength shall be reduced by 33.3 percent. No reduction is required to be made in shear strength calculations.