Use an entry field's value in body class
You've assigned the string 'work modifierClass' to the bodyClass variable, rather than adding the value of the modifierClass variable to bodyClass. 

You can assign the value of modifierClass to bodyClass like this:

{% set bodyClass = 'work ' ~ modifierClass %}


The ~ (tilde) character is Twig's string concatenation operator. 

You could even remove the modifierClass variable altogether and just do this:

{% set bodyClass = 'work ' ~ entry.shortName %}