CE 115
Introduction to Civil Engineering
Graphics and Data Presentation
Application in CE Materials
Dr. Fouad M. Bayomy, PE
Professor of Civil Engineering
University of Idaho
Moscow, ID 83844-1022
Graphics and Data Presentation
Application in CE Materials
Objective
The objective of this module is to introduce students to basics of data presentation using a
computer graphic tool such as MS-Excel. It is assumed that students have some knowledge of
how to use the MS-Excel spreadsheet software.
Why Do Engineers Need to Present Data?
“A Picture is better than a thousand words”, it is that simple. Let me take an engineering
example where a CE material engineer may need to understand the effect of “age” on the
increase of strength of Portland cement concrete (PCC) mixtures. All of us know that when you
pore concrete to build a driveway, you will have to block the driveway until you make sure that
the concrete of the driveway has gained sufficient strength to support vehicles. Let us investigate
the gain of strength with time. The following table (Table 1) shows data of a PCC mix.
Table 1 Gain of Strength with
Time
Time,
day
Compressive
Strength, psi
1 619
3 1374
7 2111
14 2642
28 3022
56 3256
84 3342
112 3387
140 3415
180 3439
200 3448
Looking at the numbers in Table 1, one can see that
strength does increase with time. But that is all. To
understand better the rate of strength increase and the
critical time(s) that may have more profound effect on
strength, it would be better to plot the data to be able to
visualize the information. The following graph, Figure 1,
shows same information on a graphical form.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 50 100 150 200
Time, day
Comp. Strength, psi
Figure 1 Gain of Compressive Strength with Time
From the graph, an engineer can predict that after about 90 days, the concrete does not gain
much strength as it does in the first three weeks. If the vehicles operating on the driveway will
impose stresses about 2500 psi, then the engineer may recommend that at least the driveway
shall blocked to traffic until at least 10-days to allow the concrete to gain such level of minimum
required strength. This simple example signifies the importance of presenting the data in a
graphical form. While the table and the graph have same data, the graph makes it more visual
and allows the engineer to interpolate and predict the in-between values.
Types of Graphs
There are several types of graphs that engineers use for data presentation. The following is a list
of most common forms. (Students should list more graph types as they find in Excel Chart
option)
Bar / Column graphs
Line graphs
x - y plots
3D effects
Bar / Column Plots
In the following we will do an example of each type of the mentioned chart types. Let us create
the data table as shown in Figure 2.
Steps:
1. Open the Microsoft Excel spreadsheet software.
2. In columns A and B insert the data entry in columns A and B as shown in Figure 2.
3. Select the data range by highlighting the range (A1:B7) as shown in Figure 3.
4. With range selected, click on the chart wizard icon or by selecting the chart fro the Insert
menu.
5. Follow the windows instructions to create a column chart as shown in Figure 4.
Let us now try to present the data in another graphical form.
After spending some time trying to present the data in Figure 2 in other forms, answer the
following question:
Q: What are other types of charts that you can use to present the data?
A:
Q: Can you use the x-y scatter plot to present the data in Figure 2? Yes or No
Why?
A:
Figure 2 Strength Data in an Excel sheet
Figure 3 Selecting the Data Range
Figure 4 Bar Chart for the Data in Range A2:B7
X- Y Plots:
This type of data presentation is suitable for “continuos functions”. For example, the increase of
strength with time, as presented in Figure 1. The increase of a person weight with the amount of
food he/she eats, the increase or decrease of electrical bill with the weather temperature. This
type of information is not discrete. In the Example of Figure 2, the strength of each mix is totally
independent of other mixes. Thus, the bar or column graph was used to depict the various
strength values of these mixes. It does not matter which mix we plot first. Thus, the plot does not
depend on the order where to replace the mix “name” on the x- axis nor the “value”. The Excel
software will place these bars at equal distances, just for convenience. The name of the mix,
whether you call it “A” or any thing else, it will not affect the plot you get.
