Judging from last weeks performance quite a few of you have forgotten how to draw BMD. So the next few questions will focus on this issue.
The question focusses on a 3 span bridge with a drop-in span in the middle similar to the Ness Bridge in Inverness Scotland, check out the Happy pontist blog: a great resource from civil engineering students.
Please identify the INCORRECT BMDs
HINT. The trick with such 'drop-in' structures is that the double pin in the middle isolates the effects of load ( moment) from either side. That is to say that a load on the first span cannot produce any moment on the middle or third span.UPDATE 15/7/13. Judging from the number of incorrect answers this question has received I will be leaving it up for a couple of days more.
If you draw the deflected shape for the case where there load is at any point between the first support and the adjacent pin, you should see that the middle span(between pins ) is always straight just rotated slightly)
Try the question again and attempt to draw the deflected shapes.
SOLUTION: 17/6/13. A,C,D are the INCORRECT BMDs (this is what you were asked to submit) the rest of them (B,E and F) are the correct BMD for the structure.