NCEES 16 Hour Structural Engineering Sample Exam Questions

[Jgivens12]

Hi I'm new to the forum and in the middle of studying for the 16 hour structural exam. I just completed the sample exam provided by NCEES and had questions about several of their solutions that I wanted to see what others of you got. See below (sorry for the lengthy post!). I wrote an email to NCEES which are why my questions are pointed to them. Didn't feel like retyping on my tablet...

Prob 132 -- Please verify solution. Equations used do not match ACI 530 (2-3) or (2-5). Solution also neglects to check ACI equation (2-4).

Prob 133 -- Please verify solution. Problem neglects eccentricity that was arise given loading configuration. Similar configuration is used in Problem 135 and this eccentricity was not ignored. Please also confirm why vertical reinforcing was included as part of compression capacity. Per ACI 530 2.3.2.2.1 compression steel shall not be used unless it has lateral ties meeting requirements of ACI 530 1.14.1.3.

Prob 601 - Please confirm validity of combining Allowable Stress Provisions of Masonry with ACI 318. 12.5.3. I believe stress in reinforcing should be calculated on a strength basis to be compatible with ACI 318 reduction equation.

Prob 602- Please confirm why slip critical bolts were not used. Per Specification for Structural Joints Using ASTM A325 or A490 bolts Section 4.3.(4) slip critical bolts shall be used when slip would be detrimental to the structure. In my opinion a moment frame constructed using a bolted connection would qualify. Please confirm why Panel Zone checks were not completed.

Prob 603 - A) Please confirm why column tie steel was not provided through beam joint. Per ACI 318 section 7.10.5.4 lateral ties are required to extend to within a half of a tie spacing of the slab steel. Provisions of 7.10.5.5 do not apply as beams only frame into two sides of the column. B) Please confirm why all of the positive steel was extended into the joint. Per ACI 318 12.11.1 only 1/4 of required positive moment is required to extent into the joint. This positive reinforcing also does not need to be lapped as shown in the sketch as only a 6" embedment is required. (Assuming the steel is not needed through the joint for adequate development)

Prob 604 - A) Please confirm why compression side of glulam is shown to be in tension in bending checks. Per moment diagram provided compression side of glulam should not be in tension. Also please confirm why even though the problem statement said to check for bending no attempt was made to check it as a Beam-Column (Obviously controlling state). Bending moment is reduced by removal of middle purlin and therefore would be ok by inspection. B) Please confirm validity of bolted connection shown in Figure 604E. It appears that lower bolts do not meet minimum requirements for the Geometry factor and therefore should not be included in calculations.

Prob 112 - Please confirm solution. It appears solution is calculating maximum reaction at column/brace intersection and not axial force in column.

Prob 802 - Please confirm why torsional irregularity was not checked in solution. It appears as though it is warranted and could be checked given relative rigidities.

Prob 804 - It appears the 0.6 factor was used twice in the solution to part B.

 

[steelhead]

Prob 132- they changed anchor bolt eqns in the code and the sample exam uses the 05 code instead of the 08.

Prob 133- I got the same answer the book did, using te (equivalent thickness) from the tables. The axial capacity doesnt change with an eccentric load, you would just apply P*e (moment) and check the wall for both, except the book is only asking for Pa (axial check). I believe the veritical reinforcement without ties is neglected in column capacity Pa calcs, not for walls, as reinforcing is never "tied" in walls. Section 1.14 applies to columns.

Prob 601- The sample solution just uses the demand/capacity ratio for the wall steel to reduce development length into the footing. Since it is just a ratio, it doesnt matter if you got it using WSD or strength design.

Prob 602- I dont believe you have to use slip critical in a moment frame unless it falls under one of the categories in 4.3, (also if it is part of the seismic load path per AISC341). If you have 3 or more bolts in std holes you can assume no slip. Check out the commentary, last paragraph, on page 16.2-24 in the steel manual. I would check the column web for panel zone strength unless there is some obvious reason "by inspection" that is wouldn't apply. I didnt check it when I worked the problem, but looking at it now I think I should have. Nice catch.

I'll look at the others later.

 

[steelhead]

Prob 133- Correction - You are right about the compression steel in the wall. I think the sample exam is incorrect.

 

[Jgivens12]

Thanks for your responses steelhead. I appreciate the feedback.

132- good to know. I didn't appreciate this had changed so much between editions. Do you not have to calculate straightening of a j-bolt under the 05 edition?

