CVEEN3510_Review3-Solutions
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CVEEN 3510-001 Civil Engineering Materials Spring 2023 Review for Exam 3 21 April 2023 Name (PRINT)
_______________________ Student ID
_______________________ Total points: 60 points Time: 120 minutes (1:00 to 3:00 PM) Instructions: 1.
This exam is closed book. 2.
You are allowed to bring ONE A4 sheet (8.5' by 11') of paper with any handwritten information. Everything on the paper must be handwritten. No computer-generated content will be allowed. In your sheet of paper, you can include concepts, examples, definitions, and ALL equations. You can use both sides of the paper. 3.
NCEES Approved Calculator, official drawing aids (French curves, templates, etc.) are approved. 4.
No cell phone, smart watch, or communication enabled are allowed. 5.
You have 120 minutes to complete. The entire exam has a value of 60
points with an option for 12 bonus points. 6.
Attempt all questions from PART A (18 x 2 = 36 points) and any four questions from PART B (4 x 6 = 24 points). 7.
Bonus Points: There are 6 bonus questions (6 x 2 = 12 points). It is an optional section. 8.
Review and sign the statement of academic integrity below. Statement of Academic Integrity As a University of Utah student and an aspiring professional engineer, your honesty and integrity are expected. By signing below, you affirm that the work provided is solely yours, that you have not used another’s assistance or work (with or without their consent), and that you will/have not discussed the contents of this exam with ANYONE prior to 3:00 PM. Printed Name -------------------------- Signature---------------------------------
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------------------------------------------------------------------------------------------------------------- PART A (Answer all questions) Each question carries two points Total points for PART A is 36 1.
C
oordination number is the number of “nearest neighbors” for a crystal structure.
The coordination number is for BCC, FCC and HCP structures, respectively are: a)
4,8,16 b) 2,4,8 c) 8,12,16 d) 8,12,12
2.
A tensile load of 190 kN is applied to a round metal bar with a diameter of 16 mm and a gauge length of 50 mm. Under this load, the bar elastically deforms so that the gauge length increases to 50.1349 mm and the diameter decreases to 15.99 mm. The Poisson’s ratio for this metal is: a)
0.23
b) -0.23 c) 0.33 d) 0.27 Poisson’s ratio = -(change in diameter/original diameter)/ (change in length/original length) = - {(15.99-16)/16}/{(50.1349-50)/50} = 0.23 3.
A given viscoelastic material is modeled using a Maxwell Model with the following constants spring constant, K = 20 N/mm; shock absorber constant, beta = 1500 Ns/mm. If a creep load with a magnitude of 100 N is applied for 60 seconds, the deformation, in mm, will be: a)
9 mm
b) 4 mm c) 5 mm d) 8 mm Maxwell model , Total deformation = F/K + Ft/beta = 100/20 + (100 × 60)/1500 = 9 mm 4.
Measurements should be reported to the nearest 1000, 100, 10, 1, 0.1, 0.01, 0.001 units, etc., depending on their variability and intended use. Using your best judgment, how should the following measurements be reported? •
Compressive strength of Portland cement concrete (psi) •
Moisture content in a concrete masonry unit (percent) a)
10 psi, 0.001% b) 100 psi, 0.01% c) 10 psi, 0.1% d) 100 psi, 0.1%
Both c and d are acceptable 5.
Which LEED credit area can be awarded the greatest number of points? a.
Water Efficiency b) Material and Resources c) Energy and Atmosphere
d) Innovation 6.
If a steel with a 33 ksi yield strength is used for a cold-formed shape, what would be the approximate yield strength of the deformed corner after cold-forming? a.
66 ksi
b) 49 ksi c) 99 ksi d) 28 ksi Cold-forming doubles the yield strength
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7.
An aluminum specimen originally 300 mm long is pulled in tension with a stress of 275 MPa. If the deformation is entirely elastic, what will be the resultant elongation? The aluminum modulus of elasticity is 75 GPa. a.
