BS8666 Bends and Shapes: K B Rebar Limited

Steel Reinforcement For Concrete - BS 8666:2005

British Standard BS 8666 the 'Specification for scheduling, dimensioning, bending and cutting of steel reinforcement for concrete'.

The previous standard (BS 4466) is available here for reference purposes.

Table 1 - Radius Of Bending

Radius of bending:- maximum values requiring bending

Bar Size	6	8	10	12	16	20	25	32	40
Radius (m)	2.5	2.75	3.5	4.25	7.5	14.0	30.0	43.0	58.0
Note. Bars to be formed to a radius exceeding the above dimensions will be supplied straight.

Table 2 - Minimum scheduling radii, former diameters and bend allowances

Nominal size of bar, d	Minimum radius for scheduling, r	Minimum diameter of bending former, M	Minimum end projection, P
Nominal size of bar, d	Minimum radius for scheduling, r	Minimum diameter of bending former, M	General (min 5d straight), including links where bend ≥ 150°	Links where bend < 150° (min 10d straight)
mm	mm	mm	mm	mm

6	12	24	110*	110*
8	16	32	115*	115*
10	20	40	120*	130
12	24	48	125*	160
16	32	64	130	210
20	70	140	190	290
25	87	175	240	365
32	112	224	305	465
40	140	280	380	580
50	175	350	475	725

* The minimum end projections for smaller bars is governed by the practicalities of bending bars. Note 1 Due to 'spring back' the actual radius of bend will be slightly greater than half the diameter of former. Note 2 BS 4449:2005 grade B500A in sizes below 8mm does not conform to BS EN 1992-1.1:2004.

Table 3 - Standard shapes, their method of measurement and calculation of length

Method of measurement of bending dimensions		Total length of bar (L) measured along centre line


		A

		A Stock lengths. See Note 4.

		A+(B)- 0.5r-d Neither A nor B shall be less than P in Table 2

		A+(B)- 0.43R - 1.2d Neither A nor B shall be less than P in Table 2 nor less than (R + 6d)

		A + 0.57B+(C)- 1.6d B shall not be less than 2(r + d). Neither A nor C shall be less than P in Table 2 nor less than (B/2 + 5d). See Note 3.
	Key 1 Semi-circular

		A + (C)- 4d Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A+(C) Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A + B + (C)- r - 2d Neither A nor (C) shall be less than P in Table 2.

		A +B +C +(D) -1.5r - 3d C shall not be less than 2(r + d). Neither A nor (D) shall be less than P in Table 2. (D) shall not be less than C/2 + 5d.
	Key 1 Semi-circular

		A + B + (C) - r - 2d Neither A nor (C) shall be less than P in Table 2.

		A + B + (C) A and (C) are at 90° to one another.

		A + B + (E) Neither A nor B shall be less than P in Table 2. If E is the critical dimension, schedule as 99 and specify A or B as the free dimension. See Note 1.

		A + B + (C) Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A +B +(C) -0.5r -d Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A +B +(C) -0.5r -d Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A + B + (C) -r -2d Neither A nor (C) shall be less than P in Table 2. See Note 1.

		A +B +C +(D) -1.5r -3d Neither A nor (D) shall be less than P in Table 2.

		A +B +C +(D) -1.5r -3d Neither A nor (D) shall be less than P in Table 2.

		2A + 1.7B + 2(C) -4d A shall not be less than 12d + 30mm. B shall not be less than 2(r+d). (C) shall not be less than P in Table 2, nor less than B/2 + 5d. See Note 3.
	Key 1 Semi-circular

		A +B +C +(E)-0.5r -d Neither A nor (E) shall be less than P in Table 2. See Note 1.

Method of measurement of bending dimensions		Total length of bar (L) measured along centre line


		A +B +C +(E) -0.5r -d Neither A nor (E) shall be less than P in Table 2. See Note 1.

		A +B +C +(D)-r -2d Neither A nor (D) shall be less than P in Table 2. See Note 1.

		A +B +C +D +(E) -2r -4d Neither A nor (E) shall be less than P in Table 2.
	May also be used for a flag link viz:

		A +B +C +D +(E) -2r -4d Neither A nor (E) shall be less than P in Table 2.

		A +2B +C +(E) Neither A nor (E) shall be less than P in Table 2. See Note 1.

		2A +B +2C +1.5r -3d (C) and (D) shall be equal and not more than A nor less than P in Table 2.
	Where (C) and (D) are to be minimized the following formula may be used: L = 2A + B + max(21d, 240)

		2(A +B +(C)) -2.5r -5d (C) and (D) shall be equal and not more than A or B nor less than P in Table 2.
	Where (C) and (D) are to be minimized the following formula may be used: L = 2A + 2B + max(16d, 160)

		A +B +C +(D) +2(E) -2.5r -5d (E) and (F) shall be equal and not more than B or C, nor less than P in Table 2.