133- I think I disagree with this. Since the axial demand is applied eccentrically though the ledger the axial capacity is coupled to the moment demand and is therefore not independent of it. This would either be solved with a PM diagram or using the simplified approach of fa/Fa + fb/Fb. Either way since the moment is caused by the axial force I don't believe you can neglect it. In my opinion if they didn't want you to include moment they should have just shown a concentric axial load on the wall.

601- I guess my point and perhaps it's nitpicky is would the stress in the rebar be the same if strength design was used. Sure it should be close but since ACI equations are calibrated for strength seems like you should compare apples to apples.

602 - I know the argument that if you have 3 bolts or more in a row the connection can't slip. I suppose the part I don't completely understand about that argument is wouldn't this only be true if the demand is below the bearing capacity of a single bolt? Otherwise the one bolt that is in bearing would deform the bolt hole and cause the connection to slip. Personally, I'd use SC bolts but I suppose that is not a building requirement. However, in the AISC 360 Design Examples they also do not use slip critical bolts either.

 

[steelhead]

Problem 804,

yes they incorrectly applied the 0.6DL factor twice. Hold down force is 3.54k (uplift) and 3.24 (compression, no uplift) on the shear wall.

 

[steelhead]

Problem 802-

I think it should have been checked, and it should probably be done for full credit? Anyway, d(max)/d(average) = 1.13 < 1.2, so it doesnt change the answer.

 

[McEngr]

ACI 530-08 indeed calculates bent bar anchor bolts. You might want to double check. Alan Williams covers this surprisingly well in the SERM.

 

[McEngr]

Problem 602 says to "neglect lateral loads and lateral criteria for this problem."

SC connections are for AISC 341.

 

[McEngr]

Problem 133 - I think it is helpful to see the forest from the trees from time to time. I believe that it's also good to have experience in identifying what has a higher degree of effect on the axial capacity. For example, if a wall that is non slender has a high load, but a small eccentricity of say, 2", you would expect an fa/Fa to be 4x as much (or more) as fb/Fb regardless of the P+M method. Because of this, the P+M diagram may not be as critical. As I'm sure you know, the P+M diagram has a "cap" for when fb/Fb is small and fa/Fa is big.

 

[McEngr]

Jgivens, another thing to consider with bolted moment connections is the concept of no shear unless bearing occurs...

I don't believe slip critical connections to be required on OMF's. The problem doesn't identify whether this is a special or ordinary moment frame...

 

[keiwong]

"Prob 604 - A) Please confirm why compression side of glulam is shown to be in tension in bending checks. Per moment diagram provided compression side of glulam should not be in tension. Also please confirm why even though the problem statement said to check for bending no attempt was made to check it as a Beam-Column (Obviously controlling state). Bending moment is reduced by removal of middle purlin and therefore would be ok by inspection. B) Please confirm validity of bolted connection shown in Figure 604E. It appears that lower bolts do not meet minimum requirements for the Geometry factor and therefore should not be included in calculations."

A) Since this was at one point a roof purlin that would have supported tension on either face due to various combinations of live load/ wind load/ and snow load, there is no garuntee that the beam was installed so that the compression face would be the compression face in the post demolition condition, therefore it would be a good idea to ensure that even if the compression face were put into tension it would be fine. However me personally, I would have included this statement in my answer "Have crew check that the compression face of the GluLam beam is facing up, if it is not facing up then the allowable stress is this..." Also I would argue that the load duration factor for the following demolition case be 1.25 for construction loads rather than .9 for dead loads since the two 2 kip loads are not present in the final configuration with the truss, therefore those 2 loads are obviously loads present durring the construction phase only. There is no attempt to check it as a beam column because the probem statement declares that the configuration is a truss which by definition, ony has members which carry axial loads.

B) you do not have enough information to determine that the geometry factor is not valid. The problem statement does not give you an end distance on the Glu Lam beam. I think you are sayng that it does not appear to be in complaince based solely on the picture presented in Figure 604E. First of all, there are no over all dimensions given for the out to out of the connector and generaly these things are not to scale. Secondly it dosent matter because the picture is a picture of the steel plate connector so the Geometry factor would not apply to that anyways.

 

[keiwong]

Problem 802-

I think it should have been checked, and it should probably be done for full credit? Anyway, d(max)/d(average) = 1.13 < 1.2, so it doesnt change the answer.

How did you determine the story drift ?

 

[steelhead]

Problem 802-

I think it should have been checked, and it should probably be done for full credit? Anyway, d(max)/d(average) = 1.13 < 1.2, so it doesnt change the answer.

