How can I have my shell always start in a certain directory that is not my home directory

I've tried putting

cd /Users/my_name/my_directory/structure

in both .bashrc and .bash_login but neither works, i.e. when I open a new terminal window I am in my home (/Users/my_name/) directory.

No error messages, just not cd'd into the directory as hoped when starting a new terminal window.

As Gerry mentioned, .bashrc is not read by login shells. New tabs are login shells by default in Terminal and iTerm 2. .bash_login is only read if there's no .bash_profile.

You could also add a cd command to .bash_profile.

First of all, if you are not using iTerm2 already, I suggest you download this free software as a replacement for Terminal.app.

Among many other extra features, in iTerm Preferences, you can configure the default working directory for new shells. You'll find these settings in Profiles - General.

The advantage here is that you can set different behaviors for opening a new window vs opening a new tab or even creating a new split pane. I personally like staying in the current working directory when adding a split pane, for example.

You could do it in your startup script as well (though I find the iTerm solution cleaner, or at least more flexible), but then I advise you to use ~/.bash_profile instead.

~/.bashrc is not automatically sourced when opening a new shell window, and ~/.bash_login is only sourced if no ~/.bash_profile is present.