A structural engineer's logbook: step-by-step designs, Python automation and lessons learned in seismic and bridge engineering.https://notas-yarm.pages.dev/https://notas-yarm.pages.dev/en/notas/series-stiffness-bridge-period/https://notas-yarm.pages.dev/en/notas/series-stiffness-bridge-period/A bridge pier is not just a column: bearings sit on top and a foundation sits below, and all three deform. In a typical case, adding them takes the period from 1.3 s to 1.9 s.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/rayleigh-fixed-beta/https://notas-yarm.pages.dev/en/notas/rayleigh-fixed-beta/Copying the same damping coefficient into every model looks neutral, but it is not: a flexible structure ends up with 1.5% and a stiff one with 5%. I explain where that comes from and how to fix it.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/opensees-reproducibility-processes/https://notas-yarm.pages.dev/en/notas/opensees-reproducibility-processes/I reran 20 analyses with the same code and the same inputs, and none matched. The cause was a material that keeps memory between models when they run in the same Python process. The fix is one line.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/koyna-dam-1967-where-it-cracks/https://notas-yarm.pages.dev/en/notas/koyna-dam-1967-where-it-cracks/In 1967 an earthquake cracked Koyna Dam, in India, right where its downstream face changes slope. I modeled it in OpenSees and the video shows how that damage appears, second by second.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/elastomeric-bearing-aashto-shear-strain/https://notas-yarm.pages.dev/en/notas/elastomeric-bearing-aashto-shear-strain/A bearing fails when its rubber layers shear too much. AASHTO puts compression, rotation and displacement into one sum. I explain it from scratch and work it out for a 350 × 450 mm bearing.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/dispbeamcolumn-vs-forcebeamcolumn/https://notas-yarm.pages.dev/en/notas/dispbeamcolumn-vs-forcebeamcolumn/OpenSees lets you model a column with two element types that look equivalent. Against a real test, one got the shear within 1% and the other overshot by 56%. I explain why, starting from the basic idea.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/capacity-protection-cap-beam/https://notas-yarm.pages.dev/en/notas/capacity-protection-cap-beam/In seismic design we choose which part of the bridge gets damaged, like a fuse. Everything else is designed for what that fuse can transmit. In a two-column bent, that is almost twice what the analysis says.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/automating-a-simple-beam-python/https://notas-yarm.pages.dev/en/notas/automating-a-simple-beam-python/We have all computed a simply supported beam by hand. In this first part we move it to Python, line by line, and see what a calculator cannot do: compute twenty beams in one second.Tue, 06 Oct 2026 00:00:00 GMThttps://notas-yarm.pages.dev/en/notas/why-i-write-these-notes/https://notas-yarm.pages.dev/en/notas/why-i-write-these-notes/For ten years I have kept notebooks on how I design, what I automate and which mistakes I make. This is the public version: a log of design, automation and lessons learned.Thu, 01 Oct 2026 00:00:00 GMT