Cross stiffness terms can be confusing at first glance, but they relate to real physical phenoma and must be understood for modelling a wide range of problems. Here I will talk about two examples: 1) Rigid links 2) Modelling a foundation system with a single spring support Example 1: Rigid Links The diagonal stiffness terms […]

It can be annoying when your modal buckling eigenvalue solver is returning a lot of negative eigenvalues and no positive ones. And they don’t make any sense. Well negative eigenvalues do have a use. They represent buckling modes which may occur if the loads on the model are reversed! Checking the behaviour of negative eigenvalue […]

Time history datasets can be big. Really big. And post processing them can be a real drag, especially if you want to do something like take a rolling average. There is a faster way though – by using a filter implementation. This is a hack which leverages how digital filters work, and by no means […]

I often find running scripts requires looping through a large number of elements in a model and this exposes some of the inefficiencies of coding in VBA. There are a few ways to get ‘free speed’ though. I have suggested a four easy wins¬†below. None of them are revolutionary,¬†but all are worth remembering! 1. Write […]

In the last post I looked at swapping segment normals in a text keyword file. It was a great excuse to jump in to the world of Perl. There is in fact a way of doing exactly the same thing with a single line in Vi (or Vim). You can use back referenced substitution to […]

Perl is a language which is best suited to manipulating text. It is efficient, and free to use (after downloading it). So you can quickly imagine it is not the most useful language for structural engineers. That is almost true, one example where it can be useful is editing keyword files. Below is an example […]

ETABS now has an API, as of the 2013. It is accessible with any ‘edition‘ of ETABS 2013 and at first blush looks well featured. Coming from working with Strand7 and GSA APIs in VBA (more on those in a later post) there isn’t an great deal of difference. The API will make ETABS appear […]