1-31 Drawing Nomenclature

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TheStructuralEngineer September 2013

Technical Technical Guidance Note

Drawing nomenclature Introduction

The reading of drawings is a much underrated skill, learnt primarily through being frequently exposed to them and driven by the need to understand their contents. Their sole purpose is to convey information in order for a structure to be designed, measured and constructed. This is fundamental to every drawing produced by a structural engineer, be it a simple sketch in an email or an A0 sized General Arrangement drawing. This Technical Guidance Note describes the basic knowledge required to read drawings that are produced by structural engineers. It explains the symbols and nomenclature used and also the relationship they have with drawings produced by other members of the design team and/or sub-contractors. This guide has been written with bias towards building structures and therefore the contractual responsibilities highlighted, reflect this.

ICON LEGEND

General W Arrangements

W Applied practice

W Further reading

W Web resources

Table 1: Common symbols found on GA drawings

General Arrangements Symbol General Arrangements (GA) are drawings created by the structural engineer. The primary purpose of these drawings is to provide information on the size and disposition of structural elements. Typically, it is the responsibility of the architect to provide setting out information for all elements of a building and for the structural engineer to incorporate these into the GA. Discrepancies between the architect’s drawings and the structural engineer’s must be brought to the design team’s attention. GA drawings typically take three forms: plans, elevations and sections. All of these drawings are referred to in the structural details, be they steel reinforcement or connections. Whatever is being drawn in a GA format can be incorporated into one of the three categories. On smaller projects it is very common to have two or sometimes all three of these forms contained on the same drawing, as well as details.

Drawing nomenclature GA drawings have a common set of symbols and nomenclature that identifies setting out information, elevation, section location and detail references. There are slight variances to these symbols, but they all follow the same form. Table 1 describes them.

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Description Elevation mark with arrow showing what is being elevated. The lower half of the circle contains the drawing number of where the elevation is drawn. Where elevations are on a gridline, it can be useful to match the reference e.g. this mark is for an elevation on gridline 3. Section mark with arrow showing the point of the slice where the section has been taken and its orientation. There is an accompanying arrow that indicates the extent of the section. The lower half of the circle contains the drawing number of where the section is drawn. Detail mark with line pointing to circle where the detail is being taken. The lower half of the circle contains the drawing number of where the detail is drawn. Level marker typically suffixed by one of the following: AOD (Above Ordnance Datum) TOS (Top of Steel) TOF (Top of Foundation) SSL (Structural Slab Level). Level marker on sections and elevations.

Thickness of slab or wall (when drawn in elevation).

Hole or ‘void’ in structural element.

Recess in structural element.

Span arrow indicating the direction a floor slab is spanning.

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Table 2: Line weights and types Line type

Elevations

Thickness (mm)

Description

0.18/0.25

Gridline, a common point of reference from which all setting out is taken.

0.18/0.25

Hidden detail that cannot be seen from the view the drawing is projecting onto.

0.25

Dimensions and labels.

0.3/0.35

Element is in elevation.

0.5

Element of structure is cut through, requiring it to be highlighted with a thicker line.

Line weights and types Line weights and types are an important component of GA drawings as they define what is being conveyed in terms of the location and size of an element. Table 2 explains these.

Units and drawing scales Units are typically stated in millimetres for setting out and element size. Levels are normally described in meters. In terms of metric scales, there is a standard set that are used when creating structural GA drawings. Their use is dependent upon the type of drawing that is being created. Table 3 provides a list of commonly used scales.

shear core walls and large voids in the floor slab. GA drawings developed by structural engineers will only show the structural elements of a building. Therefore they will not indicate finishes, fixtures and fittings, light switches, power outlets or surface water drainage. They will however, show anything from these items that have an impact on the structure. For example, voids through structural elements and steps in the structure to accommodate different finishes. Figure 1 is an example of a GA plan.

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Figure 1 Extract from a General Arrangement (GA) plan

An elevation is a side view on an element of the structure and is often confused with a section, as the latter also slice through the structure portraying a vertical plane. The location of an elevation is at the very face of the element that is being viewed. Its purpose is to describe the interaction between a vertical element and horizontal elements of the structure, which are typically floor slabs and beams. In most instances it is a shear wall or bracing that is being elevated. Any major openings within elevations for building services containment e.g. ducts and pipework as well as doorways for access to staircases and lifts, are indicated along with their size and location. For concrete structures, elevations typically show only the vertical stability elements of a building, as an overall elevation does not provide any additional information beyond that contained in the architect’s drawing (Figure 2). For other materials, such as steel framed buildings, 'whole building' elevations are more common as, crucially, they show information on levels and help to ensure that there are no clashes between vertical, horizontal and diagonal members. Elevations are also useful for showing secondary members e.g. for cladding support, which may not occur at floor level and so are difficult to show on plan.

