DOC

ASEN 3112 - Lab 3 - Experimental Methods in Column Buckling

By Ricardo Perkins,2014-06-22 11:49
8 views 0
ASEN 3112 - Lab 3 - Experimental Methods in Column Buckling

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    ASEN 3112 - Lab 3 - Experimental Methods in Column Buckling

    I. SUMMARY

    In the third structures lab, you will investigate the buckling behavior of a slender steel beam-column. The objectives of the lab are to improve your appreciation for the significance of boundary conditions in the stability of columns and to expose you to an advanced experimental method. Measurements of the critical load of the beam-column under various boundary conditions will be compared with those predicted by the theory covered in class. In doing so, you will use an experimental method which separates some inherent experimental errors from the idealized buckling behavior.

    This document provides general descriptions of the experimental apparatus and procedure.

    II. LOGISTICS AND TIMETABLE

    Timetable

    This lab spans three weeks, with a group report due on Tuesday, December 7. The calendar is shown in Figure 1. We have approval from ITLL to have this lab be unsupervised since it's relatively indestructible, thbut try not to prove us wrong. As a result, the module should be available for checkout from the 17 to Dec

    3rd, but use the sign-up board as before to avoid schedule conflicts.

    Nov. 15 16 17 18 19

    Final lecture on Module demonstration in Lecture Module available

    stability recitations Module available

    22 23 24 25 26

    Module Reading Thanksgiving Thanksgiving No Recitation!

    available quiz/Lecture holiday holiday Module available

    Module available Module available Module available

    29 30 Dec. 1 2 3

    Midterm Lecture Recitation Module available Midterm 4

    4 review Module available Module available Module available

    Module

    available

    6 7 8 9 10

    Lecture

    Lab 3 report due

    Figure 1: Timetable for Lab 3

    Groups

    Lab groups will be the same as those for Lab 2. Group members are listed in Addendum I. As before, each group should select a leader to act as coordinator and liaison with the instructors. The leader is responsible for coordination of report preparation and for rating the contributions of the individual members. A group may decide, however, not to have a leader if the members feel more comfortable with such an arrangement. The report should indicate if that was the case.

     1

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    III. MODULE DESCRIPTION

    The apparatus being used is an off-the-shelf module produced by a British company by the name of Hi-Tech Ltd.. The Beam-Column Buckling Module is shown in Figure 2. The module consists of a mobile steel frame which supports a moment arm and end conditions for the beam-column. A high-strength steel beam-column is provided with a nominal Young's Modulus of 205 GPa. Pinned and clamped conditions can be simulated at the top of the supplied beam-column with different adapters. The boundary condition at the bottom of the beam can be varied from pinned to clamped through the use of a restraint beam which provides adjustable levels of torsional stiffness at this point.

    Figure 2: Hi-Tech Beam-Column Buckling Module

    The end fixtures clamped to the beam-column also provide off-axis notches for applying eccentric loads. These notches are spaced 1.5 mm apart. Typically, an eccentric load is applied by offsetting the knife-edge contacts an equal number of notches off-center at the top and bottom of the beam-column. The ratio of the load arm lengths from the pivot point to the beam-column and from the pivot point to the load tray is 3:4 as shown in Figure 2. Remember to convert the loads applied at the load tray to those resulting at the beam-column appropriately. During loading, some friction between the load arm and frame should be anticipated. The effects of this on the deflection response can be alleviated by tapping on the frame after loads are applied.

    IV. EXPERIMENT PROCEDURE

    The experiment procedure consists of making load-displacement measurements for five different combinations of boundary conditions and eccentric loads. Initially, data will be collected for a nominally pinned-pinned beam-column using three different eccentric load configurations. This data will be used to explore the benefits of using the Southwell plot. Following this, the boundary condition at the base of the beam-column will be adjusted to a nominally clamped state and then an elastically restrained state. Do not forget to make careful measurements of the beam-column dimensions.

