part of exam

ENGIN 36 Final Exam

Take Home Exam

May 15, 2020

Laney College

Name ________________________________________________________

Read all of the instructions below before starting the exam

1. Turn in the exam on Canvas by 5:00 PM on Wednesday, May 20.

2. Be sure to read the instructions for each problem carefully. Read the question

statement fully and be sure to answer all components of the question.

3. You may use your homework, class notes, the textbook, references posted to Canvas,

and other study references as you work through the exam. You may not consult with

classmates.

4. Show all of your work! It’s much easier for me to give you partial credit if you clearly

document all of your steps when solving a problem.

5. Remember to write your units in your answer!

6. Box your answers!

7. If you run into algebra or math problems, write how you would have continued to solve

the problem to receive partial credit.

Sign the honor statement below after finishing the exam (a digital “signature” is acceptable)

I have neither given nor received help on this work, nor am I aware of any infraction of the

Honor Code.

Problem 1

A sign is supported on a hollow steel post that is fully fixed at its base, as shown in the diagram.

The internal forces and geometric properties shown were computed in the last exam.

A

B

14

6 f

t

A B

y

x

A

B

y

x

X X

Section X-X

4

”

6″

3

8

3

8

3 8″ 3 8″

W = 6,000 lb

s

I ® 32.8in4

A ® 6.94in2

Geometric Properties:

The hollow steel post is replaced by the wood post with two steel plates fastened to the faces shown on the

next page. Showing all work, find:

(a) The normal stress in the steel at the point labeled Asteel caused by bending only

(b) The normal stress in the wood at the point labeled Awood caused by bending only

(c) If the normal stress due to axial load is disregarded, is the composite member adequate? Why?

(d) What equations would you use to find the normal stress in the wood and the steel? (HINT: remember

compatibility relationships)

A B

N = 6 kips

M = 432 kip×in

page 1 of 6

Asteel

Awood

Material Properties:

Esteel=29,000 ksi Ewood=1,200 ksi

3

8

3

8

6″

4″

sall,steel=60 ksi sall,wood=1.15ksi

Problem 1 cont’d

page 2 of 6

Problem 2

The sign post from Problem 1 is now braced by cable KM which is tensioned with a force of 3,000 lbs.

A B

8′

-0

”

6 ft

A B

y

x

A

B

y

x

Section X-X

4″

6″

3

8

3

8

3 8″ 3 8″

W = 6,000 lbs

I ® 32.8in4

A ® 6.94in2

Geometric Properties:

60.0°

J

K L

M

XX

2′

-0

”

C

K

J

(a) Draw the FBD of forces at point K:

A B

page 3 of 6

Normal Force, NShear Force, V Moment, M

Problem 2 cont’d

(b) Draw the internal force diagrams for shear, moment, and normal force:

page 4 of 6

t

Shear Stress

sb

Normal Stress,

Bending

sa

Normal Stress,

Axial

A BC A BC A BC

(c) Draw the stress profiles for shear stress and normal stress due to bending and axial force. You only need

to draw the shape; magnitudes of stresses aren’t needed.

Problem 2 cont’d

(d) Draw the stress state at Point A. See the reference for positive sign conventions.

sz

tzy

sy

page 5 of 6

s

(e) Draw Mohr’s circle for the stress state A. Label the principal stresses and the maximum shear stress.

Problem 2 cont’d

page 6 of 6