A new thought-provoking whitepaper by Muangsangop Seniwongse, Ph.D., P.E., CPEng, M.ASCE, Lead Technical Marine Specialist at McLaren has been published by ASCE rethinking the specification of fixed-base and/or pinned-base columns in computer analysis and the design of steel frames.
Most structural analysis software provides a default support condition for steel frame column bases as fixed, meaning fixed against all six degrees of freedom. A release command can be used to release the restraint in any specified degree of freedom. However, some engineers have been using incorrect column base support conditions for major steel frames for years, specifying pinned supports instead of the fixed supports in all their designs. This is equivalent to assuming that plastic hinges (full plastic moment) have already formed at the bottom of the columns before any loads are applied. The result is a safe but grossly overdesigned project, due to the entire elastic range of moment resistance at the column base being ignored.
The research in Mr. Seniwongse’s paper, “Specifying Fixed-Base Columns or Pinned-Base Columns in Computer Analysis and Design of Steel Frames,” demonstrates fixed and pinned supports commonly seen, sites actual test results and uses examples of major structures that were designed with a fixed-base connection and examining their life-long integrity under actual sustained service loads. Read more about cost savings in steel structures design and download the paper here on ASCE Library.