WIDENER UNIVERSITY
DEPARTMENT OF CIVIL ENGINEERING
CE 206
STRUCTURES AND MATERIALS LABORATORY MANUAL
Spring 2018
Contents
I. LABORATORY FORMAT ............................................................................................ 4
A.
COURSE OBJECTIVES ..................................................................................... 4
B.
CLASS ORGANIZATION .................................................................................. 4
C.
LABORATORY ORGANIZATION ................................................................... 4
D.
LABORATORY REPORT FORMAT ................................................................ 5
E.
EXECUTIVE SUMMARY FORMAT ................................................................ 9
F. DESIGN-BUILD-TEST PROJECT: ..................................................................... 10
II. LABORATORY POLICIES ....................................................................................... 12
III. Technical Writing Assignent: Review of Journal Article ......................................... 13
A.
Objectives: .......................................................................................................... 13
B.
References: ......................................................................................................... 13
C.
Background: ....................................................................................................... 13
D.
Procedure:........................................................................................................... 13
IV. Lab #1 Concrete Mix Design and Compression Tests .............................................. 17
A.
Objectives: .......................................................................................................... 17
B.
References: ......................................................................................................... 17
C.
Background: ....................................................................................................... 17
D.
Materials: ............................................................................................................ 20
E.
Equipment: ......................................................................................................... 20
F. Procedure: .............................................................................................................. 20
G.
Calculations: ....................................................................................................... 22
V. Lab # 2: Measuring Tensile Properties of Metal Specimens ...................................... 24
A.
Objectives: .......................................................................................................... 24
B.
References: ......................................................................................................... 24
C.
Background: ....................................................................................................... 24
D.
Specimens: ......................................................................................................... 27
E.
Equipment: ......................................................................................................... 27
F. Testing Procedure: ................................................................................................. 27
G.
Measurements and Calculations:........................................................................ 28
VI. Lab #3 Measuring Forces in Truss Members Using Strain Gages ........................... 30
A.
Objectives: .......................................................................................................... 30
B.
References: ......................................................................................................... 30
C.
Background: ....................................................................................................... 30
D.
Specimens: ......................................................................................................... 31
E.
Equipment: ......................................................................................................... 31
F. Procedure: .............................................................................................................. 31
G.
Calculations: ....................................................................................................... 32
VII. Lab #4 Wooden Beam Tests ..................................................................................... 33
A.
Objectives: .......................................................................................................... 33
B.
References: ......................................................................................................... 33
C.
Background: ....................................................................................................... 33
D.
Materials: ............................................................................................................ 34
2
E.
Equipment: ......................................................................................................... 34
F.
Procedure:........................................................................................................... 34
G.
Calculations: ....................................................................................................... 34
IX. Lab # 5 Beam Stresses and Deflections ..................................................................... 41
A.
Objectives: .......................................................................................................... 41
B.
References: ......................................................................................................... 41
C.
Background: ....................................................................................................... 41
D.
Specimens: ......................................................................................................... 42
E.
Equipment: ......................................................................................................... 42
F. Procedure: .............................................................................................................. 42
G.
Calculations: ....................................................................................................... 43
X. Lab #6 Hot Mix Asphalt Superpave Volumetric Design and Compaction Tests ........ 45
A.
Objectives: .......................................................................................................... 45
B.
References: ......................................................................................................... 45
C.
Background: ....................................................................................................... 45
D.
Materials: ............................................................................................................ 47
E.
Equipment: ......................................................................................................... 47
F.
Procedure: (based on AASHTO T166 Test Method A) .................................... 47
G.
Measurements and Calculations:........................................................................ 48
3
I. LABORATORY FORMAT
A.
COURSE OBJECTIVES
The Structures and Materials Laboratory is intended to (1) supplement theoretical
knowledge in CE structures and construction materials; (2) acquaint students with basic
measurement and experimental techniques to examine properties of materials and
structural components; (3) develop the ability for planning and design of projects; (4)
familiarize the student with basic statistics for analysis of experimental data; (5) develop
written and oral communication skills; and (6) provide exposure to the interpersonal
relationships involved in group work.
Upon successful completion of the course, students will be able to:
1. Conduct experiments to measure properties of materials and systems for civil
engineering applications.
2. Analyze data for error analyses, comparison of experimental and theoretical results,
and application of regression analyses.
3. Prepare engineering laboratory reports using appropriate technical writing methods.
4. Design, conduct, and present an independent project.
B.
CLASS ORGANIZATION
1. The class will be divided into lab teams to perform the experimental work, but
each student is required to submit an individual lab report or executive summary
for each experiment, with the exception of the design-build-test project when a
single group report from the project team is submitted.
2. Detailed instructions for the prepared experiments are included in this manual.
Students are expected to be familiar with the objectives, scope, and content of the
lab prior to the experiment. Some labs may require preliminary calculations
(truss analyses for example), and these calculations should be prepared prior to
the lab. Deviations from the lab manual will be discussed by the instructor prior
to the lab.
3. Safety policies are posted in each laboratory and in this manual (see Laboratory
Policies). Students are expected to comply with these policies at all times. Failure
to comply with these policies will result in reductions of lab grades and possibly
dismissal from the lab.
C.
LABORATORY ORGANIZATION
1.
A schedule of lab experiments will be provided for the semester. The instructor
will discuss objectives and procedures for each experiment during the weekly
4
lecture period. Each student is expected to read and be familiar with the
objectives, background, and procedures for each week’s lab prior to lecture.
2.
All students are required to be present for, and participate in, the experimental
work done in the laboratory. All excused absences require a written request in
advance and/or proper corroboration such as a physician's note. Unexcused
absences cannot be made up and will result in the student receiving a zero for the
lab.
3.
All students are expected to participate and contribute to the success of each lab
experiment. Tasks should be coordinated within each group and should include
setting of lab equipment, making preliminary calculations and quality assurance
checks, obtaining measurements and recording data. It is the responsibility of the
entire team to ensure that the best results are obtained.
4.
One set of data should be recorded per group. The responsibility of data recorder
should rotate. At the completion of the lab, the instructor will post the data sheets
or a compilation of the data for all group members on shared files. These data
sheets should be attached in the appendix of all lab reports. It is extremely
important to clearly and accurately record all data.
D.
LABORATORY REPORT FORMAT
1.
Lab reports and executive summaries should be written from the perspective of a
practicing engineer to the extent possible. The reports should be written for a
general technical audience (such as another engineering student or faculty).
Assume that the assignments are projects that you are assigned to work on by your
project manager or client. Therefore, phrases such as: “the students were given the
test specimens ….,” should be avoided. In addition, the stated objectives of the lab
should be technical objectives, not “educational objectives.” For instance, a
practicing engineer is not likely to tell his client that he did the work to learn how to
use the equipment.
2.
All reports should be prepared using Microsoft Word and submitted through the
assignment tab in Campus Cruiser. Assignments are due at the start of the class.
Students will be responsible for maintaining copies of all reports in the event that a
file is lost or revisions are necessary.
3.
All text should be double spaced. Margins (at least one-inch) should be provided
on all sides of the page. Pages should be consecutively numbered beginning with
page 1 following the title page.
4.
All Tables and Figures must be properly numbered (Figure 1, Table 1), titled,
and labeled (including units), and they should appear as soon as possible after
they are referred to in the text. For figures (graphs, sketches, pictures, or other
illustrations), the figure number and title appear at the bottom of the figure. Table
5
numbers and titles appear at the top of each table. Original data records and
sample calculations DO NOT belong in the body of the report, but should be
included in titled appendices. The results should be presented in tabular/graphical
format, and must include all data and information so the reader can check the work.
5.
All equations must be sequentially numbered (ie. Eq. 1), and all variables in the
equation must be identified the first time they appear in the report.
6.
Avoid the use of personal pronouns such as “we” or “I”. Although these pronouns
are perfectly acceptable in other writing styles, they are not widely accepted by
technical journals in science and engineering. Science and engineering journals
prefer an objective viewpoint; the work being described should be reproducible by
anybody following the procedures described in the study. The use of “we” and “I”
is subjective and may imply that only the authors could do the work. In recent
years it has become more acceptable to use “we,” especially in situations where the
author is discussing or interpreting (such as in the introduction or conclusion
sections); however it is still good practice to avoid “we” whenever possible (for
example, write “Four cylinders from each batch of concrete were tested” instead of
“we tested four cylinders from each batch of concrete”.
6.
Avoid the use of colloquialisms, jargon, and meaningless or unnecessary phrases
(ie. - "the results were as expected", or "this was a good experiment"). All
parts of the lab report should directly support the objectives of the lab.
7.
Use proper spelling and grammar - points will be deducted from lab reports if
grammar and spelling errors persist. Help from the University Writing Center
should be considered, or may be required, if writing problems are not corrected.
References will be made available for help with technical writing.
8.
Sections and Content of the Lab Reports:
Students should view their lab report as the final product of their work, or their
“deliverable,” similar to the way a practicing engineer views the report he or she
submits to a client. Lab reports will be organized in the following sections:
a.
Title Page
b.
Table of Contents
c.
Abstract: The abstract is a brief one to two-paragraph summary of the objectives,
work conducted during the experiment, and significant results or findings.
Sometimes a background statement may be provided at the beginning of the
abstract. The abstract allows the reader to determine the nature and scope of the
report without having to read from beginning to end. The optimal length is one
paragraph, but it could be as short as two sentences. The length of the abstract
depends on the subject matter and the length of the paper. Between 80 and 200
words is usually adequate.
6
d.
o
o
o
Introduction: Background statement on the relevance of the lab from an
engineering perspective; technical objectives of the lab; overview, or scope of
work describing the major tasks or activities completed in the lab. If the
introduction is not logical, then your reader will assume that the rest of the
document is garbage. A good introduction is a clear statement of the problem or
project and the reasons that you are studying it. This information should be
contained in the first few sentences. Give a concise and appropriate discussion of
the problem and the significance, scope, and limits of your work. The Introduction
can be structured something like this:
Context: Connect the lab you are doing to real world applications to show that you
understand the problem and its relevance from an engineering perspective
Problem Description: Give a brief description of what you were required to do in
the lab - an overview, or scope, of the work.
