In this example, you round your elevations of F and G up and down respectively, which results in 's'= 1.07. Without rounding s=1.069 and L is calculated as 2620.7', which would result in a conservatively 'correct' answer of choice 'd' (2685), since the calculated curve length is a MINIMUM. I thought it would be useful to note that the decision to round (or not round) your calculations significantly affects the final calculation. In your previous 'Vertical Curve Bridge Clearance' example, you decided not to round and you used a calculated 's' = 2.436, which if rounded to 2.44, significantly affects the calculation for the curve length. I just wanted to bring this to attention. I am not certain which method of rounding choice is technically correct. My mind is returning to a grade school teacher preaching the importance of 'significant figures'.... Either way, this isn't a huge error. Your demonstrations are great! Thank you for providing.
Michael Hazlett yes, significant figures are important. Thanks for pointing out these rounding mistakes and for the great comments. I'll try to keep them up for everyone!
Civil Engineering Academy For a second there, I thought I was going crazy when I got 2620.7' as an answer. I must have plugged that into my calculator 5 times before I decided to scroll down into the comments. Would you comment on which would be the appropriate approach as it pertains to rounding? What can we expect on the exam? Great videos! Thank you for posting these great learning aids.
supermanny73 Sorry to make you crazy with checking. I rushed through this problem which was a mistake. YOU will want to pay attention to significant figures on the exam. That will get you closest to the solutions they have. I left some annotation in the video. Thanks for get great comments!
+Michael Hazlett I think where you went wrong is in the assumption that the L you calculated is a MINIMUM. I think its actually a MAXIMUM. If the L is shorter than the clearance is larger; if L is longer, than the clearance is smaller. Since you need a clearance of 14 ft 6 in, you can't choose a longer L. Your selection would have to be the closest value LESS than what your computed L is.
+Rebecca Cohen ... You are right. The calculated L should be treated as the maximum allowable L value to clear the bridge. So we should pick the answer right below the calculated value. In this case "C". Though, keep in mind that Michael Hazlett is also right because if we don't consider sufficient significant figures we would end up chosen B since the calculated value is 1/2ft less than 2585ft... I know 1/2 ft only but we never know whether this 1/2ft could really make the difference in a real case scenario :) :p
In this example, you round your elevations of F and G up and down respectively, which results in 's'= 1.07. Without rounding s=1.069 and L is calculated as 2620.7', which would result in a conservatively 'correct' answer of choice 'd' (2685), since the calculated curve length is a MINIMUM. I thought it would be useful to note that the decision to round (or not round) your calculations significantly affects the final calculation.
In your previous 'Vertical Curve Bridge Clearance' example, you decided not to round and you used a calculated 's' = 2.436, which if rounded to 2.44, significantly affects the calculation for the curve length.
I just wanted to bring this to attention. I am not certain which method of rounding choice is technically correct. My mind is returning to a grade school teacher preaching the importance of 'significant figures'....
Either way, this isn't a huge error. Your demonstrations are great! Thank you for providing.
Michael Hazlett yes, significant figures are important. Thanks for pointing out these rounding mistakes and for the great comments. I'll try to keep them up for everyone!
Civil Engineering Academy For a second there, I thought I was going crazy when I got 2620.7' as an answer. I must have plugged that into my calculator 5 times before I decided to scroll down into the comments. Would you comment on which would be the appropriate approach as it pertains to rounding? What can we expect on the exam? Great videos! Thank you for posting these great learning aids.
supermanny73 Sorry to make you crazy with checking. I rushed through this problem which was a mistake. YOU will want to pay attention to significant figures on the exam. That will get you closest to the solutions they have. I left some annotation in the video. Thanks for get great comments!
+Michael Hazlett I think where you went wrong is in the assumption that the L you calculated is a MINIMUM. I think its actually a MAXIMUM. If the L is shorter than the clearance is larger; if L is longer, than the clearance is smaller. Since you need a clearance of 14 ft 6 in, you can't choose a longer L. Your selection would have to be the closest value LESS than what your computed L is.
+Rebecca Cohen ... You are right. The calculated L should be treated as the maximum allowable L value to clear the bridge. So we should pick the answer right below the calculated value. In this case "C".
Though, keep in mind that Michael Hazlett is also right because if we don't consider sufficient significant figures we would end up chosen B since the calculated value is 1/2ft less than 2585ft... I know 1/2 ft only but we never know whether this 1/2ft could really make the difference in a real case scenario :) :p
L
Elev "E"
Clearance
1985
458.543
21.45696
ok
2085
459.666
20.33403
ok
2585
465.283
14.71701
Correct
2685
466.4068
13.59324
Wrong
* all in feet
FYI, this is Transpo DEPTH content, not civil breadth, per 1/1/2022 CBT exam specs - vertical clearance
Whay if the bridge is on the centerline and the width of the bridge is given. How do we do it?