Introduction
Reinforcement is the bone of civil engineering structures. Just as a body with a fractured bone cannot function effectively, a structure with poor reinforcement would either fail in whole or part or be unserviceable. Therefore, utmost care should be taken in reinforcement preparation and placement for utmost strength and functionality of civil engineering structures such as buildings of which I would focus here.
Structural design and structural detailing are two important aspects of reinforced concrete design. Structural design involves the estimation of the loads (external forces) coming on the structural elements, analysis of the loads to determine the internal stresses (bending moments and shear forces) due to the loads, and the provision of the required sizes and areas of reinforcing steel to ensure that the structure does not fail due to the internal stresses. This is also known as the objective of structural design. A reinforced concrete structure comprises concrete and steel. The loads on a structure produce compression and tension forces on the structure. The tensional forces are usually resisted by steel which is good in tension while the compressional forces are resisted by concrete section which is good in compression. When the structural design of building elements is done, the final end is determining the areas of reinforcement required in different members and ensuring that they satisfy certain specification limits applicable to design codes through necessary checks.
Following immediately after the structural design is structural detailing. Structural detailing involves the presentation of structural design output in such a manner that contractors, site supervisors, and fabricators would understand it and present it accurately in actual site construction. Both structural design and structural detailing are very important in building construction. Even though structural design is of utmost importance to ensure structural stability, the effectiveness of structural design can be undermined by poor structural detailing. A good structural design poorly detailed is nothing but a bad design. The structural elements of a building usually include.
Slabs
Beams
Columns
Staircases
Shear walls (usually on high rise buildings subjected to lateral forces such as wind forces or lift walls)
Foundations (pad bases, raft footings, combined footings, piles and pile caps etc)
Steps in Reinforcement Work in Buildings
A. Structural analysis of buildings
B. Structural design of buildings
C. Structural detailing of buildings
D. Preparation of bar bending schedule (BBS)
E. Preparation of reinforcement onsite or offsite according to BBS.
F. Placement and tying of reinforcement in the structural members
The first two steps are not within the scope of this article. I would focus on the last four. In a formal design office, there are distinct roles between the duties of the structural designer and the structural detailer (draughtsman). In Nigeria, most times, one person combine the role. In this case, the structural detailer understands his designs and can detail them without much stress. But where the roles are distinct, the structural designer should be able to communicate his designs very clearly to the structural detailer while the structural detailer should also be able to communicate his details very clearly to the steel fixers. The latter case is more critical because steel fixers are usually workers associated with the contractors and structural detailers usually comes from the design office (consultants) in most cases, one contractor can work with different consultants and his steel fixers does not have permanent acquaintance and understanding with the particular structural detailer. Therefore, in each situation, it is necessary that the structural detailers communicate effectively, with minimal ambiguity to the steel fixers.
A good structural detailing starts with standard practice on the following points:
1. Borders
2. Title block
3. Thickness of lines
4. Lettering
5. Dimensions
6. Scales
7. Grids
8. Suspended slabs
9. Position of reinforcement
10. Scheduling
11. Nominal sizes of bars, lengths, and overall dimensions
12. Laps, anchorage, and curtailment of bars
Borders
All drawings should have 20 mm filing borders on the left-hand side. Elsewhere, the borders should be 20 mm (minimum) for A0 and A1 and 10 mm (minimum) for A2, A3 and A4. The borderline should be 0.5 mm thick.
Table 1: Paper sizes in tabular form
Title Block
The title block should be at the bottom right corner of the drawing sheet (see Figure). Panel A should include at least the following information:
a) Office project number
b) Project title
c) Drawing number with provision for revision suffix
d) Drawing title
e) Office of origin
f) Scales
g) Drawn by (name)
h) Checked by (name)
i) Date of drawing.
Immediately above panel A, a box should be provided to contain the necessary reference to relevant bar and fabric schedule page numbers. Panel B may be developed vertically from panel A to include such information as revisions working up from panel A and notes (working down from the top of panel B).
