Structural Evaluation of Self Supporting Tower (Calculation)__Yoppy Soleman

Space Truss Design

SPA SP ACE TRUS TRUSS S DE DESI SIGN GN

1. DESIGN SPECIFICATION 1.1. Design Standard 1)

The design design basis basis of the tower tower applie applied d is EIA Standa Standard rd EIA-222 EIA-222-E -E “Stru “Structu ctural ral Standar Standards ds for Steel Steel Antenna Tower and Antenna Supporting Structure”. The fabrication and materials of the tower will be according to the relevant Indonesian Standard.

2)

The self self suppo support rtin ing g tower tower has has squa square re cros crosss sect section ions. s.

3)

All the legs legs and bracin bracings gs are made made of equals equals legs angles angles steel. steel.

4)

All the connec connection tionss in in the the field field are made made with with Steel Steel Bolts, Bolts, each each fitte fitted d with with one spring spring washer washer and nut.

1.2. Tower Structure Design Condition 1)

Tower Tower heig height ht : 42. 42.0 0 mete meterr ( loca locati tion on : Limb Limbot oto, o, Nort North h Sulaw Sulawes esii )

2)

Maxi Maximu mum m wind wind velo veloci city ty (V) (V) : V = 120 120 km/h km/hou ourr = 33.33 33.33 m/se m/sec. c.

3)

Exis Existin ting g anten antenna nass load loadin ing g ( see see the the draw drawing ing atta attach chme ment nt ) : 

2 (two) Planar type antennas antennas at 42.0 m



1 (one) Planar type antennas at 38.0 m



1 (one) Paraboloid Paraboloid grid antennas antennas 1.20 diameter diameter at 35.0 m



1 (one) Paraboloid grid antennas 1.20 diameter at 42.0 m

4)

Propo Propose sed d ante antenn nnas as load loadin ing g ( see see the the draw drawing ing atta attach chme ment nt ) : 

1 (one) Paraboloid solid antenna 1.2 diameter at 38.0 m

1.3. Loads 1)

Dead load Dead load is weight of tower, antenna, ladder, platform etc.

2) Wind load on tower structure Wind load calculation method on the tower and appurtenances are as follows F

= qz qz . GH GH . CF . AE AE and and not not to to exc excee eed d 2 . qz . GH. GH. AG

qz

= 0.61 0.613 3 . KZ . V

Kz = ( z / 10 )

2

2/7 1/7

GH = 0.65 0.65 + 0.60 0.60 / ( h / 10 ) 2

CF = 4.0 e – 5.9 e + 4.0 ( square cross section ) 2

CF = 3.4 e – 4.7 e + 3.4 ( triangular triangular cross section section ) e

= AF / AG

AE = DF . AF Where : F

= Hori Horizo zont ntal al wind wind forc forcee ( N )

qz

= Veloci Velocity ty pressur pressuree ( Pa Pa )

GH = Gust Gust response response factor factor ( 1.00 1.00  Kz  1.25 ) CF = Structu Structure re force coefficien coefficientt 2

AE = Effective Effective projected projected area of of structural structural componen componentt in one face ( m ) 2

AG = Gross area of of one tower tower face face ( m ) Kz

= Exposure Exposure coefficient coefficient ( 1.00  Kz  2.58 )

V

= Basic Basic wind wind speed speed for the struct structure ure locati location on ( m/s m/s )

Engineering Postgraduate Program Hasanuddin University

15

B. OF DUCTILE STEEL STRUCTURES.  Yoppy Soleman, 2005

Space Truss Design

z

= Heigh Heightt above above aver average age groun ground d level level to midp midpoin ointt of the the sectio section n(m)

h

= Tto Ttota tall hei heigh ghtt of of str struc uctu ture re ( m )

e

= Soli Solidi dity ty rati ratio o 2

AF = Projected Projected area of flat structur structural al component component in one face face of the section section (m ) DF = Wind direction direction factor factor 1.00 1.00

for squa quare cros crosss secti ection on and norm normal al wind ind dire direct ctio ion n

