Question
- Could you explain to me how to do question 14 on this week's lab? …. I know I have to work backwards to find the mass, but I am not sure how to do this. Could you please guide me in the right direction for how to complete this problem?
Response
Prof. Dasaro set this question to challenge you to think about the physics of what’s happening. As he noted, in most respects it’s a matter of working backwards through the same steps that you followed in Q1-13. Below are some hints that may assist.
- A key thing to note is that in calculating the bending moment we’re pushing on the pier with the maximum the DRPA allows. In essence, we’re ignoring what happens in the “plastic” region when addressing bending.
- To work backwards to the allowable tanker mass/weight you need to check whether the maximum stress specified in the question occurs in the elastic range, which includes the DRPA maximum. You can do this by comparing the moment that occurs with this stress in each pier leg to the maximum moment. If that moment is less then you can proceed assuming that you’re working exclusively in the elastic range – which simplifies the calculations.
I think in Q14 Prof. DaSaro wants to see how students understand P and its behavior, meaning of Pyield, and how P links Bending Stress and PE.
ReplyDeleteRemember to watch the units. Using one parameter in feet and another in inches won't lead to a correct answer.
I'm not sure if this will be seen before the lab is due, but I am having a similar issue. Where I am having difficulties is that the Bending Stress was entirely calculated using given values: Pyield, L, and S. Therefore, our calculations never reflect the direct influence of the tanker weight on Bending Stress. The question explicitly states that all other variables, aside from weight, will remain the same - meaning the three given values that led to the Bending Stress will remain the same. I can solve this question by analyzing impact energies that will maintain within elastic deformation. However, I feel like I am missing something by just considering energy. Is this an adequate approach?
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