Q ‘I participated in a bridge building contest through my school. My Bridge model was chosen for the final round of the contest and was not able to pass a specific deflection test. I usually utilised the trial and error method to come up with a stronger bridge model. What is the best method to determine and reduce the deflection before building an actual model of a bridge?’
A Thank you, this is a very good question. This topic is very relevant to real bridges used in the world today. In the following video, I have demonstrated a computer aided simulation method used to calculate deflection. Please watch this video I have created, which goes further into depth about this process (new terms such as Section Modulus, Finite Element Analysis, Mesh, Linear Analysis etc. are introduced in this video).
By increasing the section modulus of the cross section, we were able to reduce the resultant deflection roughly by 30% This is an example of a quick first pass analysis.
In real life bridge design scenarios, structural engineers undertake due diligence by investigating all possible failure modes and following many codes to achieve high safety standards. Other failure modes to be aware of may include seismic loads, dynamic loads, resonance, effect of wind and snow loads, corrosion etc.
The idea to take a virtual load testing of a bridge was to see the result in a quick real time environment. In addition, virtual simulation helps to reduce the product development time, improve safety as well as the product performance. Load testing (virtual simulation) is conducted using existing computer aided design data (CAD Data). The first step in this process is to create a model with correct dimensions using a CAD program.
In Finite Element Analysis, meshing is used in the simulation process to break down the structure (existing 3D model) into small elements before calculating the simulation results. When running the simulation, Coding is extensively used in the background to solve the complex mathematical equations and establish a very realistic response to real life situations.
In the completed linear simulation video, we used plain carbon steel as our material. For linear simulation we assume proportional relationship between the applied load and deflection. For metals, linear static analysis is usually undertaken to predict the elastic response until the yield point. For bridges made of wood, simulation should be conducted by considering the direction of the grain (by specifying orthotropic material properties). In real life, non-linear simulation may become essential when simulating the behaviour of certain plastic materials under an applied load because the elastic region is very narrow.
Hope you have learned something new today! Please feel free to contact me if you would like to ask questions regarding specific STEM topics, or if you would like to request for a STEM topic to be covered in the future.
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Arya Peruma is passionate about making STEM education more inclusive for the underrepresented.