MET 415 - Truss Elements

Spring 2007, MET 415 - FEA Applications I

Prof. Dave Johnson, dhj1@psu.edu, Penn State - Erie, The Behrend College

Homework 5A: 3D Truss Elements

Concepts:

Link (Truss or Spar) Element Usage (Two-Force Members)
Considerations for Pin Joints (construction and loading)
Plots Showing Thickness for Link (also used for Beam & Shell) Elements
Postprocessing of Link Elements (Element Table Usage)
Stress and Force Results for LINK Elements
Element Table Data Plots with "Stress" Values

A three-dimensional approximation of a bridge frame is shown in the figure.

All dimensions in the figure are given in feet. The members of this structure are wood:

Modulus	Poisson's Ratio	Density
1.4x10⁶ psi	0.21	0.0266 lb_m/in³

Three different sizes of construction timber are used in this frame. Each cross-sectional area is:

Strongest Section (4x4)	Medium Section (2x4)	Lightest Section (2x2)
12.25 in²	5.25 in²	2.25 in²

Analyze this structure for a static loading condition:

Pin Constraints in all DOF (UX, UY, UZ) at the four base corners (A, B, C, D in the figure)

One lateral (or transverse) constraint along the top (at point E in the figure) which gives support to the frame in the side-to-side direction.

To simulate the wood decking load on the base, apply a 200 lb_f downward load on each of the four unconstrained pins of the base.

Then, to account for a heavy load crossing the bridge, add 1000 lb_f to each of the two unconstrained pins nearest B and C on the figure (making the total load 1200 lb_f downward on each of those two pins).

Also, include the weight of the frame structure (by using a vertical gravity loading)

Turn in:

an element plot showing the different section thicknesses (by real constant I.D. numbering) and all the structure's boundary conditions
an element plot with element thickness displayed as determined from the real constants.
a results plot of forces in the link elements (with values labeled on the plot)
a results plot of stresses in the link elements (with values labeled on the plot)
a session log file with comments describing the process of modeling and loading.
a check - sum of vertical forces from ANSYS compared to hand calculation of weight + applied loads