Structures (and HVAC) Calculations and the PDD

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    David Kaplan

    Colleen,

    I was in the same boat leading up to PPD and PDD and am happy to report that my fears were unfounded.  There are NOT difficult structural and HVAC calculation questions on either exam.  Here's my recommendation:

    1) With respect to structural, know how to calculate the moment on a beam about a certain point.  Remember free body diagrams from back in school, where you have a point load and maybe a uniform load on a simple beam?  Know in general how to do that, that might come up.

    2) Gotta tell you, that's really ALL I went into these tests having memorized.  Any other calculation questions that I got, the ARE gave me the equation I was supposed to use, either in the question itself or in the references.  This was ESPECIALLY true for ANY MEP calculations questions.  I found those to be straightforward.  I had not ever used them in practice, just like you, but the equations where there, and I was able to figure out what variables to put in using the information given to me.  If an equation was X + Y = Z, I was able to figure out just from the question what X and Y were, and knew that I simply had to solve for Z.  Best piece of advice - watch the units.  Make sure you are using the correct units and that you convert whatever you need to first.  That will likely be the ONLY trick thrown at you.

     

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    Tony Young

    Colleen,

    Good morning, check the other post in this PDD community.  I am studying for the structures section of PDD right now. I am studying formulas however I think from what I 've seen you should know how to calculate uniform loads, calculating tributary area for column loads, familiar with (kips)  things like that.  I am using Ballast to study but I am not studying every formula I think it goes into too much details and too many formulas.

    For HVAC I would look at Architect Studio Companion, and Architecture Graphic Standards(Graphic Standard has a little more detail than (ASC).  You should know how to calculate BTUs and know how each system works like: all Air, Water and Air, and all Water systems along with their components.There are some really good post in the community that will give you more detail, check them.

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    Robert Hott

    I had very simple structural math questions and the variables were all given to me as well as the formula. I didn't have any HVAC calculations, which I wasted a lot of time studying. The only HVAC I was asked about were types of systems and how to detail them for fire and acoustic concerns. The more important thing is realizing the units the questions are in and what they need to be to use the formula. You might get PSI variables and the answer is in PSF.

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    David Kaplan

    ^^^ Both good posts above. 

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    Colleen Shannon

    Thank you so much everyone for your help and comments!   I am still a little curious about the 'Formulas Available While Testing' part of the ARE 5.0 Handbook.  There are a few formulas listed that call out the distance to the neutral axis which suggests to me like I need to re-learn how to find the centroid to find the neutral axis.  And, as you suggested that we need to know basic calculations for uniform loads on beams, will we also need to be able to track it down through the structure and size the columns too? Do I need to re-learn slenderness ratio and moment of gyration on a column?  I am so foggy as it was ages ago.  Am I overthinking it? 

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    David Kaplan (Edited )

    Colleen,

    I hear you on that, and yeah, it's annoying that those formulas are included in the "Formulas Available While Testing."  I can only speak to my experience, but I did NOT encounter anything like what you've identified above.  I went through others' posts on this site before my tests and the general consensus was that I didn't need to look into that level of detail for structural calculations.  Have yet to see anyone post on here that they got questions like that.

    I think I had 2-3 structural equation questions on each test.  None of them were hard.  I also told myself that if for some reason, I got the question "what is the size of a steel plate with 20 K of force acting through it and with 10 shear connections" that I was going to write "5 x 5" and quickly move onto the next question.  I don't personally feel that we should be required to know that level of detail, and I'm happy to report that from my experience, and from what others having been posting, NCARB agrees.  I was pleased with the basic level of calculations that I ended up having and found them to be fair.

    I would offer to you as well that if you should get thrown a question – either MEP or Structural related – that goes into the level of detail that you’re concerned about, the exam is going to provide you with the information that you need to solve the equation, and you essentially are being tested on your ability to properly plug the given information into the given equation and churn out the correct answer.  Back when I was in school we called these “plug and chug” equations.  You’re given a, b, c, x, and y and told to solve for z.  You’re given an equation that includes all those variables except for one (z), and you simply need to be able to put the variables into the correct spot and use basic algebra to solve for z.  Of the MEP-related calculation questions I got on my exams, I had used none of them in real life nor had I studied any of them.  However, the exam made it straightforward for me to recognize how to use the equation.  As long as I read the question, pulled out the necessary variables needed to solve for X, I was able to figure out how to solve for X even though I had never solved for X before or taught myself how to solve for X.  It was intuitive enough just from the equation given and the information given to me.  Does that make sense?

