11.1 Bolt capacities
The types of bolts covered are:
- Grades 4.6, 8.8 and 10.9, as specified in BS 4190[17]: ISO metric black hexagon bolts, screws and nuts.
- Non-preloaded and preloaded HSFG bolts as specified in BS 4395[18]: High strength friction grip bolts and associated nuts and washers for structural engineering. Part 1: General grade and Part 2: Higher grade.
Preloaded HSFG bolts should be tightened to minimum shank tension (Po) as specified in BS 4604[19]
- Countersunk bolts as specified in BS 4933[20]: ISO metric black cup and countersunk bolts and screws with hexagon nuts
Information on assemblies of matching bolts, nuts and washers is given in BS 5950‑2[1]
(a) Non-preloaded bolts, Ordinary (Grades 4.6, 8.8 and 10.9) and HSFG (General and Higher Grade):
(i) The tensile stress area (At) is obtained from the above standards:
(ii) The tension capacity of the bolt is given by:
6.3.4.2
6.3.4.3
| Pnom = 0.8pt At |
Nominal |
| Pt = pt At |
Exact |
where:
Table 34
| pt |
is the tension strength of the bolt. |
(iii) The shear capacity of the bolt is given by:
6.3.2.1
PS = ps As
Table 30
where:
| ps |
is the shear strength of the bolt |
| As |
is the shear area of the bolt. |
In the tables, As has been taken as equal to At.
6.3.2.2
6.3.2.3
6.3.2.4
6.3.2.5
The shear capacity given in the tables must be reduced for large packings, large grip lengths, kidney shaped slots or long joints when applicable.
(iv) The effective bearing capacity given is the lesser of the bearing capacity of the bolt given by:
6.3.3.2
Pbb = d tp pbb
and the bearing capacity of the connected ply given by:
6.3.3.3
Pbs = kbs d tp pbs
assuming that the end distance is greater than or equal to twice the bolt diameter to meet the requirement that Pbs ≤ 0.5 kbs e tp pbs
where:
| d |
is the nominal diameter of the bolt |
| tp |
is the thickness of the ply. |
6.3.3.2
For countersunk bolts, tp is taken as the ply thickness minus half the depth of countersinking. Depth of countersinking is taken as half the bolt diameter based on a 900 countersink.
Table 31
Table 32
6.3.3.3
| pbb |
is the bearing strength of the bolt |
| pbs |
is the bearing strength of the ply |
| e |
is the end distance |
| kbs |
is a coefficient to allow for hole type. |
Tables assume standard clearance holes, therefore kbs is taken as 1.0. For oversize holes and short slots, kbs = 0.7. For long slots and kidney shaped slots, kbs = 0.5.
(b) Preloaded HSFG bolts (general grade and higher grade):
6.4
(i) The proof load of the bolt (Po) is obtained from BS 4604[19]. The same proof load is used for countersunk bolts as for non-countersunk bolts. For this to be acceptable the head dimensions must be as specified in BS 4933[20].
(ii) The tension capacity (Pt) of the bolt is taken as:
6.4.5
| 1.1 Po |
for non-slip in service |
| 0.9 Po |
for non-slip under factored load |
(iii) The slip resistance of the bolt is given by:
6.4.2
| PSL = 1.1 Ks μ Po |
for non-slip in service |
| PSL = 0.9 Ks μ Po |
for non-slip under factored load |
where:
6.4.2
Table 35
| Ks |
is taken as 1.0 for fasteners in standard clearance holes |
| μ |
is the slip factor. |
(iv) The bearing resistance is only applicable for non-slip in service and is taken as:
6.4.4
Pbg = 1.5 d tp pbs
assuming that the end distance is greater than or equal to three times the bolt diameter, to meet the requirement that Pbg ≤ 0.5 e tp pbs.
where:
Table 32
| d |
is the nominal diameter of the bolt |
| tp |
is the thickness of the ply |
| pbs |
is the bearing strength of the ply. |
(v) The shear capacity of the bolt is given by:
6.4.1 a)
6.3.2.1
PS = ps As
where:
Table 30
| ps |
is the shear strength of the bolt |
| As |
is the shear area of the bolt |
In the tables, As has been taken as equal to At.
11.2 Welds
Capacities of longitudinal and transverse fillet welds per unit length are tabulated. The weld capacities are given by,
6.8.7.3
| Longitudinal shear capacity, |
PL = pw a |
| Transverse capacity, |
PT = K pw a |
where:
Table 37
6.8.7.3
| pw |
is the weld design strength |
| a |
is the throat thickness, taken as 0.7 x the leg length |
| K |
is the enhancement factor for transverse welds. |
Table 37
The plates are assumed to be at 90o and therefore K = 1.25. Electrode classifications of E35 and E42 are assumed for steel grade S275 and S355 respectively. Welding consumables are in accordance with BS EN 440[21], BS EN 449[22], BS EN 756[23], BS EN 758[24], or BS EN 1668[25] as appropriate.
11.3 Floor plates
Floor plates are not covered by this website. Please see Chapter 30 of The Steel Designers' Manual[26] for further guidance.
