Seismic Design of Substation Steel Structures: What Code Should I Follow?

Steel structure design requirements in high seismic zones are clearly defined in ASCE 7 in conjunction with AISC 360 and AISC 341, but these standards are more applicable to buildings. For substation steel structure designs, utilities often refer to ASCE 113 and IEEE 693. Many design aspects outlined in ASCE 113 are similar to those in ASCE 7 but were modified to better suit substation steel structures. IEEE 693 is also referenced in ASCE 113 for substation seismic requirements; however, there are some differences in seismic design requirements between ASCE 113 and IEEE 693. In this paper, the authors will first present and compare the design philosophies of each seismic design component of substation steel structures, e.g. load development, load combinations, detailing requirements, etc., as outlined in IEEE 693, ASCE 113, and ASCE 7 standards. Then, the differences in design requirements among the standards will be noted. The main focus of this paper is to make engineers aware of substation steel seismic design requirements as outlined in those standards as well as to offer opinions of how each requirement may affect design results or how to comply with an aspect of design requirements that one standard may not offer for a safe, effective, and optimal design of substation steel structures in high seismic areas.