Damaged Prestress Wire

[Zambo]

While breaking out concrete we damaged one wire (not cut just damaged)of a 7 wire strand. The strand itself belongs with a 4 strand bonded (grouted)tendon. So in effect we have damaged 50% of the prestressing steel area of 1/28 of the tendon. The Engineering Consultant now suggests that this a huge error that is almost insurmountable. Does anyone have reference to an engineering code which would allow a reduction in prestressing area due to such site difficulties.

 

[henri2]

Try ACI 318 Section 18.18.4. This is from my 95 edition. Don't have my 2002 edition around. I do not think it has changed.

 

[Ingenuity]

To add to HENRI2's reply:

ACI 318 2002 states:

18.20.4 — Total loss of prestress due to unreplaced
broken prestressing steel shall not exceed 2 percent of
total prestress.

Commentary states:

R18.20.4 — This provision applies to all prestressed concrete members. For cast-in-place post-tensioned slab systems, a member should be that portion considered as an
element in the design, such as the joist and effective slab
width in one-way joist systems, or the column strip or middle strip in two-way flat plate systems.

I have used the "2% rule" many times - sometimes a wire or two, or even a full strand may break during stressing at original construction. And during the life of the building the 'concrete coring machine' is always there to ruin your day.

I just looked at a project 2 days ago where an electrical contractor chased the underside of an existing precast/pretensioned slab panel and sawed/cut through all 7 x 1/2" strands, at MIDSPAN. Needless to say this is getting repaired with some significant $$$ being spent.