Notes on reinforcement drawings should include cross-references to general arrangements (GAs), a list of abbreviations, the grade of concrete, specified covers, and the relevant ‘schedule refs’.
Thickness of Lines
The varying thickness of lines is necessary to ensure clarity of drawings. While working with AutoCAD the thickness of lines is set up in the layers properties manager tab of the software as shown below:
The following are best practice thicknesses of lines for reinforced concrete drawings:
General concrete outlines and general arrangement drawings: 0.35 mm (0.15 mm often desirable)
Concrete outlines on reinforcement drawings: 0.35 mm (0.15 mm often desirable)
Main reinforcing bars: 0.7 mm (0.25 mm often desirable)
Links: 0.35 – 0.7 mm (0.25 mm often desirable)
Dimension lines and centerlines: 0.25 mm (0.05 mm often desirable)
Call-up line: (0.09 mm often desirable)
Lettering
Capital letters (upper case letters) should be used for all titles and subtitles while small letters (lower case letters) can be used for notes.
Dimensions
Dimensions should be written in such a way that they can be viewed from the bottom line or right-hand side of the drawing. They should, where possible, be kept clear of structural detail and placed near to and above the line, not through the line (See Figure 5).
The recommended unit for site layout and levels is metre (m). For detailing reinforcement and specifications of small sections, it should be millimetre (mm). It is not necessary to write the mm. Dimensions should be to the nearest millimetre for both metre unit and millimetre unit.
Example;
Table 2: Units of dimensions
Scales
A sensible scale should be adopted for the drawings
General arrangement drawings – 1: 100 or 1: 50
Simple wall and slab details – 1: 50
More complex slab details and slabs and wall sections – 1: 20
Beam and column elevations – 1:50 or 1: 20
Beam and column sections – 1: 20 or 1: 10
Grids
Grid notation should be agreed with the architect and would normally be numbered 1, 2, 3, etc., in one direction (usually from top to bottom), and lettered A, B, C, … X, Y, Z, AA, AB, etc. (omitting I and O) in the other direction (usually from left to right). These sequences should start at the lower left corner of the grid system. Supplementary grids, if required, can be incorporated within the system and identified as follows. Aa, Ab, Ac, Ba, 2.5, 4.2, etc. See Figures 6a and 6b below for the ideal grid system and grid system in CSC Orion structural design software which is common presently. Here, the Arabic numeral is numbered from left to right while the letters are numbered from bottom to top.
Suspended floors
For suspended floors, it is necessary to show the direction of the span and indicate the thickness of the slab preferably at centre of the panels, e.g.
Position of Reinforcement
The position of reinforcement should be established by the dimensions of the faces of the concrete or the formwork. The notation for specifying the layering of reinforcement should be as follows:
Far (face) Fl (outer layer) F2 (second layer)
Near (face) N1 (outer layer) N2 (second layer)
Bottom (face) B1 (outer layer) B2 (second layer)
Top (face) T1 (outer layer) T2 (second layer)
Or
B – bottom bars B.W. – both ways
T – top bars F.F. – far face
N.T. – near top N.F. – near face
E.F. – each face N.B. – near bottom
For the arrangement of reinforcement
alternate – alt
staggered – stgd
alternate bars reversed – a.b.r.
Detailing Rules
Elementary analysis of structural behaviour of reinforced concrete that affects detailing
A structure can be subject to any of the following conditions regardless of its structural material:
Bending
Buckling
Stretching
Twisting
Shearing
The forces set up in the members by these conditions are tension, compression, torsion, and shear. The majority of reinforced concrete members are subject to several of the conditions noted above rather than one condition only.
Foundations are mostly subject to bending and shearing, while shearing is usually the critical condition for depth. But also, where tied together by beams, stretching in the beam may occur.
Retaining walls are mostly subject to bending and shearing, while bending is usually the critical condition for thickness. But also, where subject to loading from above, buckling may occur.
Columns are mostly subject to bending and buckling, while buckling is usually the critical condition for size. But also, where subject to side pressure from wind loading, they can be subject to shearing.
