Centroid of Composite Solid in Autocad

[balimela]

I am a civil engineering and working with some pipe alignment on open surface. 2D drawings has been prepared in AutoCad for 2 m dia steel pipe on a open terrain with some verical bend to match with the terrain profile. Now the problem.

 

In order to civil design of concrete anchor blocks (a concrete block provided in pipe bend to absorb the bend forces), one has to calculate the cg of the composite anchor block with encased steel pipe. Composite material are mainly concrete anchor block with the central hollow portion to pass the pipe, weight of water in the encased pipe and the wt of steel liner in the anchor block portion.

 

This (to find out the cg) I have been doining by numeric method but which is very time consuming. Every time you have to take input from autocad, run you stability check with the helip of centroid calculated and if it is not safe then you make certain adjustment of the anchor block size, calculate cg and check the stability.......its a iterative process.

 

To have the work little bit cut out is their any possibility of calculating the cg in Autocad itself. Any suggestion will be a great help for me.

 

Thanks & Regards

 

Raj

[Lee Mac]

Perhaps something like this as a quick and short example:

 

(defun c:cg (/ ent coG)
 (if (setq ent (car (entsel "\nSelect Solid to Retrieve CoG...")))
   (progn
     (if (vl-catch-all-error-p
       (setq coG (vl-catch-all-apply 'vla-get-centroid
           (list (vlax-ename->vla-object ent)))))
   (princ "\n<!> Error Finding CoG <!>")
   (progn
     (alert (vl-princ-to-string
          (vlax-safearray->list
            (vlax-variant-value coG)))))))
   (princ "\n<!> Something Went Wrong <!>"))
 (princ))

[balimela]

I just want to know where is your density variable for the 3 composite member to calculate the combined cg. Let the algorithim will be like this.

 

X (x axis of the composite cg from any reference axis)

 

= (mass of hollow concrete anchor block x X1 + mass of weight of water in the pipe circular x X2 + mass of pipe steel liner x X3)/ (mass of hollow anchor block + mass of weight of water + mass of steel liner)

 

= (volume of Anchor Block (m3) x density of concrete (24 kN/m3) x X1 + volume of water in circular pipe x density of water ( 9.81 kN/m3) x X2 + volume of steel liner (m3) x density of steel (78.5 Kn/m3)x X3)/ (M1 + M2 + M3)

 

Y (y axis of the composite cg from any reference axis)= x value will be replaces by y axis.

 

Now, volume of Anchor = to be calculated from autocad

volume of water in pipe = Again to be calculated from drawing, Area of Inner Dia x length

Volume of steel Liner = calculated from the drawing. measure of thickness x perimeter x length of embedded pipe.

 

Sounds complicated, but can autocad be taken to little further to help engineer. any solution will be greatly appreciated.

 

Thanks

 

Raj, India

[CarlB]

AutoCAd may be helpful in determining volume of irregular solid & centroid like an anchor block, if you bother to draw it as a solid. But I don't believe AutoCAD is the right "tool" for solving the stability of a thrust block, beyond the items mentioned. The pipe & water has simple geometry; the volume & centroid should be straightforward calculations. Using AutoCAD to get precise values for small irregularities is probably "overkill" given the other assumptions in this analysis, like water pressure, surge, temperature thrust, soil friction, etc.

 

Have you tried using Excel for assisting with computations?

[Lee Mac]

Good point Carl - I just found the centroid using ACAD, but much other than that I would think just exporting these calculations to Excel and making some simple calculations

[ASMI]

It for regions: http://www.cadtutor.net/forum/showthread.php?t=24528&page=2

 

Sorry, but I havn't free time now.

[balimela]

thanks mate for all the reply and suggestion.

 

carlB & Lee: I am in the field for quite some time and do have the excel spreadsheet. but it is so time consuming, every time i have to calculate the cg of each material block in autocad by massprop command, their volume (area x width) and thereafter calculate the composite cg of the whole body in the excel sheet.

Again if I have to slight resize of structure, then again same excersise to be followed. I wanted it to do it little bit dynamic way.

right now i am calculating the individual cg by area method in autocad 2d (assuming width = 1m) by divide it into three parts, upper concrete (above pipe hollow portion), below concrete and hollow encased pipe poertion. Steel liner cg I am assuming at the same hollow pipe location.

[Lee Mac]

I think OpenOffice is readily available and may suit your needs

http://openoffice.org-2009.com/index.asp?aff=101&camp=gg_oo_uk&se=google

[CarlB]

If you could post a drawing, that would clarify a lot of things.

[balimela]

Attaching the drawing for clarification. In the drawing a portion of pipe has been taken to find out the cg of the Anchor Block numbered 3. The CG has been approximated and calculation has been shown the the same file.

 

Regards

AB3.dwg

[balimela]

As requested I have posted the file.

[apopka_pilot]

There is a piece of software that I use (Express CG) in the precast business that figures the CG automatically and inserts blocks @ the CG. It also gives you information about the product. Google Express Engineering, they are in Florida.