As stated...

diotalevi: You weren't nesting your ternaries.

A little trick I like to use is to avoid putting a nested trenary the 'then' part.
I had a little difficulty deciphering your desired result, but here's the general idea.

$result = ($major_length == 4800) ? 18
        : ($major_length != 8552) ? 0
        : ($val == 4) ? 33 
        : ($val == 1) ? 18 : 0;
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