6 minute solutions vs actual SE I exam?

[Jennifer]

Which PM will you be taking, the bridges or buildings? This will be my first time taking the SE I and II, but the morning session is completely different for a bridge guy. I would venture to guess that the PM portion is much more difficult because of the depth involved, but the AM portion has a lot more to study and refresh on if you are a bridge person.

SE1 doesn't give you a choice. You answer all the questions...buildings and bridges.

 

[buening]

SE1 doesn't give you a choice. You answer all the questions...buildings and bridges.

Sorry, I meant to say what he was choosing for the SE II not the PM portion.

 

[kevo_55]

buening,

The SEII only gives you a choice in the morning. Your PM exam must follow up with your AM exam.

Example, for the AM you can choose either the building problems or the bridge problems. For the PM exam, you must continue on with whatever you did for the AM portion.

So, if you do buildings for the AM you must do the building problems for the PM exam.

 

[Jennifer]

Good to hear from someone that can relate the three. I will be doing the NCEES practice exam this weekend, but these 6 min solutions are pretty darn tuff. Some of the solutions fill a page and a half. I'm lucky to just copy the solutions in 6 minutes, let alone look up some of the formulas and actually think for a second LOL.

Also, I've noticed that there are alot of design and analysis problems in this 6 minute solutions booklet that call out an unspecified "compressive load of 320k and moment of 200k-ft". One example would be a moment resisting base plate with anchor bolts on Problem #45. They don't state if these loads and moments are factored, yet all design should be done with LRFD according to NCEES (except masonry). The anchor bolt design of this base plate problem finds the tensile force on the anchor bolt and then pulls the ASD tensile strength of a 1" bolt from the AISC tables. The LRFD tensile strength is enough that a 7/8" bolt could be used, but that goes back to if these loads given are factored or service. These are some of the minor things that keep tripping me up. There are other problems that this has occurred. I'm hoping the NCEES exam is a bit more specific on what load is given, because I don't feel like the ASD tensile strength should have been used for the anchor bolt problem. Have you hit this problem yet?

I did this problem last night and totally missed that it was wrong...I was looking in the back to do it, though.

My thoughts...since it's telling you to design with LRFD and giving you the loads, not dead and live, it's safe to assume they are already factored.

As far as the design methods...look at the NCEES code list. http://www.ncees.org/exams/professional/pe...n_standards.pdf

You can use ASD or LRFD for steel design. Masonry is ASD except for slender walls. I'm not sure about Wood, but it's traditionally ASD, the LRFD is new, so I would use ASD there, but that's how I learned it. I think everything else is LRFD.

 

[buening]

It does say that ASD or LRFD can be used with steel at the bottom of the structural standards. I must have missed that!

 

[Jennifer]

It does say that ASD or LRFD can be used with steel at the bottom of the structural standards. I must have missed that!

Hey, did you find a mistake on problem #23 in their calculation?

 

[buening]

Nah, I looked at that problem and decided that would be one I'd save for last and would take entirely too long. I know how to do the conjugate beam method, but when it ends up with parabolic loadings is when I decide it would take longer than 6 minutes :Locolaugh: I hope the loading of the beam is a bit more simple on the actual exam.

What was the error?

 

[buening]

There is also a problem towards the end of the masonry section that requires a column interaction table for masonry columns. These aren't even in the SERM, but the solution states to look into the Masonry Designers Guide for the table. It's problems like that to where if you don't have the table, you are screwed because it'd be a half hour calculation.

 

[Jennifer]

Nah, I looked at that problem and decided that would be one I'd save for last and would take entirely too long. I know how to do the conjugate beam method, but when it ends up with parabolic loadings is when I decide it would take longer than 6 minutes :Locolaugh: I hope the loading of the beam is a bit more simple on the actual exam.

What was the error?

Actually...the conjugate beam thing wasn't as bad as I expected. I forgot all about how to do it, but it's just drawing the moment diagram and then a little more on it. Basically...I found the calculation for Rl to be calced wrong...I have no problem with the numbers added together, but I got 1038/EI not 1082/EI

 

[Jennifer]

There is also a problem towards the end of the masonry section that requires a column interaction table for masonry columns. These aren't even in the SERM, but the solution states to look into the Masonry Designers Guide for the table. It's problems like that to where if you don't have the table, you are screwed because it'd be a half hour calculation.

Guess I havent' done that yet...I'm at 46, but I've skipped some in the around that conjugate beam thing...the fixed end moments ones...

 

[Jennifer]

Ok, Buening, have you worked Problem #55? I think the solution is wrong here, too. I think it should be 65.2, not 60. The AASHTO says to take 12x the slab thickness and add half the girder flange width. Does that sound right to you?

 

[buening]

I agree! The "plus greater of web thickness or 1/2 flange width" is a new requirement in the AASHTO code, so it's likely an old problem that hasn't been updated.