1.1 mm
b) 0.1 mm c) 2.1 mm d) 0.2 mm Stress = E (strain) = E (change in length / original length) 275 = 75 × 10
3 (change in length/300) Elongation or change in length = 1.1 mm 8.
Glass used in a high-rise building is produced with an average tensile strength of 14 ksi with a standard deviation of 2 ksi. If 50 samples are tested, what is the lowest value that can be expected with 95% confidence? a.
10.08 ksi
b) 11.02 ksi c) 12.06 ksi d) 10.8 ksi Z
α/2
for 95% confidence level = -1.96 (lower bound) (x –
mean)/standard deviation = -1.96 (x –
14)/2 = -1.96 x = 10.08 ksi 9.
A sample of wet aggregate weighed 297.2 N. After drying in an oven, this sample weighed 281.5 N. The absorption of this aggregate is 2.5%. Calculate the percent of free water in the original wet sample. a.
3.08%
b) 2.08% c) 1.8% d) 3.8% Moisture content = (297.2 –
281.5) /281.5 = 5.58% Absortion = 2.5% Free moisture = 5.58 -2.5 = 3.08%
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Page 4
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10.
Select the most appropriate stress-strain for the following materials (in order) Glass, Steel, Aluminum, Concrete, Soft rubber a.
A,B,C,D,E
b) B,C,D,A,E c) C,D,A,B,E d) D,A,C,B,E 11.
The mix design for an asphalt concrete mixture requires 2 to 6% minus No. 200. The three aggregates available and their corresponding minus 200 are Coarse = 0.5% , Intermediate = 1.5%, Fine aggregate = 11.5 %. Considering that approximately equal amounts of coarse and intermediate aggregate will be used in the mix, what is the percentage of fine aggregate that will give a resulting minus No. 200 in the mixture in the middle of the range, about 4%? a.
30%
b) 25% c) 18% d) 42% Let x be the fraction of fine aggregate 4% = 0.5% {(1-x)/2} + 1.5% {(1-x)/2} + 11.5% {x} x ~ 30% 12.
As a materials engineer in charge of designing concrete mix and facing the following problems, which admixture would you use if more time is expected to be needed for finishing concrete? a.
Retarder
b) Accelerator c) Air entrainer d) Superplasticizer 13.
A continuou
sly reinforced concrete pavement cross section contains a layer of No. 6 (0.75’’ diameter) reinforcing bars at 6-in. centers, such that the steel is just above mid-depth of a 10-in. thick slab. Cover over the top of the steel is therefore about 4 in. Choose the maximum size of coarse aggregate. a.
1.5’’
b) 3’’ c) 3.5’’ d) 2.7’’
< 1/5 x 10’’
< 3/4 x (6-
0.75)’’
< 3/4 x 4’’
Max size should not be more than 2’’, typically 1
-
1.5’’ used
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14.
A center-point loading flexural test was performed on a concrete beam with a cross section of 100 mm x 100 mm and a span of 200 mm. If the failure load was 26.9 kN, find the flexure strength. a.
8.1 MPa
b) 7.8 MPa c) 4.8 MPa d) 5.4 MPa Max bending moment = M = PL/4 = 26.9 × 1000 × (200)/ 4 Moment of inertia = I = (100 × 100
3
) / 12 c = 100/2 = 50 mm Modulus of rupture = σ = Mc/I = 8.1 MPa
15.
Hollow masonry units have a net cross-sectional area in every plane parallel to the bearing surface less than ……….%
of the gross cross-sectional area in the same plane. a.
75 b) 70 c) 85 d) 80 16.
RTFO procedure is used to simulate ………………
that occurs in the asphalt during production of asphalt concrete. a.
Short term aging
b) alligator cracking c) long term aging d) distress 17.
What is the typical load duration used in designing wood structures? a.
10 years
b) 12 years c) 15 years d) 5 years 18.
