Report 60m Sandema

8/12/2019 Report 60m Sandema

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STRUCTURAL ANALYSIS OF 60M GROUND BASED

TRIANGULAR HYBRID TOWER WITH WIND SPEED 144KMPH

(40M/S) (ANTENNA LOADING AREA 7.0 SQ.M)

Site ID: UEB5508

Site Name: SANDEMA

Structure Height: 60m

Date : 24-April-2014

Version : 00

Structural Analysis Report


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Contents1. Executive Summary & Recommendations

2. Structure Line Diagram

3. Site Images and Issues

4. Rectification Requirements List

Appendix 1

5. Analysis Introduction

6. Summary of Results

7. Structure Model Showing Sections

8. Assumptions

9. Loading Equipment

10. Structure Model Showing Equipments

11. Loading - Wind

12. Foundation Loads

13. On-Site Test Results

Appendix 2

14. Bill of Materials

Appendix 3

15. Analysis Results Strengthened Tower with Additional Equipment


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Executive Summary & Recommendations

Height of Structure 59.745m

Structure Type 3 Legged Tubular Hybrid Tower

Date of Audit 16 August 2013

NGR N 10.73195 W 1.28541

Structure Capacity:The structure in current loading position is not safe and is over stressed. The maximum stress %

observed in various parts of the tower are as below:

Leg Sections 115%

Bracing Sections 125%

Bolts 88%

Members failing in L/R ratio:

Few members are not over stressed but are exceeding L/R (Slenderness ratio) ratio than what

specified in 222G. i.e 200. The maximum L/r ratio observed in the members is as below:

Leg Sections 76.53Bracing / horizontal / plans Sections 259.19

Structure Rectification Requirements:

Strengthen sections 1 and 2 legs and 1-2 bracings.

Strengthening of plan members of the sections 1, 2 and 3 is required as the L/R ratio is

exceeding 200.

Full bolt tightening and torque for the FULL TOWER leg splice bolts and bracings.

Replacement and swap out of bolts FULL TOWER. We would propose that

all bolts of indeterminate value [not grade 8.8], or corroded or missing or tooshort are replaced.

Tower repainting and cleaning of tower sections is recommended. A corrosion

remedy program needs to be implemented; the existing surface coating of the

tower sections has weathered off.

Structure Condition:

This tower condition as it stands is NOT in good condition. Tower is overstressed in the

legs and main diagonal bracings - failing on buckling at maximum design wind speed. It

is recommended to strengthen the legs and main bracings. The tower also requires

cleaning and repainting. Some bolts are found to be loose or rusted and needs to bereplaced.


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Capacity of Strengthened Tower with Existing Equipment

With the tower strengthened -

Leg Sections 94%

Bracing Sections 99.93%

Bolts 88%

Note, if an additional operator to be installed, several other members to be replaced.

L/R limits after strengthening

Leg Sections 76.53

Bracing Sections 196.90

Structure Foundation:

No data regarding foundations is available.

Maximum forces acting on Tower Leg (service load

case) Compression 381 kN

Tension/Pull 327 kN

Trans shear 24.18 kN

Long shear 31.30 kN


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Structure Line Diagram


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Rectification Requirements List

List of members that require replacement.

Item SizeTower

Quantity CommentSection

Legs 221*3.7 S235 1 3 ReplaceLegs

Legs 221*3.7 S235 2 3Replace

Legs

Bracings 60*2.3 S235 1 6Replace

bracings

Bracing 60*2.3 S235 2 6Replace

bracings

Plans EA50x50x5 S235 1 3Replace

Plan bracings

Plans

EA50x50x5 S235 2 3

Replace

Plan bracings

PlansEA50x50x5 S235 3 3

Replace

Plan bracings

This structure requires attention on maintenance:


Strengthening of plan members of sections 1,2 & 3 is required.

Cleaning and repainting of the whole tower and a corrosion remedy program.


Replacement and swap out of bolts FULL TOWER. We would propose that all

bolts of indeterminate value [not grade 8.8], or corroded or missing or too

short are replaced.


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Appendix 1

Analysis Introduction

This report covers the structural analysis of Sandema - 3 legged steel Hybrid tower59.75m high and located in upper east Ghana. The tower is triangular in plan, with a face

width 5.27m at the bottom and tapering to 1.39m at 47.75m level. All dimensions are

center to center between legs, see Figure 1.

