Problem:

I want to create a server-www alias that connects me to the SSH server and change the directory to /var/www/ right after the connection.

There it is :

ssh -t server 'cd /var/www && $SHELL'

And for the alias, add this in your ~/.bashrc:

alias server-www="ssh -t server 'cd /var/www && $SHELL'"
server-www # test it !

References :