Allocating spending over periods in general ledger workbook automatically

Hello! I am trying to figure out how to allocate spending over periods automatically in a general ledger budget spreadsheet I have for our IT Department. On the Itemized Expense and Cap Ex tabs in the workbook, expenditures are automatically sorted into monthly and yearly spending categories on the first two tabs based on their IT Code. This works well, except it does not allow for prorating spending. For example, if we were to buy a laptop for $3600 on April 1st, 2015 that has a useful life of 36 months, all $3600 would not be recorded in April. $100 would be recorded each month for 36 months. I do not know how to do this automatically. I have added a column on the expenditures tabs named "Periods" which refer to the number of months that the item's cost need to be dispensed across. I have attached the spreadsheet and would greatly appreciate any help on this. Thank you!

Also, please assume that the assets do not have a salvage value.