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[Watch & Learn]

This example is taken from Cornell University’s ANSYS AIM Learning Modules

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Contents

1. Problem Specification
2. Learning Goals
3. Pre-Analysis
4. Geometry
5. Mesh
6. Physics Setup
7. Results Evaluation

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Problem Specification

A simply-supported 3D signpost with a cylindrical cross-section is subjected to the following combined loading situation.

x1 = 6 ft, z1 = 4 ft, b2 = 13 ft, h1 = 28ft, h2 = 8ft;

The system is subjected to the following external loads:

Wz1 = weight per unit length of the sign = 900 lb/ft, Wx2 = spatially variable wind load in the x-direction = 700*z lbs,

Fy1 = net wind force in the y-direction = 8000 lb, and Fz1 = net weight of the post (using a specific weight of 490 lb/ft^3)

The signpost is made of steel, which is a homogeneous and isotropic material (same properties at all points and in all directions) with Young’s modulus E= 3.0e7 psi, Poisson’s ratio of 0, and a density of 490 lb/ft^3. It is assumed that the post is a solid cylinder of diameter, d. It is further assumed that after loading, the signpost will remain in its elastic range. This means that when the external load is removed, the material will return to its original shape without suffering permanent deformation.

Using ANSYS AIM, design the post so that the total combined normal stresses and combined shear stresses do not exceed allowable values. Assume allowable stresses of 25 ksi and 16 ksi for normal and shear stress, respectively, which already account for an appropriate factor of safety.

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Learning Goals

The purpose of this tutorial is to showcase how fully three-dimensional analysis can be applied to capture both stress states from simple combined loading as well as stress concentrations in the vicinity of sharp and/or re-entrant corners and other near-discontinuities in geometry.

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Pre-Analysis

This problem requires a relatively straightforward application of linearly superposed solutions from individual loadings. A simple spreadsheet can be prepared to give the results for the stresses associated with the separate loadings experienced by the signpost. An example is given here for the case of a solid post with a diameter of 1.12 feet:

Note that the formula for the moment about the x-axis is highlighted and shown in the formula bar above the spreadsheet. Not surprisingly, the stresses are quite low as solid posts are almost never used in practice. You may wish to begin with this case of an over-designed signpost. The tutorial contains geometry files for both solid and hollow poles. Then you will want to consider hollow poles and compare results as you attempt to optimize the post’s load-carrying capacity.

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Geometry

Download Solid Signpost geometry

Download Hollow Signpost geometry

The video below shows the steps necessary to import and prepare the geometry.

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Mesh

The following video shows how to create a basic mesh for the sign and post using size and element shape controls.

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Physics Setup

The video below demonstrates how to specify the materials and boundary conditions.  Instead of the spatially varying wind load in the problem description, we will specify a uniform pressure for WX2 equal to the maximum value, which is a worst-case scenario.

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Results Evaluation

The following video shows how to compute and analyze your results.