Goals: Discuss the technical objectives. What were you trying to accomplish?
e.
Background: Provide any information necessary for the reader to understand
subsequent sections of the report. Sometimes the Background section is combined
with the Introduction; in other reports, the Background section may be used to
explain the underlying theoretical basis for later calculations.
f.
Methods and Procedures: This section often consists of two parts:
1. Experimental Procedures: procedures performed to acquire data,
2. Analytical Procedures: methods applied to analyze the data to produce the
results and achieve the objectives.
This section can also be called “Experimental Methods” or “Materials and
Methods”. The Experimental Procedures subsection should provide a general
description of the equipment used and the work conducted during the experiment,
with particular attention to any deviations from the lab manual. This section is not
a repeat of the step by step set of instructions that are found in the lab manual!
For experimental work, give sufficient detail about your materials and methods
(both experimental procedures and methods of data analysis) so that other
experienced workers can repeat your work and obtain comparable results. When
using a standard method, cite the appropriate literature and give only the details
needed. Identify the test specimens/materials and equipment/apparatus used
for the laboratory work. Describe equipment/apparatus only if it is not standard or
not commercially available. Giving a company name and model number in
parentheses is nondistracting and adequate to identify standard equipment.
If the laboratory work will also involve calculations using theoretical equations,
then the “Methods” portion of the Procedure can be broken into two subsections –
one to cover “Experimental Procedures” and one to describe “Analytical
Procedures” or “Theoretical Calculations.” The “Analytical Procedures” subsection
should include sufficient mathematical detail to enable other researchers to
7
reproduce derivations and verify numerical results. Include all equations and
formulas necessary, but lengthy derivations are best presented in the Appendix.
Many students fail to recognize that the equations and statistical methods applied to
obtain the results are as important as the raw data. The reader expects to see these
methods discussed BEFORE the results are presented. After reading these details in
the Procedures and Methods Section (or in the Background), the reader will know
what to look for and expect in the Results and Discussion Section. Students may
wish to use subheadings, such as Experimental Procedures and Analytical
Procedures, to help write and organize this section.
The Analytical Procedures subsection should present and discuss the theories,
formulas, and equations that are applied to the data, or otherwise examined during
the experiment. Equations should be numbered and all symbols or parameters in the
equation should be identified as you would find in a technical journal article.
g.
Results and Discussion: This is where you detail the results you obtained in the
laboratory. Summarize the data collected and their statistical treatment. Include
only relevant data, but give sufficient detail to justify your conclusions. Tables and
graphs should be used where necessary to present your data, calculations, and
results. Remember that all figures and charts must be accompanied by supporting
text. Discussion must be provided to describe and explain the data and the
significance of the information in the tables and graphs. The purpose of the
discussion is to interpret and compare the results. Be objective; point out the
features and limitations of the work. Relate your results to current knowledge in the
field and to your objectives for the project. Comparison of results with theory or
accepted formulas should be discussed. Sources of error should be discussed with
respect to your findings and the significance of these errors with respect to the
objectives of the lab.
The Results and Discussion section usually follows the following format:
introduce a table, figure, or written results (Table 1 shows the material properties
found from the tensile tests), present the table, figure, or results (Table 1 is inserted
into the report), and finally discuss the table, figure, or written results (write about
the information that is included in Table 1). Only then is the next set of data (table
or figure) introduced, presented, and discussed. The section should begin with
overall results presented first, followed by more detailed results or comparisons.
h.
Conclusions: Summarize objectives, significant results, and discuss conclusions
and recommendations as they relate to your objectives. This is where you should
document the "lessons learned" during the course of the laboratory exercise. What
were your expected results? Were those results achieved? If not, why not? Have
you resolved the problem? What exactly have you contributed? Briefly state the
logical implications of your results. Suggest further study or applications if
warranted. If you were allowed different constraints in the laboratory could you
have designed a better, faster, or cheaper system? If so, how?
8
i.
References: Provide a bibliographic list of references used in the lab report.
Document the reference sources you used. That way, if you ever need to find the
information again, you'll have a head start on finding it. Use a standard method of
citation. A commonly accepted method is the MLA, given in MLA handbook for
writers of research papers, 6th ed, 2003. New York: The Modern Language
Association of America. You can find it in Wolfram Library. Call Number: M
Desk Reference Z253 .C534
j.
Appendix: original data sheets from lab, derivations, calculations (at least one
complete set of sample calculations must be included with each report), and any
other related information which supports the lab report, but does not fit in the main
report.
E.
EXECUTIVE SUMMARY FORMAT
The executive summary is a standalone section in a formal report that provides a
shortened version of the report and summarizes the key facts and conclusions
contained in the report. Sometimes the executive summary is filed separately from
the formal report. We will be using a modified form of the executive summary as
the report you will turn in for some of the experiments we do this semester. Which
experiments require full lab reports and which require executive summaries is
shown on the syllabus. Your executive summaries will be “modified” in that you
must provide a full discussion of the results and also include an appendix with all
data sheets and appropriate calculations. Your executive summary will be similar to
the requirements for the lab reports but will leave out the abstract, table of contents,
background, and methods and procedures sections from the report. Your executive
summary should NOT contain separate sections as is done in the lab report. Instead,
it should be written in paragraph format with each section starting in a new
paragraph. The executive summary shall contain:
a. Title Page
b. Background Statement: The background statement (also called the
context) connects the lab to real world applications to show you understand
the problem and its relevance from an engineering perspective.
c. Objectives: A statement of what you are trying to accomplish. Similar to
the objectives in a lab report, this section should only contain the technical
objectives.
d. Scope of Work: A brief description of what you were required to do in the
lab. Include general processes but not the details. For example, you should
state that strain gage data was collected but you don’t need to provide details
about where the strain gages were located or how the data was collected.
e. Results and Discussion: This is where you introduce, present and describe
the results you obtained in the laboratory. Summarize the data collected and
the analysis that is done with that data, giving sufficient detail to justify your
conclusions. As in the Results and Discussion section of the full laboratory
report, tables and graphs are to be used where necessary to present your
9
data, calculations, and results. Remember that discussion must be provided
to describe and explain the data and the significance of the information in
the tables and graphs. The purpose of the discussion is to interpret and
compare the results. Point out the features and limitation of your work and
relate your results to the technical objectives of the lab. Compare your
results with theory or accepted formulas and discuss the comparison.
Sources of error should be discussed with respect to your findings and the
significance of the errors with respect to the objectives of the lab. The
Results and Discussion section will follow the same format that was used in
the lab report format.
f. Conclusions: Unlike in the full lab report, in the executive summary’s
conclusions you do NOT repeat the objectives or significant results, as the
information was presented in earlier paragraphs of the executive summary.
This is where you should write about the “lessons learned” from the
laboratory. What were your expected results? Were those results achieved?
If not, why not? Have you resolved the problem? Briefly state the logical
implications of your results. Suggest further study or applications if
appropriate. If you had different constraints in the laboratory, could you
have gotten better results? If so, how?
g. Appendix: While a typical executive summary would not include an
appendix, you are required to submit the original data sheets from lab,
derivations, calculations (include at least one complete set of sample
calculations), and any other related information which supports the
executive summary.
F.
1.
2.
DESIGN-BUILD-TEST PROJECT:
Design-build-test project teams will be organized to compete in the EPDACI
Student Concrete Beam Competition. The competition objectives are to design,
construct and test a concrete beam reinforced with steel bars to achieve optimal
ultimate load; and to predict the ultimate load and the load that will result in a
midspan deflection of 1/4 inch. Two cash prizes will be awarded by EPDACI – one
prize for the student team that best achieves the optimal ultimate load and one prize
for the student team that achieves the best predictions. Student teams will be
required to develop and evaluate several alternative designs for achieving the
competition objectives, and to justify the design alternative they choose to use in
the competition. The development and evaluation of alternative solutions to the
competition problem will be an important element in the project grade, and must be
clearly explained in the project reports which are described in the next paragraph.
Each group will submit the following for their design-build-test project:
Project Proposal: The proposal must include a discussion of your team’s objectives
for the project, a description and evaluation of the alternative designs your team
considered, the design your team is proposing to build along with a justification for
your choice, dimensioned AutoCAD drawings of your proposed beam geometry
including location of reinforcement, your concrete mix design, and a bill of
materials for the supplies you will need to construct your beam. If the project will
10
require the purchase of materials or supplies (other than plywood for formwork,
steel rebar, Type I cement, sand, and generically available coarse aggregates and
admixtures), your proposal should also include information on costs for the “extra”
materials.
Written Group Project Report: In general, the same requirements that apply to
writing a full laboratory reports will apply to writing the final design-build-test
project report. However, unlike the laboratory reports which are prepared by each
student individually, the design-build-test project report is prepared as a single
group report from the project team, organized in a similar manner to the individual
lab reports. However, for this report, you will also need to include a separate section
on “Design Alternatives” which comes after the Introduction and covers the
development and evaluation of the alternative solutions you considered for
achieving the project objectives, and explains the reasons for the design you chose
to use. You will also need to include a “Theoretical Background” section, which
should help to explain the prediction calculations you will make for ultimate load
and deflections. Your “Theoretical Background” section will provide the
background for and be closely related to the “Methods of Data Analyses” that you
include in the “Methods and Procedure” section of your report. Your Conclusions
section should include your evaluation of how your chosen design performed
relative to your reasons for choosing it, “lessons learned,” and suggestions as to
what you would do differently if you had the opportunity to redo the project.
