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TheStructuralEngineer32

Technical Guidance Note

Technical

August 2012

Note 13 Level 1



Reading structural
steelwork drawings
Introduction

This Technical Guidance Note describes how drawings for structural
steelwork are developed and read. They have their own unique set of rules and
nomenclature and it is important for engineers to understand all of these rules
in order to communicate and interpret the design of steelwork structures.

This guide is split into two sections; the fi rst contains the information a
designer of the steel elements provides, whilst the second contains the
information a fabricator creates in order to manufacture and construct the
steel structure. While one feeds into the other, the level of detail each set of
information provides is very diff erent, due primarily to the end result. One is
informing the manufacture of the steelwork, while the other focusses on its
installation.

W Drawing principles

W Applied practice

W Further reading

W Web resources

ICON
LEGEND

Drawing
principles

When preparing general arrangements for
steel framed structures a diagrammatic style
should be applied. All beams and trusses
are drawn as a single thick black line and
bracing is shown as a dashed line when
drawn in plan. All general arrangement
drawings are to scale and any detail sections
through the structure have all elements
drawn as they would appear in reality. Also
beams are generally viewed and labelled
South to North/Down to Up and East to
West/Right to Left.

Design intent general arrangement
drawing protocol

For building projects, the responsibility of the
design and detailing of connections within
a steel frame falls to the steel fabricator
in most instances. This is not the case for
civil engineering based projects however,
as all of the design responsibility falls to the
design engineer. The engineer/designer
of the building structure must ensure that
the fabrication drawings and connection
calculations meet the design requirements
that they have defi ned. It is for this reason
that design general arrangements that

to the fabricator so that they can develop
the design of the connections.

In some instances the design of the
elements themselves become the
responsibility of the steel fabricator
and in such cases the design engineer
provides limits on sizes and form of the
steel elements. In other cases the design
responsibility for all elements of the steel
structure falls to the design engineer, with
the fabricator following their specifi ed
member sizes and connection details
exactly. More detail on apportioning design
responsibility for steel frame structures can
be found in the BCSA & SCI publication:
National Structural Steelwork Specifi cation

(5th Ed.) - Tables 1.2A, 1.2B & 1.2C.

Ultimate end reactions Ultimate end reactions

are developed by the design engineer do
not include any details on the sizing of
components such as bolts, fi n plates and
welds that make up the connections. They
do however show the ultimate reaction
forces that occur at each connection within
the steel frame; such as shear, bending
moment, axial and torsion forces. It is also
required of the design engineer to pass
on the details of the tie forces that occur
at all connections. This is to ensure the
robustness requirements (as stipulated
in part A3 of the Building Regulations of
England) are fulfi lled.

Details of the form the connection should
take are also described within the design
documentation. This information is provided

N Figure 1
Plan on steel beam with reactions - as shown in a design drawing

Column size shown
as depth, width
and weight/m Beam size shown as depth,

width and weight/m

Column size
shown as depth,

width and
weight/m

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33

Figure 1 shows a plan of a beam with
its reactions.

The labelling system used for steel elements
is dependent upon the type of steel section.
For traditional open sections such as I
beams and H columns the protocol is as
follows:

Depth in mm x Width in mm x Weight per
metre length in kg/m

Note that the dimensions given for these
sections are not the actual dimensions of
the element but the serial size. The actual
dimensions vary depending on the serial
weight per metre stated in the label. For
example a 203x203x86 UC is a 222mm
deep universal column section where as a
203x203x52 UC is a 206mm deep universal
column section, yet they are the same serial
size in terms of labelling.

For angle and hollow sections the label does
accurately state the actual dimensions of
the section along with the thickness of the
plate it is made from, thus:

Depth in mm x Width in mm x Thickness
in mm

Therefore a 120x120x12mm RSA is a rolled
steel angle that is 120mm deep and 120mm
wide and has a thickness of 12mm. With
regard to hollow sections, a 150x100x5 RHS
is a rectangular hollow section with a depth
of 150mm, a width of 100mm and a plate
thickness of 5mm.

Figure 2 is a general arrangement drawing
that has examples of all of the elements
described previously. Note how the beams
are drawn with gaps at the end as they
connect to the columns. This indicates that
they are separate elements from the one
they are connecting to.

An alternative method of labelling elements
within a steel structure is the use of a table
of member sizes that correspond to a code.
This code is used as a label instead of the
actual beam size on the drawings. This
is done in order to reduce clutter on the
drawings, making them easier to read.

It is important to note that the connection
detail shown in Figure 3 does not have any
information regarding the bolt, cleat, and
weld sizing. All of these elements typically
fall under the design responsibility of the
fabricator and any detail developed by
the design engineer must not be specifi c
on these components that make up
connections.

As well as connection forces and their
design intent, it is required that the design
engineer specifi es the steel grades and
sub-grades from which the structural
steelwork is to be formed. For building
structures these are typically S275J0 or
S355J0 for example. Drawings should also
highlight any assumptions regarding the
sequence of erection, temporary stability
and other unique aspects that would
aff ect construction. Furthermore, there
should also be an indication of any shear
studs required for composite beams that
are designed to work in conjunction with
the fl oor slab. Finally, drawings should
show foundations indicatively (and note
them as such) so that the fabricator
understands the interface between the
steel superstructure and the sub-structure
that supports it. This will allow them to
complete the design of the base plate to
columns along with their corresponding
holding down bolts.

There are some terms used on steelwork
general arrangements that designate the
relevant level of the elements shown on
them. The term TOS stands for Top of Steel
and is the level at which the top surface of
the steel is elevated. SSL is Structural Slab
Level i.e. the level at which the fl oor slab is
located. FFL is the Finish Floor Level and
is the upper most level of the overall fl oor
structure. It is only indicated on steelwork
general arrangements as a navigational aid.

N Figure 3
Design intent detail of beam to column connection

N Figure 2
Example general arrangement plan of a steel structure

"Note that the
dimensions for
these sections
are not the actual
dimensions of the
element but the
serial size"

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