Students in the four-year baccalaureate Construction Management Technology programs are required to take courses in structures. It is has been noted by Hein and Williams (1990), that the traditional method of presenting concepts of structures is ineffective because it does not show the construction students its relevance to construction management. An area of concern was to provide students with understanding of the basic principles of structural analysis and design, such that they can interact comfortably and competently with architects and engineers in matters relating to the structural integrity of buildings. The American Council for Construction Education (ACCE), in its Standard and Criteria for Baccalaureate programs in Construction Management Technology, requires that the Constructor must:

In the analysis and design of structures, it is absolutely essential that students understand clearly the manner in which members or components of structures react to applied loads; structures carry given applied loads along predictable paths. The ability to conceptualize how a structure will carry a given load leads to an adequate, safe and economic design. Once the loads in each component have been identified in the analysis, adequate sections of a material are supplied to carry the loads in the design. It is this understanding of the interplay of forces within and between several members of a structure that poses a problem for many students in construction management programs. They find it difficult to understand how a structure is designed to generate the internal strength to carry externally applied loads.

In order for students to be grounded in the understanding of the fundamental behavior of structures, it is strongly believed that students should participate in activities that help them have a feel of how structures respond to applied loads. To this end, some activities like showing of relevant videos, field trips to construction sites and structural design offices, seminars, workshops and guest speakers have been used to enhance the students’ understanding of structures.

The University of Maryland Eastern Shore, under its 1998, 1999, and 2000 Teaching Enhancement/Student-Centered Activity Grants, funded two proposals titled, Simplified Theory and Design of Structures for Technology Students, and Enhancing Structural Analysis and Design Courses at UMES. The objective of the first proposal was to set up a laboratory where simple structural systems in steel, were built, instrumented and tested with simple loads to enhance the learning process for students in the structural analysis and design courses. A 12 feet steel beam and an 18 feet steel roof truss with pin and roller supports were fabricated and installed in the laboratory. A set of steel loads (500 lb. steel plates complete with "S" hook and tray) was also procured. In the second grant, more materials including, a Labview automatic data acquisition system, 2 sets of 500 lb. steel plates complete with loading trays and "S" hooks, were procured.

In this paper, three student-centered activities used to enhance the study of structures are presented. These activities are: 1). Using a structural steel beam model to measure deflection, 2). Using a structural steel beam to measure strain, and 3). A service learning activity. These activities were made possible by Teaching Enhancement Grants from the School of Business and Technology and the Institute of Service Learning of the University of Maryland Eastern Shore.

 

 

Measurement of Deflection of a Steel Beam

 

In this activity, a 12-foot, W 6x12 A36 wide flange steel beam was loaded at third points of the span. Dial gages were set at different positions along the beam. The loads were added incrementally and the corresponding deflections were measured. The materials and procedure for this activity are included below. The deflections of the beam under different loads were also calculated using standard formulas. The formulas used material properties of steel like E, the modulus of elasticity of steel, and I, the moment of inertia of the section. The measured and calculated data were plotted along the span of the beam. This activity helped students to understand the behavior of a beam under loads and the engineering properties of the beam that controlled the deflection behavior of the beam.

The scope was to measure the deflection of a wide flange steel beam. 3 S hooks, a W6x12 steel beam, 1500 lb. steel plates, 6 dial gages and magnetic bases, a 50 ft. measuring tape. Cinder blocks, steel plates or channels were used in supporting the dial gages.

1. Set the left support 1-in from the end of the beam.

2. Measure the distance from center of left support to the center of the right support. This is the span, L, of the beam.

3. Measure and record the distances from the left support to the center of the three loading rings.

4. Arrange the concrete blocks at the following distances from the left support: 2 ft., 4 ft., 8 ft., and 10 ft.

5. Place the channels on top of the blocks and mount the dial gage supports on the steel channels and turn on the magnets.

6. Attach the dial gages to the support and adjust them such that the gages just touch the bottom of the beam

7. Measure the distances from the left support to the dial gages

8. Place an S hook on the center ring and hang a loading tray on the S hook. Zero the dial gages

9. Apply 500 lbs. steel plates to the beam and read all the dial gages.

10. Next put an S hook on the first ring and hang the next loading tray on it. Apply the next 500 lbs. to this tray. And read all dial gages

11. Finally, put an S hook on the last ring, hang a loading tray on it and apply the last 500 lbs. to the beam. Read all the dial gages.

