More than likely the "Structural Certification" people are referring to is in accordance with the requirements of AWS D1.1. "Structural Welding Code".
The code that you are required to certify to could change depending upon the customers requirements. The tests vary and depend upon the range of variables you would need to qualify for.
AWS also has a Welder Certification program that is sometimes accepted at many locations. You could get information from AWS. They are real good about sending out literature related to their certification programs.
Gerald Austin
http://www.geocities.com/pipewelder_1999/