Spacing between bars checks by the code, settlement calculation under footing

[Anonymous]

Hi every one...

i have 2 questions for you

-first how did robot check spacing between bars and links i have made a model i chose link 6 diameter for stirrups reinforcement but the program make the spacing between links 170 mm and it shouldn't be more than 144 mm according to bs code..

-second i tried to check the settlement of foundation by increasing the design load and calculating the immediate settlement but i have found differences between values calculated by robot and calculated by me using my excel the difference between values increases as i increase the design load of footing.... my calculation was based on the formulas of Bowles's book (Bowles - Foundation Analysis and Design)... can some one please illustrate how did robot calculate the immediate settlement under foundation (http://knowledge.autodesk.com/support/robot-structural-analysis-products/learn-explore/caas/CloudHel...

here is the link : http://www.4shared.com/rar/TQZSDsHuba/Robot_3D_With_releases_-_Copy.html

[Artur.Kosakowski]

1. What is exactly the BS part you refer to for the distance among the stirrups? I'm not considering myself an expert for BS yet for 6 mm stirrups that wold be 72 mm which seems to be a small value for a typical column. 

2. What kind of additional information you would expect in addition to the description already available in Help you already indicated which contains the formulas used by Robot?

[Anonymous]

Thank you all for your reply i really appreciate your help

for the first point: the British code specification is that the spacing between links is to be at max of (twelve times the diameter of the bar used in column) and here is in the column design i gave you, the link diameter is (6 mm), the bar diameter is (12 mm) for compression and the spacing between links created by robot is (170 mm)  which exceeds the allowable spacing for (Bar 12 mm) which is (=12*12=144 mm).. there is no errors in the design checks about this matter i explained above.

so... my question is how to check the reinforcement arrangement by Robot (sometimes the bras satisfy the design stresses but don't satisfy it in arrangement as my case is, the links satisfy shear stress but not arrangement)

and the second point i have mentioned is about the calculation of settlement under foundation, i have searched the internet and i have read the foundation analysis and design by bowles which robot makes its calculation applying the formulas of this book. i have calculated the settlement by robot and compared it to calculations i have made it myself to check the accuracy of the program and i find out at large loads the robot values for settlement differs significantly from the calculation i have made so why is that. can anyone check the settlement calculated by me and robot and see the difference, and tell me why is that difference occurs, please consider opening footing 2 (word file and excel file)  and see the difference i mentioned

Thanks again for your help

regards,

Ahmed

[Artur.Kosakowski]

1. I have some difficulty in finding this provisons in BS directly. Cold you tell me which point of the code describes this limit please? Or is it actually taken from another source?

2. The difference in the values has got two reasons:

a). Robot uses the formulas which are described in the indicated part of Help rather than the ones from Bowel's book

b). The value is calculated in the center of a foundation whereas as I understand from the first sentence in the pdf you attached at a corner of a foundation.

[Anonymous]

hi Artur, thank you for your help

the first point according to BS8110 Section 3 : Design and detailing, reinforced concrete

3.12.7 Containment of compression reinforcement

3.12.7.1 Links for containment of beam or column compression reinforcement

when i checked the column designed by robot, with another program (tedds for calculations), it shows that it isn't right according to BS 8110 because of link spacing so i have to either change the bar diameter for column or decrease the spacing between links..... Robot didn't give me any warnings of this problem and its ok for robot to use link with spacing not justify the containment section in bs 8110

and the second point i really want to know how did robot calculate the settlement under footing. i mean i need to see a calculation made by hand (solved example) to see how did robot calaculate settlement i have read the help of autodesk and i have seen the formula used but i have problems of applying them. can some one show me a full calculation step by step which illustrate all the calculations

Thanks for your support

regards

Ahmed

[Artur.Kosakowski]

1. Thank you for notifying us about this requirement.

2. Could you send the rtd file so that I could see the parameters of soil you used? Thank you.

[Anonymous]

Thanks Artur for your help...

and thanks also for SIM Squad.....

here is a small model i made for studies Robot program

i have designed a footing by the program and i intentially increase the design load on footing to study the settlement

here is the link : http://www.4shared.com/file/Sg11oPNaba/Footing_2.html

Thanks Artur for your help

Regards,

Ahmed

[Artur.Kosakowski]

Robot calculates settlement based on stress distribution in soil (along z depth) based on average stress under a rigid plate according to the following formula:

This is done up to the level where stress due to applied load is less than 30% of "natural" stress value. The comparison of Robot's approach with other methods is done in the attached xls.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Artur.Kosakowski · Accepted solution]

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@Artur.Kosakowski wrote:

1. Thank you for notifying us about this requirement.

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Corrected in SP4 for RSA 2016.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.