# This homework assignment is due at 4:00pm on Friday, October 19th (10/19) to the CEE Office (EB200) homework dropbox.

EAS211 Homework 3 201804

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This homework assignment is due at 4:00pm on Friday, October 19th (10/19) to the CEE Office (EB200)

homework dropbox. Make sure to timestamp your submission and to follow the homework formatting

guidelines and examples posted on D2L.

Rigid Body Equilibrium

The following problem requires you to analyze a real-world structure to calculate the support reactions (which

would then be used for foundation design).

Problem 1 (100 Points): “Single Mast Arm Pole”

This problem requires you to complete the tasks below related to a standard “MAP-30 Single Mast Arm Pole”

signal support, as provided in the PBOT Standard Details catalog, Dwg. No. P-601.

Figure 1: PBOT Std. Dwg. No. P-601

The standard design is proposed to be used for a new (much needed) stop light on SW 4th Ave at SW College

St, as shown in Figure 2 below. Although these “standard designs” are engineered and checked by PBOT,

assume that your supervisor has asked you to begin structural calculations because she has learned that new

lighted signs (proposed for 2020 implementation) have increased weight.

https://www.portlandoregon.gov/transportation/article/668195
https://www.portlandoregon.gov/transportation/article/658064

EAS211 Homework 3 201804

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Figure 2: SW 4th Ave. at SW College St. (Looking East)

Use the following parameters and simplifications/assumptions when analyzing the structure:

▪ Analyze the structure in 2D, as diagramed in Dwg. No. P-601

▪ Ignore the radius of the mast arm. Treat it as a straight member, inclined at angle α.

▪ The mast arm and post are fabricated from structural steel, with a unit weight of 490 pcf.

▪ Assume that the cross-sectional area (and therefore self-weight) of the mast arm and post linearly vary

along the length/height of each member. The cross-sectional area at the end of each member is:

– Mast Arm End: 4.00 in2 (at free end)

– Mast Arm Base: 10.0 in2 (at connection to post)

– Post End: 12.0 in2 (at connection to mast arm)

– Post Base: 24.0 in2 (at bottom of post)

▪ To calculate the weight per lineal foot, simply multiply the cross-sectional area by the unit weight. Be

careful with units!

– Example: (8.00 𝑖𝑛2) ∙ ( 1 𝑓𝑡

12 𝑖𝑛 )

2

∙ ( 490 𝑙𝑏

𝑓𝑡3 ) = 27.22

𝑙𝑏

𝑓𝑡

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