# José Abell's research blog

## Using my gmshtranslator python tool to interface gmsh with opensees.

I wrote the gmshtranslator tool a while back during my PhD, to easily parse gmsh msh files to any other format. I’ve been using it for years now with not much change for both research and consulting, and have been contacted by other researchers that want to use it. I will soon write a tool, powered by gmshtranslator, to more easily translate from gmsh into OpenSees. Meanwhile, here is a short example on how to use gmshtranslator to create OpenSees models. The example assumes you know gmsh formats (.geo and .msh) and python.

The example consists on the simple …

## Video of 2-D SSI model of an RC Shear Wall Building

The RC shear-wall building is modeled in OpenSees using non-linear fiber based beam column elements. Soil is modeled as a continuum using quad elements and linear stress-strain relationship. Soil shear wave-speed is varied in depth such as to obtain a $$V_{s30}$$ consistent with a class B site according to chilean seismic code. Lysmer-Kulhemeyer dashpots are used along the soil boundary to model seismic radiation and earthquake wave-field input.

The performance of the building will be assessed for varying site fundamental periods. This is an aspect of SSI that is not covered by the chilean seismic code, and has been …

## New cable element in OpenSees

With my student, Pablo Ibañez, we implemented a new catenary cable element in OpenSees. This element is based on the work by Salehi et al[1].

The stiffness of this element is obtained using a flexibility formulation. Basically the shape of the cable is determined by the integral:

 \begin{align*} \vect{x}(s) = \vect{x}_1 - \int_0^s \dfrac{\vect{w}s + \vect{f}}{\Vert \vect{w}s + \vect{f} \Vert^2}\pare{\dfrac{\Vert \vect{w}s + \vect{f} \Vert}{EA} + \pare{1 + \alpha \Delta T}} \ud s \\ \vect{w} = \brak{w_1,\, w_2,\, w_3}^T \qquad \vect{f} = \brak …

## OpenSees coming to python!

One of the gripes a lot of people have with OpenSees is that it adopts TCL as its interpreter language. Originally, OpenSees was conceived as a framework, this is apparent from the main page of the wiki:

OpenSees, the Open System for Earthquake Engineering Simulation, is an object-oriented, open source software framework. It allows users to create both serial and parallel finite element computer applications for simulating…

So, it was meant to be a neat way to build new FEM software. For years the only actual (known) application to use the OpenSees framework was what came to be known as …