The FAA has a lot of online info on aircraft loads http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/MainFrame?OpenFrameSet"
PART 23--AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
As for Books, I suggest the following
Bruhn, E.F.; 1965; Analysis and Design of Flight Vehicle Structures. It is currently out of print, but is considered by many in the field as the best
Peery, David J. and J.J. Azar; Aircraft Structures, Second Edition; McGraw-Hill Book Company; New York, NY; 1982. A very good textbook.