Oral Report: Each team will make a 20 to 30 minute oral presentation about their
project. As your audience will be other student teams who also completed the
project, your report should concentrate on the development and evaluation of the
alternative solutions you considered for achieving the project objectives, your
team’s specific project objectives, your final design and your reasons for choosing
it, discussion of results including a comparison of your predictions with your
experimental results, your evaluation of how your chosen design performed with
lessons learned and suggestions for improvements. Preparation of the oral report
should wait until the written report has been prepared. Practice speaking on your
feet without reading what you wish to say. Note cards and notes within PowerPoint
or another presentation program are certainly acceptable and are often a good idea,
but the speech should not be read word for word from them. Graphical and
technical aids should be prepared well in advance, making sure that they are
readable and not too “wordy.” Be prepared to answer questions from the audience
once everyone in your group has finished speaking. Gear your talk to the level of
the audience--do not try to "snow" them, or be flip in explaining what you did.
There is no room for technical dishonesty--if the project didn't work, concentrate on
why rather than trying to "explain away" mistakes.
11
II. LABORATORY POLICIES
Most laboratory regulations are in effect for one of two reasons: to protect the student or
to protect the equipment. The following rules must be observed by all students utilizing
the laboratory:
1.
Any accident which results in damage to person or property (yours or Widener's),
no matter how minor, must be reported to the instructor as soon as possible. First
aid materials are available from the instructor and/or lab technicians.
2.
Eye protection shall be worn at all times in the laboratory when experimental
work is being performed.
3.
Smoking, eating, and drinking are not permitted at any time in the laboratories.
4.
Horseplay, which is dangerous in a laboratory environment, will not be tolerated
and will result in dismissal and a failing grade.
5.
Laboratory experiments are designed to be completed during scheduled laboratory
periods. If for some reason a group does not complete a lab in class, it will be
necessary to make up the lab outside of class time. Makeup time must be
approved in advance by the lab instructor. Outside of class periods, students may
not work alone in a laboratory but rather, for safety reasons, must work in a
minimum group of two. When students have finished their work, they must
secure the room (close windows, disconnect power, switch off lights, clean up
work area, return equipment to storage, lock doors, etc.).
6.
Equipment must be handled carefully, with due attention paid to possible hazards.
Students should understand procedures before beginning work. Consult the
equipment manual or the instructor if there is a question about proper operation.
7.
The laboratories must be left in a clean and tidy state, with equipment put away
and messes thoroughly cleaned up. Failure to do so will result in the lowering of
your grade.
12
III. Technical Writing Assignment: Review of Journal Article
A.
Objectives:
1. To become familiar with accepted format and style of writing for engineering lab
reports, project reports, and research articles.
2. To access current civil engineering research articles, and to review these articles
in terms of technical writing standards.
B.
References:
Example Lab Report for CE 306. (Davis, 2003).
Lab Report Editing and Review Guide (Davis, 2003)
C.
Background:
The most current information on engineering topics can be found in research journals that
are often published by professional societies, such as The American Society of Civil
Engineers (ASCE). These articles are reviewed and edited before they are accepted for
publication to ensure that the article conforms to technical writing standards as well as
technical content standards of the journal.
D.
Procedure:
1. Search the library’s on-line journals for a technical research article
a. The article should include experimental work and preferably also analytical
calculations
b. The article must be approved by the instructor before you leave the lab.
c. You will need to attach an electronic copy of the article to your submission –
you can obtain an electronic copy of the article by downloading it to the
desktop and then emailing it to yourself or putting it on a thumb drive.
d. Options for articles are as follows, or you may choose your own:
Shear Behavior of Corrugated Tie Connections in Anchored Brick
Veneer–Wood Frame Wall Systems by: Nikola V. Zisi and Richard M.
Bennett, JOURNAL OF MATERIALS IN CIVIL ENGINEERING ©
ASCE / FEBRUARY 2011
13
Fire Survivability of Externally Bonded FRP Strengthening Systems by:
S. K. Foster and L. A. Bisby, JOURNAL OF COMPOSITES FOR
CONSTRUCTION © ASCE / SEPTEMBER/OCTOBER 2008
Scour at Vertical Piles in Sand-Clay Mixtures under Waves, by:
Subhasish Dey; Anders Helkjær; B. Mutlu Sumer; and Jørgen Fredsø,
JOURNAL OF WATERWAY, PORT, COASTAL, AND OCEAN
ENGINEERING © ASCE / NOVEMBER/DECEMBER 2011
Shrinkage and Fracture Properties of Semiflowable Self-Consolidating
Concrete, by: Gilson Lomboy; Kejin Wang, M.ASCE; and Chengsheng
Ouyang, JOURNAL OF MATERIALS IN CIVIL ENGINEERING ©
ASCE / NOVEMBER 2011
Results from 18 Years of In Situ Performance Testing of Landfill Cover
Systems in Germany, by: Stefan Melchior; Volker Sokollek; Klaus
Berger; Beate Vielhaber; and Bernd Steinert, JOURNAL OF
ENVIRONMENTAL ENGINEERING © ASCE / AUGUST 2010
2. To use the library:
a. Go to Widener.edu
b. Click on Library in quick links
c. Go to Wolfgram Library
d. Go to Find Articles
e. Scroll through all Journals held until you find ASCE Publications
f. Select an ASCE Publication
g. Either scroll through recent journals by table of contents or search the entire
ASCE journal for a subject of your interest.
3. Review the article with respect to the following assignment. Provide short answers to
the questions and highlight and identify (by topic #) the sections of the article that
refer to each topic.
a.
Technical Writing Assignment: Review a Technical Journal Article
b. Select a technical article in an ASCE journal (Materials or Structures) that
involves experimental measurements taken by the authors. Review the article
with respect to the following questions. THIS ASSIGNMENT IS NOT DONE
IN LAB REPORT FORMAT.
14
1. Provide a bibliographic listing (citation) of the article. Sample citations
for different types of documents are provided in Chapter 11: Ethics and
Documentation in Engineering Writing section of your textbook.
2. Outline the main headings and sub-headings
3. Figures and tables: Answer the following questions:
a. Are all tables and figures identified by number with a brief descriptive
title? If not, which tables and figures do not contain this information
b. Are the table number and title located above or below the table?
c. Are the figure number and title located above or below the figure?
d. Are all tables and figures discussed in the article and appear on the same
page or the following page after they are first discussed? Which tables and
figures, if any, do not meet these criteria?
e. Is there consistent use of abbreviations for units?
4. Equations:
a. Are equations numbered and discussed in the text? If not, state the page
number in the article where equations are not numbered or discussed.
b. Are the variables (the symbols used in the equations) defined directly after
the equation? If not, where are the symbols defined?
For the following parts, print out a copy of the journal article and highlight
the text in the article that corresponds to the question and write the type of
content beside the highlighted text (i.e. background, objective, scope of
work, conclusion, etc…).
5.
a.
b.
c.
d.
e.
Abstract
Identify a background statement (if there is one)
Identify the statement of objective(s)
Identify the statement(s) of scope of work.
Identify the significant results or findings.
Do the results address the objectives? (Yes / No) Circle One
6.
a.
b.
c.
d.
Introduction:
Identify a background statement (if there is one).
Identify the statement of objectives.
Identify the statement(s) of scope.
Identify background information or a literature review.
15
7. Methods and Procedures:
a. Circle five (5) verbs that represent past tense.
b. Circle five sentences that represent passive voice.
c. Circle any instances where personal pronouns are used. If none are used,
write “no personal pronouns” next to the heading.
d. Identify pictures or drawings used to illustrate equipment or test
procedures. If none are used, write “no drawings or illustrations” next to the
heading.
e. Identify any analytical procedures. If none are used, write “no analytical
procedures” next to the heading.
8. Results and Discussion:
a. Are all figures and tables discussed in the text before they are shown? If
not, which table or figure is not discussed in the text before it is shown.
b. Identify a table where raw or summarized data is shown.
c. Identify text that is used to discuss the data in the table.
d. Identify a graph where relationships between variables are shown.
e. Identify text that is used to discuss the figure.
9. Summary and Conclusion:
a. Identify a statement of objective (if present).
b. Identify a summary of significant results (if present).
c. Identify the concluding statements (not a summary of results, but what is
concluded from the results).
16
IV. Lab #1 Concrete Mix Design and Compression Tests
A.
Objectives:
1.
To familiarize the student with the general characteristics of concrete and
concrete materials and with laboratory methods of manufacture and test of
concrete specimens
2.
To determine the effect of varying design mixes and materials (water, cement,
sand, and coarse aggregate) on the consistency of the fresh concrete and on the
strength of the hardened material.
B.
References:
ASTM C143-12 Standard Test Method for Slump of Hydraulic-Cement Concrete
ASTM C39-05 Standard Test Method for Compressive Strength of Cylindrical Concrete
Specimens
ACI Committee 211 Standard Practice for Selecting Proportions for Normal,
Heavyweight, and Mass Concrete, ACI 211.1-91, American Concrete Institute, 2002
ACI Committee 214 Evaluation of Strength Test Results of Concrete, ACI 214R-02,
American Concrete Institute, 2002
C.
Background:
Portland cement concrete is a widely used building material for many reasons: it can be
readily formed into many shapes; it is both durable and corrosion resistant; it provides
fire protection and water tightness; and has a relatively high compressive strength.
Although concrete exhibits low tensile strength, this disadvantage can be overcome by
reinforcing it, normally with steel.
The properties of concrete, in both the freshly mixed and the hardened state, are closely
associated with the characteristics and relative proportions of its components. The solid
portion of the hardened concrete is composed of the aggregate and a new product which
is the result of a chemical combination of cement with water. The remaining portion of
the space occupied by a given volume of concrete is composed of free water and air
voids, with the air voids usually not occupying more than 1 or 2% of the volume, unless
special chemicals (air entraining admixtures) are used to trap more air voids in the
concrete. After a period of time, the amount of free water depends on the extent of
chemical combination of water and cement, called hydration, and loss from evaporation.