The tower consists of tubular steel sections for legs and bracing members of varying

sizes as listed in the table. All other members are angular section. All legs and braces

are shown on the enclosed Figure 1.

The tower and its members are analyzed to design standard code TIA-222-G,

Structural standard for antenna supporting structure and antennas. The tower is

modeled and analyzed using PLS Tower.

The purpose of the analysis is to make an assessment of the structural adequacy of

the steel lattice tower to carry existing equipment and at maximum design wind

speed.

The tower has been checked for a deflection criteria based on a maximum allowable

rotation of the tower by 1 degree at service load case maximum wind condition and 0.5

degrees at service load case survival wind condition, which is the limit generally

accepted by the telecommunications industry.

Tower leg reactions are provided for further checks later from tower overturning andconcrete base capacity when base dimensions/ drawing plans are made available.


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Summary of Results

Legs and Bracings Stress Ratios of existing tower before members

replacements:

Section

Angle

Size

Steel

Strength

(MPa)

Max

Use In

Comp.

%

Comp.

Force

(kN)

L/R

Capacity

(kN)

Tension

Force

(kN)

Net

Section

Capacity

(kN)

Maximum

stress

Ratio

Legs

1 221*3.7 235 115.03

-

569.239 494.882 501.974 534.249 1.15

2 221*3.7 235 102.98

-

509.704 494.946 451.498 534.249 1.03

3 169*5.0 235 94.15 -449.394 477.292 399.797 544.824 0.94

4 169*5.0 235 81.08

-

386.986 477.292 345.544 544.824 0.81

5 169*5.0 235 67.64

-

322.829 477.292 289.146 544.824 0.68

6 140*3.8 235 91.22

-

258.102 282.937 231.936 343.899 0.91

7 140*3.8 235 68.61

-

194.131 282.937 172.42 343.899 0.69

8 140*3.8 235 46.37

-

131.201 282.937 117.379 343.899 0.46

9 115*3.6 235 30.47 -60.165 197.442 52.748 264.375 0.3010 115*3.6 235 3.74 -7.391 197.442 4.83 264.375 0.04

Bracings

1 60*2.3 235 124.71 -21.546 17.277 20.691 88.195 1.25

2 60*2.3 235 108.84 -20.393 18.737 19.6 88.195 1.09

3 60*2.3 235 99.98 -21.026 21.03 19.677 88.195 0.99

4 60*2.3 235 92.26 -20.887 22.641 19.638 88.195 0.92

5 60*2.3 235 84.67 -19.859 23.454 19.219 88.195 0.85

6 60*2.3 235 79.74 -19.717 24.726 19.151 88.195 0.80

7 60*2.3 235 84.72 -22.229 26.238 21.68 88.195 0.85

8 60*2.3 235 84.67 -23.379 27.61 22.511 88.195 0.85

9 60*2.3 235 84.35 -24.279 28.784 23.76 88.195 0.84

10 60*2.3 235 40.15 -11.556 28.784 11.153 88.195 0.40

Horizontals

1,2 70*70*7 235 31.74 -13.599 42.844 13.619 165.544 0.32

3 to 10 60*60*6 235 32.57 -11.129 34.165 11.072 117.247 0.33

Plans3 to 10 50*50*5 235 14.72 -8.14 63.516 5.226 79.279 0.13

1 to 3 65*65*5 235 3.43 -0.925 26.984 0.923 108.844 0.03

All members with stress ratios greater than 1.0 are overstressed

The maximum rotation of antenna at service load case and maximum wind is 0.68 degrees.


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Structure Model Showing Sections

Figure 1: Tower Section and Elevations


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Assumptions

Below is a list of the basis and assumptions used in the analysis of this tower site:

1. The tower is analyzed to TIA-222-G, Structural Standard for Antenna

Supporting Structures

2. All tower members are in good condition and free from any defects.

3. All bolts are assumed to be in the condition that was found during the survey

conducted on site.

