1st study report for defining stool geometry

8/13/2019 1st Study Report for Defining Stool Geometry

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Geometry Study of Lattice Tower

A tentative model of 170m tower(height as given in received drawing) is created in STAAD andtentative property is assigned to the structure. Assuming only wind pressure acting on the structurevarying from 1 n!m" at #0m level to " n!m"(ignoring the self weight command in staad) at top andanaly$ing the structure% reaction received is &!' " *n (vertical) on each support as shown in figure 1

+elow.

,urpose of the analysis-The purpose of this analysis is to identify the +est geometry configuration for the tower. or the lowerstool with the width of " meter% the mem+er length are higher. The ma/imum mem+ers should

participate in the load ta ing mechanism. The slenderness of the mem+er should +e chec ed a+out +oththe principal a/is.

Data:-ase width of the tower considered is " m

ote- HEIGHT TO WIDTH RATIO

oo on 2ommunication Tower +y rian.3.Smith gives height to width ratio +etween -1 to #-1

Thus assuming ratio as 4-1% we get +ase width for height of 170m tower as 170!4 5 " .6 m(which is o )

eference-http-!!+oo s.google.co.in!+oo s8id5m'9hn:;7;0 2


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Calculation for e ui!alent "oint load on t#e $tool of %& metre #ei'#t

(oment at )a$e 5 " / " / " 5 E #" * 'm

E ui!alent force at to" of %& meter $tool 5E #"!10 5 E # *

*orce "er node 5 E #!E 51"E * (forces shown in fig ")

ig 1- 2omplete tower analysis for the assumed wind load of " *n!s=m

X = - 2 0 4 . 2 3 6 k N Y = 8 9 2 . 1 8 6 k NZ = 1 3 5 . 2 5 9 k NM X = - 3 .6 2 5 k N mM Y = - 0 .5 5 5 k N mM Z = - 2 .0 4 3 k N m

X = - 2 0 4 . 2 3 6 k N Y = - 8 9 2 . 1 8 6 k NZ = - 1 3 5 . 2 5 9 k NM X = 3 . 6 2 5 k N mM Y = - 0 . 5 5 5 k N mM Z = - 2 .0 4 3 k N m

X = - 2 0 4 . 2 7 9 k N Y = 8 9 2 . 1 8 8 k NZ = - 1 3 5 . 2 1 6 k NM X = 3 . 6 2 6 k N mM Y = 0 . 5 5 5 k N mM Z = - 2 .0 4 2 k N m

X = - 2 0 4 . 2 7 9 k N Y = - 8 9 2 . 1 8 8 k NZ = 1 3 5 . 2 1 6 k N

M X = - 3 .6 2 6 k N mM Y = 0 . 5 5 5 k N mM Z = - 2 .0 4 2 k N m


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ig "- Showing applied force at hip level of 10m

;ne leg is selected out of four main leg(fig 6) to design main mem+er(fig E) of the stool leg.

ig6 Showing four legs in ,lan


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or understanding purpose say mem+er 1 is selected for design as shown in fig E. @em+er 1 is furthersu+divided into five parts as other tie mem+ers are connected to the mem+er which +rea s the mem+erlength into # parts% thus ma/. force out of this # parts is to +e considered for design.

ig E showing Ceg mem+ers

Step 6-' The primary study of the ndore tower geometry reveals that many mem+ers are having tie inone direction only. Such tie can not +e considered as the effective tie for slenderness ration% the out of

plane slenderness ratio will govern the design. Iere% +racing at 10m plan(fig #) are removed as thosemem+er are directly su+Jected to +ending and serve no purpose to reduce the slenderness as shown in fig#.


