I want to run 4 horizontal 2x4s and add a plywood sheet to use as storage in my attic. The studs would run through the middle of the frame. The problem is that there are 1x4 braces where I want to put my 2x4 studs. They don't look as if they were meant to be permanent so I wanted to know if from a structural standpoint they are really needed. Here are the pictures of the 1x4s (horizontal and diagonal).
The bracing seems to be applied randomly. When we design lateral bracing, it is uniform throughout the structure, (or each section of a structure).
I doubt the bracing is "required". It was probably installed during construction to keep the components aligned.
Structural components are designed for "worse case scenarios". So, one way to test my assumptions that it's not required is to remove one diagonal brace and then stand in the attic and shift your weight from side to side. If the structure seems to "move" then it is required. (You should not be able to move the structure.) Then, remove one more brace and test again...
Another way of checking to see if the diagonal bracing is required (designed), is to check the nailing pattern from the bracing to the vertical studs. If it is the same, (say...2 nails into each stud,) then its more likely to be required. However, if it's random, (maybe 1 nail in some studs and 2 in others) then it's definitely temporary.
By the way, take a picture of each area before you start, in case you have to replace the braces.