4. All bolts have no visible grade markings and are assumed to be Grade 4.6.

5. All bolts marked 8.8 are assumed to be grade 8.8 bolts.

6. Selected sections in the tower (legs and bracing) were tested for grade. Grade

results from these tests were used in the analysis. Though the tensile strength

of the leg members is way below the minimum limit of 360MPa (for S235),

the material grade is considered as S235.

7. Equipment loadings as listed are based on equipment site survey conducted on site.

8. A sample of the tower members were measured on site and it is assumed that all

details of corresponding members at the same level as the surveyed members

have the same detail.

9. All steel is of good quality and has not deteriorated over time.

10. Weights/wind loading of ladders, platforms, antenna support steelwork, cable

ladders and feeders has been approximated.

11. No allowance has been made for weakening of the tower members,

stubs and foundations by corrosive action.

12. The holdings-down bolts are assumed to be Grade 4.6 and are firmly

connected to the foundation.

13. The tower support base was surveyed to be supported on pedestals. The

holding down bolts capacity has been checked and can accommodate the

tower legs if the embedded length of the foundation bolts is of minimum

70mm. The exact details of the length of embedment is not provided in the

report.

14. Bracings of sections 1 and 2 are considered as 60*2.3 as per form9 instead of

88*2.3 as per form 5 for existing tower analysis.


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Loading Equipment

List of Surveyed equipment

SizeElevation

Direction

al

TYPE from the Azimuth(m)*base (m)

GSM 0.16x1.3 25.2 50

GSM 0.16x1.3 25.2 170

GSM 0.16x1.3 25.2 280

GSM 0.26x2.6 55.5 50

GSM 0.26x2.6 55.5 170

GSM 0.26x2.6 55.5 290

GSM 0.26x2.6 35.5 205

GSM 0.26x2.6 35.5 360

GSM 0.26x2.6 35.5 100DISH 1.2 49.5 290

DISH 1.2 44.8 18

* All dish sizes are diameters, all GSM sizes are lengths

Note: For feeder loading: 2 No. 28mm per 1 panel, 1 no. 12mm per dish.


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Structure Model Showing Equipment

Figure 2: Computerized tower model showing equipment


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Loading - Wind

Wind Loading

Wind loading parameters to suit TIA-222G design code.

The following wind loading values and factors have been assumed:

Wind Speed

Gust wind speed with return period of 50 years is 40 m/s

Partial Safety Factors

Wind load factor 1.6

Terrain Factor

Structure is considered to be a Class 2

The tower is located at exposure category B & Topographic category 1.


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Foundation Loads

1. Maximum Support Reaction on existing tower with current loading

Compression 381 kN

Tension/Pull 327 kN


Long shear 31.30 kN

2. Check for Holding Down bolts

No of Bolts: 4No- M30 each leg, total of 12 No-M30 bolts for all legs; assumed Grade 6.8 Max

Tension Stress Ratio of Bolts: 0.88 < 1.0, Safe


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On-Site Test Results

A. Material

Thickness Tests

Not applicable

B. Hardness(Tensile) Tests

Legs S235

Bracings S235

Note: Though the tensile strength values of legs are less than 360 (minimum for S235), the

material is assumed to be S235 as per clients suggestion.

C. Concrete Base Grade Tests

Test 1 43,34,33,36,35,38,32,36,43,30Test 2 38,36,38,45,45,36,35,40,37,38

Test 3 36,37,38,32,39,45,45,37,41,34

Test 4 36,19,29,26,34,31,29,29,25,29

Recommended cube strength of concrete, 30 N/mm2


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Appendix 2 Bill of Materials

List of members that require replacement.

Item SizeTower

Quantity Comment

Section


Legs


Legs

Bracings 60*2.3 S235 1 6Replace

bracings

Bracing 60*2.3 S235 2 6Replace

bracings

Plans EA50x50x5 S235 1 3Replace

Plan bracings

Plans EA50x50x5 S235 2 3 ReplacePlan bracings

PlansEA50x50x5 S235 3 3

Replace

Plan bracings

This structure requires attention on maintenance:


Strengthening of plan members of sections 1,2 & 3 is required.

Cleaning and repainting of the whole tower and a corrosion remedy program.


Replacement and swap out of bolts FULL TOWER. We would propose that all

bolts of indeterminate value [not grade 8.8], or corroded or missing or too

short are replaced.


