Column Base Plate Design

Design of steel column base plates..

If you're in the USA please use the design procedure(s) as outlined in the AISC Manual of Steel Construction, whether it be ASD or LFRD.

To outline them here would take volumes and a lot of time, plus there are too many variables that can occur which prevents me from giving you an appropriate and safe design procedure.

PLEASE NOTE: I caution the OP that IF you have not previously taken any structural engineering courses and the engineering prerequisites, then you really shouldn't be designing column base plates, because you lack the fundementals to really understand what you are doing, the stress types and magnitudes involved, and the experience and knowledge to know what design results are valid or otherwise. To proceed with this design without this is foolhardy.

dear captmoosie,

as per the examples i saw on calculation of base plate using the LRFD method ( attached the picture for example ) , in the first example i try to solve i found that both values of required flexural strength(Mu) and required shear strength(Vu) are given , but if you are designing a platform for instance , and you want to design it`s base plates and make sure it is safe , how you are going to determine the shear and moment values on the plate ??

this is the link from where i got the example, it is example no. 1

http://www.sefindia.org/forum/files/drake_elkin_method_base_plate_design_181.pdf

Hello Ahmed,

After reading your post I have to ask you a few questions before proceeding with answer for you:

1. Do you have a formal Structural Engineering education, knowledge and experience? Did you take university courses in "Statics & Strength of Materials", "Analysis of Determinant & Indeterminant Structures", and "Structural Steel Design"?

2. Do you know how to use both the ASCE Standard 7-05 and the AISC Steel Manual, 13th Edition? Do you have both manuals?

3. You do know how to determine dead and live loads for either the ASD or the LFRD procedures, do you? Note: the AISC Steel Manual (13th Edition) uses a combination of both the ASD & LFRD procedures known universally as the "Unified Strength Design".

IMPO, IF you answer "NO" to any of the above questions, then you shouldn't be designing structural steel members for anything.

Where on this blue ball of a planet are you located, and does your country use American Engineering Standards like ASCE and AISC?

Personally, I much prefer the ASD design procedure....I think that the LFRD is a great big lie. I just don't think it's conservative enough for structural steel design, but that's my opinion.

I could provide you with a design procedure that's relatively simple, scanned from one of my steel design books or manuals, but I have to be absolutely certain that you know how to design steel structures first and not be a menace to society. You do understand fully where I am coming from, correct? Any swinging monkey can copy a procedure, but to fully understand the theory and limitations behind that procedure takes a bit of knowledge and experience.

Case in point that causes me to worry about your abilities: asking how to determine loads to further determine how to calculate the applied Moment and Shear values for a platform.

IF you do not have a clue how to determine the service loads applied to any sort of structure as a starting point, then that alone sends up a "RED FLAG" for me, and demonstrates that you haven't a clue how to proceed with the design.......

dear captmoosie,

if i followed your opinion and didn't design anything my company will fire me , i don't think this is something both of us will like ...

to answer all your questions and worries above , simply i am a mechanical engineer working in the water treatment field/design division , who is exposed sometimes in the project to deal with steel structure members mainly are pipe supports and platforms for plant equipment ( multimedia filters ....etc ).

so calm down , am not threatening the society by constructing buildings that can turn over their heads at the end ,my target is much more simple as usually these 2 types of steel structures am telling you about has reference from previous projects which is used with some modifications as per the project conditions ...but to be frank with you what i thought about is to stress out my design formulas of this part to improve the quality of my design ( as i told you i am mechanical not civil structural engineer )

but if we go back to your first question of course i know what is stress analysis as i took it as a whole course during collage and even at work am exposed from time to time to these issues....

regarding your note about the LRFD method and ASD , while go-ogling i found a paper solving some base plate examples using both methods , i`ll put your opinion in my consideration while going again through both of them .....

now the main point that caused this misunderstanding and may be i didn't express it correct , if you go back to the example i attached or the link i sent you can find 2 forces( axial and shear ) and one moment , after going through the example i imagined a scenario of ( checking the design ) of the base plates of platforms or pipe supports, and the question came to my mind was if you we estimate the axial force on the base plate either it was for pipe support ( support wt. + full pipe wt. ) or it was for platform ( column wt.+ grating wt + max.weight. of operators working on the platform) , what about the rest of the values shown in the example i saw ( moment and shear stress ) , will it be calculated on the platform and transfered to the base plate ? simply this was my question ...

at the end appreciate your worry , but forget about this red flag because am good , but as i told you am filling the gap of some design issues i have by searching for the right procedure to proof that everything is calculation wise is safe and can be used without problems ....

if you have useful info or references regarding what i mentioned it will be great , and again thanks for the references you sent in the beginning of your comment , i`ll try to search it ....

thanks ...

