The intention of 3.4.1 is to make clear that Fabrication Shop Drawings and Fabrication Data are intended primarily for the manufacture of components and should not include unnecessary information. Data necessary to simplify checking, such as grid line dimensions, may be shown but other details irrelevant to the checking or manufacturing process should be omitted.
It is normally expected that Fabrication Drawings will show components as completed for dispatch from the fabrication shop.
Components and fittings produced on automated plant are usually made directly from electronic Fabrication Data. In this case Fabrication Drawings are used for shop assembly only.
Although not stated, it is expected that a second competent draughtsman checks all hand-made drawings, and that the initials of the draughtsman and checker must appear on the drawing.
However, in the case of drawings generated by computer, it is considered to be more important to check the computer input information plus a visual check of the drawings produced to ensure that no obvious errors have been made.
Traditionally, a drawing register would have served the requirement for the manufacturing system to record dates when information is released for manufacture. Electronic systems would include comparable records and the time between release of information for manufacture and actual manufacture could often be very short in such a system. In addition, it would be important for the electronic system to record when information is sent for review by the Engineer (see Commentary on 3.6) and the issuing dates for each revision, just as a traditional drawing register would do.
3.4.2 is included in the NSSS to ensure that attachments that have to be provided to facilitate erection are shown on the Fabrication Drawings, so that such attachments can be properly positioned and checked.
It may also be necessary to locate the fitting on the centroid of the component, and any such requirements should be clearly specified on the drawings. The Steelwork Contractor should include a reference to erection attachments in the erection method statement, since the Engineer must give his approval to all design and stability matters in the statement. The requirements for the erection method statement can be found in 8.1.1.
The intention of 3.4.3 is to reflect the importance of preparations for welding as part of the connection by having them shown on the drawings. However, if a Steelwork Contractor uses a particular preparation regularly, he can reference this on the drawing without showing the detail.
There is no requirement to show weld procedures on the drawings.
The fabrication workshop’s procedure is expected to include weld inspection as specified in 5.5.1, but if a different level of inspection has to be provided, the NSSS stipulates that such information be given on the drawings.
The art and science of good detailing practice for fabrication drawings is, in many ways, encompassed in 3.4.4. The NSSS expects that the draughtsman has a full knowledge of the permitted tolerances. His job includes showing the packings and clearances required so that the component can be erected without modifications having to be made at site.
If the geometry of the completed structure is to be as shown on the Design Drawings, detailing may have to take account of camber or flexure which will occur from the self-weight of the structure. It is up to the Engineer to state if this is needed; it is not difficult for the detailer to make provision when the camber requirements are known. It is sometimes necessary to make provision for adjustment in other connections, for example:
vertical cantilevering parapet posts connecting to portal frame columns,
brackets supporting gutters requiring adjustment to accommodate a drainage fall.
The clearance requirements for hole sizes in 3.4.5 are essentially those commonly used throughout the industry. The 6mm hole clearance for holding down bolts allows for normal adjustment. However, in thick steel base plates, or if the bolt extends into a bolt-box welded to the column shaft, an even greater clearance may be needed where positional adjustment may incline the holding down bolt.
Clause 6.1.8 stipulates a nominal clearance of only 0.3mm for precision fitted bolts. It is expected that these will be used in holes which are drilled after assembly, or pre-drilled undersize and reamed when assembled.
The NSSS does not mention cleats with short horizontal slot holes as shown in Figure 3.3.
Some Steelwork Contractors may wish to adopt this detail which improves the adaptability of cleats and allows a standard cross centre dimension where web thicknesses vary. This detail can be used only if accepted by the Engineer.
F igure 3.3 — Sh ort slot hol es
Connections where adjustment is required, or where movement is necessary, need special attention when preparing detail drawings. Two such matters are the subject of 3.4.6 and 3.4.7.
Holding Down Bolts, requiring greater facility for adjustment than other bolts, have to be provided with loose cover plates or large washers ( see not e to 2.7.3) .
It is important that a bolt assembly in a movement connection, such as used at expansion joints in structures, should be made so that undue friction cannot develop between mating surfaces. Shouldered bolts, with a washer bearing on the shoulder after tightening as shown in Figure 3.4, may be used in slotted-hole connections. In other bolted assemblies lock nuts will prevent the assembly becoming loose when in operation.
Figure 3.4 — A shouldered bolt used at expansion
joints
Machining operations are the focus of 3.4.8, but they are rarely needed in normal building construction. For example Ref. 2 — Joints in simple construction, suggests that most base plates have a sufficiently flat bearing surface without machining or cold pressing. If the design does call for machining of a surface, suitable notes have to be shown on the drawing to direct the workshop's attention to the requirement.
The purpose of 3.4.9 is to identify where drilled holes rather than punched holes are required. Its aim is to ensure that punching does not take place where, for example, distortion of the surface must be avoided. Work-hardening of the metal surrounding the hole could also initiate a brittle fracture in fatigue situations, or affect plasticity in areas where plastic hinges are required.
Design codes limit the thickness of metal to be punched to the maximum values stated in 4.6.4.
The detailer must therefore show on the Fabrication Drawings where holes are to be drilled and not punched.
The locations where this restriction would apply are:
in non-slip friction grip connections made with pre-loaded bolts;
at locations where plastic hinges are assumed in the design analysis;
in elements of rigid connections where yield lines are assumed;
where repetition of loading makes fatigue critical to the member design;
where the design code of practice does not permit punched holes.
The obligation on the designer to identify such locations is given in TABLE 1.2A(viii) and (xviii).
Design standards and specific test data are used to determine the friction factor that limits the capacity of preloaded friction grip connections. 3.4.10 indicates that Fabrication Drawings must be fully specific with respect to the necessary treatment to the faying surfaces.