KMD sheet and specification example: what a member drawing consists of and what the fabricator reads first

The notional member used for the walk-through

All dimensions, numbers and designations in this article are invented. It is an illustration of what a sheet contains, not a drawing for fabrication: nothing is made to these numbers, and a real beam is designed separately first (see steel beam calculation).

The member is a welded I-beam 6000 mm long. The web is a 8×400 plate, the flanges are 12×180 plates, and 16×180 end plates with bolt holes are welded to the ends. Inside there are three pairs of stiffeners, on the top flange two lifting lugs, and on the web four seats made of L50×5 angle for purlins. The steel is notionally S345, and after fabrication the beam is hot-dip galvanized.

On the erection plan such a beam carries the mark B1, and on a KMD sheet the mark gets a KMD sequence number, so the member is called B1-3 (the same way as K1-3 in the rules for KM and KMD drawings). The example has twelve such beams.

How the sheet is laid out

The main view of a shipping piece is drawn in its working position: the beam is horizontal, so it is drawn horizontally. Scales for shipping pieces in KMD are taken from the 1:10–1:50 range, for small edge details 1:1, 1:2 or 1:5. In the example the view is 1:20, the sections 1:10 and the detail 1:5. The standard recommends placing the specification in the right-hand part of the sheet; in its examples it stands at the top right.

The zones below are typical. In a real set they depend on the member: a truss needs a geometry diagram, a bent part needs a developed view with the radius and bend direction.

The title block: what it must contain

The form of the fields and the frame sizes are set by the standard for title blocks, and there is nothing to invent. What matters to the fabricator is something else: from the block he must understand which sheet this is, which set it belongs to and which revision. So below it is not the layout but the data people look for first.

Part of this data is in practice moved from the title block into the specification or the technical requirements. The main thing is that each quantity stands on the sheet once or, if repeated, has the same value.

The shipping-piece specification with masses

The specification columns follow the rules set out in the article on KM and KMD drawing rules: part number, section, length (for flat parts the longer side of the circumscribed rectangle), quantity, mass of one and of all parts, steel, remark. At the bottom are the mass of the parts, the weld metal on a separate line and the total mass of the member.

Items 1–6 are numbered in ascending order, and the same numbers stand on the views and sections. Parts keep their final dimensions after all operations: allowances and shrinkage are not shown on the drawing, the shop’s process documents set them.

The example is notional. In a real specification the steel in each row is supplemented, where needed, with impact toughness requirements and a weldability guarantee: this is how rolled steel is ordered (see the article on steel grade selection).

Where the mass figures come from

The density of steel is taken as 7850 kg/m³, that is a plate 1 mm thick weighs 7.85 kg per square metre. For the angle the mass per metre from the angle range tables is used: L50×5 gives 3.77 kg/m. Mass is counted to 0.1 kg, rounding up. The table below shows every step so that the arithmetic can be checked.

The mass of all parts in the example is taken as the rounded unit mass multiplied by the quantity (item 2: 101.8 × 2 = 203.6), so that every row reads without discrepancy. The rounding rule adopted in your set is written in the general data and is the same on all sheets.

What is not included in the mass

The reduction in mass from bolt holes is not taken into account: the drawing rules say so directly, unless the design brief requires otherwise. Parts with cut corners, like the stiffeners, are counted by the rectangle they fit into, because it is under 0.2 m². Lifting lugs are part of the mark mass because they are shown on its drawing.

The mass in the specification is the mass of black steel before galvanizing: zinc adds mass, and it is accounted for separately when transport and lifting are calculated. Bolts, nuts and washers are not part of the mark mass: in the example they are moved to their own schedule.

Welds: what to state

For each weld the sheet must show the type of joint, the kind of weld, the leg size for fillet welds, the length or pitch for intermittent ones, whether it is a shop or a site weld and the inspection requirement if it is above the usual. The leg size is set by the design, not by the shop: a welder does not pick it by eye. The upper limit of the leg is 1.2 times the thickness of the thinner part, the lower one depends on the thickness of the thicker part and on the yield strength of the steel (guidance in the article on weld joint types).

The way welds are drawn on the views is taken from what is adopted in the set: a table of conventional symbols on the general data sheet or symbols under the standard for weld designation. In the example the welds are named in words, so as not to stand in for the standard.

The legs are notional and not taken from a calculation: only the upper limit of 1.2 times the thinner part was checked (for W1 it is 9.6 mm, for W5 6 mm). The lower limit for a real member is taken from the codes, see the section on standards.

If the beam has a butt joint

In the example the web is continuous, so there are no butt welds. If the web plate were butt-jointed, that weld would have its own designation with edge preparation, and the sheet would carry an inspection requirement, for example ultrasonic. We do not carry out radiographic testing, and such a requirement is stated in the enquiry in advance, see quality control of steel structures.

Holes and fasteners

Holes are given by number, diameter and coordinates from a datum axis or edge, not just “4 holes”. In the end plates of the example there are four Ø22 holes for M20 bolts; the hole diameter is notional, the clearance in a real joint is set by the design. The plates are 16 mm thick, so the holes are drilled, not punched: in parts over 6 mm cracks may appear near a hole after punching (see design for galvanizing).

Fasteners go into a schedule of erection items separate from the rolled steel, and for each the diameter, length, class and coating are written. The bolt + nut pair is named together: a bolt of class 8.8 goes with a nut of class 8, as in the article on fastener strength classes. The bolt length is chosen by the grip: the sum of the part thicknesses, washers, the nut and the thread protrusion.

The mass of fasteners is taken from the fastener range tables; in the example it is not part of the mark mass.

