Bar Tension Lap and Anchorage

The most important factor for successful detailing of concrete structures is ensuring that all stresses can be transferred from concrete to steel.

The information in this ARC - Reinforcement Handbook must be read in conjunction with, and with a full understanding of, the principles of reinforced concrete design and detailing given in AS3600.

In general, the parameters used to calculate the anchorage and lap lengths are given with the tables. Where there are differences between our ARC - Reinforcement Handbook and values obtained from other sources, the user should check the parameters and recalculate as seen fit.

Lengths are based only on full yield stress of the steel. It is most unwise to specify lap or anchorage lengths for a lower steel stress. For laps, this practice is not permitted in AS3600-2009.

Anchorage and Development Length of Deformed Bars in Tension, Lsy.t

The anchorage and lap length formula in AS3600, Clause 13.1.2, for a straight
piece of deformed bar in tension is:

P40_formula

Where

k1 ... is a depth factor equal to 1.3 for a horizontal bar with more than 300mm of concrete cast below the bar; or 1.0 otherwise

k2 ... is a factor relating to bar diameter and equal to (132 - db)/100

k3 ... is a factor relating to cover and bar spacing and equal to 1.0 – 0.15(cd - db)/db (within the limits of 0.7 = k3 = 1.0); where cd = a dimension as shown in AS3600 Fig 13.1.2.3(A)), see below:

Cd Definition

 

This expression shows that anchorage length:

• increases as yield stress of the bar increases
• increases as bar diameter increases
• decreases as bar spacing increases
• decreases as bar cover increases, and
• decreases as concrete grade increases

Calculations will show a dramatic reduction in the anchorage length when
cover or spacing is increased.

To assist with anchorage you can use a standard hook to provide end anchorage
of a bar where there is insufficient embedment for a straight length to develop
its design stress. A hook or cog reduces the development length by 50%.

Table: Tension Laps ≤ 300mm concrete cast below

Table: Tension Laps > 300mm concrete cast below