Beams are mostly subject to bending and shearing, while bending is usually the critical condition for depth. But also, if slender in relation to their span, they can be subject to buckling and if subject to heavy eccentric loadings, they can be subject to twisting.
Slabs are mostly subject to bending this being critical in determining depth. In the case of flat slabs, the shearing at column heads can be critical, and in two-way spanning slabs, twisting can occur at the corners of slab panels.
Shells are mostly subject to buckling and/or stretching and these dictate the thickness. Where concentrated loads occur, they may be subject to shearing and where openings occur, they may be subject to twisting.
Nominal sizes of bars, length, and overall dimensions, and quantity
The nominal size is the diameter of a circle with an area equal to the effective cross-sectional area of the bar or wire. The actual maximum size is due to the threading of the bar. These are in accordance with BS 4449.
Table 3: Nominal sizes of bars
The standard length of bars available from stock for 12 and above is 12 m. For sizes 8 and 10, the stock sizes are 8, 9, or 10 m. The maximum length of bar available and transportable is 18 m.
See Reinforcement conversion table
Number of reinforcement bars in 1 ton of steel
8 mm – 210 pieces
10 mm – 134 pieces
12 mm – 93 pieces
16 mm – 52 pieces
20 mm – 34 pieces
25 mm – 21 pieces
32 mm – 14 pieces
40 mm – 9 pieces
Important Detailing Guidelines
Important rules are followed in reinforcement detailing and they are very necessary to be followed accurately. For instance, the following rules may apply where proper;
1. Main reinforcement bars come in a shorter direction while the distribution bars come in a longer direction for slabs.
2. Plans, elevations, and sections should be clearly defined.
3. Sections through plans should always be taken looking a) to the left and b) upwards.
4. Sections through elevations should always be taken looking a) to the left and b) downwards.
5. Different parts of the drawings have different line thicknesses as shown above in thicknesses of lines.
6. Beams should be referenced in their likely order of placing to make the steel reinforcement fixers’ job straighter forward.
7. Each drawing should start from bar mark 1.
8. Cover should be shown on the section where it varies from one unit to another on a drawing.
Applicable cover to all reinforcements in millimetres
Table 4: Cover to reinforcement
9. Certain standard abbreviations may be used in calling up reinforcement e.g for the type of reinforcement, we have
Mild steel round bars – R
High tensile round bars and high tensile square twisted bars – Y or T
Other types – X
10. The bar mark and size should be grouped into a single numeral where the diameter precedes the bar mark, thus:
Table 5: Bar mark nomenclature
11. Spacing of reinforcement should be in 25 mm increments from 50 to 200 mm and 50 mm increments above this up to a maximum of 350 mm as follows: 50, 75, 100, 125, 150, 175, 200, 250, 300, 350.
12. Nominal bar diameter used should be 6, 8, 10, 12, 16, 20, 25, 32, and 40 mm.
13. Bar should be called up in the following manner:
- No required/type of steel/diameter or size/bar mark/spacing required (i.e. wall, slab, or stirrups)/location/any special considerations, e.g. for slab we have 20 R1205 – 150T (a.b.r). This signifies that 20 mild steel bars of 12 mm diameter, bar mark 5, are required at 150 mm centres in the top of the slab, each alternate bar being reversed.
14. Where only one dimension is used in a note, e.g. calling up blinding, a kicker, packing etc. mm should be used for example: 75 mm kicker.
Presentation of Bars
When the structural design of these elements is carried out by the structural designer, he presents the areas of reinforcement as follows:
Beams and columns: 3-Y1601
Slabs, footings, walls and stairs: 33 – Y1202 – 200 mm C/C
These areas are usually obtained from such tables below as applicable to BS 8110 and EC 2.