What else is written about the joint

It is stated separately whether the bolts are tightened with controlled pretensioning: that is another group of sets, and they are bought ready-made. If a joint is mixed (some connections bolted, some welded), this is visible on the sheet. For galvanized fasteners the schedule gives the galvanizing method and the threads.

Coating and dimensions for galvanizing and painting

In the technical requirements the coating is written in a phrase or two: the method (hot-dip galvanizing, powder coating or their combination), what is measured, which surfaces and threads are not coated. The zinc thickness for the piece is taken from the standard according to the steel thickness, see zinc coating thickness. For painting the RAL colour and gloss are added.

The rest is decided by the shape of the parts. The stiffeners have 20×20 corner cuts at the flange and the web: in a corner where three planes meet, zinc does not reach and the flux has no time to evaporate. The lugs, besides lifting, can be used for hanging in the bath, but the hanging points are agreed with the galvanizing plant. An open I-section has no closed cavities, so vent holes are not needed. The ratio of the greatest thickness to the smallest here is 16 : 8 = 2, and for welded assemblies we ask to keep it no more than 5 : 1.

The overall size is checked separately. Our galvanizing bath is 13 000 × 1 600 × 3 200 mm, and a 6000 × 424 × 180 mm beam lies in it with room to spare. The powder coating chamber is 6 m long, 1 m wide and 1.8 m high; the beam length equals the chamber length, so there is no margin, and before releasing a drawing that requires painting this is agreed with the shop (more in the article on powder coating cost factors). If the piece goes for a duplex system, galvanizing and painting are agreed together at the drawing stage.

Erection marks, tolerances and what goes to site

The mark on the sheet must match the mark on the erection plan: the member is found on site by it, and the partner construction company that carries out erection checks the beam position in the frame by it. Erection dimensions (grid references, levels) stand on the erection plan, while the mark sheet carries the dimensions for fabrication and for the relative position of parts.

Tolerances are written on two levels. In the technical requirements there is one phrase about general fabrication tolerances under the document named in the brief. Separately, on the views, stand the dimensions where the tolerance is tighter than the general one; in the example these are the distance between the end plate holes and the straightness of the beam axis: the joint with the column depends on them. Tolerance figures are not given in this article because they depend on the document adopted in the project.

Schedule of shipping pieces and metal take-off: how to check against the sheet

The schedule of shipping pieces collects marks with their quantity and mass, and the metal take-off lists the same metal by section and thickness, because that is how it is ordered. Both must agree with the sheet. In the example twelve beams B1-3 give 12 × 397.6 = 4 771.2 kg.

The sum agrees with the schedule of shipping pieces. If two figures differ, the error is sought in the mark specification or in the number of marks, not in the sum.

Why a mass discrepancy is a warning sign

A discrepancy of a few percent between the specification and the take-off usually means that in one of the documents the quantity was not updated, the welds were left out or the rounding was done differently. Metal is ordered from such a take-off, so the error has a price before cutting even starts.

Typical mistakes on the sheet

• the length on the main view is 6000 and in the specification 5980: a contradiction between views is found at assembly, when the parts do not come to size;
• an item on the view without a number, or a number that is not in the specification: the shop does not know what the part is or how many there are;
• the mass does not add up: the total is not the sum of the rows, the weld metal is missing or the take-off counts a different number of marks;
• no steel grade in the specification, in at least one row, and the metal is ordered “by analogy”;
• no weld leg given: neither the welder nor the process engineer picks it, and the drawing goes back for clarification;
• a weld is not called shop or site, and it is not visible what to do in the shop and what on site;
• mirror-image parts without the “т” and “н” indices or without a note that the numbering is continuous;
• a closed dimension chain, where the sum of partial dimensions is not equal to the overall size;
• a member that does not fit into the galvanizing bath: length over 13 000 mm or a closed cavity without holes. Dipping in two passes is sometimes possible, but it is agreed separately;
• one sheet corrected and the rest not updated: drawings of different revisions lie in the shop.

Checklist before release to production

Before issuing the set, the author checks each item. This does not replace a review; it is the minimum after which a drawing does not come back with obvious questions.

What the production department of POLYGONAL checks when it receives drawings

We fabricate steel structures to the customer’s drawings, so the first thing the production department does is read the set in the same order as this walk-through: drawing schedule, general data, erection plan, mark sheet. They look at whether the set is complete and whether the views, the specification and the metal take-off contradict each other.

Then the drawings are looked at through the eyes of the shop: which metal and in what thicknesses has to be bought, how to cut and bend the parts, how to assemble and weld them, whether the legs and inspection requirements are named, which holes to drill, what to galvanize or paint and whether the piece fits the bath or the chamber. Visual inspection of welds and ultrasonic testing we do ourselves, radiographic testing we do not do, and if the design requires it, it must be visible on the sheet.

Questions the drawing does not answer go back to its author before work starts, rather than being settled in the shop by guesswork. If there are no drawings, we prepare them: KM and KMD drawing design, steel fabrication. For the general logic of KM and KMD see what KMD is and KM and KMD stages, and for what a set contains see the article on KMD drawings.

Standards and validity

The article does not reproduce a single requirement of the standard for drawing presentation, and the figures of the example are notional. The rules for counting mass (steel density 7850 kg/m³, rounding up to 0.1 kg, weld metal 1 %), the content of the specification and the list of standards that apply to KM and KMD drawings are gathered in the article Rules for KM and KMD drawings.

The legs, weld types, requirements for holes for galvanizing and fastener classes in this article are taken from our separate articles, where their sources are named. Before a standard is cited in project documents, its status is checked in the current list of national standards: editions change.