Developing Mild Bars Alongside Prestressing Strand

[KootK]

Today I have thought a thought that I've never before thunk: when working out development lengths and lap lengths for mild rebar in pres-stressed members, does one need to somehow consider the splitting tendency created by the prestress-tendons? Here's what I've got for preliminaries:

1) If there's a code provision someplace for combining the splitting effects of prestressing and mild steel, I'm not aware of it.

2) The equation for the developing prestresssing is independent of things like concrete cover etc which would seem to imply that splitting is not an issue.

3) There is, of course, the Hoyer effect which would seem to imply that there is, at the least, some degree of splitting tendency.

Thoughts? The only thing that I can come up with is that prestressing strand development lengths are pretty long so maybe the splitting tendency never amounts to anything of note locally?

 

[pappyirl]

The development length calculation for prestressed strand / wire on this side of the water is similar, independent of concrete cover, section depth and provided reinforcement.

The EC2 code does give guidance on the spacing of pretensioned tendons / wires within the section, see attached. It does imply that the spacing is based on test results with respect to the anchorages. A minimum spacing from a free edge would have been useful in this regard. Typically cover to strand is more onerous than bonded reinforcement (durability and fire resistance),it is therefore embedded deeper within the section so maybe this is implied in the testing.

Cracking at the end of pretensioned members was / still is? an issue with manufacturers in applications where there is little or no mild steel provided in the anchorage zone. The Hoyer effect could be the culprit although concrete quality is always a factor.