Table 6: Areas of bar spacing for specific bar groups – beams and columns, piles
Table 7: Areas of bar spacing – slabs, walls, pad foundations
Laps, curtailment, and anchorage of bars based on (EUROCODE)
General
Bars may be set out individually, or grouped in bundles of two or three in contact. Bundles of four bars may also be used for vertical bars in compression, and for bars in a lapped joint. For the safe transmission of bond forces, the cover provided to the bars should be not less than the bar diameter or, for a bundle, the equivalent diameter (≤ 55 mm) of a notional bar with the same sectional area as the bundle. Requirements for cover with regard to durability are given in Chapter 31 of EC2. Gaps between bars (or bundles) generally should be not less than the greatest of: (dg + 5 mm) where dg is the maximum aggregate size, the bar diameter (or equivalent bar diameter for a bundle), or 20 mm. Details of reinforcement limits are given in Table 4.28 of EC 2. At intermediate supports of continuous flanged beams, the total area of tension reinforcement should be spread over the effective width of the flange, but a part of the reinforcement may be concentrated over the web width.
Ties (Stirrups) in Structures
Structures not specifically designed to withstand accidental actions should be provided with a suitable tying system (see Figures 9 and 10), to prevent progressive collapse by providing alternative load paths after local damage.
Where the structure is divided into structurally independent sections, each section should have an appropriate tying system. For instance, the typing system is provided in structures for one or many of the following reasons:
- To hold the main reinforcement bars together.
- To prevent the structures from buckling.
- To protect reinforced concrete structures from collapsing during earthquakes.
- To prevent shear failure in members.
The reinforcement providing the ties may be assumed to act at its characteristic strength, and only the specified tying forces need to be taken into account. Reinforcement required for other purposes may be considered to form part of, or the whole of the ties. Details of the tying requirements, as specified in the UK National Annex, are given in Table 4.29 of EC2.
Anchorage and Lap Lengths
At both sides of any cross-section, bars should be provided with an appropriate embedment length or other form of end anchorage. For bent bars, the basic tension anchorage length is measured along the centreline of the bar from the section in question to the end of the bar, where:
lbd = α1α2α3α4α5 lb,rqd ≥ lb,min
As a simplified alternative, a tension anchorage for a standard bend, hook, or loop may be provided as an equivalent length lb,eq = α1 lb,rqd (see figure 11 here),
where α1 is taken as 0.7 for covers perpendicular to the bend ≥ 3ϕ Otherwise α1 = 1.0.
Bends or hooks do not contribute to compression anchorages. Details of anchorage lengths are given in Table 4.30. Laps should be located, if possible, away from positions of maximum moment and should generally be staggered (see Figure 12).
Details of lap lengths are given in Table 4.31 of EC2. The radius of any bend in a reinforcing bar should conform to the minimum requirements of BS 8666 and should ensure that failure of the concrete inside the bend is prevented. A link may be considered fully anchored, if it passes around another bar of not less than its own diameter, through an angle of 90o, and continues beyond the end of the bend for a minimum length of 10 diameters ≥ 70 mm.
Details of bends in bars are given in Table 4.31 of EC2. Additional rules for large diameter bars (˃ 40 mm according to the UK National Annex) and bundles are given in Table 4.32 of EC2.
Curtailment of Reinforcement
In flexural members, such as beams, it is generally advisable to stagger the curtailment points of the tension reinforcement as allowed by the bending moment envelope. Bars should be curtailed in accordance with the rules set out in Table 4.32 of EC2. Except at end supports, every tension bar should extend beyond the point at which in theory it is no longer needed for flexural resistance for a distance not less than al. The bar should also extend beyond the point at which it is fully required to provide flexural resistance for a distance not less than al + lbd. At a simple end support, the bars should extend for the anchorage length lbd necessary to develop the force ΔFtd.
Beam Curtailment Guidelines
Slab Curtailment Guidelines
Laps, curtailment and anchorage of bars (BS 8110)
General
For the safe transmission of bond forces, the cover provided to the bars should be not less than the bar size or, for a group of bars in contact, the equivalent diameter of a notional bar with the same total cross-sectional area as the group. Gaps between bars (or groups of bars) generally should be not less than the greater of (hagg + 5 mm), where hagg is the maximum size of the coarse aggregate, or the bar size (or the equivalent bar size for bars in groups).