1.00 1.00 + 0.75 0.75ee

for for squa square re cross cross sect section ion and and 45 wind direction

0

3) Wind load on Antenna Wind load calculation method on the parabolic antenna is as follow : 2

Fa = C Caa x A x Kz Kz x GH GH x V

2

Fs = C Css x A x Kz Kz x GH GH x V Kz = ( z /10 /10 )

2/7

GH = 0.65 + 0.60 / (h/10)

1/7

Where : Fa = Axial Axial Force (lb) Fs = Side Force (lb) Ca = Wind load coefficient for axial Cs = Wind load coefficient for side Kz = Exposure coefficient ( 1.00  Kz  2.58 ) z

= Height Height above above average average ground ground level level to to midpoint midpoint of of the section section (m)

h = Total heigh heightt of the structure structure (m) (m) A = Normal Normal projected projected area of of Antenna Antenna V = Wind velocity velocity ( m/s ) 4) Load combination Herewith the following combinations are used below : a) DL + WL at 0 degree direction direction (with weight of existing existing antenna) antenna) b) DL + WL at 45 degree direction direction (with weight weight of existing antenna) antenna) c) DL + WL at 0 degree direction (with weight of existing + proposed antenna) d) DL + WL at 45 degree direction (with weight of existing + proposed antenna) Where Where : DL DL

= Dead Dead load load weig weight ht of the struct structure ure and appurt appurtena enance nces. s.

WL

= Design Design wind wind load load on antenn antennaa at above above direct direction ion..

1.4. Allowable Allowable unit stress stress The unit stresses in the structures members do not exceed the allowable unit stresses for the materials as specified in the AISC Standard (American Institute of Steel Construction Standard) 2

1. Tens Tensio ion n

: Ft = 0.60 0.60 Fy ( kg/c kg/cm m )

2. Shear

: Fv = 0.40 Fy ( kg/cm )

2

3. Compressio Compression n i) On the gross section section of axially axially loaded compress compression ion members members when kl/r is less less than Cc : 2

(kl/r)

[ 1 - ----------] Fy 2

2Cc

Fa = -----------------------------------------------------------------------------------------

2

( kg/cm kg/cm )

3

5/3 + [3/8(kl/r) [3/8(kl/r)]/8C ]/8Cc - [(kl/r) /8Cc3]


16


Space Truss Design

2

2 E Where: Where: Cc =  --------Fy

ii) On the gross section of axially loaded compression compression members, when kl/r exceeds exceeds Cc :

2

12 12 E Fa = -------------------------

2

( kg/cm kg/cm )

2

23(kl/r)

4. Bending 2

Tension and compression on extreme fibers : Fb = 0.66 Fy ( kg/cm ) 2

5. Tension on bolts : Ft = 0.60 Fy ( kg/cm ) 6. Shear Shear on on bolts bolts :

2

Ft = 0.30 0.30 Fy ( kg/c kg/cm m ) 2

7. Bearing on bolts : Ft = 1.20 Fu ( kg/cm ) 8. The maximum slenderness ratio (kl/r) are as follows : kl/r = 120 for compression members of legs kl/r = 150 for compression members of diagonals kl/r = 200 for tension members Notations : 2

Ft = Allowable tensile stress ( kg /cm ) 2

Fy = Minimum yield point ( kg /cm ) 2

Fv = Allowable shear stress ( kg /cm ) 2

Fa = Allowable compressive stress ( kg /cm ) k = Effective length factor l = Actual Actual unbraced length of member ( cm ) r = Governing radius of gyration ( cm ) Cc = Column slenderness ratio E = Modulus of elascity of steel = 2,100,000 kg/cm

2

2

Fb = Allowable Allowable bending bending stress ( kg /cm ) 2

Fu = Minimum tensile strength ( kg /cm ) 1.5. Materials Steel materials materials to be used for the towers and appurtenances appurtenances conform conform to the relevant relevant Indonesian Indonesian Standards and/or Japanese Industrial Standard.

