I've designed a few PT slabs recently, and have battled a bit with the software, and its various tweaks. Here's what i've learned recently (if you know this stuff... sorry in advance!):
- Steps in slabs are awkward: Concept does the modelling OK and comes up with the FE units easily enough, but then it tries to get smart and figure out the sections along each design strip to be able to apply design rules and calc stresses. There are various kinds of "section trimming" methods that are available in the "design strip" manager/editor, and these can be confusing. This "trimming" can lead to bogus results or unreasonable steel/section requirements. I've had conditions where i have to check punching shear using one type of trim and tensile rebar using another type of trim. Not sure what the solution here is, but we should discuss design methodology going forward so we have some kind of standard out there.
- Setting of tendon profiles: It seems that Concept snaps tendons at the slab perimeter to slab mid-height - so no need to spec a profile point here - FYI
- Concept Rebar Design to "code": Concept can design rebar to "code" requirements(set under the "design strips"). Only problem is that when it does, you sometimes get unusual results. Like all things, we have to apply judgement to each case. In reading the manual, i noted that this option can be set to none (ie don't apply code reinforcement rules). This does NOT have the effect of leaving off the rebar, but merely stops Concept from trying to apply the "code rules" and coming up with bogus or "collated" results. It will still come up with steel requirements but only at the locations where stresses dictate - not coordinated with code rebar rules... not rocket science (i don't think)... (ps the reason they are trying to approximate the code design is to better approximate rebar quantities in their take-off - thats my take anyway...)... (pps - the manual says that this should produce results similar to v2.1)
- Notes on Design Methodology: In the overview of design in PT, i still look to deflections and top rebar requirements to adjust and "massage" tendons - also looking at mid-height prestress to check on P/A (or do a hand calc). Once the slab is behaving OK, then i would look to design strips for determining appropriate rebar requirements. As mentioned, you may need to consider 2 "trim methods" in order to determine -punching - span rebar - other min/max stress related rebar...