Have you taken the NCEES practice SE I exam yet? The first few problems with the wind loads on the precast wall panels really messed me up. I'm not sure what to think now Getting ready to do the afternoon portion of that practice exam. Hopefully it's a little better than the morning portion.

 

[buening]

Have you done the morning portion of that exam? I think #125 is incorrect. If you look at the solution and enter the numbers in the Cv equation that they show, you should end up with 2.85. They show the correction factor as 0.85. With a factor of 2.85 > 1.0, then the factor is 1.0 Do you agree, or is my calculator wrong? :brickwall:

 

[Jennifer]

Have you done the morning portion of that exam? I think #125 is incorrect. If you look at the solution and enter the numbers in the Cv equation that they show, you should end up with 2.85. They show the correction factor as 0.85. With a factor of 2.85 > 1.0, then the factor is 1.0 Do you agree, or is my calculator wrong? :brickwall:

That book is at home. I did it last time, so all I did this time was to look over it. I'll check when I get home. I felt like there were some mistakes in the precast questions. In the wall connection problems, they put the diaphram force at the top of the wall instead of at the roof structure. That just doesn't make sense. The diaphram shear force is going to get into the wall at the roof diaphram, not the top of the parapet.

 

[Jennifer]

I looked it over...it looks right to me. I came up with 0.86. The solution in the back checks out for me and I punched it in my calculator again and it seems to come out right again. You are keeping L in feet, right? Although I think that would make it smaller, not bigger.

 

[buening]

Aw shoot, I was adding the three values together instead of multiplying them! :brickwall: Check the errata for the chord forces on those problems you question, the leader was pointing to the wrong line.

Got a few more questions with the same SE I practice exam, maybe you could help/clarify. The solution to 501 shows the L for the column as 13.67 ft. According to ACI, the L should be the clear distance between floors. Wouldn't that be 12ft then, not 13.67?

One other one that I think may be incorrect is the LRFD solution to #525. The section is doubly symmetric, so I think they should use section H1. You would then see if Pr/Pc > 0.2 I get Pr = 32k. The Pc = phi * Fcr * A = 0.9 * 23.7 * 15.6 = 332.75k. The ratio ends up being 0.096 < 0.2, therefore the second equation applies. Pr/(2Pc) + Mr/Mc <1. In their solution, they are finding the stress in the column (P/A) and then use an equation fa/Fa + Mr/Mc This equation lacks the 2 in the denominator of the axial portion. I end up getting 0.814 for the combined ratio compared to their 0.853

I did OK with the afternoon portion, just barely passing. The masonry expansion/contraction questions really threw me for a loop. Such an odd group of questions, and there were like 5 of them!

 

[Shaker-PE]

Ok, Buening, have you worked Problem #55? I think the solution is wrong here, too. I think it should be 65.2, not 60. The AASHTO says to take 12x the slab thickness and add half the girder flange width. Does that sound right to you?

Ok guys, Problem 55 asks for the effective width of the slab for an interior girder. The answer is located in the AASHTO 4.6.2.6.1 under effective flange width.

In the NCEES SE1 practice exam, Problem 129 asks for the effective span length for deck slab design. The answer is located in the AASHTO 4.6.2.1.6 under deck calculation of force effects.

So how do you know. which one to use? I guess if you're given deck thickness then use the first, but if not then use the second. I'm missing something, but does anyone know what the difference is between each of these two length calculations? :blink:

 

[Shaker-PE]

Ok guys, Problem 55 asks for the effective width of the slab for an interior girder. The answer is located in the AASHTO 4.6.2.6.1 under effective flange width.
In the NCEES SE1 practice exam, Problem 129 asks for the effective span length for deck slab design. The answer is located in the AASHTO 4.6.2.1.6 under deck calculation of force effects.

So how do you know. which one to use? I guess if you're given deck thickness then use the first, but if not then use the second. I'm missing something, but does anyone know what the difference is between each of these two length calculations? :blink:

I'll try to answer my own question here... in problem 129 you're designing the slab, so you go to 4.6.2.1.6 because that's the section for deck design.

In problem 55 you're designing a steel beam, so you go to 4.6.2.6.1 because that's the section for determining how wide your slab is for composite action.

So if the problem asks, what's the effective span length/width... figure out if it's for concrete slab design or for steel beam design, and then proceed to the appropriate AASHTO section. I think that's how I'm going to rationalize the difference.

 

[buening]

That's exactly right. The problem should state "for the deck design, what is the effective slab width?" or " for the girder design, what is the effective slab width?". It took me forever to find the effective slab width section for the deck design. My state DOT has a chart in the bridge manual for deck design, so I never mess with the effective width for the slab design.

Don't forget the Appendix charts for maximum positive and negative bending moments for the deck slab design. It was in the example exam, but not sure if it will be in the real one or not.

 

[Jennifer]

Don't forget the Appendix charts for maximum positive and negative bending moments for the deck slab design. It was in the example exam, but not sure if it will be in the real one or not.

huh? what are you talking about?