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Appendix 3Analysis Results Strengthened Tower with

Existing Equipment

Legs and Bracings Stress Ratios of existing tower after members

replacements:

Section

Angle

Size

Steel

Strength

(MPa)

Max

Usage

%

Comp.

Force

(kN)

L/R

Capacity

(kN)

Curve

No.

Tension

Force

(kN)

Net

Section

Capacity

(kN)

Maximum

stress

ratio

Legs

1 219.1*4.8 235 90.2 -570.587 632.551 1 501.106 683.145 0.90

2 219.1*4.8 235 80.59 -509.821 632.633 1 450.972 683.145 0.81

3 169*5.0 235 94.09 -449.07 477.292 1 399.537 544.824 0.944 169*5.0 235 81.02 -386.696 477.292 1 345.308 544.824 0.81

5 169*5.0 235 67.59 -322.594 477.292 1 288.954 544.824 0.68

6 140*3.8 235 91.16 -257.916 282.937 1 231.787 343.899 0.91

7 140*3.8 235 68.56 -193.99 282.937 1 172.318 343.899 0.69

8 140*3.8 235 46.33 -131.097 282.937 1 117.311 343.899 0.46

9 115*3.6 235 30.45 -60.128 197.442 1 52.716 264.375 0.30

10 115*3.6 235 3.74 -7.388 197.442 1 4.824 264.375 0.04

Bracings

1 76.1*3.2 235 45.58 -21.897 48.038 4 20.85 154.818 0.46

2 76.1*3.2 235 39.43 -20.541 52.096 4 19.604 154.818 0.39

3 60*2.3 235 99.97 -21.024 21.03 4 19.68 88.195 0.99

4 60*2.3 235 92.17 -20.869 22.641 4 19.624 88.195 0.92

5 60*2.3 235 84.59 -19.841 23.454 4 19.205 88.195 0.85

6 60*2.3 235 79.67 -19.7 24.726 4 19.139 88.195 0.80

7 60*2.3 235 84.66 -22.213 26.238 4 21.658 88.195 0.85

8 60*2.3 235 84.58 -23.352 27.61 4 22.502 88.195 0.85

9 60*2.3 235 84.29 -24.262 28.784 4 23.743 88.195 0.84

10 60*2.3 235 40.12 -11.549 28.784 4 11.148 88.195 0.40

Horizontals

1,2 70*70*7 235 31.64 -13.554 42.844 4 13.972 165.544 0.32

3 to 10 60*60*6 235 32.42 -11.075 34.165 4 11.012 117.247 0.32

Plans3 to 10 50*50*5 235 14.71 -8.131 63.516 1 5.228 79.279 0.13

1 to 3 65*65*5 235 3.59 -0.969 26.984 4 0.96 108.844 0.04

Note: None of the members are having stress ratio more than 1.

Note: Failed sections were replaced with section available in India. If the assumed sections are notavailable at the manufacturers location, then equivalent sections of next available higher size should

be used.

Note: As the bracing of section 3 is having stress ratio very close to 1, it is recommended to once

again check the section dimensions and material strengths. If any reduction in the values

observed than what specified in the initial filed report, then the same should be replaced with

76.1*3.2 tubular section.


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Stress ratio of bolts:

Section

Stress

ratio

Legs

1 0.71

2 0.63

3 0.88

4 0.76

5 0.64

6 0.51

7 0.38

8 0.26

9 0.17

10 0.02

Bracings

1 0.25

2 0.23

3 0.37

4 0.37

5 0.35

6 0.35

7 0.39

8 0.41

9 0.43

10 0.20

Horizontals

1,2 0.24

3 to 10 0.20

Plans3 to 10 0.02

1 to 3 0.14

Maximum Un factored Support Reactions on existing tower with current

loading

3. Maximum Support Reaction on existing tower with current loading

Compression 381 kN

Tension/Pull 327 kN


Long shear 31.30 kN

4. Check for Holding Down bolts

No of Bolts: 4No- M30 each leg, total of 12 No-M30 bolts for all legs; assumed Grade 6.8 Max

Tension Stress Ratio of Bolts: 0.88 < 1.0, Safe


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Strengthening recommendation replace bracings

& leg members in sections 1-2 and plans of sections

1,2&3

Report 60m Sandema

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