1) Steel Structural Description

Tensile Strength

Minimum Minimum Yield Yield Point Fy

( kg/cm2 )

( kg/cm2 )

Bj – 41

4100

2500

SS – 41

4100

2500

2) Bolts Description

Ft


Fv

17

Fv


Space Truss Design

A – 325 Bolts

Friction Type

Bearing Type

( kg/cm2 )

( kg/cm2 )

( kg/cm2 )

3900

1230

1476

3) Concrete Design compressive strength of concrete (f’c) at 28 days. K - 175

2

-

f’c = 175 kg/cm

4) Reinforcement steel U - 24

-

Fy = 2400 kg/cm2

1.6. Structural Analysis The purpose of the structural analysis is to find the joint translations and the design axial loads in all members of the tower. Load is applied applied and separate load cases cases combined combined to give the most most severe design conditions conditions at various section. The structural calculation is made using SAP 90 (Structural Analysis Program 90). The program will perform the static analysis of a space truss of arbitrary geometry by the stiffness method. The truss may be subjected to loads consisting of forces acting on the joints in any directions in space. The program output consists of the joint translations, tr anslations, the member forces and the support reactions. The program input contains :

a. Structure title b. Loading system : number of static analysis that applied to the structure. c. Group of data corresponding to the properties of the mathematical model of truss and the applied joint load : 

Group 1 : Joint coordinates



Group 2 : Support joint restraints



Group 3 : Material and member data



Group 4 : Joint loads



Group 5 : Loading combinations

The location of the joints in any structure are expressed as coordinates in a global right hand othogonal XYZ coordinate system. For the space structures the Z axis is oriented in the vertical direction positive upward, with the X and Y axes oriented in the major directions of the structure. Z+ Y+

Global Axis 0

X+

All applied joint loads, loads, joint displacement displacement and reactions reactions are expressed expressed as component component in the global coordinate system. Force component and translation components are positive if they act in the positive direction of an axis. The member forces and support reactions for both conditions, tower with existing antennas and tower with existing and proposed antennas, are attached in computer output. 1.7. Design Calculation Of Foundation The calculation of foundation consists of design and control of foundation. Control of foundation includes :


18


Space Truss Design

1)

Control of stability for uplift force :

Sf = W1 / T > 2.0 Where : W1= Weight of foundation and soil ( kg ) T

= Upli plift force ( kg )

2.0

= Allow Allowabl ablee safety safety factor factor

2) Control of bearing capacity of soi l : Wt M F = -------------- + ------------------------- < Q A 1/6.A . B Where :

2

( kg/m kg/m )

Wt = Total vertical vertical load load includes includes support reaction, reaction, weight weight of of foundatio foundation n and and weight weight of soil soil (kg) M = Moment Moment load ( horison horisontal tal loads loads x height height of founda foundations tions ) ( kgm ) A =

Area of the foundation foundation base ( width width x length length of foundation foundation ) (m2)

B =

Width Width of the founda foundatio tion n base base ( m )

Q =

Allowa Allowable ble bearin bearing g capa capacit city y of soil. soil.

3) Control of sliding force : SF = Wt .  / H

> 1.5

Wher Wheree : SF =

Safe Safety ty fact factor or

Wt =

Total Total vertical vertical load load includes includes support support reacti reaction, on, weight weight of foundati foundation on

and weight of soil (kg) 

= Coefficient Coefficient of soil soil friction friction

H = Hori Horiso sont ntal al load loadss ( kg kg ) 1.5 = Allowable Allowable safety factor factor

2. STRUCTURAL CALCULATION The structural analysis is made using SAP 90. Input and output program is shown as attachment.

Deflection, sway and twist are calculated as follows : a. Defl Deflec ecti tion on

: Dxn Dxn : Join Jointt disp displa lace cem ment ent at a poin pointt n Dxn’ : Joint displacement at a point n’ Dxn – Dxn’

b. Sway Sway angle angle

= arc tan ( ---------------------------------------------------------------------------------------------------- ) Distance between point n and point n’

Dxn – Dxn’ c. Twist Twist angle angle

= arc tan ( ------------------------------------------------------------------------------------------------------ ) Distance between point n and point n’