     2

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    Pinned-Pinned Response with Eccentric Loading

    For this section of the procedure, the restraining beam should be detached from the beam-column. Assemble the beam-column with zero eccentricity and with the ruler centered along the length of the beam-column as demonstrated in recitation. (Use a 2 N weight on the load tray to keep the beam-column in place during assembly.) Check that the lower knife-edge is located directly beneath the upper knife-edge by measuring the distances from these boundaries to the right hand side of the frame. (How would you model errors in this alignment?) Align the ruler with a reference point on the beam to "zero" (don't forget your 2 N load) the measurement.

    Measure the lateral deflections induced by applied loads varying from "zero" to the critical load. (You may need to help the beam-column buckle to the right as described in recitation.) Since the deflections of the beam-column will increase rapidly as the critical load is approached, reduce the loading increments near this load. It is difficult to resolve deflections to better than ?0.25 mm, so obtaining the larger deflection data near failure is important. You should have at least 10 load increments.

    Once you are satisfied with the repeatability of your data for this configuration, adjust the load eccentricity to 3 mm (2 notches) and repeat the load-deflection data acquisition procedure. You will need to shift the ruler or adjust your displacement measurements accordingly. Repeat the procedure yet again for 6 mm of load eccentricity.

    Use a spreadsheet to plot the load-deflection data and to generate Southwell plots of deflection vs. compliance. Fit lines to the three data series in the Southwell plots to derive values for the critical loads and effective eccentricities for all three cases.

    How does the load-deflection data compare to the theory?

    How does the apparent critical load in the load-deflection plots and Southwell analysis compare to the theoretical prediction? (When measuring the geometry of the beam-column, consider which dimension(s) are most critical.)

    How do the effective eccentricities from the Southwell plots compare with the intended values?

Fixed-Pinned Response

    Return the knife-edges to the on-axis notches (no eccentricity). Attach the restraint beam to the bottom of the beam-column and position the restraint beam clamps as close as possible to the bottom of the beam-column as shown in Figure 3. Place the aluminum spacer below the restraint beam and be sure to tighten the clamps to both the beam and the frame. Tighten clamps enough to prevent rotation of the beam-column specimen, but do not overtighten. During this operation, check that the upper end of the beam-column stays aligned with the knife-edge. If misalignment occurs, loosen one side slightly as necessary to keep clamps even.

    Figure 3: Detail of configuration of “fixed” end of beam-column

     3

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    This will provide a nominally fixed boundary condition. In this test, we would again like to measure the maximum lateral deflection. Consider the buckled deflection profile you would expect for these boundary conditions and adjust the vertical position of the ruler accordingly. You can proceed to buckle the beam-column to check your decision. Explain how you selected this ruler position in your lab report. Once the system is configured, repeat the above procedure for collecting and analyzing the load-deflection data.

    How do the measured values for critical load compare with the theory for a fixed-pinned beam-column? How "fixed" does the lower boundary condition appear to be?

Elastically Restrained-Pinned Response

    Loosen both restraint beam clamps and slide the left-most one completely off of the restraint beam. Position the remaining clamp 500 mm from the beam column and position the top grips of the restraining clamp to provide about 0.5 mm of clearance to allow lateral motion of the restraint beam (see Figure 4). Approximate where the maximum beam-column lateral deflection will occur for these BCs and position the ruler accordingly. Again, explain in the lab report how this was done.

    Figure 4: Detail of configuration of elastically restrained end of beam-column

    Repeat the data collection and analysis procedure one last time for this case.

    How would you model the boundary condition provided by the restraint beam? (See Addendum III for the theory.) When this is done, how does the resulting buckling load prediction compare with the experiment results?

     4

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    V. WRITING A REPORT

    Organization

    The lab reports are due Tuesday, December 7 at the beginning of class. The report must be word processed and should have a maximum length of 10 pages (excluding Appendices). It should include: Title Page. Identifies the project, lists the name of the team members and identifies the group leader. A Table of Contents as second page is optional.

    Introduction. A 1-2 paragraph description of the lab objective and approach.

    Experimental Procedure. Briefly summarize the experimental procedure which was followed focusing on aspects which have potential impact in later analysis of the results. Again, there is no need to provide a step-by-step description of the procedure. Rather, reference the experimental procedures as described below. Include measurements of the beam and fixture dimensions here.

