STAAD_ Bending Moment in Plate Elements - Structural Analysis and Design - Forum - Structural...

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STAAD: Bending moment in plateelementsHi

I've been using STAAD for quite a while for steel design, but now I need to use STAAD for design ofa 3D concrete frame, and have some difficulties with the modelling and the STAAD output.

Modelling: From steel design, I'm only used to modelling with members, but modelling a solid 0.6m thick frame (inclined walls and deck) with a width about 20 m's, I think elements might be abetter idea - any input on this?

Results: To get a felling for modelling with elements, I've made a simple slap, 1 m wide and 8.0 mspan divided into 8 elements equally length). The slap is fully fixed in both ends, and my textbookcalculation for a centrally placed force of 100 kN, should give me a bending moment of 100 kNmat both ends and at the middle of the span. Though I find it hard to get this result from STAAD.Global moments from the plate results page gives me a 10-15 % lower bending moment, due toaveraging over an entire plate element (as far as I can read in the STAAD help file). The cut along aline function, doesn't seem to work properly for me. When I want to cut the line, I can mark up forinstanse to nodes at one fixed end (transverse to span direction), but no line marking appearsin the above window. Highligthing a span over several members in the span direction will give mea cut line in the above window, but right now I'm not interested in these figures. Any help aboutthis ? as I can not design my plate for a bending moment 10-15 % below the actually maximumbending moment.

Just to clearify, with my present knowledge of STAAD, I can not use the build in RC-design



STAAD Plate bending moment

boucanier

Chris Conrad

module, because I'm designing by old danish codes. Further more, I'm interested in the bendingmoments rather than stresses, because I need to calculate the neccesary rebar area tofullfill some crack width criteria.

I found some example here in the forum regarding member properties for cracked members, butcouldn't find any additional information regarding this subject in the STAAD help file, so any inforegarding this command might be usefull as well.

I'm out of the office for the day, so I can't send my STAAD file, but if of any use, I can upload ittomorrow.

Best regards

Boucanier

9 Replies (Most Recent Reply)

Hi Boucanier,

With regard to your sample fixed-end slab, I would recommend trying a denser mesh. I havebeen able to produce results with less deviation from your theoretical values this way.

With regard to your question about property reduction factors, you can find them in theMember Specifications dialog. You can reduce Ax, Ix, Iy, and Iz. The reduced properties willbe incorporated into the analysis, but will not be considered in design formulae such asMn=AsFy(d-a/2). Also note that reducing the moments of inertia will tend to increase thedeformations that are due to bending, but it will NOT directly affect the shear deformations.

We have an online course dedicated to reinforced concrete analysis and design. You mightfind it beneficial. http://lms.bentley.com/us/desktopmodules/SearchResults.aspx?catId=0&tabindex=3&tabid=16&description=CRS-STR-STAAD-Reinf-Concrete-Analysis-Design-



boucanier

CRS&count=9&cat1=2&cat2=3&cat3=4&cat4=5&cat5=6&cat6=7&cat7=8&cat8=9&cat9=213&SortItems=Title%20DESC,StartDateNoTime%20ASC

Good Luck,

Chris

In reply to Chris Conrad:

Hi Chris

Thank you for your reply !

I'm not sure I understand the frase "density mesh". If you mean make a FE-mesh, I don't thinkthis is the solution I'm looking for.

I would like to be able to retrieve bending moments etc. in the below indicated frame (it's abridge actually):

STAAD SPACE DXF Import of Trdmodel til Staad.dxfSTART JOB INFORMATIONENGINEER DATE 05-Mar-09END JOB INFORMATIONINPUT WIDTH 79UNIT MMS KNJOINT COORDINATES3 -148312 25890.6 0; 4 -148312 83644.2 -1e-016; 5 -129712 83644.2 30;6 -129712 25890.6 30; 7 -133878 70456.3 6280.4;8 -133878 38422.7 6280.4; 9 -144146 70456.3 6249.6;10 -144146 38422.7 6249.6; 11 -148179 83644.1 200;12 -129845 83644.2 230; 13 -129845 25890.5 230; 14 -148179 25890.6 200;15 -144146 70456.3 6800.6; 16 -133878 70456.3 6831.4;17 -144146 38422.7 6800.6; 18 -133878 38422.7 6831.4;19 -144146 53709.5 6249.6; 20 -144146 53709.5 7628.6;