17
The cement-water paste is the active component in the concrete and the properties of the
water-cement paste depend upon the characteristics of the cement, the relative
proportions of cement and water, and the completeness of the chemical combination or
hydration. The completeness of the hydration requires time, favorable temperatures,
and the continued presence of moisture. The period during which the concrete is
definitely subjected to these conditions is called curing. On construction work, curing
may vary from 3 to 10 days; in the laboratory the common curing period is 28 days.
Good curing is essential for the production of quality concrete.
There are five types of Portland cement, as indicated below:
Type I.
Type II
Type III
Type IV
Type V
For use in general concrete construction when the special properties
specified for the other four types are not needed
For use in general concrete construction exposed to moderate sulfate
action, or where moderate heat of hydration is required
For use when high early strength is required
For use when a low heat of hydration is required
For use when high sulfate resistance is required
All types are made of approximately 60% lime-bearing material and 40% of a clayey
material, which are ground, mixed together, and then heated to fusion. The product is
then ground fine and mixed with about 3% gypsum. A sack of cement contains 1 cubic
foot of material and weighs 94 pounds.
The sand and gravel (fine and coarse aggregate) used in a concrete mixture should be
well proportioned or graded from fine to large particles. Sands generally vary in particle
size from 1/4" down to those that pass a 100 mesh sieve (10,000 openings per square
inch). Gravels vary upward from 1/4" to 1.5" and often to 2.5". If the sand and gravel
are well graded, the void space will be minimized and less cement paste will be needed to
produce concrete. Concrete mix proportions may be based on volume or weight of
materials and are stated, for example, as
1-2.5-3.5 mix by volume,
meaning that 1 part of cement, 2.5 parts of sand, and 3.5 parts of gravel, all by volume,
should constitute the mix.
The water-cement ratio (quantity of water divided by quantity of cement used) is the
single most important factor influencing the strength of the final product. The only
property of concrete which improves with a higher water-cement ratio is the workability,
or the ease with which the concrete can be placed.
Consistency relates to the state of fluidity of the mix and ranges from the driest to the
wettest mixtures. The most common test to determine consistency is the slump test
(ASTM C143), which is performed by measuring the subsidence, or slump (in inches), of
a pile of concrete 12" high, formed in a mold that has the shape of a cone.
18
The tendency for water to rise to the surface of freshly placed concrete is known as
bleeding, and results from the inability of the material to hold all the mixing water.
Concrete subject to bleeding is not as strong or durable as concrete that does not bleed.
The strength of concrete is taken as an important index of its quality. Strength tests are
commonly made in compression and flexure and occasionally in tension. The
compression test of a 6 by 12-inch (or 4 by 8 inch) cylinder at age 28 days, after moist
storage at a temperature of 70oF, is a standard ASTM test (ASTM C39).
The compressive strength of concrete, made and tested under standard conditions,
ordinarily varies from 2500 to 6000 psi, although much higher strengths can be obtained
by using special additives. The tensile strength of concrete is roughly 10% of the
compressive strength; and the flexural strength (strength in bending) of plain concrete, as
measured by the modulus of rupture, is about 15 to 20% of the compressive strength.
The principal factors affecting strength are:
1.
Water-cement ratio--the higher the water content, the lower the strength.
2.
Age--the strength of concrete generally increases with age, although practically
all the strength has been achieved after 28 days.
3.
Character of the cement--the finer the cement, the higher the strength.
4.
Curing condition--the greater the period of moist storage, the higher the strength.
Evaluation of strength data is required in many situations, such as:
• Evaluation of mixture submittal;
• Evaluation of level of control (typically called quality control); and
• Evaluation to determine compliance with specifications (job-site acceptance testing)
A strength test result is defined as the average strength of all specimens of the same age,
fabricated from a sample taken from a single batch of concrete. A strength test cannot be
based on only one cylinder; a minimum of two cylinders is required for each test.
Concrete tests for strength are typically treated as if they fall into a distribution pattern
similar to the normal frequency distribution curve. A sufficient number of tests are
needed to indicate accurately the variation in the concrete produced and to permit
appropriate statistical procedures for interpreting test results. To satisfy statistically based
strength-performance requirements, the average strength of the concrete fcr′ should be in
excess of the specified design compressive strength fc′. The required average strength fcr′
used in mixture proportioning depends on the expected variability of test results as
measured by the coefficient of variation or standard deviation. The strength test record
used to estimate the standard deviation or coefficient of variation should represent a
group of at least 30 consecutive tests. If the number of test results available is less than
30, a more conservative approach is needed; and when the number of strength test results
is less than 15, the calculated standard deviation is not sufficiently reliable to be of use. In
those cases, the concrete is proportioned to produce much higher average strengths fcr′
than the specified design strength fc′.
19
The strength of concrete in a structure and the strength of test cylinders cast from a
sample of that concrete are not necessarily the same. The strength of the cylinders
obtained from that sample of concrete and used for contractual (job-site) acceptance are
to be cured and tested under tightly controlled conditions. The strengths of these
cylinders are generally the primary evidence of the quality of concrete used in the
structure. The engineer specifies the desired strength, the testing frequency, and the
permitted tolerance in compressive strength. It is impractical to specify an absolute
minimum strength, because there is always the possibility of even lower strength test
results simply due to random variation, even when control is good.
D.
Materials:
Type I Portland cement, sand, gravel, and lubricant for molds
E.
Equipment:
For mixing: scale for weighing, concrete mixer or mixing pan, shovels, trowel, slump
cone, 12" scale, tamping rod, measuring beakers, mallet, wet towels, plastic, 3” by 6" or
4” by 8” cylinder molds (Note: 3 by 6” cylinders are not permissible when testing
concrete strength by ASTM C39)
.
For testing: rigid end caps, and concrete testing machine.
F.
Procedure:
This experiment requires several laboratory periods. During the first period, concrete
mixes will be designed and cylinders prepared for testing. Cylinders will be tested at four
weeks (28 days) and either one week (7 days) or two weeks (14 days) after the first
period. Specific instructions regarding the mix design will be given at the time of the
experiment, using ACI 211.1-91 Standard Practice for Selecting Proportions for Normal,
Heavyweight, and Mass Concrete. Results will be compiled from all groups, with each
group using a different water-cement ratio for comparison and analysis.
a.
1.
Concrete Mix Preparation
Design one batch of non-air-entrained concrete, following the guidelines of
the American Concrete Institute. Mix enough concrete to mold four test
cylinders and to fill a slump cone. Mix the materials by first combining the
sand and cement, then adding the gravel, and finally the water. Keep
accurate records on the amount (by weight) of each of the materials used.
2.
Once a mix has been prepared, its consistency should be measured with the
slump cone apparatus, which is a truncated cone conforming to ASTM
specifications. To make the slump test (ASTM C143), dampen the slump
cone, scoop, tamping rod, and metal working surface. Holding the cone in
position by standing on the foot pieces, fill the slump cone in three equal
layers, rodding each layer 25 times with the tamping rod, making sure to
cover the full area of the concrete with the tamping motion and that the
20
3.
4.
5.
6.
strokes barely penetrate into the previous layer. For the final layer, pile the
concrete above the top of the cone to account for settlement. If the level
settles below the top of the cone, add additional concrete. Carefully strike
off the surface using the tamping rod. Raise the slump cone by means of
the handles, without any twisting or side motion. Place the cone next to the
concrete, with the tamping rod over the cone. If one side of the concrete
falls away or shears off, repeat the test. Measure the slump to the nearest
1/4" and classify the mix as wet (over 6"), normal (1-6"), or stiff (under 1").
The slump test is a good field test for consistency and may actually be used
to determine the amount of mixing water. If the mix is outside the "normal
slump" range, mix the concrete again and make adjustments to bring it into
the normal range. If the slump is greater than that required, add more
fine and/or coarse aggregates. If the slump is less than required, water
and cement in the appropriate ratio should be added. Make sure that
accurate records are kept of whatever materials are added so that the
actual ratio of materials can be reported.
Observe the general characteristics of each mix, making note of its
troweling workability. To determine troweling workability, work the
concrete with a trowel. If it works smoothly and with little effort, the
troweling workability may be called good. Rate as good, fair, or poor.
Fill the molds completely in three equal layers, tamping each layer 12 times,
and each time tapping the sides of the mold 5 to 10 times with a mallet to
remove air voids. Overfill the third layer to account for consolidation.
Finish the top by striking off with the tamping rod and troweling it smooth.
Cover the top immediately to prevent evaporation.
Properly identify samples and clean up work area, equipment and tools.
Arrange for proper curing of your specimens (moisture and temperature).
Strip the molds from the specimens after about a 24-hour curing time. The
samples then should be submerged in water or stored under wet burlap
covered with plastic for 7 days.
b. Compression Testing of Concrete Cylinders
1.
Prior to compression testing, measure the diameter of the concrete
cylinder using calipers. Measure the cylinder at mid-height at four
different locations around the circumference of the cylinder.
2.
Before testing the compression cylinders they must be capped on the ends
to permit uniform bearing when the load is applied. A cap is a small plane
surface of suitable material, such as gypsum plaster or hardened steel.
Wipe clean the bearing faces of the hardened steel bearing caps and of the
test specimen. Insert the test specimen into the bearing caps.
3.
Place the test specimen with bearing caps in place on the table (platen) of
the testing machine directly under the spherically seated (upper) bearing
block. Wipe clean the bearing faces of the upper and lower bearing blocks.
Seat the specimen in the testing machine and close the protective doors.
4.