Ties (Stirrups) in Structures
For robustness, the necessary interaction between elements is obtained by tying the structure together. Where the structure is divided into structurally independent sections, each section should have an appropriate tying system. In the design of ties, the reinforcement may be assumed to act at its characteristic strength, and only the specified tying forces need to be taken into account. Reinforcement provided for other purposes may be considered to form part of, or the whole of the ties. Details of the tying requirements in BS 8110 are given in Table 3.54.
Anchorage and Lap lengths
Laps in fabric should be layered or nested to keep the lapped wires or bars in one plane. BS 8110 requires that, at laps, the sum of all the reinforcement sizes in a particular layer should not exceed 40% of the breadth of the section at that level. When the size of both bars at a lap exceeds 20 mm, and the cover is less than 1.5 times the size of the smaller bar, links of size not less than one-quarter the size of the smaller bar, and spacing not greater than 200 mm, should be provided throughout the lap length.
Curtailment of Reinforcement
In flexural members, such as beams, it is generally advisable to stagger the curtailment points of the tension reinforcement as allowed by the bending moment envelope. Curtailed bars should extend beyond the points where in theory they are no longer needed, in accordance with certain conditions.
Beams curtailment guidelines
As1 = area of reinforcement at Span L1; As3 = area of reinforcement at adjoining support.
For the cantilever, a = ((2M2/Gk) + d) where Gk is the characteristic dead load on span L1 and M2 is the design ultimate moment at the centre-line of support for cantilever, L2 and d is the effective depth of the reinforcement.
Slab Curtailment Guidelines
In Figure 19 above, a = [l2 (nl2/gkl1) + d] where n is the design ultimate load per m2 on the cantilever, gk is the characteristic dead load per m2 on the span l2, and d is the effective depth of the reinforcement. If the slab adjacent to the cantilever spans in diameter parallel to the beam, a = [l2 (n/gk)0.5 + d].
Sample of Reinforced Sections
Scheduling of Steel Reinforcement
After accurate reinforcement detailing comes the bar bending schedule (BBS) or bar bending schedule table (BBST). BBS is the method by which bar or fabric reinforcement is ordered for quantity, shape, and size while BBST is a list of reinforcement bars in a tabular form (see Tables) which is extracted from structural drawings given specific information on the location of bars, the shape of bending with sketches, lengths of each, total length and weight, etc.
BBST samples
Accurate preparation of BBST requires first the knowledge of the bar shape code and having it handy preferably in soft copy or reproduced as attached below.
Then the following rules should be followed scrupulously.
1. The reinforced bars used in the boundary structure should be grouped for each element and listed separately for each floor.
2. Reinforced bars should be lifted in numerical order according to the bar mark.
3. The types and shape of the bar should follow BS shape code BS 8666.
4. The cutting length and bending calculation should be done separately and not included in a detailed tabular list.
5. Each bundle of bars must be labelled according to the structural detail drawing for easy identification during placement.
6. The label of bar mark reference attached to the bundle bar must relate uniquely to an appropriate set or group of bars of defined shape, size, length, and type used in the work.
Information on the bar schedule sheet
Member: The location in which the bar is used
Bar mark: the number of the bar in its sequence in the detail drawing.
Type and size: the type of steel used and its diameter
No of members: the number of identical units which occur in the detail drawing
No in each: the number of bars of this mark which occur in each member.
Total number: the number of members x the number of bars in each
Length of each bar: being the overall length in metres and millimetres allowing for bending tolerances etc. This should always be rounded up to the nearest 5mm.
Shape: This shows the bending of the bar with critical dimensions indicated. The closing dimension is omitted to allow for bending tolerances etc.
Shape code: the number of particular bent shapes as listed in BS 8666
Dimension columns: These relate to the dimension letters as shown on the shape code in BS 8666
In general, all dimensions relate to the outer limits of bar shapes, the only exception being for closed links and stirrups which give internal dimensions since these are critical in determining steel covers.
All spacer bars for beams steel, chairs for top steel in slabs, U-bar spacers for walls, etc must be detailed and scheduled as they are the detailer’s duty.
