Seismic analysis of structures is an essential task for safe design of structures especially in earthquake-prone areas. Finite element modelling of structures plays a vital role in this regards. On the other hand, accurate modelling of a structure is still a serious concern since the finite element models always differ from the as-built structures. It comes from the fact that there are lots of structural uncertainties like boundary conditions, connections, structure’s geometry, materials properties, etc. To create a reliable and accurate finite element model of structures, one can use the model updating algorithms which are popular nowadays particularly. Model updating procedure is normally based on an optimization framework in with the model parameters updated by comparing with the ones of an experimental test in order to make the model simplified assumptions more realistic. In this paper the OpenSees.NET software, which has been recently developed by one of the authors, is used as a very suitable tool for model updating of structures modelled in OpenSees framework (http://opensees.net). OpenSees is free and well-established software widely used by civil engineering community for simulating the response of structures subjected to earthquakes. The OpenSees.NET software is Microsoft .NET framework assembly as a Wrapper for OpenSees framework. In this paper a pre-stressed concrete beam model will be updated by tracking the first natural bending mode frequency. The modelling and optimization stages have been implemented using the OpenSees.NET software in MATLAB environment. Each of the selected parameters will be changed using optimization procedure with a specific step and the updated model will be then analysed. The difference between the first bending frequency of the updated model and the experimental one will be 0.0001 after 127 optimization iterations.

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