Apply the load continuously and without shock, at a constant rate within
the range of 20 to 50 psi per second. During the application of the first
half of the estimated maximum load, a higher rate of loading may be
21
permitted. Do not make any adjustments in the controls of the testing
machine while the specimen is yielding rapidly (immediately before
failure). Increase the load until the specimen fails, and record the
maximum load carried by the specimen during the test. Note the type of
failure and the appearance of the concrete if the break appears to be
abnormal. Standard failure modes are shown in Figure 1. MAKE SURE
THE PLATEN DOES NOT RISE ABOVE THE MAXIMUM
HEIGHT MARKED ON THE TESTING MACHINE.
Fig. 1 Concrete Cylinder Compression Failure Modes
G.
Calculations:
1. Record data from all lab groups in your lab section. Develop a data table to
record the details and test results of each cylinder, including:
Group #
Specimen #
Mix date
Test date
Mix design proportions by weight
Targeted compressive strength
Cylinder size
Slump
Workability
Ultimate load
Ultimate compressive strength, and
Type of fracture.
Data tables will be shared among all groups by posting to shared files on the
Campus Cruiser course web page.
2. The actual compressive strength is calculated as the failure load divided by the
cross-sectional area of the specimen. Report the strength to the nearest 10 psi.
3. Calculate the average compressive strength and range (difference between
maximum and minimum strengths) for cylinders from the same mix (i.e. by lab
22
groups in your section) and test date (i.e. same age at testing). Discuss the effect
that age at testing has on compressive strength.
4. Using the average 28 day strengths for the different mix designs, plot a curve
showing the compressive strength as a function of water/cement ratio, and discuss
if your curve follows the expected trend.
5. Did your mix designs produce the strengths you were expecting at 28 days? What
are some reasons why the actual average compressive strengths might not agree
with the targeted compressive strengths from the mix designs?
6. The targeted compressive strength is the strength that is expected to be produced
on average from a mix design. It is also known as the required average strength,
fcr′, but is NOT the same as the specified strength, fc′, engineers use in structural
design calculations. The targeted strength must be larger than the specified
structural design strength, fc′; how much larger depends on the quantity of test
results available. The fewer the tests, the larger the amount by which fcr′ must be
greater than fc′. For cases where there are not enough strength tests to establish a
standard deviation (i.e. when there are less than 15 strength tests), the average
compressive strength fcr′ must exceed the design strength fc′ by
fcr′ ≥ fc′ + 1000 when fc′ < 3000 psi
fcr′ ≥ fc′ + 1200 when fc′ is between 3000 and 5000 psi
fcr′ ≥ 1.10 fc′ + 700 when fc′ > 5000 psi
Based on the above, make recommendations for reasonable values for design
strength fc′ for which your concrete mix designs could be used.
23
V. Lab # 2: Measuring Tensile Properties of Metal
Specimens
A.
Objectives:
1.
To measure and compare the strength and several elastic and nonelastic properties
of metal specimens
To compare the measured values of each property to reference values reported in
the literature
To observe and compare the differences in the behavior of materials under load,
To study the types of fractures.
2.
3.
4.
The specific properties to be determined are:
1.
Elastic strength in tension:
a.
Modulus of Elasticity
b.
Yield point (upper and lower if possible)
c.
0.2% Yield Strength
d.
Proportional Limit
2.
Ultimate tensile strength
3.
Rupture Strength (True and Engineering)
4.
Ductility:
a.
Percent elongation in 2"
b.
Percent reduction in area
B.
References:
Davis, Troxell, and Hauck, The Testing of Engineering Materials, 4th Edition, McGrawHill, 1982, Chapters 2, 8, and 13.
ASTM E8-04 Standard Test Method for Tension Testing of Metallic Materials
C.
Background:
The static tension test is probably the most common and simplest of all the mechanical
tests. When properly conducted on suitable test specimens, the tension test comes closest
to evaluating fundamental mechanical properties for use in design, although the material
properties found by tension testing are not necessarily sufficient to enable the prediction
of performance of materials under all loading conditions.
In the tension test, a prepared specimen is subjected to gradually increasing (i.e., static)
uniaxial load until failure occurs. This operation is accomplished by gripping opposite
ends of the piece of material and pulling it apart. The test specimen elongates in a
direction parallel to the applied load.
24
The test specimens are usually either cylindrical or rectangular in shape and of
approximately constant cross section over the length within which measurements are
made. A uniform distribution of stress should develop over the critical cross section
perpendicular to the direction of the load
In tension test of metals, the properties usually determined are yield strength, tensile
strength, ductility (percent elongation), and type of fracture. In more complete tests,
determinations of stress-strain diagrams (Fig. 1), modulus of elasticity, and other
mechanical properties are included. It is customary to compute stress on the basis of the
cross-sectional dimensions before loading and to compute strains on the basis of the
original length between gage marks. Stresses and strains based on the original
dimensions are sometimes called nominal, conventional, or engineering stresses and
strains as opposed to the true stresses and strains which are computed on the basis of
the instantaneous (and changing) dimensions. Other terms of importance in this
experiment are summarized below.
Elasticity is the property of a material by which deformations disappear upon removal of
the stress. In tests of material under uniaxial loading, three criteria of elastic strength or
elastic failure have been used: the elastic limit, the proportional limit, and the yield
strength. The elastic limit is defined as the greatest stress a material is capable of
developing without a permanent deformation (set) remaining when the stress is removed.
To determine the elastic limit would require successive applications and release of greater
and greater loads until a load is found at which permanent deformation is produced. The
determination of the elastic limit is too involved to be practical and thus is rarely made.
The proportional limit σP is defined as the greatest stress that a material is capable of
developing without deviating from straight line proportionality between stress and strain.
Most materials exhibit this linear relation between stress and strain within the elastic
range, and the values of the elastic limit for metals do not differ greatly from the values
of the proportional limit, which is determined by use of a stress-strain diagram. The
modulus of elasticity (E) of a material is the ratio of stress to corresponding strain within
the proportional limit. In terms of the stress-strain diagram, the modulus of elasticity is
the slope in the initial straight line portion of the curve.
The determination of the proportional limit can be imprecise because of difficulty in
detecting when the stress-strain curve ceases to be a straight line. Thus, the yield
strength σY can be used as a measure of elastic strength. The yield strength is most often
determined by the offset method. A given value of strain (0.002 in/in or 0.2% is most
commonly used for ductile metals) is laid off along the horizontal axis of the stress-strain
diagram. A line parallel to the initial straight line portion of the stress-strain diagram is
drawn from the offset point. The value of stress where this line intersects the stress-strain
diagram is the yield strength for the specified offset.
25
Figure 1 – Example of a Stress-Strain Diagram
If the test is conducted at an appropriate speed with a ductile material, it is possible to
distinguish between two critical points in the yield range, the upper yield point and the
lower yield point. Although the upper yield point is the one usually reported, it is very
sensitive to the rate of loading, and it appears that the lower yield point is of more
significance, as far as the fundamental properties of the material are concerned.
Stiffness has to do with the relative deformability of a material under load. It is
measured by the rate of stress with respect to strain. The greater the stress required to
produce a given strain, the stiffer the material is said to be.
As the sample is loaded in tension, it elongates in the axial direction, while the lateral
dimensions get shorter (contracts). The ratio of the absolute value of the lateral strain to
the axial strain is called Poisson's Ratio. For steel, Poisson's Ratio may range from 0.250.35, so the lateral strains are only 1/4 to 1/3 that of the axial strain.
Ductility is the property of a material that enables it to undergo considerable
deformations before rupture and at the same time to sustain a considerable load. Mild
steel is a ductile material. A nonductile material is said to be brittle; that is, it fractures
with relatively little or no elongation. Cast iron and concrete are brittle materials.
Usually the tensile strength of brittle materials is only a fraction of their compressive
strength. The usual measures of ductility are percent elongation and percent reduction
of area in the tension test. Ductile materials will "neck down" prior to fracture; that is,
the reduction in the cross-sectional area can actually be observed during the test.
The term ultimate strength has to do with the maximum stress a material can develop.
Ultimate strengths are computed on the basis of the maximum load carried by a test piece
and its original cross-sectional dimensions. The tensile strength is the ultimate strength
in uniaxial tension. The stress at failure is sometimes called the breaking stress or
rupture stress; engineering rupture stress is calculated using the original cross-sectional
area, while true rupture stress is calculated using the cross-sectional area after failure.
26
When conducting tests to failure of materials and of structural parts or members, it is
important to observe and to record the type of failure and the characteristics of the
fracture. This observation should include the phenomena associated with final rupture
and evidence of change of condition such as yield, slip, scaling, necking down, local
crack development, etc. Although observations of failure are qualitative, much can be
learned from a study of failures, and with experience it is possible to recognize from a
break the kind of stress that caused failure and the type of material. In this connection it
is important to be alert in order to discover the presence of flaws and defects, for
premature failure is often caused by defects.
D.
Specimens:
Each group will be given standard threaded specimens of different materials for testing to
failure.
E.
Equipment:
Tinius-Olsen machine, extensometer, data acquisition software, dial calipers, 2" gage
punch, reduction of area gage.
F.
Testing Procedure:
Each group will be given specimens of different materials to test. Groups will take turns
in testing the specimens. The data collected by each group will be shared with the entire
class. Repeated tests for a given specimen type will allow calculation of a mean,
variance, and standard deviation.
1. Measure and record the diameter of each specimen using the standard micrometer.
2. Make 2-inch gage marks on each specimen using the 2" gage punch.
Note: Do not hit. Push down with the hand or lightly tap.
3. Start the testing machine in accordance with the appropriate instructions.
4. Install the specimen.
4. Install the extensometer.
5. Select the appropriate testing program to plot the stress versus strain curve, and
load the data acquisition program to download the test data (load, strain, and
elongation).
7. Load the specimen, removing the extensometer from the specimen after the
material starts to yield but before necking begins.
27
8. Continue the test until the specimen ruptures (breaks). Record ultimate
(maximum) load and load at rupture. (See #1 under Measurements &
Calculations.)
9. Remove the broken specimen and shut off the machine (if finished testing)
following the operating instructions. DO NOT SHUT OFF THE MACHINE
UNDER LOAD!!!!!