12. Carefully remove all the steel plates and return to the construction lab

13. Carefully remove and pack up all dial gages.

14. All materials must be returned to the construction lab

In Figure 1, students are shown loading the steel beam. The loads are composed of steel plates. The steel plates are in two categories. The first category consisted of plates weighing 20 lbs. each. The second consisted of plates weighing 10 lbs. each. The plates were conveniently lifted and carried by the students. Once the desired level of load was attained, the dial gages were all read to determine the deflection of the beam at the location of the gages. The dial gages were easy to read and the students were taught how to properly install and accurately read them. As a part of the report for this exercise, students plotted measured and calculated deflections on the span of the beam for each load condition. A typical plot for the beam with loads of 500 lb each at third points from the left support is shown in Figure 2. The calculated and measured curves showed good correlation for most of the load cases.

In this activity, the strains along the cross-section of a loaded steel beam were measured using a Labview 5.1 automatic data collection system. Strain gages were arranged along the depth of the beam. The strain gages were connected through the Signal Condition Board to a desktop computer (Figure 3). One strain gage was installed on the center of the depth. The strains at different levels were read on the computer monitor using the Labview version 5.1.1 software, after the appropriate loads were applied. The strains could also be read continuously as the load increased. Typical strain readings are shown in Table 1.

When a beam is loaded as shown in Figure 4(a), elastic beam bending theory shows that the strain varies linearly across the section as shown in Figure 4(b). This Figure shows that the strain at the neutral axis is zero. Hooke’s law is assumed to apply, which means that the strain is proportional to the stress. That is s a e , and s = E e , where s is the stress, e is the strain and E is the modulus of elasticity of steel. This relationship shows that the stress can be obtained from strain. The stress is proportional to strain and the stress is also zero at the neutral axis as shown in Figure 8(b). Looking at the test results in Table 1, it is interesting to note the similarities of the results with the theoretical shape shown in Figure 4(b). Strain gage SG2 is positioned at or close to the neutral axis. The strain reading on this gage should theoretically be zero. This point may not have been accurately located in the activity hence the readings on the gage for all loading conditions are not exactly zero. However these readings are significantly small compared to the others. Strain gages SG0 and SG1 were located above the neutral axis and their readings were positive (compressive) strains. The readings of SG0 are larger than those of SG1 showing that the strain increases the further away you are from the neutral axis. The readings of SG3 and SG4 are negative indicating negative (tensile) strains. These strains also exhibit the same characteristics as shown for the compressive strains. The materials and procedure for setting up this activity are shown below.

3(S) Hooks, (3) Loading trays, A W 6x12 Steel Beam, 1500 lbs. Steel Plates, 1 SG-496 Super Industrial Glue, 12" Linear Ruler, 1’Yellow Cement tape, 1 Flat Head Screwdriver, (1) SC-2043-SG Eight-Channel Strain Gage Signal Conditioning Board, (1) PC-6023E-C1-11L3MR Strain Gages, 4’SH-6868-EP Data Card Cable, Labview Version 5.1.1 Software, Labview Max Version 2.1 Software.

1. Using the SG-496 super industrial glue, glue a strain gage directly on the center of the W 6x12 steel beam

2. Glue a second and a third strain gages 20 cm above and below the first strain gage.

3. Glue the fourth and fifth strain gages 2o cm from the third and fourth strain gages

4. Turn on the PC and have the write-able Labview strain gage program up and running

5. Attach and assign the five strain gages to the signal condition board (SC-2043-SG).

6. Place an S hook on the center-loading ring on the steel beam and hang a loading tray on the S hook.

7. Apply a load of 500 lbs. steel plates on the beam and read the values of the strain gages using the Labview program

8. Put an S hook on the first loading ring and hang another loading tray on it. apply the next 500 lbs. steel plates to this tray and read the new values of the strain gages using the Labview program

9. Put the third on the last loading ring and hang the loading tray on it. apply the last 500-lbs. steel plates to this tray and read the new values of the strain gages using the Labview program.

