Factor

Lab Manual

FACULTY OF ENGINEERING & BUILT ENVIRONMENTSUBJECT:EME3401 LABORATORY INVESTIGATIONS 1EXPERIMENT 1: TRUSS STRUCTURE

1.0 OBJECTIVE

To establish relationship between each truss member and applied load

2.0 THEORY/INTRODUCTION

A truss is a structure composed of slender members joined together at their end points. Joint connections are formed by bolting or welding the ends of the members to a common plate, called a gusset plate, or by simply passing a large bolt or pin through each of the members. Two important assumptions are necessary to design both the members and the connections of a truss:i. All loadings are applied at the jointii. The members are joined together by smooth pins

Because of these two assumptions Each truss member acts as a two force member The forces at the ends must be directed along the axis of the member If the force tends to elongate the member, it is a tensile force If the force tends to shorten the member, it is a compressive force (refer to Figure 1)

Figure 1 Nature of the force in a truss3.0 APPARATUSi. A modular truss kit.ii. A set of weight for applying load to the truss.iii. A 16 channels data acquisition system.

4.0 PROCEDURES1. Switch on the data acquisition module. For stability of readings, the data acquisition must be switched on 10 minutes before taking readings.2. Use the truss configuration below:

Figure 2 Modular Truss Apparatus3. Check the truss according to the selected configuration.4. One end of the plane truss on the roller support and the other on the pin support (please ensure that the centre of the joint is located on the knife edge and at the centre of the roller).5. Ensure that the pinned support is properly secured to the frame.6. Attached the weight hook to the joint to be loaded.7. Empty the weight hook so that the truss is free from applied load.8. Connect the wire from the load cell to the data acquisition module, each load cell occupying once channel of the module.9. On the module(s) that is attached to the load cell by clicking the On button on the Module on/off dialog box.10. For the selected module(s) on the channels that is connected to the truss members and the loading jack.11. Some figures will be displayed in the boxes of the chosen channels. These figures are the loads in the members measured in Newtons.12. Record the initial readings (0 Newtons in Channel 6) and other 5 channels.13. Start put on the weight to the hook to apply loads in the downward direction and observe the readings for the 6 channels. 14. Repeat step 13 for more load increments.15. At the end of the experiment, export the data to the excel spreadsheet and carry out the necessary analysis.

5.0 RESULTSTable 1 Measured Forces in Member of TrussMembers Initial ReadingsFinal Reading in Members

Load / Jack0 Newton102030405060

Member 1

Member 2

Member 3

Member 4

Member 5

Member 6

i. Draw the truss and indicate the loaded joint.ii. Calculate the average force in each member for each load increment. Remember to subtract the initial reading from the data acquired for each load increment.iii. Fill the results in Table 1.iv. Plot the graph of forces in the members verses the applied load for the experimental and theoretical case.v. Determine the percentage error by calculating the slope of each graph.

6.0 DISCUSSIONi. From the plotted graph, compare the experimental and theoretical case.ii. State the relationship between the applied load and the force in the members.iii. State the possible source of errors. Comment on the accuracy of the experiment and ways of improving it. 7.0 REFERENCESi. J.L. Meriam & E. Kraige. 2006. Engineering Mechanics Vol 1. Statics, 6th Ed. Wiley. ii. R.C. Hibbeler. 2007. Engineering Static, 11th Ed. Prentice Hall.