Hello Ahmed,

I apologize to you for being a bit cranky in my last posting, but there's a reason why: all too many times people come in here seeking advice on complicated structural design and analysis matters and ask questions how to proceed with a design. These peeps shouldn't be doing such because they lack the proper educational background, knowledge, training, and experience. A goodly amount of them are students.

[Aside: I can't understand why your engineering firm is designing something so complicated as a water filtration plant without having an experienced structural engineering on their staff. That's just plain nutz. You shouldn't be designing anything structurally-related outside your realm of education and experience. Where the heck are you located that allows such nonsense?]

Okay, with that said let's proceed to see what we can do for you.......

First thing I want to ask you is why this particular column base is subjected to both Bending Moment and Shear force as well as the axial load? Why not just simplify your framing design, and thus your columns, to eliminate the bending moment altogether? Design the platform frame (or whatever) with simply-supported beams and girders, and columns with pinned baseplates and pinned column cap plates. I'm scratching my head here wondering why you're complicating design matters. Design the columns, top and bottom, for "rotation free & translation free", and use K=1.2 (conservative approach value) when determining the Column Slenderness. If you have lateral forces due to wind or seismic loadings then use knee bracing, x-bracing, or k-bracing to eliminate the introduction of the bending moment into the column. That way you only have to deal with the horizontal force component (introduced from the lateral bracing....ie, secondary framing) at the base of the column.....this would be a shear force acting on the two steel anchor bolts (a pinned connection). Using 4 anchor bolts will be get you into "fixity issues".

In the end, keep it KISS......"Keep It Simple Stupid", as we use to say in the US Army Corps of Engineers (USACE).

IF you still want to learn how to complicate matters and design a column baseplate with Bending Moment, shear force, and axial load then I can forward to you a *.PDF file for a textbook that I have here entitled "Structural Steel Engineering and Design" by Max Kurtz, P.E.......see page 1.182 for designing a column baseplate with moment and axial load. The design procedure is based on ASD, not LRFD, which simplifies matters considerably. But first you're going to have to PM me and supply your email address so that I can email you the file as an attachment. It's a big file (8.05 MB), so make absolutely sure that you can receive it through your ISP.

Another very good book that you should have in your library is "Design of Welded Structures, 16th Printing" (2002) by Omer W. Blodgett, P.E., Editor, and written for the James F. Lincoln Arc Welding Foundation. See Section 3.3 for the design procedure (old school ASD method, not LRFD). Unfortunately I do not have this particular book in electronic format. I tried to scan the section in question for you, but the book is so thick I was afraid of pressing down harder and either breaking my scanner glass or the book binder. Maybe with a little searching on the net you'd be able to find a free e-book, but somehow I think this will be a very difficult task. You may get lucky, who knows! Anyhow, also check your firm's technical library and see if they have it there already. The book can be purchased from the foundation, but it is very expensive.

Signed,

CaptMoosie, PhD, P.E.

Civil, Structural & Environmental Engineer

hello captmoosie,

no need to apologize , it`s a pure technical discussion away from any personal feelings ,but think about it from another angle, that the presence of these peeps you mentioned is something normal as you cannot guarantee at all that all the people in this blue ball we are living in has the same educational degree or experience , so this is something you won't be able to avoid while participating here in this good mechanical forums and again thanks for your worries but usually am not designing anything without making sure that i have its basic knowledge and right procedure , and whatever i found still missing i go and ask for it as you see....