10. Note the geometry and appearance of the fracture. Measure and record the final
diameter of the necked section using the reduction of area gage or calipers.
Measure and record the final gage length between the set of 2" gage marks most
closely centered on the break.
G.
Measurements and Calculations:
a. Prepare a data table to record the following information for all specimens tested;
data tables will be shared among all groups by posting to shared files on the
Campus Cruiser course web page.
Group ID:
Specimen ID:
Material:
Diameter (in)
Cross-sectional area (in2)
Gage Length (in)
Yield Load (lb)
Ultimate Load (lb)
Rupture Load (lb)
Final Diameter (in)
Final Cross-sectional area (in2)
Final Gage Length (in)
2. Use the load and strain data from the data acquisition software to develop a stress
vs strain plot to illustrate material properties for the specimens your group tested.
The stress-strain diagrams (for your group’s specimens) should be included in the
Results and Discussion section, and the graphs should be labeled to illustrate the
material properties determined from the tensile test (for example, the value for E
should be shown as the slope of the linear portion of the stress-strain graph, the
proportional limit, yield stress, etc should be labeled).
3. Compute the following parameters for the specimens your group tested. At least
one complete set of sample calculations should be provided in the Appendix of
the report. Prepare a table to present the results for your specimens.
28
a.
b.
c.
Modulus of Elasticity (psi)
Proportional limit (psi)
Yield Point (psi) - not all specimens have a definite yield point,
while others will have both upper and lower yield points.
d.
Yield Strength at 0.2% Offset (psi)
e.
Ultimate Strength (psi)
f.
Rupture Strength (psi) - use original area
g.
True Rupture Strength (psi) - use final area
h.
Percent Reduction in Area
i.
Percent Elongation
Note: Modulus of Elasticity, yield point and yield strength at 0.2% offset can be
computed using each specimen’s load-strain-elongation data. All other properties can be
determined using information recorded in the data tables.
4. For each type of material tested (i.e. for steel samples and for aluminum samples),
prepare a table (see format below) to summarize results from all groups for yield
strength, ultimate strength, rupture strength, % elongation, and % reduction of
area. Calculate the means and standard deviations. Which property tends to be the
most uniform or consistent among different specimens of the same material?
Which properties show a large amount of variation?
Specimen Type________________________
Property
Group #1
Group #2
Group #3
Avg.
Standard
Deviation
Yield
Strength, ksi
Ultimate
Strength, ksi
Rupture
Strength, ksi
% Elongation
% Reduction
of Area
5. Reference values (modulus of elasticity, yield strength, ultimate strength, percent
elongation) for each specimen should be obtained (Matweb.com is a good data
source) and compared to your results. In your discussion of results, compare the
material properties you determined to published values for similar materials.
What sources of error or variability were significant for your results? Which
material was strongest? Which material was most ductile? How did the change in
cross-sectional area affect the value of the rupture strength?
29
VI. Lab #3 Measuring Forces in Truss Members Using
Strain Gages
A.
Objectives:
1.
To become familiar with the operation and application of electrical resistance
wire strain gages to measure stresses in simple structures.
2.
To experimentally determine the internal forces in simple structures, and to
compare those results with values obtained analytically.
B.
References:
The chapter on truss analysis in any Structural Analysis (or Statics) textbook
C.
Background:
The elastic stretching or straining of steel is of the order of one to four thousandths of an
inch for each inch of length. The accurate measurement of such strains can be made by
mechanical, optical, or electrical gages. The first strain gages were mechanical, but today
strains are usually measured with electrical strain gages.
An electrical resistance wire device, known as the SR-4 strain gage, consists of loops of
very fine wire cemented to a thin paper strip. The gage is cemented to the specimen with
a firm, tough cement that allows the gage to stretch with the specimen to which it is
attached. The changes in length of the wires alter their electrical resistance, which is
measured and calibrated to indicate the actual strain.
Proper bonding of the gages to the member is essential for obtaining reliable results. Care
must also be taken that the gage does not absorb moisture, since this will cause resistance
changes which affect gage stability.
Strains are determined by placing a wire gage in a four-arm Wheatstone bridge d-c
circuit. When the gage resistance is changed by deformation of the gage, the bridge
circuit is unbalanced. To compensate for strains caused by temperature and humidity
variations, a so-called dummy gage (a duplicate of the active gage) is connected into the
Wheatstone bridge circuit. The active gage measures strain due to stress, plus
deformations due to temperature and humidity effects, while the dummy gage measures
deformation due to temperature and humidity effects only. Although this setup can be
used satisfactorily, it is more convenient to contain the Wheatstone bridge setup within a
specially designed strain indicator. The strain indicator is calibrated to read strains (rather
than resistances), and includes electronic amplification to get a stronger signal.
30
To obtain direct or axial strain averaged from two sides of a tension or compression
member and at the same time to cancel out unwanted bending strains, two active gages
can be mounted back-to-back on opposite sides of the specimen.
In this experiment, strain gages will be used to determine the forces in the members of a
truss. A truss is defined as a structure consisting entirely of straight two-force members
that are pin-connected together at their ends. These connection points are called joints,
and it is further specified that all loads are applied to the truss at the joints, rather than
along the members. When a truss is subjected to an external load, the members develop
internal axial forces which are related to the applied external load by the geometry of the
truss and the magnitude, location, and direction of the applied load.
Figure 1 – Example of a Truss
Trusses may be analyzed by the method of joints, which consists of taking free body
diagrams of joints in the truss and solving the force equilibrium equations for the member
forces. In addition, if the strain in a member is measured, the stress in that member can
be found from Hooke's Law (stress = Modulus of Elasticity times strain). Once the stress
is determined, the axial force in a member can be found (stress = P/A so P = stress times
area).
D.
Specimens:
Several pin-connected triangular trusses, each instrumented with strain gages, and
constructed from 1018 steel (yield stress = 36,000 psi, E = 30,000,000 psi). Tests will be
conducted on the following truss configurations: 45-45-90 truss; 60-60-60 truss; and 3060-90 truss.
E.
Equipment:
Tinius-Olsen Testing Machine, digital strain equipment, dial calipers
F.
Procedure:
1.
Measure and record the cross-sectional dimensions and length of each member
and pin. Check the strain gages for broken leads, making any necessary repairs.
2.
Theoretically calculate the load to cause yielding of the most severely stressed
member of each truss. Also calculate the force to cause failure in the pin
connections. Through statics, these can be related to the external force being
31
applied to the truss by the Tinius Olsen machine. These calculations will be done
in the lecture prior to the Truss Lab.
3.
Theoretically calculate the critical buckling load for the truss. For a member to
buckle, it must be in compression. From the Euler buckling equation, the force to
elastically buckle a member equals 2 EImin/L2. Through statics, this member
force can be related to the external force on the truss. These calculations will be
done in the lecture prior to the Truss Lab.
4.
Set up a truss in the Tinius-Olsen Testing Machine, making sure that loads and
reactions are applied at truss joints and that they do not interfere with the
members.
5.
Connect the strain gages to the strain indicator and balance and calibrate all gages
per instruction manual.
6.
Apply five loads to the truss starting with the smallest load which gives a
reasonable strain reading. The maximum load applied to the truss should be
based on your calculations of the failure load divided by an appropriate factor of
safety. The load increments should be approximately equally spaced between the
first and fifth readings. Record the applied load and corresponding strain readings
for all members. NOTE: Each truss member has two strain gages mounted on
opposite sides of the member. Record readings from both gages, then average
these readings to determine the strain for that member. Using the average of two
strain gages for a single member eliminates unintentional bending effects.
G.
Calculations:
1.
Find the forces in all truss members corresponding to each experimentally applied
load, by appropriately relating average strain to stress (Hooke's Law) and stress to
force (force = stress x area).
b.
Calculate all truss member forces analytically using the method of joints.
3
Compare the experimental results with the analytical values by calculating the
absolute errors and the relative errors (%) with respect to the analytical value.
4.
Discuss the results and sources of error and variability.
32
VII. Lab #4 Wooden Beam Tests
A.
Objectives:
1.
To study the strength and rigidity of different types of wood.
2.
To determine material properties and typical factors of safety for wooden beams.
B.
References:
Western Wood Products Association Websites:
www.wwpa.org
www.lumberbasics.org
www.wwpa.org/techguide
C.
Background:
Structural lumber is graded for its strength and physical working properties; aesthetics are
secondary. The basic framing classifications are organized by size classifications and
performance capabilities.
Dimension Lumber - 2" to 4" thick and 2" (nominal) and wider. Western Dimension
Lumber design values, beginning in the Design Values section, are expressed as Base
Values. These values must be adjusted for size and repetitive member use, prior to
adjusting for other conditions of use. Dimension Lumber grades are divided into the
following 3 classifications: structural light framing, light framing, and stud
1.
Structural Light Framing
(2x2 through 4x4, used where high-strength design values are required in light framing
sizes, such as in engineered wood trusses.) Grades are: SELECT STRUCTURAL,
No. 1 & BTR (DF-L, DF & Hem-Fir species only), No. 1,No. 2, No. 3
2.
Light Framing
(2x2 through 4x4, basic framing lumber, as used in most light-frame construction, e.g.
wall framing, sills, plates, cripples, blocking, etc.) Grades are: CONSTRUCTION,
STANDARD, UTILITY
c.
Stud
(2x2 through 4x18, an optional grade intended for vertical use, as in load bearing walls.)
The grade is: STUD
Structural Joists & Planks
(2x5 through 4x18, intended for engineering applications for lumber 5" and wider, such
33
as floor and ceiling joists, rafters, headers, small beams, trusses and general framing
applications. Grades are: SELECT STRUCTURAL, No.1 & BTR (in Douglas Fir,
Douglas Fir-Larch, or Hem-Fir species only.), No. 1, No. 2, No. 3
D.
