Could a time-domain reflectometer, with no access to earth-ground, indicate if a long-wire is attached to the end of a long steel beam?
Time Domain Reflectometry works on the principals of transmission lines to find reflections and use the time of the signal from its reflection to find the length of the cable. A steel beam is not a transmission line (and cannot be made into a transmission line easily or on it's own as a transmission line needs at minimum a ground plane or secondary conductor) and would quickly attenuate any signal and not provide the necessary propagation needed to find the reflection of the signal.
Usually handheld TDR's that work with wire have a characteristic impedance, it would also be difficult to match the impedance since most cables have a set characteristic impedance of say 50 or 75Ω (there are others). One would need to match the characteristic impedance of the cable to the steel beam (with added conductor) and even then it could be impossible to match the impedance to whatever the cable of the TDR is