Calculate the modulus of elasticity of carbon
–
epoxy composite under isostrain condition if the composite consists of 40% carbon fibers and 60% epoxy by volume. The moduli of elasticity of the carbon fibers and the epoxy are 350 and 3.5 GPa. a.
142 GPa
b) 124 GPa c) 158 GPa d) 180 GPa Ec = 0.4 x 350 + 0.6 x 3.5 = 142 GPa
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------------------------------------------------------------------------------------------------------------ PART B (Answer any four questions) Each question carries 6 points Total points for PART B is 24 1)
An asphalt concrete mixture includes 94% aggregate by weight. The specific gravities of aggregate and asphalt are 2.65 and 1.0, respectively. If the bulk density of the mix is 147 pcf, what is the percent voids in the total mix? Note: Use volumetric analysis (including the phase diagram) and ignore the absorption of asphalt by the aggregates. Assume total volume V
t
= 1 ft
3
Determine mass of mix and components:
Total mass = 1 x 147 pcf = 147 lb Mass of aggregate = 0.94 x 147 = 138.2 lb Mass of asphalt binder = 0.06 x 147 = 8.8 lb Determine volume of components: V
s = 138.2/ (2.65 (62.4)) = 0.836 ft
3
Ignore absorption, therefore V
be
= V
b
V
b = 8.8/ (1.0 (62.4)) = 0.141 ft
3
Determine volume of voids: V
v =
V
t
–
V
s –
V
b
= 1-0.836-0.141 = 0.023 ft
3
Volumetric calculations: VTM = (V
v
/ V
t
) 100 = (0.023/1.00) 100 = 2.3% 2)
A severe weathering clay brick was tested for absorption and saturation coefficient according to ASTM C67 procedure and produced the following data: Dry mass of the specimen = 2.186 kg Saturated mass after 24-hr submersion in cold water = 2.453 kg saturated mass after 5-hr submersion in boiling water = 2.472 kg Calculate: a)
Absorption by 24-hr submersion b)
Absorption by 5-hr boiling c)
Saturation coefficient
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Absorption by 24-h submersion, % = [(2.453 –
2.186 ) / 2.186 ] x 100 = 12.2%
Absorption by 5-h boiling, % = [(2.472 –
2.186 )/2.186 ] x 100 = 13.1% Saturation coefficient = (2.453 –
2.186 ) / (2.472 –
2.186 ) = 0.93 3)
A glulam beam with a manufactured depth of 12 in. at 14% moisture content. Assuming common values for estimating dimensional changes, compute the new depth of the beam if the moisture content is increased to 35%? •
Assume a 30% FSP •
The change of moisture content from 14% to 30% causes swelling. Swell does not occur above the FSP. •
Assume a 1% swelling of the green dimension per 5% increase in moisture content below the FSP. Increase in depth = (30-14) / 5 = 3.2% •
X
MC
= X
FSP
(1 –
Rate of dimension change x Change in moisture content) 12 = X
FSP
(1- 0.032) New depth = X
FSP
= 12.397 in 4)
A fiber-reinforced polymer composite under isostrain condition consists of 35% fibers and 65% polymer by volume. The moduli of elasticity of the fibers and the polymer are 50 x 10
6
psi and 0.5 x 10
6
psi respectively, and the Poisson’s ratios of the fibers and the polymer are 0.25 and 0.41, respectively. Calculate the following: a)
modulus of elasticity of the composite. b)
percentage of load carried by the fibers c)
Poisson’s ratio of the composite
•
Equation 11.7 Ec = 0.65 x 0.5 x 10
6
+ 0.35 x 50 x 10
6
= 17.80 x 10
6
psi •
Equation 11.8, Ff/Fc = (50 x 10
6
/ 17.80 x 10
6
) x 0.35 x 100 = 98.3% •
Equation 11.9,
c = 0.35 x 0.25 + 0.65 x 0.41 = 0.354
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5)
What are the engineering applications of each of these tests? a)
flash point test on asphalt b)
RTFO procedure c)
rotational viscometer test d)
dynamic shear rheometer test e)
penetration test on asphalt f)
Flexure Test of Small, Clear Wood Specimen as per ASTM D143 Textbook: See sections 9.6.2 Performance Grade Binder Characterization 10.9.2 Flexure Test of Small, Clear Specimen. ------------------------------------------------------------------------------------------------------------ BONUS QUESTIONS (This section is optional. Show all work for credits) Each question carries 2 points Total points for this section is 12 1.
