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STAAD: Bending moment in plate elements

January 18, 2010, 7:22 pm
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Hi

 

I've been using STAAD for quite a while for steel design, but now I need to use STAAD for design of a 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 0.6 m thick frame (inclined walls and deck) with a width about 20 m's, I think elements might be a better 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 m span divided into 8 elements equally length). The slap is fully fixed in both ends, and my textbook calculation for a centrally placed force of 100 kN, should give me a bending moment of 100 kNm at 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 to averaging over an entire plate element (as far as I can read in the STAAD help file). The cut along a line function, doesn't seem to work properly for me. When I want to cut the line, I can mark up for instanse to nodes at one fixed end (transverse to span direction), but no line marking appears in the above window. Highligthing a span over several members in the span direction will give me a cut line in the above window, but right now I'm not interested in these figures. Any help about this ? as I can not design my plate for a bending moment 10-15 % below the actually maximum bending moment.

Just to clearify, with my present knowledge of STAAD, I can not use the build in RC-design module, because I'm designing by old danish codes. Further more, I'm interested in the bending moments rather than stresses, because I need to calculate the neccesary rebar area to fullfill some crack width criteria.

I found some example here in the forum regarding member properties for cracked members, but couldn't find any additional information regarding this subject in the STAAD help file, so any info regarding 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 it tomorrow. 

Best regards

Boucanier

 

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RE: RAM Connection

March 14, 2014, 8:02 am
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RAM Connection

January 7, 2009, 5:33 pm
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I'm trying to design both HSS Beam to HSS girder, and HSS Girder to HSS column connections.  I was hoping to use Connection to check the buckling/crippling, but seem to be out of luck with using HSS Tubes as Beams.  Does anyone have any suggestions, or workarounds for this problem?
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RE: Natural Torsion Issue

March 14, 2014, 10:18 am
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The inclusion of the natural torsion does not affect the time period calculations because the latter is calculated based on translational vibration of the structure using the Rayleigh method. This calculated period is compared against limits imposed by the seismic codes like IBC to decide on the time period to be used in the base shear calculations.

Your observation regarding torsional amplification is correct. It is not possible to calculate this amplification on a level by level basis. You need to use the highest one.

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MEMBER GROUP COMBINE

March 14, 2014, 8:21 am
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I have a series of steel members that i have put in using the general prismatic command. I beleive there is a way a can combine or group these members so i can get the maximum forces too design for the group. Has anybody done this or have more information on this procedure?

Thanks in advance for the help.

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RE: MEMBER GROUP COMBINE

March 14, 2014, 10:32 am
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Since STAAD.Pro does not design prismatic sections, I am assuming you are going to design these manually and are looking for the maximum moments, shears, axial forces etc considering the entire group. To do that you may go to the post processing mode > select the members > go to Report in the top menu > Section forces > you would then see options to sort the results based on axial force, Shear-Y, MY , MZ etc.    

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RE: MODELING RULES

March 14, 2014, 10:51 am
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For plates there is no offset option available. So one needs to model plates at the exact locations and then create dummy rigid elements to establish connectivity with the adjacent beams/columns which I generally prefer to avoid due to two reasons

A) Complexity of modeling

B) More often than not, these small stiff elements introduce more/less artificial stiffness than what exists in the actual structure and this alters the analysis results and so although we think we are better simulating the actual structure, that may not be the reality.

So I would generally avoid modeling these offsets for plates and stick with the default center to center approach.

For beams, it is at the discretion of the engineer. Modeling the offsets is very easy for beams.      

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MODELING RULES

March 13, 2014, 8:07 pm
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From the attached photo, please suggest the best model to be used using STAAD and identify the pros and con for each model (if there is one). 

Best regards,

Ryan

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RE: RAM Concept Load History Deflections

March 14, 2014, 11:10 am
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Thanks for the help.  We'll be looking more closely at some of these factors in the load history deflections.

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RE: Natural Torsion Issue

March 14, 2014, 6:52 pm
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Natural Torsion Issue

March 12, 2014, 7:55 am
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I have an issue with the new feature of Natural Torsion, it seems that the factor is not working. From what I understand from the limited documentation is that the natural torsion is the inherent torsion that will be captured in a dynamic analysis due to the offset between the center of mass and the center of rigidity. When I checked the tabulated results the total torsional offset is the dynamic offset plus the accidental offset. This total offset is supposedly multiplied by the story force to produce the torsional moment for each level. However, even if I input the factor for natural torsion as 1 or 0 there seems to be no change in the period of the structure or the dynamic base shear. Why is that so?

