Update and append to end of string in MSSQL

How do you take a string in an MSSQL table and append another string to the end of it? To do this, you can run a bit of SQL such as:

update tablename set Columnname = Columnname + 'newstring' where id = X

So if you are say updating a column that is a URL and you want all instances in the table to receive a new value at the end of the URL, your query might look like:

update url_table set urlfield = urlfield + '&additionalfield=true'