Chris Conrad

21 -133878 53709.5 6280.4; 22 -133878 53709.5 7659.4;23 -144146 55169.5 6249.6; 24 -144146 55169.5 7628.6;25 -133878 55169.5 6280.4; 26 -133878 55169.5 7659.4;27 -147362 25890.6 0; 28 -149262 25890.6 0; 29 -128762 25890.6 30;30 -130662 25890.6 30; 31 -128762 83644.2 30; 32 -130662 83644.2 30;33 -147362 83644.2 0; 34 -149262 83644.2 0;ELEMENT INCIDENCES SHELL32 9 23 25 7; 33 19 10 8 21; 34 23 24 26 25; 35 19 20 22 21;36 9 10 14 11; 37 4 11 14 3; 38 33 27 28 34; 39 31 29 30 32;40 7 12 13 8; 41 12 5 6 13; 42 9 15 16 7; 43 10 8 18 17; 44 15 16 7 9;45 17 18 8 10;FINISH

As this is a common type of frame, that I need to calculate for different geometries, I wouldlike to generate my model in fx. Excel, and thereby know the exact element numbers throughout the model, so I can automate the design calculations, as i need to design the rebars indefirent cuts of the frame. As indicated in my first post, I can't use the build in RC-designer, soI need to be able to dig out the forces in these cuts to do the calculations manually.

With regard to the online seminar - I would consider joining it, but do you have a little moreinfo about what lays underneath the different headers ?

Boucanier

In reply to boucanier:

Sorry about that. It was a typographical error on my part. I was trying to say "denser mesh".

After looking at your model, I can say with certainty that you will want to submesh it further. The model has many instances where there is improper connectivity between plates. (Platesmust always connect to other plates at common nodes. If there is no node in commonbetween two plates, then they don't connect mathematically...even if they touch each othergraphically.) You can see evidence of this if you click Tools > Check Multiple Structures. Youwill see that your model currently consists of three independent (disconnected) structures. We refer to this as a disjointed model.



boucanier

Another thing to keep in mind is that quad plates should be modeled with aspect ratios thatkeep them as close to square as possible. It's generally ok if they get a little rectangular andapproach aspect ratios of 2:1, but in no case should they be allowed to exceed an aspect ratioof 4:1. The results become suspect when plates become that long and rectangular. Withregard to internal angles of quad plates, you should try to keep them between 60 and 120degrees. if they are becoming very accute or obtuse, then the results become suspect onceagain.

In addition to the concrete class, you might also find the Modeling Structure Geometry courseto be beneficial. I have attached the Tables of Contents from both course training manuals,so you can get a good idea of the topics that are covered in each of the classes. (TheTroubleshooting Errors and Warnings module is included in the Concrete course manual forreference, but time generally does not permit going through that module as part of thatclass.)

Cheers,

Chris


Hi again Chris !

Thanks for the TOC's - they gave a much better insight to the courses. Just to get it all right,you recieve a copy of a "textbook" consisting the materiale described in the TOC when youjoin the courses, right ?

I can see that I wasn't clear in my previous post, as the posted model only was supposed toshow the geometry of my structure. The actual model is made up by a grid of points withequal distance ~1m in all directions, giving me elements of ~1x1 m, so I don't think I'll get introuble with the model - for this part. But I do have 2 questions still remaining.

1. As I want to create an automatic modelgeneration of my bridge, I need to able to generatethe model for different shapes, including angular cut off of the free sides of the deck. This



means that in some cases I would get angles outside the 60-120 degree window you advice tostay within - I think this directing me to use beam members instead ?

2. I still can't get the "cut by a line" function to work. In the model below (my test model frommy original post) if I fx. want to cut along the z-axis in the nodes at the one support line, Idon't get a line the "Results along line" window. Is there a command line for the "cut by aline"-function to type into to the STAAD editor, as all my modelling is done from Excel animported to the editor. Further if I do get it to cut at my speciefied positions, would I be ableto get a tabulated output that can be exported to fx. Excel ?

Boucanier

My test model:

STAAD SPACESTART JOB INFORMATIONENGINEER DATE 15-Jan-10END JOB INFORMATIONINPUT WIDTH 79UNIT METER KNJOINT COORDINATES1 0 0 0; 2 0.5 0 0; 3 1 0 0; 4 1.5 0 0; 5 2 0 0; 6 2.5 0 0; 7 3 0 0; 8 3.5 0 0;9 4 0 0; 10 4.5 0 0; 11 5 0 0; 12 5.5 0 0; 13 6 0 0; 14 6.5 0 0; 15 7 0 0;16 7.5 0 0; 21 0 0 0.5; 22 0.5 0 0.5; 23 1 0 0.5; 24 1.5 0 0.5; 25 2 0 0.5;26 2.5 0 0.5; 27 3 0 0.5; 28 3.5 0 0.5; 29 4 0 0.5; 30 4.5 0 0.5; 31 5 0 0.5;32 5.5 0 0.5; 33 6 0 0.5; 34 6.5 0 0.5; 35 7 0 0.5; 36 7.5 0 0.5; 41 0 0 1;42 0.5 0 1; 43 1 0 1; 44 1.5 0 1; 45 2 0 1; 46 2.5 0 1; 47 3 0 1; 48 3.5 0 1;49 4 0 1; 50 4.5 0 1; 51 5 0 1; 52 5.5 0 1; 53 6 0 1; 54 6.5 0 1; 55 7 0 1;56 7.5 0 1;ELEMENT INCIDENCES SHELL83 41 21 22 42; 84 21 1 2 22; 85 43 42 22 23; 86 23 22 2 3; 87 44 43 23 24;88 24 23 3 4; 89 45 44 24 25; 90 25 24 4 5; 91 46 45 25 26; 92 26 25 5 6;93 47 46 26 27; 94 27 26 6 7; 95 48 47 27 28; 96 28 27 7 8; 97 49 48 28 29;98 29 28 8 9; 99 50 49 29 30; 100 30 29 9 10; 101 51 50 30 31; 102 31 30 10 11;103 52 51 31 32; 104 32 31 11 12; 105 53 52 32 33; 106 33 32 12 13;107 54 53 33 34; 108 34 33 13 14; 109 55 54 34 35; 110 35 34 14 15;111 56 55 35 36; 112 36 35 15 16;ELEMENT PROPERTY83 TO 112 THICKNESS 0.6DEFINE MATERIAL STARTISOTROPIC CONCRETEE 2.17185e+007POISSON 0.17DENSITY 23.5616ALPHA 1e-005DAMP 0.05



Chris Conrad

END DEFINE MATERIALCONSTANTSMATERIAL CONCRETE ALLSUPPORTS1 16 21 36 41 56 FIXEDLOAD 1 LOADTYPE None TITLE LINELOADELEMENT LOAD97 98 PR GY -10000 -0.005 -0.25 0.005 0.25LOAD 2 LOADTYPE None TITLE POINTLOADJOINT LOAD29 FY -100PERFORM ANALYSIS PRINT STATICS CHECKFINISH

In reply to boucanier:

Hi Boucanier,

Yes, our training courses are always accompanied by a spiral-bound training manual thatincludes the material covered in the course, as well as Introductory Knowledge sections togauge your preliminary knowledge of the subject material, and Review Questions to test yourretention. The manuals are prepared using the PBT (Performance Based Training)methodology, which emphasizes learning by doing. So the training manuals lean heavilytoward using exercises as the primary presentation method.

Regarding your question about the model geometry that results in some angles outside ofthe recommended 60 to 120 degree range, I would have to take a closer look at some of thedetails to offer you a meaningful opinion. But if your initial instinct told you to use plates tomodel the structure, then I would probably consider staying with plates, but either modifyingthe mesh to minimize the number of elements that were extremely oblique, and/or evaluatethe significance of having some "less-than-ideal" plate shapes in a few limited locations. Myfirst reaction would not be to revert to using beams, though, because the behavior of a beam



sirojt

Chris Conrad

and a plate are so different.

Regarding your question about the cut by a line function, I have found that the function doesnot work when cutting through fewer than three plates. So in your model, it won't let you cuta line parallel to the z axis, because it would only cut through two plates. I submeshed yourmodel to divide each element into four elements, and then the function let me cut parallel tothe z axis.

Cheers,

Chris


I have several questions regarding the "results along line" function. 1. What is the coordinate system of the cut?2. Could you please explain each column in Total Force tab? They are Fx (line), Fy (line), Fxy (line), Mx (Line), My(Line), Mz (Line) In-Plane Moment, Mxy (Line), Qx (Line), Qy (Line). 3. Is there any document explaining thisfunction? Thank you,

In reply to sirojt:

In the online help, take a look at STAAD Graphical Environment > Post Processing > ThePages In The Post Processing Mode > Plate | Results Along Line Page.

I think that should go a long way toward answering most of your questions.

Cheers,

plate elements in staad & release

Related



sirojt

yuvarajprakash

Chris


Thank you.

In reply to sirojt:

HI Sirojt did you find what is My (line) ? if so please help me to learn about it..... (this isregarding the plate results along a line)

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