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    David Kaplan

    Last point - use the ARE Handbook and refer to those sample structural equation questions in there.  The ones you will get will very likely NOT be harder than any of those.

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    Colleen Shannon

    David,

    Thanks so much for the additional information and encouraging insights. I was in full-on panic mode.  I saw those equations listed in the back of the manual and felt a new wave of irrational fear! Now, I won't panic about the structural or MEP calcs nor waste more time trying to re-learn formulas. I can switch back to other items that need my attention. Thank you.

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    Jonathan Chertok (Edited )

    hi colleen (thanks for posting), david (thanks for answering), all.

    i feel like a character in a cormac mccarthy novel on this issue. there are five PAGES of equations provided in the handbook. in multiple cases there are variables with NO definition provided.

    for structural: the lowdown is all you need to know is reactions on a point loaded or continuously loaded or point/continuously loaded beam (not listed obviously) - have i got that right? no "flexural stress at extreme fiber", "flexural stress at any fiber", "average vertical shear" or "horizontal shearing stress at any section A-A"?!

    for lighting: i can punt my way through the first three because i went out and tried to study them. the last three would be like moonshots. i don't even know what they are for. <edit: well, the "Watts = Volts x Amperes x 'Power Factor'" has to do with AC voltage systems and some reduction or amplification due to something or other...>

    plumbing: what is 1 psi = 2.31 feet of water mean? what would it be used for? also, what type of question wants me to convert from cubic feet of water to US gallons, or vice versa? I don't need to memorize that it is 8.31 or whatever it i guess? is this saying 8+ US gallons will go into a space of 1 cu foot?

    HVAC: looks like a lotta business getting down in there. sure would be nice to run each one of them one time...

    acoustics: seems much the same as HVAC.

    i mean, i /could/ see someone saying you are just going to be given a list of equations and asked "which one of these would your HVAC consultant run?" but other than that it would be nice to at least know the variables for each and what they are used for.

    i mean, i'm probably going to get one example for each of these together just so folks down the line aren't constantly running around in the wilderness just bci find this issue confounding and it would be nice to help a brother out.

    but - in the SHORT TERM - anyone able to lay some fact based information down on what some of these mean or what they are used for or what the missing definitions for some variables are?






     

     

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    Colleen Shannon

    Jonathan,

    OMG. I loved your post. It's the first time I've been able to laugh in days! 

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    Kristen Charters

    Jonathan,

    The formulas can be found in Ballast in their respective sections and Ballast does go over them in depth. For example, 1psi = 2.31ft of water is used to calculate the static head of a fixture (Ballast 5.0 31-9 - 31-10). Amber/MEEB goes over the HVAC/Elec/Acoustics/Plumbing formulas in more depth though Amber does a better job explaining it simply without overloading on minutia. 

    Note that NCARB has stripped the variables out of some of the formulas and replaced them with the units that each variable would have.

    When do you take PPD/PDD? (Btw I passed PDD last month and am officially done!)

    I can do a more in depth write up later this weekend if you want.

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    Tony Young

    Kristen

    I'm gearing up to take PDD next month. What would you say were he key points of importance. It's so much information I feel like I've study so much content that other stuff I'm scared I'll forget. Could you share your insight

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    Jonathan Chertok

    kirsten. /thanks/
    trying to finalize these now. found the structural in ballast when i went to review. but it is like a series of Where’s Waldo puzzles trying to find resources for everything and then trying to figure out what is not mission critical..
    can you help with a static head example?. maybe i’ll post the ballast example on this i was trying to work and with luck you can eyeball it?!

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    Jonathan Chertok

    just so i am clear - “Note that NCARB has stripped the variables out of some of the formulas and replaced them with the units that each variable would have.”

    this means that in the resources supplied in the exam and in the handbook there are only /equations/ with variables and no definitions supplied for the variables? or something else entirely...?

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    Kristen Charters

    Tony,
    Yes, I can give you an overview of what are the most important things to study. Can you tell me what you’ve studied already? Have you already taken PPD?

    Jonathan,
    I’ll give you some examples for both when I’m not on mobile.