1)

Tower without pro proposed ant antenna

a. Deflection

= 6.4177 cm

b. Dxn

= 5.2096 cm


19


Space Truss Design

Dxn’

= 5.8865 cm

d

= 250 cm

Sway Sway angl anglee

= arc arc tan tan (( 5.886 5.8865 5 – 5.20 5.2096 96 ) / 250 250 ) = 0.155 0.1551 1 degr degree ee

c. Dxn

= 5.8865 cm

Dxn’

= 6.4173 cm

d

= 300 cm

Twis Twistt angl anglee


2)

Tower with proposed antenna

a. Deflection

= 6.5947 cm

b. Dxn

= 5.2534 cm

Dxn’

= 5.9388 cm

d

= 250 cm

Sway Sway angl anglee


c. Dxn

= 6.4763 cm

Dxn’

= 5.9388 cm

d

= 300 cm

Twis Twistt angl anglee


Sway and twist at 120 km/hour wind velocity without proposed antennas as follows : Actual

Allowable

Deflection (cm)

6.4177

42

Sway angle (degree)

0.1551

0 .5

Twist angle (degree)

0.1014

0.5

Sway and twist at 120 km/hour wind velocity with proposed antennas as follows : Actual

Allowable

Deflection (cm)

6.5947

42

Sway angle (degree)

0.1570

0 .5

Twist angle (degree)

0.1027

0.5


20


Space Truss Design

3. FOUNDATION ANALYSIS 3.1. Column Anchorage Bolt Calculation 

1) Stee Steell Bar Bar Bj 37



2 ) Notation :

2

--------------- Fy = 2400 2400 kg / cm

Fy

= Yiel Yield d stre strengt ngth h of of stee steell

Fv

= Allowab Allowable le shear shear strength strength of ancho anchorr bolt bolt

Ft

= Allowable Allowable tensile tensile stress stress of anchor anchor bolt

Fts = Allowable Allowable tensile tensile stress stress for bolt subject to combine combine tension tension and stress stress Fcv = Allowable Allowable bond bond stress of concret concretee



fv

= Actua Actuall shear shear stress stress of anchor anchor bolt bolt

ft

= Actu Actual al tensil tensilee stre stress ss of anchor anchor bolt bolt

f’c

= Compres Compressive sive strength strength of concre concrete te

A

= Tota Totall area area of anch anchor or bolt bolt

P

= Tota Totall com compre pressi ssion on of tower tower base base per per one leg

T

= Total Total uplift uplift force force at towe towerr base base per one leg

S

= Tota Totall shea shearr forc forcee at at towe towerr base base per one leg

Le

= Re Required quired embeded embeded length length of anchor anchor bolt in concret concretee

3 ) Maximum forces at tower base a.

Tower with existing antenna : T = 21110 – 488.09 = 20621.91 kg S = 2377 kg

b.

Tow Tower with exist isting and and pro propose osed antenna nna : T = 21110 – 488.09 488.09 = 20621.09 20621.09 kg S = 2387 kg



4 ) Allowable tensile stress of anchor bolts 2

Fv

= 0.3 0.3 Fy = 0.3 0.3 x 2400 2400 = 720 kg/cm kg/cm

Ft

= 0.6 0.6 Fy = 0.6 0.6 x 2400 = 1440 1440 kg/cm kg/cm

2

a.

Tower with existing antenna : Number of anchor bolt = 6  ¾ “ 2

2

A

= 6 x ( 0.25  x 1.905 ) = 6 x 2.85 = 17.1 kg/cm

fv

= S / A = 2377 2377 / 17. 17.1 1 = 139. 139.0 0 kg/ kg/cm cm < Fv ………….Ok !

2

Fts = 1.4 1.4 Ft – 1.6 1.6 fv

= ( 1.4 1.4 x 1440 1440 ) – ( 1.6 1.6 x 139. 139.0 0) = 2016 – 222.40 = 1793.60 kg

Fts Fts > Ft -------------------------ft b.