A fabric reinforcement schedule sheet should be kept separate from bar schedules and should contain the following information:
Location: slab, wall, or footing in which the sheet occurs.
Mark: the mark number of the sheet in its sequence on the detail drawing e.g. A1, A2, B1, B2, etc
Ref. No.: the reference number for its mesh size and weight as laid down in BS 1221 —PUT CURRENT EQUIVALENT
No of sheets: the number of sheets required. It should be remembered that mesh comes in sheet or roll form and that maximum manufactured sizes cannot be exceeded.
Length and width: These are both self-explanatory.
Bend or cut: This indicates in sketch form any bend, holes, etc. required on the sheets.
BBST enables the easy extraction of this information in addition to the weight per unit length of the bars for practical application purposes.
Note:
a. It should be remembered that fabric sheets should overlap on each side by at least one mesh size so that adjoining sheets can be tied together e.g where a mesh size of 100 mm x 200 mm is used, the laps should be 100 mm and 200 mm at the respective edges.
b. Bar lengths should remain within easily manageable sizes, where possible, and must not exceed the maximum lengths produced by steel reinforcement manufacturers;
b1. Approximately 9 m for bars up to 12 mm diameter
b2. 12m for bars up to 20 mm diameter and
b3. 14 m for bars above 20 mm diameter
c. Bar numbers should run in numerical sequence and should not be repeated for separate numbers.
d. Bar bending should be as simple as possible using straight in preference to cranked bars since bending of steel leads to high cost.
e. In scheduling, the bars (that is, type and size of rebars) are separated from the mark number such as Y20 01 instead of Y2001 in calling out. In this case, Y20 01 becomes bar mark 1 type and size Y20.
f. The shape of each individual bar should be shown alongside that bar on the schedule and not called up ‘as above’ etc.
BBST is important in the following ways
1. It aids steel suppliers to easily supply the quantity of steel required.
2. It enables steel fixers who may not be able to interpret structural drawings to prepare reinforcement bars to cut, shape, and bend on-site with minimal guidance.
3. It reduces the time required to guide these workers.
4. It aids quantity surveyors in easily extracting the quantity of reinforcement required to prepare a bill of quantities.
5. It helps to eliminate errors and wastages involved in cutting and bending of reinforcement bars.
6. It helps to foster quality of work.
7. It helps in reinforcement auditing in order to checkmate theft.
8. With BBST, cutting and bending can be done offsite and transported to site.
Reinforcement Placement Rules
Lapping/Lapping length calculation
Lapping in reinforcement should be at the zone where the point of contraflexure or point of zero moments occurs.
Slab overlap = 60 D to 70 D
Beam overlap:
In compression zone = 25 D
In tension zone = 50 D
Column overlap = 50 D to 60 D
Bend length
Column bend length at the junction where it sits on the footing mat = 9 D to 16 D
Where D = diameter of bar
Approximate percentage of reinforcement in structural members in terms of volume of concrete by Prof B.N. Dutta
Table 17: Percentage of reinforcement by volume of concrete
Important Rules in Reinforcement Placement
1. Place reinforcement in such a way that concrete and poker vibrators can pass especially in beams and columns. The difference between reinforcement bars should be a minimum or maximum size of aggregate being used (hagg) + 5 mm.
2. If the number of rebars in a 225 mm width beam which is common is more than 4 Y16 bars for instance at the top or bottom of the bar, spacer bars should be used to separate them. See the example of how reinforcement should be placed assuming we have 6 Y16 reinforcement at the bottom of the beam.
3. Always specify beam sizes in structural drawings or ensure that it is specified. To calculate stirrups (links) size, remove the concrete covers such as (20mm, 25mm, 40mm, 50mm) twice from the depth and width of the column or beam, then find the sum of twice the remaining depth and twice the remaining width and add additional 75 mm to 100 mm (or 12 x ϕ (diameter of bar)) as link anchorage. Then bend the link appropriately. When placing links, ensure that you alternate the anchor joints as shown below.