Materials:
Wood beam specimens of different types and cross sections
Adjustable beam supports, bearing plates, steel scale
E.
Equipment:
Tinius-Olsen testing machine configured for compression testing
F.
Procedure:
For each beam to be tested
1. Measure cross sectional dimensions and compare to nominal dimensions.
2. Position the beam in the Tinius-Olsen machine, to apply a concentrated load “P”
at midspan. Use bearing plates between the supports and the wood and between
the loading block and the wood. Record the beam span, and distance from
supports to the load point.
3. Select the testing software to plot applied load “P” versus deflection at midspan.
Apply load slowly until a significant failure occurs. Record ultimate load and
sketch and identify the type of failure.
G.
Calculations:
1. Draw shear and bending moment diagrams as a function of applied load “P.”
Where do the peak values for shear and moment occur?
2. Calculate the modulus of rupture for the wood fr = Mc/I at the ultimate load.
3. Using design values for wood in the National Design Specification (NDS) for
Wood Construction published by the American Forest and Paper Association and
the American Wood Council to calculate the factors of safety (modulus of rupture
divided by allowable stress) for the bending stresses. Plot the factors of safety as
a function of L/h (beam span divided by depth). Discuss any trends you see.
4. Using the formula Δ = PL3/48EI for the maximum deflection at midspan of a
simply supported beam with a concentrated load at the midpoint, calculate the
theoretical deflection at 25%, 50%, and 100% of ultimate load. Use values for
modulus of elasticity E (not Emin which is used for beam stability) and moment of
inertia I as given in the design aids from the Western Woods Producers (see
attached tables). Plot the theoretical deflections from your calculations on the
same graph as your experimental load versus deflection plot. Discuss why
theoretical deflections should diverge from the experimental deflections as the
load increases.
34
35
36
37
38
39
40
IX. Lab # 5 Beam Stresses and Deflections
A.
Objectives:
1.
To use strain measurements to obtain values of the normal stress in a beam, and to
compare the measured stress values with values computed from the bending stress
equation.
1. To compare measured and theoretical values of beam deflections.
2. To compare how different support loading conditions affect beam stresses and
deflections.
B.
References:
Beer & Johnston, Mechanics of Materials, Chapter 4 and Sections 7.1-7.4.
Chapters on beam deflections in any Structural Analysis text.
C.
Background:
In this lab, a beam overhanging both ends will be tested, which is different from a simply
supported beam, as seen in Figure 1. Although both beams have a pin (horizontal and
vertical reaction forces) and roller (vertical reaction force) support, the bending moment
and therefore the bending stresses will be 0 at the supports for the simply supported beam
in Fig. 1b with the beam reactions at the ends of the beam. However, bending moment
and stresses do not have to be 0 at a hinge or roller support when the beam overhangs the
support, as seen in Fig. 1a. In this case, depending on loading arrangement, internal
bending moment can be present at the supports. When typical gravity (downward) load
acts on the beam overhangs, the bending moment at the supports will be negative, and
thus the bending stresses at the supports will be tension on the top and compression on
the bottom of the beam.
Two different load arrangements will be tested in this lab, as shown in Fig. 2. For each
load arrangement, mid-span deflection will be measured directly by using a
deflectometer, while bending stresses at mid-span and at one of the supports will be
determined indirectly from strain gages.
Fig. 1a: Beam overhanging both ends
Fig. 1b: Simply supported beam
41
a
b
P/2
a
P/2
Fig. 2a: Loading Condition 1
a
b
a
P/2
P/2
Fig. 2b: Loading Condition 2
Although it may not be obvious, drawing shear and bending moment diagrams will show
that the loading condition in Fig. 2a is identical to that in a simply supported beam with a
length L = 2a+b; the moment (and bending stress and strain) at the hinge and roller
supports are equal to 0 and the maximum moment is positive and constant between the
two loads. However, the bending moment diagram for the beam in Fig. 2b looks entirely
different, with negative moment occurring at the supports.
Likewise, the deflections at mid-span are very different for the two loading conditions.
The loads in Fig. 2a cause the beam to deflect downward with maximum deflection at
mid-span, while the loads in Fig. 2b cause the beam to deflect upward at mid-span. The
theoretical deflections for either loading case can be calculated by several different
methods, including the moment-area method, conjugate beam, or by integrating the
differential equation of the elastic curve.
D.
Specimens:
1018 steel tubing 2 x 1.5 x 1/8” wall thickness. For the steel, E = 29 x 106 psi and σy =
50 ksi.
E.
Equipment:
Tinius Olsen machine, deflectometer, digital strain indicator
F.
Procedure:
1.
Draw shear and bending moment diagrams for both loading arrangements and
calculate safe design loads, based on an allowable bending stress = 0.6σy.
42
2.
Measure the dimensions of the beam, and mount it on the supports in the testing
machine. Carefully connect the strain gages to the digital strain indicator and
balance and calibrate all gages. Position the deflectometer under the midspan of
the beam, being careful to not disturb the strain gages. Position the load apparatus
to apply two concentrated loads in the middle of the beam span.
3.
Apply five loads to the beam. The maximum load applied should be based on
your calculations for the safe design load. The load increments should be
approximately equally spaced. Record the applied load and corresponding strain
readings for all members, as well as the deflectometer reading for the mid-span
deflection.
4.
Set up the beam as in step 2, but this time position the load apparatus to apply two
concentrated loads symmetrically on the overhangs. Repeat step 3 for the case
with loads applied to the overhangs.
G.
Calculations:
1.
Experimental Stresses: Find the stress from each strain gage corresponding to
each experimentally applied load, by appropriately relating strain to stress using
Hooke's Law.
2.
Theoretical Stresses
a.
Draw shear and bending moment diagrams for your beam for the two
loading conditions. On the moment diagram, locate the points where
strain gages are located. These are the points at which theoretical stresses
will be computed.
b.
Calculate the theoretical bending stress corresponding to each strain gage
location by using the elastic bending equation
th
c.
3.
Mc
I NA
Eq. 1
Compare the theoretical stresses calculated using Equation 1 with the
experimental stresses calculated using the experimental strains and
Hooke’s Law, and determine percent error.
Theoretical Deflections: Calculate the theoretical deflections and compare them
to the experimental deflections from the deflectometer and calculate percent
errors.
a.
For the case with two loads between the supports (Fig. 2a), the equation
for theoretical mid-span deflection is
Δ = Pa(8a2 + 12ab + 3b2)/48EI
43
b.
For the case with loads on the overhangs (Fig. 2b), the equation for
theoretical mid-span deflection is
Δ = Pab2/16EI
4.
Plot the theoretical deflections from your calculations on the same graphs as your
experimental load versus deflection plots. Discuss your observations.
44
X. Lab #6 Hot Mix Asphalt Superpave Volumetric Design
and Compaction Tests
A.
Objectives:
1. To familiarize the student with the general characteristics of Hot Mix Asphalt
(HMA) concrete and with the Superpave method of HMA mix design, and
laboratory test methods for compacted bituminous specimens.
2. To perform standard laboratory tests on compacted HMA mixtures to determine
the effect of varying design mixes and materials on the degree of compaction and
percent air voids in compacted bituminous samples.
B.
References:
AASHTO T166 Bulk Specific Gravity of Compacted Hot Mix Asphalt Mixtures Using
Saturated Surface-Dry Specimens, American Associated of State Highway and
Transportation Officials
PA Test Method No. 715 Determination of Bulk Specific Gravity of Compacted
Bituminous Mixtures, Pa. Dept. of Transportation, June 2003.
ASTM D6925-07 Standard Test Method for Preparation and Determination of the
Relative Density of Hot Mix Asphalt (HMA) Specimens by Means of the Superpave
Gyratory Compactor
ASTM D2041-03a Standard Test Method for Theoretical Maximum Specific Gravity and
Density of Bituminous Paving Mixtures
ASTM D2726-05a Standard Test Method for Bulk Specific Gravity and Density of NonAbsorptive Compacted Bituminous Mixtures
ASTM D3203-05 Standard Test Method for Percent Air Voids in Compacted Dense and
Open Bituminous Paving Mixtures
C.
Background:
Asphalt pavement is made from aggregates (stone, sand or gravel) using asphalt cement
(a derivative of crude oil refining) as the “glue” or binder. It is produced by heating
asphalt cement and mixing it with aggregates and mineral fillers. The resulting product is
referred to as “hot mix asphalt” or “HMA.” Typical proportions are 94 to 96 percent
aggregate and 4 to 6 percent asphalt cement.
Asphalt pavement is built in layers. The first step is to remove topsoil and compact the
earth. Then, a base that will help to carry the load is placed and compacted. (The base
45
may be constructed solely of stone, or it may include both stone and asphalt.) Two or
more layers of hot mix asphalt are then placed and compacted. Pavement thickness is
chosen based on what kind of stresses the pavement must withstand (trucks vs. cars) and
other factors such as soil conditions and climate. It also depends on the materials used in
the asphalt and what materials might be present in the lower layers of the pavement.
Whenever asphalt pavement is placed and compacted, there will be a certain amount of
air voids, the small pockets of air between the coated aggregate particles. The amount of
air voids is expressed as a percent of the bulk volume of the compacted paving mixture.
Efforts should be made to keep compacted air voids between 3% and 8%. Once voids
reach 8% or higher, the voids become interconnected and allow air and moisture to
permeate the pavement which reduces pavement durability. On the other hand, there must
be sufficient air voids to allow a slight amount of added compaction under traffic loading
without bleeding and loss of stability that would lead to pavement rutting. If air voids fall
below 3%, there will be inadequate room for expansion of the asphalt binder in hot
weather and when the void content drops to 2% or less, the mix becomes plastic and
unstable. Mixes are usually designed for 4% air voids (e.g. 96% compaction) in the lab
and compacted to at least 93% (e.g. less than 7% air voids) in the field. PennDOT
acceptance standards are based on an optimum 4% air voids (96% compaction) in
laboratory specimens for approved mix designs, with an acceptance range of 92% to 97%
compaction (from 8% down to 3% air voids) in field samples. When samples from the
field are tested and fall outside this acceptance range, penalties are imposed on the
contractor (i.e. contractor doesn’t get paid full price for the asphalt that was placed or
contractor may be required to remove and replace the asphalt).