Let us now work with the example that was presented in Figure 1.
Open a new sheet and type in the data given in Table 1 in columns A and B. See Figure 5.
Select the data range A2:B14 (Columns A and B) and while selected, click the Chart Wizard
icon. Follow the instructions of the Excel Windows to create an x-y plot of the Strength vs. Time
relationship as shown in Figure 5.
The plot shown is done using linear scale on both x and y axes. Therefore, sometime this may
not be convenient since the change of strength is so rapid in the early days. To expand that
period, we may choose to use Log scale on the x axis instead. This will allow us to flatten the
curve in the early days as shown in Figure 6.
Figure 5 X-Y Plot for Strength-Time Results
Figure 6 X-Y Plot of the Strength-Time Results (semi-log plot)
Data Fitting and Regression Analysis
Another example of using the x-y plots, is representing the data in a format so that we can fit
simulate its physical or mechanical behavior by a mathematical equation. It is typically referred
to as a regression model or regression equation. This helps engineers to determine,
experimentally, material properties that describe certain phenomenon of material behavior. The
following example is for modeling the creep behavior of an engineering material.
Creep is a very slow process in which a material continues to deform with time under constant
stress. Materials that exhibit creep deformation are time-dependent. The relationship that governs
the progress of creep deformation,
c
with time of loading (t) can be written in the form:
c
= (t)
………………………………… ………….. (1)
Where, and are called creep parameters.
Once the engineer determines the creep parameters for a given material, he can predict the creep
deformation at any time.
The data in columns A and B in the Excel sheet shown in Figure 7, is obtained from a creep test
performed on a polymer material. The deformation is represented in creep strains (deformation
per unit length, mm/mm). The chart in Figure 7 shows the relationship on a linear scale. The
figure shows the creep deformation progress is fast at initial times and slows down until it
reaches a steady state development.
Figure 7 Creep Deformation with Time
The data can be represented on a log-log scale, in which a power relationship transfers to a linear
relationship by taking the logarithmic values. In this case, equation 1 can be written in the form
Log
c
= Log + .Log (t)
……………… ………….. (2)
So, plotting the same data on log-log-scale allows for determining the creep parameters and
where is determined from the intercept of the y-axis at t=1, and is the slope of that linear
relation on log-log scale chart, as shown in Figure 8
From the shown fitted data, it is found that the creep parameters for this material are:
= 400 mm/mm
= 0.15
Figure 8 Creep Deformation with Time (Semi-Log)
Assignment
Purpose:
Synthesizing how to use graphics to support your engineering decisions.
Problem:
A civil engineering material engineer designed a concrete mix to be used in a floor of
an industrial store house where heavy machinery is to be transported. Due to the
expected heavy loads, the engineer decided to modify the concrete mixture by adding
steel fibers to it. One of the main challenges to design the mix was to determine how
much steel fibers that should be add to achieve the required increased strength
without detrimental effect on the mix? Therefore, a laboratory program was
established to test mixes with different steel fiber contents to answer this question.
Results are listed below.
Data:
Compressive Strength of Concrete Mixes
Normal
Mix
Steel Fiber Added
Time,
Days
0 2% 4% 6% 8% 10%
7 2111 2462 3166 3869 3377 2814
14 2642 3082 3962 4843 4226 3522
28 3022 3525 4532 5540 4835 4029
90 3354 3913 5031 6149 5366 4472
180 3439 4013 5159 6306 5503 4586
Required:
Present the data in a suitable format so that you are able to reach an engineering
decision on how much steel fiber you should add if the minimum required 28-day
strength is 5000 psi. Compare the 28-day strength of all mixes. How does the time
affect the increase in strength of these different mixes?
Hints:
To answer the main question, plot the 28-day strength versus steel fiber content for all
mixes.
To determine the effect of time, plot the strength versus time for all mixes.
