A SIMPLE EXPERIMENT IN STRUCTURAL VIBRATIONS FOR CIVIL ENGINEERING STUDENTS

Farhad Reza

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Conference: 2022 ASEE Annual Conference & Exposition
Location: Minneapolis, MN
Publication Date: August 23, 2022
Start Date: June 26, 2022
End Date: June 29, 2022
Conference Session: Experimentation and Laboratory-Oriented Studies Division Technical Session 1: Experiential Learning in Fluids, Structures, and Course/Lab Design
Page Count: 15
DOI: 10.18260/1-2--40936
Permanent URL: https://peer.asee.org/40936
Download Count: 370

Paper Authors

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Farhad Reza Minnesota State University, Mankato

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FARHAD REZA Ph.D., P.E. is a Professor and the Chair of the Department of Mechanical and Civil Engineering at Minnesota State University, Mankato. His field of specialization is in structural engineering. His research interests include nondestructive testing of structures, materials science of concrete, pavement durability and maintenance, and sustainability. In the area of pedagogy, Dr. Reza is interested in incorporating undergraduate research in the curriculum, blending in-person and online teaching, and increasing student retention.

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Abstract

The study of and measurement of structural vibrations has important applications in various aspects of structural engineering for example in health monitoring of structures, establishing comfort levels for building occupants, minimizing floor vibrations in labs housing sensitive equipment, earthquake engineering, and ensuring that the natural frequency of flexible bridges does not match the resonant frequency from applied loads. In the United States, in the typical undergraduate civil engineering curriculum, students do not get courses or laboratory experiences in structural vibrations. The author has devised and implemented a simple experiment that can be understood and performed by senior civil engineering undergraduate students that will introduce them to this important topic. End-of-semester assessment found that this was a popular, stimulating, and beneficial experiment for the students.

The experiment is tied to one important application in the structural health monitoring of bridges. The theoretical natural frequency of a bridge is dependent on both the stiffness and the mass. As the structural condition of the bridge deteriorates with time, its stiffness decreases while mass remains constant. Even if mass were to change, for example due to an overlay, it can easily be quantified. Therefore, it follows that if the natural frequency is measured annually, the deterioration over time can be quantified.

Background knowledge that is expected prior to the lab includes Mechanics of Materials or Structural Analysis including how to calculate deflections on a cantilever beam, and a working knowledge of MS Excel. In the lab description, students are introduced to displacement, velocity, and acceleration relationships and the equation of motion is developed for a simple mass on a spring. The first fundamental frequency of a cantilever beam with a concentrated mass at the end is provided as a reference.

Three aluminum cross-sections having approximately equal masses are used as cantilever beams. Three-axis accelerometers are mounted at the free ends of the cantilever and connected to a data acquisition system. Students provide a simple excitation to the beams and data is collected. Students are given the raw acceleration vs time data. They must then perform fast Fourier transform analysis to determine the fundamental frequency. This experiment provides a validation of how measuring natural frequencies can indicate stiffnesses and hence be used to track deterioration over time.

Citation
Format

Reza, F. (2022, August), A SIMPLE EXPERIMENT IN STRUCTURAL VIBRATIONS FOR CIVIL ENGINEERING STUDENTS Paper presented at 2022 ASEE Annual Conference & Exposition, Minneapolis, MN. 10.18260/1-2--40936

TY - CPAPER
AB - The study of and measurement of structural vibrations has important applications in various aspects of structural engineering for example in health monitoring of structures, establishing comfort levels for building occupants, minimizing floor vibrations in labs housing sensitive equipment, earthquake engineering, and ensuring that the natural frequency of flexible bridges does not match the resonant frequency from applied loads. In the United States, in the typical undergraduate civil engineering curriculum, students do not get courses or laboratory experiences in structural vibrations. The author has devised and implemented a simple experiment that can be understood and performed by senior civil engineering undergraduate students that will introduce them to this important topic. End-of-semester assessment found that this was a popular, stimulating, and beneficial experiment for the students.

The experiment is tied to one important application in the structural health monitoring of bridges. The theoretical natural frequency of a bridge is dependent on both the stiffness and the mass. As the structural condition of the bridge deteriorates with time, its stiffness decreases while mass remains constant. Even if mass were to change, for example due to an overlay, it can easily be quantified. Therefore, it follows that if the natural frequency is measured annually, the deterioration over time can be quantified.

Background knowledge that is expected prior to the lab includes Mechanics of Materials or Structural Analysis including how to calculate deflections on a cantilever beam, and a working knowledge of MS Excel. In the lab description, students are introduced to displacement, velocity, and acceleration relationships and the equation of motion is developed for a simple mass on a spring. The first fundamental frequency of a cantilever beam with a concentrated mass at the end is provided as a reference.

Three aluminum cross-sections having approximately equal masses are used as cantilever beams. Three-axis accelerometers are mounted at the free ends of the cantilever and connected to a data acquisition system. Students provide a simple excitation to the beams and data is collected. Students are given the raw acceleration vs time data. They must then perform fast Fourier transform analysis to determine the fundamental frequency. This experiment provides a validation of how measuring natural frequencies can indicate stiffnesses and hence be used to track deterioration over time.

AU - Farhad Reza
CY - Minneapolis, MN
DA - 2022/08/23
PB - ASEE Conferences
TI - A SIMPLE EXPERIMENT IN STRUCTURAL VIBRATIONS FOR CIVIL ENGINEERING STUDENTS
UR - https://peer.asee.org/40936
DO - 10.18260/1-2--40936
ER -