NCEES Lateral Bridge Exam PM Questions

[bbridge]

First time user, so forgive me if this has already been discussed in a previous post.  Question on NCEES Lateral Practice Exam, Bridge PM Column Design Problem #901...  

T

he problem provides Extreme I loads to design a circular RC column.  I follow the solution 100%, but don't understand why the design forces are not the lesser of 1) elastic seismic design or 2) the forces developed by inelastic hinging.  This seems to be what's required by AASHTO 3.10.9.4 for Seismic Zones 3 and 4.  I understand elastic design typically provides higher and therefore conservative forces compared inelastic hinging, but I don't understand why the solution doesn't check both or even mention the assumption made?  Bottom line...[SIZE=11pt]if I get a similar test question, what in the problem statement tips me off to make the same, simplifying assumption?[/SIZE]

 

[David Connor SE]

Bbridge,

To show that you know the subject matter, you could have certainly stated in your solution you are assuming that the elastic loads reduced by R are lesser than the inelastic hinging loads. To go through the process of actually determining what the inelastic hinging forces are would be a long iterative process per AASHTO 3.10.9.4.3c and would probably be done by computer in practice. I believe that they design some of the essay questions so that there is some ambiguity to see if you make the correct assumptions. Remember each essay question should take just slightly more than an hour, so keep that in mind when if you come across an essay question that you think would take a lot longer to do by hand. They may be trying to see if you make a correct, time-saving, assumption.  

Also, the question is testing on the design of the column reinforcement, so concentrate more on actually what the question is asking for, as opposed to caveats in the code that may or may not come into play. The structural engineer in us is always making sure we are considering everything in practice, but on the SE exam we only have an hour to work with so don't read to much into the question and show that you know about the subject matter they are asking about. 

  David

 

[bbridge]

David, thank you.  Your first sentence is exactly what I think the NCEES solution is lacking and should state.  Determining inelastic hinging forces can be iterative/long for multi-column bents, but actually the practice PM problem I have from the the school of PE class does it and well within the time constraints and level of difficulty expected for a test problem (which is why I'm kind of hung up on it).  Either way I feel fairly knowledgeable on both types of design now, I just needed a couple independent opinions to confirm I can make an assumption during the test (assuming I state it clearly).  Also, great point about concerning myself only with what's being asking for.  It's a simple idea, but they wouldn't require extensive analysis in the column design question, they have another whole 2-hr problem for that.  Thanks again for your help.

 

[bassplayer45]

From my experiences studying and taking the test, without giving any questions away, they are generally pretty straight forward when they want you to determine "the design forces". They will typically say something like "determine required reinforcement per the seismic forces determined in part c". Part C would then have a statement like "determine the design forces based on the Extreme Event 1 load combination do not consider hinging, or specifically say based on hinging". Can't say it exactly how they did, but they pretty much tell you what they want. Also, from my test experience, it was pretty darn apparent real quick if you were using the incorrect one based on what they gave you.

 

[smahurin]

I agree with Bass, typically the NCEES are fairly straightforward (which is a completely different thing than easy for what its worth).  Although there was one question on the PM portion of the SE exam when I took it where I was confused as to what they were asking.  So I wrote a paragraph explanation on what I thought they were asking and how I intended to solve it... then did.  I passed, so not sure how that was received but if there is any questions on a PM exam question I'd definitely explain your thinking since it is essay/open response.

 

[user 32699]

Agree with all the above. I'm just beginning to study this material for April, but passed the vertical last spring and I know I made some errors in calculations and misinterpreted or misused the code in some cases. It wasn't a perfect performance by any stretch. 

To start every problem, I made a column to the left of the page, and referenced every code section I used as I worked through. Then, I basically set the thing up like a third grade math word problem, with a section for Assumptions, Procedures, Solutions, and Discussion. I tried to get the main assumptions in the assumptions section and then any others that were incidental to a particular part of the solution, I added as I went along. I didn't write a novel for the discussion, just a few summary bullet points and a few things I thought of that may be better to have been done differently. 

If I noticed a clear error, I crossed it out rather than erasing, and made an end note to reference why I did that in my discussion. 

The exam problem tends to be separated into 4-6 sub-problems so organizing each part like this provided a pretty clear solution. 

 

[TCurrz1016]

David,

This isn't exactly related to this post, but I figured it would be a good place to ask this question.  I am aiming to take the SE Exam in April, but just saw on the NCEES website that they updated the required specifications and AASHTO 7th edition is now required.  I was planning on buying your SE Bridge book, but that is based on the 6th edition.  Are there a lot of changes between the 6th and 7th editions that affect the examples in your book?  Are you planning on coming out with a new SE Bridge Book before the April Exam?  I will buy it either way, just wondering if I should wait for the latest and greatest version.  Thank you!

-Tom

 

[TehMightyEngineer]

Tom, David addresses this here:

 

[David Connor SE]

TCurrz1016,

My book(s) have been updated and you can buy them by clicking on the links in my website. www.davidconnorse.com 

They haven't shown up yet on Amazon. The 6th edition book(s) are still for sale at a reduced price.

Thanks,

David