Juan Carlos Pomares Torres

Prismatic structural members: Cross section flat and normal to the axis?

DOI: 10.7764/RDLC.16.3.507 Abstract In the study of prismatic bars subjected to bending forces, the authors of Strength of Materials generally assume the Navier-Bernoulli simplifying hypothesis which states that flat cross sections (CS) normal to their axes before deformation remain flat and normal to their axes. A more detailed study in terms of Elasticity , however, shows how approximate this hypothesis can be for some basic prismatic bar problems in which displacements can readily be obtained. When or whether the surface remains flat, absolutely flat, or not is a point of debate among engineers and architects alike and even for structural specialists, who look deeper into this kind of issues. This paper proposes a detailed study of said problems and clarifies them. Contrary to what should be expected according to well-established literature, the CS of any bar subjected to pure bending forces does not remain flat after deformation. Our analysis revisits accepted displacement solutions for tension, bending and torque and will hopefully remove the misunderstanding leading to a flat geometry for the deformed CS. It also includes the correct interpretation of the warped geometry from the exact equations we obtain in this paper, which we illustrate with results from finite elastic models.

Sistemas de protección individual anticaídas sometidos a impacto. Simulaciones numéricas

Personal fall protection systems are set up by EN-363 to avoid or retain people falls safely (without relevant damages). They are the ultimate resource to prevent a fall after other measures being considered. This paper analyses the variables affecting the system behaviour: free fall height, length of retaining rope, stiffness and damping of retaining material, and worker weight. To this end, fall phenomenon has been simulated with finite elements dynamic models with an elas- tic rope and a rigid ballast. It allows obtain likely values of maximum forces on the injured and over the system during the impact. Results demonstrate the fundamental role of height fall vs. rope length rate (fall factor), which results more important than the fall height itself. The severe values obtained for maximum forces show that future research would include elastoplastic energy absorbers to decrease impact until reasonable values.