regarding my location that you asked about twice , I'll be glad to see you in Dubai if you planned for a trip to gulf ..:)

now going back to the main topic , believe me am not trying to complicate things as you mentioned here :" I'm scratching my head here wondering why you're complicating design matters" .... i respect of course your point of view in simplifying the design matters because it is already complicated .... but what i was searching for was the right procedure to crosscheck if the design in front of me( usually copied from previous projects ) is safe and reliable or not that`s why I went back to find the right basics.

to make it simple and specific for you instead of eating your head , for example i am reviewing a drawings for a support or platform fabrication drawings need to be submitted wherein i have a base plate of 150 x 150 x 8mm thk. , so the question which i asked myself and start to search based on it was : why 8 mm ?? , why not 6 why not 12 mm ??" ..... you got my point ??? ( for some reasons I don't want to speak about right now let`s consider the non presence of another source in the firm to ask …. Let it be an assumption for now please….)

now when i start to Google this issue i found a lot of references on net discussing both methods LRFD and ASD method , the first example I saw was solving the case by LRFD method ( still didn't go in deep through the ASD method ) and what i found for calculating the thickness was depending on the forth case : (MOMENT WITH UPLIFT in the attached link: http://www.sefindia.org/forum/files/drake_elkin_method_base_plate_design_181.pdf , as per the paper page 3 of 10 point no. 5 it is stated that it is the most common case in design practice) at the end of the chapter the plate thickness was defined in 3 forms : general form ( equation 45 ) and if the bearing length "Y" is bigger or smaller than the base plate bearing interface parallel to the moment direction "m" ( equations 46 and 47 in the same link attached ), now correct me if I am wrong , if I want to simplify matters as you recommended here can I consider these equations enough to check for safe design of the base plate , or I simplified it more than required ? , am trying to avoid future comments or impressions from others like what you noticed and mentioned : "complicate matters and design a column base plate with Bending Moment, shear force, and axial load "

finally thanks a lot for the references you sent but before i start something new, i am going through this reference which is solving the cases based on both methods LRFD and ASD ( attached also for reference: http://www.beardesign.net/phpmyfaq/attachments/33/AISC%20Steel%20Design%20Guide%20Series%20Column%20Base%20Plates%202003.pdf ) , just have a quick look on it and tell me your opinion ... if your reference mentioned is better you can send it to me on this mail : ahmad.youssef2009@gmail.com

thanks in advance ...

Hello Ahmed,

I had a funny feeling that you were in Saudia Arabia, Bahrain, or Dubai. Thank you for the invitation! Maybe someday I'll get there. From what I understand there is a tremendous amount of construction going on there. But for now I'm going to have to take a "pass" on visiting the Kingdom.....I already have spent roughly 8 months in the desert as a US Army Officer during Desert Shield/Desert Storm back in '90-'91 and want to avoid sand and nothing butt sand (and heat) for the time being. Heck, I don't even go to the beach on vacation, just to avoid sand and nothing but sand. Call it PTSD or whatever. It's something I have to work out in my head...

In my opinion, you could use both references that you have. I think that you'd be better served with the last one, the AISC "Steel Base Plate" paper by Professor DeWolf. What is nice and unique about that reference paper is it presents both ASD and LRFD side-by-side. I like it, and BTW, nice find Ahmed! Even I didn't have a copy of that one. As a minimum you could use the ASD procedure, but if you want to get into making matters more difficult for yourself (more calculations), then by all means try the LRFD procedure. I do think that the ASD procedure is more conservative and you'll end up with a slightly thicker column baseplate. I personally like the ASD procedure because I don't particularly like to design structural steel in the "plastic region".....and when in doubt, go with a thicker section (in this case) or larger structural member. In regard to column baseplates a few mm increase in material thickness really won't result in not much difference in material costs, unless you have many of the same baseplates throughout a project. That's the way I view it. Others may take an opposing viewpoint.

I'll be sending you the textbook that I previously mentioned authored by Max Kurtz, PE. It's good book overall, but doesn't go into detail as much as Prof. DeWolf's paper that you have now. Go with DeWolf's paper first as a primary design/analysis tool.

IF you can, try to find the Lincoln Arc Welding Foundation book by Bloggert as an ebook (free if you can find it) to download. Even though it's based on the ASD procedure, it goes into the design of all of the welds required,as well as the design of the various type of brackets used for "fixity" to resist applied design Bending Moments, etc.. You can't go wrong with this book! I tried once again to scan the applicable section, but the book is so thick it is very difficult to flatten it enough to get a good scan.....in fact I broke a hinge on the scanner lid in the process! Great big bummer! Now I have to buy a new lid, which isn't going to be cheap...

