16.1.1 This Section deals with the design and detailing requirements for joints between members. Connection elements consist of components such as cleats, gusset plates, brackets, connecting plates and connectors such as rivets, bolts, pins, and welds. The connections in a structure shall be designed so as to be consistent with the assumptions made in the analysis of the structure and comply with the requirements specified in this
For members with sway buckling mode, the equivalent uniform moment factor Cmy=Cmz=0.9.
Cmy,Cmz,CmMLT shall be obtained according to the bending moment diagram between the relevant braced points
Table 18Equivalent Uniform Moment Factor (Clause 9.3.2.2)
Bending Moment Diagram
Range
Cmy,Cmz,Cm
Uniform Loading
Concentrated Load
(1)
(2)
(3)
(4)
-1 ≤ ψ ≤ 1
0.6 + 0.4 ψ ≥ 0.4
0 ≤ αs ≤ 1
-1 ≤ ψ ≤ 1
0.2 + 0.8 αs ≥ 0.4
0.2 + 0.8 αs ≥ 0.4
-1 ≤ αs ≤ 0
0 ≤ ψ ≤ 1
0.1 - 0.8 αs ≥ 0.4
-0.8 αs ≥ 0.4
-1 ≤ ψ ≤ 0
0.1(1-ψ) -0.8 αs ≥ 0.4
0.2(1-ψ) -0.8 αs ≥ 0.4
0 ≤ αh ≤ 1
-1 ≤ ψ ≤ 1
0.95 - 0.05 αh
0.90 + 0.10 αh
-1 ≤ αh ≤ 0
0 ≤ ψ ≤ 1
0.95 + 0.05 αh
0.90 + 0.10 αh
-1 ≤ ψ ≤ 0
0.95 + 0.05 αh (1+2 ψ)
0.90 + 0.1αh (1+2 ψ)
Moment factor
Bending axis
Points braced in direction
Cmy
z-z
y-y
Cmz
y-y
z-z
CmLT
z-z
z-z
section. Connections shall be capable of transmitting the calculated design actions.
16.1.2 Where members are connected to the surface of a web or the flange of a section, the ability of the web or the flange to transfer the applied forces locally should be checked and where necessary, local stiffening provided.
16.1.3 Ease of fabrication and erection should be considered in the design of connections. Attention should be paid to clearances necessary for field erection, tolerances, tightening of fasteners, welding procedures, subsequent inspection, surface treatment and maintenance.
16.1.4 The ductility of steel assists the distribution of forces generated within a joint. Effects of residual stresses and stresses due to tightening of fasteners and normal tolerances of fit-up need not therefore be considered in connection design, provided ductile behaviour is ensured.
16.1.5 In general, use of different forms of fasteners to transfer the same force shall be avoided. However, when different forms of fasteners are used to carry a
shear load or when welding and fasteners are combined, then one form of fastener shall be normally designed to carry the total load. Nevertheless, fully tensioned friction grip bolts may be designed to share the load with welding, provided the bolts are fully tightened to develop necessary pretension after welding.
16.1.6 The partial safety factor in the evaluation of design strength of connections shall be taken as given in Table 5.
16.2Location Details of Fasteners
16.2.1 Clearances for Holes for Fasteners
Bolts may be located in standard size, over size, short slotted or long slotted hole, as follows.
a) Standard clearance hole — Except where fitted bolts, bolts in low-clearance or oversize holes are specified, the diameter of standard clearance holes for fasteners shall be as given in Table 19.
b) Oversize hole — Holes of size larger than the standard clearance holes, as given in Table 19 may be used in slip resistant connections and
PART 6 STRUCTURAL DESIGN — SECTION 6 STEEL
hold down bolted connections, only where specified, provided the oversize
c) 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).
d) 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 oversize 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).
Table 19 Clearances for Fastener Holes(Clause 16.2.1)
Sl 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 (5)
Long Slot (6)
(1)
(2)
(3)
(4)
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
16.2.2 Minimum Spacing
The distance between centres of fasteners shall not be less than 2.5 times the nominal diameter of the fastener.
16.2.3 Maximum Spacing
16.2.3.1 The distance between the centres of any two adjacent fasteners shall not exceed 32t or 300 mm, whichever is less, where t is the thickness of the thinner plate.
16.2.3.2 The distance between the centres of two adjacent fasteners (pitch) in a line lying in the direction of stress, shall not exceed 16t or 200mm, whichever is less, in tension members and 12t or 200mm, whichever is less, in compression members; where t 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.
16.2.3.3 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 t is the thickness of the thinner outside plate.
16.2.3.4 When fasteners are staggered at equal intervals and the gauge does not exceed 75 mm, the spacing specified in 16.2.3.2 and 16.2.3.3 between centres of fasteners may be increased by 50 percent, subject to the maximum spacing specified in 16.2.3.1.
16.2.4 Edge and End Distances
16.2.4.1 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.
16.2.4.2 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.
16.2.4.3 The maximum edge distance to the nearest line of fasteners from an edge of any un-stiffened part should not exceed 12tε , where ε=(250/fy)1/2 and t 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.
16.2.5 Tacking Fasteners
16.2.5.1 In case of members covered under 16.2.4.3, when the maximum distance between centres of two adjacent fasteners as specified in 16.2.4.3 is exceeded, tacking fasteners not subjected to calculated stress shall be used.
16.2.5.2 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.
16.2.5.3 All the requirements specified in 16.2.5.2 shall generally apply to compression members, subject to the stipulations in Section 6(g) affecting the design and construction of compression members.
16.2.5.4 In tension members [see Section 6(f)] 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.
16.2.5.5 For compression members covered in Section 6(g), tacking fasteners in a line shall be spaced at a distance not exceeding 600 mm.
16.2.6 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 16.3.3. 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.