pre-stressed concrete elements

huangyhg

pre-stressed concrete elements.
anyone with some opinions how best to determine the tendons and/or reinforcing, size, distribution and placement of an existing 'pre-stressed' concrete memeber.  there is no historical info., ie manufacturer, designer, shop drawings etc.  interested in investigative techniques both non destructive and destructive given that the architectural dwgs, say 'prestressed giant tee's' ... the 'giant' is the 1960's architects lingo by the way?
non-destructive: pachometer to locate and size long't rebar/strands and shear stirrups, if any. gpr (ground penetrating radar) may work depending on the spacing/congestion of rebar/strand and access to the t. gpr will be difficult to determine diameter of strand/rebar. x-ray is a pain as you will need access to both sides of element, and it is hazardous.
always best to verify the non-destructive testing results with some selected 'invasive probes' - chip the cover concrete from the stem of the t's say at 1/3rd point of span and verify strand dia, spacing etc.
i have done this on several 'old' projects using pre- and post-tensioned members. for a few $, invasive probes can give you a lot of info.