Please have a great day....and try to keep cool!!!

===CaptMoosie

Hello Ahmed,

This must be your lucky day my man! I was able to locate and download a copy of the "Design of Welded Structures", authored by Blodgett for the Lincoln Arc Welding Foundation. I tried to email you a WinRAR zipped file (~57 MB), but the file was too large for your gmail server. I believe that this is the 16th Printing (~2004), so it's still very relevant.

So, that being said, I'll provide you a link where you can download it yourself. Be forewarned that you will need the WinRAR utility to download it into *.PDF format. You can obtain a free evaluation copy almost anywhere on the web. Just do a Google search for it if you don't already have it!

Here's the e-book download link (I hope it works this way!):

https://rapidshare.com/#!download|525p2|238838131|DESIGN_OF_WELDED_STRUCTURES.zip|59329|R~C4A3AEDD2884FEAC52D52632F75CB0C0|0|0

Just copy and paste into your address bar of your browser if you have to....

Once you're at the site, go to the center pic entitled "Save to computer" and left click on the green "download" button. The download is must likely going to take a long time. It depends on your ISP connection speed and your PC/Laptop set-ups.

You're going to love this handbook!!! I've been using this particular book my entire engineering career spanning nearly 35 years.

Enjoy!

===CaptMoosie

dear captMoosie ,

you`re a " Master piece of art " , really appreciate your help to the max and really pleased to meet you here in this forum ... , i`ll go through what you sent and as

per our discussion , for sure i`ll tell you back if there`s something missing ....

have a good day !!

best regards

Ahmed.

Good Morning Ahmed, (at least it's morning here......evening where you are )

I'm very glad to have been able to help you Ahmed. You're welcome! And it has been my extreme pleasure to have met you as well!

Were you able to download the e-book "Design of Welded Structures"? Not only is it a very good reference how to design all sorts of column baseplates, it is useful for all types of structural steel elements, such as curved beams, built-up members, torsional affected beams, etc. etc.

It's going to take you a while just to review Section 3.3, which only deals with Column Baseplates.....all 32 pages of it! Anyhow, the book will serve furthering your knowledge of structural steel design for years to come and make you even a much better engineer. I hope you get a promotion within your firm for your due diligence. You've stepped-up to the plate and hit a home run Ahmed! Good going!!!!

Just curious, but what type of water filtration plant are you working on currently in Dubai? RO or Desalinization plant?

Also, I did notice that your command of English is very good. Where did you learn English? Did you attend an University in the UK or USA possibly?

Please have a wonderful evening!

===signed,

Captmoosie

dear captMoosi, how are you my friend !

sorry for the late reply , a little bit busy for the past 2 days i was ,

thanks a lot for what you wrote , something i really appreciate , actually after you sent me the link i tried it but unfortunately it didn't work , so i thought about some searching by using the link you gave me and fortunately i was able to find it on rapid share , it seams a really valid book and i hope i can me good use of it , deep thanks again for your help and useful recommendations ...

the rest of details you`asked i`ll send it to you on Ur mail , ( kind of privacy man... )

lemme hear from you soon ..

regards

Ahmed.

Dear Ahmed,

How are you today? I trust that you are doing well!!!

I'm glad that you were able to download that book from Rapidshare and will be able to use it in the future. I'm so sorry for the bad link. I suppose I should have tested it first.

You are very welcome. I'm happy to have been some help to you. If you should have any further questions about the welding book, go ahead and ask. I'll be here to answer any questions if I can!!!!

Please have a wonderful day!

Best Regards,

Mark (CaptMoosie)

I don't know about anybody else, but I'm voting this one a GA for sure!

Well done Cap! _{Didn't notice it until now... sorry!}

Hey Doorman, many thanks!

Hopefully you were able to download the textbook for free, if you have use for it! It's a very good one, I promise you! (I have 2 hard copies of it + the ebook copy......never leave home or the office without it!!!! ahahahaha).

Please have a great day!