sum multiple cells in the same row that are in colums with the same fieldname

i have a worksheet with many columns Some of the columns have the same heading ("DaySum").
HLOOKUP only ever returns a single cell (the first in a table array) but i need it to find and add ALL of the numbers under the heading "DaySum" on any given line.

In this scenario, there are three columns with the title DaySum (L1, T1, AB1, AJ1) if am putting the formula into row say, for example, I would like it to look for any numbers in

I want a formula that searched for "DaySum" and is not searching for data specified columns because I have over 50 projects and for each one, DaySum sits in different columns 9there are 2 worksheets on the attached file to show what I mean!)

Heeeelllp!

brilliant - you are a genius!......I spent hours trying to get this to work before my cry for help...thank you SO much