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    Jonathan Chertok

    thanks. i’ll probably post some “work sets” i either can’t find or had trouble working. will put them in PDD forum.

    THANKS for all the help...

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    Kristen Charters

    An example of what I mean with the formulas is this:

    NCARB gives you:

    while a study source such as Ballast will give you this:

    As you can see, it's the same formula. But rather than waste your time memorizing what V is or Qv is, NCARB gives you what the two terms are. During your study, you should come across this formula and understand when you would need to apply it.

    That being said, I never used the formulas given. Because I was worried about running out of time, I marked all the questions that looked like they would take more than a minute and answered them  when I had finished the rest of the test. You can find people's mind dumps/test recaps by searching for them. I found this one and this one and this one to be helpful when trying to figure out what to study.

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    Kristen Charters

    Ok. Static head:

    First, static head is essentially the amount of force it takes to lift water a certain number of feet (in a pipe). Without going into a ton of detail, this works out to be 0.433psi will raise water by 1'. If you invert this, 1psi will raise water 2.3ft. This is the version of the formula that NCARB gives you.

    This equation is used to find the water pressure needed at specific fixtures that are a specific height above/below the water supply/tank or the max height a fixture requiring a specific psi can be at.

    Let's work this out using question 14 in section 47 of the Ballast 5.0 Practice Problems. This  one is a bit more difficult than the example in the text. The question states the following:

    So our knowns are:

    1psi = 2.3ft of water

    Water pressure starts at 57psi.

    Pressure loss through pipes is 23psi.

    Highest fixture needs 12psi to operate.

    Solving for: Max height of fixture

    Solution:

    We know that we only have 57psi of water pressure and that the fixture must have 12psi in order to operate. So we need to calculate the number of psi that we have to work with by subtracting the psi of the fixture as well as the pressure loss through the pipes. 

    Starting water pressure - fixture's psi - pressure loss through pipes = 57-23-12 = 22psi. This is the pressure left over after taking pressure loss and the fixture's psi into account. If you were to go higher than 22psi, due to the fixture's requirement and the pressure loss in the pipes, the fixture would not be able to operate. Similarily, you could go lower, but the question is asking for the max height.

    So going back to our formula, we can adjust the formula and solve for feet. 

    Since 1psi will move water 2.3ft, 22psi will move water 22x2.3 which gives you 50.6 ft. The closest answer is (c) which is 50ft. 

    Does this help?

     

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    Jonathan Chertok

    hi kristen
    thanks a /ton/. i tried working this and will try to tackle it again this weekend.
    can i just ask how you would invert the equation? if i am not mistaken ballast gives you the former and the resources give you the latter? i just didn’t have enough brain cells left to even try to get there...

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    Kristen Charters

    Tony,

    Others have summed it up well (see my post two above this one for ones that I thought were helpful) but here is my two cents:

    Major Points:

    -Thermal (k, U, R, C) Be familiar with their relationships and their impact on a building assembly.

    -different types of HVAC and plumbing and electrical systems

    -different types of fire protection systems (sprinklers and fire extinguishers)

    -shear and moment calculations

    -seismic and lateral forces

    -ADA 2010 (all) and IBC 2012 (min. ch 3,5,6,7,8,9,29)

    -know how to navigate a CD set

    -labeling details with correct information like in the demo exam

    -Water table and waterproofing

    -Construction details and material properties (read all of Building Construction Illustrated)

    -Designing for acoustic issues

    -Lighting design

    -be able to calculate the cost of a material if given a specific area/volume

    -Specifications and project manual

    -watch your units!

     

    Other Points (from Kurt Fanderclai and Benjamin Norkin):

    -Invert distance

    -Occupancy types/load calcs

    -control/isolation/construction joints

    -watch out for your units

     

    Resources used:

    -Ballast 4.0 BDCS, BS, CDS (read plus took exams) (aim for 65% or higher)

    -Kaplan 4.0 BDCS, BS, CDS chapter quizzes plus practice exams (aim for 75%)

    -Ballast 5.0 PcM and PjM practice exams and problems

    -Building Construction Illustrated

    -Amber videos (samples here)

    -Thaddeus videos 3a-9b

    -Architect's Studio Companion (skimmed mechanical and structural, YMMV)

    -MEEB (skimmed for diagrams/things I needed clarification on)

    -FEMA 454 ch. 3-5

    -IBC 2012

    -ADA 2010

    -Architectural Graphic Standards (skimmed for construction details that I wasn't familiar with)

    If you want me to send you my study plan, you can email me: kristencharters@gmail.com

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    Jonathan Chertok (Edited )

    omg. thanks. so they have substituted UNITS for the variables in place of the /variables/ that should be there (or instead of having the variables and putting the units in parentheses) - in /some/ places and in other places they have given you just the variables. and in all cases they have left off any definitions for the variables?
    i mean, now that you explain it i guess this is what i am looking at?

