Anchorage Length
These values are derived from the following formulae: (with Yc = 1.5)
— high bond bars, fbd = (2.25fctk 0.05)/*c where fck and fctk 0.05 are as defined in Chapter 3.1.
(3) In the case of transverse pressure p in N/mm2 (transverse to the possible plane of splitting) the values of Table 5.3 should be multiplied by | 1/(1 - 0.04 p) d 1.4 |, where p is the mean transverse pressure.
5.2.2.3 Basic anchorage length
P(1) The basic anchorage length is the straight length required for anchoring the force As.fyd in a bar, assuming constant bond stress equal to fbd; in setting the basic anchorage length, the type of the steel and the bond properties of the bars shall be taken into consideration.
(2) The basic anchorage length required for the anchorage of a bar of diameter 0 is:
Values for fbd are given in Table 5.3.
(3) For double bar welded fabrics the diameter 0 in Equation (5.3) should be replaced by the equivalent diameter 0n = 0/2.
5.2.3 Anchorage
5.2.3.1 General
P(1) The reinforcing bars, wires or welded mesh fabrics shall be so anchored that the internal forces to which they are subjected are transmitted to the concrete and that longitudinal cracking or spalling of the concrete is avoided. If necessary transverse reinforcement shall be provided.
P(2) Where mechanical devices are used, their effectiveness shall be proven by tests and their capacity to transmit the concentrated force at the anchorage shall be examined with special care.
5.2.3.2 Anchorage methods
(1) The usual methods of anchorage are shown in Figure 5.2.
(2) Straight anchorages or bends [Figure 5.2 a) or Figure 5.2 c)] should not be used to anchor smooth bars of more than 8 mm diameter.
(3) Bends, hooks or loops are not recommended for use in compression except for plain bars which may be subjected to tensile forces in the anchorage zones, for certain load cases.
(4) Spalling or splitting of the concrete may be prevented by complying with Table 5.1 and avoiding concentrations of anchorages.
Figure 5.2 — Required anchorage length e) welded transverse bar
Figure 5.2 — Required anchorage length
5.2.3.3 Transverse reinforcement parallel to the concrete surface
(1) In beams transverse reinforcement should be provided:
— for anchorages in tension, if there is no transverse compression due to the support reaction (as is the case for indirect supports, for example).
— for all anchorages in compression.
(2) The minimum total area of the transverse reinforcement (legs parallel to the layer of the longitudinal reinforcement) is |25l percent of the area of one anchored bar (Figure 5.3).
n = number of bars along anchorage length
Ast = area of one bar of the transverse reinforcement
(3) The transverse reinforcement should be evenly distributed along the anchorage length. At least one bar should be placed in the region of the hook, bend or loop of curved bar anchorages.
(4) For bars in compression, the transverse reinforcement should surround the bars, being concentrated at the end of the anchorage, and extend beyond it to a distance of at least 4 times the diameter of the anchored bar [see Figure 5.5 b)].
5.2.3.4 Required anchorage length
5.2.3.4.1 Bars and wires
(1) The required anchorage length lb,net may be calculated from:
Asreq and Asprov respectively denote the area of reinforcement required by design — and actually provided lb,min denotes the minimum anchorage length:
— for anchorages in tension
— for anchorages in compression lb,min = 0.3 lb (@ 10 0)
aa is a coefficient which takes the following values: aa = 1 for straight bars aa = 0.7 for curved bars in tension (see Figure 5.2) if the concrete cover perpendicular to the plane of curvature is at least | | in the region of the hook, bend or loop.
5.2.3.4.2 Welded meshes made of high bond wires
(2) If welded transverse bars are present in the anchorage, a coefficient | 0.7 | should be applied to the values given by Equation (5.4).
5.2.3.4.3 Welded meshes made of smooth wires
(1) These may be used, subject to relevant Standards. 5.2.3.5 Anchorage by mechanical devices
P(1) The suitability of mechanical anchorage devices should be demonstrated by an Agrément certificate.
