I am a retired Civil engineer, retired in 2018 from the Babcock & Wilcox Company. In 1976 I obtained a Bachelor of Science degree in Civil Engineering from the University of Akron in Ohio. I learned FORTRAN from using a compiler and user manual from the University of Waterloo. Through the years I wrote or maintained programs using the Finite Element Method (FEA) storing only one of the upper or lower triangulars of the square, symmetric stiffness matrix. I eventually “inherited” maintenance of a piping and structural analysis where we stored only the active column heights (under the classic “skyline” down to the diagonal and stored these sequentially in a huge single-dimensioned vector, portions of which were systematically retrieved during the matrix solution of nodal deflections and rotations.

I had heard of and used non-linear formulations for structures strained in portions beyond the elastic limit but only in rudimentary exercises.

I am an admirer of Stephen Timoshenko and his well explained books on the derivation of closed-form classical solutions of statically indeterminate structures and his contribution to certain beam equations involving lateral stability and torsional buckling, which are still used in the AISC steel design manual. Another man, Miclos Hetenyi I think was a student or fellow colleague and I admire his equations for beams on elastic foundations.