10. Carefully record all strain data readings from the Labview program and exit the program.

11. Carefully disconnect all the strain gages from the Signal Board (SC-2043-SG)

This activity incorporated a service learning component to the Statics and Strength of Materials courses. These are the first and the second courses in a four-course sequence in structures of Statics, Strength of Materials, Structural Design I and Structural Design II. In this community-based activity, the students enrolled in these courses spent two Saturdays in the semester to work on housing projects in the Habitat for Humanity Kirkwood Estates in Salisbury, Maryland. Habitat for Humanity is a volunteer ministry dedicated to eliminating poverty housing. The Habitat for Humanity on the Eastern Shore is an agency of United Way. On the designated dates, students met in the Construction Workshop in the Arts and Technology Center. All the tools to be used were loaded into a van and then the team drove to the construction site. Out there the students were met by the Habitat for Humanity Project Director. The students were briefed on what activities they needed to do for the day. The students and other volunteers were divided into different groups. Each group had a group leader and specific assignments for the day.

The goal of this activity was to have students enrolled in the courses volunteer to work on all phases of the construction of the houses. They were involved in installing studs, drywalls, ceiling, roof trusses, roof shingles and painting. Figure 5 shows one of the students installing siding to the building that the class worked on. The students used skills gained from many of the core courses in the construction program to volunteer manpower (labor) towards the completion of some houses. This involved layout activities to the actual installation of building components.

The students were required to write a paper describing the activities they were engaged in during the visit. After each visit, the activities of the day were discussed in the next class meeting during which each activity was linked to the building. The role of each component in the overall behavior of the building in resisting applied loads was highlighted.

In an attempt to estimate the impact of these activities on the performances of the students in the structures courses, their grades in the final examinations were examined. The structures courses are Statics, Strength of Materials, Structural Design I (Steel and Timber Design) and Structural Design II (Reinforced Concrete Design). The records cover 1996 to 2001. A grade of C or better was considered a passing grade. The activities were effectively started in the Fall of 1998. The percentages of students passing the structures courses are presented in Table 2 below. The records show an overall gradual increase on the number of students passing the structures courses as from 1998 (especially in Strength of Materials) when the activities were introduced. This was interpreted to mean that students performed better in these courses because of their participation in these activities. The activities provided the kind of experience the students sometimes need to better grasp the basic concepts of structural behavior.

Three hands-on student-centered activities aimed at enhancing the understanding of structures have been presented. In the measurement of the deflection of a beam, students loaded a steel beam and measured the corresponding deflections at designated points along the span of the beam. They were able to see the deflection characteristics of the beam as various load intensities were applied to the beam. They also calculated these deflections using standard formulas and compared the results with the measured values. This gave them first-hand knowledge of the engineering properties of a beam used to estimate its deflection under the applied loads. In the second activity, the measurement of strain was done using the Labview 5.1 automatic data acquisition system. Compressive and tensile strains and the neutral axis of the cross section were demonstrated. The application of Hooke’s law to obtain stresses from the strains was highlighted. This activity emphasized the important concepts of stress and strain and their distribution along the cross-section of the loaded beam. The community-based service learning activity enabled students to acquire and apply some basic building construction skills while contributing to the welfare of some members of the community. An examination of the grades of students enrolled in the structures courses showed that there was a gradual increase in the number of students who passed the courses (especially in Strength of Materials) after the introduction of these activities. These activities contributed to the understanding of structural behavior of beams and supplied hands on aspects to the study of structures for the students.

References

 

Hein, F. M., & Williams, S. (1990, April 8-10). Rethinking the Structures Curriculum. Associated Schools of Construction (ASC) Proceedings of the 26^th Annual Conference, Clemson University, Clemson, South Carolina, pp. 51-57.

Pond, R. J. (2002), Introduction to Engineering Technology, 5^th edition, Princeton Hall, pp. 32-33.

The author is grateful to Dr. Eddie Boyd Jr., Dean, School of Business and Technology, University of Maryland Eastern Shore, who through Teaching Enhancement/Student-Centered Grants in 1998, 1999, and 2000 provided funds that were used to purchase materials and equipment for the Deflection and Strain Activities. The author also acknowledges the two mini-grants received from the Institute of Service Learning, University of Maryland Eastern Shore, which facilitated the Service Learning Activity.