The phrase "which I joined" is a correct and usable part of a sentence in written English.
It can be used in various contexts to describe an action that has already taken place in the past. For example, "I found an organization called the ABC club, which I joined last month."
I too belong to the hopeful tribe of the personally trained, which I joined back in 2002, when I needed to lose some 50 pounds.
The members of this walking group, which I joined (admittedly reluctantly) about 15 years ago, have become more than dear friends.
At Hobart and William Smith Colleges in Geneva, N.Y., which I joined in 1988 as assistant professor in the religious studies department, the attitudes were somewhat different.
The Sultan's army, which I joined in the southern state of Oman, was being heavily outnumbered by the Marxist People's Front when I arrived.
A feeling of glee seized the group, which I joined on the excursion: the park must be filled with Randel monuments!
Typically, she also took part in a Yale performance of the complete Façade, in which I joined her as a speaker.
The morning on which I join the hunt – following on foot with local supporter David Hicks – is a significant one.
Now there's a Facebook group calling for the free 'b' service to be scrapped, which I've joined.
"Greeted with vociferous booing", he recalled of a performance of Die Walküre at Bayreuth, "in which I enthusiastically joined".
There is also a daily sunset yoga class to help surfers stretch after a hard day in the water, which I'd joined shortly after my arrival.
I found it unfair of Glauber to have left me on the ground that I was afraid of everything, since we'd met at Group: a group for people suffering from general anxiety disorder, which I'd joined after dropping out of the group for hypochondriacs, because it didn't encompass all my worries.