Another question, what command is provided in Staadpro to incorporate the torsional amplification factor Ax as required by code for structures with torsional irregularity is it by incorporating it in the accidental torsional factor?

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RE: Grouping Surface Element

March 14, 2014, 9:21 pm
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hi midasgen,

can you be specific the purpose of grouping? maybe you can use group through thickness property..

pls. comment,

tnx..

rekcah

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Grouping Surface Element

March 14, 2014, 6:56 pm
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It seems to me that there is no way we can group surface element or am I missing something?

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RE: Grouping Surface Element

March 15, 2014, 2:28 am
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There are a lot of scenario why I want to group surface elements for example when I have a building with a lot of shear walls in the x or z direction I want to group based on each location like SWx 1, SWx2, and so on so that when I want to check the maximum stresses for each shear  wall in the post processing it is easier for the user to extract those maximum responses by group and be able to design the shear wall to comply with aci chapter 21 using spreadsheet. Or another scenarios if I have a basement with shear walls and I don't want the mass below grade included in the eigen value analysis I can easily exclude it by using group.

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RE: Recovering staad input file form system generated analysis files

March 15, 2014, 4:41 am
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There are two other files that you can use as alternative. First, you can see the .ed.backup file. Also, you can look at .ANL file which is the output file. The input data is included in the same, although you will have to edit it in notepad to remove line numbers, page breaks, etc...

Arunkumar

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Recovering staad input file form system generated analysis files

March 5, 2014, 11:18 pm
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Dear All,

I am trying to recover a staad input file which i have accidentally deleted permanently.

Are there any ways of doing that ? Like there are always bak files in autocad.....

I have the analysis files like *.num, *.rea and *.sbk file but not the original *.std file or the output file.

Please let me know if there is any way to do this.

Regards

Rajarshi Bose

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Staad Pro Column Design Result

March 3, 2014, 10:12 pm
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Hi all!

I made a design of 3 storey residential bldg and after all the inputs and analysis the result for 2nd floor column Asreq'd is greater than the 1st floor column Asreq'd.

I am expecting that the greater values of Asreq'd should be at the bottom floors. How should I consider the Asreq'd? which area should I use?

Thanks in advance for your help and explanation.

 

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RE: Staad Pro Column Design Result

March 15, 2014, 4:50 am
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1. Simulating the effect of brick wall will reduce the steel required considerably, but should be used carefully because of many reasons - for example, openings in wall will affect the wall capacity, quality of construction/material may be suspect, etc... In addition, we should not use it in case of earthquake analysis because the brick infill will yield quickly in real life and its capacity will reduce to zero rendering your analysis model unsafe.

2. In real life, it is better to take the larger steel required in upper floors and provide the same in lower floors in such situations. The reason for this is simple. The above building is three stories tall. If the construction at this time is restricted to one or two stories only, that top story will now have the large moments and low axial force that the modelled top story would have. For example, in the post by Biswa following the attached staad file, top floor column is 80, bottom floor column is 58 and mid col. is 71. Let us say that steel required as per staad output is 1000 sqmm in bottom, 800 sqmm in mid and 1500 sqmm in top floor. If only two floors are constructed now, the steel required as per constructed will be (probably) 800 sqmm in bottom and 1500 sqmm in top (originally mid floor). If only one floor is constructed now, steel will be 1500 sqmm in the bottom floor.

Arunkumar

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RE: Retaining the STAAD Input Editor in STAAD.X

March 15, 2014, 5:03 am
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IMHO, the text input format of STAAD is very good. If you compare with software like ETABS/SAP and MIDAS GEN, etc., the input data comes up crisply in the text format. This makes it easy to take a print of the input file for checking the model (input files of other software are too long for economically printing). This way, checking can be done predominantly without the use of computer thus not tying up one license.

Arunkumar

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Retaining the STAAD Input Editor in STAAD.X

March 4, 2014, 1:58 pm
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Dear STAAD.pro Users,

 

As you know we at Bentley Systems are in the process of developing our next generation STAAD products named STAAD.X. The new software would have a new state of the art graphic user interface (GUI ). However we know that many of you are fond of the input editor in STAAD.Pro and hence we are trying to see how important it is for you to have this editor facility in STAAD.X in addition to the GUI. Please share your opinion on this forum as to whether you would like to see the editor in STAAD.X or not.

 

[Please visit the site to access the poll]


 

Thanks in advance for your feedback.

 

Sye

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