›
www.thestructuralengineer.org
Note 12 Level 1
Technical Technical Guidance Note
TheStructuralEngineer August 2012
29
Reading reinforced concrete drawings Introduction
This Technical Guidance Note explains the way in which reinforced concrete drawings should be read. In many cases reinforced concrete drawings are more diagrammatic than their general arrangement counterparts and carry with them their own unique set of rules and nomenclature. Note that the guidance provided here is based on European codes of practice; for all other regions the reader is directed to local guidelines on reinforced concrete detailing methods.
ICON LEGEND
W Drawing principles
W Applied practice
W Further reading
This technical guidance note does not cover the rules governing the detailing reinforced concrete. That is a far more complex subject which is dealt with in The Institution of Structural Engineers’ publication Standard Method of Detailing Structural Concrete (3rd edition).
Drawing principles The purpose of reinforced concrete drawings is to communicate to the installer the layout of bars within concrete elements of a structure. The only dimensions provided in them are those that relate to reinforcement whose placement cannot be fixed to a clear reference point. In some instances reinforced concrete drawings are not drawn to scale. However, with the dominance of drawings that are developed using CAD, this is rarely the case. A tabulated approach is also sometimes adopted for repeatable elements that have a modicum of variety to them in terms of one or two dimensions.
in the drawing alongside other information concerning the size, steel grade, frequency and elevation within the concrete element. An example barmark call-up is given in Figure 1.
Steel designation/ notation and bar size
Number of bars
Bar mark
W Web resources
Centres of bars
N Figure 1 Typical bar call-up
the bar, its length, size and shape. In order to correlate the schedule against the bars located in the drawing, each bar is given a mark that can be cross referenced against the schedule. This ‘bar mark’ is placed within a label that is attributed to each bar
The steel designation/notation defines the grade of the reinforcement within a bar call-up and is typically designated with an ‘H’. There are other grades: A, B & C that are steel reinforcing bars with varying degrees of ductility, with ‘C’ having the highest ductility and are denoted with a corresponding letter. Grade A reinforcement bars are cold formed and are drawn from coils. They are commonly used for shear-links as they are easy to bend into shapes that feature tight bends. They cannot exceed 12mm in diameter however and this limitation does not apply to B & C grades.
All reinforced concrete drawings should be read in conjunction with general arrangement drawings, as these provide the setting out dimensions for the concrete elements themselves, in exclusion to the reinforcement within them.
Reinforcement drawing terminology All bars within reinforcement drawings have their dimensional information given on a separate document known as a ‘bar bending schedule’. This schedule lists the quantity of
TSE8_29-31.indd 29
N Figure 2 Bar bending schedule
25/07/2012 08:36
› Note 12 Level 1
30
TheStructuralEngineer August 2012
Technical Technical Guidance Note
N Figure 3 Example reinforced concrete beam drawing
E Figure 4
Example reinforced concrete column drawing
When determining the length of a bar, it must be carried out in accordance with the shape code as defined in Table 3 of BS 8666. In the example in Fig. 2 there is a U-Bar that is shape code 21. The length of such a bar is defined as: Figure 2 is an extract from the bar bending schedule the bar mark is logged against. It is appended to the reinforcement drawing it is referring to. It is important to note that a reinforcement drawing without a bar bending schedule is regarded as incomplete as one cannot be read without the other. Taking each column in turn: • The member describes which element of the structure the bar is attributed to • Bar mark is the unique identifier of each bar per drawing • Type and size is the designation/notation and bar diameter • No. of members is the number of elements this bar is located within • Total number is the number of bars denoted with this bar mark occurs within the structure • Length of each bar is the total length of the bar given in mm to the nearest 25mm • Shape code is a code given to certain bent shapes of bars as defined in Table 3 of BS 8666: 2005 Scheduling, dimensioning, bending and cutting of steel reinforcement for concrete - Specification • A to E are dimensions stated to the nearest 5mm that need to be specified for shape codes in accordance with Table 3 of BS 8666 • Revision letter is the revision of the bar bending schedule.
TSE8_29-31.indd 30
A+B+C−r−2d
(1)
Where: A and B are lengths of sections of the U-Bar C is the remaining length but is not stated in the schedule as it is written in brackets r is the radius of bending as defined in Table 2 of BS 8666 d is the diameter of the bar When calculating the lengths of bars it is important to take into account tolerances and to allow for concrete cover. Clause 10.8.1 in the National Specification of Concrete Structures provides guidance on this. In summary: a tolerance of -10mm is allowed for when assessing distances between faces of concrete that are up to 150mm thick and -15mm for elements that are more than 400mm thick. In addition, it is necessary to assume a 10mm reduction in the specified concrete cover, which is the thickness of concrete to the surface of reinforcement.
