Tanker Collision with Bridge Lab–Questions

Question – About Q8 – Maximum Weight of Oil Tanker

A student visited me today perplexed about the method of calculating the maximum weight of the oil tanker in order not to exceed the allowable stress in the bridge pier – Question 8.

Response

A key thing to note is that in calculating the bending moment (Step 6 – slide 26,27) we’re pushing on the wall with Pyield.  Pyield is the point at the top of the linear elastic range (slide-16).  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.  You can do this by comparing the moment that occurs with this stress in each pier leg to the maximum moment calculated in step 6.  If that moment is less then you can proceed assuming that you’re working exclusively in the elastic range – which simplifies the calculations.