2

use use Ft = Fts Fts = 1440 1440 kg/c kg/cm m 2

= T / A = 206 20621 21.0 .09 9 / 17.1 17.1 = 120 1205. 5.91 91 kg/cm kg/cm < Ft ……… Ok ! Tow Tower with exist isting and and pro propose osed antenna : 2

Number of anchor bolt = 6  ¾ “ fv

--------- A = 17.1 17.1 cm 2

= S / A = 2387 2387 / 17.1 17.1 = 139. 139.59 59 kg/c kg/cm m < Fv ……………. Ok !

Fts = ( 1.4 x 1440 ) – ( 1.6 x 139.59 139.59 ) = 2016 2016 – 223.344 223.344 = 1792.656 1792.656 kg/cm kg/cm Fts Fts > Ft ------------------------ft

2

2

use use Fts Fts = Ft = 1440 1440 kg/c kg/cm m 2

= T / A = 2062 20621.0 1.09 9 / 17.1 = 1205. 1205.91 91 kg/cm kg/cm < Ft ……… Ok !

Keep using anchor bolt 6  ¾ “

Required embedded length of anchor bolt : Fcv

= 0.53  f’c = 0.53  175 = 7.0 kg/cm


21

2


Space Truss Design

Le

= T / ( Fcv x 6 x  x d ) = 20621.0 20621.09 9 / ( 7 x 6 x 3.14 x 1.905 1.905 ) = 82.1 cm

Use

Le = 85 85 cm

3.2. Column Base Plate 1) Steel Concrete

: Bj – 37

Fy = 2500 kg/cm2

: K – 175

Fp = 0,35 f’c = 0,35 x 175 = 61.25 kg/cm

2

2) The formula to calculate column base plate is shown as follows : 2

Ar = P / Fp

(m )

Ab  Ar then then check check fp  Fp Ab = B x B t = ( 6M / Fb )

½

Fb = 0.75 Fy = 0.75 x 2500 = 1875 kg/cm Wher Wheree :

2

P

= Tota Totall comp compre ress ssion ion at tower tower base base per per one one leg leg ( kg )

Ar

= Required Required area of column column base plate ( m )

2

2

Ab = Designed Designed area of of column column base base plate plate ( m ) B

= Len Lengt gth h of of base base plat platee ( cm )

fp

= Actu Actual al bearing bearing pressu pressure re ( kg/cm kg/cm )

Fp

= Allowab Allowable le bearing bearing strength strength stress stress ( kg/m )

tp

= Re Requi quired red thickn thickness ess of base base plat platee ( cm, cm, mm) mm)

M

= Momen Momentt at the the edge edge of base base plate plate ( kgm kgm,, kgcm) kgcm)

Fb

= Allowabl Allowablee bending bending stress stress of base base plate plate ( kg/cm kg/cm )

Fy

= Yield Yield streng strength th of of steel steel ( kg/cm kg/cm )

f’c

= Compress Compressive ive strengt strength h of concrete concrete ( kg/cm )

m

= Distan Distance ce from steel steel structura structurall to the the edges edges of of base base plate plate ( cm )

fb

= Bendin Bending g stress stress ( kg/cm kg/cm )

2

2

2

2

2

2

The calculation is shown as follows below : a. Tower without proposed antennas Column base plate area The existing column base plate : 600 mm x 600 mm x 25 mm Maximum compression force ( P ) = 26980 kg Applied Applied load at support support join = 488.09 kg P Total = 26980 + 488.09 = 27468.09 kg 2

A = 60 x 60 = 360 3600 0 cm

2

fp = P / A = 26980 / 3600 3600 = 7.494 7.494 kg/cm < Fp …………. Ok ! Column base plate thickness Use m = (60 – 15) / 2 cm = 22.5 cm 2

