I have seen the Code of Hammurabi regulations on the maidservant/concubine/wife relationship which seems to suggest that they are all three very different concepts. The wife has precedence and the maidservant belongs to the wife (and may still be sold by the wife if she doesn't bear children - suggesting she does not automatically have the status of a concubine when she starts having sex with the husband). The husband cannot take a concubine while he has both a wife and a maidservant who has given him children (because that is to say his wife has given him children so he should need no concubine?).
In any case, my question is whether Abram was "forced", (whether by law or social custom) to take Hagar as his "wife" (Gen 16:3) in a legal sense (obviously as a second-tier wife/concubine). This makes a difference because as I understand it, a second-tier wife still had to be formally divorced - a process denied to Hagar when Sarai sent her away. So I'm trying to reconcile whether the wording in Gen 16:3 (l'isha - pretty basic) is the "polite jargon" way of saying, "and then they had sex", or whether it actually means she became his wife (because that's what it says). If she was a wife - even a concubine - it seems both law and custom are grossly violated in her treatment. (Which wouldn't surprise me, but my concern is with Abram's treatment of her initially, not Sarai's treatment of her later.)
So again, the question, did Abram:
a. CHOOSE to take her as a legal wife without being prescribed to do so?
b. HAVE to take her as a legal wife because of an existing law (I use the term loosely) or custom?
c. NOT take her as a legal wife and the text is a euphemism? (Do we have other biblical evidence of this that I'm just not seeing?)