Beam reinforcement drawing Beam reinforcement drawings are amongst the simplest of the elements to create drawings for. They provide much of the required information diagrammatically and require little in the way of unique terminology within the bar mark call-ups. What does need to be shown clearly is the extent of the
bars and how they lap with one another. This is done by showing marker arrows with a bar mark number showing how far one bar laps with another. Some bars need to be set out from a common point, typically the centreline of a support in order to locate them along the length of a beam. This is because such bars are installed to resist bending moments in the top section of a beam and therefore must be placed in such a way to cover the extent of the tension in the upper section of the beam. Figure 3 is an annotated drawing of a continuous reinforced concrete beam.
Column reinforcement drawing Column reinforcement can be more diagrammatic than other reinforcement drawings. They show the primary reinforcement together with dashed lines to indicate the extent of starter bars, which is the reinforcement that projects from the kicker (a section of concrete that is cast above the structural slab level) and extent of containment links. A section is also taken through the column to indicate how the bars within it are laid out. Figure 4 is an example of a reinforced concrete column.
Floor slab reinforcement drawing Reinforced concrete floor slab drawings tend to be the most complex of elements to draw. This is especially true of flat slabs due to the need to create concentrated sections of reinforcement that act as beams within the slab. With a minimum of four layers of reinforcement to plot and the curtailment of the bars needing to be carefully plotted out, it is common to find drawings for slabs becoming too cluttered to read. In some cases therefore
25/07/2012 08:36
www.thestructuralengineer.org
31
Eurocode 0.
Applied practice
The applicable codes of practice for reinforced concrete detailing are as follows: BS EN 1992-1-1: Eurocode 2: Design of Concrete Structures. Part 1-1 General Rules and Rules for Buildings
N Figure 5 Bar level labelling within floor slabs E Figure 6 Example reinforced concrete floor slab drawing
BS EN 1992-1-1: Eurocode 2: UK National Annex to Design of Concrete Structures. Part 1-1 General Rules and Rules for Buildings
S Figure 7 Bar level labelling within walls
BS 8666:2005: Scheduling, dimensioning, bending and cutting of steel reinforcement for concrete - Specification
Glossary and further reading Bar mark – Unique number attributed to each reinforcing bar per drawing.
Cover – Thickness of concrete between it is preferable to create two separate plans for the upper and lower layers of reinforcement. Floor slab drawings also carry with them their own form of nomenclature for the level at which the bars are located within the slab. Figure 5 defines what these labels mean.
Wall reinforcement drawing
‘Extent indicators’ are key to showing bars on a floor slab drawing. These indicators show the area that a bar occupies as well as the centres they are placed at. In instances where a bar shape is the same but has varying lengths, rather than having a bar mark for each bar, a variant marked with a letter is used. This prevents a mesh of bars being drawn on the slab. Figure 6 is a section of a reinforced concrete floor slab showing how bars are shown in such elements.
In some instances the use of N1, N2 and F1, F2 nomenclature is used in a similar fashion to floor slab reinforcement.
There are similarities between floor slab and wall drawings in that they use a unique marker to indicate where the reinforcing bars are located within the concrete element. Figure 7 defines these markers.
Walls, like columns, have kickers within them and as such all reinforcing bars are set out with respect to the existence of the kicker. Other than the presence of the kicker, there is very little difference between a drawing for a reinforced concrete wall and a floor slab, as Figure 8 demonstrates.
the reinforcing bar and face of concrete.
Curtailment – Length and location of bar. Kicker – Section of projecting concrete from structural slab level within a vertical element. Lap – Where bars are placed alongside one another to ensure continuity of reinforcement within a concrete element.
Starter bar – A bar projecting from a previously cast section of concrete, that maintains continuity from the cast concrete to a new installation. Further Reading The Institution of Structural Engineers (2006) Standard Method of Detailing Structural Concrete. 3rd ed. London: The Institution of Structural Engineers Mineral Products Association (2010) National Structural Concrete Specification. 4th ed. Camberley, Surrey: The Concrete Centre Eurocode 0.
Web resources
The Institution of Structural Engineers library: www.istructe.org/resources-centre/library N Figure 8 Example reinforced concrete wall drawing
TSE8_29-31.indd 31
The Concrete Society: www.concrete.org.uk
25/07/2012 08:37