2

M = ½ q m = ½ x 7.494 x 22.5 = 1896.92 kgcm 2

2

check check the the stress stress : fb = ( 6M / tp )= (6 x 1896.92 / 2.5 ) 2

2

= 1821.042 kg/cm < Fb (1875 (1875 kg/cm kg/cm )………….Ok ! b. Tower with proposed antennas Maximum compression force ( P ) = 27200 kg Applied Applied load at support support join = 488.09 kg P Total = 27200 + 488.09 = 27688.09 kg 2

fp = P / A = 27688.09 27688.09 / 3600 3600 = 7.691 kg/cm kg/cm < Fp …………. Ok ! Column base plate thickness Use m = (60 – 15) / 2 cm = 22.5 cm


22


Space Truss Design 2

2

M = ½ q m = ½ x 7.691 x 22.5 = 1946.78 kgcm 2

2

check check the the stress stress : fb = ( 6M / tp )= (6 x 1946.78 / 2.5 ) 2

2

= 1868.91 kg/cm < Fb (1875 (1875 kg/cm kg/cm )………….Ok ! Keep using using column column base plate : 600 mm x 600 mm x 25 mm

3.3. Design and Control Of Foundation 3.3.1. Tower with existing antennas 1) Design load :

H

= 2377

kg

( max horizontal reaction )

V

= 269 26980 kg kg

( max vertical rea reaction )

T

= 21110 kg kg

( max uplift reaction )

V1

= 488. 488.09 09 kg

( dea dead loa load at suppo upport rt join join )

P

= V + V1 = 26980 26980 + 488.0 488.09 9 = 2746 27468. 8.09 09 kg

Tt

= T – V1 = 2111 21110 0 – 488. 488.09 09 = 2062 20621. 1.91 91 kg

From data above above the design foundatio foundation n will will be checke checked d for uplift force, bearing bearing capaci capacity ty of soil soil and horizontal loads (sliding). Design of foundation : 800

200

GroungLevel

1950

Soil

2850

700 3000

2) Check stability for uplift force Concrete volume ( Vc ) : Pedestal column : 0.80 x 0.80 x 2.15

= 1.376

m

3

Footing : 3.0 x 3.0 x 0.70

= 6.300

m

3

= 7.676

m

3

Soil volume for anti uplifting ( Vs ) : Vs

= (( 3.0 3.0 x 3.0 3.0 ) – ( 0.8 0.80 x 0.80 0.80 )) x 1.95 1.95= = 16.3 16.30 0

m

3

Weight of concrete and soil : W1 = W+ Ws = 7.676 x 2.4 + 16.30 x 1.6

= 44.5024 t

S.F = W1 / T = 44.502 44.502 / 21.110 21.110 = 2.11 2.11 > 2.0 ……………… ………………..O ..Ok k! 3 ) Bearing capacity of soil 2

2

The allowable allowable bearing bearing capacity of soil is 0.267 kg/cm = 2.67 t/m

( Bearing capacity data was gathered from Tower Name / Date Plate ) 4 ) Check of compressive force Wt = 44.502 + 27.468

= 71.970 t

M

= 2.377 x 2.85

= 6.774

tm

Z

= Sectio Section n modulu moduluss of footin footing g base base

Z

= 3.0 x 3.0 x 3.0 / 6

= 4.500

m


23

3


Space Truss Design

fe

= Compre Compress ssive ive stress stress of footin footing g base base

A

= Area of foundation base = 3.00 x 3.00

fe

= 71. 71.97 970/ 0/ 9.0 9.0 + 6.77 6.774 4 / 4.5 4.5 = 7.999 t/m > 2.67 2.67 t/m ………….Fail

= 9.00

2

m

2

2

The dimensi dimension on of founda foundation tion is designed designed based based on the nomogra nomogram. m. As shown shown in calcul calculati ation on above, above, the bearing capacity of soil is unable to support the existing tower. In fact, the soil is bearable. Possibly this is due to the differenc differencee in type and and dimens dimension ion between between the existi existing ng tower tower founda foundatio tion n and the design designed ed foundation above. 5) Factor of safety against sliding Wt

= 71.9 71.970 70 t

H

= 2.377 t



= Coefficient of friction = 0.45

SF

= Wt x  / H = 71.970 71.970 x 0.45 / 2.377 2.377 = 13.62 > 1.50 1.50 …………. …………. Ok !

