Design anchorage and lap lengths to EN 1992-1-1 8.4 and 8.7, with bond stress, α1 to α6 and minimum lengths. Duplicate the calc and size your bars.
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About this Anchorage and Lap Lengths Calculator
This calculator gives the design anchorage length and the design lap length of a reinforcing bar to EN 1992-1-1 Clauses 8.4 and 8.7. It works the ultimate bond stress, the basic required anchorage length, the coefficients α1 to α6 of Tables 8.2 and 8.3, and the minimum lengths, for a bar in tension or compression.
- Detailer produce anchorage and lap lengths for a bar schedule, with the bond condition, cover and confinement taken into account rather than a blanket multiple of the diameter.
- Design engineer shorten a lap where the steel is not fully stressed, by basing the design stress on the ratio of required to provided steel.
- Site engineer check a proposed lap arrangement when the share of bars lapped at one section changes.
Every coefficient is shown with the clause it comes from, so the lengths can be traced and adjusted. It is an engineering-grade calculation on CalcTree that you can keep as a project standard.
More info on Anchorage and Lap Lengths
Ultimate bond stress
Expression (8.2) gives f_bd from the design tensile strength, the bond condition coefficient η1 and the bar diameter coefficient η2. The concrete class is chosen from the Table 3.1 classes, and the tensile strength used is not taken above the value for class C60/75, as Clause 8.4.2(2) requires. Poor bond conditions, as defined by Figure 8.2, reduce the bond stress.
Basic and design anchorage length
The basic required anchorage length of Expression (8.3) anchors the design stress in the bar, which can be the design yield strength, the yield strength reduced by A_s,req / A_s,prov, or a stress you enter. Expression (8.4) applies α1 to α5 from Table 8.2 for bar shape, cover, confinement by transverse reinforcement, welded transverse bars and transverse pressure, with the product α2 α3 α5 held to the floor of Expression (8.5). The result is not less than the minimum of Expression (8.6) in tension or (8.7) in compression.
Lap length
Expression (8.10) gives the lap length with α6 from Table 8.3, based on the percentage of bars lapped within 0.65 l_0 of the centre of the lap. For a lap, α3 is worked with the minimum transverse reinforcement of Clause 8.7.3(1), and the minimum lap length follows Expression (8.11).
Common Calculation Errors to Avoid
- Assuming good bond everywhere top bars in deep pours often fall in the poor bond zone of Figure 8.2, which cuts f_bd noticeably.
- Applying tension coefficients in compression in compression α1, α2, α3 and α5 are taken as 1.0; only α4 still applies.
- Reusing the anchorage α3 for a lap the lap uses a different minimum transverse reinforcement, so α3 for the lap differs from α3 for the anchorage.
- Ignoring the share of bars lapped α6 rises as more bars are lapped at one section, which lengthens every lap there.
- Reading c_d from the wrong figure the cover value c_d and the confinement factor K depend on the bar arrangement in Figures 8.3 and 8.4.
- Using a large bar without its extra rules bars over the size limits of Clause 8.8 and bundled bars need additional checks this page does not make.
Engineering templates
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FAQs
What is the difference between l_b,rqd and l_bd?
l_b,rqd is the basic length needed to develop the design stress through bond, from Expression (8.3). l_bd is the design anchorage length after the coefficients α1 to α5 are applied and the minimum length is enforced.
Can I reduce the anchorage length when the bar is not fully stressed?
Yes. Choose the option that reduces f_yd by A_s,req / A_s,prov, or enter the design stress directly. The basic anchorage length scales with the stress, but the minimum length still applies.
How do I pick c_d and K?
c_d is read from Figure 8.3 for the bar arrangement, and K from Figure 8.4 for the position of the transverse reinforcement. Both are inputs because they depend on the detail.
Why does the lap length grow with the percentage of bars lapped?
α6 in Table 8.3 increases with the share of bars lapped within 0.65 l_0 of the lap centre, because more laps at one section concentrate the transfer of force through the concrete.
What does the page not cover?
Anchorage by welded bars or mechanical devices, bundled bars, large bars, laps of welded mesh and the detailing of transverse reinforcement at laps are outside its scope.
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