Plans Plans are the core of GA drawings as they provide the navigation to where all the other forms stem. They describe the size of structural elements, their length and in most instances their location. They are the key to where sections through the structure are taken and present information on important elements in the structure, such as Table 3: Common scales used to create GA drawings Drawing type

Scale

Plan

1:250*, 1:200, 1:100 & 1:50

Elevation

1:100 & 1:50

Section

1:100 & 1:50

Part section

1:25*, 1:20 & 1:10

Details

1:20, 1:10 & 1:5

* Non-standard but frequently used due to space restrictions

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TheStructuralEngineer September 2013

Technical Technical Guidance Note

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Figure 2 Elevations on a concrete core and a steel braced frame

Sections Sections are a saw-cut slice through a structure that is taken in order to describe an interface between elements. They are typically taken with an orientation of ‘up’ the page or towards the ‘left’ of the page. These interfaces cannot be identified on a plan and it is clarity that which usually drives the need for a section. Where an element

is cut, its outline is drawn with a thicker line and in some cases hatched or shaded. When drawing a section there is a general rule that requires you to draw only what is 1m away from where the section is being taken. For example if a section is taken 2m away from a shear core wall, the wall is not drawn as it is too far away to be ‘seen’ by the

section slice. This rule exists for the sake of clarity; otherwise sections would be a mess of vertical elements as an attempt is made to show everything past the point of the slice (Figure 3). Flexibility of this rule is permitted as there are occasions when an element that is more than 1m away from the cut point, needs to be shown in order to describe an interface with other elements in the structure.

Details Details are referred to in all of the GA drawings, which provide navigation as to where the details apply. They are typically produced following the three forms of GA drawings, as their requirement is brought to light as the GA drawings are developed. For example if there is a need to show how a slab should to be isolated from a wall, then a detail is required to show this (Figure 4). Details can be incorporated into the section GA drawings, especially on smaller projects where it is possible to show the interface between elements and how they are fixed together.

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Figure 3 Example of a part section

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Figure 4 Detail showing isolation joint

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Figure 5 Revision cloud

Building Services Engineer’s drawings

Architect’s drawings

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Figure 6 Abeyance cloud

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Figure 7 Relationship between structural GA drawings and those produced by others

Structural Engineer’s drawings

Label protocol

From 3D to 2D

Like the symbols and nomenclature described in Table 1, there are protocols for the labelling of reference items, such as elevations, sections and details on a drawing. These labels can take the form of a number or a letter, or a mixture of both. A common restriction to the form of the label is that it should not include the letters O, I and Z. These letters are not used because they can be confused with the numbers 0, 1 and 2 respectively.

With the introduction of Building Information Modelling (BIM) the creation of drawings has altered significantly from the traditional two dimensional based methods. BIM models are three dimensional yet two dimensional drawings are typically still needed in order for design information to be passed on to contractors as well as other design team members. This is done by extracting views and details from the BIM model and placing them onto a 2D drawing. Such drawings follow the same protocols as those described here.

Change indication Design, by its nature, is an evolving process and drawings are continually revised to reflect this. Such revisions are identified through the drawing clouds around the area that has been amended and marking it with a triangle, which has a number and/or letter within it (Figure 5). This marker corresponds to the revision on the drawing while the details of the change are described in a column of text on the drawing sheet. These clouds are removed once a new revision occurs and new clouds are added. This makes the revision description of ‘as clouded’ invalid due to the absence of previous cloud iterations. Another form of cloud that is drawn (as an inverse to the revision type) is the Abeyance cloud (Figure 6). This indicates a section of the drawing that is on hold and the information contained within it should not be referred to or digested. Sometimes the reason for the abeyance cloud is added to its label. Typically, such clouds appear because outstanding information and/or confirmation from others, has not been delivered at the time the drawing is being issued.

Drawing relationship Structural GA drawings are very rarely produced in isolation and it is important that this point is understood, in order for the relevance of the structural GA to be appreciated. They typically have interactions with (and origins from) drawings developed by others. Conversely, many drawings are created on the basis of what has been shown on the structural GA. The most common relationship between the structural GA and other design documentation is illustrated in Figure 7.

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Sub-Contractors’ Design & drawings

Scheduling Where an element is common throughout large tranches of the structure, it is advisable to create a schedule for it, rather than draw the same element multiple times. This is typically done for columns where they are sometimes not drawn to scale, but simply placed on a sheet with cross section dimensions shown. Elements, such as beams, columns, piles and walls are sometimes given a unique number label and placed onto a table within the drawings. These labels are then installed onto the GA plan drawings and do much to reduce the amount of clutter on them as they are shorter than full element description. If this is adopted then then reader of the drawings must become familiar with a unique labelling system in order for them to understand the drawing.

Eurocode 0.

Applied practice BS ISO 128-30:2001 Technical drawings – General principles of presentation – Part 30: Basic Conventions for views BS ISO 128-30:1999 Technical drawings – General principles of presentation – Part 23: Lines on construction drawings BS ISO 129-1:2004 Technical drawings – Indication of dimensions and tolerances

Glossary and further reading

Drawing notes Drawing notes are located in the top right corner of a sheet within a ‘notes’ column. They provide important additional information such as material grades and concrete cover to reinforcement as well as cross reference drawings. Notes can also be used to highlight areas which will be subject to further design development, or to give information which is not easy to draw.

Further Reading Hill M. (1999) Guide to Drawn Information London: RIBA Publications HM Government (2013) The Construction (Design and Management) Regulations 2007 [Online] Available at:www.legislation.gov.uk/ uksi/2007/320/contents/made (Accessed: August 2013)

Eurocode 0. They are also a good way to place alerts on drawings of unique and unusual hazards, as is required under the Construction Design and Management (CDM) regulations in the UK.

Web resources The Institution of Structural Engineers library: www.istructe.org/resources-centre/library

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