		2A +3B +2(C) -3r -6d (C) and (D) shall be equal and not more than A or B nor less than P in Table 2.
	Where (C) and (D) are to be minimized the following formula may be used: L = 2A + 3B + max(14d, 150)

		A +B +C +2D +E +(F) -3r -6d Neither A nor (F) shall be less than P in Table 2. See Note 2.

		A See clause 10.

		π(A - d) + B Where B is the lap.

		Cπ(A-d) C = number of turns
	Where B is greater than A/5 this equation no longer applies, in which case the following formula may be used: L = C((π(A -d))² + B²)^0.5

		A +2B +C + (D) -2r -4d Isometric sketch Neither C or (D) shall e less than P in Table 2.

	All other shapes	To be calculated See Note 2.
	Where standard shapes cannot be used. No other shape code number, form of designation or abbreviation shall be used in scheduling. A dimensioned sketch shall be drawn over the dimension columns A to E. Every dimension shall be specified and the dimension that is to allow for permissible deviations shall be indicated in parenthesis, otherwise the fabricator is free to choose which dimension shall allow for tolerance.

The values for minimum radius and end projection, r and P respectively, as specified in Table 2, shall apply to all shape codes (see 7.6).

The dimensions in parentheses are the free dimensions. If a shape given in this table is required but a different dimension is to allow for the possile deviations, the shape shall be drawn out and given the shape code 99 and the free dimension shall be indicated in parentheses.

The length of straight between two bends shall be at least 4d, see Figure 6.

Figure 4, Figure 5 and Figure 6 should be used in the interpretation of ending dimensions.

Note 1 The length equations for shape codes 14, 15, 25, 26, 27, 28, 29, 34, 35, 36 and 46 are approximate and where the bend angle is greater than 45�, the length should be calculated more accurately allowing for the difference between the specified overall dimensions and the true length measured along the central axis of the bar. When the bending angles approach 90�, it is preferable to specify shape code 99 with a fully dimensioned sketch.

Note 2 Five ends or more might be impractical within permitted tolerances.

Note 3 For shapes with straight and curved lengths (e.g. shape codes 12 13, 22, 33 and 47) the largest practical mandrel size for the production of a continuous curve is 400 mm. See also Clause 10.

Note 4 Stock lengths are available in a limited numer of lengths (e.g. 6m, 12m). Dimension A for shape code 01 should be regarded as indicative and used for the purpose of calculating total length. Actual delivery lengths should be by agreement with supplier.

Table 4 -

BAR MASS per linear metre (kg/m) :-

50mm: 15.413kg/m	40mm: 9.864kg/m	32mm: 6.313kg/m	25mm: 3.854kg/m	20mm: 2.466kg/m
16mm: 1.579kg/m	12mm: 0.888kg/m	10mm: 0.616kg/m	8mm: 0.395kg/m	6mm: 0.222kg/m

Excerpts From Section 8 - Drawing Forms for Scheduling and Dimensioning

Figure 4 - Dimensioning of an acute angle

8.6 If the angle between two portions of the shape meeting at a bend is not a right angle, it shall be defined by co-ordinates and not by degress of arcs or radians.

8.7 When dimensioning an acute angle the tangential lines shown in Figure 4 shall be used.

Figure 5 - Dimensioning of cranked bars

8.8 Apart from shape code 98, bars bent in planes shall be sketched isometrically or shown in two elevations, using first angle projection. The words "bent in two planes" or "isometric sketch" shall appear on the schedule adjacent to the sketch.

8.9 The overall offset dimension of a crank shall be not less than twice the size of the bar. The angled length (see Figure 5) shall be not less than :

a) 10d for bars not exceeding a nominal size of 16mm

b) 13d for nominal sizes greater than 16mm

	Figure 6 - Example of bar with more than one bend
		8.10 For all shapes with two or more bends in the same or opposite directions (whether in the same plane or not), the overall dimension given on the schedule shall always include a minimum straight of 4d between the curved portion of the bends, as shown in Figure 6. The value of x in Figure 6 shall be not less than the following:
			a) 10d for bars not exceeding a nominal size of 16mm b) 13d for nominal sizes greater than 16mm
NOTE The minimum values of x are expressed in terms of the nominal size of the reinforcement. In practice, rolling and bending tolerances, and the fact that the circumscribing diameter of deformed reinforcement may be up to 10% greater than the nominal size, should be considered.