4. For beams that support a cantilever, just as the slab counterpart, the main reinforcement should be at the top.
5. In the slab, ensure that the main reinforcement is placed at the bottom (BB) along the shorter direction in the span, while the distribution reinforcement comes near the bottom (NB) or bottom top (BT). At the beam support, the main slab reinforcement should be at the top-top crossing over the topmost beam reinforcement, while the near top (NT) or top bottom (TB) can come under the topmost beam reinforcement. Note that in some situations where the shorter span of one panel of slab adjoins the long span of another panel, the main reinforcement along the shorter direction of the one slab, if it continues in the longer span of the adjoining slab should become distribution or secondary reinforcement in the adjoining slab. Otherwise, terminate the main reinforcement and then provide lap and secondary reinforcement for the adjoining panel. Endeavour that you don’t change the orientation of reinforcement.
6. Endeavour to understand the language of the steel fixers and be able to interpret your details to their clear understanding for accurate work.
7. The length of the return or anchor bars at the edge of the slab panel which is meant to take care of the moment associated with the fixity of the slab is a function of the span of the slab panel. The length should be within the range of 0.25 to 0.33 times the length of the slab panel in the direction of anchorage.
8. At cantilevers, the return anchorage bar length should be within the range of 1.2 to 1.5 times the length of the cantilever panel.
9. Ensure that the rules above are properly followed. There is no room for forgiveness when there is an error that can still be amended because a neglected error can be devastating Internal stresses do neither respect nor condone error.
Common errors to avoid during reinforcement placement
1. Do not lap bars are the middle of the slab.
2. Do not lap bars at beam top support.
3. Main bars in the slabs shall not be less than 10 mm based on code requirements. However, where uncertainty abounds about bar yield strength, 12 mm can be used instead.
4. When the length of the beam or slab is more than the standard 12 mm, the lapping length must be at the edge and not in the middle.
5. Important checklist for good practice during reinforcement placement.
6. Ensure that bar diameter on placement is the same as that in the schedule and structural drawings.
7. Reinforcement must be clean of mud, oil, paint, and any other liquid.
8. Ensure that end anchorages are good.
9. Ensure that column lapping extensions are good.
10. Ensure that the bar return length at cantilever sections is a minimum of 1.2 – 1.5 times the length of the cantilever.
11. Reinforcement chairs should be made with a minimum of 12 mm bar.
12. Spacing of chairs should be per 1 m or 1 no. per 1 m2.
13. Ensure a minimum number of bars in a square column is 4 and in a circular column, 6.
14. Ensure that the return bars at the edge of the slab are a minimum of ¼ (15%) of the length of the adjoining span.
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References
1. Reinforced concrete detailers manual by Brian W. Boughton, Erith College of Technology (third edition)
2. Reynolds, C.E., Steedman, J.C. And Threlfall, A.J. (2008). Reynolds’s Reinforced Concrete Designer’s Handbook. 11TH Edition. Taylor & Francis 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN
3. ISTRUCTE/Concrete Society (2006). Standard Method of Detailing Structural Concrete A manual for best practice (3rd edition). The Institution of Structural Engineers 11 Upper Belgrave Street, London SW1X 8BH, United Kingdom
4. Fapohunda, C.A. (2019): Limit State Design of Reinforced Concrete Structural Elements. 1st edition. Pęlikọṣ Publishers.
5.. Arya, C. (2009): Design of Structural Elements. 3rd edition. Taylor & Francis 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN.
Recommendation for further study
Chapter 31 of EC2
Table 4.31of EC2
Table 4.28 of EC2
Table 4.32 of EC2
Table 4.29 of EC2
Details of reinforcement limits are given in Table 3.53 for BS 8110, and Table 3.59 for BS 5400.
Details of the tying requirements in BS 8110 are given in Table 3.54.
Details of anchorage lengths, local bond stresses, and bends in bars are given in Tables 3.55 and 3.59, for BS 8110 and BS 5400 respectively
Details of lap lengths are given in Tables 3.55 and 3.59 for BS 8110 and BS 5400 respectively
Details of the general curtailment requirements in BS 8110 are given in Table 3.56.