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    Kristen Charters

    Jonathan,

    Yes that's correct as I understand it. For the ones that are only variables like f=M/S, you should know what the variables are. And they will come up as you study, so don't worry about reviewing the formulas all initially as that, I think, can become too overwhelming. Read Ballast and make note of the formulas that you are struggling with as you study.

    How far along are you in studying? Have you gone over all the material at least once? There is an overwhelming amount of information out there but if you read Ballast once through for concepts, then you should be able to dig into some of the primary material to go more in depth.

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    Jonathan Chertok (Edited )

    hi kristen, all
    under electrical references “lumens” seems to be used rather casually.
    in the second “equation” is this Desired Illumination Level and if so is it:
    E = (Nlamps x Nlumens x “lamps per fixture” x “# fixtures” x CU x LLF) / Area (ft^2)

    if so, is there s proper variable for # fixtures or lamps per fixture? or would we just see the terms on a chart or in a question? or actually i guess i can leave out the “lamps per fixture” since this is what is meant by Nlamps?

    thanks

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    Kristen Charters

    Usually most of the information would be given to you, I think. I don't think I had anything this complex on my test but if so, I think it would be more  plug and chug where they give you most  of the variables. The lighting/electrical questions that I had were more concept based like what kind of light is this based on x,y,z characteristics. 

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    Kristen Charters

    Jonathan,

    Going back to your plumbing question, do you have a particular question that you are looking at?

     

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    Jonathan Chertok (Edited )

    hey kristen!
    thanks so much again. ballast sort of explains this backwards and forwards and it is slightly confusing. also. the references should probably just say 1 psi = 2.31’ static head of water. it’s not water. it’s a technical (apparently undefined ATM) metric called static head.
    anyway, i am having one small issue with the units.
    is “lbf” pounds force. so it is 45#/in^2 of force?
    ok, wait - it is .433 #/in^2 so when you multiply by 40’ - well i guess you convert the unit from #/in^2 to #/in^2/FOOT. i guess this is basically implied by .433 being PER foot?
    but say you don’t recollect the .433 value. i guess you would /have/ to cross multiple the reference of “1 psi = 2.31 feet of water” and divide the 2.31 by one to get the 0.433 value PER foot to work this equation? or vice versa depending on the wording.
    does that question make sense?

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    Jonathan Chertok

    here's the example i've been working (ballast 31-10). will work yours next. THANKS


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    Jonathan Chertok

    hi kirsten
    awesome. thanks again. always interesting to try and figure these out on your own.
    so, just to repeat since it eliminates errors (and sometimes can help others). i left off the 23 psi loss first time on this one but -
    57 psi is what it comes in at
    12 psi is what is needed
    44 psi is “available”
    23 psi is the stated loss (which i guess is a /cumulative/ number based on the whole system or getting it to the fixture?!)
    22 psi is the final value
    and since you know 1 psi will achieve 2.3 foot of “static head” you got 22 psi x 2.3’ = 50.6 feet?
    are the units 22 psi x 2.3’/psi in this case i guess...?

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    Kristen Charters

    While you are probably technically correct, you are way overthinking this. Try solving the Ballast problem the same way I did mine. It's the same theory, there just isn't friction/pressure loss.

    You don't need to remember 0.433psi = 1' static head because NCARB gives the inverse to you (2.3' static head = 1psi). So you can solve it using either and you'll get the same answer. Does that make sense?

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    Kristen Charters

    Sorry didn't see your other response.

    That's correct. The 23psi is just the loss of pressure the water will experience over time. Whether its generally affecting the whole system or not, it doesn't matter. It affects our calc and that's all that matters.

    Yes your psi units will cancel and you will be left with feet. Looks like you have the hang of this. :)

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