How did you determine the story drift ?

Force in the wall divided by the rigidity in the wall. Since you only need to know the relative displacements to determine if there is a torsional irregularity, you can check the drift of walls/frames by taking F(total)/Rigidity, finding the average displacment, then taking the max/average and if it more than 1.4 or 1.2 you have a torsional irregularty.

Example 24 from the SEAOC IBC 2006 Structural/seismic design manual (1) has a good example if you have access to it.

 

[Chosen One]

The basic structural analysis problems still give me fits, as I'm used to computer programs doing most of the FEA stuff for me....I understand the vertical distribution of the base shear as it's straight forward in ASCE7-05. I also understand the diaphragm forces must be calculated using the story forces and weights of the floor in consideration and the stories above. Would you design the lateral bracing system (SCBF, Shear wall, etc.) based on the forces distributed by the diaphragm?

What throws me off sometimes is the accumulation of forces; for example a 2-story building and we are trying to design for shear in the 1st floor. Take the NCEES practice exam lateral essay questions; The problems with the concrete shear wall or wood shear wall considers the forces on the floors above, but in the steel problem doesn't consider the force in the 2nd story when designing the brace in the 1st story....anyone care to chime in on why the force on the 2nd floor isn't considered? I'm probably overthinking it, but want to make sure I understand the concept.

 

[McEngr]

For those of you still struggling with diaphragm vertical distribution and how it differentiates from story force vertical distribution, I would recommend the VOL 1 SEAOC manual examples 23 and 48.

For more detailed questions, I would recommend looking at ALL the examples in the AISC Seismic Design Manual. It is very well written. The SEAOC Volume III is more geared towards practicioners (assumptions for when an SCBF has eccentric joints, etc.), so the AISC 341+SEAOC VOL 1 will help iron these out.

Hopefully you guys can sharpen this area before the test coming up shortly?...

 

[keiwong]

The basic structural analysis problems still give me fits, as I'm used to computer programs doing most of the FEA stuff for me....I understand the vertical distribution of the base shear as it's straight forward in ASCE7-05. I also understand the diaphragm forces must be calculated using the story forces and weights of the floor in consideration and the stories above. Would you design the lateral bracing system (SCBF, Shear wall, etc.) based on the forces distributed by the diaphragm?
What throws me off sometimes is the accumulation of forces; for example a 2-story building and we are trying to design for shear in the 1st floor. Take the NCEES practice exam lateral essay questions; The problems with the concrete shear wall or wood shear wall considers the forces on the floors above, but in the steel problem doesn't consider the force in the 2nd story when designing the brace in the 1st story....anyone care to chime in on why the force on the 2nd floor isn't considered? I'm probably overthinking it, but want to make sure I understand the concept.

The diaphragm load and the vertical distribution are two related but different things. I think the reason you did not need to mess with the upper story load in the steel question is because you are dealing only with the overall story shear which does not take into account the story shears above it. However if the instructions were say design the tension reinforcement for the rigid diaphragm you would need to use 12.10.1.1 which prescribes how yo relate level forces to the load applied to a diaphragm and its elements.

 

[TehMightyEngineer]

Another problem I have with the NCEES sample exam. Maybe I'm missing something but on 603. A) they calculate the moment and shear for a continuous beam using a dead load and a reduced live load. All good with that. However, they use WL^2/14 or 0.07WL^2. This makes sense for the live load as it gives you the maximum (negative) moment. However, it doesn't make sense to do this for the dead load as that would mean the 3rd span would be unloaded, hard to do that with a dead load. I understand that it's conservative to do it this way but it just bugs me because they ask for "maximum moment" which could be anything. Maximum possible moment? Maximum positive moment? Maximum negative moment? Maximum moment with all spans loaded? Maximum realistic moment (no unloaded spans for dead load)?

 

[TehMightyEngineer]

Oh, I think I see my problem. I need to be using the ACI moment coefficients for frames. Gah, stupid mistake. Still, the problem is poorly worded.

 

[keiwong]

On question 137 in the lateral portion, how would one approach that problem if the eccentricity were not in middle third (e>32/6)

 

[McEngr]

keiwong - you'd solve 137 in the same way.

• With a P*e=M and vertical equilibrium check, you have 2 unknowns: the distance of bearing and qmax.

• When e<L/6, you have a qmin and qmax.
  

• With a large e (>L/6)... just a 0 and qmax.

• You might be served well by actually deriving the formulas at the very beginning of the foundation chapter of the SERM. It's basic statics.