The objective of HMA mix design is to develop an economical blend of aggregates and
asphalt. Historically asphalt mix design has been accomplished using either the Marshall
or the Hveem design method. The most common method was the Marshall, which had
been used by about 75% of the Departments of Transportation (DOTs) throughout the US
and by the Federal Aviation Administration (FAA) for the design of airfields. Then in
1995, the Superpave mix design procedure was introduced by the Federal Highway
Administration. Superpave builds on the knowledge from Marshall and Hveem
procedures. The primary difference between the three procedures is the machine used to
compact the specimens and the tests used to evaluate the mixes. Superpave procedures
are used by DOT’s throughout the US for the design and quality control of HMA
highway projects.
No matter which design procedure is used, the HMA mixture that is placed on the
roadway must meet certain mix requirements:
Sufficient asphalt to ensure a durable, compacted pavement by thoroughly
coating, bonding and waterproofing the aggregate.
Enough stability to satisfy the demands of traffic without displacement or
distortion (rutting).
Sufficient voids to allow a slight amount of added compaction under traffic
loading without bleeding and loss of stability. However, the volume of voids
should be low enough to keep out harmful air and moisture.
46
Enough workability to permit placement and proper compaction without
segregation.
The Superpave design method for hot mix asphalt (HMA) consists of three phases: (1)
materials selection for the asphalt binder and aggregate, (2) volumetric proportioning of
aggregate and binder, and (3) evaluation of the compacted mixture based on specimens
compacted using the Superpave gyratory compactor (SGC). The SGC compacts the
asphalt mixture into a mold using a gyratory motion that causes a kneading action. The
appropriate number of gyrations varies for different highway projects, and is determined
based on traffic and project site high temperature conditions. As traffic and temperature
increase, the number of required gyrations at which the asphalt mixture is evaluated also
increases. There is no general strength test to complement the volumetric mixture design
method. Industry has expressed the need for a simple strength test to complement the
Superpave volumetric mix design method and ensure reliable mixture performance over a
wide range of traffic and climatic conditions. So far, no simple strength test has been
adopted for use with the Superpave design method.
D.
Materials:
Several samples of HMA mixtures compacted in a Superpave Gyratory Compactor
(SGC). The instructor will provide the theoretical maximum specific gravity (Gmm) for
each sample. Gmm is the ratio of the weight of a given volume of voidless (no air voids)
HMA at a given temperature to the weight of an equal volume of water at the same
temperature.
E.
Equipment:
5 kg balance or scale fitted with a suspension apparatus and holder to permit weighing
the specimen while suspended in water, water bath equipped with overflow outlet for
maintaining a constant water level, oven for drying specimens.
F.
Procedure: (based on AASHTO T166 Test Method A)
For each specimen
1. Weigh and record the dry mass. Designate this mass as “A”.
2. Fill the water bath to overflow level with water at 77o F (25o C) and immerse the
specimen for 4 minutes.
3. Weigh and record the submerged weight, with the specimen in the water bath and
using a suspension apparatus and holder. Designate the submerged weight as “C”.
4. Remove the sample from the water and quickly surface dry with a damp towel.
5. Weigh and record the mass of the saturated surface dry (SSD) specimen.
Designate this mass as “B”. Any water that seeps from the specimen during the
weighing operation is considered part of the saturated specimen. Because the
47
SSD mass is more difficult to properly measure, repeat this measurement several
times until you get readings that are in reasonable agreement with each other.
G.
Measurements and Calculations:
1. Prepare a data table to record the following information for all specimens tested;
data tables will be shared among all groups by posting to shared files on the
Campus Cruiser course web page.
Group ID:
Specimen ID:
Base or Top course;
Dry Mass, “A” (kg):
Saturated Surface Dry Mass, “B” (kg):
Submerged Weight, “C” (kg):
2. Perform the following calculations for each specimen tested in lab (include data
from all lab groups so that means and standard deviations can be calculated).
a. Calculate the Bulk Specific Gravity Gmb of the asphalt mixture, which is defined
as the ratio of the weight in air of a unit volume of a permeable material at a given
temperature relative to the weight in air of an equal volume of water at the same
temperature. The Bulk Specific Gravity can be calculated from
Gmb = A/(B-C)
where
Gmb =
A=
B=
C=
Bulk Specific Gravity
Mass of dry specimen in air, g
Mass of SSD specimen in air, g
Weight of specimen in water, g
b. Calculate the Percent Water Absorbed (by volume) = 100 x (B-A)/(B-C)
If the percent water absorbed is greater than 3 percent, Bulk Specific Gravity
should be calculated using paraffin-coated specimens. Indicate whether or not
your specimens are acceptable for percent water absorbed, or if they should have
been paraffin-coated.
c. Calculate the Percent Compaction and Percent Air Voids for each sample
Percent Compaction = Bulk Sp. Gravity/Max. Th. Sp. Gravity = 100 x Gmb/Gmm
Percent Air Voids = 100 – Percent Compaction
3. Calculate averages and standard deviations using data from all samples of the same
mix design. Compare average results from different design mixes. Do the samples
fall within PennDOT’s acceptance criteria?
48
Relationship Between Turbidity and Suspended Sediments for Ridley Creek
ENGR 111-D1 (C.E. Lab #1)
Conducted: 10/3/98
Submitted to: 10/10/98
Joe Smith
Lab Group Members:
John Doe
Mary Jones
Abstract:
The objective of this experiment was to develop a predictive relationship between
turbidity and suspended sediment (SS) concentrations following storm events for Ridley
Creek. Since the turbidity of the stream can be continuously measured during a storm,
the turbidity measurements can be used to estimate the suspended sediment
concentrations washed into the stream during rain storms. Water quality samples were
collected from Ridley Creek during three storms in 2001 and analyzed for turbidity and
SS concentrations. Linear regression was used to develop a statistically significant linear
relationship for predicting SS as a function of turbidity.
2
Introduction
Runoff from storm events can wash large quantities of sediment into streams. Fish
and other aquatic life may be adversely impacted under high sediment concentrations.
The objective of this experiment was to develop a predictive relationship between
turbidity and suspended sediment (SS) concentrations for Ridley Creek. Since the
turbidity of the stream can be continuously measured, the turbidity measurements can be
used to estimate the suspended solids concentrations washed into the stream during the
entire storm. Water quality samples were collected from Ridley Creek during three
storms in 2001 and analyzed for turbidity and SS concentrations. The data were graphed
and analyzed to find the best equation to describe the relationship between sediment
concentrations and turbidity for Ridley Creek.
Background
Turbidity is cloudiness in the appearance of a liquid caused by solids, particles and
other pollutants. Turbidity is not color related, but relates rather to the loss of
transparency due to the effect of suspended sediment (SS), colloidal material, or both. A
body of water, such as a lake, is a natural example of turbidity. All of us have seen lakes
that are very clear to the eye, and are sometimes fascinated by the depth to which one can
see. On the other hand you find 'murky' waters where you couldn't see your hand at arm's
length. Typical sources of turbidity in drinking water include waste discharges, algae and
aquatic weeds, humic acids and other organic compounds resulting from decay of plant
3
matter, high iron concentrations, and runoff from watersheds flushing sediment into a
stream.
Turbidity measurement provides an indication of the clarity of water and water quality.
The nephelometric turbidimeter, which measures turbidity by the light scattered at 90
degrees to the incident beam, is the preferred method for measuring turbidity because of
its sensitivity, precision, and applicability over a wide range of particle sizes and
concentrations. Thus,
Suspended sediment (SS) load in streams and rivers include organic and inorganic
particles that are suspended in and carried by the moving water. Turbidity is generally a
much better predictor than water discharge for estimating suspended sediment (SS)
concentrations in rivers. Although it is now possible to collect continuous turbidity data
even at remote sites, sediment sampling and load estimation are still conventionally based
on water discharge. With frequent calibration, the relation of turbidity to SS can be used
to estimate suspended loads more efficiently. The sampling can be automated using a
programmable data logger which signals a pumping sampler to collect SS specimens at
specific turbidity thresholds. The approach has potential for monitoring any water quality
constituent whose concentration is better correlated with an easily measured (in situ)
parameter, such as turbidity, than with water discharge.
Methods and Procedures
Water quality samples were collected from Ridley Creek near the Widener campus
every 15 min. during three storms in 2001. The 1 L samples were immediately delivered
to the environmental lab and analyzed for SS and turbidity using procedures published in
4
Standard Methods for Water Quality Analyses (2000). Turbidity measurements were
conducted on a Hach 1000P portable nephelometric turbidimeter which was calibrated
before each use. The experimental data were then graphed and a linear regression
equation was developed using Excel.
Results and Discussion
The results of the SS and turbidity measurements are listed in Table 1 for each storm
event. Several of the turbidity samples exceeded the upper measuring limit of the
turbidimeter (indicated as “>ML” in Table 1), and these data were not used in the
remaining analyses. Figure 1 shows the graph of SS vs. turbidity for all the measurable
samples, and it is clear that a linear relationship exists between turbidity and SS.
Linear regression was applied to the SS and turbidity data using Excel, and a
statistically significant relationship was developed. Table 2 summarizes the results of the
regression analysis, and Equation 1 shows the predictive equation for SS as a function of
turbidity.
SS = 1.56 NTU – 3.1
EQ. 1
where: SS = suspended solids concentration in mg/L
NTU = turbidity measurement
This equation can be used to predict SS concentrations based on turbdity measurements
for ...
Purchase answer to see full
attachment