(2) For the transmission of the concentrated anchorage forces to the concrete, see 5.4.8.1 5.2.4 Splices
P(1) The detailing of splices between bars shall be such that:
— the transmission of the forces from one bar to the next is assured;
— spalling of the concrete in the neighbourhood of the joints does not occur;
— the width of cracks at the end of the splice does not significantly exceed the values given in Section 4.4.2.1.
5.2.4.1 Lap splices for bars or wires
5.2.4.1.1 Arrangement of lapped joints
— laps between bars should be staggered and should not be located in areas of high stress, (see also Section 2.5.3, Analysis).
— laps at any one section should be arranged symmetrically and parallel to the outer face of the member,
(2) Clauses 5.2.3.2(1) to (4) are also applicable to lap splices.
(3) The clear space between the two lapped bars in a joint should comply with the values indicated in Figure 5.4.
5.2.4.1.2 Transverse reinforcement
(1) If the diameter 0 of the lapped bars is less than | 16 mm |, or if the percentage of lapped bars in any one section is less than 20 %, then the minimum transverse reinforcement provided for other reasons (e.g. shear reinforcement, distribution bars) is considered as sufficient.
(2) If 0 T I 16 mm |, then the transverse reinforcement should:
— have a total area (sum of all legs parallel to the layer of the spliced reinforcement, see Figure 5.5,) of not less than the area As of one spliced bar (CAst T 1.0 As)
— be formed as links if a r I 10 01 (see Figure 5.6) and be straight in other cases
— the transverse reinforcement should be placed between the longitudinal reinforcement and the concrete surface.
(3) For the distribution of the transverse reinforcement, 5.2.3.3(3) and (4) apply.
5.2.4.1.3 Lap length
(1) The necessary lap length is:
with:
lb net according to Equation (5.4)
- Figure 5.5 — Transverse reinforcement for lapped splices
The coefficient a1 takes the following values:
! = 1 for lap lengths of bars in compression and of lap lengths in tension where less than 30 % of the bars in the section are lapped and, according to Figure 5.6, where a @ | 10 0 | and b @ | 5 01.
a1 = 1.4 for tension lap lengths where either i) 30 % or more of the bars at a section are lapped or ii) according to Figure 5.6, if a < | 10 p I or b < | 5_p |, but not both.
a1 = 2 for tension lap lengths if both i) and ii) above apply simultaneously.
5.2.4.2 Laps for welded mesh fabrics made of high bond wires
5.2.4.2.1 Laps of the main reinforcement
(1) The following rules relate only to the most common case where laps are made by layering of the sheets. Rules for laps with intermeshed sheets are given separately from this Code.
(2) The laps should generally be situated in zones where the effects of actions under the rare combinations of loads are not more than | 80 % | of the design strength of the section.
(3) Where condition (2) is not fulfilled, the effective depth of the steel taken into account in the calculations in accordance with Section 4.3.1 should apply to the layer furthest from the tension face.
(4) The permissible percentage of the main reinforcement which may be lapped in any one section, referred to the total steel cross section is:
— 100 % if the specific cross sectional area of the mesh, denoted by As/s, is such that
— 60 % if As/s > 1 200 mm /m and if this wire mesh is an interior mesh.
The joints of the multiple layers should be staggered at 1.3 ls [ls from Equation (5.9)].
(5) The lap length is defined by:
lb from Equation (5.3) using f^ for high bond bars
As/s in mm2/m ls,min = 0.3 !2 lb (@ 200 mm (@ st where st denotes the spacing of transverse welded wires. (6) Additional transverse reinforcement is not necessary in the zone of lapping.
5.2.4.2.2 Laps of the transverse distribution reinforcement
(1) All transverse reinforcement may be lapped at the same location.
The minimum values of the lap length ls are given in Table 5.4; at least two transverse bars should be within the lap length (one mesh).
Table 5.4 — Recommended lap lengths in the transverse direction