Laboratory specific gravity and absorption tests are run on two coarse aggregate sizes, which have to be blended. The results are as follows: Aggregate A: Bulk specific gravity = 2.491 ; Aggregate B: Bulk specific gravity = 2.773. Calculate the specific gravity of a mixture of 60% aggregate A and 40% aggregate B by weight. Bulk specific gravity of the mixture = 1
0.6
2.491
+
0.4
2.773
= 2.597
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2.
Calculate the density of iron, given that it has a BCC crystal structure, an atomic radius of 0.124 nm, and an atomic mass of 55.9 g/mole. 𝜌 =
𝑛
𝐴
V
?
(N
𝐴
)
Number of equivalent atoms for BCC = 2 APF =
Vol of atoms in unit cell
Vol of unit cell
𝑉
?
= (
4𝑟
√3
)
3
= (
4(0.124×10
−9
√3
)
3
(V
c
equation from Problem #4) 𝜌 =
2
(55.9)
(
4(0.124×10
−9
√3
)
3
(6.023
×
10
23
)
= 7904 × 10
3
kg/m
3 = 7.9 g/ cm
3
3.
An aluminum alloy rod has a circular cross section with a diameter of 8 mm. This rod is subjected to a tensile load of 4 kN. Assume that the material is within the elastic region and E= 69 GPa. What will be the lateral strain if Poisson’s ratio is 0.33?
= 4000 / (
x 0.004
2
) = 79.5774 x 10
6
Pa = 79.5774 MPa
axial = / E = 79.5774 / (69 x 10
3
) = 0.001153 m/m
lateral = -
axial = - 0.33 x 0.001153 = - 0.000381 m/m
4.
Students in the materials lab mixed concrete with the following ingredients: 9.7 kg of cement, 18.1 kg of sand, 28.2 kg of gravel, and 6.5 kg of water. The sand has a moisture content of 3.1% and an absorption of 4.2%. The gravel has a moisture content of 3.4% and an absorption of 4.4%. What is the actual water cement ratio? Water absorbed by sand = 18.1 (0.042 –
0.031) = 0.199 kg
Water absorbed by gravel = 28.2 (0.044 –
0.034) = 0.282 kg
Free water = 6.5 –
0.199 –
0.282 = 6.019 kg
w/c ratio = 6.019 / 9.7 = 0.62
5.
A wood pole with a diameter of 10 in. has a moisture content of 5%. The fiber saturation point (FSP) for this wood is 30%. The wood shrinks or swells 1% (relative to the green dimensions) in the radial direction for every 5% change in moisture content below FSP. What would be the percent change in the wood’s diameter if the wood’s moisture is increased to 55%?
•
The change of moisture content from 5% to 30% causes swelling. Swell does not occur above the FSP. •
1% swelling of the green dimension per 5% increase in moisture content below the FSP. Percent change in the wood diameter = (1/5) x (30 - 5) = 5.0%
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6.
An epoxy is randomly reinforced with E-Glass fibers with 0.0012 in. diameter, 0.5 in. length, ultimate tensile strength 0.5 x 10
6
psi , and 7.2 ksi shear strength. Does this fiber length fully strengthen the composite? What is the minimum fiber length that would make the composite continuously reinforced? L
?
= 𝜎 ?
2𝜏
= {500 (0.0012)}/ 2(7.2) = 0.042 in The fiber length > Lc. Therefore, the fiber length fully strengthens the composite. Min. length for continuously reinforced composite= 15 x 0.042 = 0.63 in
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