3.3.2. Tower with existing and proposed antennas 1) Design load :

H

= 2387 kg kg

( max horizontal reaction )

V

= 272 27200 kg kg

( max vertical rea reaction )

T

= 21160 kg kg

( max uplift reaction )

V1

= 488. 488.09 09 kg

( dea dead loa load at suppo upport rt join join )

P

= V + V1 = 27200 27200+ + 488. 488.09 09 = 2768 27688. 8.09 09 kg

Tt

= T – V1 = 2116 21160 0 – 488 488.0 .09 9 = 2067 20671. 1.09 09 kg

2) Check stability for uplift force Concrete volume ( Vc ) : Pedestal column : 0.80 x 0.80 x 2.15

= 1.376

m

3

Footing : 3.0 x 3.0 x 0.70

= 6.300

m

3

= 7.676

m

3

Soil volume for anti uplifting ( Vs ) : Vs

= (( 3.0 3.0 x 3.0 3.0 ) – ( 0.8 0.80 x 0.80 0.80 )) x 1.95 1.95= = 16.3 16.30 0

m

3

Weight of concrete and soil : W1 = W+ Ws = 7.676 x 2.4 + 16.30 x 1.6

= 44.502 t

S.F = W1 / T = 44.502 44.502 / 21.160 21.160 = 2.103 2.103 > 2.0 ………… ………………. ……..Ok .Ok ! 3 ) Bearing capacity of soil 2

2

The allowable allowable bearing bearing capacity of soil is 0.267 kg/cm = 2.67 t/m 4 ) Check of compressive force Wt = 44.502 + 27.688

= 72.190 t

M

= 2.387 x 2.85

= 6.803

tm

Z

= Sectio Section n modulu moduluss of footin footing g base base

Z

= 3.0 x 3.0 x 3.0 / 6

= 4.500

m

3

fe

= Compre Compress ssive ive stress stress of footin footing g base base

A

= Area of foundation base = 3.00 x 3.00

= 9.00

m

2

fe

= 72.190/ 72.190/ 9.00 9.00 + 6.803 6.803 / 4.50 4.500= 0= 8.022 t/m > 2.67 2.67 t/m ………….Fail

2

2

5) Factor of safety against sliding Wt

= 72.1 72.190 90 t

H

= 2.387 t



= Coefficient of friction = 0.45


24


Space Truss Design

SF

= Wt x  / H = 72.190 72.190 x 0.45 / 2.387 2.387 = 13,61 > 1.50 …………. …………. Ok !


25


Space Truss Design

4. CONCLUSION AND RECOMMENDATION

We have carefully analysed analysed the existing tower of Limboto Limboto structure for the proposed additional additional antenna at 120 km/hr wind velocity. The following major conclusions have been drawn from this analysis : -

The existing tower has strength enough to support support the existi existing ng configu configurat ration ion and the propose proposed d antennas at 120 km/hr maximum wind velocity.

-

The The anch anchor or bolt bolt and and the the base base plat platee has strength enough to resist the forces at support joint. Addit Additio iona nall forc forcee at the the towe towerr base base (max (maximu imum) m) due due to the the propo propose sed d ante antenn nnas as is is les lesss than than

2.10

% of

support reaction at tower without proposed antennas. -

The The des design igned foun oundati dation on has strength enough to resist the uplift and shear forces. The The des designed foundat dation has not strength enough to resist the compressive force. It means that the bearing capacity of soil is unable to support the structure. This is, possibly, due to the difference in type and dimension between the existing tower foundation and the designed foundation.

-

The minim minimum um requir required ed of bearin bearing g capaci capacity ty to suppor supportt the the tower tower with with existin existing g and and propose proposed d ante antenna nnass is is 2

about 8.0 t/m .

Luwuk, Januari 2001

Yoppy Soleman


26


Space Truss Design

800 200

GL

1950

Soil

2850

700

3000


27


Structural Evaluation of Self Supporting Tower (Calculation)__Yoppy Soleman

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