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Results from Truss Observations
Analysis and commentary

Arch 324, Introduction to Structural Design, University of Virginia
Last updated Friday, April 12, 1996, at 9:55 AM Copyright © 1996, Kirk Martini

The Raw Data

The following is a scatter plot based on the truss examples. The following data points were removed from the sample

Span Depth Reason
5989 35 Stiffening truss for suspension bridge
1440 50 Trussed arch rib
598 35 Mulitple spans
1 1 Error

Interpretation

The graph below shows trendline plotted on the graph (in red) using linear regression (it minimizes the sum of the squares of the differences between the approximating line and the actual data points). The blue lines correspond to common rules of thumb for truss span-to-depth ratios.

Rounding off the coefficients, the equation for the line has the following form:

depth = (span/14) + 5 feet
This result is effectively a rule of thumb for estimating truss depth, but it is clearly not very good for short span trusses, since is clearly influenced by the longer span examples, and does not apply well to short spans.

Limiting the examples to those with a span less than 100 feet gives the following result.

Rounding off the coefficients, the equation for the line has the following form:

depth = (span/6) + 9 inches
Here are a few conclusions:
Last updated Friday, April 12, 1996, at 9:55 AM
Copyright © 1996, Kirk Martini
Please send comments or questions to Martini@virginia.edu
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