Antonio,
To set up a new approval rules for expense report follow the steps below;
1. Go to Application and User Management --> Approval processes --> Highlight Default approval process for Expense Report--> Copy.
2. Add row--> Add Process Step Name --> Add Work Distribution(Approval non project expense of up to 250) and select work distribution--> add conditions and Save and close.
Hope this will help.
Regards,
Emeka