Measuring Structural Motion Caused by a Simulated Earthquake
using Smart Phone Accelerometer Technology
Baron J. Richardson
The goal of this project is to develop a series of
lessons designed to teach middle school students
basic seismology and structural engineering
principles. Using a flexible steel structure we will
be able to simulate earthquake motions. To
measure these motions we will use android smartphone equipped with an app designed to utilize
the built-in accelerometer technology to measure
the acceleration and frequency of the structure.
The students will learn about structural design
principles by investigating the effects to the
structures stiffness when the column dimensions
are changed. In addition to structural stiffness
students will also be able to experiment with
different types of seismic-safe design such as
cross-bracing and mass dampers. Once students
have experimented with these concepts, they will
then apply the design principles to build and
evaluate their own structures.
Methods:
1) Mathematically model the structural
frequency using. Using the following
formula: 𝑓 = /2π= 2π (Hz)
•
f=frequency in Hz
•
ω=frequency in rad/s
•
k=stiffness
•
m=mass
2) Perform a visual time test to measure
frequency of structure. (Counting the number
of cycles in a 10 second timeframe)
3) Measure frequency of structure using
accelerometer.
Testing:
The graph and photos below represent the motion of the structure during testing. The
left-hand photo represents acceleration in the negative direction, the center photo
represents no acceleration, and the right-hand photo represents positive acceleration.
𝑘
𝑚
Design:
The structure is designed with a simple clamping system which allows the columns to
be easily changed. In structure 1 the columns measured 24”x1”x1/8”, In structure 2
the columns measured 24”x1”x3/16”.
Structural Motion
2100
2050
2000
1950
20
0
Future Considerations:
• Android smart phone acquisition and testing.
• Testing of spring and turnbuckle cross-bracing system. (fig 1)
• Building and testing liquid mass-damping system. (fig 2)
• School visit by Dr. Fu and graduate students.
1900
1850
Smart Phone /
Accelerometer
1800
1
20
39
58
77
96
115
134
153
172
191
210
229
248
267
286
305
324
343
362
381
400
419
438
457
476
495
514
533
552
571
590
609
628
647
666
685
704
723
742
761
780
799
818
837
856
875
894
913
932
951
970
989
1008
1027
1046
1065
1084
1103
1122
1141
1160
1179
1198
1217
1236
1255
1274
1293
1312
1331
1350
1369
1388
1407
1426
1445
1464
1483
1502
1521
1540
1559
1578
1597
1616
1635
1654
1673
1692
1711
1730
1749
1768
1787
1750
Figure 1
Figure 2
Columns
Base
Structure
The structure pictured above is a model of
single-story, four columned frame building. The
building base and floor measure 12”x12” and it is
24” tall. Attached to the floor is an accelerometer
which was used to measure and record
accelerations. The excitations were caused by a
striking the top plate with a 3# hammer.
Flexibility
Column thickness Frequency estimated by Frequency Acquired by
Stopwatch
Accelerometer
Acknowledgements – This research was supported with funding from
the National Science Foundation’s Research Experience for Teachers
in Engineering Grant (ENG-1132648).
1
2
Flexible
Rigid
0.125 inch
0.1875 inch
2.2 Hz
3.0 Hz
1.906 Hz
3.617 Hz
Dr. Tat Fu- Assistant Professor of Civil Engineering, University of
New Hampshire Civil Engineering Department
Rui Zhang- Graduate Student, University of New Hampshire Civil
Engineering Department