    Theoretical Analysis. Present the analyses used for each of the five boundary condition/load eccentricity cases here. Be sure to include the modeling of the torsional stiffness of the restraint beam for the final case. Data Analysis and Presentation. Load-deflection plots and Southwell plots should be presented for each of the five boundary condition/load eccentricity cases. Theoretical values should be included on these graphs as well. Tables of the raw data may also be included but should be moved to an appendix if they begin to clutter the report.

    Discussion. Take plenty of time to consider the implications of the agreement and disagreement of the theoretical and measured behavior. Point out and explain as many significant discrepancies as possible. Include any suggestions for improvements to the module or lab procedure. We're considering purchasing an LVDT for this module in the future to provide higher resolution and more accurate measurements - do you think it would help or just complicate things?

    Conclusions. Spend one or two paragraphs summarizing your conclusions.

    References. List of references cited in the body of the report such as the textbook or operational handout. All references should be cited in the text by numbers enclosed in square brackets.

Grading

    Reports are graded for both technical content (roughly 2/3) and presentation (roughly 1/3). More details on the various factors are given in Addendum III. Individual scores may be weighted by the "contribution grading" noted by the group leader.

    Note: For sections such as Objectives it is recommended that a key rule of technical writing: "context before content," be followed. That is, briefly state what the objectives are and which approach was followed to meet the objectives before entering into the technical content.

Individual Contribution Evaluation

    The group leader submits along with the report a separate "grading sheet" rating the contribution of each team member on a scale of 0 to 10. A score of 10 indicates that the member contributed his/her expected share to the experiment and to the preparation of the report. A grade over 10 may be assigned for contributions above and beyond the call of duty, and should be briefly explained.

    If the group decided not to have a leader or leaders, a statement to that effect should be included.

     5

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    Addendum I - Lab 3 Groups

    Below is a list of the groups for Lab 3. They should be the same as those for Lab 2.

    Group A: Childers, Clifford, Coley, Fillmore, Kerker, Mc Leod Group B: Antonson, Kenney, Krieg, Mansfield, Mc Neill, Seibert Group C: Calovich, Chace, Gabriel, Garza, Smith

    Group D: Bisic, Blanchard, Bovee, Claiborne, Kelley Group E: Brooks, Koblick, Pope, Ralph, Song, Strassburg Group F: Abele, Crooks, Harano, Nibe

    Group G: Korkowski, Louis, Massey, Moore, Smith, Bamgboje Group H: Emmerich, Gentry, Hart, Reese, Reynard, Sampson Group I: Burkert, Fox, Getz, Heaton, Kilbride, Rieber Group J: Denard, Dvorkina, Goheen, Le, Shaun Reed, Bell Group K: Arrington, Crum, Sandoval, La Bonte, Pienciak, Redick Group L: Alagic, Lewis, Linam, Romanov, Ko

    Group M: Arnold, Bellinghausen, King, Nedrud, Oldenborg, Erin Reed Group N: Goettsche, Leone, Riley, Torres, Turansky, Weiss

     6

    ASEN 3112 Structures Lab 3 Description, Version 11/15/2004

    Addendum II - Report Grading

The score assigned to the lab report includes technical content (65%) and presentation (35%). This is a

    more detailed breakdown of the weights:

    Category Weight Score Contribution

    Objective 0.05

    Experimental Procedure 0.10

    Theoretical Analysis 0.15

    Data Reduction and 0.20

    Presentation

    Discussion 0.10

    Conclusions 0.05

    Organization 0.05

    Flowthrough 0.10

    Style 0.05

    Grammar 0.05

    Spelling and Typos 0.05

    Referencing 0.05

    Total 1.00

    "Flowthrough" measures smoothness of reading from start to finish and correlation of material from section

    to section, as well as adherence to guidelines of technical writing. The score within each category ranges from 0 to 100%. For example if the score for "Experimental Procedure" is 80%, it contributes 0.10 x 80% = 8% to the overall score. This group score is then multiplied

    by the "contribution factor" assigned by the team leader to individuals.

     7

Report this document

For any questions or suggestions please email
cust-service@docsford.com