Sunday, May 19, 2019

Modelling a Frame Subjected to Multiple Loading Conditions Essay

In this experiment the main aim was to modelling a frame subjected to eightfold commoveing conditions and record how the fight and demarcation vary to different blames. The frame represented a naive roof trusses and the make full conditions be similar to what a typical roof would undergo. In this experiment a universal fame was used with load prison kiosks to provide the load and digital major power and soma instruments to record the data. As the load was increased the prove went up linear showing a linear relationship amid loading and strain.After analysing results it was found that the results for experimental strengths comp bed to theoretical forces were in truth close showing that this experiment was very accurate, with very small distrust, the reason for this is due to very sensitive equipment as a change of 1? is equivalent to change of 6 N (using youngs modulus) and other factors draw in dot in the report. Table of Contents Summary 1 Introduction Pg 4 2 Theo ry Pg. 4 3. 1 Apparatus Pg 6 3. 2 Experimental procedures Pg 8 4 poster and results Pg 8 4. 1 Results Pg8 4.2 Observations Pg11 4. 3 Discussion Pg11 4. 4 Sources of error Pg11 5 Conclusions Pg12 References Pg13 Appendices Pg13 Introduction The aim of this laboratory was to channel out an experiment to mea certain the strain in segments of a frame, where load was being apply in different loading conditions. This experiment was carried out to put to use the theory learnt in lectures and see how they in reality perform in a real life model. By doing this it is possible to appreciate the limit of theoretical approach to these loading conditions and compare the errors.The model used in the experiment was that of an idealised roof truss, a roof must withstand a lot of force over a long time during its lifetime. Three 3 different loading scenarios will be modelled and the strain forces are expected to be within the range of the guessd theoretical forces. Main aims were 1. Measure th e strain in each member and record results 2. Calculate theoretical value for the experiment 3. Compare theoretical set with experimental results and auspicate percentage error TheoryIn a frame model where there is a load being apply members of the frame will feel a compressive or tensional force. The value of the force can be worked out by resolving the forces in horizontal and vertical directions and taking moments. This is through by analysing each of the joints of Fig 1 separately. In a rigid static frame the marrow squash of the vector forces add up to zero(a) Fig 1 model of experiment The first loading model has is simulated with a load of 500N. First work out the value for the reaction force at the supports. Then use these values to calculate the tension in each member of the truss. raft written theory in appendix (1) Apparatus The apparatus used in this experiment are by Tecquipment STR8 Pin-jointed Frameworks Digital force discover -500N to 500 N Digital strain boast - 110-9 ? level cell 0-500N range Screwdriver Experimental procedures mental testing 1 1. Calibrate the load adopting instruments to measure zero on channel 1 on the digital load display, if the display shows load being applied then adjust the appropriate load cell W1 by rotating the appropriate knob. Test 2 1. carefully remove the pin that is holding load W1 and reinstate load W2 2.When no load is being applied to the members check the digital strain display, there are 13 impart one for each gauge. apiece gauge must be reading zero if not use adjust the reading to read zero as close by using a small screw driver. 3. Make sure the load cell W2 does not interfere with the frame. 4. In table 1 record the strain values of each member from the digital strain display. 5. Next apply a load of 100N to the load cell W1 by turning the handle anti clockwise then read the digital strain display for channels 1 to13 and record in the table. 6. Repeat steps 5 for loads 200N, 300N, 400N and 500N7. After recording all values reduce the load to zero by rotating clockwise. 8. Using the values of strain for 500N load calculate their equivalent member forces and record them in table 3 using the following equations Test 3 1. For this model both load cells must be loaded on to the frame 2. In table record the strain values of each member from the digital strain display when no load is being applied 3. Next apply a load of 500N to the load cell W1 by turning the handle anti clockwise then read the digital strain display for channels 1 to13 and record in the table.4. Switching to channel 2 on the digital force display apply a load of 100N then read the digital strain display for channels 1 to13 and record in the table 5. Repeat steps 4 for loads 200N, 300N, 400N and 500N on load cell W2 6. After recording all values reduce the load to zero by rotating clockwise. 7. Using the values of strain for 500N load calculate their equivalent member forces How to use the strain to conve rt into force is described in the appendix (2) 4. Results and observations 4. 1 Results CENTRAL LOADINGAngled loading Multiple loading The entireness of experimental forces for loading of 500 N in loading 1 and 2 4. 2 Observation Allow the equipment to stabilise by waiting 5 minutes in order to eliminate and uncertainty due to heat feigning resistance values. There are no significant health and guard risks in this experiment. 4. 3Discussion A way in which to improve the results of the experiment would be to take repeat readings of the strain for each gauge at least three times in order to eliminate either anomalous results.Another addition would be having different loading conditions on the frame and see how they affect the two gauges EF and IJ as they experience any strain which could lead to the question are these members required and do they make any difference. In loading condition 3 by having 2 load cells you bring to pass a model where there are members which are superimp osed. When analysing table 8 and looking at the nub of the experimental values are larger than the theoretical value, when looking at member AH the values are notably are different when superimposed. 4. 4 sources of errorThe main sources of uncertainty will come from the standardization of the device as the digital strain reading instrument has an accuracy of 0. 510-10 ? and the digital force display has an accuracy of 0. 5 N. These are very small values it is difficult to zero the strain display which lead to a poor accuracy. The strain values is calculated by the change in resistance of the wire when it is under tension or compression, however change in temperature would affect the space of the wire therefore giving a different value of resistance leading to inaccurate strain reading.5. Conclusion After analysing the results in detail it is shown that the difference in theoretical and experimental results is not importantly different and therefore using the theory of resolving forces it is possible to pretend an accurate value of certain member forces and equally important to simulate and model the situation in real life scenario to gain a true understanding of what is going on.Also analysing table 3 shows that is also possible to calculate the force on a complex load by adding the forces individually. References Mechanics structures and thermo dynamics university of Warwick Mechanics lectures by Dr. T. Karavasilis http//www. tecquipment. com/Datasheets/STR8_0213. pdf 29/12/2013 Appendices Pin jointed lab briefing sheets Theory (1. ) (2). Stress strain thoery

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