15
Detailing Hints
The figures that follow show a number of connections and other details as encountered in typical steel structures. In each case the detail is presented in a 'preferred' form, as representing good economic practice, and a 'non-preferred' form, which should be avoided. Comments are provided on the pros and cons of the details. Fig 15.1 shows welded connections of an angle (or channel) to a gusset or other plate. Detail (a) is generally preferable because only two welds are required and they are easily accessible. It does, however, require a larger gusset. Detail (b) enables a larger resistance to be developed by the welds and would be applicable only to a heavily-loaded angle. The end weld on the angle contributes significantly to the strength of the connection, but a return weld on the reverse side should be avoided (unless required for corrosion protection) because of the difficulty of access.
(a)
(b)
Fig 15.1: Welded lapped connection
Where extended plates are required in a side-bolted end connection, as shown in Fig 15.2, a single plate can be aligned more easily with the holes in the member than two plates could be. The drilling of the extra four holes in the plate in detail (a) would be less costly than the more difficult location of the two separate plates in detail (b) plus the flush grinding of the welds on the far side. For simply-supported beams the detail shown in (a) of Fig 15.3 represents a standard end-plate connection and is preferable to those shown in details (b) and (c). The position of the plate is located by means of a portable jig or template (not shown) that fits over the top flange of the beam. In end connections requiring a full-depth plate, the plate ends
15.1
1 plate
2 plates
(a)
(b)
Fig 15.2: Bolted lapped connection with extended plates
could be set back (as in (a) at both top and foot, or could be slightly extended to receive a fillet weld on each flange of the beam, as shown in (b). The detail in (c) should be avoided because of the plate edge preparation that is called for.
(a)
(b)
(c)
Fig 15.3: Flexible beam end connections
For beams with end moments, as shown in Fig 15.4, it is preferable to use a thicker end plate than a fillet plate to stiffen the upstand of the end plate. Detail (b) is considerably more costly than detail (a) and is only resorted to where large moments need to be catered for. Thicker plate, no stiffener
Stiffener
(a)
(b)
Fig 15.4: Beam end moment connections
15.2
Angle cleats, when welded to column faces or other surfaces, normally require only two welds, as shown in Fig 15.5. Welding all round to achieve greater strength is usually unnecessary and only adds to the tendency of the column to distort.
(a)
(b)
(c)
Fig 15.5: Welded angle cleats
Plate cleats connected to the edges of column flanges should be lapped, as shown in detail (a) of Fig 15.6, since this makes for easier location and welding and allows for rolling tolerance in the column flange width, which is not achieved in detail (b).
(a) (a)
(b) (b)
Fig 15.6: Column cleats
Fig 15.7 shows that it is often cheaper to use a slightly thicker unstiffened column base plate than a thinner stiffened one. This applies both to column bases subject to axial load only and to bases having axial load and moment. A check should be carried out to ensure that the plate thickness is not excessive, especially if it exceeds 50 mm. Where the base plate is wide it may be necessary to use two stiffeners per flange, as shown in detail (c) where the stiffeners help to mobilise the full width of the plate. Two-way stiffeners, as shown in detail (d), are much more expensive and are seldom called for.
15.3
(a)
(b)
(c)
(d)
Fig 15.7: Column bases
Fig 15.8 shows how, in a beam-to-column moment connection, the column web stiffeners can be omitted if a thicker column flange is used. This should be carefully checked, but it is often found that the cost of an increase in mass m of the same serial size of column over a one storey height (taken at the cost of the material) is less than the cost of inserting the stiffeners, since the latter operation is an extremely time consuming one.
(a)
(b)
Fig 15.8: Column web stiffeners
15.4
Where plates have to be formed into an angle, as shown in Fig 15.9, the folding process demonstrated in detail (a) is usually much cheaper than corner-welding as shown in (b). The latter requires accurate fit-up, tack welding and final welding, all of which are slow operations.
(a)
(b)
Fig 15.9: Corner joints in plates
15.5