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ig# showing unnecessary mem+er

ig4 @em+er weight


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After analy$ing the structure and eeping the utility ratio under 1.0% the total weight of 10m stool comesaround EE@T(as shown in fig 4) with

1) @ain leg mem+er as S@2E00 ! (fig 7)") @ain hip mem+er as S@2E00 ! (fig )6) Iip tie mem+er as S@21"# ! (fig )E) ;ther mem+er as S@2100 ! (fig 10)

ig 7. @ain Ceg @em+er

ig . @ain Iip @em+er


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ig . Iip tie @em+er

ig 10. ;ther Ceg @em+er


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ig11 . Showing a/ial force distri+ution in mem+er

Conclu$ion:-

Analysis shows that there are $ero a/ial forces in many of the mem+er( as shown in fig 11) which

indicates that all mem+ers are not effectively participating in force transformation and only few mem+ersare ta ing the a/ial force and thus resulting in heavy section design for those mem+er. f all the mem+ersare participating in the force transformation than this could result in much light weight section. Iencechange in geometry is proposed.

ew geometry is proposed with same +asic assumptions and loading and varying the section properties and varying the su+'division of the main leg mem+er.;ur purpose to +uild a geometry in such a way that all mem+ers are effectively utili$ed.


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ig1". Showing ew geometry

ig16. Showing failed leg in compression


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ig.14A/ial force distri+ution in mem+er

ig.17 @em+er weight


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The total weight of the stool comes around 67@T with a com+ination of tu+ular section and 2hannelsection. Tata tu+e is of 610 grade and still lighter than channel section or ' section etc.

Conclu$ion:-

n this analysis also $ero utility( as shown in fig 1#) < $ero a/ial force(as shown in fig 14) in many of themem+er is seen.Though many mem+ers ta e participation in a/ial force transmission in this model than the previousmodel +ut their participation is very less < negligi+le.So again geometry configuration needs to +e re modeled and chec ed. or understanding the geometryits +etter to try with "D analysis.

A""endi+: ,a$ic ty"e$ of tower

Type of tower geometry possi+le-


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1) Tower with isolated mem+ers ( ig 1 ).Gvery mem+er of this tower is either single mem+er or at the most made of two sections(channel front to front% dou+le angle section). n such case the length of the mem+er should note/ceed the # meter length (prefera+ly)% to eep slenderness ration +elow 1 0. Gvery mem+ershould have effective tie in +oth direction. G/ception can +e considered for cross +racing swherein the tension mem+er can give effective tie to the mem+er in compression.

ig. 1

") Iyper+oloid tower( ig 1 ) is another possi+ility. The shape (circular in plan)% the out of plane +uc ling can +e discarded. All mem+ers can +e considered having tie in +oth direction.@oreover if we provide the cross mem+ers as shown in figure 1 % then one mem+er from crosswill go in tension and another in compression% so the mem+er in tension will give the lateralsupport to the mem+er in compression.Iyper+oloid structures are easy to +uild% for detail chec out the lin +elow-http-!!en.wi ipedia.org!wi i!Iyper+oloid:structure
http://en.wikipedia.org/wiki/Hyperboloid_structurehttp://en.wikipedia.org/wiki/Hyperboloid_structure


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ig. 1 showing hyper+oloid lattice tower

6) Giffel tower(6"Em tall) is also a geometry option( ig "0). Gach leg of the tower is made of fourindividual mem+er which are connected with cross +racings and thus ma ing a strong leg. noption 1% we had only the dou+le section mem+er% so the effective length of mem+er wasrestricted to # meter. ut if we ma e the compound mem+er then the effective length could goupto "0 meter.


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ig. "0 S eleton of Giffer tower

ollowing lin gives a +rief idea -

a) http-!!www.ce.Jhu.edu!perspectives!studies!GiffelK"0TowerK"0 iles!GT:?eometry.htm +) http-!!en.wi ipedia.org!wi i!Giffel:TowerHDesign:of:the:tower
http://www.ce.jhu.edu/perspectives/studies/Eiffel%20Tower%20Files/ET_Geometry.htmhttp://en.wikipedia.org/wiki/Eiffel_Tower#Design_of_the_towerhttp://www.ce.jhu.edu/perspectives/studies/Eiffel%20Tower%20Files/ET_Geometry.htmhttp://en.wikipedia.org/wiki/Eiffel_Tower#Design_of_the_tower


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ig. "1 Actual photo of Giffel tower

1st study report for defining stool geometry

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