Additional Information on Lap Splices

Deemed to Comply Values for Lap Splices of Main Bars in Tension

Please refer to ARC Reinforcement Handbook Table 15

The table provides tabulated values of development length and lap
splices in flexural members, provided the following rules are observed:

The characteristic compressive strength of the concrete, ƒ’_cand the
corresponding value of the cover, c, are not less than given in the table.
For slabs and walls, the clear distance between adjacent parallel bars being
designed, over the length in which they are considered to be developing
stress or over the lap length, must not be less than 150 mm. This does not
restrict the spacing to 150 mm over the remainder of the length.
For beams and columns, at least the minimum quantity of fitments
(stirrups, ties etc) must surround the main bars being designed, and the
clear distance between adjacent parallel bars must be at least twice the
cover given in the table.

The minimum cover is from the surface of the concrete to the bar being
detailed.

Intermediate values of Lsy.t must not be interpolated. Alternative combinations
must be calculated from AS3600-2009.

For bars with more than 300 mm of concrete cast below them, the above
values must be increased by 25%.

Which Should be Used – A Tension Splice or a Compression Splice?

The simple answer is that if a bar can be in tension under one loading condition,
and change to compression under another (or vice versa), then the splice must
carry the “worst case” load. As examples, the above situation can occur when
the wind blows alternately from opposite directions, or when trucks move
across a bridge.

Lap Splices vs Overlapped Bars and Cogs vs 90° Bends

There are obviously many situations where there is no need to transfer load,
however bars need to be overlapped and tied together. In these cases the
overlap may only need to be 100-150 mm for a small bar and up to 300 mm
for a large bar. The overlap should be specified in the drawings, otherwise a
full splice may be provided, or even worse, a short overlap provided where a
full lap is essential. These overlaps can be tabulated in many cases to avoid
repetitive notes.

At the end of some bars, a 90º bend can be mistaken for a 90º hook. Without
knowing the purpose of the bend, a clear distinction often cannot be made.

Where the bar dimension appears to fit into the concrete, allowing for covers,
a 90º bend would be assumed. Where it won’t fit, then the detail should be
revised to avoid the bar-end from sticking out of the concrete.